Effects of Row Orientation and Canopy Inclination on Gas Exchange and Energy Management in the Asymmetric Peach Orchard

This paper reports a study conducted in a peach orchard (Asymmetric Orchard) where row orientation and canopy inclination are varied in order to modify the timing and levels of light interception by the trees. The trees of this orchard either received their maximum light levels in the morning (W) or in the afternoon (E). A vertical, N-S oriented treatment served as control (C). Although intercepting higher daily total light levels, W trees did not show the highest CO2 net uptake and their assimilation seemed to be stomatal limited in the afternoon. Furthermore, the same trees showed the highest photodamage levels. In comparison, C trees, although intercepting the least amount of radiation in the day, showed the same net photosynthesis with a photodamage 29% lower than W. The best photosynthetic performances were recorded on E plants, with a concomitant higher daily H2O loss and a photodamage 8% lower than W. The quenching analysis conducted at the single leaf level showed the light intercepted in excess was dissipated via several photo-protective pathways. The main strategy plants used to cope with the excessive photon pressure was the controlled Delta pH-dependent thermal dissipation (Non Photochemical Quenching) supported by the non net carboxylative transports (Water-water cycle, Cyclic transport around PSI, Glutathione-ascorbate cycle and photorespiration), which were more active than the former at middle-low irradiances. This study demonstrated that modulating the timing and intensity of light interception during the day may affect the photosynthetic performance and water use efficiency. The levels of photodamage and photoinhibition can also be affected. Further research is needed to investigate the consequences of photoinhibition and the amount of resources allocated to PSII repair and removed from plant productivity.