Synergistic effects of water management and phosphate fertilization on As safety in rice: Multi-dimensional analysis of rhizospheric pe+pH and microbial communities interactions

Persistent exposure to arsenic (As) through contaminated rice poses severe public health risks. This study combined pot and field experiments to evaluate the effects of water regimes-continuous flooding (F), intermittent irrigation with prolonged dry periods (I), and moistening irrigation (M)-in combination with phosphorus fertilizers: calcium magnesium phosphate (CMP) and ammonium dihydrogen phosphate (ADP). The IADP treatment (I + ADP) achieved the highest soil pe+pH (averaging 8.33), reducing porewater As by 27-81 % and DGT-labile As by 30-70 % by inhibiting Fe(III) reductive dissolution and enhancing As sequestration into Fe (hydr)oxides. Microbial analyses indicated that IADP significantly altered the rhizobacterial communities. Functional predictions using BugBase and FAPROTAX suggested IADP with high pe+pH conditions enhanced stress-tolerant phenotypes and S-cycle bacteria while reducing N-cycle bacteria. Moreover, IADP promoted the growth of As(III)-oxidizing bacteria (e.g., Gemmatimonadaceae). These changes in bacterial communities not only contributed to the immobilization of soil As but also affected plant nutrient uptake. Path analysis confirmed that the suppression of As bioavailability was primarily driven by elevated pe+pH and microbially facilitated As stabilization. Consequently, IADP reduced inorganic As (iAs) in grains to 0.13 mg kg⁻¹ , 12-76 % lower than other treatments. Field validation further demonstrated that IADP consistently decreased iAs in brown rice to 0.10-0.13 mg kg⁻¹ , complying with Chinese food safety standards (GB2762-2022) without compromising yield. This study revealed insights into how redox-microbial interactions reduced As bioavailability and identified IADP as a well-defined, sustainable and practical strategy for safe rice production.