Water managements limit heavy metal accumulation in rice: Dual effects of iron-plaque formation and microbial communities

Understanding the mechanisms on howwater management canminimize the concentrations of heavymetals in rice grains is important. Twowatermanagementswere concerned in our studies, including continuously flooding and alternatewetting and drying (AWD). Compared to AWD, a continuously flooded culture reduces the concentration of cadmiumand other metals in the rice grains by reducing the root-to-shoot translocation and the availability ofmetals in rhizosphere. In a flooded environment, the rice rhizospherewas characterized by an increased soil pH, reduced fluorescein diacetate (FDA) activity, and lower metal bioavailability. In addition, flooding significantly decreased the iron plaque on the root surface and reduced the affinity for metals in rhizosphere. Water managements significantly changed soil microbial diversity, especially the proportion of anaerobic bacteria, including the iron-reducing bacteria Latescibacteria, Desulfuromonadales, and Geobacteraceae. Interestingly, these bacteria exhibited a significant correlation with cadmium that was adsorbed on the root. This study revealed that continuously flooded culture is a valuable strategy for minimizing heavy metal accumulation in rice grains. By increasing the abundance of unique bacterial community, iron plaque formation and the affinity of metals in rhizospherewere reduced, and the uptake and accumulation of heavymetals in rice plantswas finallymitigated. (C) 2019 Published by Elsevier B.V.