The relative sensitivity of different Mediterranean plant species to ozoneexposure

An experimental study was performed in open-top chambers to assess the rela tive O-3-sensitivity of the following Mediterranean woody plants: Quercus i lex ssp. ilex, Quercus ilex ssp. ballota, Olea europaea ssp. sylvestris, Ce ratonia siliqua and Arbutus unedo. Assessment of O-3 'sensitivity' was base d on the development of O-3-induced visible injury and the extent of the re duction in relative growth rate induced by O-3. Two-year-old seedlings were exposed in open-top chambers to charcoal filtered air (CFA), Non-filtered air (NFA) or Non-filtered air supplied with 40 ppb O-3 from 09:00 to 18:00 hours (NFA+40). No clear relationships were found between the development o f visible injury and effects on plant growth or accumulated biomass. Olea e uropea ssp. sylvestris and Quercus ilex ssp. ballota appeared to be the mos t O-3-sensitive tree species screened; a ten month exposure to ambient O-3 levels (AOT40 = 12.4 ppm.h) caused reductions in height and/or stem growth. Further research is needed to characterise the physiological, biochemical and anatomical characteristics that may underlie the 'sensitivity' of certa in Mediterranean species to O-3.