1. College of Grassland Science, Shanxi Agricultural University, Taigu 030801, China
2. Key Laboratory of Model Innovation in Forage Production Efficiency, Ministry of Agriculture and Rural Affairs, Taigu 030801, China
3. Industrial Crop Research Institute, Shanxi Agricultural University, Fenyang 032200, China
4. College of Chemistry and Environmental Science, Inner Mongolia Normal University, Hohhot 010022, China