Bacillus subtilis biofertilizer mitigating agricultural ammonia emission and shifting soil nitrogen cycling microbiomes

Excessive ammonia (NH3) emitted from nitrogen fertilizer application in farmland have caused serious disturbance to global environment, including reduction of visibility, formation of regional haze, and increase of nitrogen deposition. Application of biofertilizer has been considered as an effective approach for soil improvement and agriculture sustainability. In this study, a field experiment was conducted to evaluate the potential of B. subtilis biofertilizer on mitigating NH3 volatilization and to investigate the underlying mechanisms. Compared with organic fertilizer, the incorporation of B. subtilis biofertilizer reduced NH3 volatilization by up to 44%. Moreover, the application of B. subtilis biofertilizer reduced the abundance of ureC gene, and increased the abundance of functional genes (bacterial amoA and comammox amoA) and ammonia-oxidizing bacteria (AOB). This indicated that the conversion of fertilizer nitrogen to NH4+-N was decreased and the nitrification process was increased. In brief, the application of B. subtilis biofertilizer reduced the "source" and increased the "sink" of NH4+-N, thus reducing the retention of NH4+-N in alkaline soil, and mitigating NH3 volatilization. These results indicated that B. subtilis biofertilizer is an effective control strategy for agricultural NH3 emission, maintaining high crop yield and mitigating environmental disturbance.