Aged sediments sequester polycyclic aromatic hydrocarbons (PAHs) into slowly desorbing pools, constraining bioavailability and prolonging ecological risks. Here, we evaluated the submerged macrophyte Potamogeton crispus L. (P. crispus) for accelerating phenanthrene attenuation in artificially aged sediments over 36 days by integrating dissipation kinetics, three-compartment desorption modelling, pore-water dynamics, redox potential (Eh) and PAH-degrading bacterial abundance. Planted systems achieved 14.3% higher phenanthrene dissipation than unplanted controls, with 2.45- and 30.7-fold increases in rapid- and slow-phase degradation rate constants, respectively. Desorption modelling showed that planting maintained larger rapidly and slowly desorbing fractions (fr and fs) and higher desorption rate constants, indicating sustained bioavailability and delayed sequestration into the very slowly desorption pool. Correlation patterns supported a rhizosphere-driven "sink effect", whereby enhanced desorption was coupled with higher Eh and enriched degraders, promoting rapid consumption of desorbed phenanthrene and preventing its accumulation in pore water. In contrast, unplanted sediments exhibited passive desorption under progressive oxygen limitation, leading to pore-water phenanthrene accumulation despite limited overall removal. Collectively, these results indicated that P. crispus can partially overcome ageing-induced bioavailability constraints by coupling desorption enhancement with rhizosphere redox regulation and sustained biodegradation, thereby reducing pore-water phenanthrene exposure and informing nature-based management of PAH-contaminated sediments.