Root–rhizosphere processes and physiological trade‐offs govern polycyclic aromatic hydrocarbon fate in plant–soil systems

Abstract

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 log K _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.