Dynamics of cadmium and arsenic in the soil-rice system: Insights from different forms manganese fertilizer application

Manganese (Mn) is widely used to control cadmium (Cd) and arsenic (As) uptake by rice, but the effects of different Mn forms and concentrations on Cd/As movement in the soil-rice system are unclear. The study investigated the mechanisms by which three Mn compounds affected the accumulation of Cd/As in rice under different application rates. MnO₂, MnSO₄, and MnCO₃ treatments significantly reduced grains Cd levels by 27.6 %, 30.2 %, and 28.1 %, respectively, while As levels were less consistently affected. Three forms of Mn fertilizers enhanced the conversion of exchangeable to carbonate bound-Cd, which closely related to the increase of soil pH. MnO₂ and MnCO₃ reduced Cd translocation by increasing Cd/As adsorption on iron plaques, and MnSO₄ and MnCO₃ decreased Cd translocation by boosting root SOD and Cys levels. Transcriptome analysis revealed that Mn²⁺ upregulated genes involved in the antioxidant defense system, limited Cd transport by enhancing OsABCC1 and OsHMA3 expression, and promoted As translocation by increasing OsLsi2 expression. Overall, different forms of Mn fertilizers effectively reduced Cd toxicity by fixing Cd in soil carbonate and iron plaques, and restricting Cd transport. Although Mn fertilizers reduced As availability in soil and affected As absorption in rice, they have certain limitations and need to be further explored. These findings reveal the mechanism by which different forms of Mn regulate the fixation and migration behavior of Cd and As, providing new ideas and theoretical basis for reducing the environmental risk of Cd and As.