Effect of Silicon on Growth, Physiology, and Cadmium Translocation of Tobacco (Nicotiana tabacum L.) in Cadmium-Contaminated Soil

Silicon (Si) offers beneficial effect on plants under cadmium (Cd) stress such as promoting plant growth and increasing resistance to heavy metal toxicity. In this study, a pot experiment was performed to study the role of Si in alleviating Cd toxicity in tobacco (Nicotiana tabacum L.) plants on a yellow soil taken from Guiyang, China. Nine treatments consisting of three concentrations of Cd (0, 1, and 5 mg kg−1) together with three Si levels (0, 1, and 4 g kg−1) were established. Plant growth parameters, Cd concentration, and the malondialdehyde (MDA), chlorophyll, and carotenoid contents were determined 100 d after transplanting of tobacco seedlings. Application of exogenous Si enhanced the growth of tobacco plants under Cd stress. When 5 mg kg−1 Cd was added, Si addition at 1 and 4 g kg−1 increased root, stem, and leaf biomass by 26.1%-43.3%, 33.7%-43.8%, and 50.8%-69.9%, respectively, compared to Si addition at 0 g kg−1. With Si application, the transfer factor of Cd in tobacco from root to shoot under both 1 and 5 mg kg−1 Cd treatments decreased by 21%. The MDA contents in the Si-treated tobacco plants declined by 5.5%-17.1% compared to those in the non-Si-treated plants, indicating a higher Cd tolerance. Silicon application also increased the chlorophyll and carotenoid contents by 33.9%-41% and 25.8%-47.3% compared to the Cd only treatments. Therefore, it could be concluded that Si application can alleviate Cd toxicity to tobacco by decreasing Cd partitioning in the shoots and MDA levels and by increasing chlorophyll and carotenoid contents, thereby contributing to lowering the potential health risks of Cd contamination.