1. Key Laboratory of Resource Biology and Biotechnology in Western China, Northwest University, Taibai North Rd. 229, Xi'an, Shaanxi, China
2. Environmental Protection Research Institute, Xi'an Research Institute of China Coal Technology & Engineering Group Corp, Xi'an, China
3. Plant Ecology Department, University of Tuebingen, Auf der Morgenstelle 3, 72076 Tuebingen, Germany