1. Landcare Research, PO Box 40, Lincoln 7640, New Zealand
2. Faculty of Agriculture, Food and Natural Resources, The University of Sydney, Private Bag 4011, Narellan NSW 2567, Australia
3. Agro‐Meteorology Division, National Institute for Agro‐Environmental Sciences, 3‐1‐3 Kannondai, Tsukuba 305‐8604, Japan
4. Institut de Biologie des Plantes, Université Paris Sud 11, CNRS UMR 8618, 91405 Orsay Cedex, France
5. Department of Plant Sciences, The University of Cambridge, Cambridge, UK