Manure application enhances ARG enrichment by aged microplastics in rhizosphere networks: New insights into MP...

Aged microplastics (MPs) are recognized as potential hotspots for antibiotic resistance genes (ARGs), yet it remains unclear how manure application influences the roles of aged MPs and their associated biofilms in regulating ARG fate across soil-plant systems. This study investigated the effects of aged MPs on ARG distribution in bulk soil, rhizosphere soil, root endophytes, and MP biofilms under three fertilization types. The results showed that compared with chemical fertilizers, manure application significantly (P < 0.05) enhanced the enrichment of ARGs by aged MPs in soil and promoted ARG accumulation in root endophytes. Source Tracker analysis showed substantial compositional similarity between aged MP biofilms and ARG profiles in rhizosphere soil and root endophytes, with proportions of 41.39-51.27% and 11.71-17.72%, respectively, highlighting the potential interface role of MP biofilms in soil-root resistome assembly. Exposure to aged MPs significantly enhanced rhizosphere network complexity and intensified co-occurrence patterns among ARGs, mobile genetic elements (MGEs), and potential bacterial hosts within manure-applied soil-root systems. Manure application reshaped soil physicochemical properties and microbial communities, thereby creating a more favorable environment for aged MP biofilm development and ARG/MGE accumulation. Random forest showed that soil organic matter was a key physicochemical factor influencing ARG distribution patterns. MGEs had the strongest positive associations with ARGs across the soil-root system. The findings emphasized that the manure-applied context amplified aged MPs' facilitation of ARG accumulation in soil-plant systems, suggesting that the resistance risks associated with traditional agricultural practices may have been underestimated.