Effects of selenium with different selenium-cadmium molar ratios on cadmium transport and translocation in cadmium-contaminated soil of rice

To clarify the differences in the effects of selenium on growth and uptake of cadmium with different selenium-cadmium molar ratios in cadmium-contaminated soil of paddy rice, a pot experiment was set up with 1 - 6 selenium-cadmium molar ratio treatments named T1 ~ T6. The variations in the soil pH and available cadmium content, the differences in protective enzyme activities, chlorophyll content, biomass, selenium and cadmium content of different parts of the rice plant were analyzed. As the molar ratio of selenium to cadmium increased, the soil pH showed an increasing and then decreasing trend, reaching a maximum value (5.15) with the T2 treatment, and the available cadmium in the soil showed a wave-like change, reaching a minimum point (0.58 mg·kg⁻¹) with the T2 and T4 treatments. Compared to the T1 treatment, T2 - T6 treatments showed a decrease in MDA content ranging from 4.31% to 16.5%, an increase in GPx enzyme activity ranging from 5.04% to 22.6%, an increase in POD enzyme activity ranging from 4.38% to 13.5%, an increase in SOD enzyme activity ranging from 1.75% to 14.6% (except for T5), and an increase in CAT enzyme activity ranging from 0.59% to 18.2%. While T2 ~ T6 treatments were not significantly different from T1 in terms of chlorophyll content, brown rice and straw yield. With the increase of selenium-cadmium molar ratio, the selenium content of rice plants increased significantly, but the cadmium content in roots and straw with T2 - T6 treatments were not significantly different from T1. The cadmium content of brown rice increased and then decreased, and the cadmium content of brown rice of T5 and T6 treatments was lower than the national limit standard, which was 0.17 mg·kg⁻¹ and 0.19 mg·kg⁻¹, respectively. Brown rice Cd content was significantly negatively correlated with straw Se and TF_Se-ros but significantly positively correlated with straw Cd and chlorophyll. This study finds that selenium application increases the activity of protective enzymes in rice plants, enhances the resistance to cadmium stress, inhibits the accumulation of cadmium in aboveground straw and its transport to brown rice, and effectively reduces the accumulation of cadmium in brown rice of rice plants.