敦煌西湖荒漠-湿地生态系统优势物种生态位研究

水文情势改变会引起土壤盐分变化，直接影响到荒漠-湿地生态系统植被的分布与演替。基于对57个样地、171个样方植物物种分布影响较大的土壤pH值和土壤电导率两个环境因子，将其划分为6个梯度等级，测度分析了敦煌西湖植被群落中15个主要优势种的生态位特征，了解不同物种利用资源和占据生态空间的能力，对维持和科学保育植物群落的多样性具有重要意义。结果表明：（1）在土壤pH值和电导率梯度两个资源维上，多枝柽柳和芦苇的重要值和生态位宽度均较大，说明这两个物种适应能力强能够较好地利用环境资源，分布范围大且均匀。它们作为敦煌西湖植被群落中的广域种，具有重要的生态地位和作用。其次生态位较宽的疏叶骆驼刺、胡杨和苏枸杞对环境因子也具有较强的适应能力。（2）两个土壤因子梯度下植物种群生态位宽度相似，但也存在差异。如泡泡刺、蒙古沙枣在土壤pH值梯度资源维上的生态位宽度值远大于在土壤电导率梯度资源维上，但尖叶盐爪爪和甘蒙柽柳在土壤电导率梯度资源维上生态位宽度较大，表现出较强的耐盐能力，从而说明这些物种对不同土壤因子的利用能力和适应性不完全相同。（3）在两个资源维上优势物种间的生态位重叠值小于0.5的种对均为61对，占总种对的58.10%，因此生态位重叠值整体保持在较低水平，说明物种在土壤pH值和土壤电导率两个环境梯度上生态位分化明显。（4）敦煌西湖优势物种间总体表现为不显著的负关联，表明物种之间处于竞争关系，但竞争强度不大且群落结构稳定性较弱。

Niche of the dominant species in wetland ecosystem enclosed by extremely dry desert region in Dunhuang Xihu

Soil salinity changes caused by altering hydrological regimes can directly affect the distribution and succession of vegetation in desert-wetland ecosystem. By investigating the vegetation in 171 quadrats at 57 study sites, soil pH and soil conductivity, which were regarded as the key soil factors determining species distribution, were selected and divided into 6 levels to explore the niches of 15 dominant species in Dunhuang Xihu wetland ecosystems. This study aimed to discuss the ability of different species in resource utilization and ecological space occupation, which has important implications in maintaining and conserving the biodiversity in this desert-wetland ecosystems. Results showed that: (1) along the soil pH and conductivity gradient, both Tamarix ramosissima and Phragmites australis had highest importance values and largest niche width, which indicated these two species had stronger adaptation ability and can made better use of resources. As the generalist species, they seemed to play important roles in plant communities. Following them, Alhagi sparsifolia, Populus euphratica and Lycium ruthenicum also had strong adaptability to environmental factors. (2) The niche width of dominant species were overall similar but with differences along the two soil environmental gradients, e.g., the niche width of Nitraria sphaerocarpa and Calligonum mongolicum along soil pH gradient were larger than those along soil conductivity gradient, while Kalidium cuspidatum and Tamarix austromongolica had larger niche width along soil conductivity gradient, and showed stronger salt tolerance, thus the utilizing ability and adaptation of these species to different soil factors were not identical. (3) Most species'' niche overlap were minor, 58.10% species were lower than 0.5 across the two resource axes. It suggested that the species niches had obvious differentiation along soil pH and soil conductivity gradients. (4) There were negative (but not significant) relationships among 15 dominant species, which indicated that the species were competitive, but the competition intensity was low and the community stability was relatively weak.