| Drought and soil desert is one of the hazards the globe facing. Controlling over desert to improve ecological environment should be firstly studied and solved in the important program of the West Development. In this paper, desert vegetation in Fukang of Xinjiang as an object, plant community species diversity and niche were studied, and genetic diversity of Haloxylon ammodendron, which was listed the No. 3 grand of national protected plant and key stone species in ecosystem, was given emphasis to address characteristics of biodiversity in desert at two levels of species diversity and genetic diversity. Niche and genetic differentiation of several desert plants were detected to analyze the relationship between niches and genetic diversity of desert plants, test niche breadth variation hypothesis, and probe the reasons for Haloxylon ammodendron endangering. In this paper, the study on plant community species diversity and genetic diversity in the region will provide scientific theory basis for conquering desert.Fukang of Xinjiang involved in this paper is located between Guerbantonggute desert and Tianshan Mt, belonging ecologically to Ecotone. This paper systematically studied characteristic of species diversity in plant community. The results indicated that, species diversity of Ecotone in Fukang of Xinjiang was lower as a whole in contrast to other temperate vegetation. This was attributed to local arid ecological geographical environment. The range of Shannon-Wiener species diversity index was 0.4819~~ 1.5689, being lower than 1.8604-3.4142 of desert steppe and higher than 0.029-0.696 of sandy land, inferring that the level of species diversity of Ecotone in Fukang of Xinjiang was the results corresponding to the heterogeneous environment.Analysis of species diversity and soil factors by single factor and stepwise regression revealed soil moisture, soil salt and soil pH have significant effects on species diversity (/J<0.01). Soil organic matter and nutrients significantly fit in form of binomial by single factor analysis, but the effect of soil organic matter on species diversity was not apparent by stepwise regression, indicating uncertainty and complex of direction and mechanism of soil organic matter on species diversity.Niche analysis of plant species in Ecotone revealed that, according to community gradients, the order of niche breadth was Reaumuria soongorica (0.7010) , Haloxylon ammodendron (0.6434) , Ceratocarpus arenarius (0.4774), Bassia dasyphylla (0.3745), Kalidium foliatum (0.3541), Petrosimonia sibirica (0.3354) and Suaeda acuminata (0.2769). Reaumuria soongorica and Haloxylon ammodendron were dominant species occupying big niche breadth, and other species are companion. The two species with big niche in soil moisture, soil salt and organic matter overlapped greatly (0.4203) each other,indicating similarity of adaptation to soil salt. The two species with bigger niche overlapped greatly with other species, suggesting wider niche species also had bigger niche overlaps.Genetic analysis of 6 subpopulations with 117 of Haloxylon ammodendron in Ecotone by RAPD indicated 16 primers detected 74 loci, of which 71 loci was polymorphic, percentage of polymorphic loci accounted for 96%. Coefficient of gene differentiation (Gsr) was 0.1567, that was 15.7% of genetic variation among subpopulations, and 84.3% within subpopulation. Total genetic diversity by Shannon index was 0.5240, mean genetic diversity within subpopulation was 0.4437, genetic diversity within subpopulation accounted for 84.67% of'total genetic diversity, and that among subpopulations accounts for 15.33%, that is 85% of genetic variation within subpopulation, and 15% among subpopulations. Therefore, Haloxylon ammodendron had rich genetic diversity, and most of genetic diversity distributed within subpopulation. The reasons for higher genetic variation depend on biological character of Haloxylon ammodendron. Haloxylon ammodendron is long-life perennial tree, pollination by wind, outcrossing and widely-spred species, founde...
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