Acknowledgements
This study was partially supported by the Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, and the “Top Notch” program in China. C.S. is supported by the National Natural Science Foundation of China (41125001). L.Z. was partially supported by National Key Research and Development Program of China (2016YFC0500601) and the National Natural Science Foundation of China (41371111). X.X. acknowledged the financial assistance provided by the SPRUCE and NGEE Arctic projects, which are supported by the Office of Biological and Environmental Research in the Department of Energy Office of Science. J.B. was partially supported by the Interdisciplinary Research Funds of Beijing Normal University. I.A.J. acknowledge support from the European Research Council Synergy Grant IMBALANCE-P (ERC-2013-SyG-610028). Dr. Natalie M. Mahowald at Cornell University kindly shared her data of global depositions of N and P for this study.