Photosynthetic and respiratory response of potato leaves of different ages during and after an episode of high temperature

Little is known about net photosynthetic rates (Pn) of potato during and after the end of a high-temperature episode. We investigated Pn of potato leaves exposed to a high-temperature episode. Plants were grown in the greenhouse at 22 degrees C. Shortly after tuber initiation, plants were transferred to 30 degrees C for 9 days and then returned to 22 degrees C. High temperatures reduced Pn of older leaves but not of the youngest leaves. Effects were transitory; Pn of leaf 7 initially fell, but then increased to be higher than the control plants. High temperature increased respiration per unit area during the night and morning relative to the control plants. Leaves that emerged during the 30 degrees C episode had higher Pn than the control plants when returned to 22 degrees C. Results emphasise that it is not possible to use single-leaf measurements to infer effects on photosynthesis throughout the canopy. Similarly, the diurnal variation in effects on respiration means that Pn measurements made only at midday are inadequate. Finally, the dynamic response of Pn to the high temperature and the persistent effects after the end of the episode mean that the impact of high-temperature episodes cannot be extrapolated from experiments using constant temperature treatments.