Trophic decoupling of soil-nematode microbiomes induced by co‑contamination of silver nanoparticle and oxytetracycline.

Due to excellent antibacterial properties, silver nanoparticles (AgNPs) have been widely used as a potential alternative to antibiotics in livestock farming, agricultural disinfection, and medical materials. Consequently, excess AgNPs are released into the soil, co-occurring with other antibiotics, and forming a combined contamination. However, effects of combined contamination with AgNPs and oxytetracycline (OTC) on microbial communities across different trophic levels within the soil micro-food web remain poorly understood. In this study, we systematically compared the differential responses of soil and nematode gut microbiomes using high-throughput sequencing under single and combined contamination (Control, AgNPs, OTC, and combined AgNPs+OTC). The results revealed systematic trophic-level differentiation between soil and nematode gut bacterial community in terms of diversity, community structure, assembly mechanisms, and functional phenotypes. Both communities were dominated by stochastic processes, but nematode gut bacterial community was more strongly influenced by deterministic processes and exhibited higher stability. Pollutant exposure induced pronounced trophic decoupling: soil bacterial community remained structurally stable, whereas nematode gut community underwent significant compositional reassembly (p = 0.031) without a change in alpha diversity, indicating a species replacement pattern. AgNPs treatment enriched Escherichia-Shigella, while OTC and co-contamination enriched the potential degrader genera Pontibacter, Sphingomonas, and Sphingobium. Cross-kingdom network analysis showed that co-contamination strengthened network modularity (clustering coefficient 0.84, modularity 53), highlighting the role of shared ASVs as cross-kingdom bridges. This study introduces the concept of pollution-induced trophic decoupling, demonstrating that the impact of co-contamination on adjacent trophic levels is not a simple transmission of effects but rather a systematic decoupling of structure, function, and assembly mechanisms, thereby providing new perspectives for multi-trophic ecological risk assessment of combined pollution.