Carbon (C) fluxes in terrestrial ecosystems vary across spatial scales. However, the global patterns of the variable C fluxes and their controlling mechanisms are not very well understood and this lack of understanding hinders our ability to predict global C fluxes as well as C feedback to the atmosphere. 902 site-years of annual eddy C flux records were compiled from ChinaFLUX and global flux sites. Climate, soil and associated biological data were used to explore the controlling factors and mechanisms for the geographic distribution of global ecosystem C fluxes.
Results/Conclusions:
Our synthesis of eddy-flux data showed a strong geographic pattern of annual ecosystem C fluxes at the global scale. Generally, the largest annual gross primary production (AGPP) and ecosystem respiration (ARE) occurred in the low-latitude tropics, followed by the subtropical regions, and then the temperate regions. The global geographic patterns in AGPP, ARE and annual net ecosystem production (ANEP) were mainly controlled by the spatial variations in mean annual temperature (MAT) and precipitation (MAP). Evidence from eddy-flux measurements suggests three underlying biogeographic mechanisms: 1) temperature and precipitation influence growing season length and C-uptake capacity and thus control AGPP across spatial scales; 2) ARE is controlled by the AGPP supply and the respiratory responses of the stored ecosystem organic matters to temperature across spatial scales; 3) The responses of AGPP to climate pattern and the impacts of disturbances on ratio of ARE/AGPP co-determined the geographic pattern of ANEP. The three interrelated mechanism combinedly contributes to the climate-driven geographic distributions of ecosystem C fluxes at the global scale.