Distribution Pattern Of Plant Diversity Along An Elevation Gradient In Southern Gaoligong Mountain

Mountains are centres of biodiversity and perform important ecosystem functions.The Southwestern Mountain of China is one of the global biodiversity hotspots,and it is a vital ecological security barrier in China.Gaoligong Mountain is located in the core area of this region,which is sensitive to climate change.It is south–north oriented and species-riched.The distinct vegetations are distributed in this region.However,it remains unclear how the diversity and community assembly along elevational gradient in this region.Furthermore,due to the differences in climate and topography of mountain aspect,different slopes might have different species composition.Surprisely,much remains unknown about whether aspect plays a vital role in determining the similar or disimmilar pattern of mountain diversity along an elevational gardient.In this study,we focus on the forest plots(32 0.1 ha in total)at diifent slopes along elevational gradient in Gaoligong Mountain.Based on the species composition,DNA barcoding and functional traits,we evalualted the species diversity across different growth forms(including tree,shrubsand herb)along elevational gradient.In addition,we also examined the phylogenetic and functional diversity and its potential community assembly mechanisms of trees along elevational gradient.Finally,we compared the difference between eastern and wersten slopes.Our main results are as follows:1.Species diversity along an elevational gardientIn this study,a total of 705 species were identified,which belong to 347 genera 125 families.279 tree species,189 shrub species,and 237 herb species were recored.The species richness showed a decresed trend along an elevation gradient at both eastern and western slopes,and the decreased rate is higher in western slope than eastern slope.However,the species diversity along elevational gradient were different among different growth forms.Specifically,tree species richness showed a decreased trend along elevations,shrubs showed unimodal(‘‘hump-shaped'')patterns and herbs showed U- shaped patterns at both slopes.However,we could not find a distinct pattern when using Shannon & Wiener and Pielow evenness index.The species composition was difference at different slopes,especially among the lower elevational communities at different slopes according NMDS.The ? diversity increased with increasing elevational distance.When the elevational interval is up to 1000 m,the species turnover completely.2.Phylogenetic diversity of tree along elevational gradientA total of 694 sequences of rbc L,mat K,trn H-psb A and ITS were obtained by using DNA barcoding,and 194 sequences were downloaded from NCBI.We constructed the community phylogentic tree by using maximum likelihood(ML)approach.The phylogenetic diversity of trees is significantly correlated with species diversity,and it is deceased along elevational gradient.The phylogenetic structure at eastern slope showed a deceasing trend along an elevation gradient.The clustering structure was observed at lower elevations,indicating environmental filering paly an important role and this could be related with disturbance or drought at lower elevations.And the overdispersion structure were observed at higher elevations,the competition exclusion could be a driving process due to trait convergence at higher elevations.The ? diversity of phylogentic diversity exhibited the clustering-random-overdispersed with increasing elevational distance.This indicating that low elevational distance,the community phylogenetic similarity showed more similar than null models,and when increasing elevational distances,the similiarty were deceased significantly.2.Functional diversity of tree along elevational gradientWe measued the five functional traits of trees [including leaf thickness,specific leaf area(SLA),leaf carbon content(LCC),leaf nitrogen content(LNC)andleaf phosphorus content(LPC)],community-weighted mean(CWM)of SLA was negatively correlated with elevation.LCC showed a unimodal pattern,and the leaf thickness,LNC and LPC showed U-shaped patterns.There is contrast pattern when campare the functional structure and phylogentic structure.Our results demonstrated the trait convergence at high elevations,and the functional structure exhibited the clustering at both the end ofelevations at eastern slope.While the functional structure showed the change from overdispered to clustering along elevations at western slope,this in linked with the trait differeniation at low and medium elevations.The ? diversity of functional diversity exhibited decreaed with increasing elevational distance.