Abstract
The innovative Web-O3-Fumigation (WOF) is a suitable technique to study O3 effects in plants. Through WOF, a very high dose of O3 fumigation may be obtained at the level of selected leaves, while allowing a gradient of ozone stress in branches at different distance from branch directly fumigated with O3 diffusing from perforated Teflon tubes. We used WOF to study the impact of O3 on the emission of isoprene, a putatively powerful antioxidant, in leaves of Quercus pubescens. In our experiment we produced with WOF: i) approximately 300 ppb O3 on the leaves of the branch directly exposed to the pollutant; ii) approximately 190 ppb on the leaves of the branches distant less than 30 cm from the treated branch; iii) a summer ambient O3 concentration (100 ppb) on the leaves of the branches distant more than 30 cm from the branch directly fumigated. High O3 concentrations induced a long-lasting inhibition of photosynthesis and isoprene emission in leaves which were directly fumigated. However, isoprene emission was stimulated by intermediate O3 concentration 288 hours after the end of the treatment. Isoprene stimulation, and the activation of the related antioxidant mechanism, may therefore be dependent on the O3 concentration and may be different in plant canopies depending on their exposure to the pollutant.