Canopy light management in kiwifruit: effects on leaf photosynthetic performance, fruit growth dynamics and carbon storage

This thesis investigated the influence of canopy light environment on leaf photosynthetic performance, fruit growth dynamics, and carbon storage in kiwifruit. Light availability was manipulated using different netting and reflective cloth systems. The experiments were conducted in the 2023 and 2024 seasons in a yellow-fleshed ‘Jinyan’ kiwifruit orchard located in Faenza, Italy. In the 2024–2025 season, the experiments were conducted in a green-fleshed ‘Hayward’ kiwifruit orchard located in Te Puke, New Zealand. In Chapter II, the application of a reflective cloth improved kiwifruit within-canopy light, markedly increasing shade-leaf maximum photosynthetic rate and light saturation point, while maintaining apparent quantum yield; thus, demonstrating greater overall light-use efficiency. Furthermore, the conversion of inner-canopy leaves from carbon neutral to positive net assimilation, led to more abundant flowering in the following season. In Chapter III, the reflective cloth enhanced within-canopy light, increasing early-season kiwifruit berry transpiration. This led to greater xylem flows to the fruit, favoring also calcium accumulation. Furthermore, higher light availability increased fruit dry matter and yield. The light environment affected fruit development mainly at the beginning of the season, when fruits exchange large amounts of water, while its influence decreased approximately 110 days after full bloom, with the increase in importance of apoplasmic phloem unloading. In Chapter IV, shading vines (~60%) reduced fruit growth rate, final weight, dry matter, and soluble solids content. Moreover, it decreased replacement cane total non-structural carbohydrate concentration by 20–30% near harvest, possibly affecting following year productivity; while cane vigor exhibited minor effects. Collectively, the results reveal that increased light distribution within the kiwifruit canopy enhances shade leaves light-use efficiency and improves early-season fruit xylem inflow, improving yield and berry quality. On the other hand, shading negatively affects current-year production as well as the accumulation of reserve carbohydrates for subsequent year productivity.