The aim of this study was to examine the effects of increased tropospheric ozone concentrations on the growth and morphology of five native herbs commonly found to coexist in calcareous grassland in areas of Britain and continental Europe: Anthyllis vulneraria L., Cirsium acaule (L.) Scop., Festuca ovina L., Pilosella offtcinarum F. Shultz & Shultz-Bip and Lotus comiculatus L.<br/><br/>In a chronic fumigation (mean O3 concentration of 71 ppb (71 nl 1?1) for 7 h d?1 AOT40 4585 ppb-h) which lasted for 21 d, the effects of ozone were assessed using classical growth analysis. Large reductions in mean relative growth rates for shoot and root weight and root length were observed for the two legumes (Fabaceae) Lotus corniculatus and Anthyllis vulneraria, although these were only statistically significant for Lotus corniculatus. Significant reductions in specific root length (length per unit dry weight) were found for Cirsium acaule and Pilosella officinarum (Asteraceae), while for Festuca ovina (Poaceae) the allometric coefficient was reduced significantly following exposure to ozone.<br/><br/>An acute fumigation (mean O3 concentration of 196 ppb, 7 h) resulted in a range of visible injury, from no injury (Festuca ovina and Pilosella officinarum) through moderate levels of injury (Cirsium acaule and Lotus corniculatus) to extensive and widespread injury (Anthyllis vulneraria). Scoring of visible damage showed that this was only statistically significant for the two legumes, Lotus corniculatus and Anthyllis vulneraria.<br/><br/>These results suggest that native herbs may differ in their sensitivity to tropospheric ozone. Both chronic and acute exposures revealed that members of the Fabaceae may be most sensitive to ozone pollution, but the study also suggests that subtle changes in root morphology occurred for members of the Asteraceae. These findings are discussed in relation to the critical levels of ozone set recently for plants and the implications of increasing tropospheric ozone for the conservation of native plant communities
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