Taxonomy,Leaf Hair Function And Leaf Defense Strategy Of The Dove Tree

As a leaf surface structure,leaf trichome has multiple functions.Leaf trichome plays an important role in resisting herbivores,regulating water and the heat exchange of boundary layer of leaves,meanwhile,the leaf trichome is of great taxonomic value.The delimitation of species is an important basis for biological research,especially in the realms of conservation biology,but the concept of species boundary has been controversial.The mismatch between named species and observable phenotypes may endanger species protection.Thus,for species delimitation,the current paradigm holds that using multiple evidences is more accurate than using single evidence.Insect herbivory causes plant(especially rare and endangered plants)renewal restrictions or supplement bottlenecks.Leaf hair,as a physical defense trait of leaves,can significantly reduce the insect feeding of leaves.Therefore,it is is vital to comprehend the relationship between leaf trichomes and leaf defense strategies,especially for rare and endangered plants,insect herbivory and defense strategies may be closely related to the endangered mechanism of species.For D.involucrata,leaf hair not only plays an important role in the intraspecific delimitation of D.involucrata,but also is closely related to the leaf insect herbivory of D.involucrata species.In this study,we collected leaf samples of D.involucrata and D.involucrata var.vilmoriniana throughout their distribution areas in China.We detected Leaf hair density by electron microscope,and analyzed leaf morphology by geometric morphometric analysis(GMMs).We used whole-genome resequencing to identify genome-wide single-nucleotide polymorphisms(SNPs).We built the phylogenetic tree with Camptotheca acuminata as an out group speices and analyzed population genetic structure by SNP data.We used linear regression and redundancy analysis(RDA)to analyze the function of leaf hair and its relationship with environment.We measured the physical defense functional traits and the content of secondary metabolites in leaves.The physical-chemical anti-herbivore defence tradeoffs of leaf was examined.The results showed that:(1)Integrated taxonomy approaches coupled D.involucrata var.vilmoriniana from D.involucrata,suggesting that both are the same species.In this study,the leaf scanning electron microscopy experiments showed that there is an intermediate state in the leaf hair density of the two taxa.They were mixed in most sampling sites.We processed geometric morphology to analyze leaf morphology of the two taxa,and fully considered the symmetrical components and asymmetric components of leaves,as well as the allometric growth of leaves.The results indicated that the two taxa could not be distinguished by the shape of the leaf neither at the leaf level nor at the individual level.Therefore,we conclude that leaf hair density and leaf shape cannot be used as a morphological evidence for the delimitation of the two taxa.The phylogenetic analysis and population genetics analysis showed that the two taxa were a monophyletic group in the same sampling site,and they could not be distinguished.Three well-supported genetic clusters:West-Sichuan Basin populations,East-Sichuan Basin populations and Hengduan Mountains populations,were consistently inferred from the population genetics structure and phylogenetic tree.The leaf hair(or the density of leaf hair)was a variation between individuals and may be an adaptation of different individuals to their environment.With the results of morphological,molecular and community population ecology surveys,we believe that D.involucrate does not exist in this variant of D.involucrate var.vilmoriniana.In terms of delimitation,it is recommended to incorporate D.involucrata var.vilmoriniana into D.involucrate.(2)There was a significant negative correlation between leaf hair density and leaf insect herbivory rate of D.involucrata,that is,the leaf hairs of D.involucrata have the function of resisting the herbivory of phytophagous insects.The leaf hair density was significantly positively correlated with temperature,that is,the leaf hairs can improve the adaptability of D.involucrata leaves to tolerate high temperature.Environmental factors such as temperature,precipitation and soil nutrients have significant effects on leaf hair density.(3)The leaves of D.involucrata generally adopt defence syndromes,rather than physical-chemical defense traits.The defense strategy of Davidia involucrata leaves is between two extreme strategies: leaves with good physical-chemical defense;or leaves with poor physical-chemical defense.This defense strategy of D.involucrata verified the ’Plant Escape/Defense Continuum Hypothesis’.When leaves of D.involucrata respond to insect-herbivory pressure,the insect-herbivory leaves produced a physical-chemical defense strategy trade-off,compared with the intact leaves.The leaves of D.involucrata chose to enhance the chemical defense intensity and weaken the physical defense intensity.The physical-chemical defense trade-off and defense syndrome are not mutually exclusive.The defense strategy of D.involucrata leaves has the conversion of physical-chemical defense trade-off and defense syndrome between different research scales.In this study,D.involucrata was taken as the study species,and the leaf hair of D.involucrata was used as the clue throughout the full text to study the intraspecific classification,the function of leaf hair and the antiherbivore defense strategy of leaves.This study emphasizes the role of integrating species concepts and comprehensive delimitation methods in dealing with complex species classification.At the same time,it brings new insights into the insect defense strategy of rare and endangered plants,and provides a case for the study of plant-insect interaction.