| This paper deals with the influences of Hg to the morpha. some physiological and biochemical parameters such as chlorophyll(chl), superoxide dismutase(SOD), catalase(CAT) of a kind of submerged macrophyte Egeria najas; some parameters for the amelioration of water quality and agamogenesis of Egeria najas were also studied. The results as follow:1 Effect of Hg2+ to the physiological and biochemical parameters of Egeria najasAfter 24h of exposure, the color of leaf of Egeria najas became greenish at 10mg/L Hg, the color of leaf of Egeria najas was not affected significantly under 10mg/L Hg. After 48h of exposure, the color of leaf of Egeria najas became greenish badly and the leaf was conglutinated, and the chlorophyll content of leaf declined significantly when the Hg concentration were above 2.00mg/L.By the changes of chlorophyll content, the lethal concentration of Hg to Egeria najas was 0.10-2.00mg/L. The variational rules of the activity of SOD and CAT of Egeria najas is coincident for all durations of exposure, at first the activity of SOD and CAT were increased, subsequently the activity of SOD and CAT were declined. By the changes of the activity of SOD and CAT, the lethal concentration of Hg to Egeria najas was 0.10-1.00mg/L.But the changes of the activity of CAT was more sensitive than SOD, So the changes of the activity of CAT of Egeria najas are expected to be used to biomonitor Hg pollution in the aquatic ecosystem.2. Effects of Hg2+ on water purification functions of Egeria najas(1) Effect of Hg2+ to the physical and chemical characters of water bodiesAfter exposure of 48h and 96h, experimental groups with different concentrations showed significant difference (P<0.05) on the electric conductivities in the water. The electric conductivities in control experimental group were remarkably less than the experimental group in which Hg concentration was 1.00,1.50,2.00 and 4.00 mg/L, respectively (P<0.05). After exposure of 24h, 48h and 96h, the pH of each group was not significant difference (P>0.05). After 96h, the DO of experimental groups declined 80% in the experimental groups with Hg concentration above 1.00mg/L compared with the control, indicated that the photosynthesis of Egeria najas already became very weak and plant near death. The extinction coefficient in the controlled group was significantly higher than the experimental group in which which Hg concentration was 1.00mg/L 0.50,1.00,1.50 and 4.00mg/L, respectively (P<0.01), also higher than 0.10mg/L (P<0.05).(2)Effects of Hg2+ on plant nutrient elementsThe concentration of NH4+-N in the water increased with the time of exposure, and peaked at 1.00mg/L. From 24h to 96h, the removal rates of NH4+-N in every experimental group were all negative indicated that when being exposure to Hg2+, Egeria najas not only couldn't remove NH4+-N from water, but also would increase its concentration. During all the time, the variety of the concentration of NO3 -N in the water body had no obvious rule, but the varieties of removal rate of NO3-N were consistent which increased at the first, then declined and kept invariable at final. The concentration of EN in the water was relative stable and the remove rate of Egeria najas to EN varied consistently especially when at 0.10,0.50,1.00 and 1.50mg/L, namely increased at first and then declined. As to TR, the water TP contents of the controlled and the 0.10mg/L group declined with the Hg2+ exposure time, and 0.50 and 1.00 mg/L had no remarkable variety but increased with time when Hg concentration above l.OOmg/L. The removal rates of Egeria najas to TP varied consistently which declined with the time exposure to Hg2+.3. Effects of Hg2+ on agamogenesis of Egeria najasWhen Hg concentration was above 1.50mg/L, leaf of shoot fragment faded severely, compared to the control even the sprout also faded much. When the concentration of Hg2+ increased the germination rate of Egeria najas showed a degressive trend, and the germination rate of shoot fragment in June was higher than Novemb...
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