Setting ozone critical levels for annual Mediterranean pasture species: Combined analysis of open-top chamber experiments.

Annual Dehesa-type pastures comprise semi-natural vegetation communities dominated by annual species characteristic of the Mediterranean basin areas of Southern Europe. This study analyses all the datasets available on the effects of ozone (O3) on annual pasture species in order to review and propose new exposure- and flux-based O3 critical levels (CLes) following the methodology of the Convention on Long-Range Transboundary Air Pollution (CLRTAP). Based on the potential effect on pastures main ecosystem services, the availability of data and the statistical significance of the regressions, three variables have been selected for establishing CLes: total above-ground biomass, consumable food value (CFV), as a nutritional quality index, and reproductive capacity based on flower and seed production. New CLes proposed for a 10% loss (with 95% confidence intervals between brackets) of above-ground biomass and reproductive capacity were, respectively, AOT40=3.1 (2.6, 3.8) and 2.0 (1.5, 2.8) ppmh and POD1=12.2 (8.9, 15.5) and 7.2 (1.1, 13.3) mmolm(-2). The provisional AOT40- and POD1-based CLes for CFV were 2.3 (1.6, 4.0) ppmh and 4.6 (2.7, 6.5) mmolm(-2) respectively. By using only O3-sensitive species for the exposure and dose-response functions, the proposed CLes should be used for risk assessments. Their use for quantifying O3 damage may lead to an overestimation of the effects.