OZONE AND DROUGHT STRESS - INTERACTIVE EFFECTS ON GAS-EXCHANGE IN ALEPPO PINE (PINUS-HALEPENSIS MILL.)

Two-year-old Aleppo pine seedlings were exposed over twenty months in open-top chambers to either above-ambient ozone (O-3) concentrations o r charcoal-filtered air. Subsequently, water was applied following pla nt requirements in the well watered treatment (WW), while it was withh eld for 11 days in the water-stressed seedlings (WS). Then, the seedli ngs of both water treatments were irrigated to field capacity. Four se edlings per water treatment were used within each chamber. The daily v ariation in gas exchange rates of Aleppo pine seedlings from the diffe rent treatments were studied during and after water stress. Ozone expo sure and a moderate water shortage induced similar reductions in the g as exchange rates. An antagonistic response modulated by the severity of water stress followed the combined exposure to both O-3 and water s tress; a partial recovery from water stress was observed two days afte r rewatering to field capacity, while the seedlings that were not expo sed to O-3 showed a faster recovery. (C) 1998 Elsevier Science Ltd.