Comparative performance of Populus spp. and Salix spp. for growth, nutrition, and heavy metal uptake in a wastewater hydroponic system.

This research aimed to ascertain the growth, biomass, and phytoremediation capacity of poplars and willow cultivated using wastewater in a hydroponic system. The cuttings were exposed to two water treatments for eight weeks: (1) tap water supply with 1/4 strength Hoagland's solution (TW) as a control and (2) urban raw wastewater with 1/4 strength Hoagland's solution (WW) in a completely randomized experimental design and growth parameters and nutrient and heavy metal content distribution in various plant tissues were assessed. Our results suggest that compared with the TW, seven studied species/clones revealed an increase in growth and biomass parameters (stem height by 16.4%, and root, shoot, and total biomass by 37.3%, 26.9%, and 29.3%, respectively) caused by WW treatment, except the root length and stem diameter that remained the same under two water treatments. Poplars and willow showed a remarkable variability in growth and biomass parameters, with the highest stem diameter, stem height, and root, shoot, and total biomass in Populus nigra L. 62.154. Expression of growth responses to WW treatment with tolerance indices (Tis) indicated the tested poplars and willow as highly tolerant (Ti >100%) with no significant differences among them based on this index. Plant analysis showed that WW treatment increased the concentrations of nutrients and heavy metals in the shoots and roots. Overall, under both water treatments, the capability of the tested species/clones to uptake and accumulate micro-nutrients (except copper (Cu) in shoots) and heavy metals (except chromium (Cr) in shoots) in the plant tissues varied noticeably. However, for all tested plants, the roots had higher concentrations of micro-nutrients (iron (Fe), zinc (Zn), and Cu concentrations in the roots were about 36.8%, 107.6%, and 30.1% of that in the shoots, respectively) and heavy metals (nickel (Ni), Cr, and lead (Pb) concentrations in the roots were about 115.3%, 344.2%, and 198.9% of that in the shoots, respectively), suggesting their capability for micro-nutrients and heavy metals rhizofiltration. Concerning obtained results under hydroponic culture, it can be concluded that these poplars and willow might be promising candidates for wastewater applications. However, data obtained by a hydroponic system need to be confirmed in pot and field experiments.