Aqueous PFOS exposure decouples gaseous carbon loss from mineral-associated carbon retention in controlled wetland-interface mesocosms.

Wetland interfaces regulate greenhouse-gas exchange and carbon retention, yet contaminant exposure may disrupt the relationship between these two processes. Whether aqueous perfluorooctane sulfonate (PFOS), a persistent aquatic contaminant, alters this relationship remains unclear. Here, we used a controlled rhizobox mesocosm with paired planted and unplanted treatments across an aqueous PFOS gradient (0, 10, 100, and 1000 μg L-1) to resolve plant-mediated and background soil responses. We combined endpoint, time-weighted 24-h CO2 and CH4 flux partitioning with 13CO2 tracing of root-derived carbon, rhizosphere priming estimates, soil organic carbon fractionation into particulate organic carbon (POC) and mineral-associated organic carbon (MAOC), and metagenomic profiling. PFOS induced clear exposure-dependent and non-linear responses. Low-to-medium PFOS stimulated root-associated CO2 fluxes and maintained positive rhizosphere priming, whereas high PFOS suppressed rhizosphere CO2 and root respiration, weakened net plant CO2 uptake, and shifted soil organic carbon priming to a net negative response. In contrast, at H-P, MAOC was significantly higher than the control in both bulk and rhizosphere compartments, indicating that mineral-associated carbon retention can persist even when biological carbon processing weakens. Metagenomic profiling further suggested compartment-specific microbial filtering, reduced genetic potential for polymer depolymerization, and reweighted methane-related functions under PFOS exposure. Together, these results show that aqueous PFOS exposure can decouple gaseous carbon loss from mineral-associated carbon retention in controlled wetland-interface mesocosms. These findings indicate that lower gaseous carbon release under PFOS exposure should not be interpreted straightforwardly as stronger carbon-retention function or enhanced carbon sequestration, particularly without longer-term field validation.