| Celtis sinensis Pers.,a deciduous tree belongs to the genus Celtis within the eudicot family Cannabaceae sensu.Celtis sinensisis not only a typical native tree species in East China,but also a typical pioneer tree species in the process of community succession of mountain plantation,which plays an important role in the succession and restoration of zonal vegetation community.it is often found on hillsides,forest edges,villages,roadsides and courtyards,and is used as garden ornamental plants and street trees.In this study,Celtis sinensis was selected as the research object,and the whole genome of Celtis sinensis was sequenced by Illumina Hi Seq TM Xten sequencing platform to assemble the complete chloroplast genome of Celtis sinensis.At the same time,population genetics of 13 Celtis sinensis populations(426 plants)were studied based on 10 nuclear microsatellite markers((Nuclear Microsatellite,n SSR)),including limestone mountain area of Xuzhou City,Jiangsu Province,Huangzangyu Provincial Nature Reserve of Anhui Province and three villages around Xuzhou City.On the one hand,the purpose of this study is to explore the dynamic changes of genetic structure in the process of population succession through the dynamic changes of genetic diversity of pioneer tree species in different succession stages of Platycladus orientalis plantation in Xuzhou limestone mountain area.On the other hand,the influence of human activities such as urbanization on the genetic diversity of native plants was analyzed and evaluated,and the corresponding suggestions for the protection of native tree species in rural ecological construction were put forward.The main results are as follows:(1)The chloroplast genome of C.sinensis was 159,092 bp long and displayed a typical quadripartite structure consisting of a pair of inverted repeats with a length of26,895 bp and separating by two single-copy regions(LSC,86,085 bp and SSC,19,217 bp).Besides,the chloroplast genome of C.sinensis totally contained 131genes,including 87 protein coding genes,36 transfer RNAs and eight ribosomal RNAs.(2)A total of 205 alleles were amplified from 10 microsatellite loci in 13populations,and the number of alleles at each locus(N_A)ranged from 11 to 43,with an average of 20.60.The observed heterozygosity(H_O)of each locus ranged from90.101 to 0.791 with an average of 0.561,the expected heterozygosity(H_E)ranged from 0.140 to 0.945 with an average of 0.661,the genetic diversity(H_S)within populations ranged from 0.099 to 0.844 with an average of 0.600,and the(H_T)of genetic diversity among populations ranged from 0.136 to 0.950 with an average of0.662.The information index of polymorphic loci(PIC)ranges from 0.138 to 0.941,with an average of 0.638.(3)The genetic diversity of 13 C.sinensis wild populations was high,of which in Gengji village had the highest genetic diversity(A_R=8.729,Ho=0.633,H_E=0.581),and the genetic diversity of population in Yeyao village was the lowest(A_R=5.664,Ho=0.450,H_E=0.552).According to the order of the age of Platycladus orientalis plantation in limestone mountain area:Taishan(1950s),Quanshan(1960s),Lali Mountain(1970s)and Moshan(1980s),the genetic diversity of each C.sinensis population decreased in turn,and the difference of genetic diversity among populations was significant(P<0.05).The above results show that in the process of plantation succession,the gradual increase of habitat heterogeneity in the community reduces the species selection pressure.Furthermore,it provides more space and resources for the growth of C.sinensis under the forest.In the process of succession from coniferous forest to deciduous broad-leaved forest in Xuzhou area,the genetic diversity of C.sinensis population increased at first and then decreased,and the genetic diversity of two populations(LLSM and QSM)in coniferous and broad-leaved mixed forest was the highest.The results showed that the change of genetic diversity was consistent with the community dynamic characteristics of pioneer tree species.The genetic diversity of C.sinensis(native tree species)in rural areas around Xuzhou was negatively correlated with the degree of rural urbanization and gardening,and there was significant difference(P<0.05).The genetic diversity of C.sinensis population on the natural forest edge of Huangzangyu was higher than that of the gap population,and the difference was significant(P<0.05).To sum up,we suggest that in the process of beautiful rural construction,it is necessary to retain native tree species as far as possible and maintain their genetic diversity,and the introduction of different provenances will also improve the genetic diversity of C.sinensis.Among them,the two C.sinensis populations on the forest edge of Gengji Village and Huangzangyu have high genetic diversity,indicating that they have high protection value of genetic resources.(4)13 C.sinensis populations were clustered into two genetic lineages,of which2 populations in Anhui Huangzangyu Nature Reserve and Taishan population in limestone mountain area of Xuzhou belonged to the same branch,and the other 10populations belonged to another branch.Among them,the genetic distance of Gengji village population is close to that of the previous branch,and it is speculated that there is artificial introduction in its population.The coefficient of genetic variation((FST))of C.sinensis was 0.1289,which indicated that there was moderate genetic differentiation among populations.0.2%of the total genetic variation of C.sinensis population existed between groups,12.69%among populations and 87.11%within populations(P<0.001). |
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