Sulfur fertilization integrated with soil redox conditions reduces Cd accumulation in rice through microbial induced Cd immobilization

Sulfate and water management can be respectively applied to control Cd accumulation in rice, but the interaction mechanisms remain unclear. Three water management coupled with five sulfate application concentrations were employed to investigate rice Cd uptake. Results showed there was a significant interaction between sulfate application and soil redox state, and the highest sulfate treatments reduced rice grain Cd by 63.2, 53.5, and 59.4% under the flooding, flooding-moist alternate (FM), and moist irrigation (M) conditions, respectively. It could be explained by the reduction in rhizosphere soil available Cd and lower transport coefficient from root to aboveground. The Desulfovibrio was demonstrated to participate in CdS precipitation, and its abundance was promoted by sulfate especially under flooding. Additionaly, sulfate application facilitated Cd bounded to FeMn oxides, as rhizosphere soil pH raising under flooding. Under FM and M treatments, sulfate application reduced the abundance of Fe-reducing bacteria Geobacter, and correspondingly reduced Fe and Cd availability in rhizosphere soil. Summarily, Cd transfer from soil to rice can be reduced by applying sulfate fertilizer; which is favored by higher soil moisture because of the higher abundance of Desulfovibrio and lower abundance of Geobacter.