Variation Of Leaf Trait Network Among Different Vegetation Types And Its Influencing Factors

Plant functional traits refer to the measurable properties of plants after long-term adaptation to the external environment and evolution,and are closely related to plant growth,reproduction and survival functions,such as chlorophyll content,leaf nitrogen content,specific leaf area,etc.Plant functional traits do not exist independently,and the interdependence of multiple traits allows plants to perform multiple functions,however most studies only focused on single trait or paired trait-trait correlations,which hinders our overall understanding of plant adaptation strategies.Unfortunately,there are no existing methods that can reveal the complex relationship of multiple traits,so it urgent to establish a new theoretical system and method to explore the complex relationship between multiple traits.Therefore,this study first proposed plant trait network(PTN)to answer above questions,and took leaf trait network(LTN)as case studies to shed light on the potential applications of PTN.The main results are as follow:We successfully applied network analysis to the study of plant functional traits,and put forward the construction method of PTN: traits are presented as nodes and bivariate trait relationships are presented as edges in PTN.Network parameters were used to quantify the complex relationship among multiple traits.PTN with shorter diameter,average path length and higher edge density means that close relationship among multiple traits,plants with such PTN denoted higher functional efficiency.PTN with higher modularity and average clustering coefficient means that groupuscule of specific traits is more obvious,denoting the differentiation of plant traits into different functional modules.Network-node parameters were used to identify the topology of traits in PTN,such as traits with more connection with others indicates its “degree” are higher,and the environmental selection of these traits might impact the whole phenotype,and traits with a higher betweenness serve as brokers.Traits with higher degree and betweenness are“hub”traits.We systematically measured 34 leaf traits of 394 tree species in nine forest communities from tropical to cold-temperate zones in China.The spatial variation of leaf trait network and its influencing factors were explored based on systematic measured trait data at a large scale.and established leaf trait networks at each site.The results show that the diameter,average path length,and average clustering coefficient of LTN appear to decrease with increasing temperature and precipitation.This means that in colder temperate forests with lower temperatures,plants enhance the ability to coordinate between specific traits to aggregate into small functional groups,and fewer connections between small groups results in a looser network as a whole.Thus,it reveals the spatial response mechanism of the plant trait network.In addition,traits related to leaf thickness and leaf economic traits are central traits in the leaf trait network.As hypothesized,economic traits,e.g.,nitrogen,chlorophyll concentrations,and specific leaf area,have a higher degree of connectivity to other traits,and anatomical traits are main mediators.We also established LTNs using six leaf economic traits to reveal the different adaptation strategies of different types of plants.We found that the traits of broad-leaved trees had tighter trait relationships than those of conifers;thus,broad-leaved trees are more efficient,explaining why angiosperms dominate the planet.The traits of shrubs had a tighter relationship than trees because shrubs require multiple traits to co-operate efficiently to perform multiple functions for thriving in limited light.Furthermore,leaf nitrogen and life span had the highest centrality in LTNs;consequently,the environmental selection of these two traits might impact the whole phenotype.This study uses the method of plant trait network to visualize and quantify the complex relationship among plant multiple traits,which provides a new idea and method for the study of plant multiple traits.At the same time,through the differences and influencing factors of the leaf trait network at the spatial scale and different plant types,it provides a case for the study of the plant trait network.However,this study is only a preliminary exploration of leaf trait networks,and further research is needed in the future.