Microbial drivers controlling arsenic mobilization in paddy soils and arsenic accumulation in rice grains

Arsenic (As) accumulation in rice poses a substantial global threat to food security and public health, especially in rice-consuming regions. While individual geochemical and microbial processes contributing to As release in paddy soils have been studied, a comprehensive understanding of the dominant drivers and their interactions remains limited. In this study, 14 representative paddy soils from paired soil-rice sampling sites in the Xiangjiang River Basin were subjected to controlled anaerobic incubation to examine geochemical changes and microbial dynamics driving As mobilization. Results showed that As mobilization is primarily driven by the reductive dissolution of Fe(Ⅲ) minerals, as evidenced by strong positive correlations between dissolved Fe and As levels. 16S rRNA gene sequencing and multivariate analyses identified Geobacteraceae and Clostridium sensu stricto 10 as core taxa driving Fe(Ⅲ) reduction and As release. By integrating analyses of paired soil-rice samples, we further revealed that dissolved As concentrations in the soil solution under anaerobic conditions as a reliable predictor of rice grain As accumulation (coefficient = 0.78, P < 0.001). These findings reveal key microbial taxa in mediating Fe and As mobilization in flooded paddy soils, offering microbial indicators for risk prediction and management strategies to mitigate grain As accumulation.