Arbuscular Mycorrhizal Fungi and Intertidal Wetland Sediment Enhanced the Constructed Wetlands on the Purification of Marine Aquaculture Tailwater

Marine aquaculture tailwater, rich in nitrogen and phosphorus, threatens aquatic ecosystems and human health. This study optimized constructed wetlands (CWs) by bioaugmenting with arbuscular mycorrhizal fungi (AMF) and intertidal wetland sediment (IWS) to enhance pollutant removal under variable salinity. Four bioaugmenting strategies─AMF inoculation (A), IWS inoculation (I), combined AMF-IWS (AI), and control (CK)─were tested at salinities of 5 and 10 ppt. Results showed that AI CWs achieved the highest removal rates of NH4+-N (up to 76.59 vs 49.91% in CK), total inorganic nitrogen (up to 87.59 vs 73.49% in CK), and inorganic phosphorus (up to 77.94 vs 26.80% in CK), maintaining superior and stable performance across both low and high salinity conditions. Microbial analyses indicated that IWS introduction enriched key genera (Denitromonas, Thauera, and Desulfuromonas), while AMF promoted plant–microbe interactions that contributed to pollutant reduction. Functional gene predictions revealed that the combined inoculation enhanced denitrification while suppressing nitrification and dissimilatory nitrate reduction pathways. These findings demonstrate the synergistic benefits of AMF and IWS in CWs and provide new insights into bioaugmented wetland design for the treatment of saline wastewater in marine aquaculture.