ACKNOWLEDGEMENTS
This work was supported by National Key Research and Development Program
of China (No. 2018YFC0507005, No. 2016YFA0602301) and National Natural
Science Foundation of China (No. 41401304; No. 41571526). We thank staff
of Jiusan soil and water conservation experimental station of Beijing
Normal University, Prof. Hongyan Zhang and Dr. Yanfang Hao for data
collection, Dr. Zhongqiang Wang for comments. The authors indicate no
potential conflicts of interest.