Temperature-dependence of carbon acquisition and demand in relation to shoot growth of kiwifruit (Actinidia deliciosa) vines grown in controlled environments

Kiwifruit (Actinidia deliciosa (A. Chev) C.F. Liang et A.R. Ferguson) vines were grown at day/night temperature regimes of 28/22 and 17/12 degrees C for 5 months starting from budbreak to measure the relationship between shoot growth and carbon demand and to determine the temperature-sensitivity of these processes. Leaf area, internode length, photosynthesis and respiration were measured on the same leaves at regular intervals in both growth temperatures. From daily net carbon acquisition of the shoots and carbon accumulation in biomass, daily net carbon balance per shoot was determined. High temperature-grown shoots had 100% more leaf area and 20% longer stems than low temperature-grown shoots and, although photosynthetic and respiration rates were only slightly affected by temperature, shoots at 17/12 degrees C acquired a net gain of 35 g carbon and 182 g at 28/22 degrees C, of which 94% and 54%, respectively, were used in shoot biomass growth. Net carbon balance was negative for 35-57 days after budbreak, but shoots at 17/12 degrees C had a total surplus of 1.4 g over 5 months whereas shoots at 28/22 degrees C accumulated 46 g of carbon in this time. Results suggest potential for growth of fruit from surplus carbon is likely to be highly dependent on temperatures in early summer.