The “neighbor avoidance effect” of microplastics on bacterial and fungal diversity and communities in different soil horizons

Microplastics are a new type of environmental pollutant, and pose a serious threat to soil ecosystems. It is important to study microplastics effects on soil microorganisms to better understand their effects on terrestrial ecosystems. Therefore, we collected soil and microplastic samples from corn, pepper, peanut and cucumber fields in Shunyi District, Beijing, China, and used Illumina MiSeq high-throughput sequencing technology to analyze bacterial and fungal community composition and diversity. We focused on microplastic surface and its surrounding "rhizosphere-like" soil in the 0-10 cm (humus) and 10-20 cm (eluvial) deep horizons. Microbial richness and diversity on microplastic surface were significantly lower than those in surrounding "rhizosphere-like" soil, and microbial richness and diversity were reduced to a greater extent in the humus horizon than in the eluvial horizon. Microplastics likely enriched the microbes involved in their biodegradation. The relative abundance levels of Cyanobacteria and Basidiomycota on microplastic surfaces were significantly higher than those in surrounding "rhizosphere-like" soil, while the relative abundance levels of Acidobacteria, Chloreflexi, and Mortierellomycota were higher in "rhizosphere-like" soil. Furthermore, the relative abundance levels of pathways related to human diseases, animal pathogen, and fungal parasites were significantly higher on microplastic surfaces than in "rhizosphere-like" soil. These results show that the microbial diversity, richness, community structure and function between microplastic surfaces and surrounding "rhizosphere-like" soil are significantly different, leading to a "rhizosphere-like neighbor avoidance effect" between microplastic surfaces and the surrounding soil.