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资助项目
GST, P < 0.05) were exhibited by this species. The SAMOVA revealed seven diverging groups of related chlorotypes, six of them had distinct nonoverlapping geographical ranges: one in the northeast comprising 10 populations, a second with a southeast distribution comprising 22 populations, and the remaning four groups comprising 15 populations located in the west part of the species’ range along different river valleys. The genetic clustering of populations into three regions was also supported by analysis of molecular variance, which showed that most genetic variation (82.43%) was found among these three regions. Two clusters were distinguished by both phylogenetic analysis and genealogical analysis of chlorotypes, one consisting of chlorotypes from the western region and the second consisting of those from the eastern region. Significant genetic differences between the two regions might be attributed to vicariance and restricted gene flow, and this vicariance could be explained by the physical environmental heterogeneity on each side of the Tanaka-Kaiyong Line. Following the uplift of the Tibetan Plateau, the reorganization of the major river drainages was primarily caused by river separation and capture events. These historical events could change the distribution of S. davidii from fragmented to continuous (Upper/Lower Jinshajiang and Yalongjiang/Daduhe), and from continuous to fragmented (Nujiang and Jinshajiang/Honghe). However, spatial and temporal patterns of phylogeographic divergence are strongly associated with historical disjunction rather than modern drainage connections. Moreover, the following north-south split in the eastern region and effective isolation with their genetic diversity were essentially modelled by genetic drift. The higher chlorotype richness and genetic divergence for populations in western region compared with other two regions suggests that there were multipe refugia or in situ survival of S. davidii in the Himalayan-Hengduan Mountain region. Fixation of chlorotypes in the northeastern region and near fixation in the southeastern region suggest a recent colonization of these areas. We further found that this species underwent past range expansion around 37-303 thousand years ago (kya). The southeastern populations likely experienced a demographic expansion via unidirectional gene flow along rivers, while northeastern populations underwent a more northward expansion, both from initial populations (s) (21, 22, 23) preserved on eastern refugia (Jinshajiang). This process might have been accompanied with a series of founder effects or bottlenecks making populations genetically impoverished. 3. Phylogeographic analysisbased on nuclear sequence，We sequenced the nuclear (ncpGS) region in all populations sampled, recovering 23 nuclear haplotypes. Compared to cpDNA, both NST (0.470) and GST (0.338) were relatively lower, but NST was also significantly larger than GST. 37.10% of the total variation was distributed among regions which was much lower than that shown by chlorotypes. Thus, more extensive distribution of nuclear haplotypes was exhibited across the geographical range instead of the strong population subdivision observed in chlorotypes. Similarly to the chloroplast data, we found that genetic differentiation of nDNA was positively correlated with the geographical distance, but the increase in the geographical distance between populations did not increase the genetic differentiation of nDNA as rapidly as that of cpDNA. These contrasting levels between the chloroplast and nuclear genomes of S. davidii are likely due to limited gene flow of cpDNA by seeds vs. the extensive gene flow of nDNA by wind-mediated pollen in the population history. We also determined from nuclear markers that haplotype diversity was reduced in the southeastern and northeastern regions due to the loss of rare haplotypes in western region. This reduction of gene diversity is also a signature of founder events or recent bottleneck during post-glacial colonization. However, nuclear diversity within populations remains high. This provides evidence that regionally pollen flow might be sufficiently high to blur the genetic identity of founder populations over a reasonably large spatial scale.3. Relationships among three varieties，The phylogenetic analysis identified two phylogroups of chlorotypes, corresponding to S. davidii var. davidii and var. chuansinesis. The former was distinguished by the abscence of predonminant nuclear haplotype H1 of the latter. The monophyletic group of chlorotypes in var. davidii and var. liangshanesis showed their relatively close relationship. And their genetic divergence from the third variety appears to be relative to their slight morphological difference in leaf size and the divergent environmental niche spaces they occupy. Thus, the observed differences in morphological characters between var. chuansinesis and other two varieties can be explained by the seed dispersal limitation illustrated above (as inferred by geographical separation) and by environmental heterogeneity (as inferred by precipitation or elevation) or by a combination of both. After all, the geological changes, drainage reorganization, and floristic differences following the Himalayan uplift have been suggested to affect the genetic structure of S. davidii. These results provide new insights into the phylogeographic pattern of plants in China. In addition, the unique population genetic structure found in S. davidii has provided important insights into the evolutionary history of this species. The genetic profile uncovered in this study is also critical for its conservation management. Our study has uncovered the existence of at least two ‘evolutionary significant units’ independent units within S. davidii, corresponding to var. davidii from eastern region and var. chuansinensis from western region. The conservation efforts should first focus on most western populations and on the southeastern ones exhibiting high levels of genetic diversity, while the genetically homogeneous northeastern populations located in the degraded Loess Plateau should require much greater conservation 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doichangensis is an endangered plant. In this paper, the megasporogenesis and development of female gametophyte, seed morphological traits and seed germination, seed conservation, micropropagation and acclimatization of this species were studied. Combined with the published results of cytology, molecular genetics and other researches,the mechanisms of extinction, basic biology and technology of germplasm conservation and acclimatization of T. doichangensis were discussed. The main results are summarized as follows:1. Megasporogenesis and development of female gametophyte，Stamens exist under the stigma of T. doichangensis, and the pollen is aborted on the later development stage of pistil, therefore, the pistillate flower in function is hermaphrodite flower in morphology. The ovule is anatropous, bitegmic and crassinucellate. The primary archesporium is hypodermal and single-celled and the sporogenous cell of the nucellus functions directly as a megaspore mother cell which goes meiosis to form a linear tetrad. The chalazal megaspore of the tetrad is functional. The development of embryo sac conforms to the polygonum type. There are six ovules in the ovary of T. doichangensis, and only one develops into a seed in normal fruits. In the process of megasporogenesis and development of female gametophyte, there are several links of abortion, and 93.3% of mature embryo sacs is aborted.2. Morphological characters and germination of seeds，Most of the variation occurred among individual trees within populations in seed morphological traits (length, width and 1000-seed weight) and germination-related indices (germination percentage, germination index and vigor index). In addition, the variation in percentage of well-developed seeds among populations and among individual trees within populations is equal, each accounting for 48%. Each of seed morphological traits has significantly positive correlation with each other (p < 0.01), but they have no significant correlation with percentage of well-developed seeds and germination-related indices. In the same batch of seeds of T. doichangensis, there are light-colored and dark-colored seed coats, and development of light-colored seeds is significantly poorer than that of dark-colored seeds.The sensitivity of seeds to high temperature varys in different stages of seed imbibition. In each stage, heat acclimatization don’t increase germination percentage, germination index and fresh weight of seedlings. If the distilled water is substituted by solution of SA during seed imbibition, seed germination and germination index after heat shock are not significantly different from control, but they are significantly higher than that of other treatments. Moreover, when the seeds are treatmented with SA, the fresh weight of seedlings is significantly higher than that of control and other treatments.3. Seed conservation，Seeds of T. doichangensis belong to orthodox seeds which can tolerate certain level of dehydration. The condition of low temperature and low water content of seeds is conducive to seed conservation.Germination of fresh seeds shows significant variation among populations, howerer, germination of the seeds after storage for one year in room temperature shows no significant variation among populations.High temperature and high relative humidity damages the seeds more severely than high temperature does. In addition, low water content of seeds enable the seeds to be more tolerant to high temperature.The electrical conductivity, dehydrogenase activity and germination percentage have no significant correlation with each other.4. Micropropagation and in vitro conservation，Cotyledonary nodes are a kind of efficient explants. Low salt media are conducive to shoot propagation and root induction.The maximum multiplication rate (20-25 shoots/explant within 4 months) is achieved on quarter-strength Murashige and Skoog (1/4 MS) medium supplemented with 1 mg·L-1 6-benzyladenine (6-BA) and 0.05 mg·L-1 α-naphthaleneacetic acid (NAA).Rooting is promoted by auxins, however, IBA alone or low concentrations of NAA are preferable due to small amount of callus induced. The research has established an efficient protocol for micropropagation of T. doichangensis, and it provides technology support for in vitro conservation of special germplasm of the species.5. Acclimatization，Quercus variabilis, Cyclobalanopsis glaucoides and T. doichangensis belong to the family of Fagaceae, and the natural distribution ranges of the 3 species are decreasing in turn. The research suggests that the ranges of temperature tolerance of the 3 species are decreasing corresponding to their distribution ranges.The high and low semi-lethal temperature of one-year old T. doichangensis is 49.5℃ and -5℃ respectively. It suggests that T. doichangensis has a wide range of basic temperature tolerance. Short-term heat and cold acclimatization cannot expand the range of temperature tolerance. It can be inferred that T. doichangensis may lack induced tolerance to temperature. Under proper conditions, ABA can increase the cold tolerance, and SA can increase the heat tolerance of leaf discs of T. 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