EFFECT OF CANOPY POSITION ON THE SUSCEPTIBILITY OF KIWIFRUIT (ACTINIDIA-DELICIOSA) LEAVES ON VINES IN AN ORCHARD ENVIRONMENT TO PHOTOINHIBITION THROUGHOUT THE GROWING-SEASON

Kiwifruit (Actinidia deliciosa (A. Chev) C.F. Liang and A.R. Ferguson) planes grown in an orchard were studied over several seasons to assess the impact of photoinhibition on the leaves using chlorophyll fluorescence and photosynthetic measurements. Leaves above were compared with those below the vine canopy. In addition, temperature and photon flux densities above and below the canopy were monitored. A gradient of sun to shade photosynthetic characteristics developed in leaves from above to below the canopy. There was a 10% higher F-v/F-m ratio in the shade leaves (0.810) but a 30% lower photosynthetic capacity and a 30% higher photon yield than in sun leaves. In addition, F-o and F-m were both higher (20-60%) in shade leaves. Little variation in F-v/F-m occurred throughout the growing season, except during spring, when F-v/F-m was about 0.4-0.5, especially in small, rapidly expanding leaves. Changes in F-v/F-m during spring were correlated with leaf diameter, indicating development of photosynthetic competence was an important factor in the rise in F-v/F-m. However, increasing night temperatures also correlated with the increase in F-v/F-m during spring.