Cascading effects of nano-biochar mitigate antibiotic resistance via phage-host interactions in the soil-crop ecosystem

Controlling the spread of antibiotic resistance genes (ARGs) in agroecosystems is central to One Health, yet whether nano-biochar-amended organic fertilizers can mitigate phage-mediated ARG dissemination along the fertilizer-soil-crop continuum remains poorly understood. Here, we analyzed 120 viral metagenomes to examine how biochar-amended organic fertilizers modulate ARG dynamics, phage-associated functions, and phage-host interactions across the fertilizer-soil-lettuce continuum. The lettuce phyllosphere served as a key endpoint for ARG accumulation, exhibiting 4.1-4.9 times the total ARG abundance and 56.8-66.3% higher phage-encoded ARG abundance compared with rhizosphere and non-rhizosphere soils. Source-tracking analysis indicated that manure and soil inputs accounted for 50.8-57.0% of phyllosphere ARGs, while 111 manure-associated viral populations were shared with the phyllosphere at the viral cluster level. Notably, nano-biochar-amended vermicompost exerted a cascading mitigation effect, reducing manure- and soil-derived ARG inputs to the phyllosphere by 20.4-21.6% and manure-associated viral sharing by 51.6%. Meanwhile, nano-biochar-amended vermicompost reduced lysogenic phage-host interactions, phage-encoded ARGs, and auxiliary metabolic genes associated with antibiotic-resistant bacteria, which may contribute to reduced phage-associated ARG dissemination potential. Consequently, total ARG abundance in the phyllosphere decreased by 68.9-76.3%, while lettuce biomass increased by 54.1-61.5%. This work suggests that nano-biochar-amended vermicompost may mitigate antibiotic resistance risks and enhance crop productivity partly by attenuating phage-associated ARG dissemination across the fertilizer-soil-crop continuum, highlighting its potential for One Health-oriented resistance-risk control in agricultural production.