Canopy Design Drives Photosynthetic Performance, Light Environment, and Fruit Quality in Peach (Prunus persica L. Batsch)

Training system selection critically influences peach orchard productivity through its effects on canopy light environment, physiological responses, and fruit quality. This study evaluated two contrasting training systems: a 2D planar fruiting wall system (Four-Axis, 1020 trees ha^-1) versus a 3D Quad-V system (590 trees ha^-1) using two peach cultivars, fresh table 'Platibelle' and clingstone 'Mirel' in Central Macedonia, Greece. Comprehensive physiological measurements including leaf gas exchange, chlorophyll fluorescence, and fruit quality parameters were assessed across two canopy zones (lower 0-1.2 m vs. upper 1.8-3.3 m) during the 2023 and 2024 growing seasons. Results demonstrated that the 2D system achieved superior leaf area index (LAI), but lower light interception, leading to enhanced photosynthetic performance with 15-20% higher net photosynthetic rates and improved water-use efficiency compared to the 3D system. Notably, the photosynthetic apparatus of fruiting wall trees maintained significantly greater efficiency (6.26 μmol CO₂ m^-2 s^-1) in the lower canopy zone than in Quad-V trees (3.6 μmol CO₂ m^-2 s^-1), indicating a more uniform and functional light environment. The 2D system produced fruits with improved flesh firmness and color development in 'Mirel', while higher dry matter in 'Platibelle'. Correlation analysis revealed that Four-Axis trees enhanced the interdependence among thermal, gas exchange, and compositional traits, reflecting a shift from morphology-driven to metabolically integrated canopy function. In terms of yield, fruiting walls achieved higher efficiency and total production (Mt ha^-1) in 'Mirel', supporting their adoption to enhance productivity and peach fruit quality in Mediterranean conditions.