Growth response to ozone of annual species from Mediterranean pastures

Ozone (03) phytotoxicity has been reported on a wide range of plant species. However, scarce information has been provided regarding the sensitivity of semi-natural grassland species, especially those from dehesa Mediterranean grasslands, in spite of their great biological diversity and the high O-3 levels recorded in the region. A screening study was carried out in open-top chambers (OTCs) to assess the O-3-sensitivity of representative therophytes of these ecosystems based on the response of selected growth-related parameters. Three O-3 treatments and 3 OTCs per treatment were used. Legume species were very sensitive to O-3, because 78% of the tested species showed detrimental effects on their total biomass relative growth rate (RGR) following their exposure to O-3. The Trifolium genus was particularly sensitive showing O-3-induced adverse effects on most of the assessed parameters. Gramineae plants were less sensitive than Leguminosae species because detrimental effects on total biomass RGR were only observed in 14% of the assessed species. No relationship was found between relative growth rates when growing in clean air and O-3 susceptibility. The implications of these effects on the performance of dehesa acidic grasslands and on the definition of ozone critical levels for the protection of semi-natural vegetation are discussed. (C) 2004 Elsevier Ltd. All rights reserved.