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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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relationship between leaf physiognomy and climate is widely used to reconstruct paleoclimates of Cenozoic floras. Previous works demonstrate that LMA show regional constraints. Until now, no equation has been set up directly from Chinese forests. This relationship is exhaustively studied based on 50 samples from mesic to humid forests across China. Models including Leaf Margin Analysis (LMA), Single Linear regression for Precipitation, and Climate Leaf Analysis Multivariate Program (CLAMP), are set up and used to quantitatively reconstruct paleoclimates of Chinese Neogene floras. Meanwhile, a paleoflora, i.e., Yangjie flora, which belongs to the Upper Pliocene Sanying formation in West Yunnan Province, is studied. The species assemblage, paleoclimate and paleoecology of Yangjie flora are discussed. Conclusions in this dissertation are as following: 1. Chinese leaf physiognomy-climate models based on regression analyses，LMA is a widely used method that applies present-day linear correlation between the proportion of woody dicotyledonous species with untoothed leaves (P) and mean annual temperature (MAT) to estimate paleotemperatures from fossil leaf floras. The Chinese data indicate that P shows a strong linear correlation with MAT, but the actual relationship is slightly different from those recognized from other regions. Among all currently used LMA equations, the one resulting from North and Central American and Japanese data, rather than the widely used East Asian LMA equation, yields the closest values to the actual MATs of the Chinese samples (mean absolute error = 1.9°C). A new equation derived from the Chinese forests is therefore developed, where MAT = 1.038 + 27.6 × P. This study not only demonstrates the similarity of the relationship between P and MAT in the Northern Hemisphere, but also improves the reliability of LMA for paleoclimate reconstructions of Chinese paleofloras. Besides, regression analyses are used to explore the relationship between leaf physiognomy and precipitation. In contrast to former studies, entire leaf margin shows the highest correlation with the Growing Season Precipitation (GSP). A new equation is proposed: GSP = 228.0 + 1707.0 × P. 2. The new calibrated CLAMP dataset – PHYSGCHINA，CLAMP, which is based on canonical correspondence analysis, is improved by the inclusion of 50 Chinese samples. The result indicates that, new calibrated data from 50 Chinese sample sites are situated away from the former 144 samples in the physiognomic space, which may be caused by the unique characters of leaf physiognomy under monsoon condition. Therefore, a new calibrated CLAMP dataset, i.e., PHYSGCHINA, is set up based on 50 new Chinese samples, and 144 former samples from PHYSG3BRC. This new dataset could improve the accuracy of paleoclimate reconstructions for floras under the monsoon climate condition. When it is applied to Chinese Neogene floras, PHYSGCHINA could improve the accuracy of paleoclimate parameters, especially parameters related to precipitation. 3. Paleoclimate reconstructions of Chinese Cenozoic floras，Paleoclimates of Chinese Cenozoic floras are reconstructed using leaf physiognomy- climate models being set up in this study. The Chinese paleoclimate history in Eocene is similar to the trend from worldwide record. That is, hot climate presented in early Eocene and early Middle Eocene, and then, climate cooled down from late Middle Eocene to Late Eocene in China. Moreover, paleoclimates of two Late Miocene floras from Yunnan province, i.e., Xiaolongtan flora and Bangmai flora, are reconstructed using different models. The results indicate that, temperature of Yunnan is slightly higher than that in nowadays, but the precipitation is much higher than that at present day, which may be caused by the uplift of Hengduan Mountain. 4. Late Pliocene Yangjie flora in West Yunnan Province, China，A Late Pliocene Yangjie flora form Yongping County, western Yunnan province, which belongs to Sanying formation, is studied in this dissertation. Yangjie flora is dominated by Quercus sect. Heterobalanus (Oerst.) Menits. (evergreen sclerophyllous oaks), and this forest type is quite common in SW China at present. The discovery of Yangjie flora provides evidence that, vegetations of Yunnan in Miocene were dominated by evergreen forests, and the dominant families were Fabaceae, Fagaceae and Lauraceae. In Pliocene, this vegetation type changed gradually to evergreen sclerophyllous oak forests. This vegetation change may have been caused by the uplift of Hengduan Mountain in Neogene. A polypodiaceous fern, Drynaria callispora sp. nov., is described from the upper Pliocene Sanying Formation in western Yunnan Province, southwestern China. The species with well-preserved pinnae and in situ spores is the first convincing Drynaria fossil record. Detailed morphological investigation reveals that D. callispora is characterized by 1) pinnatifid fronds with entire-margined pinnae having straight or zigzag secondary veins; 2) finer venation showing void quadrangular areoles, but occasionally with one unbranched veinlet; 3) one row of circular sori on each side of the strong primary vein; and 4) in situ spores with verrucate exospores elliptical in polar view and bean-shaped in equatorial view. A morphological comparison shows that D. callispora is significantly different from all the fossil species previously identified as drynarioids. A phylogenetic analysis of D. callispora supports that the fossil is closely related to D. sinica Diels and D. mollis Bedd., two extant species distributing in the Himalayas. The discovery of the new fern indicates that the genus Drynaria became diversified in its modern distribution region no later than the late Pliocene and had retained the similar ecology to that of many modern drynarioid ferns ever since. 5. Paleoclimate reconstruction of Yangjie flora，LMA, Single Linear Regression for Precipitation and PHYSGCHINA are applied to reconstruct paleoclimate of Yangjie flora. MAT calculated by LMA and CLAMP is 22.0 ± 2.4°C and 20.0 ± 1.4°C, respectively, and GSP calculated by Single Linear Regression for Precipitation and PHYSGCHINA is 1521.9 ± 131.3 mm and 2084.7 ± 223.1 mm, respectively All methods agree that, both temperature and precipitation were higher in Late Pliocene than in nowadays. Meanwhile, precipitation parameters calculated by CLAMP gets high values. 6. Preliminary study of insect herbivory in Yangjie flora，Insect herbivory on leaves of Quercus preguyavaefolia Tao and Q. presenescens Zhou, two dominant species in Yangjie flora, is reported by the preliminary research. Each of these two species has a high diversity of insect damage. Among all damage types, margin feeding and surface feeding are most common, and skeletonization, piercing and sucking, and galling are less found. Most of these damage types belonge to the high host specialization (HS = 1). However, the proportion of leaves without insect damage in Q. presenescens is much higher than that in Q. preguyavaefolia. According to the log-log linear regression model, both Quercus preguyavaefolia and Q. presenescens have very high leaf mass per area (with 184.8 ± 6.7 g/m2 and 155.3 ± 10.7 g/m2, respectively). The high diversity of insect herbivory demonstrates a warm climate in the Late Pliocene of West Yunnan 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