Cascading effects of microplastic-pollutant co-exposure in coastal wetland soil-plant-microbe systems: Mitigation potential through nutrient management

Coastal wetlands are increasingly threatened by microplastics (MPs) and co-occurring contaminants, however, their combined ecological impacts remain poorly understood. In this study, we examined the interactions between a representative microplastome (MPE) and two widespread pollutants—tris(2-chloropropyl) phosphate (TCPP) and oxytetracycline (OTC)—in wetland soil–plant systems. Our findings revealed that co-exposure to MPE and TCPP significantly enhanced plant biomass, soil organic matter (SOM), and microbial diversity, while also stabilizing microbial co-occurrence networks. In contrast, exposure to OTC alone or in combination with MPE increased soil salinity, lowered pH, and reduced SOM, resulting in microbial community disruption and the lowest observed levels of ecosystem multifunctionality. Random forest analysis and structural equation modeling identified total carbon (TC), total nitrogen (TN), total phosphorus (TP), SOM, and soil catalase activity (S-CAT) as key drivers of multifunctionality, with soil fertility exerting the strongest direct and indirect influences through plant–microbe feedback mechanisms. Moreover, greater plant diversity was associated with increased microbial network complexity and functionality. Collectively, these results underscore the cascading effects of co-contamination and suggest that enhancing soil nutrient management may help mitigate wetland ecosystem degradation. • MPE/TCPP co-exposure increased plant biomass and microbial network stability. • MPE/OTC co-exposure reduced ecosystem multifunctionality via nutrient depletion and microbial assembly disruption. • Soil fertility (SOM, nutrients) is the dominant driver of ecosystem functions. • Pollution impaired multifunctionality through soil fertility loss and plant diversity decline, exacerbated by MPE co-exposure.