1. State Key Lab. of Earth Surface Process and Resource Ecology; Beijing Normal Univ.; Beijing 100875 China
2. State Key Lab. of Earth Surface Process and Resource Ecology; Academy of Disaster Reduction and Emergency Management Ministry of Civil Affairs and Ministry of Education Beijing Normal Univ.; Beijing 100875 China
3. Center for Agricultural Resources Research; Inst. of Genetics and Developmental Biology Chinese Academy of Sciences; 286 Huaizhong Rd. Shijiazhuang Hebei 050021 China