Abstract
Increasing nitrogen (N) deposition may alter soil N status and dynamics, as well as the emission of soil greenhouse gases (GHGs). Most of the experimental N manipulations performed so far have neglected the interaction with the canopy, which influences both quantity and quality of the N input into the soil. Here, we assess the effects of N fertilizer application method on N mineralization, and soil GHG fluxes. The experimental site is a sessile oak (Quercus petraea L.) stand in Northern Italy and consists of a set of three plots, replicated three times. In each replication, one plot is not fertilized (control plot); one plot receives the fertilization on the forest floor (below-canopy treatment), and one plot receives the fertilization above the canopy (above-canopy treatment). After 5 years of experimental N applications, equal to 20 kg N ha−1 y−1 distributed equally five times during the vegetative season, net soil N mineralization was assessed with the in-situ soil core incubation method. Soil CO2 flux was measured with a portable infra-red gas analyzer, while the soil CH4 and N2O fluxes were assessed using static closed chambers. No treatment effect was evidenced on soil mineral N content. However, during the last two vegetative seasons, topsoil N leaching increased in the treatment below, and not in the treatment above. On the contrary, N mineralization was lower compared to the control only in the treatment below. These results indicate that the tree canopy can mitigate the effect of N deposition on soil N cycling, which may therefore have been overestimated in previous studies using ground N fertilization. On the other hand, differences in soil GHG fluxes among treatments were not significant, even when the effect of soil temperature and soil moisture was considered. Nevertheless, given the complex relationships between N depositions, soil N dynamics and GHG emissions, long-term investigation is needed to determine whether the presence of the forest canopy, and/or differences in forest type, can mitigate or delay N saturation in the medium to long term.
Data availability
The data supporting the findings of this study are available from the corresponding author, upon reasonable request.
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Acknowledgements
The study was supported by the COST Action CA15226-CLIMO “Climate-Smart Forestry in Mountain Regions”. We would like to thank Stefano Minerbi of the Forest Service of Bolzano Province for the help provided in the identification of the experimental site. L.D.R. was supported by the European Social Fund Plus (ESF+) 2021–2027 of the Autonomous Province of Bolzano–South Tyrol (project “Potenziare la resilienza delle foreste in Alto Adige – ENFORS”, project code ESF2_f3_0005, CUP B56F24000100001).
Funding
This research was funded by the Free University of Bolzano, through the research projects NITROFOR (grant number 141J12000820005), DECANITRO (grant number I52F15000170005) and INSIDE (grant number I54I19001020005). This work was supported by the Open Access Publishing Fund of the Free University of Bozen-Bolzano.
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L.D.R. and A.B. conducted the experimental work, performed the investigation, prepared the visualizations, and wrote the original draft. M.V. and G.T. conceived the study; M.V. also contributed to the experimental work and investigation, revised the manuscript, and acquired funding. G.T. revised the manuscript and acquired funding. P.P. contributed to the experimental work and revised the manuscript. C.M. and F.F. performed the analytical work and revised the manuscript. M.R. and R.T. revised the manuscript. All authors reviewed and approved the final manuscript.
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Da Ros, L., Anna, B., Pietro, P. et al. Above-canopy versus below-canopy nitrogen addition affects nitrate leaching and mineralization but not greenhouse gas fluxes in a sessile oak stand.
Sci Rep (2026). https://doi.org/10.1038/s41598-026-36532-z
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DOI: https://doi.org/10.1038/s41598-026-36532-z
Keywords
- N deposition
- Canopy nitrogen uptake
- Leaf nitrogen uptake
- Canopy added nitrogen
- Nitrogen saturation process
Source: Ecology - nature.com
