Iron-modified biochar (FeOS) is known to be effective at immobilization of arsenic (As) in soils. A pot experiment was conducted to investigate the effects of FeOS on As availability and ttransportation in the soil-rice system at different growth stages of rice with different pollution levels. The results showed that Fe concentration decreased and As concentration increased in paddy soils with the FeOS addition, especially in 120 mg/kg As treatment, the As concentration decreased by 16.46% and 30.56% at the maturity stage with 0.5% and 1% FeOS additions, respectively. Compared with the control, the application of FeOS reduced the arsenic content in rice tissues and increased the biomass, with the root biomass increased by 12.68% and the shoot biomass was increased by 8.94% with the addition of 1% FeOS. This may be related to the promotion of iron plaque formation and the transformation of microbial community structure in FeOS treatments, in accordance with the result of gene abundance and Fe/As contents of iron plaque in the study. This study is expected to provide further support and theoretical basis for the application of FeOS in the remediation of As contaminated paddy soil.
