中文摘要：

采用化学分析法、微生物平皿分离计数和形态鉴定技术研究了青海三江源地区天然与退化植被下的土壤养分和微生物生态特征。结果表明，随着三江源地区天然草地植被退化，土壤有机质含量急剧下降，退化高山草甸土的有机质平均含量为14．85gkg^-1，较天然高山草甸土的平均含量降低54．3％，较高山草原土和沼泽化草甸土分别降低74．5％和90．7％，其他养分含量也有不同程度的降低，土壤养分状况明显恶化．不同类型植被下土壤微生物区系特征变化显著，退化高山草甸土的细菌、真菌、放线菌（GA）平均数量分别为8．8×10^6、9．5×10^3、8．1×10^5 cfu g^-1，较天然高山草甸土降低65．8％、46．6％、57．3％，较高山草原土降低37．1％、23．3％、62．6％，较沼泽化草甸土降低90．3％、48．1％、69．6％；退化草地土壤微生物组成较天然草地更为简单，退化高山草甸土的真菌种类数明显降低，土壤放线菌组成趋于简单化，其小单孢菌和其他菌属所占比例明显低于天然草地．三江源高寒湿地生态系统中土壤养分与微生物数量之间存在密切关系，土壤全磷对微生物数量影响最大．

英文摘要：

This study aimed to investigate soil microflora and nutrient cycling under different vegetation types in the Sanjiangyuan region, Qinghai. Soil organic matters and nutrient contents were determined by conventional chemical methods, while microbial populations were studied using spread-plate techniques and classified by their morphological features. The data indicated that deterioration of the vegetation resulted in a loss of soil nutrients and an overall decline in soil fertility in the Sanjian- gyuan region. The soil organic matters averaged 14. 85 g kg^-1 in degraded alpine meadow soil, which was 54% - 91% lower than that of non-degraded soil. Soil nitrogen, phosphorus and available potassium levels were also much lower in degraded than those in non-degraded soil, but there was no consistent pattern change in total soil potassium or pH. Soil microflora in the alpine marshland soil was negatively affected by the change in vegetation and decline in fertility. Specifically, the bacterial population in the degraded alpine meadow soil was 8. 8 × 10^6 cfu g^-1 compared to fungal population of 9. 5 × 10^3 cfu g^-1 and actino- mycete population of 8. 1 × 10^5 cfu g^-1. These populations were 47% - 66% lower than microbial populations in the non-de- graded alpine meadow soil, 23% - 63% lower than those in the alpine grassland soil and 48% - 90% lower than those in the marshy meadow soil. The microbial community structure simplified along with the vegetative degradation. The number of fungal species dropped from seven under non-degraded vegetation to three in degraded areas. Nearly 97% of the actinomycetes isolated from degraded meadow soil were streptomycetes, while the others declined significantly. In conclusion, there was a close relationship between soil nutrient content and soil microflora in the Sanjiangyuan alpine ecosystem. The analysis of soil nutrient factors and microbial populations showed that total soil phosphorus was the key nutrient to affect the populations of the three main types of soil microorgani