|Other Abstract||Decline of aquatic macrophytes commonly occurs in freshwater habitats. In fluvial ecosystem, the decline was about fall of biodiversity and degradation of habitats, and in lacustrine ecosystem, it was about the decay of the macrophytes. This thesis mainly focuses on the stress of eutrophication on lake aquatic macrophytes and biodiversities of river aquatic plants.
The first part is the compasion about the effects of water and sediment from mesotrophic and eutrophic area of Lake Donghu, respecitively, on the growth of Vallisneria natans. There were four treatments in this study, including eutrophic and mesotrophic culture conditions, and mesotrophic condition with inorganic nitrogen and phosphorus addition, respectively. The present study was measured growth indices, including biomass, the number and length of leaves and the number of buds, and biochemical indices, including soluble carbohydrate content and free amino acid content. The results showed that biomass, number of leaves and buds of V. natans grown in mesotrophic condition were the highest, then were those in the mesotrophic condition with phosphorus addition, then were those in mesotrophic condition with nitrogen addition, and the lowest were those in eutrophic condition. The results indicated that high trophic condition could inhibit the growth of V. natans significantly (p<0.05). Increase of inorganic nitrogen in mesotrophic water inhibited the growth of the plant more than did the increase of the phosphorus, suggesting nitrogen enrichment during eutrophication might be more important than phosphorus for the contribution in decline of macrophytes. Soluble carbohydrate and free amino acid contents of V. natans in eutrophic condition were markedly higher than those mesotrophic conditions, indicating that carbon and nitrogen metabolism of the plant were affected which might be attributed to excessive accumulation of N in eutrophic waters.
The second part was about a field study on floristic diversity of aquatic vascular plants throughout River Yili. The main results were as follows:
1. The results of this field study showed that a total of 46 species belonged to 2 phylum, 18 families and 28 genera were found. Except Ephedra sinica, all species belonged to Angiosperm. Among these species, 11 families 19 genera and 33 species belonged to Monocotyledon, and 6 families 8 genera and 12 species Dicotyledon.
2. Analyses of field data showed that there were significant positive relations between α - diversity of species and α - diversity of genus and family in River Yili, respectively, and between β- diversity of species and β- diversity of genus and family were also significantly positively related. The results suggested that change of diversity in higher taxon units was similar to that in the species unit.
3. The results indicated a unimodal relationship between α - diversity and elevation. For β - diversity, there were similar changes among species, genus and family among different altitudinal intervals. The similarity indices of Jaccard between different sample sites increased with increasing elevation, suggesting the greater difference in elevation, the smaller similarity in aquatic plants.|