1. School of Life Sciences, Hebei University, Baoding, China
2. Erguna Forest-Steppe Ecotone Ecosystem Research Station, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, China
3. CSIC, Global Ecology Unit CREAF-CSIC-UAB, Bellaterra, Spain
4. CREAF, Cerdanyola del Vallès, Spain
5. State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing, China