1. Photosynthesis Research Unit, Agricultural Research Service, United States Department of Agriculture, Urbana, Illinois 61801, USA:
2. Departments of Plant Biology and Crop Sciences, University of Illinois, Urbana, Illinois 61801, USA:
3. Universitá degli Studi della Tuscia, Department of Forest Environment and Resources (DISAFRI), Via S. Camillo de Lellis, I‐01100 Viterbo, Italy;
4. Department of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, UK