Altered precipitation regimes mitigate N2O flux response to nitrogen addition in an alpine steppe

Anthropogenic-driven global change, including changes in atmospheric nitrogen (N) deposition and precipitation patterns, is dramatically altering N cycling in soil. How long-term N deposition, precipitation changes, and their interaction influence nitrous oxide (N2O) emissions remains unknown, especially in the alpine steppes of the Qinghai-Tibetan Plateau (QTP). To fill this knowledge gap, a platform of N addition and altered precipitation experiments was established in an alpine steppe of the QTP in 2013. N addition significantly increased N2O emissions, and alterations in soil NO3-N, pH, temperature, and belowground biomass modulated N2O emissions. In addition to abiotic parameters, ammonia-oxidizing bacteria dominated N2O emissions in nitrification compared with ammonia-oxidizing archaea. Changes in the denitrifying microbial community, namely a high ratio of (nirS+nirK) gene-containing to nosZ gene-containing organisms, were responsible for N2O emissions in denitrification. Altered precipitation did not affect N2O emissions. This unexpected finding, which is inconsistent with the conventional view that N2O emissions are controlled by soil water content, indicates that N2O emissions are particularly susceptible to N deposition in the alpine steppes. Notably, whereas N2O emissions were affected by N addition as a single factor, they were not significantly affected by the combination of precipitation changes and N addition, indicating that altered precipitation patterns may mitigate the positive feedback effect of N addition on N2O emissions. Consequently, our study suggests that the response of N2O emissions to N deposition in future global change scenarios will be affected by precipitation regimes in the alpine steppes.