1. Key Laboratory of Dryland Agriculture, Ministry of Agriculture, Institute of Environment and Sustainable Development in Agriculture Chinese Academy of Agricultural Sciences Beijing 100081 China
2. State Key Laboratory of Vegetation and Environmental Change, Institute of Botany Chinese Academy of Sciences Beijing 100093 China
3. Food Security and Safety Niche Area, Faculty of Natural and Agricultural Sciences North‐West University Private Bag X2046 Mmabatho 2735 South Africa