Leaf movements: an efficient strategy against photoinhibition in Robinia pseudoacacia L.

The exposure to high irradiance and high temperature conditions may result in PSII photoinhibition. Among different mechanisms engaged by plants to prevent photodamages, leaf movement (heliotropism) may represent an important strategy to avoid direct exposure to sunlight. To assess the contribute of leaf movements in PSII photoprotection on R. pseudoacacia plants, chlorophyll a fluorescence measurements were made at 12:00, 14:00, 16:00 and 18:00 on attached blocked leaves to prevent leaf movements and to maximize the daily radiation interception (BL) and on control unblocked leaves (UL). At midday as well as at 14:00 and 16:00, a significant decrease of FPSII, qP, Fv’/Fm’ and an increase of qN and EEE was observed in BL as compared to UL leaves that maintained these parameters almost constant throughout the day. However at 14:00, when temperature and irradiance reached the highest values, the differences between BL and UL became more pronounced. At 18:00, with sunlight and temperature decline, BL leaves showed a strong recovery of FPSII, qP, Fv’/Fm’ and a significant decrease of qN and EEE compared to 12:00, 14:00 and 16:00. Nevertheless, in spite of recovery, BL maintained FPSII, qP and EEE values lower than UL. Data presented suggest that in Robinia pseudoacacia L. under high irradiance and temperature,leaf movements, by reducing light interception, represent an efficient strategy to avoid photoinhibitory risks.