Plastic mulch film residues have been accumulating in agricultural soils for decades, but so far, little is known about its consequences on soil microbial communities and functions. Here, we tested the effects of plastic residues of low-density polyethylene and biodegradable mulch films on soil suppressiveness and microbial community composition. We investigated how plastic residues in a Fusarium culmorum suppressive soil affect the level of disease suppressiveness, plant biomass, nutrient status, and microbial communities in rhizosphere using a controlled pot experiment. The addition of 1% plastic residues to the suppressive soil did not affect the level of suppression and the disease symptoms index. However, we did find that plant biomasses decreased, and that plant nutrient status changed in the presence of plastic residues. No significant changes in bacterial and fungal rhizosphere communities were observed. Nonetheless, bacterial and fungal communities closely attached to the plastisphere were very different from the rhizosphere communities with overrepresentation of potential plant pathogens. The plastisphere revealed a high abundance of specific bacterial phyla (Actinobacteria, Bacteroidetes, and Proteobacteria) and fungal genera (Rhizoctonia and Arthrobotrys). Our work revealed new insights and raises emerging questions for further studies on the impact of microplastics on the agroecosystems.

The amplicon library preparation and sequencing was carried out at the McGill University and Genome Québec Innovation Centre (Montréal, Canada). The PCRs of the bacterial 16S rRNA gene V3-V4 region were performed with the primer set 515F (5’-GTGCCAGCMGCCGCGGTAA-3’) and 806R (5’-GGACTACHVGGGTWTCTAAT-3’). The PCRs of the fungal rDNA gene ITS region was performed with the primer set ITS1F (5’-CTTGGTCATTTAGAGGAAGTAA-3’) and 58A2R (5’-CTGCGTTCTTCATCGAT-3’). Sequencing was carried out on an Illumina MiSeq platform with 4 biological replicates per treatment.