Pigment Concentrations and Ratios of Aleppo Pine Seedlings Exposed to Ozone

Abstract

Two-year-old Aleppo pine (Pinus halepensis Mill.) seedlings were exposed to ambient air+50 ppb O3 in open-top chambers (24 hours/day, 7 days/week) during May-October 1997 and to ambient air+70 ppb O3 from May 1998 onwards. One growing season fumigation with ozone did not affect the pigment concentrations of the current-year (c) needles, nor were there any differences in photosynthesis or stomatal conductance. In May 1998, however, a marked carry-over effect was seen in the chlorophyll a and b and total carotenoid concentrations of the O3-fumigated one-year-old (c+l) needles. The chlorophyll a and b and total carotenoid concentrations of newly flushed needles of the O3-fumigated seedlings also seemed to be slightly decreased, as was their net photosynthesis when compared to the values of the filtered-air control needles. The chlorotic mottle and the changes in chloroplast pigments and photosynthesis of the c and/or c+l needles of the NFA+O3 seedlings in May 1998 indicate that frequent episodes of ozone concentrations of ≥ 100 ppb, especially when they also occur during the evening and night hours, as in some areas in southern Europe, may result in visible needle damage on Aleppo pine.