Study On Plant Community Succession And Ecophysiology Of Dominant Species In Hangzhou Bay Coastal Wetlands

Coastal wetlands, occupying zones of transition between terrestrial and marine ecosystems, are the interface of the costal landscape. Coastal wetlands are suggested to offer many important ecosystem services, such as high productivity and diversity, providing habitats for flora and fauna, and helping to moderate water quality, water conservation, reduce and resist typhoon and tsunami, etc. Hangzhou Bay coastal wetlands is the intersection of north and south costal wetlands in China, and is suggested to be high value for scientific research, maintaining ecological balance and acting as a safeguard to prevent from erosion, attenuate waves and encourage sediment deposition.Following community ecology and ecophysiology principles, succession process were found out using clustering and ordination through vegetation distribution investigation in Hangzhou Bay wetlands, and community structure and biodiversity were analyzed. Environmental factors were employed to find out the main influencing factors for succession using DCCA, and the physiological responses of dominant herbs at different stages were monitored to salinity and seawater stress. Finally, ecophysiological characteristics, and the relationship with environmental factors were determined in whole growth season. The main results were showed as follows:1. Vegetation succession process, community structure and biodiversity in Hangzhou Bay wetlands17 taxa, belonged to 17 genus and 7 families, were found in 50 plots in Hangzhou Bay wetlands. TWINSPAN and DCA were introduced to find out the succession process as follows: Comm. Scirpus mariqueter→Comm. Phragmites australis→Comm. Tamarix chinensis—Phragmites australis→Comm. Salix matsudana—Imperata cylindrical. As the succession going, soil moisture and salinity decreased significantly, species number increased and life form changed complication. Species richness increased significantly, while the evenness decreased obviously, the diversity increased firstly, then decreased at the later period of succession, and community biomass was found same trends with diversity index.2. Influence of environmental factors on vegetation community distributionDCCA was introduced to analyze relationship between vegetation community and environmental factors. The first DCCA axe, composed by the main influence factors soil salinity, soil moisture and altitude, explained 58.1% of relationship between vegetation community and environmental factors.Four base cations (K+, Ca2+, Na+, Mg2+) were monitored, Ca2+(with average 91.48 mmol·kg-1), Na+ (with average 79.44 mmol·kg-1) were found to be main base cotions in soil. DCCA was also introduced to analyze relationship between vegetation community and base cations. The first DCCA axe, primarily influenced by Ca2+, explained 59.0% of relationship between vegetation community and base cations, and the second DCCA axe was 25.0%. With the increasing of each base cation, richness and diversity indices increased and evenness index decreased gradually.3. Response of dominant herbs to salinity and seawater stressS. mariqueter and P. australis, the dominant herbs in early and mid succession stages, had higher resistance to salinity and seawater stress than later species I. cylindrical. Meanwhile, S. mariqueter had higher tolerance to Ca2+ stress, and could resident on beach wetlands with high Ca2+ content, but P. australis had higher tolerance to Na+ stress, and could resident on beach wetlands with high Na+ content. This probably was induced to the transferring from early stage to mid stage. I. cylindrical had lower tolerance to salinity and seawater stress than species in early and mid stage, especially in seawater stress, there were significantly difference between I. cylindrical and S. mariqueter, P. australis. This can be suggested to be the main influencing factor for transferring from mid stage to later stage.4. Ecophysiological characteristics of dominant species in different stagesThe results from light response curve indicated that the values of net photosynthesis rate showed sequences, Scirpus mariqueter>Carex scabrifolia>Phragmites australis> Tamarix chinensis>Imperata cylindrical>Salix matsudana, and the values of light compensation point (LCP), light saturation point (LSP), the maximum photosynthesis rate (Pmax) and the dark respiration rate (Rd) showed the similar sequences to Pn, but the sequences of apparent quantum efficiency (AQY) were contrary absolutely to Pn. The results from A/Ci curve showed that the carboxylation efficiency (CCE) at early succession was lower than later succession, but the CO2 compensation point (CCP) were higher. It was suggested there was a good correlation between photosynthetic characteristics of dominants and community succession. The daily dynamics of photosynthesis and transpiration of each dominants showed that species at early succession, whether herbs or woods, had higher net photosynthesis (daily assimilation) and transpiration (daily amount of transpiration), with the succession going, every index decreased, but lower water use efficiency (WUE) were found for herbs at early stage, higher values were displayed at later stage, and higher photosynthesis and WUE of herbs were found than woods. Leaf chlorophyll contents with species at early stage were lower than species at mid and later stages, but chlorophyll a/b were adverse. Path way analysis between photosynthesis and environmental factors were found that photosynthesis of species at early stages were mainly influenced by photosynthetic active radiation (PAR), and by leaf temperature and vapor press deficit (VPD) for species at later stages.N, P stoichiometry was relatively stable at later period of growth season through study on dynamics of species in whole growth season in Hangzhou Bay wetlands. With succession development, N, P content decreased and N:P increased for herbs, and N, N:P increased and P decreased for woods.