Nitrogen addition, rather than altered precipitation, stimulates nitrous oxide emissions 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 (10 g m⁻² yr⁻¹) and altered precipitation (± 50% precipitation) experiments was established in an alpine steppe of the QTP in 2013. Long-term N addition significantly increased N₂O emissions. However, neither long-term alterations in precipitation nor the co-occurrence of N addition and altered precipitation significantly affected N₂O emissions. These unexpected findings indicate that N₂O emissions are particularly susceptible to N deposition in the alpine steppes. Our results further indicated that both biotic and abiotic properties had significant effects on N₂O emissions. N₂O emissions occurred mainly due to nitrification, which was dominated by ammonia-oxidizing bacteria, rather than ammonia-oxidizing archaea. Furthermore, the alterations in belowground biomass and soil temperature induced by N addition modulated N₂O emissions. Overall, this study provides pivotal insights to aid the prediction of future responses of N₂O emissions to long-term N deposition and precipitation changes in alpine ecosystems. The underlying microbial pathway and key predictors of N₂O emissions identified in this study may also be used for future global-scale model studies.