Rhizosphere regulation by three Bacillus species and tomato productivity: A feasible approach for moderately saline-alkali soil remediation

Soil salinization can restrict the cultivation of plants. Utilizing plant growth-promoting bacteria (PGPB) to aid plant growth and saline-alkali land improvement, which is one of the hotspots in agricultural green development and global food security. This study employed three Bacillus species of B. amyloliquefaciens, B. licheniformis and B. subtilis as core functional microorganisms existing in a bio-organic fertilizer (BOF), to investigate the rhizospheric effects of PGPB belonging to the same genus but different species. Results showed that all the three PGPB species had successfully colonized the rhizosphere soil, enhancing the diversity of rhizosphere bacterial communities during the tomato's seedling stage. The enhancement of soil microbial activity further increased the activities of protease, sucrase, alkaline phosphatase and polyphenol oxidase, thus increasing the absorption and consumption of nitrogen and phosphorus by plants. In addition, the microbial activity and metabolites increased soil porosity and refined soil particles, thereby improving the soil physical structure. Significantly, the BOF application notably reduced soil total calcium, exchangeable calcium and water-soluble salts through the complexation of salt-based cations. Our results confirmed that the saline-alkali resistance of Bacillus species could improve soil quality and plant productivity, thereby providing novel insights into the effective application of PGPB in saline-alkali soils.