Quantitative impact of manganese fertilizer across different growth stages on simultaneous reduction of soil arsenic and cadmium accumulation in rice grains

Application of manganese (Mn) fertilizer is a promising strategy to reduce the accumulation of cadmium (Cd) and arsenic (As) in rice grains. However, the quantitative impact of Mn in co-contaminated soils on Cd and As accumulation at different growth stages remains unclear. This study employed controlled pot experiments to investigate the effect of Mn at varying dosages on As and Cd mobility in the soil-root-crop system during booting, heading, and maturity stages. The results revealed that Mn regulated heavy metal uptake in rice throughout its entire growth period, leading to significant reduction in grain Cd and As contents by 30–60 % and 20–25 %, respectively. The relative contribution of Mn to reducing grain Cd was 30.5, 33.9, and 35.6 % at the booting, heading, and maturity stages, respectively, while its contributions to reducing grain As were 37.7, 19.0, and 43.2 %. Mn influences grain total arsenic accumulation by promoting rice growth, enriching Mn in Fe-Mn plaques at the root surface, and reducing available As in soil. For Cd, Mn reduces grain Cd content by promoting growth, modulating root iron- manganese plaques, and adjusting gene expression at maturity. These findings offer new insights into the role of Mn in reducing grain Cd and As at different rice growth stages and aid in developing strategies for remediating As and Cd co-contaminated paddy soils and increasing crop yield. • Mn impact on grain Cd and As at different growth stages was investigated. • Contributions of Mn to grain Cd and As reduction were quantified across stages. • Mn regulated Cd and As uptake in rice throughout its growth period. • Grain Cd mitigation under Mn was associated with root plaques and gene regulation. • Mn reduced grain As mainly by influencing plant growth and soil As availability.