Farmland soil is one of the most important anthropogenic sources of nitrous oxide (N₂O).In this paper,four plant growth-promoting rhizo bacteria were used as the candidate strains,namely Bacillus albus Lv5A,Bacillus subtilis sp.subtilis NRCB002,Pseudomonas stutzeri NRCB010,and Bacillus siamensis NRCB026.The greenhouse pot experiment,soil microcosm experiment,and field plot experiment were established to explore the effect of these growth-promoting rhizo bacteria on N₂O emission from farmland soil.The results showed that cumulative N₂O emissions from tested soils were NRCB002 > Lv5A > NRCB026 > NRCB010 after the inoculation with these four growth-promoting rhizo bacteria in the greenhouse pot experiment.The cumulative N₂O emissions were decreased by 2.3%,33.1%,34.2% and 40% after the inoculation with these four strains compared with that from the non-inoculated control.Then two strains of NRCB010 and NRCB026 were chosen for further soil microcosm experiment and field experiment.The inoculation with NRCB010 decreased the cumulative N₂O emissions by 21% and 44% in soil microcosm and field plot experiment,respectively;while the inoculation with NRCB026 decreased the cumulative N₂O emissions by 48% and 73% in soil microcosm and field plot experiments,respectively.In conclusion,plant growth-promoting rhizo bacteria NRCB010 and NRCB026 can effectively mitigate N₂O emission from farmland soil.Our results provides critical scientific basis for N₂O mitigation in farmland soil and important practical guidance for development of novel biofertilizer with both plant growth-promoting and greenhouse gas mitigating effects.