Comparison of the Effects of Exogenous Selenium and Silicon on Alleviating Cadmium Stress in Artemisia argyi

Selenium (Se) and silicon (Si) have been demonstrated to mitigate the adverse effects of cadmium (Cd) stress on the growth of various higher plants. However, the distinct mechanisms by which Se and Si, when applied to soil, alleviate the toxicity of Artemisia argyi under Cd stress remain unclear. This study employed A. argyi as the experimental material and simulated a Cd stress environment in soil pot experiments by adding CdCl2·2.5H2O at concentrations of 4 mg kg−1 and 10 mg kg−1. Exogenous Se in the form of Na2SeO3 (2 mg kg−1) or Si in the form of Na2SiO3 (20 mg kg−1) was applied simultaneously. After 90 days of combined exposure, the study investigated the differential mechanisms by which Se and Si application influenced Cd uptake by roots, its translocation within aboveground and underground tissues, and the antioxidant system of A. argyi under two levels of Cd stress. The results indicate that under Cd stress conditions, the application of Se significantly promotes the growth of A. argyi. Under both Cd concentration treatments, the application of Se or Si alone markedly reduces the Cd content in the aboveground parts of A. argyi. This reduction may be attributed to alterations in the subcellular distribution of Cd, decreased Cd content in organelles, and increased Cd sequestration in cell walls and soluble components. Furthermore, the application of Se or Si in soil can enhance the content of osmoregulatory substances, chlorophyll, and plant chelating agents in A. argyi leaves while reducing the levels of malondialdehyde (MDA) and reactive oxygen species (ROS), particularly at high Cd concentrations. The findings suggest that the alleviation of Cd toxicity by exogenous Se is primarily due to its role in inhibiting Cd uptake and translocation to shoots, as well as strengthening Cd compartmentalization in root cell walls and enhancing the antioxidant defense system. In contrast, exogenous Si primarily mitigates Cd toxicity by restricting Cd translocation from underground to aboveground plant tissues.