Exogenously Applied Citric Acid Enhances Antioxidant Defense and Phytoextraction of Cadmium by Willows (Salix Spp.)

The effect of exogenously applied citric acid (CA) on phytoextraction and antioxidant defense was analyzed using willow species (Salix viminalis, S. alba, and S. matsudana) grown in soil contaminated with cadmium (Cd). Citric acid has been used as a chelating agent for the purpose of accelerating the solubility of Cd in soil and enhancing the phytoextraction of selected plants. Willows were exposed to 6 mg/kg of Cd, following the same with citric acid (20 mM/kg soil). Results revealed a positive effect of citric acid in mobilization of accumulated Cd from roots to shoots and leaves. The addition of citric acid alleviated Cd toxicity by helping plants to overcome oxidative stress, through CA’s chelating properties and the increased activity of antioxidant enzymes. Different protection strategies were evident through modification of activities of antioxidant enzymes such as catalase (CAT), ascorbate-peroxidase (APx), and guaiacol peroxidase (GPx) in young versus mature leaves in plants exposed to Cd. Furthermore, results revealed that addition of citric acid may be beneficial in the reduction of the negative effect of Cd stress on photosynthesis. The efficiency of coupling phytoextraction with the chelating agents represents a good strategy for decreasing damages caused by cadmium and has good potential in decontamination of a polluted environment.