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 l –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).