Nitrogen transport in a tundra landscape:the effects of early and late growing season lateral N inputs on arctic soil and plant N pools and N 2 O fluxes

• Published in: Biogeochemistry
• Main Authors: Rasmussen, Laura H., Zhang, Wenxin, Ambus, Per, Michelsen, Anders, Jansson, Per Erik, Kitzler, Barbara, Elberling, Bo
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2021
• Subjects: Arctic tundra; Climate change; Nitrate; Solute transport; Winter N mineralization; Arctic; Greenland; Tundra
• Online Access: https://curis.ku.dk/portal/da/publications/nitrogen-transport-in-a-tundra-landscape(cca66734-f6b3-416b-b30a-120f77e775ad).html; https://doi.org/10.1007/s10533-021-00855-y; https://curis.ku.dk/ws/files/305690750/Nitrogen_transport_in_a_tundra_landscape.pdf

Understanding N budgets of tundra ecosystems is crucial for projecting future changes in plant community composition, greenhouse gas balances and soil N stocks. Winter warming can lead to higher tundra winter nitrogen (N) mineralization rates, while summer warming may increase both growing season N mineralization and plant N demand. The undulating tundra landscape is inter-connected through water and solute movement on top of and within near-surface soil, but the importance of lateral N fluxes for tundra N budgets is not well known. We studied the size of lateral N fluxes and the fate of lateral N input in the snowmelt period with a shallow thaw layer, and in the late growing season with a deeper thaw layer. We used 15 N to trace inorganic lateral N movement in a Low-arctic mesic tundra heath slope in West Greenland and to quantify the fate of N in the receiving area. We found that half of the early-season lateral N input was retained by the receiving ecosystem, whereas half was transported downslope. Plants appear as poor utilizers of early-season N, indicating that higher winter N mineralization may influence plant growth and carbon (C) sequestration less than expected. Still, evergreen plants were better at utilizing early-season N, highlighting how changes in N availability may impact plant community composition. In contrast, later growing season lateral N input was deeper and offered an advantage to deeper-rooted deciduous plants. The measurements suggest that N input driven by future warming at the study site will have no significant impact on the overall N 2 O emissions. Our work underlines how tundra ecosystem N allocation, C budgets and plant community composition vary in their response to lateral N inputs, which may help us understand future responses in a warmer Arctic.