中文摘要：

人为活动影响下陆地生态系统退化对于土壤碳库损失的影响规模是当前全球变化研究的热点。在青海省三江源区选择了8个高寒草甸典型样区，划分4种不同退化程度样地（原生植被、轻度退化、重度退化、极度退化），收割法采集地上部植物生物量，10cm等深度采集表土土壤样品，分析了地上生物量、可食牧草生物量以及土壤有机碳含量变化。结果表明，随着退化程度的加剧，地上生物量和饲草生物量均表现强烈下降的趋势，但后者的下降幅度更大，在极度退化下损失达99％。研究区内高寒湿地土壤的表土有机碳含量出现极大的变异性，随退化程度的加剧而呈显著下降。与原生植被下相比，轻度退化、重度退化和极度退化下0-30cm土壤有机碳含量分别平均降低了25％、44％和52％。这种损失固然与地上部生物量下降有关，有机碳分层系数显示土壤侵蚀也是重要因素。估计退化下土壤有机碳平均下降36tC·hm^-2，累积退化下表土有机碳损失可能在200TgC以上，保护高寒草甸生态系统，对于三江源区土壤的畜牧业可持续发展和我国陆地生态系统碳库具有极重要的意义。

英文摘要：

Degrdation of terrestrial ecosystems under human disturbance and the effects on soil organic carbon stock change have been paid grteat attetion in the context of global change issues. In this study, 8 typical areas of high altitude grsaalands in the source area of the Yellow River, Yangtze River and Lancangjiang River, Qinghai Province, China were selected and 4 types of vegetation decline （primary vegetation, slight declined, seriousle declined and severely declined vegetation ）,were identified for vegetation plant mass and soil sampling. In each sampling plot, aboveground plant biomass were collected using total-cutting method and animal feed grass biomass were manually separated, and were weighed before and after ovendrying. Topsoil（0-30 cm） samples were collected using 10 cm depth interval sampling with a soil auger. And soil organic carbon content was measured with wet digestion and pyrochromate oxidation Results showed that total aboveground plant biomass and feed biomass was dramatically decreased as the vegetation declined. Decline in feed biomass was more intense with alo- most 99% of feed biomass lost under severely declined vegetation, much variable contents of soil organic carbon was found with different vegetation decline status. Compared to under primary vegetation, topsoil（0-30 cm） SOC stock was shown in decline at 25%, 44% and 52% under slightly declined, seriously declined and severely declined vegetation respectively. SOC stratification within the topsoil indicated that soil truncation as a result of enhanced soil erosion by vegetation decline may have also impacted topsoil SOC stock decline apart from the decreased organic matter input due to vegetation decline. It is estimated, a topsoil SOC stock reduction of 36 t·hm^-2 on average under vegetation decline. A total of over 200 Tg C may have been lost due to vegetation decline in this area. Therefore, preservation of the high altitude grasslands is cricial for bothensuring the sustainability of animal husbandry in Qinghai Province