中文摘要：

以甘肃小陇山林区8～30年林龄日本落叶松林（外来树种）、油松林（乡土树种）及次生林为研究对象，研究了不同树种森林的土壤质量和细菌多样性变化．结果表明：不同树种森林土壤pH无明显变化；林龄越长，土壤含水量越高．土壤总氮与有机质含量以次生林最高，其次为日本落叶松，油松最低．不同林龄森林土壤总氮与有机质含量无明显变化，表明树种是影响土壤质量的主要因素．与乡土树种油松相比，外来树种日本落叶松显著提高了土壤全氮及土壤有机质含量．变性梯度凝胶电泳（DGGE）图谱显示，次生林土壤细菌多样性最高，而外来树种日本落叶松土壤细菌多样性最低．对DGGE图谱的聚类分析发现，小陇山不同森林土壤细菌类群分属变形杆菌、噬纤维黄杆菌和高G＋C含量革兰氏阳性细菌类，其中分属变形杆菌为主要类群．进一步分析发现，日本落叶松的细菌群落组成具有更高的相似度，说明日本落叶松正在使该地区土壤细菌多样性发生变化．

英文摘要：

The study on the soil quality and bacterial diversity under 8-30 years old exotic Larix kaempferi, native Pinas tabulaeformis, and secondary deciduous broadleaf forest stands in Xiaolongshan Mountains of Gansu, Northwest China showed that the soil pH under different forest stands had no distinct variation, but soil moisture content was increased with increasing age of forest stands. Soil organic matter and nitrogen contents were the highest under secondary deciduous forest, followed by under L. kaermpferi, and P. tabulaeformis. However, the soils under different ages of forest stands had no obvious variations in their organic matter and nitrogen contents, suggesting that tree species was the main factor affecting soil quality. Compared with P. tabulaeformis, exotic L. kaempferi could significantly increase soil organic matter and nitrogen contents. PCR-DGGE banding patterns suggested that the soil under secondary deciduous broadleaf forest had the highest bacterial diversity, followed by under L. kaempferi, and P. tabulaeformis. The sequenced DGGE bands were classified into three bacterial groups, i. e. , Proteobacteria, Cytophaga -Flavobacterium -Bacteroides, and high G ＋ C content gram-positive type, among which, Proteobacteria occurred most frequently. Further detailed analyses suggested that the soil bacterial compositions under exotic Lar/x stands were more similar to each other than those under pine and secondary deciduous broadleaf forests. It was concluded that exotic L. kaempferi induced the changes of microbial diversity in the forest soils of this region.