Chloride application weakens cadmium immobilization by lime in paddy rice soil

Contamination of agricultural products by cadmium (Cd) is a global health problem, causing chronic abnormalities. The consumption of rice, the most-consumed foods, is an important exposure route of Cd to human body. Chloride (Cl^-) is reported to increase Cd uptake by rice; however, the effect on Cd uptake and accumulation by rice in the presence of lime is not clear. Therefore, a pot culture experiment was performed to explore the influence of Cl^- on the absorption and accumulation of Cd in rice plants under lime remediation and its possible mechanisms. The results showed that Cl^- promoted Cd accumulation in rice grains, mainly because of increased Cd bioavailability in the soil and by impeding the formation of iron plaques on rice roots, which reduced chelating and precipitation of Cd. Moreover, increased overexpression of the main transporters of Cd in rice roots, including OsNramp5, OsNramp1, OsIRTs and OsHMA2, favored the upward translocation of Cd from the root to shoot and increased the transfer factors (TFs) from soil to root, root-stem, leaf to grain, and soil to grain. Therefore, the application of Cl-rich materials to Cd-contaminated rice fields should be avoided during liming of the soil for Cd immobilization.