Impacts of exogenous mineral silicon on cadmium migration and transformation in the soil-rice system and on soil health

Exogenous silicon has been shown to enhance plant growth and alleviate heavy metals toxicity, but the regulation mechanism of silicon on cadmium migration and transformation in the soil-rice system is still unclear, which is worth further study. In this study, a pot experiment was carried out to explore the influence of different doses (0, 1 and 5%) of mineral silicon on soil properties, nutrient availability, rice growth, soil enzyme activities, Cd bioavailability, and uptake and accumulation of Cd in high-accumulating (H) and low-accumulating (L) rice cultivars grown in contaminated soils. Results showed that mineral-Si treatment could increase the total biomass and grain yield, with an increased rate of 17.7–27.3% and 14.7–19.1% for H; while 26.2–33.4% and 21.3–30.3% for L. Compared with non-mineral-Si treatment, the soil EX-Cd decreased by 3.9–13.3% (H) and 2.3–10.7% (L). Additionally, the Cd content in rice grain was significantly declined by 29.5–31.3% (H) and 34.9–35.2% (L). Mineral-Si enhanced urease, sucrase, and neutral phosphatase activities in both cultivars, but suppressed catalase activity in H. A selective change in bacterial community structure was observed under mineral-Si treatment, however, the bacterial community remained stable, suggesting that the mineral-Si had no adverse effect on the microbial community. The positive response of soil enzymes activities, rice growth and the overall stabilization of microbial environment for mineral-Si addition to the Cd contaminated soils indicated that mineral-Si could mitigate the risk of Cd and well maintain the soil health, proving it to be eco-friendly and low-cost amendment for soils remediation.