Responses of Hydrilla verticillata (L.f.) Royle and Vallisneria natans (Lour.) Hara to glyphosate exposure

Glyphosate is a broad-spectrum herbicide that is frequently detected in water bodies and is harmful to aquatic systems. We conducted an experiment to explore the ecological sensitivity of Hydrilla verticillata (L.f.) Royle and Vallisneria natans (Lour.) Hara to glyphosate. Our research focused on the physiological responses of H. verticillata and V. natans after exposure to various concentrations of glyphosate (0, 1, 10, 20, 30, 40, 50 and 80 mg/L) in hydroponic culture after one day (1D) and seven days (7D). The results show that after 1D, the soluble protein content of H. verticillata was significantly stimulated under low herbicide concentrations. Other indices for H. verticillata and V. natans had no remarkable changes at 1D. After 7D of treatment, the soluble protein content of H. verticillata showed no significant differences, while the malondialdehyde (MDA), pigment contents and catalase (CAT) activity significantly increased at low glyphosate concentrations. Guaiacol peroxidase (POD) activity in H. verticillata significantly increased with increasing herbicide concentrations. The chlorophyll a/b ratio of H. verticillata sharply decreased above 10 mg/L. For V. natans, soluble protein, chlorophyll a, and carotenoid content; and CAT activity declined significantly after glyphosate application, while other indicators showed no significant changes. Our results indicate that glyphosate concentrations from 0 to 80 mg/L can induce oxidative stress in H. verticillate and may impede metabolism processes for protein and pigments without causing oxidative stress in V. natans. Taken together, our results suggest that the sensitivity of H. verticillata to glyphosate exposure is higher than that of V. natans.