Response of microbial community in the soil plastisphere of polypropylene microplastics to the stress of phenanthrene...

Microplastics (MPs) accumulate in soils, forming microbial habitats termed the "plastisphere", which can concentrate hydrophobic pollutants like phenanthrene (PHE). This study investigated how PHE stress influences the microbial community in the polypropylene-amended soil plastisphere compared to bulk soil, revealing its "microbial refuge" function. Significant differences in microbial composition were observed. Under PHE stress, the number of unique genera in the plastisphere increased from 4 (without PHE) to 9, and the composition of significantly enriched genera changed substantially, with only 1 out of 6 enriched genera shared between PHE-stressed and non-stressed conditions. In contrast, the depleted genera remained largely consistent. Functional prediction indicated that PHE stress was associated with reduced health risks in the plastisphere relative to bulk soil. Carbon and methane metabolism pathways were significantly enriched in the plastisphere regardless of PHE stress. In contrast, nitrogen metabolism, aromatic compound degradation, and PAH degradation pathways did not differ significantly between the plastisphere and soil. Although several pathways reached statistical significance, fewer than 8.33% exhibited an absolute log₂FC > 1. This discrepancy indicates that microplastics exert a limited biological impact on the overall metabolic potential of the soil microbiome, irrespective of PHE contamination. Microbial co-occurrence networks initially showed similar complexity between plastisphere and soil. However, PHE stress markedly reduced network complexity (degree) in the plastisphere and increased the proportion of negative correlations (indicating competition/antagonism) from ~ 60% to ~ 50% in both habitats. This study advances the mechanistic understanding of pollutant-driven microbial responses in soil plastispheres, with a focus on how this unique plastic-associated microbial niche mediates microbial composition, function, and network under PAH stress, thereby informing targeted bioremediation and ecological risk models for microplastic-organic co-contaminated environments.