Physiological Changes and Antioxidative Mechanisms of Alternanthera philoxeroides in Phytoremediation of Cadmium

Abstract

This study evaluated the physiological characteristics (e.g., growth parameters, chlorophyll content, metabolites and antioxidative enzymes activity) of Alternanthera philoxeroides (A. philoxeroides), as a hyperaccumulator plant, during the phytoremediation of cadmium (Cd) from water. After cultivating A. philoxeroides in a Cd-containing medium for 30 days, the growth rate was inhibited by up to 33.5% as the exposed Cd concentration increased to 0.80 mmol·L–1. Cd exposure interfered with the photosynthesis of A. philoxeroides and caused oxidative stress as indicated by the rise of malondialdehyde (MDA) and H2O2, which increased by 8 times and 3 times compared to the control group. Moreover, high exposure concentrations of Cd also reduced the activities of multiple antioxidants (e.g., GSH and AsA), indicating the inhibition of Cd on the plant’s ability to mitigate oxidative damage. Finally, the fluorescent patterns of the rhizosphere dissolved organic matter (rDOM) revealed three major components (humic, fulvic substances and protein-like substances) well correlated with the changes in antioxidant activities. Partial least-squares discriminant analysis (PLS-DA) visualized the difference in the activity of the antioxidative enzymes between different groups. The study unravelled deep insights into the potential mechanisms of tolerance and resistance of A. philoxeroides for phytoremediation of Cd pollution.