1. Finnish Forest Research Institute, Jokiniemenkuja 1, FI-01370 Vantaa, Finland.
2. Institute of Physicochemical and Biological Problems in Soil Science, Russian Academy of Sciences, 142290 Institutskaya ul., 2, Pushchino, Moscow Region, Russian Federation.
3. Department of Forest Sciences, University of Helsinki, Latokartanonkaari 7, FI-00014 University of Helsinki, Finland.