|其他摘要||China, characterized by extremely complex topology of mountain systems, is central piece of flora of seed plants of East Asia. The complex topography results in a wide range of climatic conditions. Climatic and topographic conditions engender a wide variety of vegetation types. These loft mountains shaping plant dispersal passages or barriers make China become centers of origin, and/or genetic diversity and refuges of many species. Floristic regions in china are divided into seven subkingdoms among which Sino-Japanese Forest Subkingdom and the Sino-Himalayan Forest Subkingdom possess the richest temperate plant biodiversity. Central China, South China and East China are the major floristic regions in the Sino-Japanese Forest Subkingdom. So elucidating evolutionary history, gentic diversity and genetic structure of endemic tree species to this region is of far-reaching significance. Fagus is a small genera of the Fagaceae including 8 to 10 species which are dominant in many deciduous forests of the temperate zone of the northern hemisphere. Because of their wide distribution in the north temperate zone and great economic importance, species of Fagus have been becoming studying focuses in many areas, such as phylogeny, biogeography and genetics. Fagus species in China are distributed in the mountain regions of Central China, South China and East China regions. In this thesis, two studies were conducted. One is on the genetic diversity and structure of Fagus lucida, a species endemic to China, inferred by microsatellite markers. The other is the phylogeography of F. longipetiolata based on two non-coding cp DNA regions. Conclusions are sumarized as following:
1. Genetic diversity and genetic structure of F. lucida based on microsatellite markers
Genetic diversity and genetic structure of fifteen populations of F. lucida were studied by using six microsatellite loci. It revealed a high degree of genetic diversity. That Fst value 0.056 indicated that there was very weak differentiation among F.lucida populations. AMOVA analysis indicated most of genetic variance was within populations (94.35%), while only 5.65% of genetic variance was among populations. These results were in common with previous results of long-lived, outcrossing tree. Fis value (0.019) indicated that inbreeding existed, and it was resulted from 5 populations deviated Hardy-Weinberg Equilibrium. No bottleneck effect was detected among the sampled populations. Gene flow value whether it was estimated using typical method or private alleles method was more than 1, and it was sufficient to counteract the action of genetic drift on the genetic composition of individual populations. Mantel test indicated that positive significant correlation was detected between the genetic distances and geographic distances (r=0.357, p=0.012). Cluster analysis of UPGMA based on genetic distance also showed that sampled populations are spatially genetically structured. Eastern populations are differentiated from central and south populations. Two populations, ZJB and FJW, possessed higher genetic diversity.
2. Phylogeography study of F.longipetiolata based on two non-coding cp DNA regions
Intraspecific genetic variation in two non-coding chloroplast DNA (cp DNA) regions (atpI-atpH spacer and ndhJ-trnF spacer) among 20 populations of F. longipetiolata from throughout the distributing range was investigated. 134 individuals were sequenced. Fourteen different haplotypes were detected. It revealed that there were high genetic diversity (Ht=0.945) and high genetic differentiation (Gst=0.918, Nst=0.941) among populations in F.longipetiolata, but genetic diversity within populations (Hs =0.078) was very low. The high genetic diversity may be caused by its evolutionary history. The high level of differentiation among populations indicated a low efficience in seed dispersal mechanism. But we could not exclude the probability of long distance dispersal because of wide geographical span for haplotype H6 and H9. Network of cp DNA haplotypes indicated that H3 and H6 were the ancestral haplotypes from which other haplotyes were evolved. In addition, the difference between Gst and Nst for the species is very significant(U=3.05，P<0.01), suggesting that the phylogeographic structure is strong. Nested clade analysis indicated that the genetic structure of F. longipetiolata was resulted from the effect of population’s contiguous range expansion, allopatric fragmentation and restricted gene flow with isolation by distance. Wulingshan mountain range may be a dispersal corridor of F. longipetiolata, because haplotype H3 in this region evolved to form five haplotypes toward the west, the south and the east. Nanling mountain range and Luoxiao mountain range may be haplotype diversity center because of its rich haplotypes. In the evolutionary history, there might be not less than two migrating routes. The first one might be to expand to the west, the south and the east regions from Wuling mountain range. It seemed that F. longipetiolata had continuous distribution in that time. The second one might be to expand to the west, the south and the east regions form Nanling and Luoxiao mountain range. The first one may be occurred earlier than the second one. It may be caused by isolation that Zhejiang populations did not contribute to the population colonization of central and south China. Populations of Sichuan Basin Edge may be evolved from population KKS of Central China region.|