草地退化对三江源区高寒草甸生态系统CO_2通量的影响及其原因

Impacts of the rangeland degradation on CO2 flux and the underlying mechanisms in the Three-River Source Region on the Qinghai-Tibetan Plateau

为了揭示草地退化对三江源地区高寒草甸生态系统碳通量的影响,利用涡度相关技术,于2006年12月1日~2007年11月30日对三江源地区的退化高寒草甸生态系统的碳通量及生物和环境因子进行观测.结果发现：草地退化对高寒草甸生态系统的碳通量产生了深刻影响,与未退化的高寒草甸生态系统相比,退化高寒草甸生态系统全年总初级生产力（GPP）下降了36.6%,全年生态系统呼吸（Reco）下降了7.9%,全年净生态系统CO2交换（NEE）也由退化前的负值（碳吸收）转变为正值（碳排放）,二者相差132.5gC/（m2.a）,生态系统由原来的碳汇转变为目前的碳源.这些变化与高寒草甸退化后,生态系统植物地上生物量锐减、植物生长期缩短（NEE〈0的天数）、植物多样性下降、土壤含水量降低等因素密切相关.

To assess the effect of rangeland degradation on CO2 exchange,the eddy covariance technique was used to measure CO2 flux,biological and environmental factors for one year（from December 2006 to November 2007） in a degraded alpine meadow ecosystem in Three-River Source Region located on the Qinghai-Tibetan Plateau.The results showed that the degradation had a significant impact on the CO2 flux in this region.Compared with non-degraded ecosystem,annual GPP and Recoof the degraded alpine meadow ecosystem decreased by 36.6%,7.9%,respectively.Also the value of annual NEE raised from negative（carbon uptake） to positive（carbon emission） in the deagraded ecosystem,and its difference between degraded and non-degraded alpine meadow ecosystem was 132.5gC/（m2.a）.It is suggested that the alpine meadow ecosystem changed from a carbon sink to a carbon resource due to degradation.Those results can be caused by the reduction in the plant aboveground biomass and plant diversity,shorter growing season length（the days of NEE0）,and declining of soil water content after the rangeland degradation.