Seasonal and daily changes in carbon acquisition of kiwifruit leaves with and without axillary fruit

Potted kiwifruit (Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson) plants were transferred to a controlled environment at monthly intervals throughout the growing season (October-May). Daily time-courses of net photosynthesis and respiration were measured on vegetative and fruit-subtending leaves that emerged in October, November, December, and February. Net carbon acquisition of each leaf was determined from daily and seasonal changes in gas exchange. Maximal rates of photosynthesis were coincident with or shortly after leaves became fully expanded and photosynthetic development was dependent on the environmental history of leaves. Photosynthesis declined during the day by 10-40% in vegetative leaves and 20-50% in leaves subtending fruit. Carbon acquisition of leaves subtending fruit was 60% lower than vegetative leaves. Results imply that competition between fruit and vegetative sinks has a regulatory role on carbon acquisition of leaves but further elucidation to understand how this affects variation in fruit size is required.