对湘西北猛洞河和德夯河谷9 类小生境(凹槽、干旱石壁、滴水岩壁、石土坡、瀑布、微土台、溪沟、岩溶洞穴和河水浸没带)的土壤环境因子(包括含水量、pH 值和矿质元素含量)和植物物种组成及区系成分进行了调查,并采用RDA 排序法分析了该区域植物区系成分与土壤环境因子的相关性。结果表明:该区域生境异质性较高,各类小生境土壤的含水量、pH 值和矿质元素含量均有差异;其中,瀑布生境中土壤含水量最高(达51. 9%),干旱石壁土壤含水量最低(仅13. 0%);绝大多数生境土壤偏碱性,仅石土坡土壤偏酸性(pH 6. 4);9 类小生境土壤中Al、Ba、Cd、Co、Cu、K、Mg、Mn、Se 和Zn 含量差异明显,其中Al 含量均最高。各生境中分布的植物种类数量有明显差异,其中,石土坡生境中植物种类最多(共735 种)、岩溶洞穴生境中植物种类最少(仅6 种);有724 种植物的分布辐射范围为1 个小生境,分布辐射范围达7 个小生境的植物仅1 种。各类小生境中植物科、属的分布型数量变化规律基本一致,即以热带分布型为主,但温带分布型属的数量略有增加。RDA 排序结果显示:土壤环境因子的12 个变量分别可解释科、属区系成分变异信息量的75. 9%和88. 9%,其中矿质元素含量及pH 值与科、属区系成分呈不同程度的正相关或负相关;总体上看,土壤Cd、Se、Zn 和Ba 含量及pH 值是影响该区域植物区系组成的主要土壤因子。研究结果显示:湘西北河谷特殊生境中植物物种分布生境较为专一,植被抗干扰能力较差,不利于物种多样性的长期维持;生境异质性在一定程度上影响植物区系成分的变化,但在科、属层次上影响程度有差异。

Soil environmental factors (including water content, pH value and mineral element content) and species composition and floral element of nine micro-habitats (groove, drought cliff, dripping rock,soil-rock slope, waterfall, soil platform, stream-ravine, cavern and river creep) in valley of Mendonghe and Dehang in Northwestern Hu’nan Province were investigated, and the correlation between floral element and soil environmental factors in the region was analyzed by RDA ordination. The results show that there is high habitat heterogeneity in this region, and water content, pH value and mineral element content in soil of different micro-habitats all have difference. In which, soil water content in waterfall habitat is the highest (51. 9%) and that in drought cliff habitat is the lowest (only 13. 0%); the soil ofmost habitats is partial alkaline, only soil of soil-rock slope is partial acidity (pH 6. 4); contents ofAl, Ba, Cd, Co, Cu, K, Mg, Mn, Se and Zn in soil have obvious differences among nine micro- habitats, in which, Al content is the highest. Species number distributing in different micro-habitats has an obvious difference, in which, that in soil-rock slope is the most (735 species), that in cavern is the least (only 6 species). And the distribution radiating range of 724 species is one micro-habitat, while only one species has the distribution radiating range of seven micro-habitats. The change regularity of areal-type number at family and genus levels in different micro-habitats is basically same, namely the tropical areal-type is major, but the number of temperate areal-type genus has a slight increase. The result of RDA ordination shows that twelve variables of soil environmental factors can explain 75. 9% and 88. 9% variation of total information of flora composition at family and genus levels, respectively. In which, mineral element content and pH value in soil have positive or negative correlations with floran components of family or genus in different degrees. And generally, contents of Cd, Se, Zn and Ba and pH value in soil are the major soil factors effecting flora composition in this region. It is concluded that the species distribution in special-habitats of valley in Northwestern Hu’nan Province is very special and the anti-interference capability of vegetation is weaker, as a result, which is unfavorable for the long-termmaintain of species diversity in the region. The habitat heterogeneity could exert some impact on the flora composition change, but its impact exists difference at family and genus levels.