Phosphate-solubilizing bacteria reduce Cd accumulation in spinach by forming P-Ca adhesive films in the roots and altering the structure of soil macroaggregates.

Phosphate-solubilizing bacteria are crucial for plant growth promotion and heavy metal remediation in contaminated soils. However, the mechanisms underlying phosphate-solubilizing bacteria-mediated regulation of phosphorus (P) and calcium (Ca) availability and cadmium (Cd) bioavailability reduction remain unclear. This study investigated the effects and mechanisms of phosphate-solubilizing bacteria Kluyvera sp. M8 on P and Ca regulation, soil aggregate structure modification, and Cd uptake inhibition in spinach. Untargeted metabolomics showed that strain M8 secreted substances such as 3-Indolepropionic acid, N1-Acetylspermidine, and uric acid for the release of P and Ca and the immobilization of Cd. Strain M8 facilitated P and Ca enrichment on spinach root surfaces, forming a protective P-Ca film that reduced Cd into the root. Furthermore, it enhanced Cd immobilization in root cell walls and increased macroaggregate proportions in rhizosphere soil. Notably, strain M8 enriched active inorganic P and Ca components within macroaggregates while disrupting CaCO structure, promoting insoluble CdCO formation, enhancing Cd immobilization and decreasing the concentration of active Cd in the pore water. These findings provide valuable insights for Cd pollution management in agricultural fields and Cd uptake reduction in vegetables.