Air injection in paddy soil reduces N2O and NH3 emissions and regulates the nitrogen cycle

Rice (Oryza sativa L.) is a staple food and a significant source of pollutant gases, such as nitrous oxide (N₂O) and ammonia (NH₃). While aeration irrigation can significantly increase rice yield, its impact on N₂O and NH₃ emissions, particularly the nitrogen (N) cycling mechanisms, remains unclear. Here, we analyzed the effects of soil air injection (SAI) on N₂O and NH₃ emissions, soil properties, rice N uptake and microbial N cycling, compared with soil without air injection (the control). SAI increased soil oxygen diffusion rate (SODR) by 31–107 %, raised soil pH by 0.4–0.9 units, enhanced total N uptake by rice by 8.3 %, and reduced N₂O emissions by 17 % and NH₃ volatilization by 16 %. The increase in SODR enhanced the N content in rice leaves, which subsequently suppressed NH₃ volatilization. The reduction in N₂O emissions was mainly attributed to the decline in norC gene abundance, while the increased abundances of amoB and GDH1 genes contributed to the suppression of NH₃ volatilization. The abundance of norC was negatively correlated with Actinobacteria, whereas amoB and GDH1 abundances were positively correlated with Thaumarchaeota and Proteobacteria, respectively. Actinobacteria abundance initially increased and then decreased with rising SODR, while Thaumarchaeota abundance consistently increased as SODR rose. Additionally, the increase in soil pH promoted the abundance of Proteobacteria. In conclusion, SAI increased N uptake in rice leaves and influenced key N-cycling microorganisms (Actinobacteria, Thaumarchaeota, and Proteobacteria) and genes (norC, amoB and GDH1) by enhancing SODR and soil pH, thereby reducing N₂O and NH₃ emissions.