We would first like to acknowledge the flux data providers and the organizers of the FLUXNET. The data used in this study are archived at the FLUXNET networks (https://fluxnet.ornl.gov/) and the Coordinated Enhanced Observation Network of China (http://observation.tea.ac.cn/). Funding: This work was supported by the National Natural Science Foundation of China (grant 41271039 and 41571016);
State Key Project for Typical Fragile Ecological Restoration and Protection Research (2016YFC0500203);
Higher Specialized Research Foundation for Doctoral Program (grant 20100211120006);
and Fundamental Research Funds for the Central Universities (862151). We also thank Shuang Sun and Dong Liu for their assistance in the data collection;