Physiological responses of Vallisneria spiraslis L. induced by different hydraulic conditions when exposed to copper and nitrogen
A two-flume experiment with submerged plant Vallisneria spiraslis L. was conducted to investigate the effects of different hydraulic conditions on physiological responses when exposed to water polluted with copper (Cu) and nitrogen (N). Plants were divided into two groups and grown for 120 h in hydrodynamic and hydrostatic flumes, respectively, using the same nutrient solution with fixed concentrations of 0.64 mg l–1 CuSO4 and 4.0 mg l–1 total N. Combined pollution with Cu and N resulted in rapid increase in chlorophyll in the first hour and relative growth rate of plants in hydrodynamic water increased from 0 to 0.073 in the first 8 h. Meanwhile, peroxidase (POD) activity in shoots sharply increased to alleviate supraoptimal oxidative stress. And proteolytic degradation in shoots was observed to be catalyzed as protein contents in shoots decreased. Persistent decline in total chlorophyll and relative growth rate was noticed in longer duration. In roots, POD activity increased only at 8 h and decreased after 24 h. Malonaldehyde (MDA) content in roots also increased only at 8 h and MDA content was lower (P < 0.01), while protein content was higher (P < 0.01) after prolonged exposure than those at 0 h. Comparison of different hydraulic groups indicated that hydrodynamic condition induced higher POD activity in shoots in the first hour to alleviate the toxicity resulted by Cu and N. Thus, relative growth rate of plants was significantly higher than that in hydrostatic group (P < 0.05). While roots in hydrodynamic condition were less influenced by water flow, its protein contents in hydrodynamic group were significantly higher (P < 0.01) than those in hydrostatic group at all durations. These results suggested that hydrodynamic condition alleviated combined toxicity of Cu and N in V. spiraslis L shoots and enhanced the accumulation of protein in roots.
Key words: Physiological response, hydrodynamic, copper, nitrogen, Vallisneria spiraslis L.