Flora Characteristics And Plant Adaptability To Representative Valley Habitat In Northwest Of Hunan

The northwestern region of Hunan province is made up largely by theWuling Mountains, which is bordering on Hunan, Hubei, Chongqing, and Guizhouprovince, belonging to the transitional region between west eastern and north southernin central China. This region contains high species diversity and is rich in endemismand relict taxa, and is a significant element of the Central China, Chinese and EastAsian Flora. Based on in-depth investigations, extensive collections and literaturesconcerned, the species composition and floristic character of representative valleyspecial-habitats in Xiaoxi have been analyzed, and the flora in different gradient ofvalley, typical community and different micro-habitat also have been discussed.Meanwhile, the correlation between valleys habitat heterogeneity and species would bestudied to demonstrate the importance of the valley special-habitats in process of floraformation and diversity protection at northwestern of Hunan. The concrete results ofthis research are as following:1. The Xiaoxi national nature reserve is rich in flora and there is found to have2252species including varieties of803genera in174families, the endemic and rareplants are also rich. There are14areal-types of genera in the region. The flora in generadisplayed significant temperate feature, but the tropical is also obvious. It has a certaintransitional nature with temperate and tropical, for it has45.94%(including368genera)of temperate elements and41.60%(including334genera) of tropical elements. Theareal-types of species are dominated by the China endemic elements which are occupied56.85%of the total species, and the temperate elements are further developments. Thenumber of endemic species in C. China, Mt. Wuling and Xiaoxi are respective194,94and10, which is the most obvious flora characteristic of the low-elevation subtropicalevergreen broad-leaved forest in China. Cluster analysis show that the flora of this areais very closely related to Mt. Huping and Wulingyuan, while it is far from Shennongjieregion.2. The valleys in this region may be firstly classified into three gradients, i.e.“U”(e.g. Mengdonghe River),“V”(e.g. Denghang) and “(?)”(e.g. Xiaoxi), according to theincluded angle between slope and base of valley, width of its base and runoff. Speciescomposition showed obviously different in three gradients of valley, and thecomparability coefficients get to more than80%and70%, respectively, at the familyand genus levels, while the comparability coefficients of species is only about50%. Thepercentage of tropic component tended to decrease with weakening the gradient ofvalleys, accounting for50.63%(Mengdonghe River),41.83%(Dehang) and41.61%(Xiaoxi), while the temperate component are37.11%,45.71%and45.82%respectively, with a trend of ascend. Although there are certain gradient and difference among thethree valleys, all of them are both a refuge for relict taxa and a cradle for breeding newspecies.3. There is quite different among plant composition, structure and diversity of thecommunities. There is the highest species diversity in the Evergreen and deciduousbroad-leaved mixed forest,74species, and the most abundance arbor species in theEvergreen broad-leaved forest,20species. The statistics of species diversity indicesshow that both Shannon-Wiener index (6.70) and Uniformity (3.83) in the secondarybamboo forests are the highest. Study on the flora in different communities show thenumber of tropical families is higher than temperate ones at the families level, while theflora display significant temperate feature at genus level. In addition to differences innatural habitats, the different degrees of human disturbance may cause the main reasonfor the change in community characteristics.4. There was high habitat heterogeneity in this region in terms of soil water contentand elemental composition. There was the highest species diversity in the soil-rockslope micro-habitat (735species, accounting for62.8%of total species number), whilethe lowest diversity occurred in the cavern micro-habitat (only6species, accounting for0.5%). The statistics of species distribution radiativity showed that the species numberof distribution radiating at one habitat was the724species, accounting for61.8%oftotal species number. This observation could be believed that species distribution wasvery special in these regions, and the anti-interference capability of vegetation was low,which was adverse to the long-term maintain of species diversity in special-habitat.Study on the flora in different micro-habitat showed the floristic characteristics ofmicro-habitat basically had the same changes at the families and genus levels, namely,the flora of family displayed significant tropical feature, and the flora of generadisplayed significant subtropical feature. The ordination of applying the redundancyanalysis (RDA) showed environmental factors significantly affected the composition offlora, but the effect at the family level was different from that at the genus level. Twelvevariables explained75.9%and88.9%of total information, respectively, at the familyand genus levels. Flora component showed positive or negative correlation with eachchemical element, indicating habitat heterogeneity could exert some impact on thecomposition of the flora.5. Sinosenecio jishouensis are always found in habitat of waterfall and theStream-ravine with an altitude from300m to370m, and its communities are alwaysgrasses, bushes and secondary bushes. To measure the environment factors in thehabitats, we found that water content of soil get to34.28%, the pH values varies from8.51to8.60, organic matter changes of10.75%to14.33%, and total nitrogen contentswith a variable from0.28%to0.35%. And low contents of water, organic matter, totalnitrogen and high contents of copper soil are probably the important environmentfactors to influence development of S. jishouensis population. The distribution patterns of the only three natural S. jishouensis populations are clumped, and the intensity ofclustering is different among different populations. The variance/mean ratios of thesepopulations were6.68,14.39and11.53, respectively, t test show remarkably difference.The area for highest congregation with in64m~2and8m~2, respectively, at the Liushapopulation and Hangxia population, but the patch at Leigongdong population can not bedemonstrate. Study on floral dynamic and breeding system shows that the floweringperiod of the S. jishouensis population lasted about45-50days and with inconspicuoussecond blooming. The life span of individual plant was usually about10-22days. For asingle capitulum, it could last3-5days. The stigma was obviously higher than thecanister when pollen dissemination. As a result, there is a spatial isolation of corolla,anther canister and stigma with in the same floret. The out-crossing index andpollen-ovule ratio of S. jishouensis were5and3188±394.50, respectively. The breedingsystem is out-crossing with partial self-compatibility, needing pollinators andreproduction is obligate xenogamy. After the inflorescences were bagged, there werefew fruits produced. Hence, it is demonstrated that the breeding system is predominantin cross-pollination and fruit setting is depended on pollinators of this species. Theresults of researching on clonal architecture are as follows the ramets and rhizomes perclone averaged3.61±0.23and4.74±0.30, respectively. Branching angle betweenrhizomes usually was30°. The architectural form of rhizomes of S. jishouensis belongsto phalanx system for the branch distance of rhizomes is short. The anatomic studiesshowed that the rhizome rupture is the result of the tissue piecing.6. Morphological comparison of Sambucus chinensis in outside valley and insidevalley showed the difference in number of unfertile flowers, long/wide of leaflets, fruitcolor and stipule shape, but there are no obvious difference in number of arris, numberof lateral branch, number of pitch, length of longest internodes and number of leaflets.The leaf epidermal cells are usually irregular bearing with the anticlinal walls undulate,and stomatal density of S. chinensis in inside population is obviously higher than theoutside,37.6±7.47per mm~2and26.8±5.81per mm~2, respectively, while stomatal indexof S. chinensis in outside population (accounting for31.38%) is slightly higher than theinside (accounting for29.17%). Mitotic chromosome numbers of S. chinensis in outsideand inside valley are diploidy with2n=36, and is unconformable to previous reference.Karyotype of S. chinensis is2B and inside population with a karyotype formula of2n=36=16m＋14sm＋2st＋4t, and2n=36=22m+14sm for outside population, besides,the population of inside valley revealed more advanced than the outside population forthe Ask value is67.76%and61.97%respectively.