| As the strengthening of freshwater eutrophication, the original aquatic vegetation gradually reduced or even disappeared, leading to the well-functional grass-type water degraded to algae-based water. According to the study, aquatic vegetation is a key factor for the construction of stable, well-functioning freshwater ecosystems. So, reconstruct-tion and restoration of aquatic vegetation is a very important part for the prevention and control of eutrophication. Due to the characteristics of submerged plants, their growth, development, decline and extinction are closely related with environmental factors. In our study, we aim to make a thorough inquiry about the effects of light intensity, temperature, total nitrogen concentration and their interactions on the growth and development of three kinds of common submerged plants. This study can shed new light on the mechanism of decline of aquatic vegetation in the eutrophic water, and supply a theoretical basis for species selection in the process of the reconstruction and restoration of eutrophic water.In this study, we chose Yangtze River Basin common submerged plants Hydrilla verticillata, Potamogeton malaianus, and Vallisneria natans, using orthogonal test to study the effects of light intensity, temperature, total nitrogen concentration and their interaction on these three s submerged plants by a serial of laboratorial experiments. Recorded changes of the growth indices (height, biomass, and branch/tiller numbers), photosynthetic indices (the concentration of chlorophyll a+b, chlorophyll a/b, and total chlorophyll content), and physiological activity indices(root activity, soluble sugar content, and MDA content) in different combinations of three environmental factors, then found out the main environmental factors and the effects of their interactions.Major conclusions from the research are as follows:1. Under the experimental conditions, H. verticillata can grow well under the conditions of 5320-120001x light intensity,20-30℃temperature, and 4-8mg/L total nitrogen concentration. 50% of light intensity (53201x) is the most favorable light factors for H. verticillata to grow, and H. verticillata is more appropriate for growth at higher temperatures, what's more, the changes of total nitrogen concentration have no significant effect on the growth of H. verticillata; 50% of light intensity also is the most beneficial light factors for H. verticillata to conduct its synthesis of photo synthetic pigment, only changes of temperature and total nitrogen concentration have no significant effect on the synthesis of photosynthetic pigment; weak light have significant effect on the physical activity of H. verticillata, under the conditions of 10% light intensity, its root activity and soluble sugar content are very low, and MDA content is high, what's more, its physical activity is inhibited under lower temperature, however, changes of total nitrogen concentration have no significant effect on its physical activity.Analysis results show that light intensity and temperature are main environmental factors in the process of the growth and the synthesis of photosynthetic pigment of H. verticillata, furthermore, the interaction of light intensity and temperature have significant effect on the growth of H. verticillata. So H. verticillata can be a pioneer plant for eutrophication ecological management in warm and hot season.2. Under the experimental conditions, P. malatanu can grow well under the conditions of 5320-120001x light intensity,30℃temperature, and 2-8 mg/L total nitrogen concentration.Light intensity, temperature, and their interaction significantly affect the growth of P. malatanu. Total nitrogen concentration have no sigificant impact on the growth of P. malatanu; Changes of light intensity have significant effect on the synthesis of photosynthetic pigment of P. malatanu, therefore low transparency water is not suitable for the reconstruction and restoration of P. malatanu. The synthesis of photosynthetic pigment of P. malatanu can well conduct under the conditions of 10-30℃and 4-8 mg/L total nitrogen concentration. The physical activity of P. malatanu will be inhibited under lower (10251x) or higher (120001x) light intensity and 10℃, however, changes of total nitrogen concentration have no significant effect on the physical activity of P. malatanu.Analysis results show that light intensity is the main environmental factor in the process of the growth and the synthesis of photosynthetic pigment of P. malatanu, the interaction of these three environmental factors has no significant effect on the growth of P. malatanu, So P. malatanu can be a pioneer plant for eutrophication ecological management in hot season.3. Under the experimental conditions, V. natans can grow well under the conditions of 53201x light intensity,10℃temperature, and 2-4 mg/L total nitrogen concentration.V. natans can grow well under the conditions of 50-100% of light intensity, and it is more suitable for V. natans to grow in cold freshwater. V. natans is more sensitive to changes of total nitrogen concentration than H. verticillata and P. malatanu. Its physical activity will be inhibited under lower (2 mg/L) or higher (8 mg/L) concentration of total nitrogen; 50% of light intensity (53201x) and 10℃are the most favorable conditions for its synthesis of photosynthetic pigment, however, changes of total nitrogen concentration have no significant effect on it; the physical activity of V. natans will be inhibited under lower (10251x) or higher (120001x) light intensity or higher temperature (30℃) or higher total nitrogen concentration (8 mg/L).Analysis results show that light intensity and temperature are main environmental factors in the process of the growth and the synthesis of photosynthetic pigment of V. natans, the interaction of light intensity and temperature have significant effect on its synthesis of photosynthetic pigment and physical activity. According to our experimental results, V. natans can be a pioneer plant for eutrophication ecological management in cold season. |
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