Bacillus velezensis combined with phosphogypsum promotes the growth of Cynodon dactylon L. by influencing rhizosphere soil nutrients, Pb bioavailability and microbial community composition in lead–contaminated soil

Phosphate–solubilizing bacteria play an essential role in enhancing soil fertility by solubilizing solution insoluble inorganic phosphate and organophosphorus. However, the role of phosphate–solubilizing bacteria combined with phosphogypsum (PG) in driving lead (Pb) bioavailability and soil nutrients remains poorly understood. In this study, the inoculation of Bacillus velezensis combined with PG in the rhizosphere soil of Cynodon dactylon L. significantly increased soil available phosphorus (AP) and ammonium nitrogen (NH 4 + –N) contents and acid phosphatase (ACP) and urease activities. Moreover, the absorption of nitrogen and phosphorus by C. dactylon L. increased, increasing its biomass. Inoculation with B. velezensis alone or in combination with 10 and 30 g/kg of PG significantly increased soil residual Pb, strong organic–bound Pb, iron–manganese oxide–bound Pb and carbonate–bound Pb, thereby reducing Pb bioavailability. Inoculation with B. velezensis combined with 10 and 30 g/kg of PG considerably reduced soil Pb bioaccumulation in roots and enhanced Pb translocation from root to leaves in C. dactylon L. This combination was more conducive to promoting soil AP, biomass and Pb bioaccumulation in the leaves of C. dactylon L. compared to inoculation with B. velezensis alone. Soil Pb bioavailability and urease induced by the combination of B. velezensis and PG play a positive role in enhancing the relative abundances of the predominant soil Sphingomonas and Massilia genera, increasing microbial resistance to soil Pb. Therefore, we concluded that the utilization of PG strengthens the role of phosphate–solubilizing bacteria in changing rhizosphere soil nutrients, Pb bioavailability and microbial community composition for eco–friendly soil Pb remediation. • The combined application of phosphate-solubilizing bacteria and phosphogypsum promotes the growth and the absorption of soil nutrients of Cynodon dactylon L. by enhancing the soil available phosphorus (AP), ammonium nitrogen (NH 4 + -N), the activities of acid phosphatase (ACP) and urease. • The action of phosphate-solubilizing bacteria and phosphogypsum is beneficial to reduce the bioavailability of heavy metal Pb in soil, and the Pb bioaccumulation in roots of Cynodon dactylon L. were also reduced. • The inoculation with B. velezensis and PG can promote the translocation of Pb from root to leaves and change the pattern of bioaccumulation soil Pb in tissue parts of Cynodon dactylon L. • The inoculation with B. velezensis and PG changes the abundance of the dominant bacteria Arthrobacter, Sphingomonas and Massilia genera, which related to soil available phosphorus, soil urease and iron-manganese oxide-bound Pb.