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

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.