Species Diversity Characteristics of Plant Community in Xihu Desert Wetland of Dunhuang,Gansu Province

The plant species diversity in Xihu desert wetland of dunhuang,Gansu province has been studied based on the surveying of 375 sampling plots and 150 sampling transects.Results showed that:(1) 26 species belonging to16 families,24 genera were recorded in the area.Phragmites communis,Tamarix ramosissima and Populus euphratica are dominant species,Lycium ruthenicum,Alhagi sparsifolia and Glycyrrhiza inflata are main associated species,and their average importance values are 0.4728,0.4563,0.4342,0.2908,0.2594 and 0.2455 respectively.The plant communities are composed of 8 types,including Tamarix ramosissima community,Populus euphratica community,Glycyrrhiza inflate community,Alhagi sparsifolia community,Tamarixramosissim community,Lycium ruthenicum community,Phragmitescommunis community and Phragmites communis community.(2) The plant community species diversity indexes are generally low(0.784-1.379),in which the species diversity indexes of Tamarix ramosissima community,Populus euphratica community and Phragmitescommunis community are larger(1.379,1.266 and 1.194),the species diversity indexes of Alhagi sparsifolia community and Lycium ruthenicum community are second(1.154 and 1.077),and the species diversity indexes of Glycyrrhiza inflate community,Phragmites communis community and Tamarixramosissima community are lower(0.919,0.881 and 0.784).(3) Shrub and tree are main vegetation layers in Xihu desert wetland ecosystem,and the species diversity indexes of shrub and tree(0.549-1.077) are larger than that of the herb layer(0.052-1.038).(4) The species diversity indexes such as Shannon-Wiener diversity,Simpson diversity,Simpson superiority and Margalef richness significantly decrease with the increase of elevation,while the Simpson superiority value shows an opposite trend,the change of evenness index is not significant.(5) With change of horizontal sites,the Shannon-Wiener diversity,Simpson diversity,Simpson superiority and Margalef richness show similar trend,being decreased at first at relatively low-longitude and low-latitude sampling area and then increased at relatively low-longitude and high-latitude sampling area,and decrease at last at relatively high-longitude and high-latitude sampling area,but the change trend of the Simpson superiority value shows an opposite trend.