| Sinocalycanthus chinensis Cheng et S.Y. Chang, the only representative in the genus Sinocalycanthus in the family Calycanthaceae, is an endangered deciduous shrubs and mainly distributed in Lin'an City and Tian'tai County, Zhejiang Province, China. As a relic species from the tertiary, S. chinensis with limited wild resources is recorded as protection plant at the national second class. S. chinensis is of high ornamental value and of high medicinal value, moreover, it is in unique classification status and in narrow distribution area. But the natural environment where S. chinensis inhabits is severely damaged, and it is a threat to the survival and multiply, therefore, the endangered process, status, mechanism need urgently to be explored in order to protect the relic species better. Using ISSR and cpSSR molecular markers, the genetic structure and molecular phylogeography of S. chinensis were analyzed and the endangered mechanism was explored. The study aimed at providing scientific and practical protection strategy for the endangered speices. Results showed as follows:1,Genetic structure of five populations of S. chinensis in Daming Mountain was analyzed by ISSR. Genetic diversity at species level was relative high, while that was relative low at population level, moreover, genetic differentiation among populations was significant (Gst = 0.4107). It was indicated that genetic differentiation among populations was significant in smaller scale.2,There was significant genetic structure of space within population of S.chinensis, and the modle of spatial distribution was aggregated-random-uniform, according to the effect of isolation by distance. Based on plant size, the plants were divided into three age levels. Individuals at ageâ… didn't show significant aggregated distribution in the smaller distance class, but showed significant aggregated distribution in the moderate distance class. Individuals at ageâ…¡and ageâ…¢all showed significant genetic structure of space and aggregated in the smaller distance class. This showed that the dispersal distance by pollen might be about 36 m, and the possible dispersal distance by seeds was about 24 m with severely limited gene flow which might attribute to the low genetic diversity at population level.3,The genetic diversity of the eight populations of S. chinensis was also analyzed using cpSSR molecular markers. Results also showed that genetic diversity at species level was relatively high, and genetic diversity within populations was relatively low, furthermore, genetic differentiation among populations was significant (Gst = 0.7558), and gene flow by calculation based on Gst was severely restricted with only 0.1616. Because chloroplast genome is not recombined, different locus could be combined based on the rule of no recombination, and 4 haplotypes were found among 160 individuals. Among them, three haplotypes were distributed in Lin'an City, and another one was distributed in Tian'tai County, moreover, no share haplotype was found in the two areas.4,Phylogeography pattern of S. chinensis was that, two kinds of haplotypes were widely distributed in Tian'tai County and Lin'an City, and the other two haplotypes were restricted in Daming Mountain and Qingliang Feng National Nature Reserve, due to the limited gene flow. Phylogeography structure of S.chinensis was divided into three main lineages: the first-class lineage was Daming Mountain in Lin'an City and Dalei mountain in Tian'tai County; the second-class lineage was Qingliang Feng National Nature Reserve; the third-class lineage was population QK in Jiakou town and population SSB in Longgang town.This suggested that Daming Mountain and Dalei mountain might be the refuge of S. chinensis. After the ice age in the Quaternary Period, S.chinensis might dispersed from Daming mountain to Qingliangfeng National Nature Reserve, and then to where population SSB and QK inhabited, respectively. Due to some historical events and the role of the geographical environment likely, the populations in Dalei mountain didn't outspread. The protection unit in priority was Daming mountain,Qingliangfeng National Nature Reserve in Lin'an City and Dalei mountain in Tian'tai County.5,The endanger factors of S.chinensis would resulted from historical reasons, ecological factors such as habitat fragmentation, micro-habitat heterogeneity, various geographical reasons, etc., and reproductive biology, example for the limited gene flow, genetic recession, the mating system with outcrossing mainly,self-propagation by way of parenthesis, etc. Based on the above, the protection strategy for S. chinenesis was proposed.
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