1. Environmental and Biochemical Sciences Group, Enhancing Crop Production and Utilisation Theme, The James Hutton Institute, Invergowrie, Dundee, DD2 5DA, Scotland
2. Norwegian Institute for Agricultural and Environmental Research, Bioforsk Nord Holt, Box 2284, N-9269 Tromsø, Norway
3. Department of Arctic and Marine Biology, University of Tromsø, N-9037 Tromsø, Norway
4. School of Life Sciences, Heriot-Watt University, Riccarton, Edinburgh, EH14 4AS, Scotland