PSII photochemistry and carboxylation efficiency in Liriodendron tulipifera under ozone exposure

Liriodendron tulipifera is an important forest plant which is commonly used in urban environments as a shade tree. Young plants have been exposed (under controlled conditions) to 120 ppb of O-3 for 45 consecutive days (5 h d(-1)). The aim of this investigation was to clarify if O-3 limits the physiological performance of L tulipifera. In treated plants, dynamics related to membrane injury, gas exchange and chlorophyll a fluorescence leads to: (i) increase in lipid peroxidation (maximum value of +78% 15 days after the fumigation, compared to controls): (ii) reduction of photosynthetic activity (up to 66% 28 days after the exposure), twinned with a partial stomatal closure and a store of CO2 in substomatal chambers: (iii) reduction in carboxylation efficiency (-11% at the end of exposure): (iv) damage to PSII, as demonstrated by the increase in the PSII excitation pressure (-57%28 days after the treatment). On this basis, O-3 should be considered very harmful to L tulipifera, although the reduction of total chlorophylls content and the activation of xanthophyll cycle take place in order to attempt to regulate light absorbed energy limiting oxidative damage. (C) 2010 Elsevier B.V. All rights reserved.