中文摘要：

利用细菌通用引物，对从黄土高原5个地区土壤样品以及西峰剖面26个土壤样品中提取的总DNA进行聚合酶链式反应（PCR）扩增，采用变性梯度凝胶电泳（DGGE）技术对PCR产物进行分析，以揭示黄土高原土壤中细菌群落结构的多样性。针对黄土高原土壤微生物特点进行DGGE试验条件优化，获得最佳变性梯度为40％～70％，最佳电泳时间为17h（100V）。对不同深度土壤细菌DGGE图谱的聚类分析表明，不同深度土壤细菌呈现2种不同的群落结构，推测其成因可能与季风性气候引起的温湿环境变化及冰期有关。在夏季风加强而冬季风减弱的时期，气候温暖潮湿，风化成壤作用强烈，在DGGE图谱中表现为土壤样品条带多而密；反之，风化成壤作用较弱，在DGGE图谱中表现为条带少而疏。对洛川、西峰等5个地区土壤细菌Shannon—Weiner指数的测定结果表明，Shannon—Weiner指数受条带亮度及迁移率的影响。

英文摘要：

Soil samples were collected from five regions and 26 soil samples from the Xifeng Profile of the Loess Plateau. Total DNA was extracted from those samples with the aid of bacterial universal primer and amplified by means of PCR and its product analyzed with the DGGE technique to explore diversity of bacterial communities. Oriented towards the features of the microbes in the soil of the plateau, conditions of the DGGE experiment were optimized with an optimal denaturant gradient ranging between 40% and 70% , and an optimal electrophoresis duration being 17 hours （100 V）. Analysis of DGGE profiles of bacteria in soils at various depths revealed that there are two different types of bacterial community structures in soils at various depths in the Loess Plateau, which is presumably attributed to changes of the warm-humid environ- ment caused by monsoon climatic conditions, and ice age. In the age when monsoon got stronger in summers and became weak in winters, the climate was warm and humid, and weathering and soil formation were intensive, which showed muhipie and dense bands in the DGGE profile, whereas conversely, weathering and soil formation are weak, which showed sparse bands in the profile. The determination of Shannon-Weiner indexes of soil bacteria in the five regions of the plateau indicated that the Shannon-Weiner indexes were influenced not only by the amount of bands, but also by brightness and moving rates of the bands