Effects of Amendments on Nh3 Volatilization, N2o Emissions, and Nitrification at Four Salinity Levels

Abstract

Abstract: The marked salinity and alkaline pH of coastal saline soil profoundly impact the nitrogen conversion process, leading to a significantly reduced nitrogen utilization efficiency and substantial gaseous nitrogen loss. Biochar, manure, and gypsum are commonly employed as soil amendments in the restoration of saline-alkali land. However, research is indispensable to delve into the effects of amendments on nitrogen transformation under various salinity conditions. In this study, biochar, manure, and gypsum were applied in low-, moderate-, high-, and severe-salinity soils in order to explore the effects of amendments about NH3 volatilization and N2O emissions. High-throughput sequencing and qPCR analyses of key nitrification and denitrification genes were conducted to characterize responses of ammonia-oxidizing bacteria (AOB), archaea (AOA) amoA, and the nirS, nirK, and nosZ to amendments in saline soils. The results demonstrated that AOA was significantly and positively correlated with the NO3--N content (r = 0.137, P < 0.05) and N2O emissions (r = 0.174, P < 0.01), which indicated that AOA dominated N2O emissions from nitrification in saline soils. Structural equation modeling indicated that the amendments affected N2O emissions by affecting the soil pH, electrical conductivity, mineral nitrogen content, and functional genes (AOA-amoA and nosZ). A two-way analysis of variance further illustrated that salinity and the amendments significantly affected N2O emissions. In conclusion, this research offers valuable insights to better comprehend the effects of amendments about gaseous nitrogen in saline soils, thereby enhancing the accuracy and efficacy of future greenhouse gas emission predictions and modeling.

Keywords: Saline soil, biochar, Manure, Gypsum, Nitrification, N2O