Effects Of Climate And Phylogeny On Plant Leaf Functional Traits And Community Assembly Mechanism In Forests In Southwest China

Leaf is the organ of plant photosynthesis and transpiration,it is useful for us to understand the strategies of plants in adaptation to environment and resource utilization by exploring the influencing factors of leaf functional traits and the correlations between traits.In this study,35 plots were set up in the typical forests in Southwest China(Wolong in Sichuan Province,Ailao Mountain in Yunnan Province).We measured four leaf functional traits(SLA: Specific leaf area;TC: Total carbon concentration;TN: Total nitrogen concentration;C:N: Leaf carbon-nitrogen ratio).This study mainly focused these following questions:(1)The correlations among leaf functional traits,the changes in leaf functional traits along a latitude gradient,and the relative contributions of climate,species characteristics(plant life form and phylogenetic group)to the leaf functional traits;(2)The effects of phylogenetic relationship on leaf functional traits and relationships among traits;(3)The changes of community phylogenetic structure along a climate(altitude)gradient,the influence of habitat filtration and interspecific competition on the community assembly.The main results were summarized as follows:(1)Leaf functional traits had significant changes in climatic gradients,Wolong had a higher latitude,plants living here with high leaf SLA and TN concentration,low leaf TC concentration and C:N;however Ailao Mountain had a lower latitude,plants living here with low leaf SLA and TN concentration,high leaf TC concentration and C:N.Climatic and environmental factors and species characteristics had significant effects on leaf functional traits,but leaf SLA and leaf TC concentration were mainly affected by species characteristics(41.16%-68.82%);while leaf TN concentration and leaf C:N were mainly affected by climatic and environmental factors(43.42%-44.77%).The explanatory power of climatic and environmental factors in leaf functional traits was small(0.38%-3.31%),however the explanatory power of species characteristics was strong(29.11%-68.82%).The commonly explained parts of climatic and environmental factors and species characteristics also had a greater influence on plant functional traits(14.15%-44.74%).The results of the overall and local analysis(Wolong and Ailao Mountain)of the leaf functional traits in Southwest China showed that those traits have relatively consistent correlations.However,plants in Wolong tended to adopt acquisitive strategies to increase production rate,while plants in Ailao Mountain tended to adopt conservative strategies that can better protect themselves,meanwhile there were some differences between these two strategies.(2)The four leaf functional traits(SLA,TN concentration,TC concentration,C:N)were significantly affected by phylogenetic relationships,this suggested that leaf functional traits were more similar for species with closer affinity.After excluding the influences of phylogeny,the correlations between SLA and other leaf functional traits became no longer significant,while there was still a significant correlation between leaf element concentration and C:N.Our study indicated that there may be a co-evolution between leaf element concentration and C:N;the correlations between SLA and other traits were greatly affected by phylogenetic relationships,and divergence events in the early stage of ancestral species differentiation may be one of the possible reasons.Ancestral characteristics reconstruction indicated that when the ancestral species in Southwest China differentiated to form species in Wolong and Ailao Mountain,the former showed an increase in SLA and TN concentration,however the TC concentration and C:N decreased;the latter showed an increase in TC concentration and C:N,however the SLA and TN concentration decreased.(3)The trend of phylogenetic index with altitude was significantly affected by climate.In low altitude region of Wolong,the divergence degree of community phylogenetic structure decreased as the altitude increased.However,with changes in the altitude gradient from low to high in Ailao mountain,the community phylogenetic structure shifted from phylogenetically overdispersed to phylogenetically clustered.In low altitude region of Wolong and Ailao mountain,interspecific competition was the main driving factor for community assembly,habitat filtering was the driving force for community assembly in high altitude region of Ailao mountain.The process of community assembly in middle and high altitude region of Wolong and the middle altitude region of Ailao mountain were more complicated and its phylogenetic index may be the result of several mechanisms working together.In addition,the same community assembly mechanism(abiotic assembly or biotic assembly)has different effects on species in different regions and environmental conditions.Southwest China is one of the most important biodiversity centers in China,with a complex and diverse species composition.According to the results of this paper,when conducting research on plant traits in this area,it is necessary to comprehensively consider climate,phylogenetic relationships,and community assembly mechanisms,which is helpful to explore the differences in plant functional traits and related adaptation strategies in Southwest China under climate change.