1. Beijing Key Laboratory of Biodiversity and Organic Farming, Key Laboratory of Plant-Soil Interactions of the Ministry of Education, College of Resources and Environmental Sciences, China Agricultural University , Beijing 100193 , China
2. South China Botanical Garden, Chinese Academy of Sciences , Guangzhou 510650 , China
3. Key Laboratory of Oasis Ecology of Education Ministry, College of Ecology and Environment, Xinjiang University , Urumqi 830017 , China