Responses of biomass production and reproductive development to ozone exposure differ between european wild plant species

A screening study with 25 common European wild plant species were performed over three consecutive growing seasons to investigate the effects of ozone on plant growth, reproductive development, and resource allocation. Species were grown from seedling stage until the flowering stage or seed maturity, respectively, in open-top chambers in different ozone-enriched atmospheres at environmentally-relevant concentrations. Ozone treatments covered a range of concentrations from 20 to 55 ppb ozone (seasonal 8 h daily mean). The experiments revealed significant differences between species with respect to the sensitivity of different end points toward ozone exposure. Ozone caused a significant reduction in leaf biomass of more than 20% in six species, and a significant increase in leaf biomass in three species. The relative ozone sensitivities of the species in terms of leaf biomass were different from those inferred from total shoot biomass or seed production, indicating that ozone alters resource allocation patterns in wild plants but there was considerable variation between species in effects on the allocation to leaves, stems, flowers/fruits and seeds. Germinability of seeds was affected by ozone such that germination rate was up to 30% lower in ozone-treated plants compared to control plants. Based on the genotypes screened and by combining different sensitivity criteria (vegetative growth, reproductive growth, exposure-growth response relationships) Malva sylvestris must be regarded as the most sensitive species in this study.