中文摘要：

以内蒙古克鲁伦河流域呼伦贝尔典型草原为对象，设置了轻度、中度和重度退化3种类型样地，研究不同程度退化草原的物种组成、地上生物量、土壤理化性状、土壤微生物数量和酶活性，以及微生物生物量的变化．结果表明：中度退化样地的群落物种丰富度最大，轻度退化样地的地上生物量显著高于重度退化样地．退化样地的土壤水分、养分（有机质、全氮），微生物量碳、氮，以及微生物数量和酶活性显著下降，土壤容重显著增加．退化样地的土壤微生物生物量碳、氮在128～185和5．6～13．6g·kg-1，土壤脱氢酶和脲酶活性均与土壤容重呈显著负相关，与土壤全氮、有机质、微生物数量以及微生物生物量碳、氮呈显著正相关，地上生物量与土壤细菌和真菌数量呈不同程度的正相关．

英文摘要：

To investigate the influence of degradation on grasslan three sites respectively under light, moderate and severe d d, we sampled soil and plants at egradation in Hulunbeir Grassland in northern China and analyzed the differences and relationships among soil physicochemical charac- ters, enzyme activity, soil microorganism quantity and aboveground biomass. The results showed that species richness of the moderately degraded site was highest while the aboveground biomass at the lightly degraded site was significantly higher than at the severely degraded site. Soil moisture content, nutrients （organic matter and total nitrogen） concentrations, soil microorganism quantity and enzyme activity were all decreased significantly in the degraded sites, whereas both the soil hardness and bulk density showed an opposite trend. The soil microbial biomass carbon and nitro- gen contents ranged from 128 to 185 g ~ kg-I and from 5.6 to 13.6 g ~ kg-~ , respectively. The soil dehydrogenase and urease activities negatively correlated with soil bulk density but positively corre- lated with total nitrogen, organic matter, microbial biomass carbon and nitrogen. The aboveground biomass showed significantly positive correlation with the number of soil bacteria and fungi.