1. State Key Laboratory of Desert and Oasis Ecology; Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences; 818 South Beijing Rd Urumqi 830011 China
2. University of Chinese Academy of Sciences; 19A Yuquan Rd Beijing 100049 China
3. Earth System Science Interdisciplinary Center, University of Maryland; 5825 University Research Ct. College Park MD 20740 USA