Effects of ozone on photosynthesis of Mediterranean urban ornamental plants

Measurements of leaf gas exchange under saturating light were performed on plants of six species during and after a short-term treatment with ozone (200 ppb, 5 h). Reductions of photosynthetic activity were observed in all the species; they were associated to stomatal closure and/or mesophyll limitations. Laurus nobilis and Hedera canariensis var. azorica showed a quick reduction of stomatal conductance, with a consequential limitation of photosynthetic activity; this species was able to fully recover before the end of the fumigation. Nerium oleander and Hedera helix also showed a significant reduction of photosynthetic activity, associated to a partial stomatal closure. Photosynthetic efficiency of Viburnum tinus and Arbutus unedo was affected only after the end of the treatment, the main effects being non-stomatal