1. The State Key Laboratory of Earth Surface Process and Resource Ecology, Beijing Normal University, Beijing 100875, China
2. College of Resources and Environment, Ningxia University, Yinchuan 750021, China
3. College of Agricultural Sciences, The Pennsylvania State University, State College, PA 16803, USA
4. Center of New Technology Application and Research, Ningxia University, Yinchuan 750021, China