1. Key Laboratory of Grassland Ecosystem, Ministry of Education, Lanzhou 730070, China
2. Sino-U.S. Centers for Grazing Land Ecosystem Sustainability, Lanzhou 730070, China
3. Pratacultural Engineering Laboratory of Gansu Province, Lanzhou 730070, China
4. Pratacultural College, Gansu Agricultural University, Lanzhou 730070, China
5. Grassland Technique Extension Station of Gansu Province, Lanzhou 730000, China