1. Alfred Wegener Institute for Polar and Marine Research, Telegrafenberg A43, D-14473 Potsdam, Germany
2. State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Xiangshan Nanxincun 20, 100093 Beijing, China
3. Department of Plant Ecology and Natural Conservation, Institute of Biochemistry and Biology, University of Potsdam, Maulbeerallee 2, D-14469 Potsdam, Germany
4. Department of Earth and Environmental Sciences, University of Potsdam, Karl-Liebknecht-Strasse 24-25, D-14476 Potsdam, Germany