Ozone and water deficit reduced growth of Aleppo pine seedlings

The effects of ambient and elevated ozone (O-3) levels on photosynthesis, growth, pigment, biomass and element contents of Aleppo pine (Pinus halepensis Mill.) were studied for two growing seasons (1997, 1998). Two-year-old seedlings were exposed to elevated O-3 in open-top chambers. The treatments were charcoal-filtered air and non-filtered air + 50 nl(-1) O-3 (24 h per day, 7 days per week). In summer 1998, half of the seedlings were drought-stressed (leaf water potential down to approximately -2 MPa), while the other half were kept well-watered. At the beginning of the season (1998), current (c) and previous-year (c + 1) needles under O-3 stress showed an increase in stomatal conductance and net photosynthesis. During the drought period, only stomatal conductance increased in both needle age-classes, whereas the net photosynthesis decreased. At the end of the measuring period, both parameters were reduced in the O-3 treatment. Both O-3 and drought decreased chlorophyll a and b concentrations, growth and biomass. A carry-over effect of O-3 on pigments was also observed. Needle K content was increased in the O-3 treatment. Drought protected Aleppo pine against O-3 (less chlorotic mottle and less decrease of stem and branch biomass). (C) 2003 Editions scientiliques et medicales Elsevier SAS. All rights reserved.