The phosphate-solubilizing capacity of Rhizobium tropici LNP6 and its growth-promoting effects on Ormosia hosiei seedlings

Globally, available phosphorus is generally scarce in terrestrial soils, despite the abundance of potential phosphorus sources. Therefore, isolating and utilizing microbial strains with both phosphate-solubilizing and nitrogen-fixing capabilities is crucial for enhancing the environmental adaptability and growth performance of woody leguminous plants in phosphorus-deficient conditions. This study employs the highly efficient plant growth-promoting strain Rhizobium tropici LNP6, which was isolated from the root nodules of Ormosia hosiei and verified through re-inoculation screening, to explore its phosphorus solubilization mechanisms and evaluate its growth-promoting effects in soils with three different phosphorus sources. The results indicated that strain LNP6 is capable of solubilizing both insoluble organic and inorganic phosphorus. Analysis of its metabolites revealed that the strain exerts its phosphorus-solubilizing function through the production of organic acids and the secretion of phosphatases. The pot experiment demonstrated that LNP6 significantly accelerated the release of available nutrients in the seedling rhizosphere soil through two pathways: symbiotic nitrogen fixation and free-state phosphate solubilization. This enhancement resulted in a substantial improvement in the uptake efficiency of N, P, K by O.hosiei seedlings, thereby robustly promoting seedling growth and biomass accumulation. The greatest promoting effect was observed following the application of Calcium phytate under low-phosphorus conditions. This study establishes a theoretical foundation for the development of nitrogen and phosphorus-efficient microbial agents for O. hosiei, which is essential for alleviating the impacts of soil phosphorus deficiency on its growth.