Inoculation with native phosphate-solubilizing bacteria modulates growth, ginsenoside biosynthesis, and rhizosphere ecology of Panax ginseng under varying phosphorus availability

Phosphate-solubilizing bacteria (PSB) promote plant growth by mobilizing soil phosphorus; however, the effects of PSB inoculation on ginseng under varying phosphorus levels are not well characterized. This study isolated two highly efficient PSB, Bacillus subtilis N124 (BS) and Ensifer 53 (EA), from the rhizosphere of ginseng. Ginseng was inoculated with BS, EA, or their mixture (MIX) under low, medium, and high phosphorus supply, and plant biomass, photosynthetic pigments, ginsenosides, phosphorus uptake, soil phosphatase activities, and rhizosphere microbial community composition were measured. The results demonstrated that all treatments significantly increased ginsenosides of Rf, Rb1, Rb2, and Rc, with MIX showing the strongest effect. All inoculation treatments increased acid phosphatase and alkaline phosphatase activities, soil microbial biomass phosphorus, and rhizosphere microbial diversity; MIX outperformed the single strains in enhancing plant physiological traits. Under medium phosphorus levels, all inoculation treatments produced the highest root activity, soil available phosphorus content, and total ginsenoside content in ginseng. Spearman analysis revealed that alkaline phosphatase activity, soil total phosphorus, and microbial biomass phosphorus were negatively correlated with the Sphingomonas ; soil total phosphorus, alkaline phosphatase activity, and available phosphorus were negatively correlated with the genus Gemmatimonas . Predictions from KEGG and FUNGuild databases revealed that EA modulated environmental response pathways, that BS enhanced basal metabolism, and that MIX integrated these functions to improve metabolic stability. In summary, the same strain exhibited different effects under phosphorus concentrations. These results provide a scientific basis for screening and applying effective microbial biofertilizers across ginseng-growing regions.