1. Key Laboratory of Surface Processes and Resource Ecology Faculty of Geographical Science Beijing Normal University Beijing 100875 China
2. Beijing Key Laboratory of Traditional Chinese Medicine Protection and Utilization Faculty of Geographical Science Beijing Normal University Beijing 100875 China
3. Grassland Research Institute of Chinese Academic of Agricultural Science Hohhot Inner Mongolia 010021 China
4. Key Laboratory of Cell Proliferation and Regulation Biology of Ministry of Education College of Life Sciences Beijing Normal University Beijing 100875 China