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

• Published in: Journal of Ecology
• Main Authors: Pedersen, Emily P., Elberling, Bo, Michelsen, Anders
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2022
• Subjects: arctic hillslope; climate change; permafrost thaw; plant species-specific N uptake; plant–soil (belowground) interactions; stable isotope labelling N; topographical N transport; tundra; Arctic; Greenland; Climate change; permafrost; Tundra
• Online Access: https://curis.ku.dk/portal/da/publications/upslope-releasedownslope-receipt-multiyear-plant-uptake-of-permafrostreleased-nitrogen-along-an-arctic-hillslope(bb24f6bc-f053-48fa-851d-3107d271aaab).html; https://doi.org/10.1111/1365-2745.13925; https://curis.ku.dk/ws/files/315987908/Upslope_release_Downslope_receipt_Multi_year_plant_uptake_of_permafrost_released_1_.pdf

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 ( 15 N) to simulate upslope release of ammonium (NH 4 + ) and nitrate (NO 3 − ) 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 NO 3 − was more easily redistributed vertically within the soil column compared to NH 4 + 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 ...