Mechanism Of Habitat Selection On A Homoploid Hybrid Pinus Densata And Its Parental Species From A Reciprocal Transplant Experiment

Pinus densata originated from natural homoploid hybridization from Pinus tabuliformis and Pinus yunnanensis,and molecular study have provided its gentic path.P.densata is one of the most important documented cases for studying the origin of homoploid hybridization of species.P.densata formed a large area of pure forest in the high-altitude habitat of Tibet Plateau,and its habitat characteristics was significant variations with its parental species.Therefore,adaptive differentiation was considered to be the main driving force for the hybridization of P.densata.but this hypothesis still lacks experimental evidence.In the theory of homoploid hybridization origin of P.densata,what is the biological genetic basis of the adaptive evolution of P.densata in a special habitat?Is it possible that P.densata has a certain degree of fitness in parents habitat?Does habitat selection will promote the morphological and physiological characteristics of preserved populations has similar performance or trends with native species?It is still an important issue that needs to be solved urgentlyIn this study,we conducted a transplant experiment in habitat of P.densata,P.tabuliformis and P.yunnanensis with geographic populations from P.densata,P.tabuliformis and P.yunnanensi.s.By comparing adaptive divergence and selection effect of pine species in different habitats,and assessing the variation of photosynthesis traits,morphological traits and electrical impedance among the species and populations,we expected to find the main factors in adaptive divergence among P.densata and parental species,to explained mechanism affected the adaptation of the pine species,and to provided experimental evidence and information for adaptive variation and evolution of species(1)P.densata and its parent species,P.tabuliformis and P.yunnanensis had significant adaptive differentiation.In different habitats,in situ tree species had an adaptive advantage over the other two species.The habitat of P.yunnanensis had a smaller selection pressure to pine species,but the habitat of P.tabuliformis and P.densata had a greater selection pressure to pine species.The adaptive divergence of three pine species in different habitats was genetically affected by the environmental factors,genetic variation and genetic X environment effects.(2)Significant genetic variation and species specificity were found in P.tabuliformis and P.yunnanensis.P.densata had a large variation of needle morphological and anatomical traits,showing the characteristics of hybrid origin.Needle morphological and anatomical traits variation had influenced by genetic variation,environmental factors,genetic X environment effects in differentiation habitats.It would provide a useful reference for understanding the sources of needle phenotypic variation.(3)Significant differentiation in Pn(net photosynthesis rate),Ci(intercellular CO2 concentration)and Ls(transpiration and stomatal limitation)were observed among and within species in different habitats.The most of values in P.densata were between parental species,a few traits showed transgressive heterosis.The values of P.densata was similar to P.tabuliformis values,while showed differentiation with P.yunnanensis values.(4)Significant differentiation in the electric impedance were found among P.densata,P.tabuliformis and P.yunnanensis.Most of electric impendance of three pine species had the similar trend in different habitats,and electrical impedance of P.densata was between parental species.(5)In different habitats,photosynthesis traits and needle morphological and anatomical traits showed significant correlation,which net photosynthetic rate,stomatal conductance and transpiration rate were related to stomatal traits,section traits,resin canal and vascular bundle.The results indicated that variation of needle traits could reflect the photosynthetic physiological diversity among geographical populations.The number of needle stomata and regulation capacity of stomata would increase with the decreased precipitation,and the change of the number of resin canals mesophyll area.(6)Most of electrical impendence were positively correlated with the morphological traits in low current frequency.With the increase of the current frequency,most of electrical impendence gradually became negatively correlated with the morphological traits.After removing of the position effect,the net photosynthetic rate,transpiration showed a positive correlation with stomatal traits,the needle thickness traits and vascular bundle traits,while showed a negative correlation with resin canal traits.Stomatal conductance and intercellular CO2 concentration were negatively correlated with most of the needle morphological and anatomical traits.The water use efficiency was positively correlated with most of the needle morphological and anatomical traits.This study showed genetic and adaptive variation of species or populations from photosynthesis,water use efficiency,electrical impedance and morphological traits,revealed the biological genetic basis of hybrid evolution under specific habitats,elucidated the adaptability and genetic variation among P.densata,P.tabuliformis and P.yunnanensis populations in different habitats,analyzed the main roles of natural selection among P.densata,P.tabuliformis and P.yunnanensis populations,and veri fied the values of electrical impedance parameters in plant adaptation study.It provided an experimental evidence for the theory of homoploid hybrid speciation of P.densata,and provided a new reference and ideas for germplasm conservation and genetic improvement of pine species.