Fluorescence transient in ozonated mediterranean shrubs

Three Mediterranean evergreen broadleaves, viz., laurel (Laurus nobilis), strawberry tree (Arbutus unedo) and phillyrea tree (Phillyrea latifolia), were exposed to 0, 55 or 110 nmol mol-1 O3. After 90 days, Chl a fluorescence was recorded and analysed with the 0JIP technique. Results confirmed that these species may be considered O3-tolerant. Even with slight responses to O3, the analysis of fluorescence transient gave useful information and highlighted a reduction in the density of active reaction centers in a PSII cross-section, and an increase of their activity in ozonated L. nobilis and mainly P. latifolia leaves. The realistic ambient spring concentration of 55 nmol mol-1 O3 slightly depressed the energy dissipation in A. unedo, and increased the performance index and the maximum quantum yield of primary photochemistry in L. nobilis and A. unedo. These responses are interpreted as over-compensation due to counter-O3-reactions. It is concluded that present ambient O3 levels do not impair the photosynthetic performances of these Mediterranean species in a 90-day term, even if recovery processes during the O3-free periods cannot be excluded.