The effect of nitrogen input on NO emission depends on precipitation in a temperate desert steppe.

Nitrous oxide (NO) is the third most important greenhouse gas, and can damage the atmospheric ozone layer, with associated threats to terrestrial ecosystems. However, to date it is unclear how extreme precipitation and nitrogen (N) input will affect NO emissions in temperate desert steppe ecosystems. Therefore, we conducted an in-situ in a temperate desert steppe in the northwest of Inner Mongolia, China between 2018 and 2021, in which N inputs were combined with natural extreme precipitation events, with the aim of better understanding the mechanism of any interactive effects on NO emission. The study result showed that NO emission in this desert steppe was relatively small and did not show significant seasonal change. The annual NO emission increased in a non-linear trend with increasing N input, with a much greater effect of N input in a wet year (2019) than in a dry year (2021). This was mainly due to the fact that the boost effect of high N input (on June 17 2019) on NO emission was greatly amplified by nearly 17-46 times by an extreme precipitation event on June 24 2019. In contrast, this greatly promoting effect of high N input on NO emission was not observed on September 26 2019 by a similar extreme precipitation event. Further analysis showed that soil NH-N content and the abundance of ammonia oxidizing bacteria (amoA (AOB)) were the most critical factors affecting NO emission. Soil moisture played an important indirect role in regulating NO emission, mainly by influencing the abundance of amoA (AOB) and de-nitrification functional microorganisms (nosZ gene). In conclusion, the effect of extreme precipitation events on NO emission was greatly increased by high N input. Furthermore, in this desert steppe, annual NO flux is co-managed through soil nitrification substrate concentration (NH-N), the abundance of soil N transformation functional microorganisms and soil moisture. Overall, it was worth noting that an increase in extreme precipitation coupled with increasing N input may significantly increase future NO emissions from desert steppes.