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 pi ne (Pinus halepensis). Seedlings of this species were enclosed in open -top chambers during the summer and exposed to either Charcoal Filtere d 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 c hlorophyll and nutrient levels were measured throughout the year. Clea r seasonal fluctuations were observed since chlorophyll levels, stomat al conductance and net photosynthesis rates were lower during the summ er, and higher in winter. O-3-induced effects were apparent on previou s year needles from the second Lear of exposure. A reduction in net ph otosynthesis, 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 concentration s 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.