Plant Diversity Characteristics And Ecological Adaptation To Canyon Special Microhabitat In North Western Hunan, China

The northwestern region of Hunan province, located next to Hubei, Chongqing and Sichun provinces, belonging to the Metasequoia Flora, is made up largely by the Wulingshan Mountains. It forms the core of one the three"Centers of Endemism"in China, the eastern Sichuan and western Hubei Center, and is an important element of the Chinese and East Asian Flora. A typical and important physical feature of this region is the natural habitats associated with the deeply cut river valleys. Much like isolated mountains and cliffs, these river valley microhabitats are isolated"islands"of diverse endemic plants, making them ideal for studying species differentiation and diversity. In addition, plants of this region show a great diversity of adaptive morphological features, obviously as a result of the special environment of these microhabitats. Therefore, the plant species these valley microhabitats are of special interest for studying ecosystem structures and functions, and adaptive evolutionary mechanisms. However, previous studies on the flora of this region are few.Two typical canyons of this kind, the Dehang Canyon and Mengdong River Canyon, in the northwestern Hunan region were chosen as research sites in this study. We made extensive collections of plant specimens in both sites throughout the growing season. All specimens collected were later identified to species. The floristic characteristics and apparently adaptive plant features were analyzed. We further examined the functional type and reproductive system diversity and ecological correlates, the distribution characteristics of notable species (i.e., endemic and niche-specific species), and patterns of diversification and adaptation of plant species in the two sites. The results of this study is sumarized as below:1. The term Canyon micohabitat was defined for the first time in this study, and the possible causes for the formation of this speical habitat were discussed. Based on geomorphologic features, 9 submicrohabitats were identified. The environmental characteristics of this special ecosystem were systematically characterized, the factors likely to disrrupt this fragile ecosystemwere fully analyzed, and corresponding management and conservation measures were suggested.2. The plant floristic components, characteristics and origins of the special Eco-environment of Dehang Canyon and Mengdong River were analyzed at the Family, Genera and Species levels, and its floristic correlations with other floras were made. The results showed that there were 1162 vascular species belonging to 566 genera and 148 families in this region. Fern and Vine plants were the most diverse groups. The flora in Dehang Canyon were mainly tropical components at Family and Genera levels. Mengdong River, where the species were rather endemic, contained 670 vascular species belonging to 389 genera and 129 families. Floristic geographical analysis at the genera level indicated that this flora was an obvious transitional one from tropical to temperate flora. The species level analysis showed that this flora was the mixed one of East Asia and Tropical Asia. The results of clustering and principal components analyses between Wulingshan region and other domestic Areal Types by using STATISTICA software showed the importance of the Canyon microhabitatin this region. The parameters, such as relative richness, differentiation index, and IM value, were used to evaluate the diversity characters of microhabitats. The results showed that all the parameters of Tutai were high, while the Yanrong low.3. There were 160 niche-specific species belonging to 71 families and 121 genera in the canyon microhabitat of North Western Hunan. Most of the niche-specific species distributed in the herb layer and the shrub layer, while seldom in the tree layer. The Canyon microhabitat niche-specific species evolved a series of ecological features, including growth type, organ morphology, life history, ecological adaptation groups and areas of ecological adaptation, adapting to the special habitats,. With the succession of plant community, the niche-specific plant species increased, while in the later stage they were fewer.4. Two typical Canyon microhabitat species (Sinosenecio jishouensis and Aspidistra fenghuangensis) were studied in detail for life history traits, differentiation and speciation of the niche-specific species. Results of the study on the ecological distribution, phenology and reproductive characteristics of S. jishouensis showed that the floral structures, high degree of synchronization in the flowering pattern and "brush-like mechanism", and small achene without pappus, together with relying mainly on clone production while making sexual production subsidiary, are the consequences of long-term ecological adaption to the Canyon Fall special habitat. The morphological and cytologic methods were used to studied the patterns of morphological differentiation of A. fenghuangensis. Amendment and supplement on morphology of A. fenghuangensis were made. The genetic relationship was discussed by analyzing chromosome number and karyotype dynamic, and the possible origin, evolution and speciation of A. fenghuangensis were stuided from the cytogeographical aspect. The loss of satellite chromosomes was an evolutionary features, because this might be beneficial to its adaptation to new environment.5. The roots, stems, leaves, flowers and fruits of species in the Canyon microhabitat were studied to reveal their functional diversity and adaptive significance. There were 5 types of roots and 3 types of flowers. The leaf with medium size was the main leaf type, leaf quality was mainly paper type, and most leaves were hairless on both sides. Small type flowers accounted for a large proportion, and most flowers were light colored. Most of the fruits were of dry type, and mainly dependent on mechanical transportation. The analysis of sexual reproduction systems further corroborated the relationship between the canyon microhabitat and the Tropical Flora. The phylogenetic constraint on sexual reproduction systems and ecological correlations, and the effects of ecological environment on the differentiation and evolution of sexual reproduction systems were discussed.This study could provide further evidence for solving the major scientific issues, such as the differentiation and adaptive evolution of specific habitated species, and the plant diverstiy formation and its maintaining mechamisms. It also provided important data for the compilation of the Hunan Flora, and for the conservation, sustainable utilization, and comprehensive management of local natural resources.