Soil properties and microbial abundance explain variations in N2O fluxes from temperate steppe soil treated with nitrogen and water in Inner Mongolia, China

Abstract

Microbe-mediated soil nitrification and denitrification processes affect the variations in soil N2O fluxes. Researchers are concerned about how the abundances of nitrifiers and denitrifiers and the N2O fluxes from temperate semi-arid grassland soil vary as nitrogen (N) and water inputs vary. In this study, we report the results from a field experiment that was set up in a temperate semi-arid grassland area in northern China in May 2017. In August 2018, we collected samples to investigate how a range of physical, chemical and biological characteristics of soil, including the pH, moisture, dissolved organic carbon content (DOC) and available N content, N2O fluxes, and the abundances of ammonia oxidizers and denitrifiers in the soil, changed after N (4 g N·m−2·year−1 NH4NO3) and water (112.5 mm·year−1) were added over a period of 1 year. We analyzed the abundances of AOA amoA, AOB amoA, nirS, nirK and nosZ using quantitative PCR. We found that the soil N2O emissions were negatively affected by the water additions, but were not affected by the N additions. We also found that the AOA amoA and nosZ genes responded positively to the N additions. Watering had a positive effect on the nirS gene abundance, while N additions and water together intensified the effect of only water on the nirS gene abundance. The nirS gene abundance, soil pH, and DOC content explained 46.1%, 20.1% and 12.0% of the variations in the soil N2O fluxes, respectively. These results provide improved insights into how microorganisms affect N cycling, and may be used to help predict how soil N2O fluxes might change in the future, as N deposition and precipitation change.