Photosynthetic response, antioxidase activity, and cadmium uptake and translocation in Monochoria korsakowii with cadmium exposure

To identify the tolerance mechanisms of wetland plants exposed to heavy metal, a hydroponic experiment was used to investigate variations in photosynthetically physiological parameters and antioxidant enzyme activities in leaves of Monochoria korsakowii exposed to 0.05, 0.15, 0.30, and 0.45 mM Cd for 7 d. The Cd concentrations in the plant roots, stems, and leaves were also investigated. Cd exposure significantly decreased the total chlorophyll content, net photosynthetic rate, intercellular carbon dioxide concentration, and stomatal conductance, while stomatal limitation value had the opposite trend (P < 0.05). During Cd stress, ascorbate peroxidase activity significantly increased (P < 0.05). The translocation factor for Cd was significantly lower than that of the control, and both were less than 1 (P < 0.05). Cd stress damaged the photosynthetic apparatus in the leaves. During Cd stress, M. korsakowii alleviated oxidative stress by increasing the activities of antioxidant enzymes, such as APX. Under 0.45 mM Cd stress, increased heat dissipation was responsible for alleviating the photooxidative damage to photosynthetic organs in the leaves. Meanwhile, the majority of Cd was immobilized in the roots, thus alleviating excessive Cd phytotoxicity in the aboveground parts. Generally, M. korsakowii has potential application in the phytoremediation of low-cadmium-polluted water.