Contrasting effects of ozone under different water supplies in two Mediterranean tree species

The effects of ozone (O-3) exposure under different water availabilities were studied in two Mediterranean tree species: Quercus ilex and Ceratonia siliqua. Plants were exposed to different O-3 concentrations in open top chambers (charcoal-filtered air (CF), non-filtered air (NF)) and non-filtered air plus 40 ppb(nu) of O-3 ((7:00-17:00 solar time) (NF +)) during 2 years, and to different water regimes (IR, sample irrigation, and WS, reduced water dose to 50%) through the last of those 2 years. AOT40 in the NF+ treatment was 59265ppb(nu)h (from March 1999 to August 1999) while in the NF treatment, the AOT40 was 6727ppb(nu)h for the same period. AOT40 was always 0 in the CF treatment. WS plants presented lower stomatal conductances and net photosynthetic rates, and higher foliar N concentrations than IR plants in both species. The irrigation treatment did not change the response trends to ozone in Q. ilex, the most sensitive species to O-3 ambient concentrations, but it changed those of C siliqua, the least sensitive species, since its ozone-fumigated WS plants did not decrease their net photosynthetic rates nor their biomass accumulation as it happened to its ozone-fumigated IR plants. These results show interspecific variations in O-3 sensitivity under different water availabilities. (C) 2004 Elsevier Ltd. All rights reserved.