Effect of malic acid and citric acid addition on Cd transformations in soil and Cd uptake in amaranth

The low-molecular-weight organic acids (LMWOAs) secreted by plant roots can modify the mobility of Cd through formation of soluble complexes in the soil rhizosphere. Studies are needed to determine Cd transformations and bioaccumulations as influenced by organic acid addition. The present work highlights Cd-LMWOAs interactions with special reference to their plant availability. Pot experiment and laboratory culture were carried out to investigate the effect of malic acid and citric acid addition on transformations of Cd forms in Latosolic red soils and yellow brown soils, as well as Cd accumulation in amaranth (c.v. Tianxingmi, a high Cd accumulator). Compared with Cd 25 mg/kg treatment, Cd 25mg/kg + malic acid, and Cd 25 mg/kg + citric acid treatment had no effect on amaranth biomass, but significantly increased Cd accumulation in both amaranth root and shoot. Further, malic acid and citric acid addition could lower concentration of specific adsorbed Cd, but increase exchangeable Cd, carbonate bound Cd and organic bound Cd significantly. Above results demonstrated that malic acid and citric acid addition could significantly modify Cd forms to enhance Cd accumulation in amaranth.