Classification and Ordination of the Wetland Plant Communities in the Jiansanjiang Farming Bureau,the Sanjiang Plain

To assess and characterize wetland vegetation and to find its relationship to environmental attributes in the Sanjiang Plain,the Jiansanjiang Farming Bureau,which is located in the northeastern interior of the Sanjiang Plain,was selected.A total of 86 phytosociological samples,each including 3 quadrats,were surveyed from open-water pools,marshes and wet meadows,moreover,some grass fields in the Sanjiang Plain.The vegetation and environmental characteristics were investigated in these quadrats.The plant sub-communities were defined using techniques of numerical classification(two-way indicator species analysis,TWINSPAN) and ordination(detrended correspondence analysis,DCA).Species with important value bigger than 10 were classified into eight groups and samples were divided into eight plant associations using TWINSPAN.The difference between each of the eight plant associations on the aboveground biomass,stem density,diversity index,and dominant index were significant(ANOVA,n=7,p=0.000).Also,significant differences were found among the environmental factors of these associations such as water depth,soil pH,soil organic content,and total nitrogen were also different significantly(ANOVA,n=7,p0.01),while total phosphorous excluded.The results of TWINSPAN were represented well upon the DCA ordination diagrams.The species in the same groups or the samples in the same associations showed a similar distribution in the diagrams.The first and the second DCA axis together explained 23.5% of the variation in the species and sample data.The low information of the DCA axis and the dispersed pattern of the species and samples responded to the significant differences among the environmental factors of these wetland plant communities dominated by herbs,as well as to the community structure with outstanding dominant species and a few common species.The first axis which explained 14.5% of the variation separated the species and samples with good water condition from those with poor water condition,and the second axis explained 9.0% of the variation.The ordination reflected the relationship between the plant communities and the environments and suggested the water condition determined by the microtopograhpy was one of the predominant factors leading to the wetland vegetation pattern.