Impacts of ozone on Aleppo pine needles: Visible symptoms, starch concentrations and stomatal responses

In order to study the physiological responses of Aleppo pine (Pinus halepensis Mill.) to ozone, 18-month old seedlings were treated with 1.2-1.8 x ambient ozone concentrations (cumulative exposure) over one or two seasons in an open-air experiment. In another experiment, two-year old plants were exposed to ozone (150 nl l(-1)) in an environmental growth chamber for five weeks (12 h d(-1)). Slight chlorotic mottling developed on the needles in the chamber experiment. Ozone induced variable effects on starch contents. A significant decrease was observed in the chamber experiment but in the open-air experiment this was not confirmed. The discrepancies in starch changes between the different experiments might be connected with the different ozone exposure designs as wed as different developmental and environmental conditions. Diffusive resistance was measured with Li-Cor LI65 porometer six times in the chambers and three times in the open-air experiment. Ozone induced an increase in diffusive resistance. This study shows that ozone can be a potential factor interfering Aleppo pine physiology. (C) 1998 Elsevier Science Ltd.