Responses of Soil Nitrogen Transformation and N2O Emission to Soil pH and Hydrothermal Changes

Soil nitrogen fate determines nitrogen availability for crops and their environmental impact, which is regulated by nitrogen transformation processes that are mediated through soil properties (e.g., pH) and environmental factors (e.g., hydrothermal conditions). Incubation experiments were conducted on soils with different pH levels (covering acidic to calcareous ranges) to study the effects of soil pH and hydrothermal conditions on nitrogen transformation and N2O emissions. The results showed that the net ammonification rate was negatively correlated with soil pH, whereas the net nitrification rate, net nitrogen mineralization rate, and N2O emission rate showed positive correlations. Structural equation modeling (SEM) indicated that soil pH and hydrothermal conditions exerted primary influences on soil net nitrogen transformation rates, consequently affecting N2O emissions. Soil pH and hydrothermal conditions had 83% and 93% effects, respectively, on net nitrogen transformation rates, while they had 77% effects on N2O emissions. Consequently, soil pH and hydrothermal conditions might be the key drivers influencing soil nitrogen transformation and N2O emissions. Specifically, in subtropical regions characterized by high temperatures and abundant summer rainfall, regulating soil moisture could mitigate NO3−-N accumulation and N2O emissions, providing a targeted strategy for sustainable nitrogen management.