Modelling impacts of lateral N flows and seasonal warming on an arctic footslope ecosystem N budget and N 2 O emissions based on species-level responses

• Published in: Biogeochemistry
• Main Authors: Rasmussen, Laura H., Zhang, Wenxin, Ambus, Per, Jansson, Per Erik, Kitzler, Barbara, Elberling, Bo
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2022
• Subjects: Arctic tundra; Climate change; CoupModel; Solute transport; Winter N mineralization; Arctic; Greenland; Tundra
• Online Access: https://curis.ku.dk/portal/da/publications/modelling-impacts-of-lateral-n-flows-and-seasonal-warming-on-an-arctic-footslope-ecosystem-n-budget-and-n2o-emissions-based-on-specieslevel-responses(f664bbd6-1e7b-4c02-9ec2-2590fa8881d3).html; https://doi.org/10.1007/s10533-022-00894-z; https://curis.ku.dk/ws/files/358500860/d1dbf018_6a19_4c65_aef9_91482371394e.pdf

Future Arctic tundra primary productivity and vegetation community composition will partly be determined by nitrogen (N) availability in a warmer climate. N mineralization rates are predicted to increase in both winter and summer, but because N demand and –mobility varies across seasons, the fate of mineralized N remains uncertain. N mineralized in winter is released in a “pulse” upon snowmelt and soil thaw, with the potential for lateral redistribution in the landscape. In summer, the release is into an active rhizosphere with high local biological N demand. In this study, we investigated the ecosystem sensitivity to increased lateral N input and near-surface warming, respectively and in combination, with a numerical ecosystem model (CoupModel) parameterized to simulate ecosystem biogeochemistry for a tundra heath ecosystem in West Greenland. Both measurements and model results indicated that plants were poor utilizers of increased early-season lateral N input, indicating that higher winter N mineralization rates may have limited impact on plant growth and carbon (C) sequestration for a hillslope ecosystem. The model further suggested that, although deciduous shrubs were the plant type with overall most lateral N gain, evergreen shrubs appear to have a comparative advantage utilizing early-season N. In contrast, near-surface summer warming increased plant biomass and N uptake, moving N from soil to plant N pools, and offered an advantage to deciduous plants. Neither simulated high lateral N fluxes nor near-surface soil warming suggests that mesic tundra heaths will be important sources of N 2 O under warmer conditions. Our work highlights how winter and summer warming may play different roles in tundra ecosystem N and C budgets depending on plant community composition.