1. College of Resources and Environment, University of Chinese Academy of Sciences, Beijing, P. R. China;
2. College of Life Science, University of Chinese Academy of Sciences, Beijing, P. R. China;
3. Key Laboratory of Alpine Ecology and Biogdiversity, Institute of Tibetan Plateau Research, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, P. R. China;
4. Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, P. R. China