1. Soil and Ecosystem Ecology Laboratory; Lancaster Environment Centre, Lancaster University; Lancaster LA1 4YQ UK
2. School of Agriculture; Food and Rural Development, University of Newcastle; Newcastle NE1 7RU UK
3. Rothamsted Research; North Wyke Okehampton Devon EX20 2SB UK
4. Centre for Agri-Environmental Research; University of Reading, Reading; RG6 6AR UK
5. Département de Biologie; Université de Sherbrooke; Sherbrooke (Qc) J1K 2R9 Canada
6. Systems Ecology; Department of Ecological Science; Faculty of Earth and Life Sciences, VU University; 1081 HV Amsterdam The Netherlands
7. Max Planck Institute for Biogeochemistry; 07745 Jena Germany