中文摘要：

该文以宁夏哈巴湖自然保护区四儿滩湿地为研究对象,探讨西北干旱、半干旱区湿地——草原生态系统植物群落空间分布特征及影响群落空间分布格局的主要环境因子。外业调查选择每年的植物生长季节,从东、东北、西、西北4个方向沿着湿地——草原生境梯度布设4条样线,每条样线均超过1km。调查内容包括植物盖度、生物量、密度、频度、高度等,以及土壤环境因子。采用TWINSPAN数量分类方法和DCA排序方法对四儿滩湿地植被进行数量分类和排序,同时进行排序轴与土壤环境因子间的秩相关分析。研究表明：研究区植被分为3个植被型14个群丛。第一组为盐生沼泽植被,以湿生、盐生植物为主,代表群丛为芦苇＋盐爪爪,主要分布在湿生带;第二组为草甸植被型,以湿生、中生植物为主,代表群丛为白刺＋白草群丛,主要分布在湿地——草原交错带;第三组为草原植被型,以中生、旱生的赖草＋新疆猪毛菜＋苦豆子群丛为主,分布在草原旱生带。秩相关分析结果表明：土壤含水量、全盐含量、土壤养分含量（全N、速效K、有机质等）均是影响植被沿湿地——草原梯度分布格局的主要环境因子;湿地——草原不同方位间植被分布格局差异的主要影响因子是地形及放牧等。此外,该文还对重要值的完善与改进进行了探讨。

英文摘要：

The spatial distribution characteristics of plant communities in a wetland-dry grassland ecosystem in arid ＆ semi-arid region in northwestern China and the main influencing factors were studied. Siertan Wetland in the Haba Lake Nature Reserve was the study area. Four transect lines, each of which was about 1 km long, were set up in the growing season along the biotope gradient in four directions： east, northeast, west and northwest. Attributes measured were the frequency of occurrence, height, density, coverage, biomass, etc. and soil environmental factors. The data were analyzed using two-way indicative species analysis （TWINSPAN）, detrended correspondence analysis （DCA） and Spearman＇ s correlation. On this basis, the vegetation in Siertan Wetland was classified into three types and 14 associations. The first vegetation type was halophytic marsh vegetation, which was mainly distributed in the wetland zone. This vegetation type mainly contained halophyte and hygric plants and its representative association was Association. Phragmites communis, Kalidiumfoliatum. The second type was meadow vegetation, which distributed in the ecotone. The species of meadow vegetation was mainly mesophytic and its representative association was Association. Nitraria tangutorum, Pennisetum flaccidum. The third vegetation type was grassland vegetation, which mainly consisted of mesophyte and xerophytes, and distributed in arid-grassland zone. The representative association of the third vegetation type was Association. Anaeurolepidium secalium, Saussurea runcinata. Correlation analysis between the axes of DCA and the soil environment factors shows that the soil moisture content, organic matter, soil salt content, total nitrogen etc. are the main environmental factors influencing the vegetation distribution pattern along the biotope gradient from wetland to arid grassland. Other influencing factors are microtopography and grazing pressure. Additionally, this paper reports modifications and improvements to the importance va