1. Department of Biophysics, Huygens Laboratory, Leiden University, P.O. Box 9504, 2300 RA, Leiden, The Netherlands, Institute of Soil Science and Photosynthesis, Russian Academy of Sciences, Pushchino, Moscow Region 142292, Russian Federation, and Faculty of Physics and Astronomy, Vrije Universiteit, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands