Evidence for the role of microbes in the silicon-regulated arsenic concentrations of rice roots in the soil environment

Soil arsenic (As) pollution poses a threat to human health, and the role of silicon (Si) in decreasing the xylem loading of arsenite in rice has been demonstrated. However, whether microorganisms are involved in Si-mediated in planta and ex planta As translocation and absorption remains unclear. We combined hydroponic and potted stages to obtain Si previously accumulated in rice, and exogenous Si was added to native and sterilised soils to investigate As uptake and the microbial traits of the bulk soil, rhizosphere, and root endosphere. The addition of Si to rice and soil reduced the root As levels in native soils, but not in sterilised soils. The reassembled microbial communities in sterilised soils exhibited no effect of Si on reducing root As absorption, whereas this regulation was observed in native soils. The ex planta regulation of As absorption by Si was processed by signalling molecules or interactions among microorganisms, and Mycobacterium, Streptomyces, Anaeromyxobacter, and Geotalea were closely linked to this regulation, either independently or jointly. Furthermore, the Si previously accumulated in shoots decreased root-to-shoot As translocation, and in planta regulation was stable and not easily affected by reassembled microbial communities. This study provides evidence that microorganisms play a role in Si-mediated root As absorption in the soil environment.