Growth tolerance, concentration, and uptake of heavy metals as ameliorated by silicon application in vegetables

Abstract

Lead (Pb) and cadmium (Cd) are among the heavy metals with phytotoxic and toxic effects on vegetables resulting in a significant decrease in crop yields. On the contrary, silicon (Si) has beneficial effects in enhancing plants’ tolerance to biotic and abiotic stresses such as that imposed by heavy metals. This study evaluated the effects of Pb and Cd on the growth, biomass, and ameliorative mechanism of Si on concentration and uptake by leafy vegetables: spinach, kale, and amaranth. The greenhouse experiment treatments were Pb, PbþSi, Cd, CdþSi, Si, and control. These were arranged as a split-plot in a complete randomized design (CRD): main plots constituted vegetable species and treatments as subplots. The field experiment was carried in the Kenyatta University Research Farm, and treatments included Si application and control, arranged in a randomized complete block design (RCBD). Cadmium application reduced root biomass by 53–70% while Pb reduced it by 54–61% when compared with control. Silicon fertilization enhanced biomass tolerance by three-folds’ and significantly (p<0.001) reduced concentration and uptake of Pb and Cd. Results indicated a strong negative correlation between Cd concentrations and growth parameters (r¼0.8). The study recommends Si application to enhance leafy vegetables’ tolerance to Pb and Cd. NOVELTY STATEMENT Heavy metals’ effects on different cereal crops have been studied extensively. However, such studies on vegetables are rare. The current study assessed the role of silicon in alleviating effects of heavy metals on growth and biomass in three leafy vegetables: spinach, kale, and amaranths grown in soils contaminated with lead and cadmium. The study presents a new approach to enhanced safe vegetable production, responsive to increasing urbanization, industrialization, pollution, and human population.