The Effects of Inoculation with Rhizosphere Phosphate-Solubilizing Bacteria on the Growth and Physiology of Reaumuria soongorica Seedlings Under NaCl Stress

Soil salinization significantly exacerbates the deficiency in plant-available phosphorus in the soil, thereby adversely affecting plant growth and development. Through various processes, phosphate-solubilizing bacteria in the rhizosphere significantly increase soil-soluble phosphorus content, boosting plant development and stress resistance. This study focused on annual R. soongorica seedlings to examine how rhizosphere phosphate-solubilizing bacteria enhance growth under NaCl-induced stress conditions. This study isolated and characterized rhizosphere phosphate-solubilizing bacteria, evaluating their phosphate solubilization capacity and effects on R. soongorica seedling growth and physiology under NaCl stress through pot experiments, with potential applications in saline soil improvement and desert ecosystem restoration. This study used four treatment groups (control group, NaCl treatment group, bacterial inoculation treatment group, and bacterial and NaCl mixed-treatment group) with twelve treatments and four replicates per treatment. The experimental results demonstrated that five phosphate-solubilizing bacterial strains exhibited a significant phosphate solubilization capacity, accompanied by a notable reduction in pH within the inorganic phosphorus medium. Compared to the NaCl treatment, the net growth of the plant height of R. soongorica seedlings inoculated with strains J23, J24, and M1 under NaCl stress increased significantly (p < 0.05), and all of them more than doubled, and the net growth of the stem diameter of R. soongorica seedlings inoculated with strain J24 increased significantly by 144.17%. The physiological characteristics of R. soongorica seedlings demonstrated significant alterations following inoculation with the five phosphate-solubilizing bacterial strains. The inoculation of R. soongorica seedlings with the five phosphate-solubilizing bacterial resulted in a statistically significant increase in both foliar total phosphorus content and available phosphorus levels within the rhizosphere soil (p < 0.05). Additionally, under NaCl stress conditions, R. soongorica seedlings inoculated with the five phosphate-solubilizing bacterial strains exhibited varying degrees of salt tolerance, with the following descending order of effectiveness: J24 > P2 > J23 > P3 > M1. In conclusion, the rhizosphere phosphate-solubilizing bacteria J24 represents a potentially valuable microbial resource for saline soil amelioration, demonstrating the most pronounced enhancement in both the growth parameters and salt tolerance of R. soongorica seedlings under 300 mmol·L−1 NaCl stress.