Upslope release—Downslope receipt? Multi-year plant uptake of permafrost-released nitrogen along an arctic hillslope

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As arctic permafrost continues to thaw, previously inaccessible nitrogen (N) becomes available to N-limited arctic plants. Increased N availability could enhance plant growth and thereby potentially offset climate-induced carbon release. Arctic plants can take up newly available permafrost-N locally upon release. However, in a topographically diverse arctic landscape, permafrost-N may be transported along hillslopes, away from the point-of-release. The extent to which topographical N transport can impact arctic vegetation change depends on whether N is retained locally, captured by downslope recipient plant communities, or transported away. We used stable isotope labelling (15N) to simulate upslope release of ammonium (NH4+) and nitrate (NO3) from thawing permafrost on an arctic hillslope, western Greenland. We tracked the plant species-specific uptake of simulated permafrost-released N from the upslope point-of-release to the bottom of the slope through 4 years. We found that arctic tundra plants successfully acquired locally released permafrost-N, even in sloping terrain, and that N was strongly retained in the plant–soil system through multiple years. At the same time, we also importantly demonstrate that permafrost-N can be transported and taken up by plants up to 30 m downslope from the point-of-release. Especially NO3 was more easily redistributed vertically within the soil column compared to NH4+ and therefore potentially more accessible to plants. Specifically, plant species with fast N uptake capacity and deep-soil foraging strategies may have competitive advantages for capitalising on deep-soil released and topographically transported permafrost-N (here exemplified by Equisetum arvense and Salix glauca). Nevertheless, even mosses gained access to permafrost-N via vertical and lateral redistribution on the slope. Ultimately, the intricate balance between strong local N retention, downslope transport and plant species-specific uptake strategies may contribute to shaping arctic vegetation change. Synthesis. Across spatially complex arctic ecosystems, arctic plants can take up permafrost-released N both at the local point-of-release and at a considerable distance downslope. The potential for arctic plants to take advantage of topographically transported permafrost-N could lead to long-term and landscape-scale changes in species composition, plant productivity, and ultimately carbon and climate feedbacks across the Arctic.

OriginalsprogEngelsk
TidsskriftJournal of Ecology
Vol/bind110
Sider (fra-til)1896–1912
Antal sider17
ISSN0022-0477
DOI
StatusUdgivet - 2022

Bibliografisk note

Funding Information:
This work was supported by the Danish National Research Foundation (Center for Permafrost, CENPERM DNRF100). Arctic Station, Qeqertarsuaq, provided excellent logistical support during fieldwork. We sincerely thank Kristine Dyrnum for her contributions to the development of the experimental design, initiation of the experiment and for taking the lead on the first field campaign. We are grateful to Joseph Gaudard for valuable field assistance and to Anna Polaskova for help with sample processing in the laboratory. We also thank Gosha Sylvester, Terrestrial Ecology, University of Copenhagen, for assistance with laboratory analyses, and we thank Bo Markussen, Department of Mathematical Sciences, University of Copenhagen, for valuable advice on the statistical analyses. We appreciate the constructive feedback provided by five anonymous reviewers and two editors on previous versions of this paper. We respectfully acknowledge that this research was performed on the land of Kalaallit Nunaat, and we hope that this research may contribute to a continued sustainable and protected Arctic.

Publisher Copyright:
© 2022 The Authors. Journal of Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Society.

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