Multi-omics reveals manure-borne doxycycline and fragmented oversized microplastics co-disrupt pak choi growth and amplify antibiotic resistance in agroecosystems.

The intensification of livestock farming and plastic consumption has led to widespread co-contamination of agricultural soils with veterinary antibiotics (e.g., doxycycline, DOX) and microplastics (MPs). This study employed an integrative multi-omics approach (transcriptomics, metabolomics, microbiome analysis, qPCR) to investigate the synergistic effects of fragmented oversized microplastics (OMPs; 5-20 mm) and manure-borne DOX on pak choi growth and antibiotic resistance gene (ARG) dissemination in a realistic rhizobox system simulating manure-amended soil. We observed that co-exposure to DOX and OMPs significantly reduced pak choi biomass by approximately 29 % compared to controls. This co-exposure induced synergistic stress responses, altering root transcriptomes and causing metabolic disturbances in both plants and rhizosphere soil. Crucially, OMPs acted as "dual carriers", not only concentrating DOX but also facilitating ARG dissemination. Co-exposure amplified total ARG abundance in rhizosphere soil by 2.8-fold and implicated key hosts like Lysobacter for tetracycline ARGs. Furthermore, microbial community restructuring occurred, marked by a decline in beneficial taxa like Pseudomonas and an increase in potentially detrimental genera like Brevundimonas. These findings demonstrate intricate synergistic interactions where OMPs enhance DOX bioavailability, exacerbating phytotoxicity and ARG spread. This poses significant risks to crop productivity and environmental health. Our results underscore the critical need for long-term monitoring, pre-treatment of manure to remove plastics/antibiotics and adoption of biodegradable mulches, among other measures, to ensure sustainable agriculture and mitigate public health risks.