Although selenium (Se) application is known to reduce arsenic (As) accumulation in rice, the mechanisms by which Se alleviates As toxicity-particularly those involving the regulation of rhizosphere reactive oxygen species and influence of Fe-(hydro)oxide-As dynamics at the root-soil interface-remain unclear. Therefore, to clarify the mechanisms underlying the inhibition of Se-mediated As uptake, this study investigated how different Se dosages (0, 50, 200, and 400 μg Na2SeO3 kg⁻1 soil) affect antioxidant enzyme activities and phytochelatin (PC) biosynthesis in rice grown in As-contaminated soil and promote As transformation in the rhizosphere. The results showed that the Se-200 and Se-400 treatments significantly reduced As levels in brown rice by 52.4 % and 35.7 %, respectively, compared with the control. The Se-200 treatment significantly enhanced root superoxide dismutase and catalase activity and PC content (P 2O2 concentrations in the rhizosphere (P < 0.05). In addition, Se promoted the formation of Fe-(hydro)oxides and oxidation of As(III) to As(V), with the As(III)/As(total) ratio increasing by 18.9 %, which decreased As mobility in the rhizosphere. Microbial analysis further revealed a 91.4 % increase in the abundance of the aioA gene (encoding As(III) oxidase) under the Se-200 treatment, with Bacillus and Pseudomonas identified as the dominant genera. Collectively, the Se-200 treatment mitigated As-induced oxidative stress in rice roots, enhanced As(V) immobilisation via Fe-(hydro)oxides, and altered the rhizosphere microbial community to reduce As bioavailability. These findings provide new insights into Se-based strategies for managing As-contaminated paddy soils.
Yang et al. (Sun,) studied this question.