Interactive effects of warming and nitrogen level on N₂O fluxes and associated soil processes in an alpine wet meadow

How warming modifies nitrogen (N)-level-dependent nitrous oxide (N₂O) responses and associated soil processes in alpine wet meadows remains unclear. In this study, we conducted an open-top chamber warming and two tested N addition levels on the northeastern Qinghai-Tibet Plateau, with control (CK), warming (W), N addition at 20 kg N ha^-1 yr^-1 (N₁) and 30 kg N ha^-1 yr^-1 (N₂), and their corresponding combined warming treatments (WN₁ and WN₂). N₂O fluxes, soil carbon and nitrogen components, and enzyme activities were measured during the growing seasons of 2021 and 2023. The results showed that observation-period cumulative net N₂O exchange under W was -128.61 and -71.87 mg m^-2 in 2021 and 2023, respectively. Compared with CK, N₁ increased cumulative fluxes by 53.0%-70.8%, which was higher than the effect of N₂, ranging from -1.5% to 45.1%. WN₁ and WN₂ increased cumulative fluxes by 195.8%-219.1% and 89.0%-121.3%, respectively, showing significant positive non-additive effects. Integrated analysis indicated that soil moisture and inorganic N showed the strongest overall associations with N₂O variation. The decrease in soil moisture under W, the significantly lower enzyme-activity score under N2, and reductions in microbial biomass were associated with N₂O variation. Overall, under the OTC warming treatment tested here, N₂O responses did not increase monotonically from N1 to N2, highlighting the importance of jointly considering soil moisture, inorganic N availability, microbial biomass, and N-transformation enzyme responses when assessing N₂O dynamics in alpine wet meadows under future environmental change.