1. State Key Laboratory of Grassland Agro-ecosystems, School of Life Sciences, Lanzhou University, No.222, Tianshui South Road, Lanzhou, Gansu 730000, China.
2. Yuzhong Mountain Ecosystem Observation and Research Station, Lanzhou University, No.222, Tianshui South Road, Lanzhou, Gansu 730000, China.
3. Department of Environmental Sciences, University of Virginia, Charlottesville, VA, USA.
4. Shapotou Desert Research and Environment Station, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, No.320, Donggang West Road, Lanzhou, Gansu 730000, China.