Global synthesis reveals how initial concentrations, metal types, and acidity control woody plant phytoremediation efficacy

Woody plants show great potential in phytoremediation, while how metallic properties or environmental factors affect phytoremediation efficacy remains unclear. Here we synthesize 2766 observations from published data covering 104 woody plant genera and 10 contaminants. We used a multi-level random-effects meta-analysis, with log response ratios calculated from treatment and control means, standard deviations and sample sizes. Heavy metals or metalloids reduced biomass by 18.2%-25.1%, while increasing contaminant accumulation in whole-plant, aboveground, and underground tissues by 8758.9%, 1275.6%, and 1689.4%, respectively. Leaf superoxide dismutase, peroxidase and malondialdehyde increased by 24.2%, 34.2% and 29.3%, respectively. Ilex, Ficus, Euonymus, Platycladus, Tamarix and Salix showed metal-specific accumulation or growth responses under cadmium, lead or zinc exposure. Plant genus, environmental pH, metallic type and concentration predicted the dendroremediation performance. These findings provide a quantitative basis for selecting woody plants for soil dendroremediation and support field validation under multi-contaminant conditions. Heavy metal exposure reduces woody plant biomass by about 18 to 25 percent while strongly increasing metal accumulation and stress responses, shown by a multi-level meta-analysis of 2766 observations from two databases using log response ratios.