LAUSR

Abstract In the current study, the integrated influence of four concentration levels of pollutants (COD, TN, NH 4 + -N and TP) in contaminated water on phytoremediation efficiency by aquatic macrophytes community (emergent, floating-leaved and submerged species) and physiological responses in submerged macrophyte were investigated in microcosms. The removal efficiency of COD elevated as the increase of pollutants concentration and reached a maximum value (92.4 %). Moreover, the purification efficiencies of TN, NH 4 + -N and TP elevated within a certain pollutant concentration range, however inhibited in high concentration levels. Furthermore, Chlorophyll content, malondialdehyde (MDA) content, Catalase (CAT), superoxide dismutase (SOD) and peroxidase (POD) activities in submerged macrophyte were explored as physiological characteristics to estimate correlation among them and pollutants concentrations. Significant positive correlations were found except for chlorophyll. Oxidative stress was proved by the consistently higher MDA content as increasing of pollutant concentrations. In addition, antioxidant enzyme responses were induced to remove reactive oxygen radicals which damage plant structure, and maintain plant health. Nonetheless, the adaptive physiological regulations were inhibited in high pollutant concentration levels, and unhealthy symptoms of plants were also spotted. Considering both the physiological response and pollutant removal efficiency, the range level of COD, TN, NH 4 + -N and TP that suitable for phytoremediation was within 75 mg L−1 ,15 mg L−1, 13 mg L−1 and 3.5 mg L−1, respectively. And the related maximum removal rates were 90.3 %, 76.0 %, 95.9 % and 77.4 %. These findings suggested that pollutant concentrations significantly affect phytoremediation efficiency, and excessive concentrations of organics and nutrients may be partly responsible for macrophytes recession and phytoremediation efficiency reduction by inhibition of adaptive physiological regulations.