A pot experiment was conducted to investigate the effects of root oxidation on arsenic(As) dynamics in the rhizosphere and As sequestration on rice roots. There were significant differences(P < 0.05) in pH values between rhizosphere and non-rhizosphere soils, with pH 5.68–6.16 in the rhizosphere and 6.30–6.37 in non-rhizosphere soils as well as differences in redox potentials(P < 0.05). Percentage arsenite was lower(4%–16%) in rhizosphere soil solutions from rice genotypes with higher radial oxygen loss(ROL) compared with genotypes with lower ROL(P < 0.05). Arsenic concentrations in iron plaque and rice straw were significantly negatively correlated(R =-0.60, P < 0.05). Genotypes with higher ROL(TD71 and Yinjingruanzhan) had significantly(P < 0.001) lower total As in rice grains(1.35 and 0.96 mg/kg, respectively) compared with genotypes with lower ROL(IAPAR9, 1.68 mg/kg; Nanyangzhan 2.24 mg/kg) in the As treatment, as well as lower inorganic As(P < 0.05). The present study showed that genotypes with higher ROL could oxidize more arsenite in rhizosphere soils, and induce more Fe plaque formation, which subsequently sequestered more As. This reduced As uptake in aboveground plant tissues and also reduced inorganic As accumulation in rice grains. The study has contributed to further understanding the mechanisms whereby ROL influences As uptake and accumulation in rice.
The effects of root oxidization ability and P fertilization on As mobility in soils, and subsequently As uptake, translocation and speciation in rice plants were investigated. Results show that root oxidation significantly influences As mobility in rhizoshphere.Genotype TD71 with higher radial oxygen loss(ROL) induces more Fe plaque formation and sequesters more As and P in iron plaque and rhizoshphere soil, leading to the reduction of As accumulation in rice plants. Additionally, P addition mobilizes As in soil solution, and increases As accumulation in rice plants. Arsenic speciation results show that the majority of As species in husks detected is inorganic As, accounting for 82%-93% of the total As, while in grains the majority of As is inorganic As and dimethyl arsenic(DMA), with DMA accounting for 33%-64% of the total As. The fraction of inorganic As decreases while fraction of DMA increases, with increasing As and P concentrations. The study further elucidates the mechanisms involved in effects of ROL on As tolerance and accumulation in rice.
