[Detoxification Effect of Selenium Application on Pak Choi in Arsenic-contaminated Soil and Its Mechanism]

Exogenous application of appropriate selenium (Se) can alleviate the stress of metal cations on plants. Arsenic (As) is an anionic metalloid, and the detoxification mechanism of Se on As in soil-plant systems remains unclear. Therefore, pak choi was selected as the experimental material. A pot experiment was conducted to investigate the effects of the co-application of exogenous Se and As on the growth, physiological metabolism, photosynthesis, uptake, and transport of Se and As in pak choi, as well as the transformation of Se and As fractions in the soil, aiming to reveal how exogenous Se alleviates As stress. The results showed that low Se treatment (0.5 mg·kg^-1) promoted pak choi growth under low and medium As treatment (30 mg·kg^-1 and 60 mg·kg^-1), though the differences were not significant (P≥0.05). In contrast, the co-application of high Se (2.5 mg·kg^-1) and high As (100 mg·kg^-1) significantly inhibited the growth of pak choi (P < 0.05). Under low and medium As stress, low Se treatment effectively alleviated the toxicity of As to pak choi. Compared with those in the treatment without Se application, the glutathione peroxidase activity, nitrate reductase activity, and photosynthesis (net photosynthetic rate, stomatal conductance, intercellular CO₂ concentration, transpiration rate, and SPAD value) of pak choi were significantly increased by 0.45%-32.53% (P < 0.05), while the electrolyte leakage, superoxide anion radical content, malondialdehyde content, and proline content of pak choi were significantly decreased by 6.47%-22.84% (P < 0.05). High Se and As co-application showed a synergistic toxic effect. In addition, compared with that in the treatment without Se application, the translocation factor value of As in pak choi under high Se treatment was significantly decreased by 27.95%-56.57% (P < 0.05), reducing the enrichment of As in the edible parts. The application of Se decreased the proportion of soluble As in soil by 0.1%-14.00% and increased the proportion of residual As by 2.28%-10.13% compared with that in the treatment without Se application, thus reducing the availability of As in soil. These findings demonstrate that 0.5 mg·kg^-1 Se mitigates low-medium As stress by enhancing plant physiology and immobilizing As in soil.