Silicon alleviates the toxicity of cadmium and zinc for maize (Zea mays L.) grown on a contaminated soil

Although silicon (Si) is not an essential element, it presents a close relationship with the alleviation of heavy-metal toxicity to plants. This work was carried out to evaluate the effects of Si application to soil on the amelioration of metal stress to maize grown on a contaminated soil amended with Si (0, 50, 100, 150, and 200 mg kg(-1)) as calcium silicate (CaSiO3). Additionally, the cadmium (Cd) and zinc (Zn) bioavailability as well as their distribution into soil fractions was also studied. The results showed that adding Si to a Cd- and Zn-contaminated soil effectively diminished the metal stress and resulted in biomass increase in comparison to metal-contaminated soil not treated with Si. This relied on Cd and Zn immobilization in soil rather than on the increase of soil pH driven by calcium silicate application. Silicon altered the Cd and Zn distribution in soil fractions, decreasing the most bioavailable pools and increasing the allocation of metals into more stable fractions such as organic matter and crystalline iron oxides.