Impacts of Organic Amendments on the Phytoremediation Capacities of Two Salicaceae Taxa

Using by-products from local industries as fertilisers is an innovative way to connect urban and rural systems. However, positive results have been observed only in food production, while research on phytoremediation, particularly in peri-urban areas, is lacking. This study assessed the effectiveness of frass in improving the phytoremediation capabilities of two Salicaceae taxa in Cu-contaminated soils. The study was conducted over three months. Soils were amended to reach 1,000 mg Cu kg^− 1 and fertilised with either frass or chicken manure (250 kg N Ha^− 1). After the harvest, soil samples were analysed for nutrient (available N and P) and metal (e.g. Cu, Fe, Zn) concentrations. Plant yields were documented, photosynthetic activity was monitored, and nutrient utilisation rates were examined. Nitrogen use efficiency was higher in the Salix containers amended with manure (12%) than frass (7%), although not significantly. On the other hand, P use efficiency was greater in Populus trees treated with frass (3x increase). In parallel, frass and traditional amendments both promoted tree biomass similarly (+ 19%), while frass also stabilised stomatal conductance over time in Salix clones compared to manure amendments (-20% vs. -50%) and led to initially higher photosynthetic activity. Although Cu aboveground concentrations were similar across all treatments, treatments with increased biomass resulted in greater Cu extraction and stabilisation. Frass was identified as a viable alternative, exhibiting comparable effects to traditional fertilisation methods. Ultimately, its promotion of NH₄⁺ in soil, a form less prone to leaching, underscored its potential for more sustainable phytoremediation efforts.