Phytoextraction potential of herbaceous plant species and the influence of environmental factors – A meta-analytical approach

Heavy metals account for a notable share of soil and water body contaminations. For restoring contaminated soils, phytoremediation is considered an eco-friendly and sustainable practice. However, the implementation in the field requires a well-thought-out plant selection and comprehensive knowledge of the influence of various environmental factors. Therefore, a quantitative evaluation of 330 studies was done using a meta-analytical approach. The systematic assessment included the calculation of bioconcentration factors for roots and shoots (BCFROOT, BCFSHOOT) and translocation factors (TF) of 48 herbaceous species, as well as the identification of the most important soil and plant factors that regulate the heavy metal uptake into plant tissues. The results showed substantial variations in roots' and shoots' heavy metal uptake capacity among the diverse plant species. The uptake also varied depending on the type of heavy metal. Most species revealed a higher accumulation of heavy metals in roots than shoots, indicating a limited heavy metal transport from below-ground into above-ground plant parts. Among the different heavy metals, Cd showed the highest median BCFSHOOT and BCFROOT, followed by Zn, Cu, Ni, Cr, and Pb, which can partly be explained by the solubility and plant availability of the elements. The strongest significant and positive correlations of heavy metal contents in plant tissues were found with the total and available soil content. Clay and silt content showed a weak negative, and sand content a slight positive correlation. Further, root, shoot and total biomass revealed weak negative correlations to the plants' heavy metal contents. Overall, this study forms a basis for the minimum accumulation capacities of various species and thus makes an essential contribution to the planning and practical application of phytoremediation projects.