Effect of Canopy Position on the Susceptibility of Kiwifruit (Actinidia deliciosa) Leaves on Vines in an Orchard Environment to Photoinhibition Throughout the Growing Season

Abstract

Kiwifruit (Actinidia deliciosa (A. Chev) C.F. Liang & A.R. Ferguson) plants 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.