Mitigation mechanism of Cd-contaminated soils by different levels of exogenous low-molecular-weight organic acids and Phytolacca americana

Phytolacca americana L. (pokeweed) is a promising plant for phytoremediation of cadmium (Cd)-contaminated soil, with its large biomass and fast growth rate. Pot experiments were conducted to investigate the effects of low-molecular-weight organic acids (LMWOA) at different levels (10, 20, 30, 40 mmol kg(-1)) on the growth, oxidative stress and antioxidant system of pokeweed. Their role in Cd transportation and accumulation and the ameliorating effects of Cd-induced oxidative stress were also studied. The results showed that the tolerance threshold of Cd stress for pokeweed was 50 mg kg(-1) dw. Moreover, Cd transfer can be effectively enhanced from root to shoot by lower concentrations (10 and 20 mmol kg(-1) dw) of organic acids. Cd adsorption of pokeweed was obviously increased (312.5%, 142.9%, 305.9% in leaves and 130.9%, 103.6%, 119.9% in roots, respectively) when 10 mmol kg(-1) dw citric acid (CA), 20 mmol kg(-1) dw malic acid (MA) and 10 mmol kg(-1) dw oxalic acid (OA) were added to the Cd-contaminated soil. The cadmium transfer coefficient of pokeweed was found to be effectively improved by certain concentrations of LMWOA. In conclusion, this study provides an important reference for further application of the pokeweed to soil remediation.