Effects of microplastics on soil microbiome: The impacts of polymer type, shape, and concentration

Increasing research has recognized that the ubiquitous presence of microplastics in terrestrial environments is undeniable, which potentially alters the soil ecosystem properties and processes. The fact that microplastics with diverse characteristics enter into the soil may induce distinct effects on soil ecosystems. Our knowledge of the impacts of microplastics with different polymers, shapes, and concentrations on soil bacterial communities is still limited. To address this, we examined the effects of spherical microplastics (150 μm) with different polymers (i.e., polyethylene (PE), polystyrene (PS), and polypropylene (PP)) and four shapes of PP microplastics (i.e., fiber, film, foam, and particle) at a constant concentration (1%, w/w) on the soil bacterial community in an agricultural soil over 60 days. Treatments with different concentrations (0.01-20%, w/w) of PP microplastic particles (150 μm) were also included. The bacterial communities in PE and PP treatments showed a similar pattern but separated from those in PS-treated soils, indicating the polymer backbone structure is an important factor modulating the soil bacterial responses. Fiber, foam, and film microplastics significantly affected the soil bacterial composition as compared to the particle. The community dissimilarity of soil bacteria was significantly (R² = 0.592, p < 0.001) correlated with the changes of microplastic concentration. The random forest model identified that certain bacteria belonging to Patescibacteria were closely linked to microplastic contamination. Additionally, analysis of the predicted function further showed that microplastics with different characteristics caused distinct effects on microbial community function. Our findings suggested that the idiosyncrasies of microplastics should not be neglected when studying their effects on terrestrial ecosystems.