Rice-fish coculture without phosphorus addition improves phosphorus availability in paddy soil by regulating phosphorus fraction partitioning and alkaline phosphomonoesterase-encoding bacterial community

Rice-fish coculture (RFC) has aroused extensive concern for its contribution to food security and resource conservation, but whether it can improve soil phosphorus (P) availability and affect microbe-mediated P turnover remains elusive. Herein, we conducted a microcosm experiment to assess the impacts of RFC combined with (50 mg P kg^-1 as KH₂PO₄) and without inorganic P addition on P fractions, P availability, and phoD-harboring bacterial community composition. The results revealed that RFC without P addition significantly improved P availability and phosphatase activity in paddy soil, while soil available P (AP), pH, and microbial biomass P (MBP) contributed to regulating P fractions. Moreover, the phoD-harboring bacterial abundance was linked to phosphatase activity, AP, total carbon (TC), and total P (TP) contents, and the ratios of TC to total nitrogen (TN) and TN to TP. We also found that the keystone taxa of phoD-harboring bacteria contributed to phosphatase production as well as organic P mineralization, thereby improving P availability. Our findings suggest that RFC without P addition is beneficial for promoting the expression of phoD-harboring bacterial functions to improve the capacity of P mineralization. Overall, our study provides insights into the responses of phoD-harboring bacterial functions for P turnover to RFC combined with and without P addition, showing the potential utilization of P resources in agricultural soil and the contribution of phosphatase activity to P acquisition in agriculture ecosystem.