The Ecophysiological Mechanisms Of Ecological Divergence Of Homoploid Hybrid Species Picea Purpurea

Homoploid hybrid speciation,characterized by hybrid speciation without a change in chromosome number,is well known in angiosperms but rare in gymnosperms.The generation of ecological divergence between the hybrid species and its progenitors is the precondition of this kind of speciation,and the production of transgressive phenotypes within the hybrids has play an important role.Molecular evidence demonstrated that Picea purpurea originated from the homoploid hybridization between P.likiangensis and P.wilsonii and it is distributed in northeastern Qinghai-Tibet Plateau at higher altitudes and latitudes than its parental species.High altitude regions are usually characterized by low air temperature and atmospheric CO₂concentrations,as well as strong solar radiation with a large fraction of shortwave radiation compare to the low altitude.Generally,plants were suffering from the occurrence of cell dehydration and xylem embolism induced by freezing-stress in winter,whereas the gas exchange and stomatal development were affected by the low atmospheric CO₂ concentrations and shortwave radiation.So far,researches on whether these ecophysiological traits had been transgressive segregation in the hybrid species and thus promoted it occupy the novel extreme habitat were still lack.In this paper,we analyzed the environmental divergence between the homoploid hybrid species P.purpurea and its progenitors,and predicted the change of their potential distribution under climate change.Besides,we also compared the frost tolerance of photosystem stability,water relations,xylem resistance to dysfunction of leaves?current-year twigs?and stems?annual shoots?,leaf gas exchange properties at two level of CO₂ concentration(C_a:200 and 400?mol mol^-1),light responsive curves of photosynthesis under three light qualities?blue,red,red&blue?and stomatal anatomical for three Picea species with the aim of reveal the mechanisms of P.purpurea colonized the novel extreme habitat on the basis of ecophysiology.The main results were listed below:?1?The results of ecological divergence indicated that the water and heat availability for P.purpurea were all significantly different from its parental species.That is,despite of the precipitation of coldest and warmest quarter of P.purpurea was intermediate between its progenitors,its soil moisture was significantly higher than them;the min temperature of coldest month of P.purpurea was significantly lower than that of its parental species,and the ground-frost frequency of P.purpurea was inversely higher than that of its progenitors.Furthermore,results from simulation-based estimates revealed that the potential distribution area for P.purpurea would decrease?about 5%?in the 2080s only under RCP2.6,while in the 2050s of this scenario and under other two scenarios,its distributional area in two time periods were higher than the current.?2?The results of water physiological showed that P.purpurea had significantly lower osmotic potential at full turgor,water potential at turgor loss point,water potential at 12%loss of conductance of stem and the maximum hydraulic conductance of stem than its parental species.In contrast,the leaf and stem xylem pressure inducing 50%loss of hydraulic conductivity(leaf?₅₀and stem?₅₀,respectively)and hydraulic safety margin in leaf?₅₀,stem?₅₀ in P.purpurea showed no significant difference with those of P.wilsonii,but significantly larger values than those of P.likiangensis.The freezing temperature response experiment indicated that the temperature causing a 50%reduction in initial F_v/F_m of P.purpurea was apparently lower than that of its parental species.As for the results of photosynthesis responsive curves under different light qualities,P.purpurea was demonstrated that quantum yield of CO₂ assimilation???and maximum CO₂ assimilation rate(A_max)were higher than its progenitors under blue and red light.P.purpurea also exhibited higher stomatal conductance at low CO₂ concentrations and instantaneous water use efficiency under all light qualities,have greater leaf pigments content,longer guard cell length and lower linear stomatal density relative to its progenitors.In summary,this paper demonstrated the environmental divergence between the homoploid hybrid species P.purpurea and its parental species:i.e.the higher soil moisture and the low temperature in the winter were the key factors that driving the ecological divergence in P.purpurea from its progenitors and the potential distribution area of P.purpurea would significantly increase in the 2050s and 2080s.This suggested that P.purpurea would play an important role in the ecological security barrier in the future.The results of ecophysiological and morphological research indicated that the frost tolerance of photosystem stability,cell dehydration tolerance,gas exchange properties under different light qualities and low CO₂ concentration and stomatal anatomical characters in P.purpuea were superior to its parental species.These traits may enhance the physiological fitness of P.purpurea and facilitated its colonization and successful establishment to alpine habitats.