Warming and N addition amplify alpine peatland N₂O emissions via divergent microbial and nutrient pathways

Alpine peatlands are critical global reservoirs of soil carbon and nitrogen (N), making them hotspots for greenhouse gas feedbacks under climate change. However, the mechanisms underlying nitrous oxide (N₂O) emissions in these ecosystems remain poorly understood. Here, we investigated the effects of warming (+2 °C), N addition (20 kg N ha^-1 yr^-1), and their combination on N₂O emissions in an eight-year field experiment (2017-2024) in an alpine peatland on the Zoige Plateau. Both warming (W) and N addition (N) significantly increased N₂O emissions, with mean fluxes rising by 243% and 318%, respectively. Notably, the combined treatment (W + N) exerted a synergistic effect, increasing emissions by 661%, a magnitude significantly greater than the sum of individual treatments. Denitrification was the dominant source of N₂O, and treatments shifted production pathways by suppressing nitrification and stimulating denitrification. Warming enhanced lignin-degrading fungal activity, and upregulated nirK while suppressing nirS and nosZ, indicating increased denitrification potential but reduced N₂O reduction. In contrast, N addition decreased soil pH, intensified the combined carbon and phosphorus scarcity for microbes, increased the fungal-to-bacterial ratio, and favored acid-tolerant denitrifies, selectively inhibiting nosZ while activating nirK and norB. Our findings reveal distinct microbial pathways mediating N₂O emissions under warming and N deposition, providing mechanistic insights for predicting greenhouse gas dynamics in alpine ecosystems under future climate scenarios.