Effects of Long-Term Experimental Warming on Nitrogen Uptake and Partitioning During Arctic Tundra Shoulder Seasons

Spring and autumn, often termed shoulder seasons, represent key transitional phases in Arctic tundra ecosystems, during which nutrient dynamics become highly variable. Biogeochemical cycling during these periods is particularly responsive to warming. Here, we quantify nitrogen uptake and allocation across soil, plant, and microbial fractions in tundra ecosystem at Abisko, northern Sweden, where experimental warming has been maintained for 7 and 17 years, alongside ambient controls. A dual-labeled ¹³C¹⁵N-glycine tracer was used to trace nitrogen incorporation over short-term (24 h) and longer-term (one month) timescales. Isotope recovery across ecosystem pools will be used to determine how warming duration alters the partitioning of nitrogen during seasonal transitions. Based on fieldwork completed last year, this work reports preliminary results from ongoing analyses, with only a limited number of initial findings presented. Once analyses are complete, the results will contribute to improve our understanding of nitrogen dynamics during transition periods under warming in Arctic tundra ecosystems.