Ozone effects on Aleppo pine seedlings (Pinus halepensis Mill) grown in open-top chambers

A three-year term experiment was performed in eastern Spain to assess the effects of ozone (O-3) on the physiological behaviour of Aleppo pine (Pinus halepensis). Seedlings of this species were enclosed in open-top chambers during the summer and exposed to either Charcoal Filtered Air (CFA) to exclude O-3, Non Filtered Air (NFA) or Non Filtered Air plus 40 ppb O-3, 9h/day, 5 days/week (NFA+40). Gas exchange, foliar chlorophyll and nutrient levels were measured throughout the year. Clear seasonal fluctuations were observed since chlorophyll levels, stomatal conductance and net photosynthesis rates were lower during the summer, and higher in winter. O-3-induced effects were apparent on previous year needles from the second Lear of exposure. A reduction in net photosynthesis, stomatal conductance, chlorophyll, N and P was found in the NFA + 40 plots. The results showed the sensitivity of this species to ozone, since a three-month exposure to realistic O-3 concentrations over three consecutive years induced important alterations in Aleppo pine performance, The application of the results to the definition of a critical O-3 level for forest trees is discussed.