Warming enhances nitrogen priming of N20 emissions in subarctic soils under high nitrogen availability

High-latitude soils store a disproportionate share of global soil carbon (C)  and nitrogen (N) and are expected to play a critical role in future greenhouse gas feedbacks to climate warming. Despite this importance, the mechanisms controlling N losses from subarctic soils under warming, particularly nitrous oxide (N₂O) emissions, remain poorly constrained, largely due to strong interactions between temperature and microbial resource availability. Here, we assessed how warming interacts with C and N availability to regulate microbial N₂O production and N priming in a subarctic grassland ecosystem.

Soils were collected from a subarctic grassland exposed to a natural geothermal warming gradient for two years and subsequently incubated in the laboratory at the same in situ temperatures (ambient, +2 °C, and +6 °C). We applied four substrate addition treatments (water control, glucose, ammonium nitrate, and combined glucose + ammonium nitrate) using highly ¹³C and ¹⁵N-enriched substrates, allowing isotopic partitioning of N₂O sources and quantification of N priming.

Warming increased total N₂O emissions across treatments, but the magnitude and underlying mechanisms strongly depended on substrate availability. Nitrogen addition alone caused substantial accumulation of NH₄⁺ and NO₃⁻, stimulated N₂O emissions, and enhanced N₂O derived from native soil N, indicating strong positive N priming. This priming effect intensified with increasing temperature, consistent with accelerated microbial N turnover, and increased denitrification and nitrification rates under elevated inorganic N availability. In contrast, C addition reduced inorganic N accumulation and strongly suppressed N₂O emissions, indicating enhanced microbial N immobilization. Combined C and N addition reduced NH₄⁺ accumulation but not NO₃⁻ accumulation, moderated the temperature sensitivity of N₂O emissions, and shifted N₂O production toward substrate-derived N, suggesting tighter microbial coupling of C and N metabolism under balanced resource supply, reducing reliance on native soil N pools even under warming.

Together, these results show that warming-induced N₂O emissions from subarctic soils are highly contingent on microbial resource balance. Carbon availability can constrain N losses under warming, whereas excess N amplifies priming-driven emissions, with important implications for predicting high-latitude greenhouse gas feedbacks and soil N losses under climate change.