No significant change noted in annual nitrous oxide flux under precipitation changes in a temperate desert steppe

As the third most important greenhouse gas, nitrous oxide (N2O) poses a significant threat to global warming and the ozone layer. However, the effects of precipitation changes on N2O emissions in arid areas remain unclear, particularly in desert steppe environments. Therefore, an in situ control experiment was conducted from July 2018 to July 2020 to examine the N2O emissions with changes in precipitation in the Urat Desert Steppe, northwestern China. The results showed that the N2O emission rate was relatively low in this desert steppe, at −0.04 to +15.0 μg N m−2 hr−1 with an annual flux of 0.20 ± 0.03 kg N ha−1. An increasing trend of N2O emission was observed in the early growing season (February to June 2019) when the precipitation was increased by 40% and 60% of its natural level. In contrast, no significant change in N2O emissions was observed when the precipitation was decreased during the same period. During the middle and late growing season and in the nongrowing season, precipitation changes did not significantly affect N2O emissions. In particular, no significant change in the annual N2O flux was observed during the entire observation period whether the precipitation was increased or decreased. Furthermore, the results of a structural equation model showed that the most important controlling factor for N2O emission is an abundance of key functional ammonia monooxygenase genes of ammonia-oxidizing archaea, which are restricted by the soil NH4+-N content, followed by abundances of key functional NO2− reductase (nirK) and N2O reductase (nosZ) genes. In contrast, the indirect effect of soil moisture on the abundance of nosZ compensated for the direct effect of soil moisture on N2O emissions. These results show that the primary and secondary origins of N2O emissions are soil ammonia oxidation and soil denitrification processes, respectively. In these two processes, N2O emissions are influenced more by the abundance of key functional microorganisms than by soil moisture, which might be limited mainly by the available soil nitrogen. Overall, the N2O emissions in the desert steppe environment were not sensitive to precipitation changes and were regulated mainly by nitrogen-related key functional microorganisms.