The driving effect of nitrogen-related functional microorganisms under water and nitrogen addition on N2O emission in a temperate desert

Nitrous oxide (N2O) is an important greenhouse gas and a precursor of ozone depletion in the upper atmosphere, thus contributing to climate change and biological safety. The mechanisms and response characteristics of N2O emission in desert soils to precipitation and nitrogen (N) deposition are still unclear. To further elucidate this, an in-situ experiment was conducted in the Gurbantunggut Desert, a temperate desert in China, between June and September 2015 and 2016. The response in N2O flux to water addition (equivalent to 5 mm precipitation) was very transient in summer, only lasting one to two days.This was attributed to the rapid decrease in soil moisture following the water addition, due to the high temperature and drought conditions, and there was no significant change in N2O emission or in the abundance of N-related key functional genes. In contrast, N2O emissions increased significantly in response to N addition. This was associated with an increase in functional gene abundances of amoA (ammonia oxidizing bacteria (AOB)) and ammonia-oxidizing archaea (AOA), which responded positively to increasing soil NH4+-N content, but were inhibited by increasing soil NO3--N content. The abundance of the nirS (nitrate reductase) gene was significantly increased by increasing soil NO3--N content. Interestingly, the indirect effect of increased soil moisture in enhancing N2O emission by increasing the abundance of AOA was offset by a direct effect of soil moisture in inhibiting soil N2O emission. Overall, N2O emissions were mainly controlled by AOA rather than AOB in summer, and were more sensitive to soil available N than to soil moisture in this temperate desert.