LAUSR

In this study, we investigated the mechanism of decrease in arsenic (As) bioavailability after addition of biochar (BC) supplemented with iron (Fe)- manganese (Mn)- cerium (Ce) oxide (FMCBC) to As-contaminated paddy soil. We explored the effects of these composites on the oxidation, reduction, microbial community, and soil enzyme activity of As-contaminated paddy soil. Results showed that FMCBCs improve soil pH, significantly improve the redox capacity of soil, and reduce bioavailable forms of As. FMCBCs can convert As from a specifically or non-specifically bound form into amorphous hydrous oxide bound- and crystalline hydrous oxide bound form. The application of FMCBCs increased soil enzyme activity (urease, catalase, alkaline phosphatase, and peroxidase), and greatly influenced the relative abundance of certain microorganisms (Proteobacteria, Acidobacteria, and Gemmatimonadetes), which improved soil enzyme heavy metal tolerance and prevented their denaturation. Thus, FMCBCs can not only change the form and distribution of As in soil but also create an environment suitable for microbial growth, consequently affecting the geochemical cycling of As in soil.