Combination of Functional Complementary Salt-Tolerant PGPR and Organic Amendments Modulates the Soil Micro-Environment and Promotes Wheat Growth

The individual application of salt-tolerant plant growth-promoting rhizobacteria (ST-PGPR) or organic amendments exhibits certain limitations in remediating saline-alkali soils. This study developed a co-application treatment by combining a functionally complementary ST-PGPR consortium (Bacillus velezensis and Bacillus marisflavi) with optimized organic amendments (biochar at 22.5 t·ha−1 and sheep-manure organic fertilizer at 7.5 t·ha−1) to enhance soil quality and wheat growth. Compared with the control, the combination of the ST-PGPR consortium with organic amendments significantly reduced soil electrical conductivity by 52.69%. while soil organic matter, alkaline nitrogen, available phosphorus, and available potassium increased by 54.37%, 7.68%, 11.85%, and 39.57%, respectively (p < 0.05). The activities of sucrase, urease, and catalase also increased by 147.69%, 28.56%, and 30.26%, respectively (p < 0.05). Furthermore, the combined treatment significantly promoted wheat growth, increasing plant height, root length, and fresh weight by 12.11%, 26.60%, and 35.00%, respectively (p < 0.05), while alleviating osmotic and oxidative stress. β-diversity analysis revealed distinct microbial community compositions across treatments, and microbial composition indicated that Actinobacteriota and Starmerella were enriched under the co-application. Additionally, the co-application significantly enhanced the complexity and interconnectivity of the bacterial network, while reducing the stability of the fungal network. Partial least squares path and random forest models identified soil chemical properties as the key factors driving wheat growth. This synergistic system presents a promising and sustainable strategy for remediating saline-alkali soils and enhancing crop productivity.