Joint Effects of Nutrient Salts and Tetracycline Hydrochloride on Physio-Biochemistry of Vallisneria natans

An in-laboratory experiment was carried out to simulate Vallisneria natans growing in wastewaters different in eutrophication degree (moderate, high and super-high) and in tetracycline hydrochloride (TH) contamination degree (0, 0.1, 0.2 and 0.5 mg·L^-1). Leaves of the plants were sampled 30 days after the initiation of the experiment for analysis of activities of peroxidase (POD) and superoxide dismutase (SOD) and contents of malondialdehyde (MDA), soluble proteins and chlorophyll for responses of the plants to changes in the environment. Results show that TH, N and P worked together affecting soluble protein, SOD, Chl-a and Chl-b in the plant significantly. In the super-eutrophication group, addition of 0.5 mg·L^-1 TH affected soluble protein the most significantly, which dropped by 47.4% in content vs that in CK of the group (0 mg·L^-1 TH). In the super-eutrophication group, addition of 0.2 mg·L^-1 TH enhanced SOD activity significantly or by 1.45 times vs that CK. In the group of moderate eutrophication, addition of 0.5 mg·L^-1 TH affected the concentrations of Chl-a and Chl-b the most significantly, which was increased by 75.7% and 64.6%, respectively, vs that in CK of the group.