Abstract
Nitrous oxide (N(2)O) is one of the most important greenhouse gases contributing to global climate warming. Recently, studies have shown that arbuscular mycorrhizal fungi (AMF) could reduce N(2)O emissions in terrestrial ecosystems; however, the microbial mechanisms of how AMF reduces N(2)O emissions under climate change are still not well understood. We tested the influence of AMF on N(2)O emissions by setting up a gradient of precipitation intensity (+50%, +30%, ambient (0%), -30%, -50%, and -70%) and manipulating the presence or exclusion of AMF hyphae in a semiarid grassland located in northeast China. Our results showed that N(2)O fluxes dramatically declined with the decrease in precipitation gradient during the peak growing season (June-August) in both 2019 and 2020. There was a significantly positive correlation between soil water content and N(2)O fluxes. Interestingly, N(2)O fluxes significantly decreased when AMF were present compared to when they were absent under all precipitation conditions. The contribution of AMF to mitigate N(2)O emission increased gradually with decreasing precipitation magnitudes, but no contribution in the severe drought (-70%). AMF significantly reduced the soil's available nitrogen concentration and altered the composition of the soil bacteria community including those associated with N(2)O production. Hyphal length density was negatively correlated with the copy numbers of key genes for N(2)O production (nirK and nirS) and positively correlated with the copy numbers of key genes for N(2)O consumption (nosZ). Our results highlight that AMF would reduce the soil N(2)O emission under precipitation variability in a temperate grassland except for extreme drought.