Lead accumulation and biochemical responses in Rhus chinensis Mill to the addition of organic acids in lead contaminated soils

Abstract

Adding organic acid is an effective approach to assist phytoremediation. The effects of organic acids on phytoremediation efficiency are unknown in Rhus chinensis. This study aimed to evaluate the effect of citric acid (CA) and oxalic acid (OA) on the lead phytoremediation potential of R. chinensis with significantly inhibited growth in Pb-contaminated soil. The experimental pot culture study evaluated the long-term physiological response and metal accumulation patterns of R. chinensis grown in varying Pb-treated soil, and examined the effects of 0.5 and 1.0 mmol L⁻¹ CA and OA on the growth, oxidative stress, antioxidant system, and Pb subcellular distribution of R. chinensis grown in pots with 1000 mg kg⁻¹ Pb. Compared with the control, the biomass, leaf area, root morphological parameters, and chlorophyll concentration of R. chinensis decreased, whereas the carotenoid, malondialdehyde, H₂O₂, and O₂˙⁻ concentrations, and superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activity increased under Pb stress. A copious amount of Pb was taken up and mainly stored in the cell walls of the roots. The application of CA and OA increased plant growth. The highest shoots and roots biomass increase recorded was 44.4 and 61.2% in 1.0 mmol L⁻¹ OA and 0.5 mmol L⁻¹ CA treatment, respectively. The presence of CA and OA increased SOD, POD, and CAT activities and decreased the H₂O₂, O₂˙⁻ and malondialdehyde content. A concentration of 0.5 mmol L⁻¹ CA significantly increased the Pb concentration in the organs. The other organic acid treatments changed root Pb concentrations slightly while increasing shoot Pb concentrations. The translocation factor values from organic acid treatments were increased by 38.8–134.1%. Our results confirmed that organic acid could alleviate the toxicity of stunted R. chinensis and improve phytoremediation efficiency.