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.