Effects of the three amendments on NH3 volatilization, N2O emissions, and nitrification at four salinity levels: An indoor experiment.

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. The application of soil amendments (e.g. biochar, manure, and gypsum) was proved to be effective for the remediation of saline soils. However, the effects of the three amendments on soil nitrogen transformation in soils with various salinity levels, especially on NH₃ volatilization and N₂O emission, remain elusive. Here, we reported the effects of biochar, manure, and gypsum on NH₃ volatilization and N₂O emission under four natural salinity gradients in the Yellow River Delta. Also, high-throughput sequencing and qPCR analysis were performed to characterize the response of nitrification (amoA) and denitrification (nirS, nirK, and nosZ) functional genes to the three amendments. The results showed that the three amendments had little effect on NH₃ volatilization in low- and moderate-salinity soils, while biochar stimulated NH₃ volatilization in high-salinity soils and reduced NH₃ volatilization in severe-salinity soils. Spearman correlation analysis 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 biochar, manure, and gypsum affected N₂O emission by influencing soil pH, conductivity, mineral nitrogen content, and functional genes (AOA-amoA and nosZ). Two-way ANOVA further showed that salinity and amendments (biochar, manure, and gypsum) had significant effects on N₂O emissions. In summary, this study provides valuable insights to better understand the effects of gaseous N changes in saline soils, thereby improving the accuracy and validity of future GHG emission predictions and modeling.