Screening and optimization of salt-alkali tolerant phosphate-solubilizing Enterobacter sp. AD8: applications in soybean growth promotion and saline-alkali soil remediation.

Soil salinization severely limits crop growth, nutrient availability and phosphorus use efficiency. Combined saline-alkali stress and phosphorus deficiency greatly restrict soybean productivity. Applying salt-alkali tolerant phosphate-solubilizing bacteria is an effective biological strategy to improve crop performance and soil fertility. In this study, 15 strains were isolated from local saline-alkali soil. After functional screening, Enterobacter sp. AD8 showed excellent phosphate-solubilizing (264.21 mg/L soluble P) and IAA-producing (58.09 µg/mL) capacities. Its optimal culture conditions were determined as 25 °C, pH 6 and 3% inoculum size via optimization tests. Pot experiments showed AD8 significantly improved soybean seedling growth, enhanced antioxidant enzyme activity, reduced MDA content, and increased osmotic regulators. It also lowered soil pH (from 7.98 to 7.75) and salinity (from 0.304% to 0.265%), increased available phosphorus by 20.97% and available potassium by 54.54%, and boosted phosphatase and cellulase activities by 59.63% and 32.07%, respectively. This multi-functional strain and its optimized conditions support microbial inoculant development, providing valuable resources for soybean production and ecological remediation of saline-alkali soils.