Plant growth and metal uptake by a non-hyperaccumulating species (Lolium perenne) and a Cd-Zn hyperaccumulator (Noccaea caerulescens) in contaminated soils amended with biochar

Biochar could be used as a soil amendment in metal contaminated soils, for safe crop production or soil remediation purposes. This work was conducted to study the effects of biochar amendments on metal uptake by two contrasted plants grown on metal-contaminated soils. A non-hyperaccumulating plant (Lolium perenne) and a Cd- and Zn-hyperaccumulator (Noccea caerulescens) were grown in pots on acidic (A) and alkaline (B) soil contaminated by Cd, Pb and Zn, both amended by a wood-derived biochar. Biochar amendments decreased the availability of metals by increasing soil pH, but also decreased Ca, P and N availability. Growth of L. perenne was increased and shoot metal uptake decreased by biochar addition in both soils, although increasing biochar dose above 0.5 % resulted in a progressive decrease of shoot production on soil B. Growth of N. caerulescens was not significantly affected by biochar. But an increase of Cd uptake with 5 % biochar was recorded on both soils, and of Zn uptake on soil B. Beside immobilizing metals, biochar may decrease the availability of nutrients, leading either to plant deficiency or to a decreased competition with cations for metal uptake, thus enhancing extraction of metals by hyperaccumulators.