Calcium supplementation alleviates cadmium toxicity in contaminated soil and rice (Oryza sativa) seedlings

ABSTRACT: Calcium (Ca) reduces cadmium (Cd) toxicity in crops by limiting its mobility in soil. However, the effect of different Ca-compounds on remediating Cd-contaminated soil is still unclear. Herein, we studied the Cd uptake and subcellular distribution in rice seedlings to screen a low-Cd accumulating rice variety via hydroponic experiments. Subsequently, pot experiments were performed to examine the effect of Ca on the soil pH, available soil Cd, and Cd uptake and transport in the rice by adding calcium silicate (CaSiO3), calcium carbonate (CaCO3), calcium polysulfide (CaS•X), and calcium acetate (Ca(COOCH3)2). The results from hydroponic experiments show that the rice variety Taixiangyou (TXY) 5318 has the lowest Cd content, and the Cd is mainly accumulated in the cell wall and the soluble components within the subcellular fraction. The results from pot experiments indicate that the soil pH can be effectively increased and the available Cd content in soil can be decreased, especially via CaSiO3. Meanwhile, Cd uptake and transport in rice plants can be significantly reduced through CaSiO3 treatment. In addition, the CaSiO3 has a significant negative correlation with the Cd content in the roots, stems, and leaves of the rice, suggesting that CaSiO3 proved to be the most effective remediator for Cd-contaminated soils among these four Ca-compounds, making it suitable for safer agricultural production.