Study of the floristic diversity and distribution of plant species in urban areas

Cities are characterized by adverse growing condition which include high temperatures, drought and heavy metal pollution, that have led to the selection of highly tolerant plant species that can thrive in these environments. Cities can be therefore primary sources of useful plants for metal biomonitoring and phytoremediation purposes.

The floristic diversity of urban environment has been investigated through surveys in the city centre of Bologna, with particular attention to the different habitats of the city: streets, walls, roofs and green areas. Comparative studies were also performed aimed at determining the influence of climate and urban changes on the flora of the city of Bologna in the last century. In parallel, the possibility of using herbaceous plants typical of the urban environment like Poa annua L. and Senecio vulgaris L. to bioindicate the presence of heavy metals in the soil is being studied. The factors (e.g. pH) that influence the availability, absorption, root / shoot translocation and accumulation of metals are also evaluated. Finally, studies are also carried out on the hormesis effect (increase in growth caused by the application of micro-quantities of toxic elements) caused by Cd, Pb and Cr micro-doses, on urban herbaceous species. Crop and hyperaccumulator species are being tested, to evaluate the possibility of using these plants to perform sewage sludge phytoremediation. This study in collaboration with HERA SpA, aims at finding and alternative and green approach for the recovery of valuable elements for sewage sludges (e.g. selenium), while removing unwanted toxic metals (e.g. Cd, Zn, Ni). Different techniques (i.e. confined phytoextraction), and plants associations are being tested to achieve the maximum removal of toxic metals from sewage sludges. Former results suggest that after the remediation process, sewage sludges have improved texture and a lower metal content, and can be possibly used as soil amendments or plant growing substrates.