Alternate wetting and drying (WD) irrigation is an effective water-saving practice for rice production but often increases nitrous oxide (N₂O) emissions.  Plant growth-promoting bacteria such as Bacillus subtilis (BS) can enhance crop growth; however, the combined effects of WD and BS on rice yield and N₂O emissions remain unclear.  A 3-year field experiment using two japonica rice cultivars was conducted to evaluate the effects of two irrigation regimes (continuous flooding (CF) and WD) and BS application (without BS, –BS; and with BS, +BS) on rice yield and N₂O emissions.  The results showed that BS application significantly increased the rice yields under both irrigation regimes.  Compared with CF–BS, CF+BS and WD+BS increased the yields by 3.9–9.0% and 5.8–12.6%, respectively, mainly due to a higher total spikelet number.  CF+BS had no significant effect on N₂O emissions, whereas WD–BS markedly increased cumulative N₂O emissions, while WD+BS reduced emissions by 34.8–45.9% compared with WD–BS.  The WD+BS treatment enhanced root oxidation activity and increased root surface area and volume density in the 20–40 cm soil layer.  It also reduced the soil NO₃⁻-N content, raised the NH₄⁺/NO₃⁻ ratio, and enhanced urease and sucrase activities, thereby promoting the accumulation of dissolved organic carbon (DOC) and microbial biomass nitrogen (MBN), along with a higher abundance of the nitrous oxide reductase gene (nosZ) associated with N₂O reduction.  Overall, integrating WD with BS increased rice yield while mitigating N₂O emissions.  The enhanced root function and aboveground agronomic traits, improved soil enzyme activity, and optimized nitrogen transformation and microbial processes were the key mechanisms for achieving a high yield with reduced environmental impacts.

rice (Oryza sativa L.)  /  alternate wetting and drying irrigation  /  Bacillus subtilis  /  yield  /  N₂O emissions