Soil application of PE and PLA microplastics alter earthworm (Eisenia nordenskioldi) gut bacterial community and soil microbiome-metabolome dynamics

Non-biodegradable polyethylene (PE) and biodegradable polylactic acid (PLA)pose potential risks to soil ecosystems. However, there is a lack of in-depth studies to fully understand the ecological toxicity of these two types of microplastics (MPs) on soil microbiomes and their underlying mechanisms. Therefore, this study investigated the ecological risks of PE and PLA at environmentally relevant concentrations over a 120-day microcosm experiment, utilizing 16S rRNA high-throughput sequencing and untargeted soil metabolomics analysis. The results suggest that, compared to PLA, PE had a more significant impact on both earthworm gut and soil bacteria. PE significantly reduced the Shannon diversity index of the earthworm gut microbiome and decreased the relative abundance of Actinomycetota in soil by 5.79 % compared to control, while PLA exhibited a more pronounced interaction with soil metabolites. The introduction of MPs disrupted multiple metabolic pathways, significantly reducing the abundance of lipids, carbohydrates, and amino acids-key components closely associated with the multifunctionality of soil ecosystems. These metabolites were significantly negatively correlated with soil dissolved organic carbon levels. Two genera involved in the degradation of MPs, Paenibacillus and Acinetobacter, were identified in the earthworm gut after MPs exposure. Partial least squares path modeling analysis revealed that MPs addition was negatively correlated with the levels of lipids, carbohydrates, and amino acids. Overall, this study may provide valuable insights into assessing the impact of pollutants on soil health and offers important evidence for evaluating the ecological risks to soil ecosystems.