1. Institute of Ecology, College of Urban and Environmental Sciences, Peking University , Beijing 100871 , China
2. State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences , Beijing 100093 , China
3. The Key Laboratory for Silviculture and Conservation of Ministry of Education, Beijing Forestry University , Beijing 100083 , China
4. State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences , Beijing 100093 , China
5. Key Laboratory of Plant-Soil Interactions of the Ministry of Education , , Beijing 100193 , China
6. College of Resources and Environmental Sciences, China Agricultural University , , Beijing 100193 , China