Paraheliotropism in Robinia pseudoacacia L.: an efficient strategy to optimise photosynthetic performance under natural environmental conditions

Abstract

We assessed the contribution of leaf movements to PSII photoprotection\ud against high light and temperature in Robinia pseudoacacia. Gas exchange\ud and chlorophyll a fluorescence measurements were performed during the\ud day at 10:00, 12:00, 15:00 and 18:00 hours on leaves where paraheliotropic\ud movements were restrained (restrained leaves, RL) and on control unrestrained\ud leaves (UL). RL showed a strong decrease of net photosynthesis\ud (An), stomatal conductance (gsH2O), quantum yield of electron transport\ud (FPSII), percentage of photosynthesis inhibited by O2 (IPO) and photochemical\ud quenching (qP) in the course of the day, whereas, a significant increase\ud in Ci ⁄Ca and NPQ was observed. Contrary to RL, UL had higher photosynthetic\ud performance that was maintained at elevated levels throughout the\ud day. In the late afternoon, An, gsH2O, FPSII and qP of RL showed a tendency\ud to recovery, as compared to 15:00 hours, even if the values remained lower\ud than those measured at 10:00 hours and in UL. In addition, contrary to UL,\ud no recovery was found in Fv ⁄ Fm at the end of the study period in RL. Data\ud presented suggest that in R. pseudoacacia, leaf movements, by reducing light\ud interception, represent an efficient, fast and reversible strategy to overcome\ud environmental stresses such as high light and temperature. Moreover, paraheliotropism\ud was able to protect photosystems, avoiding photoinhibitory\ud damage, leading to a carbon gain for the plant