Long-term straw return promotes soil phosphorus cycling by enhancing soil microbial functional genes responsible for phosphorus mobilization in the rice rhizosphere

Straw incorporation is a widely used agricultural practice that remarkably influences the availability of phosphorus (P) in soil, owing to the tight correlation between carbon (C) and P cycles. However, the microbial mechanisms that drive P mobilization after straw return are unclear. We used metagenomic sequencing to explore how P-cycling microorganisms respond to varying levels of straw return in long-term field experiments. We also analyzed their associations with P fractions and turnover parameters to elucidate the microbial mechanisms driving P mobilization in paddy soil. The results showed that straw return increased labile P fractions, including H2O-P and NaHCO3-P, as well as Qmax, n, and PhoS activity; at full straw return, these values ranged from 16.4% to 27.1%, 81.2% to 97.6%, 3.9% to 36.8%, 9.3% to 32.0%, and 17.2% to 19.8%, respectively, compared with the values observed without straw return from the tillering stage to maturity stage. Structuralequation modeling indicated that straw return increased the relative abundance of genes involved in the solubilization and mineralization of P, particularly acid phosphatase and quinone protein glucose dehydrogenase (PQQGDH). In addition, PQQGDH indirectly enhanced the H2O-P content and its conversion to NaHCO3-P by elevating Qmax. We identified Rhizobiales as crucial microorganisms for P mobilization. These results enhance our understanding of the microbial mechanisms by which straw return improves P availability in paddy fields and provide theoretical support for the development of P-mobilizing microbial technologies.