ACKNOWLEDGEMENTS
We thank Ruzhen Wang, Zhirui Wang, Yongyong Zhang, Wentao Luo, Xiaobin Li, Xue Wang, Xue Feng, Zhan Shi, Peng He and Fei Yao for assistance in the field, and Shiping Chen and Zijia Zhang for providing meteorological data. We acknowledge staff at the Erguna Forest-Steppe Ecotone Ecosystem Research Station for their logistical support. This study was financially supported by grants from the National Natural Science Foundation of China (32060284 & 31870441), the Natural Science Foundation of Inner Mongolia, China (2019JQ04), and the National Science Foundation of the United States (DEB-1856318 & CBET-1833988).