Belowground biomass changed the regulatory factors of soil N2O fluxes under N and water additions in a temperate steppe of Inner Mongolia

Abstract Purpose： Simulations of N deposition and precipitation via N and water addition experiments are important for studying how soil nitrous oxide (N2O) fluxes in temperate steppes will respond to future global climate change. Methods： In June 2017, we conducted an N and water application experiment on a temperate steppe in Inner Mongolia, Northeast China, to investigate the impacts of N and water additions upon N2O fluxes and how the soil physicochemical properties, vegetation, and microbes regulate this process regulate this process. In this study, we collected samples and measured the variations in soil N2O fluxes and physicochemical and biological properties under N, and water additions in July and August of 2019 and 2020. Results： The results indicated that N addition significantly decreased soil pH, increased the NH4 + -N and DON contents, decreased the MBC content, and promoted PER activity, while water addition significantly increased soil pH, SWC, and the root-shoot ratio. Soil N2O fluxes were significantly increased by a factor of 2.2 under the 2020 N treatment alone. A structural equation model (SEM) showed that the soil N2O fluxes in response to N and water additions were mainly driven by DON in 2019, and pH was the key factor that affected the N2O fluxes in 2020. Conclusions： Our findings suggested that the leading factors differed between the two years due to the differences in BGB caused by different distribution of precipitation during the growing season.