Study Of Ecological Response Of Aquatic Plants To Stress

The living space and environment of organisms, even those of the human beings, on the earth, are threatened by environmental deterioration. Changes within surface atmosphere and water body, two important parts of the biosphere, have drawn extensive attention from scientists and governments.The vast water-bodies have become the main receiver of contaminants, and most contaminants finally accumulate onto the sediment that in turn becomes a pollution source. As two most important contaminants, heavy metal that can't be biodegraded and PAHs that typify carcinogenicity have not only brought severe ecocatastrophes in many developed countries, but also caused an ecocrisis in most developing countries.Since 1958, atmospheric concentration of CO2 has shown a steady increase at a rate (~ 0.45 % per year) because of anthropogenic factors. At present, the current atmospheric CO2 concentration, 360 umol/mol, is approximately 30 % higher than the pre-industrial level and conservatively projected to reach about 700 umol/mol by 2100. This becomes one of the prominent and incontrovertible reasons of global climate change, especially, resulting in a significant increase of the average global surface air temperature.In order to analyze the purifying capacity, the ecophysiological response and ecological adaptation of aquatic plants in different stress treatments, in this paper, pollution stress (high concentrations of Pb and PAHs in water phase and sediment) and non-pollution stress (elevated CO2, 1000 umol/mol) were imitated in laboratory and the contamination accumulation and biodegradation, clonal growth", biomass accumulation, photosynthesis, risk spreading and energy metabolism of lower plants. (Chora globular is, Hydrodictyon reticulatum) and vascular plants (Vallisneria asiatica, V. spinulosa), under above environmentwere studied. The main results are as follows:Aquatic plants can remarkably retard the settling process in water phase and greatly absorb contaminants in the aquatic environment. The absorption of Pb by aquatic plant has marked time and concentration effect, the accumulation in the plant increasing with time and concentration; but the accumulation of Pb by H. reticulatum shows the symptom of saturation. The accumulation of anthracene in H. reticulatum is higher than V. asiatica and C. globularis, which is related with the high content of hydrophobicity lipid of cell. With the extension of time, anthracene is transferred and biodegradated in the plant.Contaminants in water phase exerted marked oxidabitlity damage upon aquatic plant, and complex effects on antioxidative enzymes. The general trend being that enzyme activity reduces with the increase of concentration of contaminant. Comparison showed that the hardiness of lower plant is greater than vascular plant. Among the three aquatic plants, although H. reticulatum does not have POD activity, but it has strong SOD activity, and therefore performs greatest tolerance towards Pb. However, tolerance of H. reticulatum to anthracene is probably related to non-enzymic antioxidants.Sprouting of V. spinulosa turion was not affected by heavy metal Pb in sediment. This was explained by the fact that nutrition for seedling depended on the carbohydrate in turion and reduced the dependence of sprouting on environment. After root grew under high concentration of Pb, the seedling developed visible symptoms of toxicity such as chlorosis, necrotic lesions and decline of biomass accumulation. In order to escape the stress habitat, V. spinulosa developed another kind of architecture, which was different from that in the control. The architecture in the control tended to be "guerilla" with few branches and dispersed feeding sites. Ramets reproduced by ortets that grew in low concentration of Pb (below the tolerance threshold value) could grow in both the healthy habitat and low concentration of Pb habitat in linearity pattern. However, ramets didn't survive in high concentration of Pb but grew in healthy habitat in phalanx pattern and the ortet grew in high concentration...