Population Ecology And Genetic Diversity Of Pinus Dabeshanensis C.Y.Cheng & Y.W.Law,an Extremely Small Population

Pinus dabeshanensis C.Y.Cheng&Y.W.Law is a rare endangered species that is endemic to the Dabieshan Mountains of China.In this study,we focused on the species diversity and floristic analysis of community,population dynamics,intra-and inter-specific competition,transcriptome sequence and development of EST-SSR markers,genetic diversity of populations by the methods of plant population ecology and population genetics.These results provided some evidence for conservation and management of the endangered species.The main results were as follows:1 Features of species diversity and floristic analysis of P.dabeshanensis communityIn P.dabeshanensis community,there were 218 vascular plant species belonging to 141 genera of 72 families,among which there are 4 families,4 genera,6 species in Pteridophyte;3 families,3 genera,4 species in Gymnosperm and 65 families,134 genera,208 species in Angiosperm.Rosaceae,Lauraceae,Compositae,Ericaceae,Leguminosae and Gramineae were the dominant families in P.dabeshanensis community.The floristic analysis revealed that the flora was ancient and the geographical components were complex.Among 68 families,21,32 and 15 families belonged to cosmopolitan,tropical and temperate distribution,respectively.40 and 82 genera belonged to tropical with 32.79%and temperate distribution with 67.21%in the total,respectively.The measurement of Margalef?R?,Simpson?D?,Shannon-Wiener?H?and Pielou?E?indices on arbor,shrub and herb layers was carried out.In addition to the diversity index E,the other diversity indices of shrub layer were the highest,followed by arbor layer,and those of herb layer were the lowest.The value of E of shrub layer had the similarity with that of herb layer,both of which were higher than that of arbor layer.2 Population dynamics of P.dabeshanensisWe used spatial series substituting for time sery to analyze the population structure.And the time-specific life table,mortality rate,vanish rate as well as the four survival functional curve of the population were calculated,respectively.Additionally,spectral analysis was used to analyze the population dynamics.The results showed that P.dabeshanensis population was extremely small and population structure fluctuated.Although the seedlings were more abundant,young trees were very deficient,suggesting that the population was decreasing.The survival curve of the population followed a pattern between Deevey ? and Deevey ?,the curves of mortality rate and vanish rate exhibited a similar variation tendency:peak exsisted in the 5th age class period.Four survival functional curves showed that the population decreased rapidly at the early ages,grew stably at the intermediate ages and declined in the late lifespan.Spectral analysis of the population showed that the population dynamics had a clear periodic fluctuation in the growth except for the influence of fundamental wave.3 Intraspecific and interspecific competition of P.dabeshanensisThe intraspecific and interspecific competition was studied using Hegyi individual competitive indices?CI?model.The results showed that intraspecific and interspecific competition intensity of P.dabeshanesis accounted for 17.11%and 82.89%in the total competition intensity,respectively,indicating a remarkable effect of the interspecific competition.The intraspecific competition mainly came from the roles of Quercus serrata var.brevipetiolata,Pinus taiwanensis,Rhododendron mariesii and Castanea seguinii.Notably,the competition intensity of P.dabeshanesis decreased inversely to diameter of the breast height?DBH?,which showed a stronger competition at DBH of<25 cm and appeared weaker at DBH over 25 cm.The relationship between the whole forest competition intensity and DBH of the target tree followed the power function?CI=AD-B?.4 Population fecundity of P.dabeshanensisThrough our investigations,we found that the percentages of abortive seeds were 61.08%and 89.88%,the viability percentages of full seeds were 100%and 89.76%from the natural population and cultivated population,respectively.Lower temperature was appropriate for the preservation of seed viability.Seeds could germinate in a wide range of temperatures and the final germination percentage of seeds storaged under room temperature was higher than that at 4?.Moreover,the germination percentage of seeds from natural population was higher than that from the cultivated one.Scarifying seed coat promoted the water absorption of seeds while had non-significant promotion in rate of germination.5 Transcriptome sequence and development of EST-SSR markersUsing Illumina HiSeq^TM 2000 sequencing platform and de novo assembly,a total of 1,966 expressed sequence tag-simple sequence repeats?EST-SSRs?derived from unigenes obtained,with an average distribution density of one EST-SSR locus per 23.08 kilobases?kb?.The most abundant repeat motif was trinucleotide?41.6%?,followed by dinucleotide?23.25%?,mononucleotide?21.41%?,hexanucleotide?7.83%?,pentanucleotide?4.43%?and tetranucleotide repeats?1.53%?.The top tri-and di-nucleotide motif was AGC/CTG and AT/AT,respectively.After randomly selecting 82 from 431 for further validation,19 could reliably amplify polymorphic bands from 24 individuals of P.dabeshanensis.A total of 57 alleles were identified,with an average of 3.0 alleles per locus.The observed and expected heterozygosity per locus ranged from 0 to 0.958 and 0.082 to 0.759,respectively.PIC value ranged from 0.077 to 0.707,with an average of 0.380.6 Genetic diversity and structure of P.dabeshanensisA total of 50 alleles were identified across 233 individuals,with an average of 3.85 alleles per locus.Our results revealed that intermediate level of genetic diversity?H_E=0.458 vs.H_E=0.423?among natural and conserved populations and low genetic differentiation(F_ST=0.028)between populations.Both contemporary and historical migration rates among populations were high.Bayesian coalescent-based analyses suggested that 3 populations underwent reductions in population size ca.10,000 yr ago.Using BOTTLENECK software based on two models of TPM and SMM,two natural populations might have experienced recent genetic bottleneck effect under the TPM model.Bayesian clustering revealed that individuals from the natural populations and the conserved one were divided into two groups?K=2?,the conserved population was gathered into one gene pool while the natural ones were assigned to two.Additionally,our results identified private alleles in the natural populations but not in the ex situ population,suggesting that the ex situ conserved population insufficiently represents the genetic diversity present in the species.Past decline in population size is likely to be due to Holocene climate change.7 Endangered mechanism and conservation strategiesAccording to our aforementioned researches,the major endangered mechanisms for P.dabeshanensis may be as follows:1)The low percentage of seed setting and high percentage of abortive seeds resulted in lower fertility;2)High seedlings death rate and deficient young trees accelerated the population degeneration;3)The weak interspecific competition compelled population standing at a disadvantage;4)Small population effect resulted in severe inbreeding depression which attenuated the risk-resisting capabilities.As a result,we propose here the following conservation strategies:1)Adopting appropriate artificial disturbance including logging woods for the seedlings and young tree's growth,and to reduce the competition;2)Utilizing artificial pollination in order to improve the seed quality;3)Conserving the three DWG populations,especially those individuals harboring private alleles so as to preserve the genetic diversity;4)Collecting seeds,especially from DWG1,DWG3 populations and those individuals with private alleles,for seedlings recruitment that might be an effective way to increase the population size.