Screening and selection of heavy metal tolerant ornamental plants for urban or peri-urban areas

Urban and peri-urban gardens can often be polluted by heavy metals released from the high vehicular traffic. Those gardens have increasing significant relevance due to social, cultural, and economic, benefits, they may pose a potential risk for dwellers or frequenting the area. In the past, the predominant polluting metal in the urban and peri-urban area was lead (Pb) since it was a component of fuel. Nowadays, vehicles are still a source of heavy metals since the tire wear can still release Pb but also zinc (Zn) and cadmium (Cd). In addition to their aesthetic value, ornamental plant species grown in urban areas could present several benefits related to soil conservation and wind mitigation, and reduction of heavy metal pollution. Some species have the ability to accumulate trace elements in different plant tissues thus, their selection is very important to choose species suitable to the pollution degree. Ornamental plants must adapt to environmental conditions and improve the visual appearance of the area contributing with their aesthetical quality. It is extremely important that plants do not show eco-physiological alterations such as leaves yellowing, necrosis or abscission induced by heavy metal toxicity. Considering that soils are often polluted by different metals, and that plants might accumulate only few pollutants, special attention should be paid to the possibilities to use plant consociation such as ornamental woody and herbaceous species that could be integrated in urban and peri-urban garden. In this work, a scheme for the screening and selection of ornamental plants tolerant to heavy metal and suitable for urban and peri-urban garden will be proposed.