Effects of micro(nano)plastics on nutrient removal and greenhouse gas production under heavy metals cooccurence in AMF-enhanced constructed wetlands

Co-occurring micro(nano)plastics (MNPs) and heavy metals (HMs) may interact synergistically or antagonistically with microorganisms, thereby influencing wastewater treatment performance. Constructed wetlands (CWs) inoculated with functional microbes such as arbuscular mycorrhizal fungi (AMF) offer a promising approach to enhance pollutant removal. Here, we established CWs with and without AMF inoculation to examine how varying concentrations (1 and 10 mg/L) of polystyrene MNPs (PS-MNPs) affect nutrient removal and greenhouse gas (GHG) production in wastewater co-contaminated with copper/lead. Our results show that in CWs without AMF inoculation, compared with single HMs, the addition of PS-MNPs increased the average effluent concentration of ammonium nitrogen and phosphate by 11.84-134.73 % and 2.04-109.79 %, respectively, while their effects on nitrate and COD removal depended on concentration and HM levels. Inoculation with AMF reduced average effluent concentration of ammonium nitrogen and phosphate by 22.01-69.24 % and 21.89-50.47 %, respectively, and also produced a significant decrease in nitrate concentration. PS-MNPs suppressed organic matter and nitrogen transformations, leading to methane (CH₄) And nitrous oxide (N₂O) production elevated 2.18-53.78 % and 24.19-162.23 %, whereas AMF reduced their production. Enzyme assays indicated that PS-MNPs decreased key microbial activities in the upper layer, but AMF mitigated these impacts. Microbial community analysis revealed that AMF enhanced nitrogen cycling by promoting denitrifying bacteria (e.g., Dechloromonas, Zoogloea, Terrimonas, Thauera) and nitrifiers (Nitrospira). These findings highlight that AMF can alleviate the negative impacts of MNPs-HM co-occurrence on CWs, improving both nutrient removal and climate co-benefits. This work provides insights into pollutant interactions and offers strategies for optimizing CWs treating complex wastewater mixtures.