Biodegradable Microplastic Diversity Drives Soil Carbon Lability via Phage-Boosted Bacterial Degradation of Recalcitrant Compounds

Microplastic (MP) pollution threatens soil carbon stability, yet the effects of diverse MPs, particularly biodegradable MPs, on the soil carbon cycle and the associated microbial mechanisms remain poorly understood. Here, we established a gradient of MP diversity to examine its impact on soil dissolved organic matter (DOM) chemodiversity, integrating multiomics analysis to reveal coupled bacterial and viral metabolic strategies. Our results revealed that elevated MP diversity increased the proportion of low-molecular-weight compounds among newly generated DOM, reducing DOM aromaticity and stability. The enrichment of genes related to recalcitrant organic compound degradation, coupled with decreased energy metabolism gene abundance, suggested that the bioprocessing efficiency was enhanced at the expense of bacterial proliferation, facilitating DOM conversion to bioavailable forms. Accordingly, elevated MP diversity remarkably increased the diversity of soil phages and strengthened phage-host interactions, which might reflect phage-host coadaptation. Importantly, the increased abundance of phage-encoded auxiliary metabolic genes, especially those related to recalcitrant organic compound degradation, might enhance the utilization of recalcitrant DOM by the host bacteria. Collectively, these findings advance our understanding of bacterial mechanisms underlying carbon dynamics following exposure to diverse MPs, highlighting the critical role of phage-host interactions during this process.