1. Department of Environmental, Biological and Pharmaceutical Sciences and Technologies; Second University of Naples; Caserta 81100 Italy
2. Centre for Bio-Archaeology and Ecology, Institut de Botanique; Ecole Pratique des Hautes Etudes (PALECO EPHE); University of Montpellier 2; Montpellier F-34090 France
3. Deptment. of Agricultural Sciences; University of Naples Federico II; Portici (Naples) I-80055 Italy
4. Max Plank Institute for Biogeochemistry; Jena D-07701 Germany
5. Paul Scherrer Institute; Villigen CH-5232 Switzerland
6. Swiss Federal Research Institute; Birmensdorf CH-8903 Switzerland