Characteristics Of Seed Plant Community In Nianchu River Basin And Its Environmental Interpretation

The Qinghai-tibet Plateau has the most unique ecosystem,geographical pattern and rich in species diversity in the world,and it plays an irreplaceable role on the ecological security and biodiversity protection in China.The watershed area located between land and water ecosystem,as one of the ecologically vulnerable areas is sensitive to climate change and various disturbances.Therefore,the study on the characteristics,structure,distribution pattern and response to environmental variables of the plant community in the watershed area should be strengthened and it is of great significance in promoting the protection of watershed ecosystem,biodiversity and sustainable development of environment.In this paper,the Niangchu River Basin as study site the composition and floristic characteristics of seed plants,the relationship between plant community structure and environmental variables,the distribution pattern of species richness and its environmental interpretation and the ecological characteristics of dominant plant species and their interspecific association were studied.According to habitat and vegetation types in Nianchu River Basin,total of32 plots with 3-5 samples for each plot and 114 samples were selected by 2m×2m for meadow vegetation and 5m×5m for shrub vegetation.The abundance,coverage,height and aboveground biomass of each species were recorded in the each sample,in the same time the soil samples in each plant sample were also collected for determining its physical and chemical factors including soil water content,water soluble salt content,conductivity,p H,total nitrogen,total phosphorus,hydrolysis nitrogen,phosphorus,potassium etc.The geographical variables,such as longitude and latitude,altitude,slope,and interference factors were recorded for each sample.The climate variables(including mean annual temperature,the hottest month mean temperature,potential evapotranspiration,mean annual precipitation,actual evapotranspiration and moisture index)were calculated for each plot based on the data from meteorological stations around and near the study site by the Co-Kriging interpolation method with altitude as a co-variable.The Two-Way Indicator Species Analysis(TWINSPAN)and the Detrended Correspondence Analysis(DCA)applied to analyse plant community structure.The Canonical Correspondence Analysis(CCA)was applied to analyse the relationship between plant community and environmental variables.The Generalized Additive Models(GAM)was used to perform the regression fitting of the Transformed Species Richness(TSR)with climate variables.The Variance Decomposition Analysis(VPA)was used to determine the explanatory degree of environmental variables on the distribution pattern of species richness.The niche characteristics and interspecies associations of dominant plant species in community were analyzed by using Levins niche breadth index(Bi),the niche overlap index(Oik),the variance ratio(VR)method,interspecies association coefficient(AC),Jaccard index(IA)and point correlation coefficient(?).The results as follow:1)Seed plant composition and characteristics of flora in Nianchu River Basin: a total of 295 species of seed plants(including variants)were recorded,belonging to 168 genera in 58 families,among which dicotylete plants take absolute advantage.The plant life form is mainly herbaceous plants,among which perennial herbs are the most dominant,and the resource type of plant is mainly medicinal plants followed by forage plants(grazing source and honey source).In the composition of the family,large family is the dominant family,including Asteraceae,Poaceae and Fabaceae.The single species genera and small genera are the main components in the composition of genus.The geographical distribution type of family is dominated by the temperate type and followed by the tropical one,except the world wide distributed family.The geographical distribution type of genus shows the obvious temperate type and the uniqueness of the genus is not high in the study region.2)The characteristics of seed plant community and their relationship with environmental factors in Nianchu River Basin: total of 114 plant samples divided into 8 clusters by TWINSPAN classification in the Nianchu River Basin,such as Sophora moorcroftiana+Pennisetum flaccidum(ASS),Elymus brevipes+Poa litwinowiana+Stipa purpurea(ASS),Artemisia wellbyi+Anaphalis xylorhiza+Stipa capillacea(ASS),Potentilla parvifolia+Kobresia humilis+Polygonum viviparum+Kobresia pygmaea(ASS),Kobresia pygmaea +Potentilla anserine+Blysmus sinocompressus(ASS),Rhododendron fragariiflorum+ Kobresia humilis+Cassiope fastigiata(ASS),Hippophae gyantsensis+Myricaria elegans+Potentilla anserina+Blysmus sinocompressus(ASS),Potamogeton pusillus+Halerpestes tricuspis+Batrachium bungei(ASS).The result of classification is highly consistent with the DCA ordination result.According to the method of plant community physiognomy ecology,the vegetation in the study arae can be classified into deciduous broadleaf shrub,dwarf shrubby grassland,tufted grassland,evergreen leather leaf shrub,rhizome Carex meadow and clustered Kobresia meadow,and mixed herb marsh meadow.The CCA analysis showed that the species composition and distribution pattern of plant community was mainly affected by the soil water content and altitude.3)Distribution pattern of species richness and environmental explanation in Nianchu River Basin: there is a linear relationship between species richness but not significant.There are complex curve relationships between species richness and latitude,altitude but the relationship between the two factors and species richness showed an opposite changing trend.Climate variables(energy and moisture)were negatively correlated with longitude and altitude significantly,and were positively correlated with latitude significantly.The climatic variables showed a pattern of increasing energy and decreasing moisture from the upstream to the downstream in the Nianchu River Basin.The energy and moisture played a dominant role in the distribution pattern of plant species richness in the study area.The effects of annual mean temperature and the hottest month mean temperature on species richness are basically consistent with the effect of latitude on species richness,roughly showing a "U"-shaped distribution pattern.There was a significant negative correlation between species richness and potential evapotranspiration.However,the species richness showed a decreasing-increasing-deceasing trend with the increase of moisture.Climate variables(energy and moisture)were the dominant variables in the formation of species richness patterns in this region,and geographical variables were also important variables in the change of species richness patterns.4)The niche characteristics and interspecies correlation of dominant plant species in Nianchu River Basin: the niche width of dominant species in community varies greatly,Poa litwinowiana and Kobresia humilis have the largest niche width and Artemisia persica has the smallest niche width.The species with medium and narrow niches width were dominant species in the study area.The niche overlap value of between dominant species was generally low.The overall association of seed plant communities was significantly negative in Nianchu River Basin,and the number of species pairs with negative associations among dominant species is much larger than the number of species pairs with positive associations.Most of the interspecific relationships showed significant negative associations and the plant community is in unstable primary stage of succession in the study area.