1. Geoecology Univ. of Tübingen; Rümelinstraße 19-23 72070 Tübingen Germany
2. Dep. of Biogeochemical Processes; Max-Planck-Institute for Biogeochemistry Jena; Hans-Knöll-Straße 10 07745 Jena Germany
3. Institute of Geography and Geoecology Karlsruhe Institute of Technology; Reinhard-Baumeister-Platz 1 76131 Karlsruhe Germany