Growth And Reproductive Strategies Of Vallisneria Natans And Hydrilla Verticillata Under Eutrophic Water

As a major primary producer of lake ecosystems,aquatic plants play a vital role in material circulation and energy flow.In the process of aquatic plant growth,water bodies and sediments are important nutrient sources for plant growth and reproduction,It is important media for establishing stable communities and purifying water quality for aquatic plants.Aquatic plants have both sexual and asexual reproduction modes.Aquatic plants exhibit adaptive growth of physical and chemical properties of water bodies,and the physical and chemical properties of water bodies also promote or stress the aquatic plants.In recent years,the intensification of eutrophic water has serious negative impacts on aquatic plants,water quality has deteriorated,lead to decline in aquatic plant diversity,and severe damage to the structure and function of aquatic ecosystems,with the most obvious impact on aquatic plants.When aquatic plant habitats are suffered of eutrophication stress,aquatic plants will adopt different breeding strategies to adapt to external conditions and continue to survive,and less relevant research.In this paper,the combination of control experiment and field investigation is used to explore the effects of germination,growth and reproduction strategies of two submerged plants Vallisneria natans and Hydrilla verticillata.The mechanism of aquatic plant growth adaptation is analyzed from the perspective of morphology and physiology,so as to provide ideas for the restoration of eutrophic water.The first part of this thesis is the control experiment.1.The main research on the morphological and physiological dynamics change of different breeding species(seed and winter bud)of submerged plant V.natans under different nutrient water conditions.2.The morphological and physiological responses of plants grown by winter buds and fragments of H.verticillata to eutrophic water.The second part is the field investigation and research: 3.Mainly study the physiological and ecological responses of different propagule types of aquatic plants to eutrophic water in the process of restoration and restoration of typical eutrophic aquaculture lakes in the middle reaches of Yangtze River,the research results are as follows:(1)In May,the asexual seedlings of V.natans germinated earlier than the sexually seedlings,and had more advantages in morphological characteristics than the sexually seedlings.For example,the underground biomass,root-shoot ratio and relative growth rate of the asexually seedlings were significantly higher than those of the sexually seedlings.Different plant types have significant effects on plant physiological characteristics.For example,the carbon content in leaves of asexual seedlings is significantly higher than that of sexual seedlings,and the phosphorus content in leaves of sexual seedlings is significantly higher than that of asexual seedlings.Nutrition treatments significantly affected the accumulation of elements in sexual seedlings,such as high phosphorus treatment significantly inhibited the carbon content of leaves.In July,different plant types and nutrient treatments had significant effects on plant morphology.For example,the total biomass and aboveground biomass accumulated by asexual plants were significantly higher than those of sexual plants except for high phosphorus treatment,while the biomass of various parts of sexual plants was significantly reduced by high phosphorus treatment.Different reproductive types had significant effects on leaf phosphorus content and root nitrogen and phosphorus content,but had no significant effects on other physiological characteristics.For example,in high nitrogen and phosphorus treatments,the leaf nitrogen content of sexual plants was significantly higher than that of asexual plants.In October,different plant types had significant effects on the above-ground and underground biomass of plants.For example,compared with the control group,the underground biomass of clonal plants in other nutrient treatments was significantly higher than that of sexual plants,while the under-ground biomass of sexual plants was significantly reduced in high nitrogen and phosphorus treatments.For example,in addition to the control group,the leaf nitrogen content of the sexual plant was significantly higher than that of the asexual plant,while the high nitrogen treatment significantly reduced the leaf nitrogen content of the asexual plant.(2)Different nutrient treatments had significant effects on the number of new winter buds and nitrogen and phosphorus content of H.verticillata.For example,the nitrogen content of the new propagator of winter bud-type plants under high phosphorus treatment was significantly higher than that under high nitrogen and phosphorus treatment,while the phosphorus content of the new propagator increased significantly compared with the control.Different plant types have significant effects on aboveground biomass and ramets of H.verticillata.For example,in high nitrogen and high phosphorus treatments,the number of ramets of winter bud type plants is significantly higher than that of branched type plants,while in high phosphorus treatment,the number of ramets of winter bud type plants increases significantly.(3)In October,the biomass per unit area of V.natans was significantly higher than that of H.verticillata,but the coverage of V.natans community was lower than that of H.verticillata community.There were significant differences in elemental contents of different organs between V.natans and H.verticillata in different periods.For example,the nitrogen content of leaves and roots of V.natans decreased gradually with the growing season,but the change trend of phosphorus content of leaves and roots was opposite.Nitrogen content and N/P ratio in leaves of H.verticillata decreased significantly in October,while C/N ratio increased significantly in October.There was no significant difference in other indicators.In this study,we found that different reproductive types of V.natans and H.verticillata exhibit diverse morphological and physiological plasticity responses to eutrophic water,and this ecological adaptability change is related to plant phenophase.