title: Physiological response of Pinus halepensis needles under ozone and water stress conditions.
abstract: The aim of this study was to evaluate how physiological processes of potted Pinus halepensis plants, grown under controlled conditions, were affected by ozone (O3) and/or water stress, integrating the gas exchange and biochemical data with fluorescence OJIP polyphasic transient data. Plants submitted to only water stress (T1) and with ozone (T3) showed a strong decrease in stomatal conductance and gas exchange, coinciding with a reduction of maximum yield of photochemistry (varphipo) and very negative values of leaf water potential. Simultaneously, a great increase of both PSII antenna size, indicated by absorption per reaction centre, and electron transport per reaction centre were found. The reduction of photosynthesis in the O3-treated plants (T2) by a slowing down of the Calvin cycle was supported by the increase of related fluorescence parameters such as relative variable fluorescence, heat de-excitation constant, energy de-excitation by spillover, and the decrease of varphipo. We suggest an antagonistic effect between the two stresses to explain the delayed ozone-induced decrease of stomatal conductance values for T3 with respect to T1 plants, by an alteration of the physiological mechanisms of stomatal opening, which involve the increase of intra-cellular free-calcium induced by ABA under co-occurring water shortage. We emphasise the importance of considering the intensity of the individual stress factor in studies concerning the interaction of stresses.
authors.affiliation: Department of Plant Biology, University of Rome 'La Sapienza', Piazzale Aldo Moro, 5, I-00185 Rome, Italy Department of Environmental Sciences, University of Molise, Via Giuseppe Mazzini, 8, I-86170 Isernia, Italy.
authors.forename: Fausto
authors.initials: F
authors.lastname: Manes
authors.forename: Eugenio
authors.initials: E
authors.lastname: Donato
authors.forename: Marcello
authors.initials: M
authors.lastname: Vitale