Advenella alkanexedens, a specific phosphate-solubilizing bacterium from rapeseed rhizosphere soil, highly activates...

Phosphorus fixation represents a primary constraint limiting the agronomic efficiency of phosphate fertilizers in calcareous soil. Rapeseed roots secrete amounts of organic matter, which can mobilize and decompose insoluble phosphorus in the soil. However, the activation mechanism of sparingly insoluble phosphorus in calcareous soils by rapeseed rhizosphere microorganisms remains unclear. This study aimed to screen and identify phosphate-solubilizing microorganisms from the rapeseed rhizosphere of calcareous soil, and to elucidate their key metabolic pathways for activating insoluble phosphorus. The results demonstrated that (i) fourteen dominant phosphate-solubilizing strains were isolated from rapeseed rhizosphere soil. Among these, Advenella alkanexedens was verified to significantly promote wheat growth and increase soil available phosphorus content. (ii) The culture condition optimization and functional characterization for Advenella alkanexedens revealed that its optimal growth temperature was 30°C, with an initial pH of 7. Its phosphate-solubilizing ability was regulated by Mg²⁺, K²⁺, and Ca²⁺ ions, and the strain exhibited considerable salt tolerance and the ability to produce siderophores. (iii) Advenella alkanexedens increased soil available phosphorus content by 11.49%-81.91% and elevated phytase activity by 36.87%-82.49%. Correlation analysis indicated that soil available phosphorus and phytase activity were significantly positively correlated with Ca₂-P, Ca₈-P, and Al-P fractions. (iv) Amino acids and organic acids were identified as the key metabolites influencing the phosphate-solubilizing function of Advenella alkanexedens. The KEGG pathway analysis showed these metabolites were primarily enriched in β-alanine metabolism and arginine and proline metabolism pathways. Our findings confirm that Advenella alkanexedens not only promotes crop growth but also significantly increases labile P fractions (Ca₂-P, Ca₈-P, Al-P) while reducing more stable forms (Ca₁₀-P), thereby enhancing soil phosphorus use efficiency. This study holds important implications for planting rapeseed to activate insoluble phosphorus in soil, to reduce phosphate fertilizer application, and to promote sustainable utilization of soil phosphorus resources. Furthermore, it provides a theoretical foundation for developing agricultural microbial inoculants.IMPORTANCEOur results confirm that Advenella alkanexedens not only benefits crop growth but also converts insoluble phosphates (O-P, Ca10-P) into highly active inorganic phosphorus components, thereby enhancing the utilization efficiency of soil phosphorus. This study was of great significance in activating the insoluble phosphorus in the soil, reducing the input of phosphate fertilizers, achieving the sustainable utilization of phosphorus resources, and protecting the environment. Additionally, it provided a basis for developing agricultural microbial agents.