Unimodal response of N2O flux to changing rainfall amount and frequency in a wet meadow in the Tibetan Plateau.

The rainfall amount and the frequency of extreme rainfall events have been predicted to increase in the Qinghai-Tibetan Plateau during the growing season. These changes will likely affect ecosystem processes, including those that control nitrogen (N) cycling and storage; however, the direction of the changes remains unclear. In this study, we experimentally altered the amount and frequency of precipitation events during the growing season (May through October) at an alpine wetland in the Qinghai-Tibetan Plateau. The treatments included ambient rain (CK) plus 25 mm of extra water for each irrigation event but with different irrigation frequency, i.e., weekly (DF1), biweekly (DF2), every three weeks (DF3) and every four weeks (DF4). During the growing season, the N 2 O flux showed a large seasonal variation. Compared with the treatment of natural rainfall events, the increase in the rainfall amount promoted the N 2 O emission flux. As the frequency of rainfall events increased, the aboveground biomass increased significantly from 85.82 g·m−2 to 245.79 g·m−2, and the accumulated N 2 O emissions first increased and then decreased; we observed the peak of the N 2 O flux at the DF2 rainfall frequency. We also found the significant linear relationships between soil N 2 O flux, nitrate nitrogen, and microbial biomass nitrogen content. Furthermore, among the soil microbial factors, higher rainfall frequency (DF1) significantly reduced the relative abundance of the original dominant species (Alphaproteobacteria) in the studied wetland soil. Our results indicate that alpine wetlands are highly sensitive to increased precipitation variability and high frequencies of extreme rainfall events could significantly reduce N 2 O emission. Future precipitation patterns could weaken the contribution rate of wetland N 2 O emission to the global warming. • The increase in rainfall amount promotes the flux of N2O. • N2O flux presents a unimodal response to rainfall frequency. • The increase in rainfall frequency increases vegetation biomass. • The increase in rainfall frequency reduces the abundance of dominant microorganisms. • The maximum N2O flux appears in the early stage of plant. [ABSTRACT FROM AUTHOR]