Cistus ladanifer metal uptake and physiological performance in biochar amended mine soils

Abstract

Biochar amendments are known to have a considerable influence on phytoremediation processes. Considering this, in the present work, we aimed to evaluate the effect of biochar amendments in metal-contaminated mine soils focusing on the metal uptake by Cistus ladanifer and its physiological consequences. Plants were exposed to mine soils with different biochar supplementations and the plant's physiological performance was evaluated (photochemistry, pigment profiles, oxidative stress). The biochar concentration gradient led to an increase in the plant metal burden, both in the root and aerial organs, pointing out an improvement in metal bioavailability. This increased metal uptake and translocation were accompanied by a reduction of several photochemical traits, namely, light-harvesting, oxygen-evolving, electron transport chain structure and function, leading to a reduction of the overall photochemical efficiency of the plants. Nevertheless, this was accompanied by efficient energy dissipation mechanisms, which prevented irreversible photoinhibition events. Regarding oxidative stress levels, an increase in the superoxide dismutase activity was observed, without a proportional increase in peroxidasic activity. This led to the accumulation of reactive oxygen species (ROS), with considerable damage effects at the lipid membrane level, as observed by the increased lipid peroxidation values in the plants exposed to the highest biochar concentration and, thus, with a higher metal burden. The plants exposed to 1% biochar concentration exhibited improved metal uptake and preserved metabolic activity, thus, indicating that this would be the most suitable amendment for phytoremediation purposes, without jeopardizing plant biomass production.