Impacts of urban levels of ozone on Pinus halepensis foliage

Between May and September, 1996, seedlings of Pinus halepensis were placed at a site adjacent to an automated air pollution monitoring station within the urban area of Florence. Additional 'control' plants were placed in cham bers ventilated with charcoal/Purafil(R)-filtered air. All trees were well watered throughout the whole experimental period. During the exposure perio d, ambient levels of sulphur dioxide were very low, whilst the accumulated hourly exposure to ozone above 40 ppb (i.e. AOT40) exceeded 20 000 ppb h(-1 ) peak hourly ozone concentrations rising to levels above 100 ppb. Trees ex posed to ambient levels of air pollution exhibited typical symptoms of ozon e damage (chlorotic mottle) on previous year needles toward the end of the summer. Similar symptoms were not observed on equivalent trees exposed to f iltered-air, nor were visible symptoms accompanied by insect or pest infest ation. Anatomical and ultrastructural observations made on symptomatic need les revealed degeneration in mesophyll cells bordering sub-stomatal cavitie s and alterations in chloroplast ultrastructure (fat accumulation, starch a nd tannin pattern modifications). These observations are consistent with th e known effects of air pollutants (namely ozone) recorded in the literature . Findings are discussed in relation to the impacts of ozone on P. halepens is in the Mediterranean region. (C) 2000 Elsevier Science B.V. All rights r eserved.