中文摘要：

土壤质量变劣是沙化的本质，核心内容为土壤物质流失，理化性质和生物特性退化，以及土体构型的变化。弃耕前土壤沙化程度和性质对弃耕地植被恢复进程、演替方向等产生重要影响。为了深入认识弃耕恢复草地不同覆沙厚度条件下，土壤环境因子和植物之间的关系，以宁夏盐池荒漠草原弃耕恢复草地为研究对象，应用冗余分析（ｒｅｄｕｎｄａｎｃｙａｎａｌｙｓｉｓＲＤＡ），研究弃耕恢复草地随地表覆沙厚度在空间上的连续变化，植被分布及其多样性变化与主要土壤因子间的关系。结果表明，１）随着覆沙厚度的增加植被由达乌里胡枝子群落向苦豆子群落转变；达乌里胡枝子的重要值由０．３３４降低到０．１０４，苦豆子的重要值由０增加到０．４０４。２）植物群落物种多样性指数从０．３２增加到０．７９，丰富度指数从０．１３增加到０．４０，均匀度指数从０．１１增加到０．２２。３）对弃耕地植物群落分布及其物种多样性变化有显著影响的主要土壤环境因子分别为碳酸钙和全盐（０～１０ｃｍ）、碳酸钙（１０～４０ｃｍ）。表层土壤碳酸钙含量的变化表征了地带性灰钙土的沙化程度和退化阶段，弃耕恢复草地当前植物分布格局的形成主要还是特定土壤退化状态约束下物种随机扩散竞争的适应性结果，覆沙厚度所决定的表层土壤环境因子的直接或间接作用是主要的决定因子，土壤养分对植被的直接作用尚未充分体现。

英文摘要：

The essence of desertification is that soil quality deteriorates. Loss of soil materials, soil physical and chemical properties, deterioration of biological characteristics and the changing of soil structure are the princi- pal features. The previous degrees and nature of soil desertification have important effects on the process of vegetation recovery and the direction of succession after land is abandoned. To develop a deeper understanding of the relationship between plant and soil environmental factors under different thicknesses of sand bed, we studied the relationship between plant distribution, diversity and major soil factors with the changing of surface sand bed thickness in space by redundancy analysis, taking a recovered grassland on abandoned cultivated land in the desert steppe region of Ningxia as the test area. With an increase of sand bed thickness, the Lespedeza bicolor plant community was substituted by that of Sophora alopecuroides, and the importance of L. bicolor decreased from 0. 334 to 0. 104 while the importance value of S. alopecuroides increased from 0 to 0. 404. The plant diversity index of Margalef, Shannon--Wiener and Pielou were correspondingly increased： the plant di- versity index of Margalef increased from 0.32 to 0.79, that of Shannon--Wiener from 0.13 to 0.40,and that of Pielou from 0.11 to 0.22. The main significant soil environment factors affecting plant distribution and diversi- ty were soil salt and calcium carbonate in the 0--10 cm soil layer and soil calcium carbonate in the 10--40 cm soil layer. The change of soil calcium carbonate content on the surface represented the degree of desertification and the stage of degeneration of the zonal sierozem. At present, the form of plant distribution patterns on re- covered grassland in abandoned lands, was mainly the result of adaptability of species diffusing and randomly competing under the given constraints of a specific state of soil degradation. The crucial factors were the direct or indirect effects of surface soil environm