Ecophysiological and micromorphological characterization of green roof vegetation for urban mitigation

Urban greening helps to improve environment quality and human health thanks to the ability of plants to absorb greenhouse gases and remove significant amounts of air pollutants. Green roofs, providing vegetated surfaces in dense cities, can help to mitigate the negative effects of urban pollution. The present study aimed to evaluate the potential ability of fifteen green roof species (Lonicera pileata, Satureja repandens, Hypericum moserianum, Erigeron karvinskianus, Solidago praecox, Rudbeckia sullivantii 'Goldsturm', Filipendula purpurea, Filipendula vulgaris 'Kahome', Gaura lindheimeri, Campanula persicifolia, Veronica longifolia, Sedum spectabile, Origanum vulgare, Salvia nemorosa, and Achillea millefolium) to mitigate carbon dioxide (CO2) and urban pollutant concentration analysing the leaf physiological traits (gas exchange) and morphological structures (stomata, trichomes, epicuticular waxes and cuticular ornamentation) involved in pollutant removal. Furthermore, considering the important role of biogenic volatile organic compounds (BVOC) on the photochemical reactivity of the atmosphere, their species-specific emission was also assessed together with the derived ozone forming potential (OFP). Our results suggested that the potential mitigation capacity based on the investigated traits of the shrubs and herbaceous species was species-specific. The very low potential of all the tested species to form ozone indicated their suitability for urban planning programs.