中文摘要：

为探明生态脆弱区土地利用方式转换对土壤有效态微量元素的影响,以贵州喀斯特地区草地及其相应开垦的农田为对象,采用成对设计的方法研究了草地开垦对土壤微量元素（铜、锰、铁、钼、硼、锌）的影响,并探索基于土壤微量元素密度的区域土壤微量元素丰缺评价指标。结果表明：研究区土壤有效态微量元素在土壤剖面上呈表面富集现象,其含量随土层深度的增加而降低;草地开垦导致土壤有效态铜、铁、硼和钼的含量出现不同程度的降低,降幅为4.97%～79.17%,而土壤有效锌含量则增加,增幅为11.76%～46.06%;开垦导致土壤有效锰含量在剖面上的下降速率加快。建立了研究区6种有效微量元素的丰缺评价指标,该指标以土壤微量元素密度为参数,以参数值的不同范围界定微量元素的丰缺程度,消除了微量元素空间异质性对判定结果的影响。根据该评价指标,研究区土壤有效铁、锰处于极高水平,草地开垦导致土壤有效铜、钼、硼的丰度下降,而有效锌的丰度上升;结合微量元素有效性评价指数,整个研究区土壤有效硼处于低水平,不能够满足植物正常生长发育的需要。该研究结果可为生态脆弱区土地的科学管理和土壤微量元素科学评价体系的建立提供参考。

英文摘要：

With population growth, most of the grasslands in China were converted into croplands. The structure, process and function aspects of the ecosystem changed as a result from the conversion of the grassland, and led to a decline in soil quality and productivity, soil erosion acceleration, and destruction of the vegetation. These phenomena are especially obvious in karst areas, because the typical characteristics of karst areas are harsh habitats and ecological vulnerabilities. Nowadays, most investigations mainly focus on biodiversity, soil and water conservation, soil productivity, and soil carbon density. However, the studies of soil trace elements are scarce. The available trace elements of soil are very important for plant growing, especially when major elements, such as N, P, and K are rich. In order to explore the effects of the conversion of grassland into cropland on soil trace elements （Cu, Fe, Mn, Zn, B, and Mo）, a paired-site design was employed between grasslands and corresponding croplands of karst area in Guizhou. At the same time, the regional indices of trace soil elements were developed based on trace soil element density. In this study, the contents of available trace soil elements in different depths were measured and the element densities were calculated for the grasslands and their counterpart croplands, and consequently the regional indices of trace soil element was built for evaluating the study area. The results showed that trace soil elements decreased with soil depth. The soil contents of available Cu, Fe, B, and Mo decreased, ranging from 4.97% to 79.17%, resulting from the conversion of grassland to cropland. The soil content of available Zn in every soil depth in cropland was higher than in grassland, increasing in range from 11.76%to 46.06%;also, the declining rate of available Mn content in cropland areas was faster than in grassland areas after the grassland conversion. As the contents of trace soil elements varied with soil depth, the previous evaluation standard, based on the t