Influence of arbuscular mycorrhizal fungi symbiosis on S-metolachlor and its metabolites dynamics in constructed wetlands

Abstract

Arbuscular mycorrhizal fungi (AMF) symbiosis has shown promise in enhancing constructed wetlands (CWs) treatment capabilities, though its influence on pesticide behavior and microbial interactions needs further examination. This study explores AMF's impact on S-metolachlor behavior within CWs, focusing on how AMF colonization affects organic carbon content, metabolite transformation, and microbial community composition. AMF presence yielded higher mean total organic carbon after 32 days in outflows (13.2–13.7 mg/L) compared to AMF absence (10.5–10.6 mg/L), with significant differences in both treated (p = 0.008) and untreated (p = 0.004) systems. Although S-metolachlor removal rates were comparable (90.2 % vs. 92.7 %), pesticide retention was mainly in substrates (54.2–64.0 %, 1.8–2.0 μg/kg), followed by liquid phase (34.7–43.8 %, 15.4–20.7 μg/L), roots, and leaves. The liquid phase exhibited the highest metabolite diversity (17 types), and AMF presence lowered concentrations of 15 metabolites. Metagenomic analysis indicated that AMF enriched bacterial communities associated with organic breakdown and nitrogen cycling, such as Acidobacteria and Catenulispora. The change of metabolic pathways revealed that AMF presence shifted bacterial pathways away toward enhanced biosynthesis and metabolic capabilities, including the production of steroids, siderophores and ansamycin. Besides, AMF boosted functional genes linked to biosynthesis, notably CcmB, nrdA, and glpX. The findings highlight AMF's potential in supporting S-metolachlor bioremediation within CWs by enhancing pollutant resilience mechanisms and microbial diversity.