人工固沙区与流沙区准噶尔无叶豆种群数量特征与空间格局对比研究

准噶尔无叶豆(Eremosparton songoricum) 是中亚荒漠特有小半灌木,稀有种,在我国仅片段化分布于新疆古尔班通古特沙漠;它是流动沙丘的先锋物种,也能成功定居于人工固沙区(草方格)。对比研究了人工固沙区及自然流沙区的准噶尔无叶豆群落物种组成、种群密度、高度、盖度、生物量等特征及种群空间分布格局。结果表明:人工固沙区内的准噶尔无叶豆群落物种的科、属、种数均明显多于流沙区,而且2种生境物种相似性指数仅为0.522,表明人工固沙生境显著改变了群落物种组成与结构。除植株密度外,人工固沙区种群的高度,盖度,地上、地下及总生物量密度,单株地上、地下及总生物量等数量特征均显著高于流沙区。2种生境中准噶尔无叶豆种群空间分布的关联维数均接近2.0,体现了较强的个体空间相关性和空间占据能力。2种尺度(1 m和2 m)下的聚集度分析表明,2种生境中种群基本为随机分布。因而,人工固沙生境并未明显改变种群空间分布格局,这可能是种群的固有特性。人工固沙区的土壤有机质、全氮和有效氮含量显著高于流沙区,且与种群数量特征(植株密度除外)呈显著正相关。总之,与流沙区相比,人工固沙使地表得到固定,提高了土壤有机质和氮素含量,明显改变了定居于其中的准噶尔无叶豆种群主要数量特征,增强了种群的生存和适应能力。该结论对荒漠濒危植物的保育具有重要指示意义。

Comparisons of quantitative characteristics and spatial distribution patterns of Eremosparton songoricum populations in an artificial sand fixed area and a natural bare sand area in the Gurbantunggut Desert, Northwestern China

Eremosparton songoricum is a rare desert perennial shrub found only in Central Asia. In China, its distribution is limited to the Gurbantunggut Desert. Eremosparton songoricum is a pioneer species that can become established on bare sand, where it acts as a sand stabilizer, and also occurs in artificial sand fixed areas, created using sand fences. In the sand fixed areas, the increased stability from the fences leads to the existence of biological soil crusts. This further stabilizes the surface physical structure and enhances the soil nutrient content, thus creating favorable plant growth conditions which, in turn, increase plant species diversity. In contrast, the natural bare sand is barren with high mobility due to high winds and thus no stability develops to create plant growth conditions. The spatial distribution patterns of E. songoricum were investigated in both bare sand areas and artificial sand fixed areas by plotting coordinates of every E. songoricum ramet in each sample plot. To assess the quantitative population characteristic differences of E. songoricum between artificial sand fixed areas and natural bare sand areas, species composition, abundance, height, coverage and biomass were assessed in both habitats. Results showed that the numbers of families, genera and species of E. songoricum communities in the artificial sand fixed habitat were significantly higher than those in the bare sand habitat. The similarity index value between communities in the two habitats was only 0.522, indicating that the artificial sand fixed habitat changed the species composition and structure of the E. songoricum community greatly. The quantitative characteristics of height, coverage, above ground, below ground and total biomass densities and above ground, below ground and total biomass per individual were also significantly higher (P <0.05 or P <0.01) in the artificial sand fixed habitat than those in the bare sand habitat. The correlation dimension values of the population spatial distribution in the two habitats were all close to 2.0, indicating strong spatial relevance and holding space ability for individuals. The aggregation analysis at two scales (1 m and 2 m) indicated that almost all of the populations were randomly distributed; thus the artificial sand fixed habitat had no effect on the degree of spatial aggregation. Random distribution pattern may therefore be part of the intrinsic properties of E. songoricum populations and it is possible that it forms the same way regardless of habitat. The organic matter, total nitrogen and available nitrogen contents in the artificial sand fixed habitat were significantly (P <0.01) higher than those in the bare sand habitat, and were significantly (P <0.05 or P <0.01) positively correlated with the population quantitative characteristics except for abundance of E. songoricum individuals. In comparison with the bare sand habitat, the surface of the artificial sand fixed habitat was stable and the soil organic matter and nitrogen contents were higher. This meant that the coverage, height, biomass densities and biomass per individual of the E. songoricum population were markedly different and that the survival and adaptation ability of E. songoricum is stronger in these plots. This conclusion is important for the protection and conservation of this and other endangered desert species.