The mechanism of Bacillus subtilis to guarantee the safe utilization of brackish water by improving soil physical properties and cotton production

Although brackish water (BW) irrigation alleviates freshwater (FW) scarcity in arid regions, it risks soil salinization, deterioration of soil physical properties, and productivity decline. The application of Bacillus subtilis has great potential in reducing these potential risks, but the specific effects and mechanisms remain unclear. Therefore, in cotton cultivation within arid regions of Xinjiang, China, we established two irrigations (FW and BW) and two Bacillus subtilis application rates (0 and 45 kg·ha −1 ) to explore the feasibility of promoting the safe utilization of BW by applying Bacillus subtilis. The results showed that Bacillus subtilis could effectively reduce soil salinity and enhance the stability of soil water-stable aggregate (WSA), thereby achieving the optimization of soil water holding characteristics. Notably, Bacillus subtilis enhanced the resistance of soil physical properties to the adverse effects of BW irrigation, which is conducive to forming a long-acting protection. On this basis, the Bacillus subtilis increased the SPAD, net photosynthetic rate (Pn), and total biomass of cotton; reduced malondialdehyde (MDA) in cotton leaves, This ultimately increased the seed cotton yield and water use efficiency (WUE) by 3.33 %-5.04 % and 1.81–7.52 %, respectively, ensuring the safety and economic benefits of cotton production under BW irrigation. In the structure and function of microbial community, we found that under the application of Bacillus subtilis, the soil main biomarkers of FW and BW irrigations were Proteobacteria and Gemmatimonadota, respectively. Moreover, the increase in bacterial community evenness and total abundance of predominant bacterial phyla, as well as the function enhancement of carbohydrate and amino acid biosynthesis, are the key drivers for Bacillus subtilis to achieve the improvement of soil quality and cotton production. In summary, this study demonstrated the effectiveness and clarified key mechanisms of Bacillus subtilis in guaranteeing the safe utilization of BW, providing a feasible solution for sustainable agricultural development in arid regions. • Bacillus subtilis improved soil physical properties and inhibited soil salinization. • Bacillus subtilis promoted cotton production and safe utilization of brackish water. • Bacillus subtilis optimized soil bacterial community structure and function. • Bacillus subtilis improvement offered long-acting protection advantages.