Adaptive Mechanism Of Elevations And Acid Environment Of Rhododendron In Southwestern Mountains,China

The change patterns of environmental factors(climate and soil factors)along the elevation gradients not only provide living environments for plants at the spatial scales,but also represent climate change at the temporal level.Therefore,the research for adaptation mechanism of alpine plants to elevations will provide the scietifical basis for its effective conservation and management under global climate.Rhododendron species,which have irreplaceable economic and ecological values,are dominant components of alpine and sub-alpine vegetation to maintain and preserve biodiversity,ecological security,and ecosystems function.And,the Rhododendron species perform to grow on the acid soil conditions.Furthermore,Rhododendron species have a large range of elevation distributions which making it is an excellent model-group to explore the mechanism of perennial woody species’ continuous adaptative to elevation gradients.In the present study,phenotypic traits(physiological,biochemical,and functional traits),environmental factors,and transcriptome were compared and analised to explore the adaptative mechanism and response to environmental changes of Rhododendron.The main results and conclusions are summarized as follows:1.The variation of phenotypic traits and its driving factors along elevations of Rhododendron speciesThe variation of phenotypic traits of 17 Rhododendron species along elevations and its driving factors were investigated by 20 phenotypic traits of leaf and 8 climate and soil factors.As a result,the SLA and LW were decreased along elevations.Conversely,the content of LMA,LDMC,C,N,P were increased along elevations.The content of NSC,chlorophyll,carotenoid,and phenolic substance were increased along elevation.These results suggest that the phenotypic traits were adjusted through resource tradeoffs to adapt to environmental changes along elevations.In addition,phylogenetic signal analysis showed that the most phenotypic traits of Rhododendron had not significantly phylogenetic signal.However,the variations phenotypic traits of Rhododendron along elevations were presented obvious interspecific variance by mixed effect model,and affected by phylogentic relationships.The temperature,precipitation,and UV are important environmental factors to affect variation of phenotypic traits along elevations of Rhododendron.In summary,the variations of physiological,biochemical and functional traits response to environment changes along elevations of Rhododendron were affected by climate factors(temperature,precipitation,UV),interspecific differences and phylogenetic relationships.2.The molecular basis of Rhododendron species adapts to environment changes along elevation gradientsIn this study,two Rhododendron species(R.decorum and R.rubiginosum),which are distributed along widely elevations,were sampled in the field at three elevations.Based on the data of phenotypic traits,transcriptome,and environment factors,the adaptation molecular mechanism of Rhododendron species along elevation gradients in the wild parents and F1 progeny were investigated by common garden and transcriptome sequencing.The results showed that the changes of phenotypic traits along elevation gradients were presented obvious interspecific variance among R.decorum and R.rubiginosum.Specifically,the change trends of chlorophyll and carotinoids along elevation gradients were similar between wild parents and F1 progeny of R.decorum,conversely,the change trends of phenotypic traits were unobserved of R.rubiginosum.The multidimensional scaling analysis showed that genes involved in energy,carbohydrate,amino acid,and lipid metabolism pathways have plasticity capacity for adaptation to the changes of continuous elevations in the natural environment.The pathways of flavone and flavonol biosynthesis,anthocyanin biosynthesis,and homologous recombination are essential for adaptation to UV radiation changes.Soil fertility and pH could regulate gene expression of plant-pathogen interaction to improve defense ability of R.decorum and R.rubiginosum.In F1 progeny,the pathways of phenylpropanoid and brassinosteroid biosynthesis,starch and sucrose metabolism,anthocyanin biosynthesis,flavonoid biosynthesis,plant-pathogen interaction,and DNA repair were mirrored from wild parents,indicating transgenerational plasticity could rapidly response to environmental changes.The present study manifested that transgenerational plasticity provide an opportunity to explore the reponse to environment change of Rhododendron species under climate change scenarios.3.The molecular basis of Rhododendron species response to acid environmentIn the present study,three species(R.protistum var.giganteum,R.griersonianum,R.decorum)were selected to preform different pH experiments.The molecular mechanism of Rhododendron species response to external pH changes were investigated by transcriptome sequencing.The results showed that genes of flavonoids and isoflavonoid biosynthesis,glutathione metabolism,and amino acid metabolism were common significantly enriched in R.protistum var.giganteum,R.griersonianum,and R.decorum.Meanwhile,the genes involved in pathways of photosynthetic processes were regulated to improve capacities of light absorption,electron transfer efficiency,and carbon assimilation to response to pH changes of R.protistum var.giganteum and R.griersonianum.The genes involved in lignin synthetic processes were regulated to modify secondary structure and function of cell wall to response to different pH of R.protistum var.giganteum and R.decorum.Additionally,the genes of alpha-Linolenic acid were regulated to involve in jasmonic acid synthesis of R.protistum var.giganteum under different pH conditions.The Homologous recombination could repair DNA damage result from high pH values,and it is important biological process to response to high pH conditions of R.griersonianum.Meanwhile,the pathways of brassinosteroid and carotenoid biosynthesis which involved in osmotic balance and photooxidation protection could also participate the species’ response to different pH conditions.In addition,the pathway of galactose metabolism may play an important role in R.decorum to response to different pH conditions.