Studies On Physiological Reactions In Adverse Circumstances Of Submerged Plants And Their Purifying Functions

This dissertation studied the decontamination abilities, the physiological and biochemical reactions of Hydrilla varticillata, Myriophyllum spicatum L, and Ceratophyllaceae under different water conditions, effects of LAS on their growth, physiological and biochemical reactions, photosynthesis responding to pH and DIC. It explored not only the stress physiology and the decontamination abilities of submerged aquatic plants, but also the degeneration and restoration mechanism of aquatic macrophytes, which had the important scientific significance. Major conclusions were described as follows:1. The results showed that Hydrilla verticillata could clear sewage effectively, and the removal rates for CODcr and TN were 81.51% and 71.36% respectively. It also indicated that Hydrilla verticillata had the abilities of decontaminating and the adaptation to sewage, but they were varied when were planted into different laboratory conditions. When Hydrilla verticillata was put into wastewater, the changes of SOD activities and CAT activities had a similar trend that declined after increasing, and the highest activities appeared at the 3rd day and the 10th day. The result showed that high COD and excessive concentration of NH4+-N would stress the growth of Hydrilla verticillata and led it to death, and that Hydrilla verticillata could resist and adapt to sewage to a certain extent. However, its endurance ability would gradually become weakened at high concentrations of sewage, eventually resulted in death.2. Damage degree of Myriophyllum spicatum L and Hydrilla verticillata was directly responded to concentrations of LAS. There was little changes of SOD, CAT and POD in the range of experimental LAS concentrations (0-0.5 mg-L"1), which indicated that no apparent effects took place in physiological activities of these aquatic plants. When concentrations of LAS were between 1.0 and 5.0 mg-L-1, activities of SOD, CAT and POD increased, Myriophyllum spicatum L. suffered apparent effects. When LAS was higher than 5.0 mg-L-1, SOD defensing system collapsed, and made macrophytes to death. For Hydrilla verticillata, however, this situation happened when LAS was higher than 20.0 mg-L-1, which indicated that both Myriophyllum spicatum L and Hydrilla verticillata could resist and adapt to sewage, but the latter was more sensitive than the former. 3. The damage degree of Myriophyllum spicatum L and Hydrilla verticillata was directly related to the contacting time of LAS. When concentration of LAS was below 10.0 mg-L-1 for Myriophyllum spicatum L., and below 1.0 mg-L-1 for Hydrilla varticillata, no apparent effects took place on the physiological activities of SOD, CAT and POD in the first 48 h, but it sharply increased at the 72th h to Myriophyllum spicatum L. and at the 96th h to Hydrilla varticillata, which indicated that the tolerance of Myriophyllum spicatum L was higher than that of Hydrilla varticillata, and Myriophyllum spicatum L should be the pioneer species to the restoration of submerged macrophytes for the urban sewage treatment.4. The microscopic observation showed that in LAS polluted environment, chloroplasts of Hydrilla varticillata deformed and assembled when LAS was 5.0 mg-L-1; and when LAS was 10.0 mg-L"1, chloroplasts disintegrated gradually, a lot of leaves lost their color, the cell walls were separated from the others, the circular movement of the plasma stopped, and gas passages disappeared. In LAS (5.0 mg-L-1) polluted environment for ten hours, the photosynthetic rate of Hydrilla varticillata was only 58% of the control group, the rates of uptake N and P was 61% of the control group. The resuls showed that due to LAS penetrated the cell wall of the plants, the protein changed properties, the chloroplasts stopped circular movement, photosynthesis of Hydrilla varticillata and metabolism of nitrogen and phosphorus was inhibited. This was one of main causes of aquatic vegetation degeneration.5. The result also showed that obvious stress and physiological damage of Hydrilla varticillata appeared when concentration of LAS was higher than 5.0 mg-L"1. In China, however, LAS in eutrophication lakes did not reached this level, which indicatd that LAS was not an important role in degradation of aquatic macrophytes caused by eutrophication, but might be an indirect factor that affecting growth and evolution of plants in water environment.6. Through investigating variations of photosynthesis and respiration of the submerged plants including Hydrilla varticillata, Myriophyllum spicatum L. and Ceratophyllacea, this paper compared photosynthetic productivity and photosynthetic characteristics. Different ranks of photosynthetic productivity were observed for different plants at different light intensity. At the light intensity of 10-890μmol-m-1·s-1, the photosynthetic rate of Ceratophyllaceae was the highest, followed by Hydrilla varticillata and Myriophyllum spicatum L. Photosynthesis of 3 submerged plants was inhibited by high-light. Hydrilla varticillata and Ceratophyllaceae adapted to high-light, and were dominant species in surface water layer. Myriophyllum spicatum L had the lowest light requirement and could adapte to a deep water layer.7. The effects of pH and DIC (dissolved inorganic carbon) on photosynthesis of Hydrilla varticillata, Myriophyllum spicatum L and Ceratophyllaceae were investigated. The results showed that photosynthesis of these three plants was different for various pH and DIC conditions. A lower affinity to carbon was observed as pH decresed from 9.0 to 6.0, and Myriophyllum spicatum L was adaptable to extensive pH ranges. When the concentration of DIC reached the saturated level, the highest photosynthesis rate for Ceratophyllaceae was much greater than those for Hydrilla varticillata and Myriophyllum spicatum L.