中文摘要：

以短花针茅（Stipabreviflora）荒漠草原为研究对象，采用巢式样方法分析在不同绵羊载畜率下草地的α多样性以及物种组成的变化，探讨荒漠草原生态系统在放牧利用下仪多样性对载畜率的响应。结果表明：物种数和α多样性指数随着载畜率的升高而下降。放牧会减少群落非优势物种的相对多度，非优势物种能够反映仅多样性。40m2为短花针茅荒漠草原多样性研究的最佳取样面积。种-面积关系以及α多样性指数．面积关系符合对数增长模型：Y=aln（x）＋b。随着取样面积尺度的增加，α多样性指数沿载畜率梯度差异性逐渐增大，在取样面积为0．16m2到0．64m2时可以体现中、高载畜率和零、低载畜率水平间的差异性，在160m2时可以体现各载畜率水平之间的差异显著性。

英文摘要：

Plant diversity is a crucial component of biodiversity, and it has attracted growing attention in recent years. For desert steppes, however, how grazing and the sample area used in these studies affect species diversity, and through what mechanisms, is still unclear. Stipa breviflora grasslands typically represent desert steppes, which in turn occupy a special place among the grassland ecosystems. In this study, a long-term （ 11 years） grazing experiment with four levels of grazer stocking rate in the S. breviflora desert steppe in Siziwang Banner of Inner Mongolia was used. The study aims to provide a scientific basis for grassland biodiversity protection and sustainable development, and therefore explored the influence of different grazer stocking rates on plant diversity （using four alpha diversity indexes： the Margalef, Shannon-Wiener, Simpson, and Pielou index）. Grassland alpha diversity and species composition change was assessed for different stocking rates, and the sample area sizes （from 0.01 m2 to 650 m2） were analyzed to determine the optimal sampling area for this desert grassland.The results showed that ： （ 1 ） The number of species and alpha diversity indices declined with increasing stocking rate. （2） Compared with the relative density of the dominant species （e. g. S. breviflora and Cleistogenes songorica） , grazing reduced the relative density of non-dominant species. Dominant species have a strong adaptability and endurance, whereas non-dominant species have a sensitive response to grazing. Moreover, a decrease in non-dominant species resulted in a lower alpha diversity index. This suggests that non-dominant species are important indicators that reflect how plant species respond to grazer stocking rate changes, and underline the variety in adaptive strategies for resources changes. （3） The best sampling area size to investigate the species number and alpha diversity was 40 m2. （4） The species-area relations and alpha diversity index-area relations both conform