The suitability of short rotation forestry for phytoremediation of urban soil, development of a protocol for urban areas

This field work was conducted to verify the effectiveness of phytoremediation on a former industrial Zn-contaminated soil within the city of Torino. The aims were: to verify the suitability of applying phytoremediation in urban settings; to assess the viability of Short Rotation Forestry for soil remediation; to determine the heavy metal uptake of different plant species and to establish an operational protocol for planting and agronomic maintenance of the parcels. For the experiment, nine different plants well adapted to the Piedmont area with rapid growth and large biomass production were selected: Populus xcanadensis Mönch, Populus deltoides Marsh, Populus alba L., Salix alba L., S. viminalis L., S. matsudana Koidz and three Robinia pseudoacacia L. genotypes. Parallel field and greenhouse experiments were conducted were plants were grown for two years. In field experiment, Short Rotation Forestry technique was adopted, with a plant density of 10000 plants per hectare. Biomass growth and soil were monitored throughout the trial to compare the plant response and metal uptake rates in all plant tissues (roots, stem and leaves). In the urban contaminated soil, Salix resulted to be the best accumulator with regard to Zn, with a maximum uptake in stem and leaves, although the produced biomass was low. After two years, no change in soil total metal content was observed, while bioavailable fraction of Zn and Cu decreased significantly using all species, from the 26% of Robinia to the 36% decrease using Salix. In the pedoclimatic conditions of the urban site, the most productive species was Robinia, leading to higher extraction rate per hectare and giving promising results also in pot experiments, suggesting the possibility to increase plant density to 16000 plants per hectare, to increase the phytoextraction and limit the access to the contaminated area.