?-diversity Along Environmental Gradients Wetland Plant In Poyang Lake

The present study based on the detailed investigation and analysis of historical data of Poyang Lake wetland ecosystem, and performed a series of field survey on wetland plant community of Poyang Lake. We studied the patterns of beta diversity of wetland plant in response to environmental gradients(e.g., soil water content, water level and disturbance), analyzed how wetland plant community structure varied along environmental gradients; Combined with distance-based redundancy analysis, we quantified the interpretation of environmental variables(spatical factors, hydrologic factors, soil elements) to community structure vary, disentangled the relative importance of deterministic(hydrologic factors, soil elements) and stochastic processes(spatical factors) affecting beta diversity, tried to clarify the mechanisms of community assembly of wetland plant in Poyang Lake(i.e., habitat filtering and niche differentiation). The results showed as followings:1. According to field surveys of plant communities in wetlands of Poyang Lake, total species richness of 27(? diversity) in 129 1m×1m plots were found and the species abundance in each plot ranged from 1 to 12 species(? diversity). The most dominant species in Poyang Lake is Carex. spp, the sub-dominant species were Phalaris arundinacea, Triarrhena lutarioriparia, Zizania latifolia, Artemisia selengensis, Phragmites australis, Heleocharis valleculosa and Cynodondactylon(Linn.) Pers., and typical accompanying species were Polygonum hydropiper, Potentilla limprichtii, Polygonum sieboldii and Polygonum hydropiper.2. The results of our on-site investigations showed that there was a significant zonation distribution of wetland plant community along elevation gradient. The dominant species exhibited a significant change from high land to low land: Cynodondactylon Pers., Artemisia selengensis, Triarrhena lutariotipatia, Carex cinerascens, Phalaris arundinacea, Heleocharis valleculosa. Typical patch distribution pattern and vertical structure of wetland plant community was also observed, the most typical community vertical structure from top to bottom followed as Phragmites australis, Triarrhena lutarioriparia, Carex spp., Potentilla limprichtii, Polygonum hydropiper. There were significant differences in ? diversity of wetland plant community among different regions and among different grassland, while ? diversity showed no significant differences.3. Beta diversity responded to environmental factor in significantly different patterns with regards to diversity metrics. Jaccard dissimilary showed a uni-model with elevation, soil water content and soil nitrogen content, consistent with the intermediate disturbance hypothesis. In addition, jaccard dissimilary exhibited a decrease pattern with increasing soil carbon content and an increase pattern with increasing soil phosphuros content; Bray-curtis dissimilary showed a uni-model with soil water content and carbon content, an increase pattern with increasing elevation, a decrease pattern with increasing soil nitrogen content; Raup-crick dissimilary showed a uni-model with evelation, soil water content, soil carbon/nitrogen/phosphorus content, consistent with the intermediate disturbance hypothesis. Evelation, soil water content, soil carbon/nitrogen/phosphorus content and their interaction showed significangt effect on three different diversity metrics, suggesting that both deterministic and stochastic factors have impotant influences on wetland plant community structure in Poyang Lake. In addition, effects of environmental filtering on wetland community assembly could also be observed.4. According to distance-based redundancy analysis, spatial factor, hydrological factor, soil factor and their interaction explained more than 90% inertia of beta diversity metrics. Our results suggested that deterministic processes were the major ecological processes affecting community assembly at local scale. Hierarchical nested deterministic processes were the major ecological processes affecting community assembly. Environmental factors sorted plant species in specific habitat through habitat fitering, while other species were filtered out from the local communities. However, biological interaction became intensity with increased interspecific similarity. Some species would be filtered again due to competitive exclusion, while competitive species would became dominator.