Temperature and light response curves for photosynthesis in kiwifruit (Actinidia chinensis) cv. Hayward

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Abstract
Kiwifruit (Actinidia chinensis Planch) cv. Hayward plants were grown at constant day/night temperatures of 10, 15,20,25, and 30°C at a vapour pressure deficit of 0.8 kPa. At each temperature, plants were grown at 2 photosynthetic photon flux densities (PPFD); 280 and 650 μmol-2 s-1. The short term response of photosynthesis to temperature was measured for selected leaves of plants grown at each temperature and 650 μmol-2 s-1. For plants from each growth temperature, the temperature optimum for photosynthesis was higher at higher growth temperatures. Between growth temperatures of 15 and 30°C, the slope of the line relating the optimum temperature for photosynthesis to the growth tempetature was 0.58. The maximum rate of photosynthesis per leaf area increased with an increase in growth temperature to an interpolated optimum at 16°C, and then fell again at higher growth temperatures. In contrast, when the rate of photosynthesis was expressed on a leaf weight basis, the maximum rate rose assymptopically with increasing growth temperatures to become constant above 15T. The difference in response was because specific leaf weight declined with increased growth temperatures. The response of photosynthesis to PPFD was measured for plants grown at 10 and 25°C at both growth PPFD treatments. The rate of photosynthesis for plants grown at 2YC adapted to the light conditions. Photosynthetic rates of plants grown at 650 μmol-2 s-1 saturated at a higher PPFD than plants grown at 380 μmol-2 s-1. Also, the photosynthetic rates were higher in plants grown at the higher PPFD. However, plants grown at 10° showed little adaption to the light conditions under which they were grown. The overall results are similar to results reported for other warm temperate plants subjected to a varied temperature environment.