1. Department of Crop Production Ecology, Swedish University of Agricultural Sciences, P.O. Box 7043, SE-75007 Uppsala, Sweden
2. Department of Forest Mycology and Plant Pathology, Uppsala BioCenter, Swedish University of Agricultural Sciences, P.O. Box 7026, SE-75007 Uppsala, Sweden
3. Faculty of Agricultural and Environmental Sciences, Soil Science, University of Rostock, Justus-von-Liebig Weg 6, DE-18057 Rostock, Germany