Physiological responses of Egeria densa to high ammonium concentration and nitrogen deficiency

Abstract High ammonia (i.e. the total of NH 3 and NH 4 + ) concentration or nitrogen deficiency in water can exert stress on growth and health of many aquatic plants. To investigate the physiological impacts of high ammonia-N (NH 4 Cl) concentration and nitrogen deficiency on plant physiology, apical shoots of submerged macrophyte Egeria densa were first treated with five levels of nitrogen: 0, 1, 10, 30, 60 mg L −1 ammonia-N (NH 4 Cl) for 5 d. After having explored the stress range of ammonia-N, its effect on E . densa was further examined at three levels of ammonium (0, 1, 30 mg L −1 ammonia-N) and at six exposure times (0, 1, 2, 3, 5 and 7 d). In testing the concentration-dependent stress, the increase of ammonia-N reduced the amounts of total chlorophyll (chl a and b ), soluble proteins and soluble carbohydrates, but increased the activity levels of malondialdehyde (MDA), superoxide dismutase (SOD), catalase and peroxidase in E . densa . In the N-free medium, total chlorophyll, soluble proteins, soluble carbohydrates and the activities of SOD and peroxidase in E . densa decreased significantly compared with the control (1 mg L −1 ammonia-N). When comparing the ammonia-N impacts over time, the plants showed a declining trend in total chlorophyll, soluble proteins and soluble carbohydrates, but an rising trend in MDA, SOD, peroxidase and catalase in 30 mg L −1 ammonia-N over 7 d. Compared with the control, the N-free medium significantly decreased the amounts of total chlorophyll, soluble proteins, soluble carbohydrates, SOD and peroxidase in E . densa over time. Our study indicates that high ammonium (ammonia-N ⩾ 10 mg L −1 ) affects the growth of E . densa through inducing oxidative stress and inhibiting photosynthesis, and nitrogen deficiency can also induce an abiotic stress condition for the E . densa growth by reducing photosynthetic pigments, soluble proteins, soluble carbohydrates, and the activity of antioxidant enzymes.