Variation In Functional Traits Of Plants In The Subtropical Evergreen And Deciduous Broad-leaved Mixed Forest

Functional traits greatly facilitate community ecology study and prompt our understanding of the pattern and mechanisms of species coexistence.Interspecific trait variation is the important foundation for species coexistence in natural communities.The trait values of individual varies in different environmental conditions due to genetic differentiation and phenotypic plasticity and might affect the spatial distribution of species and interspecific competition.However,our knowledge of how plant intraspecific variability in different communities is lacking.Thus it is essential to understand the relative contribution of intraspecific traits variations to the community assemblage especially in the subtropical evergreen and deciduous broad-leaved mixed forest,one of the representative vegetation types of subtropical mountainous areas in China.The most distinct feature of this vegetation types is the coexistence of evergreen and deciduous trees species coexistence in the local communities.The differences in plant leaf habits generally decides the ecological strategies of different tree species therefore,a deep understanding variations in leaf traits of tree species will provide important scientific evidence on species coexistence.In this thesis,we focused on the inter-and intraspecific traits variations of plants in subtropical evergreen and deciduous broad-leaved mixed forest in Hubei Province.Individuals with a DBH(diameter at breast height)more than 10 cm and the 1-5 largest trees of each species were sampled in 48 forests dynamic plots(20 m x 20 m)in Hubei Xindoushan National Nature Reserve.The four major plant functional traits,including specific leaf area(SLA),leaf dry matter content(LDMC),leaf area(LA),and specific stem density(SSD)was measured in all the studied individuals.Firstly,we explored the variation resources of four functional traits between tree species with different leaf habits(14 evergreen and 14 deciduous tree species,respectively).Then,the traits value of each species among each plot were divided into alpha and beta values by using trait gradient analysis.Beta trait is species' s position on the traits gradient,representing responses of species to environmental change.And alpha trait is the difference value of a species and community average trait,representing adaptive strategy of the coexistence to the same community environment.Through trait gradient analysis,the variation characteristics of different leaf habit species within and among communities were explored.The main results were showed as follow:1: The differences between interspecific and intraspecific variations of four functional traits were explored by using four functional traits:(SLA),leaf dry matter content(LDMC),leaf area(LA),and stem specific density(SSD)in subtropical evergreen and deciduous broad-leaved mixed forest in Hubei Xingdoushan National Nature Reserve.The results indicated that there were significantly differences in four functional traits between evergreen and deciduous trees.The SLA and LA of evergreen species were significant lower than deciduous species but LDMC and SSD show opposite patterns.Leaf habit was the main source(57.5%)for variation of SLA.The interspecific variability(66.8%)played more important roles than intraspecific variability(27.5%)in LA.The variation in LDMC was contributed relatively equally by interspecific(38.12%)and intraspecific(33.88%)variability.On the contrary,the variation in SSD was explained more by interspecific(51.5%)than intraspecific(32.5%)variability.The correlations of different functional traits on intraspecific level of both evergreen and deciduous trees were higher than those on interspecific level.2: The result of trait gradient analysis showed that alpha value range was greater than beta value for four functional traits of evergreen trees and deciduous tree species.Excepting for SSD,there existed differences for alpha value range for SLA,LDMC and LA between evergreen and deciduous tree species.Compared with the distribution of alpha value,trend of beta distribution was more consistent.There were no significant correlations in niche breadth and the average value of evergreen and deciduous trees species.The traits alpha values of evergreen and deciduous tree species and average trait value of species were significantly positively related,but there were no significant relationships between alpha and beta values.Most plot mean trait values,beta values and alpha values showed significant correlations,and the correlation coefficients of beta value of all traits showed the highest values.The tendencies were still consistent for beta value of different plant functional traits and the average species trait value,but the correlation was more apparent.Compared with plot mean trait values and beta value,the correlations between species mean traits value and alpha value were weaker.The species mean values and alpha values of SLA and LDMC were significantly correlated.However,the species mean values and alpha values of SSD showed significantly positive and negative correlation to LDMC and LA,respectively.