Characteristics And Biodiversity Of Natural Wetland Plant Communities Along Rural-Urban Continuum In Yangzhou

Wetland is an important component of urban natural ecosystems and contributes greatly to maintain the balance of urban ecosystems. Urbanization has significant influences on the urban wetland. For example, the area of the urban wetland decreased, the water quality became worse and the community structure altered along with urbanization. In this paper, the structure and floristic composition of the wetland plant communities on the urban-rural continuum in Yangzhou have been analyzed based on the data from the field investigation of wetland vegetation and water quality. The main factors which affect the species diversity in the wetland plant communities have also been discussed. The main results show that:(1) Totally70species belonging to53genera27families are identified in the wetland plant communities in the study area. Herbaceous plants are dominant (accounting for about95%). Plants from Poaceae and Asteraceae are distributed widely in the study site. There is no significant difference of the floristic composition of wetland plant communities along urban-rural gradient of Yangzhou. Phragmites australis, Typha angustifolia、Zizania caduciflora and Alternanthera philoxeroides are the common dominant species in the wetland plant communities.(2) There are15invasive alien species belonging to15genera8families. The exotic species is about21.3%of total wetland species in the study region. Many foreign species originate from Americas and Asia. Among of these species, Alternanthera philoxeroides is distributed widely in Yangzhou wetland, and it is also the only dominant species in the wetland plant communities in some parts of the study area. It is one of the worst weeds in this area.(3) Therophytes and Hemicryptophytes are absolutely dominant in the life-form spectrum (accounted for more than70%) in Yangzhou wetland plant communities. The urbanization is uneven along the rural-urban continuum. Microenvironment is one of the important factor which obviously affects the importance value, SLA and biomass of wetland plants.(4) The water quality becomes worse and worse, especially the TN, TP and DO increase significantly with urbanization. The changes of water quality and human activities are the main factors which have impacted the biodiversity of wetland communities. In the rural area, the human activities and water pollution are not very serious compared with urban area. Meanwhile, eutrophication of water bodies is very common because of domestic sewage and other kinds of human activities. So species diversity in wetland plant communities shows a trend of increase along the rural-urban continuum. Additionally, there is an exception in T2because of uneven urbanization along this gradient.