Foliar spraying with silicon and selenium reduces cadmium uptake and mitigates cadmium toxicity in rice

Foliar spraying with silicon (Si) and selenium (Se) can regulate the accumulation of cadmium (Cd) in rice (Oryza sativa L.), but the effects on different cultivars and the main determining factors remain unknown. Field experiments were conducted to investigate the ability of foliar spraying with Si, Se, and mixture of Si and Se to decrease Cd accumulation and translocation in rice cultivars WYHZ, NJ5055, and ZF1Y. All three spray treatments significantly decreased the Cd concentration in WYHZ brown rice, but had no such effect in NJ5055 or ZF1Y, relative to controls. WYHZ had a higher ability to translocate Cd than the other two cultivars. Foliar spraying changed this pattern by decreasing Cd translocation from roots to stems and from stems to brown rice, and increasing Cd translocation from stems to leaves. Foliar spraying also increased the photosynthetic rate, stomatal conductance, and transpiration efficiency in WYHZ. Structural equation modelling revealed the negative effects of photosynthetic rate, transpiration efficiency, and leaf Cd concentration, and the positive effects of stem and root Cd concentration on brown rice Cd concentration. Structural equation modelling further highlighted the significant role of stem Cd concentration in determining brown rice Cd concentration, which had the highest standardized total effects (direct plus indirect effects). These findings demonstrate that foliar spraying with Si and Se is effective in reducing Cd accumulation in rice cultivars with high Cd translocation ability, mainly by reducing stem Cd concentrations and ameliorating plant photosynthetic processes.