Study On Ecological Adaptation Of Exotic Aquatic Plants Under Global Warming

In this paper, simulated and controlled experiments were employed to study the physiological and ecological adaptation of native and exotic aquatic plants in response to warming, nutrition addition and other factors under global warming, the results are as follows:1. Simulated warming experiments in the greenhouse were conducted to investigate the effects of winter warming on overwintering survival rate, clonal propagation and invasiveness of invasive species Eichhornia crassipes. Overwintering survival rate of E. crassipes was significantly improved by winter warming. More biomass of E. crassipes was allocated to shoot to support its rapid propagation and spread. Moreover, the size and sedimentation of stembase were also critical for overwintering survival rate and growth of E. crassipes. Meanwhile, combined with nutrition addition in the water, responses of biomass allocation and carbon/nitrogen balance to warming and nutrition addition were also studied, elevated temperature and water eutrophication significantly promoted the growth and clonal reproduction in E. crassipes, and more biomass was allocated to aboveground fraction to support its rapid growth and clonal propagation in favorable conditions. In addition, the photosynthesis and nutrition storage of E. crassipes were promoted by increasing the N concentration in leaves and stems, while nutrient turnover was accelerated by low C/N ratio, which increased the available nutrition for E. crassipes. 2. By comparing the effects of fluctuating resources in plant communities due to warming, flooding and nutrition addition on invasive plant Alternanthera philoxeroides and native plant Jussiaea reppens, the results showed that the growth, clonal propagation and biomass allocation of invasive species A. philoxeroides performed better in response to resources fluctuation, making a competitive advantage over native plants and facilitating its invasiveness. In the meantime, photosynthetic physiology and carbon/nitrogen balance of submerged plant P. crispus in response to simulated warming and DIC concentration increasing were also studied. Effects of warming and DIC addition on P. crispus were direct opposite:spring warming reduced its photosynthetic rate and biomass accumulation, while DIC enrichment significantly improved its photosynthetic efficiency. Moreover, in combination with inorganic N addition, physiological and ecological responses of three plants (Hydrocharitaceae) to warming, DIC enrichment and inorganic N addition were investigated. Biomass of Hydrilla verticillata was significantly increased by N addition in the water column; the growth of Egeria densa was improved by the increase of carbon source, but inhibited by warming; while elevated temperature markedly reduced biomass accumulation of Elodea nuttallii. Concentrations of N and free amino acid (FAA) increased with inorganic N addition.3. A glasshouse experiment was conducted to investigate the effects of clonal integration on a non-native clonal plant Myriophyllum aquaticum subjected to spatial and temporal heterogeneity of water supply. The daughter ramets were grown with stolon connections either severed from or connected to the mother plant and provided by different combinations of amount or frequency of water supply. Clonal integration significantly improved growth and photosynthetic performance of daughter ramets. Biomass allocation to roots of offspring ramets changed with water supply to enhance the capacity of water resource’s uptake and the decrease of the maximum quantum yield of photosystem Ⅱ (Fv/Fm) with reduced amount of water supply was greatly alleviated by stolon connection. Moreover, Clonal integration facilitated stabilization of foliar N concentration and C/N ratio to support healthy growth of the ramtes. Via simulated warming by means of open top chambers (OTCs), effects of warming on emergent aquatic plant community in water-land ecotone were studied. Reponses of emergent plants to warming were species-specific. Warming increased the proportion of Scirpus yagara Ohwi and other big-and-middle-sized plants in the community, made the plants become larger, and reduced the species diversity of plant communities. Furthermore, the disappearance rate of small plants was accelerated by warming.