Bacillus tequilensis S40 inoculation alleviates salt stress by modifying bacterial community structure and regulating elemental cycling rhizosphere of Reaumuria soongorica.

Plant growth‒promoting rhizobacteria (PGPRs) are pivotal in forest cultivation and saline‒alkaline soil improvement by altering the structure of rhizosphere bacterial communities and improving soil nutrient utilization efficiency. However, there are few reports on the exploration of PGPR bacterial resources and the mechanism by which PGPR enhance the salt tolerance of Reaumuria soongorica (R. soongorica) in desert shrubs. This study focused on Bacillus tequilensis (B. tequilensis) S40, which is a PGPR isolated from the rhizosphere of R. soongorica by our research group. We investigated the effects of the S40 strain on the rhizosphere microbial community and functional genes of R. soongorica through pot experiments. The results demonstrated that inoculation with the S40 strain could alleviate the negative effects of NaCl stress on the plant height, total root length, and rhizome leaf biomass. Proteobacteria, Bacteroidetes, and Planctomycetota were the dominant phyla. Notably, inoculation with S40 strain significantly increased the absolute abundances of functional genes involved in carbon (C), nitrogen (N), and phosphorus (P) cycling (p < 0.05). Furthermore, the genes related to C, N, and P cycling were significantly correlated with soil properties (available phosphorus, urease activity, sucrase activity), and the biomass of R. soongorica leaves, stems, and roots (p < 0.05). In conclusion, the PGPR strain S40 mediates the reorganization of bacterial community, drives the element cycle, and enhances soil nutrient availability, thus promoting plant growth and enhancing salt tolerance of plants and providing a method and scientific basis for cultivating shrub seedlings and alleviating the degree of soil salinization.