The impact of land-use/land-cover and climate changes on ecosystem productivity and carbon cycle is one of the most important issues in global change studies.In the past 20 years,the climate and land-use in China have changed significantly and have had important ecological consequences,especially in ecologically sensitive regions,e.g.the cropping-grazing transition zone(CGTZ).Here we present a study that used a process-based ecosystem model and data of land-use changes based on remote sensing and of climate change at high spatial and temporal resolution to estimate the impacts of land-use and climate changes on net primary productivity(NPP),vegetation carbon storage,soil heterotrophic respiration(HR),carbon storage and net ecosystem productivity(NEP)in the CGTZ of China.The results show that the warming and decreases in precipitation in CGTZ reduced NPP by 3.4%,increased HR by 4.3%,and re-duced annual mean total NEP by 33.7Tg from the 1980s to the 1990s.Although carbon storage in vegetation and soil was increasing because the mean NPP for the period was higher than HR,the decreasing NEP indicate that climate change reduced the carbon uptake rate.However,land-use changes in this zone caused increases in NPP by 3.8%,vegetation carbon storage by 2.4%,and annual total NEP by 0.59Tg.The land-use changes enhanced ecosystem carbon up-take,but not enough to offset the negative effect of the climate change.The climate change had greater impacts than the land-use change for the whole CGTZ zone,but had smaller impacts than the land-use change in the regions where it occurred.
