Root-rhizosphere processes and physiological trade-offs govern polycyclic aromatic hydrocarbon fate in plant-soil...

Plant-soil interactions play a central role in determining the fate of polycyclic aromatic hydrocarbons (PAHs) in terrestrial systems, where soil-derived PAHs are a major exposure source at contaminated sites and root-rhizosphere processes contribute to removal. Root sorption of PAHs increases with hydrophobicity, whereas translocation to shoots follows partition-based behavior with an intermediate logK_OW optimum, achieved most readily by low-molecular-weight compounds and supplemented by evidence for a proton-coupled, carrier-mediated component in wheat; more hydrophobic high-molecular-weight compounds are retained mainly in roots and translocate poorly. Evidence for individual PAH transport proteins remains preliminary, drawn mainly from binding, proteomic, and docking evidence rather than in-planta loss-of-function tests. In the rhizosphere, root exudation, arbuscular mycorrhizal fungi, and PAH-degrading microorganisms increase contaminant accessibility and degradation, though contributions vary with species and soil conditions. Foliar uptake via cuticular and stomatal pathways is a parallel atmospheric route, while cellular detoxification and sequestration act downstream of root and foliar inputs, with finite capacity. We organize these processes into three coupled trade-offs at the plant-soil interface: uptake versus exclusion, internal translocation versus rhizosphere processing, and detoxification versus storage. These trade-offs form a directional cascade in which the uptake-exclusion balance constrains all downstream processes, while rhizodeposition, canopy wash-off, and litter return feed back to the soil PAH pool. Because each balance point depends on hydrophobicity, plant traits, and soil conditions, this framework can guide plant-soil system design. It identifies the root-rhizosphere interface as the primary leverage point for phytoremediation and shows that remediation and food-safety objectives require different plant traits.