Response of microbial community diversity and the abundance of nitrogen-cycling genes to Bacillus subtilis application in mulberry field soil

Context Bacillus subtilis (BS) is a widely used microbial agent that could improve soil fertility and soil microenvironment. There is still uncertainty about the suitability of BS for cultivating crops with high demand for nitrogen fertiliser. Aims To evaluate the effects of BS agent on microbial community diversity and nitrogen-cycling genes in mulberry rhizosphere soil. Methods Pot experiments were conducted. Different dosages (CK, 0; T1, 0.5 × 106 CFU g−1 soil; T2, 1 × 106 CFU g−1 soil; T3, 2 × 106 CFU g−1 soil) of BS agent were applied to irrigate the mulberry soil. The soil nutrient content, enzyme activity, bacterial community, and nitrogen-cycling genes were determined. Key results T1 had the highest Chao1 and Shannon index, while T3 had the lowest. BS-treated samples had higher relative abundance of Actinobacteria and Chloroflexi than that of CK. Specially, BS-treated samples had higher relative abundance of Sphingomonas, Reyranella, and Hyphomicrobium, which was significantly positively correlated with the content of organic matter, total soluble nitrogen, ammonium nitrogen, and the activity of sucrase. The abundance of genes involved in amino acid metabolism, energy metabolism, metabolism of cofactors, and vitamin functions also increased in the BS-treated samples. BS treatment significantly increased the abundance of AOA-amoA and nirK genes, but decreased the abundance of nirS and nifH genes. Conclusions An appropriate amount of BS agent could improve soil fertility, regulate the dominant bacterium communities, and affect the abundance of functional genes involved in nitrogen cycling. Implications BS is probably a good choice for mulberry cultivation to improve nitrogen fertiliser utilisation efficiency.