Fig. 5. Relationship between reduction in leaf carbon exchange rate (CER) after a 16-h exposure to 4°C in the dark and incident photosynthetic photon flux density (PPFD) following cold exposure without acclimation in ‘Pioneer 3902’. In the growth-room study, plants were moved to PPFD levels of either 400, 650, or 1200 mmol m^-2 s^-1 at 0900 h, and depicted values are means derived from measurements made at 1000, 1200, 1400, and 1600 h. In the field study, plants were moved to the field at 1000 h, and the depicted value at 2000 µmol m^-2 s^-1 is a mean derived from measurements taken at 1100 and 1500 h across five stages of development (cf., Table 1).