EFFECT OF LIGHT INTENSITY,TEMPERATURE,TOTAL NITROGEN CONCENTRATION AND THEIR INTERACTION ON HYDRILLA VERTICILLATA

With the strengthening of freshwater eutrophication,the original aquatic vegetation gradually reduced and even disappeared,resulting in the well-functional grass type water degraded to algae-based water.Submerged plant is a key factor for the construction of stable and well-functioning freshwater ecosystems.Therefore,restoration and recon-struction of submerged plants is very important for prevention and control of eutrophication.The growth and develop-ment,decline and extinction of submerged plants are closely related with environmental factors due to their aquatic characteristics.In this study,we aim to explore the effects of light intensity,temperature,total nitrogen concentration and their interactions on the growth and development of submerged plants.Our study can shed new light on the mecha-nism of decline of submerged plants in the eutrophic water,and supply a theoretical basis for species selection in the process of the restoration and reconstruction of eutrophic water. Hydrilla verticillata is a common submerged plant species in fresh water of the middle-lower reaches of the Yang-tze River in China.In order to find out the main environmental factors,search decline and fall mechanism of submerged plants in eutrophic water body,and choose the pioneer plant for restoration,we used orthogonal test to investigate the effects of light intensity,temperature,total nitrogen concentration and their interaction on H.verticillata by a serial of laboratorial experiments. The experimental results showed that(1) light intensity and temperature,as well as their interaction significantly affect the growth of H.verticillata,H.verticillata grew well under the conditions of the light intensity in 5320 lx,water temperature at 30癈,and total nitrogen concentration in 8 mg/L.In addition,H.verticillata could grow normally when the light intensity were 12000 lx,and all of growth parameters were the largest when total nitrogen concentration was 8mg/L.However,2mg/L total nitrogen concentration as well as 10癈;the growth of H.verticillata was inhibited.(2) The concentration of photosynthetic pigment was the highest under the conditions of the light intensity in 5320 lx,water temperature at 30癈 than other conditions;however,the effect of total nitrogen concentration on the synthesis of photosynthetic pigment of H.verticillata was little.(3)The physiological activity of H.verticillata was inhibited under the conditions of the light intensity less than 1025 lx,or temperature lower than 10癈,or total nitrogen concentration in 2 mg/L.(4) The results of analysis of variance indicated that,in the process of the growth of H.verticillata,the light intensity and temperature were main factors.Light intensity,temperature,total nitrogen concentration,as well as all the interaction of light intensity and temperature all had significant impact on the synthesis of photosynthetic pigment of H.verticillata. Conclusion: H.verticillata can grow well under the conditions of 5320-12000 lx light intensity,20癈-30癈,and 4-8 mg/L total nitrogen concentration.So H.verticillata can be a pioneer plant for eutrophication ecological manage-ment in spring and summer.