Pigment concentrations and ratios of Aleppo pine seedlings exposed to ozone

Two-year-old Aleppo pine (Pinus halepensis Mill.) seedlings were exposed to ambient air+50 ppb O-3 in open-top chambers (24 hours/day, 7 days/week) du ring May-October 1997 and to ambient air+70 ppb O-3 from May 1998 onwards. One growing season fumigation with ozone did not affect the pigment concent rations of the current-year (c) needles, nor were there any differences in photosynthesis or stomatal conductance. In May 1998, however, a marked carr y-over effect was seen in the chlorophyll a and b and total carotenoid conc entrations of the O-3-fumigated one-year-old (c+1) needles. The chlorophyll a and b and total carotenoid concentrations of newly flushed needles of th e O-3-fumigated seedlings also seemed to be slightly decreased, as was thei r net photosynthesis when compared to the values of the filtered-air contro l needles. The chlorotic mottle and the changes in chloroplast pigments and photosynthesis of the c and/or c+1 needles of the NFA+O-3 seedlings in May 1998 indicate that frequent episodes of ozone concentrations of greater th an or equal to 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.