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Soil organic carbon fractions and their associated bacterial and fungal abundance in alpine ecosystems


Abstract

Soil organic matter (SOM) has a key role in the carbon (C) cycle and consists of particulate organic matter (POM) and mineral-associated organic matter (MAOM), which differ in stability and turnover. This study investigates C dynamics and microbial abundance at two alpine sites (1526 and 2500 m a.s.l). Soil samples were fractionated, and the C:N ratio, pH, and microbial abundances were analysed. While the MAOM/POM ratio remained stable across sites, the higher-elevation soil, dominated by N-poor alpine graminoids, showed an increased C:N ratio, consistent with reduced decomposition and transfer of litter into mineral-associated pools under colder, more acidic conditions. Bacteria predominated in MAOM, supporting their role in SOM stabilisation, whereas fungal abundance was highest in MAOM only at 2500 m. Fungal abundance remained stable across sites, indicating greater tolerance to low temperatures and pH compared to bacteria, which declined at higher altitudes. This suggests fungi play a key role in decomposition in colder environments. Correlations between fungi and bacteria were context-dependent: negative in MAOM and positive in POM, but only at 2500 m. These findings highlight how the composition and stability of SOM and microbial abundance differ between fractions and at different elevations, underscoring the value of integrating microbial data with SOM fractionation to better understand alpine soil C dynamics.

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Data availability

The data used to support the findings of this study are available from the corresponding author upon request.

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Acknowledgements

We want to offer special thanks to Dr. Angela Augusti, who, although no longer with us, continues to inspire us through her dedication and contributions to research. The authors are grateful to Fondazione Montagna Sicura (http://www.fondazionemontagnasicura.org/en/), which made the realization of this study possible.

Funding

This study was supported by the Italian Ministry of University and Research, PRIN 2020 (Projects of Relevant National Interest), Prot. 20204KF4RW, CUP: I53C21000140001 and by the Open Access Publishing Fund of the Free University of Bozen-Bolzano.

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I.F. and L.F. contributed equally to the present study (first authors) by conceptualizing the work, conducting the investigation, performing formal analysis, curating the data, preparing visualizations, and writing the original draft of the manuscript. R.T. and P.B. contributed to resource provision and participated in reviewing and editing the manuscript. A.A., O.G., L.Z., and L.M. contributed resources and assisted in reviewing and editing the manuscript. L.B. supervised the research, contributed to the methodology and resource acquisition, and participated in manuscript review and editing. T.M. conceptualized the work, supervised the project, contributed to the methodology and resource provision, and participated in reviewing and editing the manuscript. All authors discussed and commented on the methods and results and contributed to the final version of the paper.

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Ilaria Fracasso or Tanja Mimmo.

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Fracasso, I., Foley, L., Tiziani, R. et al. Soil organic carbon fractions and their associated bacterial and fungal abundance in alpine ecosystems.
Sci Rep (2025). https://doi.org/10.1038/s41598-025-31187-8

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  • DOI: https://doi.org/10.1038/s41598-025-31187-8

Keywords

  • Carbon fractions
  • POM
  • MAOM
  • Soil ecology
  • Fungal abundance
  • Bacterial abundance


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