1. Max Planck Institute for Biogeochemistry, Department of Biogeochemical Processes , Hans-Knöll-Str.10, Jena 07743 , Germany
2. Department of Environmental Sciences–Botany, University of Basel , Schönbeinstr. 6, Basel CH-4056 , Switzerland
3. Department of Forest Botany and Tree Physiology , Laboratory for Radioisotopes, , Büsgenweg 2, Göttingen 37077 , Germany
4. Georg-August University Göttingen , Laboratory for Radioisotopes, , Büsgenweg 2, Göttingen 37077 , Germany
5. Institute for Forest Protection, Julius Kühn-Institute, Federal Research Centre for Cultivated Plants , Erwin-Baur-Str. 27, Quedlinburg 06484 , Germany