中文摘要：

以三江源区高寒草甸草原、退化高寒草甸草原、退化高寒草原和人工草地4种土地利用方式为研究对象,研究了不同土地利用方式的地上、地下生物量,土壤容重和土壤主要养分有机碳、全氮、全磷、有效氮和有效磷含量,结果表明总生物量的排序为高寒草甸草原〉退化高寒草原〉退化高寒草甸草原〉人工草地,退化草地和人工草地的生物量明显降低,尤其是地下生物量,退化高寒草甸草原、退化高寒草原和人工草地的地下生物量分别为高寒草甸草原的31.9%,54.8%和13.9%,总生物量分别仅为高寒草甸草原的32.8%,49.4%和29.5%。人工草地的表层土壤容重显著降低,而退化对土壤容重没有明显影响,3种天然土地利用方式土壤容重在土壤剖面的变异也不明显。4种类型草地土壤碳氮磷养分含量均处于很低的水平,退化主要造成表层土壤碳氮的严重损失,平均分别损失了53.0%和52.4%,4种利用方式土壤有效氮和有效磷含量极低,而退化对土壤的全磷和有效磷影响不大。

英文摘要：

The four land use patterns, alpine meadow steppe, degraded alpine meadow steppe, degraded al- pine steppe and artificial grassland, were selected to study the effects of land use pattern changes on alpine grassland, and the differences in biomass, soil hulk density and soil nutrients, soil organic carbon, total nitrogen, total phosphorus, available nitrogen and available phosphrous content were determined in Qum- alai county, Three-river headwater area. The results showed that total biomass presented the order of al- pine meadow steppe〉degraded alpine steppe〉degraded alpine meadow steppe〉artificial grassland. Total biomass decreased significantly after degradation and artificial planting, especially the root biomass. The root biomass of degraded alpine meadow steppe, degraded alpine steppe and artificial grassland were only 31.9 %, 54.8% and 13.9%, and the total biomass were only 32.8%, 49.4% and 29.5% of alpine meadow steppe ,respectively. The above ground biomass of artificial grassland was the highest, but the root biomass was the lowest, which led to the lowest total biomass in the four land use patterns, only 29.5% of alpine meadow steppe pattern. Soil bulk density in 0--10cm soil of the artificial grassland decreased significantly, and degradation had no significant effect on soil bulk density. The variation of soil bulk density in the soil profile of the three natural grassland types was not obvious. Soil carbon, nitrogen and phosphorus content were at a low level in the area. Degradation mainly caused heavy decrease of soil carbon and nitrogen in surface soil, and 53.0% and 52.4% loss of the alpine meadow steppe, respectively. The available nitrogen and phosphorus of the four types were all at a lower level, which could not support plant growth. The degradation had little effect on soil total phosphorus and available phosphorus.