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    Relatively open vegetation landscapes promoted early Pleistocene hominin evolution

    AbstractVegetation structure and landscape openness are key ecological factors influencing human behavioural and cultural adaptation strategies. However, there is ongoing debate and lack of quantitative assessment about which vegetation landscape and openness levels were more conducive to hominin dispersal during the early Pleistocene. Here, we selected the early Pleistocene Majuangou archaeological site in China, which is the earliest site in the Nihewan Basin with reliable stratigraphic chronology and abundant archaeological materials, as the research object. We conducted pollen analysis across eight artefact layers and the natural sediments (1.75–1.29 Ma), and carried out the first quantitative reconstruction of vegetation openness. The results demonstrate that vegetation openness in the artefact layers was predominantly between 60% and 90%, while layers with vegetation openness below 50% or above 90% had either no or very few artefacts. The global comparison revealed that hominins’ preference for relatively open habitats was a consistent global pattern, challenging the view that relatively closed forest vegetation landscapes were more conducive to their dispersal. Our findings suggest that enhanced resource abundance, accessibility and mobility in these environments facilitated both hominin dispersal and cultural development, highlighting the pivotal role of relatively open vegetation landscapes in shaping hominin evolution.

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    IntroductionThe relationship between vegetation ecosystems (the compositional, structural, and landscape characteristics) and the dispersal and evolution of hominins has long been a major focus in palaeoecology, archaeology, palaeoanthropology, and related disciplines1,2. The early Pleistocene was a critical period for global climatic and environmental changes, characterised by cooling and aridification trends, as well as for the migration and dispersal of Homo erectus3,4,5,6. Hominin dispersal first occurred from Africa to Eurasia7,8,9. While existing studies have predominantly emphasised the climatic drivers of hominin evolution10,11,12,13, emerging evidence underscores the crucial role of vegetation ecosystems in shaping dispersal corridors and adaptation strategies14,15,16,17,18. The open savanna vegetation of Africa is widely regarded as having facilitated the evolution and dispersal of H. erectus19,20. Nevertheless, the climatic patterns and vegetation types of Eurasia diverge markedly from those of Africa, rendering the African model difficult to apply to Eurasia21. Specifically, Eurasia may exhibit distinct patterns of vegetation landscapes and hominin dispersal evolution.Over the past decades, a series of innovative studies have been conducted on the relationship between hominin evolution and vegetation landscapes in Eurasia2,17,21. This has resulted in two different hypotheses: (i) the open habitat hypothesis, in which hominins were better adapted to occupying open steppe or forest-steppe ecological environments21,22, where the open vegetation landscape provided favourable conditions for the migration, hunting, and survival of early H. erectus17; (ii) the relatively closed habitat hypothesis, in which the environmental characteristics during the period when H. erectus was active were forest vegetation landscapes23,24. This forest vegetation not only provided rich food sources for hominins but also offered safe tree-dwelling habitats23,25. However, there have been no detailed studies on to which the vegetation landscape was open to be suitable for the migration, hunting and survival of early hominins.The main reasons for this debate and the lack of in-depth research are: (i) Issues, including discontinuous sedimentation or the poor preservation of sedimentary strata, have resulted in limited information about the changes in past vegetation ecosystems near archaeological sites16,26. (ii) Most studies are limited to a single artefact layer or a relatively short time span, and have a low temporal resolution, making it difficult to comprehensively reconstruct vegetation ecosystem processes before and after the activities of H. erectus27,28. (iii) Most research is based on qualitative analysis, and there is a lack of systematic quantitative studies of the impact of vegetation ecology and landscape characteristics on the evolution of H. erectus29. Therefore, to better understand the influence of early Pleistocene vegetation composition and landscape openness on the migration and evolution of early hominins, it is necessary to conduct quantitative research on paleovegetation and landscape openness, based on stratigraphic sequences with continuous sedimentation, and employing multiple artefact layers, sensitive proxy indicators, a high temporal resolution, and covering a long interval.Pollen analysis plays an irreplaceable role in revealing the paleovegetation and past landscapes openness30,31. Early studies relied on non-arboreal pollen (NAP) percentages to infer vegetation openness32, but this approach fails to account for pollen productivity variations and dispersal biases, resulting in vegetation–pollen mismatches33. Subsequent semi-quantitative alternatives, such as the arboreal/non-arboreal pollen ratio (AP/NAP)34 and the difference between the maximum score of forest biomes and that of open biomes within the biome classification, have yielded improved insights but lacked precise quantification35. Application of the Regional Estimates of Vegetation Abundance from Large Sites (REVEALS) model has resulted in significant research progress by incorporating pollen productivity corrections and nonlinear vegetation–pollen relationships to quantify openness, its exclusion of the bare land proportion has remained a constraint33. To address these limitations, our study employs a transfer function methodology to establish pollen assemblage–vegetation openness relationships. This approach enhances the reconstruction reliability by utilising entire pollen spectra rather than individual taxa to minimise single-type interpretation biases36.The Nihewan Basin in northern China has the largest and most concentrated group of early Pleistocene Palaeolithic sites in East Asia37. More than 280 Palaeolithic sites have been found in this region, of which 23 are older than 1.0 Ma38,39 (Fig. 1a, b, Supplementary Table 1). Among them, the Majuangou (MJG) archaeological site is the earliest hominin site, and it is also the earliest stone-flake tool site in Northeast Asia in terms of reliable stratigraphic relationships and abundant discovered materials40. Ten artefact layers have been identified at the MJG site, which provide a framework for the cultural sequence of hominins from 1.76 to 1.32 Ma, in the early Pleistocene39. Notably, the activity surface of a mammoth butchery site was revealed within the MJG–Ⅲ artefact layer (~ 1.66 Ma), and more than 60 mammoth footprints were identified in MJG–Ⅱ (~ 1.64 Ma) (Supplementary Fig. 1)39. This is the earliest and the richest artefact assemblage among the early Pleistocene sites in the Nihewan Basin40. In addition to archaeological research, environmental change research has also been conducted at the MJG site37. Qualitative studies have been conducted on several artefact layers, including of mineral composition, ostracods, and animal fossils, which have revealed the burial environment and fossil animal assemblages of the artefact layers37,41,42. However, quantitative studies are lacking and several key questions have not been addressed, including: What was the relationship between hominin activities and vegetation landscape openness? What degree of vegetation openness was conducive to hominin activities?Fig. 1: Location and field photos of the MJG archaeological site in the Nihewan Basin, China.a Location of the Nihewan Basin (map source: https://search.earthdata.nasa.gov/) (Supplementary Note 1). b Distribution of sites over 1 Ma in age in the Nihewan Basin. For detailed information about sites 1–23, see Supplementary Table 1 (map source: https://www.gscloud.cn/). c Site profile and artefact layers of the MJG site in the Nihewan Basin, from Northwest to Southeast (image by Fagang Wang).Full size imageIn this study, based on the existing paleomagnetic chronology and 26Al/10Be burial dating37,43, ages of the eight artefact layers in the section of the MJG site (40°13′31.066″N, 114°39′50.493″E, 832.6 m a.s.l) were calibrated using the sedimentation rate (Fig. 1c). We conducted pollen analysis on 422 samples collected at 10-cm intervals from eight artefact layers and natural sedimentary layers. The REVEALS model33 and transfer function methods36 were then utilised to quantitatively reconstruct the changes in vegetation cover and landscape openness during and around the period of hominin activity in the Nihewan Basin. This study aims to reveal which types of vegetation landscape and openness degree in the early Pleistocene of the Nihewan Basin were more conducive to attracting hominin activities. Overall, we hope to provide detailed and reliable evidence for the study of the impact of paleoenvironmental changes on the migration and evolution of hominins during the early Pleistocene in China and even the world.Results and discussionStratigraphy and chronology of the MJG archaeological siteThe MJG archaeological site is located in the northeastern Nihewan Basin, northern China40,44 (Fig. 1a, b). Due to the submersion of the bottom two artefact layers by groundwater during sampling, we selected eight artefact layers and their surrounding natural layers for analysis40. Sedimentological analysis, incorporating grain size metrics and field stratigraphic evidence, indicates that the studied profile consists predominantly of silt (average of 70%), which is consistent with the characteristic depositional of the Nihewan Formation38,45 (Fig. 2, Supplementary Note 2).Fig. 2: Lithology and chronology of the sedimentary profile at the MJG archaeological site.a Lithology and grain size composition of the MJG profile (Supplementary Note 2, Supplementary Data 1). b Lithology and chronology of the MJG profile37.Full size imageThe lithology of the MJG profile from bottom to top is as follows (Fig. 2): 60.5–58.1 m, grey and greyish-brown clayey silt with horizontal bedding; 58.1–42.5 m, grey and greyish-yellow clayey silt; 42.5–18 m, greyish-brown and grey silty clay with horizontal bedding (Supplementary Note 1). Samples of the MJG profile were collected continuously from the bottom upwards at 10-cm intervals, with some samples taken at 12-cm intervals. The total sampled interval was 60.5–18 m, with a thickness of ~42.5 m. A total of 422 samples were collected.The chronology of the MJG profile was well constrained by magnetostratigraphy37 and 26Al/10Be burial dating43. In 2004, Zhu et al.37 established the magnetostratigraphic framework for the profile (Fig. 2b), confirming that the BS, MJG–Ⅰ, MJG–Ⅱ, and MJG–Ⅲ artefact layers reside in the Matuyama reverse chron, bracketed by the Olduvai and Jaramillo normal subchrons37. Based on average sedimentation rates, their ages were derived as: BS (1.32 Ma), MJG–Ⅰ (1.55 Ma), MJG–Ⅱ (1.64 Ma), and MJG–Ⅲ (1.66 Ma)37. In 2008, extrapolated ages for MJG–Ⅳ (1.69 Ma) and MJG–Ⅴ (1.74 Ma) were derived using these chronologies and sedimentation rates (Fig. 2a)44. In 2024, Tu et al.43 applied 26Al/10Be burial dating to BS, MJG–Ⅰ, MJG–Ⅱ, and MJG–Ⅲ layers, with results concordant with Zhu et al.’s magnetostratigraphic ages, providing robust cross-validated chronological constraints.Two additional artefact layers (MJG–Ia and MJG–Ib) discovered in 2013 occur stratigraphically above MJG–Ⅰ40. The MJG–Ia layer is located ~4.5 m above the MJG–Ⅰ, while MJG–Ib layer is ~4.2 m above MJG–Ia and ~16.8 m below BS (Fig. 2, Supplementary Note 1 and Note 2)40. Their ages were determined through grain size variations (Fig. 2a): The average sedimentation rate (~ 11 cm/ka) between MJG–Ⅰ and BS was calculated from stratigraphic separation and age difference. Sediments between MJG–Ⅰ and MJG–Ia show coarser grain size, while MJG–Ia to MJG–Ib intervals are finer, with a grain size difference factor of ~1.35. Based on these parameters and sedimentation rates, MJG–Ia and MJG–Ib were dated to 1.51 Ma and 1.45 Ma, respectively.Quantification of modern vegetation landscape opennessVegetation landscape openness, a key component of landscape ecology, is utilised in modern vegetation research to gauge the cover of non-arboreal vegetation (e.g., grasses and shrubs). This index ranges from 0 (representing 100% arboreal canopy closure, as in a dense forest) to 100% (indicating the complete absence of woody vegetation, characteristic of open grassland). Empirical studies demonstrate an inverse relationship between arboreal cover and openness: lower arboreal plant coverage rates correspond to higher vegetation landscape openness values46.In this study, we first assessed the consistency between the reconstructed and modern observed vegetation landscape openness. To achieve this, we conducted field validation across 57 systematically selected sites spanning a gradient from closed forest to open grassland within the study region (see Methods, Supplementary Note 4). The vegetation landscape openness quantification utilised MOD 44B Version 6 Vegetation Continuous Fields product (250 m spatial resolution), accessed via NASA’s Earthdata platform (https://search.earthdata.nasa.gov)47. This dataset quantifies three land-cover components: % tree cover, % non-tree cover, and % non-vegetated cover. For this analysis, vegetation landscape openness was calculated as:Vegetation landscape openness = 100%−% Tree coverApplication of this model showed that 85.9% of the reconstructed vegetation landscape openness samples were within the error range (Fig. 3a). The change trend between the reconstructed and observed values was also relatively consistent, with the correlation coefficient (R2) of 0.87 (p < 0.05) (Fig. 3b). The reconstructed vegetation landscape openness was consistent with the observed values, indicating that the model was dependable. This showed that this technique could then be applied to the stratigraphic data to reconstruct temporal changes in the openness of the vegetation landscape at the MJG site during the early Pleistocene.Fig. 3: Comparison of observed and reconstructed vegetation landscape openness in modern surface samples.a Sample numbers 1–18 correspond to forest vegetation, 19–29 to forest-steppe, and 30–57 to grassland (see Methods, Supplementary Data 2). The figure shows observed and reconstructed vegetation landscape openness values across three vegetation types: forest, forest-steppe, and grassland. The two light blue columns represent the critical errors for forest/forest-steppe and forest-steppe/grassland. b Correlation coefficient between observed and reconstructed openness values for forest, forest-steppe, and grassland vegetation landscape openness.Full size imageVegetation cover and landscape openness of the MJG sitePrior to quantitatively reconstructing vegetation landscape openness at the MJG site, we compared the performance of different distances, models, and methods (Supplementary Table 2). The comparative analysis revealed that a 1000-km radius modern pollen dataset achieved the highest predictive accuracy (R2 = 0.82, Fig. S3), which was incorporated into the quantitative reconstruction of vegetation openness at the MJG site. Subsequently, we tested the degree of matching and its statistical significance between the fossil pollen assemblage of the MJG profile and modern pollen assemblage (see Methods, Supplementary Fig. 4). The MJG profile fossil pollen samples exhibit a high degree of correspondence with the regional modern pollen assemblage (Supplementary Fig. 4a), and the results of vegetation landscape openness reconstructions have statistical significance (p < 0.05) (Supplementary Fig. 4b). The vegetation landscape openness reconstruction outcomes are consistent with independent vegetation cover estimates (excluding bare ground) and the biome type derived from pollen assemblages (Fig. 4, Supplementary Fig. 5b, Supplementary Note 5; Supplementary Tables 3 and 4). These comparisons confirm the reliability of our quantitative reconstruction of vegetation landscape openness and vegetation cover. This result is supported by independent global climate records, including the LR04 benthic δ¹⁸O stack48 and the magnetic susceptibility record of the Lingtai loess section in China49 (Supplementary Fig. 5e, f). This consistency with independent multi-proxy records strengthens our confidence in the accuracy of our vegetation cover and landscape openness reconstruction.Fig. 4: Changes in vegetation cover and landscape openness during the early Pleistocene at the MJG site.a Percentages of the principal pollen types. b Vegetation cover reconstructed based on the REVEALS model. c The openness of the vegetation landscape was quantitatively reconstructed based on the transfer function method (Supplementary Note 4, Supplementary data 3).Full size imageThe vegetation landscape openness of the eight artefact layers of the MJG site during the early Pleistocene is mainly between 60% and 90% (Fig. 4). The average vegetation landscape openness for each artefact layers were as follows: MJG–Ⅴ (average of 88.3% and the same below), MJG–Ⅳ (66.4%), MJG–Ⅲ (78.7%), MJG–Ⅱ (58.5%), MJG–Ⅰ (91.9%), MJG–Ia (78%), MJG–Ib (65.9%), and BS (60.8%).Based on vegetation composition, the eight artefact layers could be divided into two main types (Fig. 4). The first group consists of six artefact layers (MJG–Ⅴ, MJG–Ⅳ, MJG–Ⅲ, MJG–Ⅰ, MJG–Ia, and MJG–Ib), dominated by Artemisia, Chenopodiaceae, and Poaceae, and the herb pollen content is >50%, while the tree pollen content is relatively low, <30%. This suggests a forest-steppe vegetation landscape in the study area. The openness of these six layers (>65%, up to 90%) further supports their classification as forest-steppe (Fig. 3). The second group comprises two artefact layers (MJG–Ⅱ, and BS), dominated by Pinus, with the tree pollen content up to 80%, while the herb pollen content was ~20% on average. The vegetation landscape openness at this was ~60%, which indicates an open temperate forest vegetation landscape.However, when vegetation openness was <50% or >90%, there was minimal or no evidence of hominin activities. Where Picea pollen percentages exceeded 30% (e.g., in the natural layers located at the upper part of MJG–Ⅴ, MJG–Ⅳ, MJG–Ⅱ, and MJG–Ib) and vegetation openness was <50% (even <20% in some layers), it indicates that the vegetation landscape was a cold temperate coniferous forest. When herbaceous plants consistently accounted for a high proportion (>90%), accompanied by vegetation openness exceeding 90% (e.g., in the natural layers located at depths of 47.2–43.8 m (~1.55–1.52 Ma), 33.8–31.3 m (~1.41–1.39 Ma), and 27.7–24.8 m (~1.36–1.34 Ma)), indicating a steppe environment. In these layers, neither the steppe environments characterised by persistently excessive vegetation openness nor the forest environments with relatively high canopy density constituted the most favourable habitats for hominin.In summary, through the comparison between the natural layers and the artefact layers, openness of the vegetation landscape reconstructed for the eight artefact layers is mainly between 60% and 90%, which indicates that a relatively open vegetation landscape was more conducive to the migration, hunting, and survival of hominins in the Nihewan Basin.Relatively open vegetation landscape in the early Pleistocene promoted the evolution of early homininsThis study provides compelling evidence for hominin adaptation to a relatively open vegetation landscape. The openness of the vegetation landscape reconstructed from the eight artefact layers was mainly between 60% and 90%. In contrast, when the openness of the vegetation landscape was <50% or >90%, there was no or very little evidence of hominin activities. This comparison indicates that hominins selectively occupied the Nihewan Basin during their dispersal process, where relatively open vegetation landscapes facilitated their dispersal.To investigate whether this linkage between a relatively open vegetation landscape and hominin activity extended beyond the Nihewan Basin, we compiled all the published data from other early Pleistocene archaeological sites in Eurasia. A total of 24 archaeological sites from the early Pleistocene period (1.8–1.0 Ma) across Eurasia were collected in our study (Supplementary Data 4). Although the majority of these prior studies provided qualitative methods, we performed a statistical analysis of the available data, using the vegetation descriptions provided by the original authors (e.g., forest, forest-steppe, and grassland)50 (Fig. 5a). Forest vegetation landscapes are categorised as closed vegetation landscapes, while forest-steppe and grassland are categorised as open vegetation landscapes. Completely open grassland vegetation landscapes, defined as those lacking any tree cover, were excluded from the final statistical comparison.Fig. 5: Location and vegetation landscape of global archaeological sites for the interval of 1.8–1.0 Ma.a Global distribution of 1.8–1.0 Ma archaeological sites and the proportion of open and closed vegetation landscapes in Eurasia (archaeological sites are listed in Supplementary data 4). b Pattern diagram of open and closed vegetation landscapes. Credit: elements such as trees, herbs, hominins, and animals are from Huaban.com. Drawing on both these elements and the insights from this study, I reconceived and drew this diagram.Full size imageThe results show that >83.3% of Nihewan archaeological sites, 77.8% of China’s archaeological sites, and 73.9% of Eurasian archaeological sites had a dominantly relatively open vegetation landscape during the period of early Pleistocene hominin activity51,52,53 (Supplementary Fig. 5a). A comprehensive study also supports the inference that a relatively open vegetation landscape in the early Pleistocene was conducive to hominin evolution and migration26. This common pan-Eurasian pattern suggests that a relatively open vegetation landscape was critical for the dispersal and adaptive success of H. erectus (Fig. 5b).Interestingly, this preference for relatively open vegetation landscapes was not unique to Eurasia1,54,55. Evidence from Africa also indicates a similar environmental preference among hominins. In northern Kenya’s Turkana Basin, carbon isotope analysis (δ13CVPDB) of pedogenic carbonates from the early Pleistocene suggests that hominins inhabited savanna ecosystems with ~40% woody cover and >60% open vegetation54. In the Awash and Omo-Turkana Basins of eastern Africa, using stable carbon isotopes analyses from the late Pliocene epoch, combined with 13C/12C ratios from 1300 palaeosols in adjacent areas, further indicate that woody cover was at most sites below ~40%, reinforcing the prevalence of open landscapes in hominin habitats1. In east and south African, a comparative analysis of Plio-Pleistocene mammalian fossil assemblages, alongside 31 extant mammalian communities from eight different habitat types, reveals that Homo was the first hominid to occupy fairly open, arid grasslands55. Across Africa, environmental data from 22 early Pleistocene archaeological sites consistently depict a predominantly open tropical savanna landscape as the primary background for early hominin evolution (Supplementary Data 4).Conversely, relatively closed forest vegetated areas might have impeded the migration56 and visibility of H. erectus, while long-term open grassland vegetation landscape areas could have been unfavourable for hominin survival due to arid climate, scarce food resources, and lack of habitat57. This ecological constraint may explain the relative scarcity of early Pleistocene (1.8–1.0 Ma) archaeological sites in both low-latitude dense forest regions and mid-to-high latitude arid grassland zones (Fig. 5). It was precisely these vegetation characteristics, either excessively closed or overly open, that might have restricted hominin dispersal.In summary, our findings, which are corroborated by evidence from multiple regions worldwide, indicate that relatively open vegetative landscapes were key to facilitating the migration and dispersal of early Pleistocene hominins. This pattern appears to be a prevalent and global phenomenon, deeply intertwined with the ecological preferences and adaptive strategies of H. erectus.Mechanisms of hominin evolution in a relatively open vegetation landscapeDuring the early Pleistocene, relatively open vegetation landscapes likely played a significant role in facilitating the early hominin evolution17,52. These landscapes provided an increased abundance of animal and plant resources, enhanced visibility for resource acquisition, and reduced the risk of predation, all of which favoured ecological adaptation and cultural innovations17. Our study demonstrated that such relatively open vegetation landscapes exhibited a high Simpson’s diversity index (generally >0.6) and species richness, with a diverse vegetation composition, which provided diverse and abundant plant resources for early hominins (Supplementary Fig. 5c, d, Supplementary Note 3).Moreover, sedimentological evidence indicates that the hominin occupation layers are associated with coarse-grained, lakeside facies deposits58 (Fig. 2), which would have ensured sustained access to water resources for early hominins44,53. These lakeshore environments not only promoted the growth of herbaceous plants, creating relatively open vegetation landscapes that attracted herbivores intensively exploited by hominins for hunting14,59, but also provided an abundance of local lithic raw materials1,38,60,61. The availability of these resources enhanced hominins’ ability to exploit both animal and plant resources, thereby promoting the development of stone tool technology, as evidenced by the increased core exploitation efficiency within the MJG–Ib artefact layer40.The animal and plant fossils discovered in the artefact layers at the MJG site support our conclusions in this study38. Specifically, fossils of steppe animals including rhinoceros, deer, and horse have been discovered in the MJG–V, MJG–IV MJG–Ia, and MJG–Ib artefact layers40,62 (Supplementary Note 1). Abundant mollusk shells (including Gyraulus chihliensis and Planorbis youngi), and the leaves and seeds of aquatic plants were found in MJG–Ⅲ, suggesting a lakeside or swamp environment suitable for large herbivores and carnivores38. A substantial quantity of fossils of Mammuthus trogontherii, exhibiting signs of smashing and scraping, were discovered in MJG–Ⅲ (Supplementary Fig. 1). These fossils indicate scenes of hominins dismembering animals, scraping bones for meat consumption, and utilising bones, and they confirm that large animals were a crucial food source for these hominins38 (Supplementary Fig. 1). The analysis of mammal fossils from the MJG–Ⅲ artefact layer by Qiu et al.62 revealed that steppe animals accounted for ~70%, while forest animals accounted for ~15%. More than 60 intact elephant footprints were uncovered in the MJG–Ⅱ artefact layer (Supplementary Fig. 1). The analysis of biological fossils recovered from the BS layer revealed elephantids, cervids, and rhinocerotids that were adapted to a forest environment, while Equus was adapted to a grassland environment38,63. This evidence indicates that, in addition to forest, a significant area or areas of grassland existed within the regional vegetation during the period of hominin activity64. Qiu et al.62 analysed animal fossils in the BS layer and found that steppe animals accounted for ~60% of the total. Fossil evidence from the MJG site demonstrate that during the period of hominin activity, the relatively open vegetation landscape offered a diverse range of resources. The co-occurrence of fossils from both forest-adapted and grassland-adapted animals, coupled with evidence of hominin utilisation of large animals, suggests that this mixed vegetation setting was conducive to hominins survival.Notably, similar scenarios highlighting the importance of relatively open vegetation landscapes for hominins are also evident at multiple early Pleistocene H. erectus archaeological sites around the world65,66,67. In northwestern Kenya in Africa, data from 481 fossil tracks, including 97 hominin footprints attributed to H. erectus, reveal that the open vegetation landscape of the lakeshore provided hominins with water resources, abundant food resources (including aquatic and terrestrial animals and plants), offering efficient hunting/scavenging opportunities, and enhanced visibility that facilitated migration65. Similarly, the open vegetation landscapes in Java, Indonesia, and at Kocabaş in the Denizli Basin (Southwestern Turkey) attracted large numbers of big herbivores, providing H. erectus with potential animal resources for survival66,67.In summary, our results suggest that a relatively open vegetation landscape facilitated the evolution and migration of early H. erectus, while dense forest vegetation hindered hominin dispersal and technological development. Although climate played an important role in the migration and evolution of early hominins68,69,70, the influence of vegetation landscape openness cannot be ignored2,17. Overall, our findings offer a novel perspective on human–environment interactions during the period of hominin evolution, emphasising the role of the vegetation landscape as a key selective pressure alongside climatic change.MethodsPollen analysisPollen analysis was performed at 10-cm intervals on 422 samples, with a sample temporal resolution of approximately 1000 years. Sample preparation followed the conventional HCl–NaOH–HF treatment71. For each sample, 300 g of sediment was weighed and one tablet of Lycopodium spores (27,560 grains) was added to calculate the pollen concentrations. After chemical treatment, pollen and spores were extracted using heavy liquid flotation. These procedures were conducted at the School of Geographical Sciences of Hebei Normal University. Pollen identifications were made at ×400 under a Zeiss Imager A2 optical microscope with the aid of standard pollen reference publications for China72 and reference material preserved in the Key Laboratory of Environmental Evolution and Ecological Construction of Hebei Normal University. A minimum of 400 terrestrial pollen grains was counted for each sample. The common pollen types are illustrated in Supplementary Fig. 6. Pollen diagrams were drawn with Tilia 1.7.1673.Quantitative reconstruction of vegetation landscape opennessSources of modern pollen and vegetation landscape openness dataThe modern pollen dataset we used is based on China’s modern pollen database, comprising a total of 4164 samples74 (Supplementary Fig. 2). The data on vegetation landscape openness corresponding to the modern sampling points are MODIS satellite data provided by the National Aeronautics and Space Administration (NASA), with a spatial resolution of 250 m (https://search.earthdata.nasa.gov/).Screening the modern pollen dataScreening of modern pollen data is crucial for ensuring the accuracy of quantitative reconstructions. The selection process we applied to the modern pollen dataset employed the following criteria: 1) Air trap and dust samples were excluded due to differences in the preservation of modern pollen compared to fossil pollen. 2) Samples with latitude, longitude, and altitude that did not match the real situation were excluded (a total of 18 samples were excluded in this study). 3) Fan et al.75, based on modern pollen data and the Human Influence Index (HII, 0–64) (https://sedac.ciesin.columbia.edu/)76, successfully distinguished the threshold values of native/secondary vegetation and secondary/anthropogenic vegetation by using the error inflection point–discriminant technique (EIPDT) (HII = 22 and 38, respectively). Vegetation begins to be affected by human activities when HII > 22; therefore, modern pollen samples with HII > 22 were deleted in this study.In the study, the pollen assemblage was dominated by temperate taxa, with only trace amounts of subtropical and frigid zone types detected (Fig. 4). This composition suggests that the past vegetation likely developed under a temperate climatic regime. Consequently, to accurately reconstruct past vegetation landscape openness, it is crucial to select modern pollen data from a comparable spatial range. Given the dominance of temperate pollen and this regional climatic context, the space-for-time substitution approach was applied. The selection of an appropriate spatial range for the modern training set is therefore critical for model performance77. An excessively small range may not capture the full variation within the reconstruction sequence, while an excessively large range can weaken the pollen-landscape relationship and introduce errors77. Based on principles of quantitative reconstruction, we established modern pollen training sets within multiple distance intervals (800–1500 km from the study site, at 200-km intervals) for analysis77. Among the tested intervals, the training set within a 1000 km radius yielded the optimal model performance (Supplementary Table 2). This optimal dataset comprised 1201 modern pollen samples (Supplementary Fig. 2). It covers a wide gradient of vegetation landscape openness (27%–100%) and includes all the principal pollen assemblage taxa found in the fossil record (Fig. 4).Quantitative reconstruction of vegetation landscape opennessWe selected the three most widely used methods for the quantitative reconstruction of vegetation openness: the Weighted Averaging Partial Least Sequence (WA-PLS), the Modern Analogue Technique (MAT)36 and Random Forest (RF)78. These three methods are currently the most widely used79,80. We compared the results obtained using these three methods to select the most suitable method in this study. The predictive performances of all the calibration models were assessed via self-cross-validation, with reference to the performance statistics of each calibration model, including the root mean square error of prediction and R2 between observed and predicted values36 (Supplementary Fig. 3, Supplementary Table 2). We also used non-metric multi-dimensional scaling to test the degree of matching between modern and fossil pollen assemblages81, and the random TF method was used to evaluate the statistical significance of the pollen and landscape openness reconstructions81.First, to verify the reliability of the reconstruction results of the chosen model, we selected 57 modern samples from the transition between forest and grassland in the vicinity of the study area (the Taihang mountains, Guancen mountains, Nihewan, and Zhangbei regions in North China), which covered the major pollen assemblages within the strata (Supplementary Note 4). Then, the vegetation landscape openness was reconstructed for two purposes: to verify the correlation between the reconstructed and observed values, and to determine the critical values of the vegetation openness of forest, forest-steppe, and grassland (Fig. 3). All these analyses were conducted using R (4.0.3) with the “rioja” (version 1.0–7) and “palaeoSig” (version 2.0–7) packages.Quantitative reconstruction of vegetation coverThe Landscape Reconstruction Algorithm (LRA) is based on the relative pollen productivity of the dominant plant taxa in a given study area, and the relative vegetation abundance is reconstructed using the REVEALS model33. The REVEALS model is intended for reconstructing regional vegetation using pollen records from large lakes (e.g., larger than 100 ha) or a combination of multiple small lakes33. It can correct the differences in pollen productivity and dispersal characteristics among taxa, while also accounting for the type and size of sedimentary basins33. This model has been widely applied in vegetation reconstruction from the late Pleistocene in Europe and Asia82,83,84. The results demonstrate that, compared to unadjusted pollen percentages, the plant abundances estimated by the REVEALS model more accurately reflect true regional vegetation coverage83. Previous studies have shown that the Nihewan paleo-lake began to form during the late Pliocene85. The paleo-lake covered an area of ~10,000 km² between 2.18 and 1.87 Ma, being the largest at the time85. From 1.87 to 0.73 Ma, it retreated by 3–4 km, reducing its area to an estimated ~8000 km285. Consequently, since this conforms to the underlying assumption of large lakes, the REVEALS model is appropriate for reconstructing past vegetation cover in this region.The REVEALS model was run using the LRA. REVEALS.v6.2.2 with model parameters consisting of the radius of the depositional area (m), the fossil pollen count, pollen fall speeds (m/s), relative pollen productivity, and the regional vegetation range and its variance–covariance matrix33. The relative pollen productivity values of 10 plant taxa were selected (Supplementary Table 5), and their pollen percentages accounted for ~90% of the pollen assemblages, covering the principal pollen types in the strata. The pollen productivity of tree taxa was obtained from data on the relative pollen productivity of mountain areas in the upper reaches of the Sanggan River in the Nihewan Basin in Guancen, in the same research area; this was because the pollen productivity of tree taxa is close in the same climate area86. The pollen productivity of herbaceous plants is affected by a wide range of climatic factors, and therefore, the relative pollen productivity of herbaceous plants was selected based on integrated research results for northern China87.

    Data availability

    All data (Supplementary Data 1–4) used in this study are freely available online (https://doi.org/10.6084/m9.figshare.30415381).
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    Download referencesAcknowledgementsThis research was supported by the National Natural Science Foundation of China (NSFC) (Grant no. 42377439), the National Key Research and Development Programme of China (Grant no. 2023YFF0804600), and NSFC (Grant nos. T2192954, 41877433, 42507605). We would like to express our gratitude to Dr. Guoqiang Ding from Lanzhou University and Dr. Wensheng Zhang from Hebei GEO University for their assistance in collecting samples. We are grateful to Associate Professor Shengrui Zhang from Hebei Normal University and Dr. Zijing She from Nanjing University for their valuable suggestions.Author informationAuthors and AffiliationsHebei Technology Innovation Center for Remote Sensing Identification of Environmental Change, Hebei Key Laboratory of Environmental Change and Ecological Construction, School of Geographical Sciences, Hebei Normal University, Shijiazhuang, Hebei, ChinaBaoshuo Fan, Yuecong Li, Jiaxing Yang, Qinghai Xu, Yawen Ge & Bing LiState Key Laboratory of Lithospheric and Environmental Coevolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, ChinaBaoshuo Fan, Qingzhen Hao, Deke Xu, Chenglong Deng & Houyuan LuHebei Provincial Institute of Cultural Relics and Archaeology, Shijiazhuang, Hebei, ChinaFagang Wang & Fei XieCollege of Earth Sciences, Hebei GEO University, Shijiazhuang, Hebei, ChinaZhen ZhangAuthorsBaoshuo FanView author publicationsSearch author on:PubMed Google ScholarYuecong LiView author publicationsSearch author on:PubMed Google ScholarFagang WangView author publicationsSearch author on:PubMed Google ScholarJiaxing YangView author publicationsSearch author on:PubMed Google ScholarZhen ZhangView author publicationsSearch author on:PubMed Google ScholarQinghai XuView author publicationsSearch author on:PubMed Google ScholarQingzhen HaoView author publicationsSearch author on:PubMed Google ScholarYawen GeView author publicationsSearch author on:PubMed Google ScholarBing LiView author publicationsSearch author on:PubMed Google ScholarDeke XuView author publicationsSearch author on:PubMed Google ScholarFei XieView author publicationsSearch author on:PubMed Google ScholarChenglong DengView author publicationsSearch author on:PubMed Google ScholarHouyuan LuView author publicationsSearch author on:PubMed Google ScholarContributionsB.F., Y.L., and H.L. conceived the study; Q.X. provided the modern pollen data; F.W. and F.X. provided field materials; B.F., Z.Z., Y.G., and B.L. collected the samples; B.F., J.Y., and Z.Z. treated and identified the pollen samples; B.F. and D.X. performed statistical analyses; B.F., Y.L., H.L., C.D., and Q.H. wrote the text. All authors commented on the interpretation of the results and gave final approval for publication.Corresponding authorsCorrespondence to
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    Entomopathogenic fungi disrupt the feeding behavior of Euschistus heros in soybean

    AbstractThis study evaluated the effects of the entomopathogenic fungi on the feeding behavior of the Neotropical brown stink bug, Euschistus heros, using electropenetrography (AC-DC) technology. Twenty females per treatment were reared under controlled conditions and exposed to soybean pods treated with fungal suspensions (2 µL on the pronotum with 5 × 106 and 6.15 × 108 conidia mL− 1 for Cordyceps javanica and Metarhizium anisopliae, respectively), chemical insecticide (Thiamethoxam + Lambda-cyhalothrin, 0.025/100 mL), and aqueous solution of Polysorbate 80 (0.01% v/v) (control). Response variables associated with count and duration of feeding behavior over 72 h of recording were modelled using GAMLSS (generalized additive models for location, scale, and shape) to assess the statistical significance of treatments and for pairwise comparisons of means (p < 0.05). The fungal treatments and chemical insecticide significantly reduced the frequency and duration of feeding events, especially stylet penetration and seed ingestion, compared to untreated controls. Additionally, insects treated with fungi spent more time in non-feeding behavior, indicating disrupted feeding behavior. Both fungi also shortened the duration of the final feeding probe by about 13 h. Furthermore, electropenetrography enables assessment of pest–plant interactions and biocontrol efficacy beyond mortality.

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    Data availability

    The raw datasets generated during the current study are available in the Zenodo repository at: [https://doi.org/10.5281/zenodo.16572536](https:/doi.org/10.5281/zenodo.16572536).
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    Download referencesAcknowledgementsThe authors gratefully acknowledge the financial support provided by the National Council for Scientific and Technological Development (CNPq), [grant number: 309733/2021-9] and the Fundação de Amparo à Pesquisa do Estado de Goiás (FAPEG), [grant number: 1721]. We also thank the Instituto Federal Goiano and the Center of Excellence in Bioinputs (CEBIO) for their institutional support throughout this study.FundingThis research was supported by the National Council for Scientific and Technological Development–CNPq [grant number: 309733/2021-9] and the Fundação de Amparo à Pesquisa do Estado de Goiás–Fapeg [grant number: 1721]. The research also received institutional support from Instituto Federal Goiano and the Center of Excellence in Bioinputs (CEBIO).Author informationAuthors and AffiliationsDepartamento de Ciências Agrárias, Instituto Federal Goiano – Campus Rio Verde, Rio Verde-GO, BrazilGuilherme Pereira de Oliveira, Frederico Antonio Loureiro Soares & Pablo da Costa GontijoDepartamento de Agronomia, Instituto Federal Goiano – Campus Urutaí, Urutaí-GO, BrazilAndré Cirilo de Sousa Almeida & Kaylaine Aparecida Gomes de SouzaLaboratório de Estatística e Geoprocessamento, Instituto Federal Goiano – Campus Urutaí, Urutaí-GO, BrazilAnderson Rodrigo da SilvaAuthorsGuilherme Pereira de OliveiraView author publicationsSearch author on:PubMed Google ScholarFrederico Antonio Loureiro SoaresView author publicationsSearch author on:PubMed Google ScholarAndré Cirilo de Sousa AlmeidaView author publicationsSearch author on:PubMed Google ScholarKaylaine Aparecida Gomes de SouzaView author publicationsSearch author on:PubMed Google ScholarPablo da Costa GontijoView author publicationsSearch author on:PubMed Google ScholarAnderson Rodrigo da SilvaView author publicationsSearch author on:PubMed Google ScholarContributionsMr. Guilherme Pereira Oliveira*, ORCID: 0000-0001-7440-6773. Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Resources; Software; Supervision; Validation; Visualization; Writing – original draft; Writing – review & editing. *Corresponding Author. Professor Frederico Antonio Loureiro Soares, ORCID: 0000-0002-4152-5087. Conceptualization; Formal analysis; Investigation; Methodology; Project administration; Resources; Supervision; Validation; Writing – review & editing. Professor André Cirilo de Sousa Almeida, ORCID: 0000-0001-9786-2990. Conceptualization; Data curation; Formal analysis; Methodology; Resources; Software; Supervision; Validation; Writing – review & editing. Ms. Kaylaine Aparecida Gomes de Souza, ORCID: 0009-0008-6124-4427. Data curation; Formal analysis; Investigation; Methodology; Software; Validation; Visualization. Professor Pablo da Costa Gontijo, ORCID: 0000-0001-8173-0539. Conceptualization; Data curation; Investigation; Methodology; Resources; Software; Writing – review & editing. Professor Anderson Rodrigo da Silva, ORCID: 0000-0003-2518-542X. Conceptualization; Data curation; Formal analysis; Project administration; Resources; Supervision; Writing – review & editing.Corresponding authorCorrespondence to
    Guilherme Pereira de Oliveira.Ethics declarations

    Competing interests
    The authors declare no competing interests.

    Additional informationPublisher’s noteSpringer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.Rights and permissions
    Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.
    Reprints and permissionsAbout this articleCite this articlede Oliveira, G.P., Soares, F.A.L., Sousa Almeida, A.C.d. et al. Entomopathogenic fungi disrupt the feeding behavior of Euschistus heros in soybean.
    Sci Rep (2025). https://doi.org/10.1038/s41598-025-31096-wDownload citationReceived: 29 July 2025Accepted: 28 November 2025Published: 17 December 2025DOI: https://doi.org/10.1038/s41598-025-31096-wShare this articleAnyone you share the following link with will be able to read this content:Get shareable linkSorry, a shareable link is not currently available for this article.Copy shareable link to clipboard
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    KeywordsBiological control
    Cordyceps javanica

    Metarhizium anisopliae
    ElectropenetrographyIntegrated pest management More

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    Insight in transformations of nano-metallic and ionic platinum forms in different soil types in the context of Pt immobilization

    AbstractPlatinum is emitted by road traffic mainly in the form of metallic particles. Interaction of Pt-NPs with soil causes their chemical transformation that may result in dissolution. Investigation of soil – Pt-NPs interactions presented in this study focuses on assessing the influence of soil type on Pt mobility in soil enriched in its metallic and ionic forms. Studied soil types included peat soil (high content of organic matter), sandy soil, chalk loam soil and transformed soil collected next to a road with high traffic (Zabrze, Poland), to which citrates were added to mimic the rhizosphere activity. Solid-liquid extractions based on modified BCR protocols were applied to establish mobile and organic fractions, and Pt was determined with both voltammetry and ICP-MS. Cross-comparison of the results of these two techniques allows to conclude about Pt-NPs transformation into Pt(II). The mobility of Pt in transformed soil and sandy soil (about 10% extractability with CH3COOH) is significantly higher than in clay (4–5%) and peat soil (0.4–0.8%). Metallic Pt-NPs with small diameters can be effectively transformed into ionic forms. Their content in mobile fraction reaches 30–50%, and in oxidizable fraction – even 75–80%. Higher mobility of Pt was observed after incubation in the presence of citrates, however it is not due to a transition of Pt-NPs into ionic forms but results from limited interaction of small NPs with the soil matrix.

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    Additional data will be made available on request addressed to the corresponding author.
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    Download referencesAuthor informationAuthors and AffiliationsFaculty of Chemistry, University of Warsaw, ul. Pasteura 1, Warsaw, 02-093, PolandJoanna Kowalska, Paulina Brusik, Monika Sadowska, Katarzyna Kińska & Beata Krasnodębska-OstręgaAuthorsJoanna KowalskaView author publicationsSearch author on:PubMed Google ScholarPaulina BrusikView author publicationsSearch author on:PubMed Google ScholarMonika SadowskaView author publicationsSearch author on:PubMed Google ScholarKatarzyna KińskaView author publicationsSearch author on:PubMed Google ScholarBeata Krasnodębska-OstręgaView author publicationsSearch author on:PubMed Google ScholarContributionsConceptualization: Joanna Kowalska, Beata Krasnodębska-Ostręga; Methodology: Joanna Kowalska, Katarzyna Kińska, Beata Krasnodębska-Ostręga; Formal analysis and investigation: Joanna Kowalska, Paulina Brusik, Monika Sadowska, Beata Krasnodębska-Ostręga; Writing – original draft preparation: Joanna Kowalska, Monika Sadowska, Katarzyna Kińska, Beata Krasnodębska-Ostręga; Writing – review and editing: Joanna Kowalska, Monika Sadowska, Katarzyna Kińska, Beata Krasnodębska-Ostręga; Resources: Beata Krasnodębska-Ostręga; Supervision: Beata Krasnodębska-Ostręga.Corresponding authorCorrespondence to
    Beata Krasnodębska-Ostręga.Ethics declarations

    Competing interests
    The authors declare no competing interests.

    Additional informationPublisher’s noteSpringer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.Rights and permissions
    Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.
    Reprints and permissionsAbout this articleCite this articleKowalska, J., Brusik, P., Sadowska, M. et al. Insight in transformations of nano-metallic and ionic platinum forms in different soil types in the context of Pt immobilization.
    Sci Rep (2025). https://doi.org/10.1038/s41598-025-30219-7Download citationReceived: 30 June 2025Accepted: 21 November 2025Published: 17 December 2025DOI: https://doi.org/10.1038/s41598-025-30219-7Share this articleAnyone you share the following link with will be able to read this content:Get shareable linkSorry, a shareable link is not currently available for this article.Copy shareable link to clipboard
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    KeywordsPlatinum nanoparticlesPlatinum mobilitySoil type effectRhizosphere activityFractionationUltrasound assisted extractionVoltammetry More

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    Elevational distribution patterns of bryophytes in Eastern China – A comprehensive species-trait dataset

    AbstractClimate change significantly affects the dynamics of mountain ecosystems, impacting not only species distributions but also their phenological characteristics. Nevertheless, our comprehension of the effects of climate change on biodiversity is still limited, primarily due to insufficient historical data. The dramatic temperature variations over short distances make permanent monitoring plots along elevational gradients an ideal natural laboratory for investigating species’ responses to climate change. Drawing on field survey information gathered from 2018 to 2022, we have developed a bryophyte species-trait dataset that encompasses 16,920 trait measurements across four categories: taxonomy, distribution, resistance traits, and reproductive traits, derived from 549 species in Eastern China. The compilation of this bryophyte species-trait dataset offers valuable opportunities to deepen our understanding of the factors, constraints, and effects associated with biodiversity variability, while also providing richer insights into predicting species distributions and implementing targeted in-situ conservation strategies.

    Code availability

    No specific code was employed for the generation and analysis of the data presented.
    Data availability

    Bryophyte species-trait dataset is available from the Figshare repository. The direct link is: https://doi.org/10.6084/m9.figshare.29826515.v5.
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    Download referencesAcknowledgementsWe are grateful to the BEST (Biodiversity along Elevational gradients: Shifts and Transitions) Network, the Tianmushan National Nature Reserve of Zhejiang, the Tianma National Nature Reserve of Anhui, the Guanshan National Nature Reserve of Jiangxi and Daiyunshan National Nature Reserve of Fujian, China. We would like to thank Luyan Tang, Shichen Xing, Xing Chen, and Xuan Lü for field assistance. We specially thank Xiaorui Wang from Shijiazhuang University (Hebei Province), Yongying Liu from Jiaozuo Normal College (Henan Province), and Dongping Zhao from Inner Mongolia University (Inner Mongolia) for their assistance in bryophyte species identification. This work was supported by the National Natural Science Foundation of China (nos. 32070228), and the Innovation Program of Shanghai Municipal Education Commission (2023ZKZD36).Author informationAuthor notesThese authors contributed equally: Yi-ran Wang, Xue Yao, Peng Zheng.Authors and AffiliationsBryology Laboratory, School of Life Sciences, East China Normal University, Shanghai, ChinaYi-ran Wang, Zun Dai, Xing Chen, Shu-wen Tu, Yu-ting Yang, En-dao Wang, Qi Wu, Hong-yu Zhang, Yu-ling Xiong, En-qi Lou, You-fang Wang & Jian WangSchool of Life Sciences, Fudan University, Shanghai, ChinaXue YaoLijiang Normal University, Lijiang, ChinaPeng ZhengConservation and Research Center for Collections, Shanghai Natural History Museum (Branch of Shanghai Science & Technology Museum), Shanghai, ChinaRui-ping ShiCollege of Life Sciences, Hebei Normal University, Shijiazhuang, ChinaMin LiSchool of Ecological and Environmental Sciences, East China Normal University, Shanghai, ChinaKun SongCollege of Forestry, Fujian Agriculture and Forestry University, Fuzhou, ChinaZhong-sheng HeKey Laboratory of Ecology and Resources Statistics, Fujian Colleges, Fuzhou, ChinaZhong-sheng HeCross-Strait Nature Research Center, Fujian Agriculture and Forestry University, Fuzhou, ChinaZhong-sheng HeLushan Botanical Garden, Jiangxi Province and Chinese Academy of Sciences, Jiujiang, ChinaZhao-chen ZhangSchool of Life Sciences, Sun Yat-Sen University, Guangzhou, ChinaJian ZhangShanghai Institute of Eco-Chongming (SIEC), 3663 Northern Zhongshan Road, Shanghai, ChinaJian WangZhejiang Zhoushan Island Ecosystem Observation and Research Station, School of Ecological and Environmental Sciences, East China Normal University, Shanghai, ChinaJian WangAuthorsYi-ran WangView author publicationsSearch author on:PubMed Google ScholarXue YaoView author publicationsSearch author on:PubMed Google ScholarPeng ZhengView author publicationsSearch author on:PubMed Google ScholarRui-ping ShiView author publicationsSearch author on:PubMed Google ScholarMin LiView author publicationsSearch author on:PubMed Google ScholarZun DaiView author publicationsSearch author on:PubMed Google ScholarXing ChenView author publicationsSearch author on:PubMed Google ScholarShu-wen TuView author publicationsSearch author on:PubMed Google ScholarYu-ting YangView author publicationsSearch author on:PubMed Google ScholarEn-dao WangView author publicationsSearch author on:PubMed Google ScholarKun SongView author publicationsSearch author on:PubMed Google ScholarZhong-sheng HeView author publicationsSearch author on:PubMed Google ScholarZhao-chen ZhangView author publicationsSearch author on:PubMed Google ScholarQi WuView author publicationsSearch author on:PubMed Google ScholarHong-yu ZhangView author publicationsSearch author on:PubMed Google ScholarYu-ling XiongView author publicationsSearch author on:PubMed Google ScholarEn-qi LouView author publicationsSearch author on:PubMed Google ScholarYou-fang WangView author publicationsSearch author on:PubMed Google ScholarJian ZhangView author publicationsSearch author on:PubMed Google ScholarJian WangView author publicationsSearch author on:PubMed Google ScholarContributionsJ.Z. and J.W. secured funding and organized the fieldwork. J.W., Y.R.W. and X.Y. drafted the paper; X.Y., P.Z., R.P.S., Z.D., X.C., S.W.T., K.S., Z.S.H., Z.C.Z., Q.W., J.Z. and J.W. engaged in field investigation; Y.F.W., M.L., X.Y., S.W.T. and J.W. participate in species identification; Y.R.W., Y.T.Y., E.D.W., H.Y.Z., Y.L.X. and E.Q.L. compiled dataset information; Y.R.W. and X.Y. made the figures and tables; all authors contributed to the final version of the paper.Corresponding authorsCorrespondence to
    Jian Zhang or Jian Wang.Ethics declarations

    Competing interests
    The authors declare no competing interests.

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    Reprints and permissionsAbout this articleCite this articleWang, Yr., Yao, X., Zheng, P. et al. Elevational distribution patterns of bryophytes in Eastern China – A comprehensive species-trait dataset.
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    The expression of father-daughter bond behaviors influences adult partner attachment in titi monkeys

    Abstract

    Coppery titi monkeys (Plecturocebus cupreus) are socially monogamous monkeys that display strong pair bonds similar to human romantic attachments, preceded by infant attachment to their fathers. To understand how father-daughter bonds impact adult relationship dynamics, we established a novel method for quantifying expression of bond-related behaviors. We assessed behavioral and neural correlates of preference, stress buffering, and separation distress to identify how females’ current and former attachment figures impact female attachment. Whereas all females (n = 9) shifted to preferring their partner over father six-months post-pairing, females that exhibited higher expression of juvenile parent preference maintained a relationship with their father six-months post-pairing, as evidenced by higher-than-expected father proximity. Higher expression of juvenile measures of proximity following a brief separation predicted slightly increased partner proximity in adulthood. Neural activity patterns in brain regions assessed pre- and post-pairing showed high similarity in glucose metabolism, despite overall activity being lower post-pairing. While there was some inconsistency in results, higher expression of juvenile proximity following a separation was associated with enhanced reduction in activity within social bonding brain regions (social salience network, periaqueductal gray, cerebellum), suggesting a potential stress buffering benefit via reduced threat-related brain activation, like that seen in high-quality human relationships. These findings advance current knowledge of how early relationships may shape adult bond-related behavior and neural activity.

    Data availability

    The datasets generated during and/or analyzed during the current study are available in the Zenodo repository, https://doi.org/10.5281/zenodo.15660221.
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    Download referencesAcknowledgementsWe would like to thank the following for their invaluable assistance: Jaleh Janatpour, Kevin Theis, Charles Smith, the veterinary staff at California National Primate Research Center (CNPRC), and the Bales Laboratory undergraduate and international interns. We would also like to thank Alan Conley and Rebecca Cotterman for the work measuring plasma cortisol. This research was funded by the National Institute of Child Health and Human Development [grant number R01HD092055 to Karen L. Bales], by the National Institutes of Health base grant [grant number P51OD011107 to Prasant Mohapatra and the CNPRC], and the National Institutes of Health [grant number S10OD021715 to Simon Cherry].FundingThis research was funded by the National Institute of Child Health and Human Development [grant number R01HD092055 to Karen L. Bales], by the National Institutes of Health base grant [grant number P51OD011107 to Prasant Mohapatra and the CNPRC], and the National Institutes of Health [grant number S10OD021715 to Simon Cherry].Author informationAuthors and AffiliationsDepartment of Psychology, University of California, Davis, Davis, CA, USALynea R. Witczak, Allison R. Lau, Emilio Ferrer & Karen L. BalesCalifornia National Primate Research Center, University of California, Davis, Davis, CA, USALynea R. Witczak, Allison R. Lau, Brad A. Hobson, Pauline B. Zablocki-Thomas, Madison Dufek, Abhijit J. Chaudhari & Karen L. BalesGraduate Program in Animal Behavior, University of California, Davis, Davis, CA, USAAllison R. Lau & Karen L. BalesCenter for Molecular and Genomic Imaging, University of California, Davis, Davis, CA, USABrad A. Hobson & Abhijit J. ChaudhariDepartment of Biology, Utah State University, Logan, UT, USASara M. FreemanDepartment of Radiology, University of California, Davis, Davis, CA, USAAbhijit J. ChaudhariDepartment of Neurobiology, Physiology, and Behavior, University of California, Davis, Davis, CA, USAKaren L. BalesDepartment of Biology, 100 Campus Drive, Elon, NC, 95616, USALynea R. WitczakAuthorsLynea R. WitczakView author publicationsSearch author on:PubMed Google ScholarAllison R. LauView author publicationsSearch author on:PubMed Google ScholarBrad A. HobsonView author publicationsSearch author on:PubMed Google ScholarSara M. FreemanView author publicationsSearch author on:PubMed Google ScholarPauline B. Zablocki-ThomasView author publicationsSearch author on:PubMed Google ScholarMadison DufekView author publicationsSearch author on:PubMed Google ScholarEmilio FerrerView author publicationsSearch author on:PubMed Google ScholarAbhijit J. ChaudhariView author publicationsSearch author on:PubMed Google ScholarKaren L. BalesView author publicationsSearch author on:PubMed Google ScholarContributionsL.R.W. lead study conceptualization, methodology, formal analysis, investigation, and visualization. L.R.W. and A.R.L. wrote the paper. M.D. and P.B.ZT. assisted with investigation and project administration. S.M.F., B.A.H., and A.J.C. assisted with methodology. E.F. provided guidance on formal analysis. K.L.B. acquired funding for the project, providing essential resources, and was the supervisor for L.R.W, guiding project conceptualization and methodology. All authors had access to the data, commented on the manuscript drafts, and approved the final submitted version.Corresponding authorCorrespondence to
    Lynea R. Witczak.Ethics declarations

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    Reprints and permissionsAbout this articleCite this articleWitczak, L.R., Lau, A.R., Hobson, B.A. et al. The expression of father-daughter bond behaviors influences adult partner attachment in titi monkeys.
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    Selenium speciation analysis for the investigation of selenium uptake for the hydroponically cultivated garlic samples

    AbstractSelenium is a significant nutrient source for humans and plants. Currently, inorganic selenium, including selenate and selenite, is used to cultivate selenium-rich crops to manage people’s selenium deficiency problems. Garlic, being a major accumulative plant in the Allium genus, can absorb selenium concentrations beyond 1000 mg/kg when grown in soils rich in selenium. In this study, garlic samples were germinated in a soilless medium and transfered to hydroponic cultivation medium containing three different levels of sodium selenite (Na2SeO3). The total amount of selenium in the roots and leaves of lyophilized 150 μM garlic extracts was 43.8 ± 33.2 and 62.7 ± 16.4 mg/kg (n = 4), while the total amount of selenium in the enzyme-extracted leaves and roots was 10.3 ± 2.0 and 10.6 ± 5.9 mg/kg (n = 4). Furthermore, selenium speciation analysis revealed that MeSeCys and SeMet as the main organoselenium compounds in garlic. Additionally, unknown selenium species were detected, indicating the need for further research to identify them.

    IntroductionGarlic is a horticulture crop that has been propagated vegetatively for a very long time1. Garlic has been utilized since ancient times, not only for enhancing the taste of food, but also for its therapeutic properties2. The primary reason for its health benefits is the existence of allicin molecules3. Garlic possesses a diverse range of molecules and minerals including carbohydrates, fiber, protein, magnesium, potassium, etc4. Organosulfur molecules contribute to the medicinal, culinary and insecticidal properties of garlic. Garlic’s organosulfur components contribute to its pungent and astringent odour5.Selenium has a close relationship with sulphur. Selenium (Se) can act as a substitute for sulfur (S) in several metabolic processes6. Due to the analogous chemical and physical characteristics of selenium and sulfur, selenium can be used as a substitute for sulfur in the metabolic processes of plants. This results in their rivalry in the absorption, transportation, and incorporation in plants. Selenate (SeO42−) is chemically reduced using the same assimilation mechanism as sulfate (SO42−), and it becomes part of Se-containing amino acids, such as selenocysteine (SeCys) and selenomethionine (SeMet). This mechanism substitutes the amino acids cysteine and methionine, which contain sulfur SeCys and SeMet are presumed to be capable of being integrated into proteins7.Selenium is a vital micronutrient that is necessary for human health in small amounts8. This element, as an essential dietary element for humans, promotes the improvement of human antioxidant and immunological activities9. Hence, a scarcity of selenium in the human body can lead to various health ailments, including stunted growth, cardiovascular disorders, cancer, and numerous other complications. The World Health Organization (WHO) suggests that individuals consume a daily amount of selenium ranging from 55 to 200 mg10. The organism can absorb selenium by dietary intake. Selenium is of great importance due to its potential to have both positive and negative effects on human health, with a very small margin between a deficit and toxicity11. The toxicity and bioavailability of selenium can be influenced by its chemical form12. Each variant of selenium serves a distinct purpose in the metabolic processes of the human body13. Selenium exists in both inorganic and organic forms in nature and has four distinct oxidation states. Inorganic selenium compounds include selenite (SeO32−), selenate (SeO42−), selenide (Se2−), and elemental selenium (SeO)14. Moreover, selenomethionine (Se-Met) and selenocysteine (Se-Cys) are involved in various biological activities. The amino acids that include selenium are essential components of protein structures and can be found in various food products15. Se-amino acids including methyl-selenocysteine (methyl-SeCys), Se-Met and SeCys have much higher antioxidant activity compared to their sulfur compounds16. The analogue’s biosynthetic activity, sulfur, joins Se to form Se-amino acids (SeCys and SeMet). Proteins that substitute Se-amino acids for S-amino acids (cysteine and methionine) can produce harmful and abnormal proteins. In order to preserve crops, it is essential to determine the optimum levels of Se for biofortification. This will help to keep the Se content of grains or edible parts within safe limits, avoiding any potential toxicity17. Plants use the S-assimilation pathway for Se metabolism, which replaces sulfur in important S-amino acids such as cysteine (Cys) and methionine (Met), as well as their associated proteins18. Crops are humans’ primary source of Se intake. However, the selenium level of crops generally inadequate to supply the selenium needs of humans. Hence, the approach of increasing the selenium level in the edible section of plants, commonly referred to as Se biofortification, provides an effective way for addressing selenium insufficiency According to reports, the use of exogenous Se can not only increase the amount of Se in crops but also inhibit heavy metal absorption by crops from the soil19.In literature, garlic has been analyzed qualitatively and quantitatively using anion exchange chromatography (AEC), size exclusion chromatography (SEC), hydride generation atomic fluorescence spectrometry (HG-AFS)16, atomic absorption spectrometry (AAS)11, double-channel atomic fluorescence spectrophotometry (AFS)19 and gas chromatography mass mass spectrometry (GC–MS)20. It was typically chosen for IP-RP-HPLC because the system is known to be effective in determining the speciation of selenium in plant samples21.The extent of selenium insufficiency in the population of developing nations, including Türkiye, remains uncertain, and there has been limited researches conducted to assess the selenium levels in the edible portions of food crops. In order to increase the Se content while reducing the accumulation of heavy metals in edible parts of garlic, hydroponic cultivation was used, including the sprouting phase. The study’s main goal was to conduct in-depth research on the enrichment of hydroponically grown garlic with different concentrations of selenite. The goal of this study was to find out how garlic takes in selenite and what kinds of selenium are being produced in the garlic body.Materials and methodInstrumentationThe determination of total selenium in all samples were performed by inductively couple plasma tandem mass spectrometry (ICP-MS/MS) model 8800 ICP-QQQ (Agilent Technologies, Japan) and it was hyphenated with Agilent 1100 series HPLC system equipped with an auto sampler and a binary pump for measurement of selenium species in the samples.The elimination of spectrum interferences caused by the matrix in totally digested samples was accomplished by implementing a mass shift technique using O2 for the isotopes 76Se, 78Se, and 80Se and simply collision gas of H2 was utilized in speciation analysis to reduce molecular interferences resulting due to the plasma. All operating parameters for the speciation and total analyses of Se were applied according to the previously conducted study in our research group22.Digestion of garlic samples was carried out by using Mars 5 microwave digestion unit (CEM Corporation, USA) in a temperature- and pressure-regulated program.The Agilent 1100 series HPLC system was utilized for the separation of analytes. The outlet of the column was directly connected to the ICP-MS/MS nebulizer via PEEK tubing. For speciation analysis, a Phenomenex Synergi Hydro-RP C18 column (250 × 4.60 mm, 4 µ) was employed.ReagentsAll reagents used in the study were analytical grade unless otherwise stated. Elga Veolia’s PURELAB Flex system was used to produce ultrapure deionized water for mobile phases, as well as all sample and standard preparations.In the enzymatic digestion of garlic samples, Protease XIV (from Streptomyces griseus) and Proteinase K (from Tritirachium album) were employed and both of them were Sigma-Aldrich, Germany. Tris-hydroxymethane (min. 99%, ITW Reagents) was used as a buffer solution (pH 7.5) and the prepared solution was utilized in the enzymatic digestion procedure.Reverse phase ion pairing chromatography (RP-IP-HPLC) was used for the speciation analysis of selenium and the mobile phase containing 3.0% (v/v) methanol was prepared using heptafluoorobutyric acid (HFBA) which was purchased form Alfa Aesar with 99% purity. In order to obtain 1000 mg/kg Se for selenate and selenite, and 100 mg/kg Se for the other organo-selenium species, appropriate amounts of sodium selenate (Na2SeO4) (anhydrous 99.8 + %, Alfa Aesar), sodium selenite (Na2SeO3) (Alfa Aesar, 99% min), seleno-DL-cystine Se(Cys)2 (Sigma, USA), seleno-methylselenocysteine (MeSeCys) (95%, Sigma, USA) and selenomethionine (SeMet) (Sigma, USA) were dissolved in deionized water. For speciation analysis, stock solutions were kept at + 4.0 °C, and working solutions were prepared daily by serial dilution using stock solutions.In the determination of total selenium, sub-boiled HNO3 produced by Milestone SubPUR sytem from Emsure grade nitric acid (Merck, 65%) and H2O2 (Merck, 35%, w/w) were used in sample digestion and also further sample preparation steps. Certified reference material of NIST coded as SRM 3149 were used for plotting calibration curve in total Se determination.Cultivation of selenium-enriched garlicThe origin of garlic samples used throughout the study was Kastamonu/Türkiye. Garlic cloves were kept in a refrigerator at + 4.0 °C for two weeks. Selenium enrichment studies were carried out by using bulbs of the garlics. Garlic samples were rinsed with deionized water and completely dried at ambient temperature. Then, the garlic samples were weighed and sprouted in tap water, which is a soilless medium, at room temperature for 4 days. At the end of the sprouting period, samples were transferred into selenium-enriched nutritional solution which was prepared by adding 0.50 g of plant nutrient into tap water and spiking with an appropriate amount of sodium selenide. The garlic samples were cultivated in three different selenium-enriched media containing 50 μM, 100 μM, and 150 μM sodium selenit (Se(IV)) in 14 g tap water (Table 1). Additionally, control samples were prepared without spiking selenium solution in order to assess the impact of selenium presence for the garlic growth. The samples were kept to be grown in the hydroponic medium for 10 days under regular daylight and room temperature conditions.Table 1 Garlic samples in hydroponic cultivation.Full size tableThe growth of the garlic plants was carefully observed day by day during the cultivation period. Changes in the color, size, or general condition of the plants were visually recorded on a daily basis. The plant’s height was also measured each day and recorded. The roots were also examined for signs of yellowing or abnormal development. During the growing period, the nutritional solutions were checked every two days and increased to 14 g to maintain ideal growth conditions for the garlic plants by using tap water. Figure 1 shows a visualization of the experimental setup for the cultivation of garlic. At the end of the 10th day, the hydroponic environment was terminated before yellowing/ripening began. Root and leaves were separated from the harvested plants. The roots and leaves of the garlics were weighed separately; the length of the leaf was measured by using a ruler, and the nutrient medium was diluted from 14 to 50 g with water. The root and leaf of garlic were cut into smaller pieces with a plastic knife to increase the surface area of the samples for more efficient lyophilization. After lyophilization, garlic samples were stored at − 80 °C.Fig. 1Sprouting garlic in a hydroponic medium (A), Sprouting garlic (4th day) (B), Selenium-enrichment process in hydroponic medium (day 0) (C), Harvest time for garlic enriched with selenium (9th day) (D).Full size imageQuantification of total seleniumTotal selenium was determined in the root and leaf of lyophilized garlic and in enzymatically digested solutions of them. In addition, nutrient solutions at the end of growth were analyzed for total selenium remaining after cultivation. The digestion procedure which was developed and validated in our previous research study on leek samples was applied for mineralization of the samples described above as the matrixes are quite similar with those previously22. The program consists of increase in temperature to 135 °C in 5.0 min, followed by a further increase to 180 °C in 5.0 min, held for 20 min and then cooled to ambient temperature. To digest the samples, approximately 10 mg of lyophilize root and leaf of garlic was weighted and transferred into vessels. Then, 3.0 mL of sub-boiled HNO3 solution (65% v/v), 1.0 mL of 30% (w/w) H2O2, and 1.0 mL of H2O were added to the vessels. The digested samples were diluted to 10 g with ultrapure deionized water.The nutritional solutions were also digested to evaluate selenium levels remained. The vessels contained approximately 0.15 mL of nutritional solution samples, all from the control and selenium hydroponic mediums. It was carried out by adding 2.0 mL of sub-boiled HNO3, 1.0 mL of 30% H2O2, and 2.0 mL of H2O. The digested samples were diluted to 10 g with ultrapure deionized water.For the analysis of enzymatically extracted root and leaf of garlic solutions, 2.0 mL of solution was weighted into vessels together with 2.0 mL of sub-boiled HNO3 solution (65% v/v), 1.0 mL of 30% H2O2. The digested samples were diluted to 10 g with ultrapure deionized water.The total selenium amount in all digested samples was determined applying a matrix-matched external calibration method and whole sample and standard preparation steps were performed gravimetrically.Extraction procedure by the help of enzymeThe enzymatic hydrolysis process was used to release selenoamino acids from proteins. Enzymatic extraction protocol described by Ari et al.22 was applied to both lyophilized roots and leaves of selenium enriched garlic. 10 mg of garlic samples were mixed with 5.0 mL of an extraction solution made from 5.0 mg of protease XIV and proteinase K prepared in 30 mM Tris–HCl with 1.0 mM CaCl2 (pH: 7.5). Protease was added to hydrolyze the peptide bonds. The solutions were centrifuged and filtered with 0.45 μm filters after shaking at 50 °C for 18 h. The root and leaf of the garlic samples cultivated in 150 μM sodium selenit (Se(IV)) fortified medium were analyzed to demonstrate the representative extraction efficiencies of the proposed method. The evaluation of the extraction yields was carried out by comparing the total selenium content in the enzymatically extracted solutions and in solid samples. The mineralization of these extracted solutions was carried out according to the procedure described in Sect. “Quantification of total selenium”. The total selenium in the solution was then quantified using ICP-MS/MS, employing a matrix-matched external calibration technique under optimized tuning parameters.Selenium speciation analysisHPLC-ICP-MS/MS was used to perform speciation analysis (inorganic and organic Se) on enzymatically extracted root and leaf of garlic samples. All standards and garlic samples were prepared gravimetrically, and measurements were performed using an external calibration approach.For speciation analysis, a Phenomenex Synergi Hydro-RP C18 (250 × 4.60 mm, 4µ) column was used. 0.10% (v/v) HFBA, 3.0% (v/v) MeOH, and a pH 6.0 mixture were utilized as a mobile phase with 1.0 mL/min of flow rate, and 20 µL of the injection volume. Optimum instrumental and chromatographic conditions are applied as it was used by Ari et al.22 and the enzymatically extracted samples were analyzed directly without applying further dilution.Quantification of Se(Cys)2, SeMet, and MeSeCys in garlic was achieved using the external calibration method. The calibration curves for selenoamino acids were created separately for both the root and leaf of garlic. Calibration plots of both samples were prepared for selenoamino acids in the concentration range of 0.49–100.9 ng/g. For the leave samples, the regression coefficients of the calibration curves were recorded as 0.9997, 0.9998, 0.9979 for Se(Cys)2, MeSeCys, and SeMet, respectively. Similarly, the regression coefficients of the calibration curves for the root samples were calculated as 0.9995, 1.0000, 0.9990 for Se(Cys)2, MeSeCys, and SeMet, respectively (Table 1).System analytical performances in terms of limit of detection (LOD) and quantification (LOQ) values were tested with 0.50 ng/g standard solution in 3.0% MeOH for sodium selenit (Se(IV)), Se(VI), Se(Cys)2 and SeMet, while it was evaluated using 5.0 ng/g standard solution in 3.0% MeOH for MeSeCys. The following equations were used in calculation of LOD and LOQ.$$begin{gathered} {text{LOQ}} = {1}0{text{sd }} + {text{ C}}_{{{text{std}}}} hfill \ {text{LOD}} = {text{3sd }} + {text{C}}_{{{text{std}}}} hfill \ end{gathered}$$The calculated LOD and LOQ valued for all selenium species are given in Table 2.Table 2 LOD and LOQ for selenium species in the employed instrumental conditions.Full size tableResult and discussionHydroponic cultivation of garlicThe average weight of Taşköprü garlic before hydroponics was known; thus, the roots and leaves were evaluated for the effect of selenium fortification on the growth of garlic samples. Average weight for different parts of the garlic samples are given in Table 3. The results showed that inorganic selenide supplementation significantly increased the growth of both the root and leaf of garlic compared to the control plants.Table 3 The effect of selenium on the growth parameters of garlic. *n = 4.Full size tableWhen only the increase in mass of the roots is evaluated, it is observed that even the dry masses of the plants growing in the medium supplemented with 50 μM and 100 μM sodium selenit (Se(IV)) are higher than their initial wet weights, while the control group remains at a dry mass, which is considered to be equivalent only to water loss22. However, roots cultivated in 100 μM selenide fortified medium showed a similar behavior with the control group. Therefore it is concluded that 150 μM sodium selenit (Se(IV)) concentration may be toxic level for garlic plants and lead to reduced growth.High Se levels can inhibit photosynthesis and nutrient transport. Studies have shown that changes in the mineral balance of plants, specifically the buildup of large amounts of phosphorus, may have caused problems with their growth and a decrease in their biomass when there were high selenium levels in the nutrient solution23.Investigation of selenium uptake rate and translocation of selenium in edible parts of garlic samplesOne of the advantage of hydroponic cultivation is to be able to calculate the uptake rate of fortified analyte by plants. In this study, theoretically total selenium amount in the nutrient solutions in 50 μM, 100 μM and 150 μM sodium selenit (Se(IV)) were calculated as 3.9 mg/kg, 8.0 mg/kg and 11.9 mg/kg, respectively. The amounts of total selenium in each nutritional solutions after the completion of growing process of the plants were measured by ICP-MS/MS and reported as 0.85 ± 0.26, 2.5 ± 0.8 and 2.6 ± 0.4 mg/kg, respectively. Therefore, the relative average uptake amount were found as 78%, 69% and 78% for each concentration levels, respectively. These data support that garlic samples were efficiently uptaking Se from the solutions during the growth period. As discussed in Sect. “Hydroponic cultivation of garlic”, the evaluation of the increase in the masses of samples shows that selenium application alone significantly improved the growth parameters of garlic which is in agreement with previous reports24. It is thought that selenium’s effect on plant growth stems from its ability to detoxify heavy metals, thereby positively contributing to growth25.In order to investigate typical localization of Se, the total selenium amount of the roots and leaves of the garlic samples cultivated in 150 μM selenium enriched growth medium were separately determined by ICP-MS/MS. Total selenium contents of lyophilized root and leaf of garlic samples were found as 43.8 ± 33.2 and 62.7 ± 16.4 mg/kg (n = 4), respectively. According to the data obtained, the difference in Se accumulation ability between roots and leaves of garlic samples seems to be significant considering the standard deviations on the average values. Therefore, it can be concluded that the conversion of Se(IV) into organic forms of selenium takes time in the root and are more likely to be accumulated in leaves rather than the root parts in a given enough time during the cultivation time period. These findings are consistent with those reported in the literature that selenium levels are generally higher in the stems and leaves of most plants than the roots26.Investigation of extraction efficiency rateTotal selenium amounts in the extracts were determined as described in Sect. “Quantification of total selenium” by ICP-MS/MS and extraction efficiencies of the applied method in roots and leaves were tested in the highest sodium selenit (Se(IV)) fortified samples which is 150 μM.The total amount of selenium in the enzyme-extracted leaves and roots was 10.3 ± 2.0 and 10.6 ± 5.9 mg/kg (n = 4), respectively. The average extraction efficiencies measured for root and leaf were calculated as (33 ± 22)% and (17 ± 3)% (n = 4) respectively. These low extraction efficiency values indicate that about 70–80% of total Se in each part of the garlic cannot be extracted. In our previous study22, the extraction efficiency rates of the proposed extraction protocol for leaves and stems of leek samples (n = 53) were recorded as (70 ± 20)% and (67 ± 19)%, respectively. On the other hand, efficiencies of different enzymatic extractions procedures applied on Allium families were also reported as significantly higher than the observed values in this study27. Therefore, the authors are suspecting form that the particle size of the garlic samples is not small enough as in our previous study, hence the extraction efficiency were found to be relatively low compared to previously reported studies.Selenium speciation analysisIt is reported that, SeMet breaks down into free SeCys via the transsulfuration pathway and enters metabolic reactions28. Food sources that are rich in selenium, particularly organic selenium such as selenomethionine (SeMet), can enhance the absorption and use of selenium in the human body26. Plants can contain selenium in the form of inorganic or organic molecules, which can become high-molecular-weight compounds such as proteins. Studies have shown that higher plants have a Se pathway. After being absorbed by the roots, Se is metabolized within the plant, resulting in the formation of organoselenium compounds. These compounds can either be stored within the plant or released into the air via volatilization21. In Allium plants (including garlic), “Alliins” are the primary source of active compounds and flavors. Many selenides, which are possible breakdown products of selenium compounds (Se compounds) and are similar to “alliins” (Se-“alliins”), have also been found in selenium-enriched garlic29.Although experimental results based on the rate of uptake showed garlic could collect high amounts of selenium, further investigation into the mechanism of selenium translocation in garlic samples was required to determine selenium amount in the edible sections. The nutritional solutions of control garlic samples contained selenium below the detection limits of ICP-MS. Therefore, while the results from the measurements of the selenium-enriched samples were consistently analyzed, speciation analysis was not performed on the control samples whose Se concentrations were expected to be significantly lower than those of the selenium-enriched samples. For the speciation of organoselenium species in the plant, a number of ion-pairing agents are used in a reverse phase high performance liquid chromatgrams (IP-RP-HPLC) coupling with ICP-MS30. In this study, the presence of selenium species in different parts of garlic samples were determined by means of IP-RP-HPLC-ICP-MS/MS system using HFBA as ion-pairing agent which has capability of separating more organoselenium species than trifluoroacetic acid (TFA), pentafluoropropanoic acid (PFPA) and triethylammonium acetate (TEAA)21,31. Inorganic selenium species are not separated as efficiently as organoselenium species in this separation method as seen Fig. 2. However, it helps to qualitative determination of inorganic selenium species in the extracted samples. As any significant peak belonging to selenite or selenate were detected in the IP-RP-HPLC system, any futher chromatograpic separation such as strong anion exchange HPLC system were not applied in this study.Fig. 2Chromatograms obtained by IP-RP-HPLC-ICP-MS/MS (A)—20 ng/ mL spiked into enzymatically extracted garlic (root) and—enzymatically extracted garlic (root) samples supplemented by 150 µM sodium selenite (Se(IV)); (1) Se (VI), (2) Se(IV), (3) Unknown, (4) Se(Cys)2, (5) MeSeCys, (6) SeMet. (B)—20 ng/ mL spiked into enzymatically extracted garlic (leaf) and—enzymatically extracted garlic (leaf) samples supplemented by 150 µM sodium selenite (Se(IV)); (1) Se (VI), (2) Se(IV), (3) Unknown, (4) Se(Cys)2, (5) MeSeCys, (6) SeMet.Full size imageThrough sulfate transporters, selenium is taken up by plant roots and subsequently transported into the xylem of the leaves, where it undergoes sulfur assimilation in chloroplasts to produce SeMet, SeCys, and other organic selenium. Selenite is rapidly transformed into organoselenium compounds in the root, while selenate is carried to the xylem and transferred to the shoot, where it is integrated into organoselenium compounds and transported throughout the plant similarly to S32. This chromatographic separation method identified only Se(Cys)2, SeMet, and MeSeCys and unknown species in the roots and leaves of the garlic samples (Fig. 2). All the species detected in garlic samples including the unknown species were consistent with the literature review. Raw garlic was observed to contain different Se species, including MeSeCys, Se(VI), SeMet, and unknown species16,20. Garlic (Allium sativum), onions (Allium cepa), leeks (Allium ampeloprasum), and broccoli (Brassica oleracea) all have high amount of Se-methylselenocysteine (MeSeCys), which makes up about half of the total Se33. Our study also demonstrated that the most dominant species present in garlic are MeSeCys and SeMet. Moreover, it should be clearly stated that the recorded peak areas for unknown peaks in both leaves and root of garlic samples are as detectable as SeMeCys and SeMet in all samples. As summarized in Table 4, the percentage distribution of selenium species (SeMet and MeSeCys) in leaves and roots of garlic samples across different sodium selenite Se(IV) treatments reveals distinct tissue-specific metabolic responses to selenium exposure. In general, the selenium level in the stems and leaves of most plants is greater when compared to the roots34.Table 4 Summary of average concentration values of organoselenium species quantified in leaves and roots.Full size tableIn leaves, SeMet is the dominant form at lower sodium selenite Se(IV) concentrations (50–100 µM), accounting for approximately 60–62% of the total measured selenium species. However, at 150 µM sodium selenite Se(IV), the proportion shifts markedly in favor of MeSeCys (57.3%), suggesting a metabolic shift toward MeSeCys biosynthesis at higher selenium levels. This shift may reflect an adaptive detoxification mechanism, as MeSeCys is known to be a less toxic, non-proteinogenic form of selenium that can be stored or excreted more safely than SeMet.In roots, the SeMet and MeSeCys proportions remain more balanced across all sodium selenite Se(IV) concentrations, with a nearly 1:1 ratio at 100 and 150 µM. This indicates that roots exhibit a relatively stable selenium speciation profile, potentially due to a more passive role in selenium metabolism compared to leaves or due to the early-stage processing of Se before translocation to aerial parts. Overall, the data suggest that selenium speciation is dose- and tissue-dependent. While SeMet dominates at lower concentrations, higher selenium exposure induces a shift toward MeSeCys, especially in leaves, likely as a protective response to mitigate Se toxicity. SeMet is the primary selenocompound found in cereal grains, grassland legumes, and soybeans. On the other hand, MeSeCys is the primary selenocompound found in Se-enriched cruciferae plants, including garlic, onions, sprouts, broccoli, and wild leeks35. MeSeCys has been previously reported in the literature as a selenium compound with notable anticancer potential33 which was also found as one of the most dominant organoselenium species detected in the garlic samples in this study.In the literature, it is shown that plants accumulate selenite and transform it into organic selenium species via the metabolism pathway33. In this study, the pathway was used to investigate selenium accumulation and transformation in the garlic samples. While uptake selenium was transformed into organoselenium species, all the species were not qualitatively and quantitatively determined. Although the existing separation method has been commonly used in the literature, further studies are needed to be conducted to determine the observed unknown species which contributed significantly to the Se signal. In the literature, unknown peaks in garlic were identified by accurate mass determination, further confirming the identities of the structurally characterized Se species30,36.ConclusionEnvironmental and genetic factors can influence a plant’s growth. This study investigated the effect of selenium enrichment, which affects plant metabolism, and selenium supplementation on garlic growth, uptake, transport, extraction efficiency, and differentiation. Hydroponic garlic can effectively absorb selenite, but its growth may be inhibited when the concentration exceeds 100 μM. This study also revealed that garlic plants took the selenium efficiently, with the uptake rates of 78% at 50 μM and 69% at 100 μM sodium selenit (Se(IV)). Selenium is more likely to accumulate in garlic leaves, indicating a time-dependent conversion of inorganic Se into organic forms, aligning with earlier studies. Selenium speciation analysis confirmed that MeSeCys and SeMet are the dominant organoselenium compounds present in garlic, with differing concentrations in roots and leaves. These results suggest that selenium accumulation and transformation into organoselenium compounds are influenced by factors such as the plant’s growth stage, the specific organ, and selenium concentration. Moreover, the study detected unknown selenium species, as indicated by notable peaks in chromatographic analysis, suggesting further research is needed to identify and characterize these unidentified compounds. The enzymatic extraction method used in this study is relatively inefficient and may affect the representativeness of morphological analysis. Morphological analysis identified MeSeCys and SeMet as the main organic selenium forms, and there were also significant unknown selenium species, which are worthy of further study. Future studies should employ advance techniques such as ESI–MS/MS or LC-HRMS to elucidate the identity of the unknown chromatographic peaks.

    Data availability

    Data will be made available with reasonable request from corresponding author.
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    Download referencesAcknowledgementsThe authors thank to the Scientific and Technological Research Council of Türkiye-National Metrology Institute (TUBITAK- UME) for the permission of conducting the instrumental measurements in their research laboratory.FundingNot applicable.Author informationAuthors and AffiliationsDepartment of Chemistry, Faculty of Arts and Science, Yıldız Technical University, 34220, Istanbul, TürkiyeÜmmügülsüm Polat Korkunç, Buse Tuğba Zaman, Sezgin Bakırdere & Emine KarakuşScientific and Technological Research Council of Turkey, 41470, Gebze, Kocaeli, TürkiyeBetül Ari EnginTurkish Academy of Sciences (TÜBA), Vedat Dalokay Street, No: 112, 06670, Çankaya, Ankara, TürkiyeSezgin BakırdereAuthorsÜmmügülsüm Polat KorkunçView author publicationsSearch author on:PubMed Google ScholarBetül Ari EnginView author publicationsSearch author on:PubMed Google ScholarBuse Tuğba ZamanView author publicationsSearch author on:PubMed Google ScholarSezgin BakırdereView author publicationsSearch author on:PubMed Google ScholarEmine KarakuşView author publicationsSearch author on:PubMed Google ScholarContributionsÜmmügülsüm Polat Korkunç: Formal analysis; methodology; validation; roles/writing—original draft. Betül Ari Engin: Formal analysis; methodology; validation; roles/writing—original draft. Buse Tuğba Zaman: Formal analysis; methodology; validation; roles/writing—original draft. Sezgin Bakırdere: Conceptualization; investigation; methodology; supervision; writing—review & editing. Emine Karakuş: Investigation; methodology; supervision; writing—review & editing.Corresponding authorsCorrespondence to
    Sezgin Bakırdere or Emine Karakuş.Ethics declarations

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    Reprints and permissionsAbout this articleCite this articleKorkunç, Ü.P., Engin, B.A., Zaman, B.T. et al. Selenium speciation analysis for the investigation of selenium uptake for the hydroponically cultivated garlic samples.
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    Keywords
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    Interannual variability of net primary productivity in the northwest African coastal upwelling system and their relation to Dakar Niños

    AbstractThe Canary Current upwelling system, located along the northwest African coast between approximately 10ºN and 35ºN, is among the most productive marine ecosystems globally, supporting a rich marine biodiversity. In the southern part (9ºN–18ºN), pronounced interannual variability in net primary production (NPP) is influenced by extreme warm and cold events, known as Dakar Niños and Niñas, respectively. In this study, we analyze the physical mechanisms driving the interannual variability of NPP from 2003 to 2023, using a combination of satellite observations, reanalysis data, and ocean model outputs. Our results indicate that the interannual NPP variability is closely linked to changes in sea surface temperature, with the most pronounced effects occurring during March-April-May, i.e., the main upwelling season. A total of six undocumented extreme coastal low NPP events are identified, nearly all of which are associated with Dakar Niños. These low NPP events are linked to both local and remote forcing. The local forcing is associated with fluctuations of alongshore winds and near-coastal wind stress curl. The remote forcing involves the propagations of coastal trapped waves emanating from the equator and the northern Gulf of Guinea. Part of the local and remote forcing can be associated with large-scale climate modes.

    IntroductionThe Canary Current upwelling system (CCUS), located along the northwestern coast of Africa, is among the most productive marine ecosystems globally, supporting local and regional fisheries1,2. Based on the upwelling intensity throughout the year, the CCUS can be divided into three subregions (Fig. 1; adapted from Gómez-Letona et al.3): a weak permanent upwelling zone (from 26°N to 33°N), a permanent upwelling zone (18°N to 26°N), and a seasonal upwelling zone (from 9°N to 18°N), the latter being the focus of the present study.Fig. 1(a) Climatological mean NPP (shading), Optimum Interpolation sea surface temperature (OI-SST, blue contours, every 1 °C), and ERA5 wind field at 10 m (arrows) during the upwelling season from March to May. The position of the ITCZ is denoted by the red contour which indicates the 0 m s−1 meridional wind speed at 10 m. (b) Same as (a) but during the relaxation season from July to August. The climatological means are calculated over the period 2003-2023.Full size imageThe pronounced seasonality in the southern part of the CCUS depends mostly on the strength and position of the Azores high-pressure system4, and the seasonal migration of the Intertropical Convergence Zone (ITCZ)5. From March to May (MAM), the ITCZ is closest to the equator, allowing for strong upwelling favourable alongshore winds resulting in high net primary production (NPP; Fig. 1a). After its northward migration, the ITCZ reaches its northernmost position at about 12°N from July to September, leading to weak alongshore winds, i.e., unfavourable for upwelling, and to low NPP along the coasts of Senegal and Mauritania (Fig. 1b). The seasonal upwelling zone features large interannual sea surface temperature (SST) variability dominated by extreme coastal warm and cold events called Dakar Niños and Niñas6, respectively. Dakar Niños/Niñas typically peak in February-March-April during the early upwelling season in the coastal Dakar Niño index (CDNI, 2°-width coastal band from 9°N and 18°N, magenta domain in Fig. 2a) region. These events are reported to be driven locally by modulations of the alongshore winds conditioning anomalous coastal upwelling/downwelling as well as changes in the mixed-layer temperature by anomalous heat fluxes6. Moreover, the reduction in local wind speed will decrease the latent heat loss from the ocean to the atmosphere, thereby contributing to the development of Dakar Niños. Additional forcing may originate from the equator via the propagation of equatorial Kelvin waves (EKW) and subsequent poleward propagating coastal trapped waves (CTWs)7. The analysis of the satellite altimetry over the period 2002-2012 by Illig et al.7 revealed that some CTWs of equatorial origin propagated north up to the latitude of Liberia (~ 6°N). A downwelling (upwelling) CTW reaching the CDNI region would deepen (shoal) the thermocline and nutricline, leading to a reduction (enhancement) of local upwelling, positive (negative) SST anomalies, and ultimately anomalously low (high) NPP. Similar impacts of CTWs on SLA, SST and NPP variability have already been well demonstrated along the southwestern African coast in the Angola Benguela upwelling system8,9,10,11,12,13,14. However, the role of CTWs in the development of Dakar Niños/Niñas and their impacts on the NPP has, to our knowledge, not yet been discussed. Further, Koseki et al.15 showed, using a high resolution regional coupled model, that under a warmer climate, Dakar Niños may intensify without changing their location and timing. NPP in the CCUS can be modulated by climate modes operating in the Atlantic Ocean. The North Atlantic Oscillation (NAO)16, a hemispheric meridional oscillation in atmospheric mass with centers of action near Iceland and over the subtropical Atlantic17, has been reported to influence the upwelling intensity in all three parts of the CCUS by intensifying (reducing) the upwelling favourable winds during a positive (negative) phase18,19. Additionally, Gómez-Letona et al.3 showed significant correlations between the NAO index and the NPP in the seasonal upwelling area in January-February-March over the period 2003-2015. Furthermore, the Atlantic Meridional mode (AMM)20, characterized by an interhemispheric SST gradient in the tropical Atlantic and peaking during the upwelling season (i.e., MAM), can also impact the NPP in the CDNI region by affecting the position of the ITCZ. In fact, during a positive (negative) phase of the AMM, significantly reduced (enhanced) northeasterly trade winds generate a large-scale warming (cooling) in the tropical North Atlantic that extends to the CDNI region through a reduction (strengthening) of surface evaporative cooling21. Yet, additional modulation of the NPP in the CCUS may originate from other basins. For example, Roy and Reason22 reported that between 1957 and 1995, coastal SST anomalies in the southern part of the CCUS were preceded by El Niño-Southern Oscillation (ENSO) events in the Pacific by several months. The authors suggested a remote forcing through an atmospheric bridge between the Pacific and Atlantic Oceans with positive (negative) ENSO events leading to a relaxation (intensification) of the trade winds in the Atlantic affecting the coastal upwelling and highlighted by warm (cold) SST anomalies in the southern part of the CCUS. However, a previous study by Wang et al.23 showed that the relationship between ENSO and SST anomalies (SSTA) in the tropical North Atlantic (including the CDNI region) is modulated by the Atlantic multidecadal variability (AMV). Over the period 1982-2011, Oettli et al.6 did not find a consistent response of the SST off the coasts of Senegal and Mauritania to ENSO. Similarly, Gómez-Letona et al.3 investigated correlations between the Multivariate ENSO index and the Southern Oscillation index with the SST in the three subregions of the CCUS and did not find any significant relationships over the period 1993-2014. Yet, López-Parages et al.24 showed, using an ocean model, that over the period 1985-2009, ENSO influenced the round sardinella population biomass and distribution in the central to southern part of the CCUS. Hence, the remote effect of ENSO on the NPP in the southern part of the CCUS remains an open question.Here, building on previous studies investigating the seasonal to decadal variability of the NPP in the CCUS3, we document for the first time the interannual variations in NPP occurring in the CDNI during the upwelling season (MAM) over the period 2003-2023. The link between extreme NPP events and the occurrence of Dakar Niños/Niñas is examined. Furthermore, potential remote forcing through CTW originating in the northern Gulf of Guinea or in the equatorial Atlantic, as well as the influence from different climate modes are investigated.ResultsInterannual NPP variabilityAn area of large NPP variability, defined by the standard deviation of the monthly NPP anomalies (NPPA), is observed off the coasts of Senegal and Mauritania mostly within the CDNI region (Fig. 2a). Concomitantly, this coastal region presents large variability of the SST as shown by the standard deviation of the monthly SSTA (blue contours in Fig. 2a).The large SST variability is driven by the occurrence of extreme warm and cold events called Dakar Niños and Niñas6, respectively. Moreover, the NPP in the CCUS features a pronounced annual cycle with a maximum in NPP during MAM and a minimum in July-August-September (JAS; Fig. 1, Fig. 2b). However, the seasonal cycle of the standard deviation of the NPP anomalies features two peaks, a first peak in March and a second peak in May. This suggests that the variability of the NPP can be seen as a modulation of its annual cycle, i.e., an earlier or later seasonal peak in NPP and/or a smaller or larger annual maximum. The interannual variability of the NPP in MAM is preceded by large variations in SST in February-March-April (Fig. 2c). The time series of detrended anomalies of NPP averaged in the CDNI region is shown in Fig. 2d. The NPPA clearly exhibit a strong year to year variability marked by the occurrences of extreme NPP events. Since the interannual variability of the NPP is maximum in MAM, for this study, only the extreme events that peaked during MAM are considered. Therefore, nine anomalous coastal events are identified and highlighted by their corresponding years in Fig. 2d. They are classified into 3 extreme high NPP events (2012, 2015, 2016) and 6 extreme low NPP events (2005, 2008, 2010, 2020, 2021, 2023). More details on the extreme NPP events can be found in the supplementary tablesS1 and S2. Yet, to our knowledge, there are no studies in the literature that have described the interannual variability of the NPP in the CDNI region. In order to allow for significant and meaningful results we will focus on the extreme low NPP events for the rest of the study. Despite the lack of a long time series of NPP, Fig. 2d shows indications of a decadal variability signal of the NPPA in the CDNI region with prevailing phases of negative NPPA from 2003 to 2011 and after 2020 and a positive phase of NPPA between 2011 and 2020.Fig. 2(a) Standard deviation of detrended net primary production anomalies (NPPA, shading) estimated by the standard vertically generalized production model and OI-SST anomalies (SSTA, blue contours, every 0.2 °C). The magenta region in (a) represents the coastal Dakar Niño Index region (CDNI, 9°N-18°N, 2°-coastal band). The dashed red line represents the isobath 2000 m. (b) Seasonal cycle of the standard deviation of CDNI-averaged detrended NPPA (red) and climatology (black) of the CDNI-averaged detrended NPP. (c) Same as (a), but for NPPA averaged in March-April-May (MAM) and SSTA averaged in February-March-April (FMA). (d) Monthly detrended CDNI-averaged NPPA. The horizontal green and blue dashed lines indicate the ± 0.8 standard deviation of the interannual NPPA. Green and blue shaded areas represent the extreme high and low NPP events, respectively, and are identified when the CDNI-averaged NPPA exceeds ± 0.8 standard deviation (± 0.551 gC m−2 day−1) for at least 2 consecutive months. Only the NPPA events that peak during MAM are highlighted by their corresponding years. All anomalies have been calculated over the period 2003/01–2023/12.Full size imageRole of local processes and remotely forced CTWsTo better characterize the relation between extreme low NPP events, surface wind stress and SST along the northwest African coast, Fig. 3a shows a 95% statistically significant composite analysis of detrended anomalies of those parameters relative to the peaks of the low NPP events. Details about the selected years for the composite are provided in the caption of Fig. 2.Fig. 3(a) Composite map of monthly detrended NPPA (shading), SSTA (red contours, every 0.5 °C) and ERA5 wind stress (arrows) computed from peak months of six extreme low NPP events (2005; 2008; 2010; 2020; 2021 and 2023). Shaded areas (NPPA), contours (SSTA) and black arrows (wind stress) displayed in (a) are statistically significant at 95% confidence level. (b) Time series of composite anomalies of the CDNI-averaged: SSTA (solid red line), NPPA (green line), meridional wind stress anomalies (TYA, blue line), sea level anomalies (SLA, orange line), model potential temperature anomalies at 10 m (PT10A, dashed red line) and model mixed layer depth (MLDA, gray line). The composite anomalies displayed in (b) are relative to the peaks of the extreme low NPP events, ranging from 3 months before to 3 months after those peaks. Values significant at the 95% confidence level are denoted by a filled circle.Full size imageThe mature phase of the extreme low NPP events that peak during MAM is marked by the presence of low NPPA limited to latitudinal boundaries of the CDNI region and extending from the coast to ~ 22°W with anomalies below -2 gC m−2 day−1. The low NPPA occurs simultaneously with statistically significant warm SSTA (> 1 °C), in the CDNI region. Since the standard deviation of CDNI-averaged SSTA in FMA is around 0.71 °C, the warm SSTA that are observed during the peak of extreme low NPP events could indicate the occurrence of Dakar Niños. Therefore, Dakar Niños are linked to the reduction of NPP. Additionally, during the mature phase of the extreme low NPP events, statistically significant southwesterly anomalies over the warm SST and low NPP areas south of 17°N are observed. In fact, these reduced trade winds will induce a reduction in the offshore Ekman transport and coastal upwelling leading to a warming and negative NPPA. Averaged in the CDNI region, Fig. 3b shows the time evolution of composite anomalies of local observed SST, model potential temperature at 10 m (PT10), NPP, meridional wind stress, mixed layer depth and SLA. As expected, statistically significant positive anomalies of meridional wind stress (~ 0.01 N m−2) are observed only during the peak of the low NPP events. Further, positive meridional wind stress anomalies are already observed two months before the peak of low NPP events even though they are not statistically significant. This will reduce the coastal upwelling which will generate statistically significant coastal warm SSTA (statistically significant at 95% from one month before to one month after the peak). Note that additional coastal warming effect may come from reduced latent heat loss through the weaker northeasterly trade winds. Likewise, model PT10 anomalies (model PT10A) are quite consistent with observations and show significant values during the peak and one month after the peak. Simultaneously, the mixed layer is anomalously thin (less than - 0.9 m) for about 3 months (from two months prior to the peak until the peak). Note that the shoaling of the mixed layer favours a warming by the shortwave heat fluxes. In response to the reduced meridional wind stress, warm SSTA and thin mixed layer, coastal NPP is reduced with a maximum reduction of - 1.53 gC m−2 day−1 during the peak. Statistically significant low NPPA persist in the region until 2 months after the peak where they reached - 0.77 gC m−2 day−1. In addition to the low NPPA, Fig. 3b also portrays a local maximum positive anomaly of SLA (downwelling coastal SLA signal) of 2.3 cm one month before the peak of low NPP events which decays by 0.35 cm up to 2 months later. Since maximum downwelling coastal SLA signal precedes minimum negative coastal NPPA by one month, we further analyse the downwelling coastal SLA signal. Spatial composite maps of anomalies of SLA, surface wind stress and wind stress curl are shown in Fig. 4. Indeed, besides the reduced local meridional wind stress, statistically significant negative near-coastal wind stress curl anomalies (WSCA; cyan contours and dots in Fig. 4a with shading in Fig. S1a) are observed concomitantly with coastal positive anomalies of SLA one month before the peak of the low NPP events (Fig. 4a). These significant WSCA are less than - 0.15 × 10–7 N m−3 (Fig. S1a). Note that a negative near-coastal WSCA indicates a reduction of the mean near-coastal cyclonic wind stress curl, resulting in weakened Ekman suction, i.e., downwelling anomalies and reduction of the coastal upwelling. This weakened Ekman suction has contributed to coastal warming (Fig. 3b) and led to positive coastal anomalies of SLA. The statistically significant negative WSCA extend offshore to the west until the western and central equatorial Atlantic (Fig. S1a). Off equatorial negative WSCA pattern as the one observed in Fig. 4a have already been shown to be efficient to trigger downwelling Rossby waves25. Note that Fig. 4a also shows a C-shape like pattern about the equator in the surface wind stress anomalies which can be seen as the signature of the wind-evaporation-SST (WES) feedback21 indicating that the AMM is in its positive phase. Statistically significant offshore reduced northeasterly trade winds are associated with the reduction of the Azores high-pressure system (not shown, sea level pressure anomalies < -200 Pa). A strong reduction of the surface wind stress in the CDNI region is only observed during the peak of low NPP events (Fig. 4b) as shown in Fig. 3b for the meridional wind stress.Fig. 4(a–d) Composite maps of monthly detrended anomalies of: SLA (shading with contours indicate areas statistically significant at 95% confidence level), negative wind stress curl (cyan contours and dots indicate areas statistically significant at 95% confidence level, see Fig. S1) and surface wind stress (arrows, with black arrows representing wind stress statistically significant at 95% confidence level). The composite anomalies are relative to the peaks of the extreme low NPP events (2005; 2008; 2010; 2020; 2021 and 2023) with in (a) Peak (− 1), (b) Peak, (c) Peak (+ 1) and (d) Peak (+ 3) representing one month before, peak, one month and 3 months after the peak months of extreme low NPP events, respectively.Full size imageFigure 4a also portrays statistically significant easterly wind stress anomalies, spreading from ~ 5°S to the northern Gulf of Guinea (mainly coastal regions of Ghana and Côte d’Ivoire) and from 15°W to 0°N. We suggest that these easterly wind stress anomalies might provide additional forcing of downwelling coastal trapped waves (CTWs), that would propagate along the northwest African coast, deepening the thermocline and contributing to positive anomalies of SLA and SSTA in the CDNI. These downwelling CTWs also deepen the nutricline, thereby reducing the local NPP. Additionally, off the equator, part of the energy of the downwelling CTWs is transmitted westward as downwelling Rossby waves. This could explain the statistically significant positive anomalies of SLA spreading to the west at ~ 3°N.One month later (Fig. 4b), i.e., during the peak of the low NPP events, the negative WSCA persist north of the equator (see also Fig. S1b) providing additional forcing of the downwelling Rossby wave. This downwelling Rossby wave then propagates westward and is associated with off-equatorial positive anomalies of SLA exceeding 3 cm (Figs. 4b-c). Upon reaching the South American coast, that downwelling Rossby wave will be completely reflected into an eastward propagating downwelling equatorial Kelvin wave at around two months after the peak of the low NPP events (Peak (+ 2), not shown) and will then influence the equatorial Atlantic variability one month later (Peak (+ 3), Fig. 4d).Although not statistically significant, negative anomalies of SLA observed along the equator (east of 20°W) and along the western African coast east of 0°E mark the signature of wind-forced upwelling equatorial Kelvin waves and subsequently upwelling CTWs triggered by easterly wind stress anomalies along the equator (Fig. 4a).Mixed-layer heat budget analysisGiven that low NPP events coincide with occurrences of Dakar Niños, based on output from an ocean model (see Data and Methods section for description and validation of the model outputs), an analysis of a mixed layer heat budget is performed to investigate the drivers of mixed layer temperature under the assumption that these mechanisms may also account for the observed NPP variability. The rate of change of the mixed layer temperature anomalies is expressed in Eq. 1 and the results are shown in Fig. 5. The monthly climatology of all the terms is shown in Fig. 5a. Climatologically, the analysis shows that within the CDNI region, the net surface heat flux term is the dominant contributor to the mixed layer warming from February to October with highest contribution during MAM, the period of high NPP (Figs. 1a, 2b). Also, a minor contribution from lateral diffusion to mixed layer warming is evident throughout the year, with a maximum around MAM. In contrast, vertical diffusion, which is a proxy for vertical mixing, dominates the mixed layer cooling throughout the year, with an important contribution also during MAM. Additional cooling during MAM also arises from zonal advection, while vertical advection contributes to a lesser extent. In the CDNI region, meridional advection seems to not contribute to the mixed layer temperature during MAM, but shows minor contribution to the mixed layer warming in June, July, November and December.Fig. 5(a) Monthly climatology of the CDNI-averaged terms of the model mixed layer heat budget from 2003 to 2023, where Tot is the total mixed layer temperature tendency, Xadv, Yadv and Zadv are the zonal, meridional and vertical advection, respectively, and Ldf, Zdf and Qnet are the lateral and vertical diffusion and the net surface heat flux, respectively. (b) Time series of composite anomalies of the CDNI-averaged of each term of the model mixed layer heat budget. The composite anomalies are relative to the peak of the extreme low NPP events ranging from 3 months before to 3 months after the peak months of the extreme low NPP events. (c) Same as (b), but for contribution to model mixed layer temperature due to surface heat‐flux anomalies acting on climatological mixed layer depth (Q’ term), mixed layer depth anomalies acting on climatological heating/cooling (H’ term) and the residual. The detrended anomalies of the contribution to model mixed layer temperature due to net surface heat flux is also represented (Qnet_ano). (d) Same as (b) but for anomalies of modelled non-solar flux (Qns_ano), solar radiation flux (Qsr_ano) and net surface heat flux (Qnet_ano). Climatology and anomalies are calculated relative to the period January 2003 to December 2023.Full size imageThree months before the peak of the extreme low NPP events, the mixed layer is anomalously warmed (0.02 °C day−1, Fig. 5b) solely by the net surface heat flux, however cooled by the other terms. Note that the anomalous warming of the mixed layer is obtained by summing the anomalies from all terms with positive values. Two months prior to the peak of the extreme low NPP events, the anomalous warming of the mixed layer (0.032 °C day−1, Fig. 5b) is primarily driven by anomalies of the net surface heat flux explaining 58% and to a lower extent by anomalous lateral diffusion (28%), meridional advection (12%) and to an even lesser extent by anomalous residual (2%). One month later, anomalies of the net surface heat flux explaining 44% are still the main contributor to the anomalous warming of the mixed layer which has now dropped to 0.02 °C day−1. Note that the same contributors as for the previous month are still observed with a reduced anomalous lateral diffusion (20%), and increased anomalous meridional advection (24%) and residual (5%). However, a minor anomalous contribution from vertical advection (7%) is now observed. During the mature phase of the low NPP events, most of the anomalous warming of the mixed layer (0.028 °C day−1) is induced by anomalous vertical diffusion (44%) and zonal advection (30%), while anomalous meridional and vertical advection only play minor roles. This is consistent with surface warming associated with low NPP due to reduced coastal upwelling caused by significantly weakened local coastal wind stress and negative WSCA (Figs. 3, 4b, S1b). However, anomalies of the net surface heat flux largely explain the anomalous cooling of the mixed layer (damping effect) one and three months after the peak, while anomalies of the net surface heat flux, zonal advection and vertical diffusion equally contribute to the anomalous cooling of the mixed layer two months after the peak (Fig. 5b).Since anomalies in the net surface heat flux largely contribute to the anomalous warming or cooling of the mixed layer, we have decomposed this contribution into two terms as displayed in Eq. 2 and shown in Fig. 5c. The two terms are the model’s mixed layer temperature tendency due to net surface heat flux anomalies acting on climatological mixed layer depth (Q’ term) and climatological heating/cooling applied to an anomalous mixed layer depth (H’ term) as done by Senapati et al.26. A residual which is rather small is also estimated as the difference between net surface heat fluxes and summed up contributions of the Q’ and H’ terms. Over the entire time series, results show that the Q’ term largely dominates the contribution of anomalies of the net surface heat flux to anomalous warming or cooling of the mixed layer (Fig. 5c). This indicates that anomalous warming or cooling of the mixed layer in the CDNI region during Dakar Niños or Niñas is a direct response to positive or negative anomalies of the net surface heat flux, respectively, which are largely driven by anomalies the of non-solar flux (Fig. 5d). Note that the anomalies of the non-solar flux are dominated by anomalies of the latent heat flux which are linked to surface wind speed fluctuations in the CDNI region. The anomalous solar radiation term is only playing a minor role in the CDNI region during the extreme low NPP events (Fig. 5d).Role of climate modes on the NPP variability in the CDNI regionPast studies have shown that in boreal spring, the northern tropical Atlantic is influenced by the large-scale climate forcing of the AMM6, the preceding boreal winter ENSO22,24,27,28, and by other modes of variability such as the NAO28. Hence, we have also examined whether these climate modes may also contribute to NPP variability in the CDNI region.Figure 6a portrays the relation between the strength of the AMM events occurring during MAM and the MAM CDNI-averaged NPPA. Results show that over the period 2003-2023 and during MAM, the NPPA in the CDNI region and the AMM index are significantly (at the 95% level) linked, with a correlation of -0.62. In other words, in the CDNI region, years of positive phase of AMM are linked to anomalous surface warming in the tropical North Atlantic causing reduced northeasterly winds through the WES feedback resulting in reduced latent heat loss and coastal upwelling ultimately inducing low NPP. The opposite is observed for years of negative phase of AMM. Note that out of nine extreme NPP events recorded in the CDNI region during MAM (Fig. 2d), six extreme NPP events (66.66%, low NPP in 2005, 2010, 2023 and high NPP in 2012, 2015, 2016) have occurred during an AMM event. In addition, during MAM, SSTA in the CDNI region are linked to the AMM since the sliding correlation (with a 21-year moving window) between AMM index and CDNI-averaged detrended SSTA exhibits highly significant correlations (> 0.6), statistically significant at 95% between 1948 and 2024 (not shown). In contrast, the results from Fig. 6b clearly reveal that between 2003 and 2023, DJF ENSO events are not significantly correlated to NPP events in the CDNI region, even though some NPP events are in phase with ENSO events (for instance low (high) NPP events in 2005, 2010 (2012) in phase with El Niños (La Niña)). This means that over the period 2003-2023, other forcing mechanisms such as the local physical processes with the contribution of the remote ocean dynamics described above or the large-scale forcing of the AMM played a more important role than the remote forcing from ENSO in driving the CDNI NPP variability.Fig. 6(a) Scatter diagram of the Atlantic Meridional Mode (AMM) index averaged during March–April-May (MAM) and CDNI-averaged NPPA during MAM. (b) Same as (a), but for detrended anomalies of SSTA averaged during December-January-February (DJF) in the Niño 3.4 region (120°W-170°W; 5°S-5°N) and CDNI-averaged NPPA during MAM. The AMM index is calculated following the method of Chiang and Vimont20. For ENSO intensity, the DJF values of the ONI are used. See the Data and Methods section for details on the AMM and ONI indexes. The horizontal green and blue lines in (a) and (b) represent the ± 0.8 standard deviation of the interannual CDNI-averaged NPPA (± 0.551 gC m−2 day−1). In (a) the vertical red and blue lines represent ± 1 standard deviation of the AMM index (± 2.56 °C). The vertical red and blue lines in (b) represent the threshold (± 0.5 °C) used to identify the warm and cold periods in the Niño 3.4 region. Only the extreme low and high NPP events that peak during MAM are highlighted in blue and green as in Fig. 1a. (c) Time series of the Atlantic multidecadal variability (AMV, black line). An 11-year centered sliding window is applied to compute annual means of the AMV. The Pearson correlation between the detrended Niño 3.4 index in DJF and the detrended CDNI in MAM (red line, with red dots indicating correlations statistically significant at 95% confidence level) is evaluated using SSTA within 21-year centrered sliding windows with the first window covering the period 1871-1891 and the last window the period 2004-2024. SSTA are defined as deviations from the monthly climatology over the period 1870–2024. The Pearson correlation between the NAO index during December-January-February-March (DJFM) and the detrended CDNI in MAM (blue line, with blue dots indicating correlations statistically significant at 95% confidence level) is evaluated using the Hurrell North Atlantic Oscillation (NAO) Index (station-based) over 21-year centered windows with the first window for 1870–1890 and the last for 2004-2024.Full size imageSince NPP data is only available for a short period of time and highly significant correlation (-0.68) exists between CDNI-averaged SSTA and NPPA in MAM from 2003 to 2023, we use longer time series of SSTA to investigate the link between ENSO as well as NAO with the CDNI region on longer time scales. Therefore, to further characterize the relation between DJF Niño 3.4 index and MAM SSTA, a sliding correlation (with a 21-year moving window) of detrended SSTA from the Niño 3.4 index in DJF and the CDNI in MAM is performed between 1870 and 2024 and displayed in Fig. 6c (red line). Results show that Niño 3.4 index and MAM CDNI-averaged SSTA are positively correlated over the period 1870 to 2024. However, the two indexes are significantly correlated (> 0.42, with red dots) during two periods (around 1881–1920 and late 1950s to late 1980s) and weakly correlated (not statistically significant at 95%) over the remaining periods including the period from ~ 1995 to 2014 (correlation < 0.3). The period of weak correlation (~ 1995 to 2014) between the two indexes also encompasses our study period (2003–2023) which is consistent with findings of Fig. 6b. Likewise, the same analysis is repeated using the December-January-February-March (DJFM) NAO index and MAM SSTA in the CDNI region (blue line in Fig. 6c). Results show that although the correlation between the two parameters is mostly negative all the time, it remains not significant at 95% except for the period ~ 1965 and 1975 where the correlation is below -0.4. Indeed, insignificant correlation between NAO and coastal SST was previously reported by Cropper et al.18 who showed that NAO is more strongly correlated with coastal upwelling intensity derived from winds than SST in the seasonal upwelling zone (CDNI region) between boreal winter and spring. In general, the positive (negative) phase of the NAO is associated with a strengthening (weakening) of the northeast trade winds driven by the intensification (weakening) of the Azores high-pressure system, which in turn leads to cooler (warmer) SSTA in the CDNI region. Despite this insignificant correlation, a clear multidecadal variability in the evolution of the correlation between DJFM NAO index and MAM CDNI-SSTA is observed with periods of weak and quasi-null correlation.Since the correlations between DJF Niño 3.4/DJFM NAO indexes and MAM SSTA undergo distinct multidecadal variations (periods of high and low correlation, Fig. 6c), we have also checked if these multidecadal correlations were linked to the Atlantic Multidecadal Variability (AMV) index (black line in Fig. 6c). Interestingly, there is a clear significant correlation at 95% of – 0.60 between the time evolution of the AMV index and the sliding correlation between DJF Niño 3.4 index and MAM SSTA. This suggests that during periods of negative (positive) phases of AMV, there is a high (weak) correlation between DJF Niño 3.4 index and MAM SSTA in the CDNI region. Therefore, ENSO strongly influences the CDNI region during periods of negative AMV phases. However, the time evolution of the AMV index and the sliding correlation between DJFM NAO index and MAM SSTA shows a period in phase until about 1965 and in anti-phase thereafter.Summary and discussionIn this study, we have investigated the interannual variability of the NPP in the seasonal upwelling region of the CCUS, extending from 9°N to 18°N within a 2°-coastal band (named CDNI). In this region, high interannual NPP variability occurs during the main upwelling season that marks the seasonal maximum of NPP (i.e., March-April-May, Figs. 1a, 2). Over the period 2003–2023, nine extreme NPP events peaking in MAM have been identified: six extreme low events (2005, 2008, 2010, 2020, 2021, 2023) and three extreme high NPP events (2012, 2015, 2016). Given the short time series and the limited number of extreme high NPP events, this study has focused on the extreme low NPP events. Using a composite analysis of the six extreme low NPP events, the drivers of these events have been investigated.Over the study period, our results have shown that extreme low NPP events are linked to both local and remote forcings. On the one hand, during the growing and peak phases of the extreme low NPP events (from two months before to the peak), the local forcing has resulted from a reduction of local wind stress and positive WSC (Ekman pumping, Figs. 4, S1). This has resulted in reduced latent heat loss and local upwelling and generated anomalously warm SSTs (Dakar Niños, Oettli et al.6) and positive anomalies of SLA. During these phases, anomalous shoaling of the MLD has also been observed (Fig. 3b). Our findings agree with previous studies6,15 which, using reanalysis and model data, found that reduced alongshore winds were among the main drivers of Dakar Niño events. On the other hand, our results suggest that easterly wind stress anomalies in the northern Gulf of Guinea (Fig. 4a) might force downwelling CTWs (highlighted by positive SLA) one month before the peak of extreme low NPP events. These downwelling CTWs would propagate along the northwest African coast and reach the CDNI, where they impact SST and NPP through deepening of the thermocline and nutricline, thus representing a remote forcing. Moreover, part of the downwelling CTW energy is transmitted westward as downwelling Rossby waves (Fig. 4). Note that the role of remotely wind-forced CTWs on the interannual SST or NPP variability in the CDNI in MAM has not been discussed in the literature before. In a previous study, Oettli et al.6 showed that Dakar Niños are mainly driven by local processes over the period 1982-2011, whereas Illig et al.7, using satellite altimetry data (2002-2012, all months), evidenced that some CTWs of equatorial origin propagate north up to the latitude of Liberia (~ 6°N) within 45 days. Similarly, Polo et al.29, using altimetry and model data, showed that intraseasonal (25-95 days) CTWs of equatorial origin can propagate north up to ~ 10°N. In this study, independent of the season, we show that these CTWs can propagate as far north as 24°N (for instance 2010/2011, Fig. 7), and have an impact on the coastal upwelling, thereby contributing to the development of anomalous SST events in the CDNI region. However, anomalies of SLA during extreme low NPP events in MAM show only two downwelling CTW signals of equatorial origin (2005 and 2020, see Fig. 7) with equatorial positive anomalies of SLA associated with downwelling EKW signals observed in the western or central equatorial Atlantic. Zooming into 2005 and 2020 shows that it takes ~ 5 months (from December 2004 to April 2005) and 4 months (November 2019 and February 2020) for downwelling EKWs forced in the western and central equatorial Atlantic, respectively, and subsequent downwelling CTWs to reach the CDNI region (Fig. S2). Also, note that the slopes (propagation speeds) of the positive anomalies of SLA change along the northern coast of the Gulf of Guinea (from 5°E in Figs. S2c, S2g) for both years. This change in the slope of the positive anomalies of SLA along the northern coast of the Gulf of Guinea likely reflects a shift in the dominant downwelling CTW mode from faster (low order) baroclinic modes to slower (higher order) baroclinic modes. We suggest that the slowdown of CTWs along the northern Gulf of Guinea likely reflects the influence of the narrow, steep shelf, which enhances bottom friction and favors scattering into higher baroclinic modes. Coastal stratification and river-induced density gradients (e.g., from the Niger and Volta) may provide additional contributions. The other low NPP events are linked to downwelling CTWs emanating from the northern Gulf of Guinea, except in 2021 (Fig. 7) where local positive anomalies of SLA (< 4 cm) are present between 8°N and 10°N and negative anomalies of SLA are observed along the northern coast of the Gulf of Guinea.Fig. 7(a) Hovmoeller diagram of monthly detrended anomalies of SLA along the equator averaged over 1°S – 1°N. (b) Same as (a) with SLA averaged within 1°-coastal band from equator to around Cameroon (4°N). (c) Same as (a) but for SLA along the northern coast of the Gulf of Guinea averaged within 1°-coastal band along the African coast. (d) Same as (a) but for SLA averaged within 1°-coastal band along the northwest African coast from 7.8°N to 24°N. The anomalies are calculated relative to the monthly climatology defined over the period January 2003 to December 2023 with the decadal contribution filtered out using a high‐pass Fast Fourier Transform filter with a cut off frequency of 10 year−1 and the subseasonal fluctuations removed by applying a 1‐2‐1 running weighted average as in Illig et al.7.Full size imageAdditional forcing of downwelling Rossby waves (positive anomalies of SLA, Fig. 4) arises from persistent negative local WSCA (i.e., Ekman pumping, cyan contours and dots, see also Fig. S1) observed from one month before the peak to the peak of the extreme low NPP events, between ~ 5°N-10°N east of 30°W. This downwelling Rossby wave is reflected at the coast of South America as a downwelling EKW around two months after the peak of the low NPP events and takes one month to reach the eastern equatorial Atlantic (20°W-0°E) as shown in Fig. 4d, where it could be linked to a boreal summer Atlantic Niño. Similar findings in terms of location of the forcing of Rossby wave were reported by Vallès-Casanova et al.25 who investigated the influence of boreal winter Saharan dust on equatorial Atlantic variability using observational and reanalysis data. Their Fig. 6, showing the monthly lagged regression analysis of SLA and WSC onto their January-February-March dust index, revealed that negative WSCA at ~ 20°W, 3°N-6°N force a downwelling Rossby wave that will reflect into downwelling EKW in July and later precondition a winter Atlantic Niño. Note that for our study, we did not find any significant link between NPPA and Saharan dust.Since extreme low NPP events are strongly linked to the occurrence of Dakar Niños, we have used a model mixed-layer heat budget analysis to investigate the processes driving the mixed-layer temperature during these events (Fig. 5). We found that the anomalous warming of the mixed-layer during the growing phase (three to one months before the peak) of the extreme low NPP events is predominantly explained by net surface heat flux anomalies, driven by anomalous non-solar fluxes, themselves dominated by latent heat flux anomalies which are linked to surface wind speed fluctuations. Although a shallow mixed layer (Fig. 3b) could amplify the temperature response to climatological heat fluxes (the H′ term, see Eq. 2), our analysis shows that this contribution is relatively small compared to the Q′ term (Fig. 5c). This result is in contradiction with the findings of Oettli et al.6, who found using reanalysis data, that anomalous warming of the mixed layer temperature during Dakar Niños comes from the heating of the anomalously thin surface mixed-layer even when the net surface heat flux (mostly from solar radiation) is close to climatological values. During the peak phase of the low NPP events, anomalous vertical diffusion and zonal advection are the major contributors to the anomalous warming of the mixed layer (Fig. 5b), consistent with reduced coastal upwelling caused by significantly weakened coastal wind stress and negative WSCA (Figs. 3, 4b, S1b). The demise of the extreme low NPP events is marked by anomalous cooling of the mixed layer due to anomalies of net surface heat fluxes, zonal advection and vertical diffusion.In the CDNI region, the composite analysis shows that extreme low NPPA in MAM occur concomitantly with significant southwesterly wind anomalies and warm SSTA (Fig. 3). Past studies have suggested that the tropical North Atlantic is connected to the Equatorial Pacific via an atmospheric bridge22,24,27,30,31,32,33. In contrast to these previous studies, our findings show that over the entire study period, MAM NPPA were not significantly correlated with DJF Niño 3.4 index. Note that three out of nine extreme NPP events (2005, 2010, 2012) occurred in a boreal spring season following an ENSO event (Fig. 6b). Between 1870 and 2024, the 21-year sliding correlation between MAM SSTA in the CDNI region and DJF Niño 3.4 index shows multidecadal variations strongly linked to the AMV (with a significant correlation at 95% of − 0.60). During negative phases of AMV, strong and significant correlations at 95% between DJF Niño 3.4 index and MAM SSTA in the CDNI region are observed, while during positive AMV phases, as in our study period (2003–2023) and present day conditions, MAM SSTA in the CDNI region are not connected to the DJF Niño 3.4 index (Fig. 6c). These results suggest that the multidecadal correlation of Niño 3.4 with CDNI SSTA is modulated by the AMV, consistent with past studies which suggested that the AMV modulates ENSO variability: ENSO variability is intensified during negative AMV phases, while during positives phases it is weakened34,35. Over the study period, during MAM, in contrast to the weak link between DJF Niño 3.4 index and CDNI NPPA, coastal NPPA were strongly connected to the AMM (Fig. 6a) as also shown by Oettli et al.6 for Dakar Niños occurring in February-March-April.A potential decadal variability of the NPP has been noticed in the CDNI region (Fig. 1d). Gómez-Letona et al.3 proposed that the decadal NPP variability in the seasonal upwelling zone (CDNI region) could be linked to the nutrient content of the upwelled waters, which depends on the source of the water mass: North Atlantic Central Waters (low concentration of nutrients) or South Atlantic Central Waters (high concentration of nutrients). However, longer observations of the NPP in the CCUS are needed to investigate this decadal variability.Data and methodsDataTo investigate the NPP variations in the CDNI region, we use monthly mean NPP from the standard vertically generalized production model (VGPM)36. This product is based on Moderate Resolution Imaging Spectroradiometer (MODIS) chlorophyll, SST data and photosynthetically active radiation and estimates of the euphotic zone depth. The standard VGPM NPP data are available from July 2002 to January 2024 at a horizontal resolution of 1/6°, but has been interpolated onto a 0.25° × 0.25° spatial grid to reduce noise and match the spatial grid of other parameters such as SST. A comparison of standard VGPM to other NPP products in the CCUS is available in Gómez-Letona et al.3.We use monthly means of SST from the Optimum interpolation SST version 2.1 (OI-SST)37 produced by the National Oceanic and Atmospheric Administration (NOAA) available at 0.25° horizontal resolution from September 1981 onwards. Additionally, the Hadley Centre Sea Ice and Sea Surface Temperature (HadI-SST)38 data set produced by the Met Office available from 1870 to present at 1° horizontal resolution is used to examine the multidecadal correlation between ENSO and the CDNI and to calculate the AMV index.We also use the 10 m winds and wind stress from the European Centre for Medium-Range Weather Forecast (ECMWF) reanalysis version 5 (ERA5)39 available at 0.25° horizontal resolution from January 1940 onwards.To investigate the multidecadal correlation between the NAO and SSTA along the coasts of Senegal and Mauritania, the Hurrell NAO index (station-based) is used40. This index is based on the difference of normalized sea level pressure (SLP) between Lisbon, Portugal and Stykkisholmur/Reykjavik, Iceland and is available from January 1865 to June 2023.The Chiang and Vimont20 index for the AMM produced by the NOAA Physical Sciences Laboratory, is used to investigate its potential influence on the NPPA. The AMM index corresponds to the leading expansion coefficient of the maximum covariance analysis applied to SST between 75°W-to the West African coastline, 21°S-32°N with ENSO signal regressed out.The AMV index is computed following a method similar to Trenberth and Shea41: monthly SSTA averaged over the global oceans (60°S-60°N) are subtracted from the monthly SSTA averaged over the North Atlantic region (80°W-0°E, 0°N-60°N).The Ocean Niño index (ONI) produced by the Climate Prediction Centre is used to investigate the effect of ENSO in DJF on the NPPA in MAM. The ONI index is the 3-month running mean of ERSST.v542 SST anomalies in the Niño 3.4 region, based on centered 30-year base periods updated every 5 years and is available from 1950 onwards.Monthly means of SLA from the delayed-time multi-mission (all satellites merged) product are used to investigate a potential role of remote forcing onto NPPA variability in the CDNI region. SLA data are distributed by the European Union Copernicus Marine Service Information and are available at 0.25° horizontal resolution from January 1993 onwards.Ocean model description and validationThe mixed layer heat budget used in this study has been calculated from outputs of a regional configuration of the Nucleus for European Modeling of the Ocean program version 4.2 (NEMO-v4.2.1; Madec et al.43, https://doi.org/10.5281/zenodo.8167700). It solves the Navier‐Stokes primitive equations under spherical coordinates discretized on a horizontal Arakawa C grid and fixed vertical levels (z coordinate). This regional simulation has a 0.25° horizontal resolution and covers the tropical Atlantic (100°W–25°E, 35°S–35°N). Also, there are 75 vertical levels, with 12 levels within the first 20 m and 24 levels within the first 100 m. The momentum advection scheme is a second-order centered scheme in vector form, with a bilaplacian horizontal diffusion on momentum. Tracers are advected with a Flux Corrected Transport (FCT) scheme and an adaptative Laplacian isopycnal diffusion. The model time step is 1800s. The vertical diffusion coefficient is estimated using the generic length‐scale scheme with a k‐epsilon turbulent closure44. More details can be found in Reffray et al.45. The model is initialized in January 1958 and forced at the boundaries with interannual monthly fields from the ECMWF ORAS5 ocean reanalysis46. The atmospheric fluxes of momentum, heat, and freshwater at the surface are prescribed following bulk formulae47 using hourly fields of wind speed, atmospheric temperature, and humidity, and daily fields of longwave, shortwave radiation, and precipitation fields from the ERA5 reanalysis39. Daily and interannual river runoff are obtained from the ISBA-CTRIP discharge product (Decharme et al.48; https://zenodo.org/records/12755130). Heat budget terms (see Eq. 1) are computed online, at each model time step and vertically integrated in the mixed layer. The mixed-layer depth (MLD) is computed following a density criterion: a 0.03 kg m−3 difference relative to the density at 10 m49. Model outputs are available from 1958 to 2023. Over the period 2003-2023, monthly averages of the model PT10 have been validated against the OI-SST (Fig. S3) and all mixed layer heat budget terms analyzed (Fig. 5).Fig. S3 shows the model PT10 validation against observations (OI-SST) from 2003 to 2023 in the northeastern tropical Atlantic and the CDNI region. Compared to observations, the model has a cold SST bias along the northwest African coast (Fig. S3a) in the CDNI region. Overall, when averaged over the CDNI region, the model exhibits a cold SST bias of - 0.47 °C. Furthermore, the model slightly overestimates the interannual SST variability near the coast in the CDNI region (Fig. S3b). The seasonality of the SST and its interannual variability in the CDNI region is overall well captured by the model (Fig S3c). The monthly climatology of the SST in the CDNI region in both model and observations features a minimum in February/March and a maximum in September/October. However, we also observe that the cold SST bias from the model is sharper during MAM compared to other seasons. In observations, the seasonal cycle of interannual SST variability in the CDNI region (Fig S3c) portrays a major (minor) peak in February (May), whereas in the model, it shows a major (minor) peak in June (February). Yet, the peak in February is slightly underestimated by the model. Quite good agreement is found between model and observational data from July till December with the interannual SST variability reaching its minimum during September/October. Model and observation time series of detrended SSTA averaged over the CDNI region exhibit a high correlation of 0.87 with root mean squared error of 0.39 °C (Fig. S3d), demonstrating especially good agreement. The model effectively accounts for the majority of the observed interannual SST fluctuations, including events such as the Dakar Niños of 2005 or 2008 (Fig. S3d). The model slightly overestimates variability in the CDNI region, with the standard deviation of interannual SSTA being 0.72 °C in observations and 0.78 °C in the model. Nevertheless, the model matches well with observations and, therefore, can be used to investigate the mixed layer heat budget in the CDNI region. Moreover, the ocean model used in this study builds on the physical configuration described in Gévaudanet al.50. Previous versions of this configuration have demonstrated skill in reproducing the interannual variability of temperature and salinity in the Tropical Atlantic51,52,53, making it a suitable tool for studying Dakar Niños.MethodsCalculation of detrended anomalies and standard deviationsTo obtain the monthly detrended anomalies over the period from January 2003 to December 2023, the linear trend evaluated pointwise is removed from the original data. Then the detrended data is deseasonalized by removing the climatological mean seasonal cycle evaluated over the whole period. For the NPP, after calculating the interannual NPPA between January 2003 to December 2023, for each month individually (over the entire time series), we estimate the standard deviation of the interannual NPPA which is shown in Fig. 2b, d, respectively. Similarly, in Fig. 2a, c, the standard deviation of the interannual NPPA are computed pointwise during the whole study period (only in MAM), respectively.Bootstrapping methodIn this study, the evaluation of statistical significance of our composites was conducted employing a nonparametric bootstrap method54,55. Note that the bootstrap testing without replacement is chosen, which means that the months among each randomly picked group are all different. In this case, the initial monthly data set is resampled 10,000 times to form 10,000 artificial averages. These 10,000 artificial averages are then sorted in ascending order leading to a distribution. Therefore, each grid point (Figs. 3a, 4) or each value of the time series (Fig. 3b) of the composite will be statistically significant at 95% if its value fell outside the 2.5th–97.5th percentile range of this distribution (e.g. thick gray line in Fig. 4). A similar method was used in Imbol Koungue et al.53, but for statistical significance at 90%.Pearson correlationPearson correlation coefficients in Fig. 6c were computed to quantify linear relationships among the variables. Statistical significance at the 95% confidence level was assessed using a two-tailed Student’s t-test. Because the correlation coefficients were calculated using 21-year centred sliding windows (yielding 20 degrees of freedom), correlation coefficients exceeding ± 0.42 (the critical threshold) are therefore considered statistically significant.Model mixed layer heat balanceTo understand the physical processes that drive the mixed layer temperature fluctuations during the extreme low NPP events, a mixed layer heat budget computed online is analyzed. The mixed layer heat budget is expressed as follows56,57:$$begin{gathered} < partial_{t} T > = – < , upartial_{x} T , > – < , vpartial_{y} T , > – < , wpartial_{z} T , > + < , Ldiffleft( T right) , > hfill \ + < frac{{Q_{ns} + Q_{sr} left( {1 – f_{z = – H} } right)}}{{rho_{0} c_{p} H}} > – frac{1}{H}(Kz_{{}} partial zT)z = – h hfill \ end{gathered}$$
    (1)
    with < (cdot) >  = (frac{1}{H}mathop smallint limits_{ – H}^{0} .partial z).where T represents the model potential temperature, (u, v, w) are the velocity components, Ldiff(T) represents the lateral diffusion operator (Ldf), (frac{1}{H})(Kz∂zT) is the vertical mixing (Zdf) with Kz the vertical diffusion coefficient for tracers. H is the MLD, (rho_{0}) is the seawater density (i.e., 1027 kg/m3) and (c_{p}) the specific heat capacity of water (i.e., 4000 J/(kg K)). Here, (Q_{ns}) and Qsr are respectively the non-solar (latent, sensible and longwave heat fluxes) and solar components of the air–sea heat flux (shortwave radiation), and fz = -H is the fraction of the shortwave radiation that reaches the MLD. Tot (< ∂tT >) represents the total mixed layer temperature tendency and Qnet ((frac{{Q_{ns} + Q_{sr} left( {1 – f_{z = – H} } right)}}{{rho_{0} c_{p} H}})) is the air–sea heat flux storage in the mixed layer, Xadv (< u∂xT >), Yadv (< v∂yT >), Zadv (< w∂zT >) are the zonal, meridional and vertical advections, respectively.To further explore the heat flux contributions to the mixed layer temperature anomalies, we decompose the contribution of the air–sea heat flux storage in the mixed layer (see Eq. 1) into two parts (as done in Senapati et al.26) as follows:$$delta left( {frac{{ Q_{ns} + Q_{sr} left( {1 – f_{z = – h} } right)}}{{rho_{0} c_{p} H}}} right) = delta left( {frac{Q}{{rho_{0} c_{p} H}}} right) = frac{delta Q}{{rho_{0} c_{p} overline{H}}} – frac{{delta Hoverline{Q}}}{{rho_{0} c_{p} overline{H}^{2} }} + {text{Residual}}$$
    (2)
    with (delta ()) and the overbar representing anomalies and climatology, respectively. The term on the left-hand side represents the detrended anomalies of the air–sea heat flux storage in the mixed layer. The first term on the right-hand side indicates the contribution to the model mixed layer temperature anomalies due to net surface heat flux anomalies acting on climatological mixed layer depth (Q’ term = (frac{delta Q}{{rho_{0} c_{p} overline{H}}})). The second term on the right-hand side represents the contribution to the model mixed layer temperature anomalies due to climatological heating/cooling applied to an anomalous mixed layer depth (H’ term = (frac{{delta Hoverline{Q}}}{{rho_{0} c_{p} overline{H}^{2} }})).

    Data availability

    In the following we provide links to the different datasets used for the study: OI-SST : https://psl.noaa.gov/data/gridded/data.noaa.oisst.v2.highres.html; ERA5: https://cds.climate.copernicus.eu/datasets/reanalysis-era5-single-levels-monthly-means?tab=download HadI-SST: https://www.metoffice.gov.uk/hadobs/hadisst/ Standard VGPM NPP: https://orca.science.oregonstate.edu/1080.by.2160.monthly.hdf.vgpm.m.chl.m.sst.php Hurrell NAO station-based index: https://climatedataguide.ucar.edu/climate-data/hurrell-north-atlantic-oscillation-nao-index-station-based AMM index: https://psl.noaa.gov/data/timeseries/month/AMM/ ONI ENSO index: https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ONI_v5.php SLA: https://marine.copernicus.eu/
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    Download referencesAcknowledgementsThis work was funded by the German Research Foundation through grant 511812462 (IM 218/1-1).FundingOpen Access funding enabled and organized by Projekt DEAL.Author informationAuthors and AffiliationsGEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, GermanyRodrigue Anicet Imbol Koungue & Peter BrandtEarth System Physics, The Abdus Salam International Centre for Theoretical Physics, Trieste, ItalyArthur PrigentInstitute of Environmental Physics, University of Bremen, Bremen, GermanyJoke F. LübbeckeMARUM – Center for Marine Environmental Sciences, University of Bremen, Bremen, GermanyJoke F. LübbeckeFaculty of Mathematics and Natural Sciences, Kiel University, Kiel, GermanyPeter BrandtLEGOS, IRD, CNRS, CNES, Université de Toulouse, UPS, Toulouse, FranceJulien JouannoAuthorsRodrigue Anicet Imbol KoungueView author publicationsSearch author on:PubMed Google ScholarArthur PrigentView author publicationsSearch author on:PubMed Google ScholarJoke F. LübbeckeView author publicationsSearch author on:PubMed Google ScholarPeter BrandtView author publicationsSearch author on:PubMed Google ScholarJulien JouannoView author publicationsSearch author on:PubMed Google ScholarContributionsR.A.I.K and A.P. designed the study, produced the figures, and drafted the manuscript. J.J provided Ocean model outputs. All co-authors contributed to the writing of the manuscript.Corresponding authorCorrespondence to
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    Strengthening mechanisms of indigenous bacteria in granite residual soil improvement via microbial induced calcite precipitation

    AbstractMicrobially induced carbonate precipitation (MICP) has proven to be an effective method for soil reinforcement. Sporosarcina pasteurii is widely used due to its high urease activity. However, being an alkaliphilic bacterium, its limitations in acidic soil environments tend to be overlooked. This study isolated a native urease-producing bacterial strain Bacillus aryabhattai with acid tolerance, and comparative analysis of the growth characteristics of B. aryabhattai and S. pasteurii. The grouting and spraying techniques were employed to reinforce granite residual soil by the B. aryabhattai and the S. pasteurii, and the reinforcement mechanisms were systematically investigated. Experimental results indicated that despite exhibiting slightly lower urease activity and growth, the indigenous urease-producing bacterium B. aryabhattai demonstrated superior environmental resilience in terms of both environmental temperature and pH range. The soil samples reinforced by grouting with B. aryabhattai and S. pasteurii exhibited increases in ultrasonic wave velocity, unconfined compressive strength, cohesion, and cumulative disintegration rate to varying degrees compared to the untreated soil samples. Meanwhile, the resistance value of the soil samples reinforced by spraying with B. aryabhattai and S. pasteurii decreased by 84.39% and 79.79%, respectively. Additionally, the calcium carbonate content in the upper section of soil reinforced with B. aryabhattai was comparable to that of S. pasteurii; however, while in the lower section, it exhibited a 36.22% higher precipitation rate than the S. pasteurii-treated soil. Overall, the indigenous strain B. aryabhattai demonstrated remarkable reinforcement effectiveness, attributed to its rapid adaptation to weakly acidic soil conditions and moderate urease activity, which promoted a homogeneous distribution of calcium carbonate. These findings provide significant insights for soil reinforcement applications through MICP.

    Data availability

    The datasets generated and analysed during the current study are available in the NBCI repository, [https://www.ncbi.nlm.nih.gov/nuccore/PX257993].
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    Download referencesAcknowledgementsThis work was supported by funding from the Natural Science Foundation of Fujian Province under Grant No. 2024J01912, the transportation Science and Technology Project of Fujian Province under Grant No. 202231. The authors gratefully acknowledge the English editing services provided by Ms. Qiannan Ma from Scientific Compass (www.shiyanjia.com).FundingThis work was supported by funding from the Natural Science Foundation of Fujian Province under Grant No. 2024J01912, the transportation Science and Technology Project of Fujian Province under Grant No. 202231. The authors gratefully acknowledge the English editing services provided by Ms. Qiannan Ma from Scientific Compass (www.shiyanjia.com).Author informationAuthors and AffiliationsSchool of Civil Engineering and Architecture, Wuyi University, Wuyishan, 354300, ChinaRong Wang, Chao Peng, He Zhao, Haixing Liu, Taibing Wei & Huawei LiKey Laboratory of Smart Town Construction of Hilly Mountains (Wuyi University), Fujian Province University, Wuyi University, Wuyishan, 354300, ChinaRong Wang & Huawei LiSchool of Civil Engineering, Fuzhou University, Fuzhou, 350108, ChinaChao Peng, He Zhao, Haixing Liu & Lijuan WangAuthorsRong WangView author publicationsSearch author on:PubMed Google ScholarChao PengView author publicationsSearch author on:PubMed Google ScholarHe ZhaoView author publicationsSearch author on:PubMed Google ScholarHaixing LiuView author publicationsSearch author on:PubMed Google ScholarTaibing WeiView author publicationsSearch author on:PubMed Google ScholarLijuan WangView author publicationsSearch author on:PubMed Google ScholarHuawei LiView author publicationsSearch author on:PubMed Google ScholarContributionsRong Wang, Chao Peng, and He Zhao wrote the main manuscript text; Rong Wang, Haixing Liu, and Lijuan Wang prepared all figures; Taibing Wei, and Huawei Li administrated the projects; All authors reviewed the manuscript.Corresponding authorsCorrespondence to
    Lijuan Wang or Huawei Li.Ethics declarations

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    Reprints and permissionsAbout this articleCite this articleWang, R., Peng, C., Zhao, H. et al. Strengthening mechanisms of indigenous bacteria in granite residual soil improvement via microbial induced calcite precipitation.
    Sci Rep (2025). https://doi.org/10.1038/s41598-025-32718-zDownload citationReceived: 30 August 2025Accepted: 11 December 2025Published: 16 December 2025DOI: https://doi.org/10.1038/s41598-025-32718-zShare this articleAnyone you share the following link with will be able to read this content:Get shareable linkSorry, a shareable link is not currently available for this article.Copy shareable link to clipboard
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    KeywordsMICPGranite residual soilGrowth characteristicsReinforcement mechanismEnvironmental adaptability More