1. Dep. of Agroecology Faculty of Science and Technology; Aarhus Univ.; Blichers Allé 20 P.O. Box 50 DK-8830 Tjele Denmark
2. Dep. of Biotechnology, Chemistry and Environmental Engineering; Aalborg Univ.; Sohngaardsholmsvej 57 DK-9000 Aalborg Denmark