Genetic Diversity And Population Ecology Of Salix Taishanensis C.Wang & C.F.Fang

Salix taishanensis C.Wang&C.F.Fang is a speculiar plant in China.It is distributed in the warm and temperate high-altitude mountainous regions of China in isolation.Salix taishanensis is highly ornamental and has gardening development value.Based on the wild investigation of S.taishanensis,through field investigations and laboratory experiments,we conducted a comprehensive study on the survival status,genetic diversity and genetic structure,community characteristics,population structure and dynamics,and intra-and inter-species competition of S.taishanensis aim to reveal the genetic diversity level and distribution of genetic variation among wild populations of S.taishanensis,and by analyzing the survival status of S.taishanensis in the endangered state of Mount Tai area,we clarified its threatened factors,which can provide scientific basis for the protection of S.taishanensis in Mount Tai area.The main findings and conclusions are as follows:1 Genetic diversity and population structure of S.taishanensis based on CDDP.By using conserved DNA-derived polymorphism markers?CDDP?technique,this paper studied the genetic diversity and population structure of four populations of S.taishanensis.The results showed that a total of 128 discernible loci were obtained from 115 individuals using13 primers,and 73.44%of the loci were polymorphic.Nei's genetic diversity index?H?was0.2227 and Shannons diversity index?I?was 0.3505,indicating the genetic diversity of S.taishanensis was at a low level.At the population level,the percentage of polymorphic loci?PPL?averaged 53.71%,the Nei's genetic diversity index?H?averaged 0.1932,and the Shannon information index?I?averaged 0.2864.The highest level of genetic diversity was in the PQG population?PPL=58.59%,H_e=0.2040 I=0.3044?,while the lowest was in the MT population?PPL=49.22%,He=0.1808,I=0.2680?.Analysis of molecular variation?AMOVA?showed that there was significant genetic differentiation within and between populations?P<0.001?,of which 79.71%of the variation existed among the populations,and 20.29%existed within the populations.Genetic variation analysis showed that the coefficient of gene differentiation is0.1723 and the gene flow is 2.4014 among populations.The results of Mantel test and cluster analysis showed that there was no significant correlation between genetic distance and geographic distance between populations?r=-0.3189,P=0.7083?.According to structure and Principal coordinates analysis?PCoA?,115 individuals could be divided into four genetic clusters,which were significantly correlated with geographic distribution.2 Analysis on characteristics of S.taishanensis communityThe species composition,vertical structure and species diversity of S.taishanensis community in Mount Tai were analyzed by using the method of community ecology.The results showed that there were 84 vascular plant species in the community belonging to 43 families and 65 genera,in which,the families containing monotypic genus were more.The important values of Pinus tabuliformis and Sorbus pohuashanensis in arbor layer of this community were relatively high,which were 58.94%and 31.67%,respectively.While those of S.taishanensis and Rubus crataegifolius in shrublayer were relatively high,which were 19.87%and 19.21%,respectively.While those of Phlomis umbrosa and Carex lanceolata in herbaleous layer were relatively high,which were 27.75%and 10.95%,respectively.The Margalef index,Shannon-Wiener index,Simpson index and Pielou index of species diversity in S.taishanensis community were all showed the pattern of herbaleous layer>shrub layer>arbor layer.The four indices in various plots showed significant differences.In general,the species diversity of S.taishanensis community was low and the community stability was poor.It was suggested to strengthen the monitoring and management of its habitat to promote the renewal and stable growth of S.taishanensis population.3 Population structure and dynamic characteristics of S.taishanensisBased on the field investigation of S.taishanensis population on Mount Tai,the population development trend of S.taishanensis was analyzed from the population size structure,static life table,survival analysis function and time series prediction model.The results showed that there were few individual seedlings in the existing population of S.taishanensis population,the population structure was atypical bell-shaped with a narrow base,and the population survival curve tended to Deevey-?,indicating that the population was relatively stable.The mortality?q_x?and disappearance rate?K_x?curves show peaks in the third diameter stage,which indicates that there was a certain bottleneck effect in the development of S.taishanensis from the third diameter stage to the fourth diameter.The survival function indicates that the life state of S.taishanensis population fluctuated in the early stage and was relatively stable in the later stage.The time series forecast of the population for the next two and four years shows that the population of S.taishanensis will have a slight upward trend,but due to insufficient seedling reserves,maintaining the existing habitat is difficult to guarantee the stable and continuous growth of the S.taishanensis population.4 Intraspecific and interspecific competition of S.taishanensisThe intraspecific and interspecific competition intensities of the shrub plant,S.taishanensis,were analyzed using Hegyi's single-tree competition index model and integrated basal diameter?BD?instead of diameter at breast height?DBH?.The intraspecific and interspecific competition intensity of S.taishanensis accounted for 35.01%and 64.99%of the total competition intensity?86.11?,respectively,indicating that interspecific competition had a larger effect.The competition intensity of S.taishanensis gradually increased along with BD.There were nine main species of tree that exerted a competitive influence on S.taishanensis.For those nine species,the competition intensity of intraspecific and interspecific competition with S.taishanensis were ranked in the following order:S.taishanensis>Sorbus pohuashanensis>Tilia amurensis>Pinus tabuliformis>Forsythia suspensa>Malus hupehensis>Viburnum opulus var.calvescens>Lonicera chrysantha>Syringa pubescens.The relationship of the BD of objective trees and the competition intensity between competitive trees and objective trees in the whole forest and other competitive trees nearly conformed to the power function(I_C=AB^–K).According to the prediction of the model,when the BD of S.taishanensis reached 10 cm,the competition intensity tended to be stable.S.taishanensis trees whose BD was less than 10 cm,were under strong competition pressure,while for individuals whose BD was less than 10 cm,some of the surrounding competitive trees could be removed to give them enough living space,and thereby conserve the species.5 S.taishanensis conservation strategies in Mount Tai areaBased on the results of the above studies,the main reasons for S.taishanensis population difficult to regenerate naturally were:1)The level of genetic diversity of S.taishanensis was low,and small population effect resulted in sever inbreeding depression;2)The dominant position of the population in the community was not obvious,and the generation of seedlings was difficult?low seed setting rate,poor seedling growth conditions,etc.?;3)the habitat conditions were poor and the S.taishanensis population had weak competitiveness.4)The habitat of S.taishanensis will be severely disturbed by humans?tourism hotspot development zone?,which hinders the effective expansion of the population and further exacerbates endangered trend of the population.Therefore,the following suggestions are put forward in population protection strategies:1)adopt genetic rescue methods to promote gene communication between populations;2)protect the original habitat of the population and strengthen artificial management;3)artificially breed bell seedlings and perform field regression;...