EFFECT OF MODERATE LIGHT REDUCTION ON ABSORBED ENERGY MANAGEMENT, WATER USE, PHOTOPROTECTION AND PHOTO-DAMAGE IN PEACH
Net carbon assimilation increases with irradiance to a saturation point, above which absorbed light is in excess. Besides the temperature increase, with attendant water losses, light excess can increase the photoinhibition risks due to Reactive Oxygen Species (ROS) production. Plants developed a multi-pronged and synergistic photoprotective strategy involving the thermal dissipation, via the xanthophylls cycle, and the photochemistry transports (alternative electron transports and photorespiration). Plants, however, cannot completely avoid photo-damage, and have developed an effective, efficient and energy-dependent recovery system to repair the damaged photosystem II (PSII). This study reports the effect of 40% neutral shading of peach leaves on their gas exchange parameters, the absorbed energy management, and the PSII damage susceptibility during the day. Light reduction did not affect net carboxylation but, decreasing stomatal conductance and temperature under the highest daily irradiance, it increased water use efficiency (WUE). During the same time of the day the xanthophylls cycle quenched more energy in CTRL than in SHD, dissipating 65 and 50% of the absorbed energy, respectively. On the contrary SHD funnelled more energy to photochemistry than CTRL probably because at medium-low irradiance the xanthophylls cycle is pH limited. The susceptibility of PSII to photoinhibition was similar between the two treatments as the same exponential decay of the active PSII against the photon exposure (light intensity × time of exposure) was recorded. The maximal amount of active PSII damaged by a photon unit (Quantum yield of photoinactivation, Qy) was also not influenced by light reduction therefore, the more the absorbed photons, the more the photo-damage to be repaired (at energy cost). These preliminary results suggests that optimizing light interception can ameliorate the plant water use efficiency, without affecting net carbon assimilation and reducing carbon and energy costs for photosystems recovery.
Losciale, P., Zibordi, M., Manfrini, L., Morandi, B. and Corelli-Grappadelli, L. (2011). EFFECT OF MODERATE LIGHT REDUCTION ON ABSORBED ENERGY MANAGEMENT, WATER USE, PHOTOPROTECTION AND PHOTO-DAMAGE IN PEACH. Acta Hortic. 907, 169-174
photochemistry, photosynthesis, quenching partitioning, shading net, xanthophylls cycle