Allocation plasticity and plant–metal partitioning: Meta-analytical perspectives in phytoremediation

In this meta-analysis of plant growth and metal uptake parameters, we selected 19 studies of heavy metal (HM) phytoremediation to evaluate trends of allocation plasticity and plant–metal partitioning in roots relative to shoots. We calculated indexes of biomass allocation and metal distribution for numerous metals and plant species among four families of interest for phytoremediation purposes (e.g. Brassicaceae, Fabaceae, Poaceae, and Solanaceae). We determined that plants shift their biomass and distribute metals more to roots than shoots possibly to circumvent the challenges of increasing soil-HM conditions. Although this shift is viewed as a stress-avoidance strategy complementing intrinsic stress-tolerance, our findings indicate that plants express different levels of allocation plasticity and metal partitioning depending on their overall growth strategy and status as ‘fast-grower’ or ‘slow-grower’ species. Accordingly, we propose a conceptual model of allocation plasticity and plant–metal partitioning comparing ‘fast-grower’ and ‘slow-grower’ strategies and outlining applications for remediation practices.