Long-term manure inputs induce a deep selection on agroecosystem soil antibiotic resistome

Although the enrichment of antibiotic resistance genes (ARGs) in diverse organic soils have been explored, understanding of the ecological processes governing the composition of ARGs in long-term organically fertilized soils still remains limited across typical agricultural regions. Thus, the distribution and assembly of ARG profile in three typical agricultural soils (black soil, fluvo-aquic soil, and red soil) under long-term contrasting fertilization regimes (chemical-only vs organic-only) were investigated using high-throughput qPCR (HT-qPCR). The application of organic manure significantly increased the abundance and number of ARGs across soils, as compared to those with chemical fertilizer. Organic manure application enriched the abundance of mobile genetic elements (MGEs), which were positively associated with ARGs. In addition, it is long-term organic fertilizer that enriched the number and abundance of opportunist and specialist ARGs in the fluvo-aquic and red soils, but not black soils. The number and abundance of most generalist ARGs did not change significantly among different fertilization or soil types. The assembly process of the ARG profiles tends to be more deterministic in organically fertilized soils than in chemically fertilized soils. These results suggest that long-term organic fertilizer application may contribute to the persistence and health risk of the soil antibiotic resistomes (especially specialist ARGs).