Microplastic pollution in Morocco's High Atlas: First evidence and selective impact on soil microbiome across an elevational gradient

Microplastics (MPs) are emerging contaminants in terrestrial ecosystems, yet their distribution and ecological impacts in remote mountain soils remain poorly understood. This study investigated MP contamination along an elevational gradient on Mount Toubkal (500-4,167 m), the highest peak in North Africa. Soil samples were collected from nine elevations and analyzed for MP abundance, morphology, size, color, and polymer composition. MPs were quantified via density separation and stereomicroscopy, with polymer confirmation by FTIR and surface analysis using SEM-EDX. DNA was extracted from each sample and sequenced (Illumina MiSeq) targeting bacterial 16S rRNA and fungal ITS regions. MPs were found across all sites, with 1,693 particles identified and an average concentration of 23.2 MPs/kg of soil. Fibers dominated, especially at higher altitudes, while smaller particles (<500 μm) and lighter polymers (e.g., polystyrene, cellulose acetate) increased with elevation. Surface degradation features confirmed environmental weathering. Correlation analyses linked MPs traits to microbial composition: bacterial communities showed no significant response, but fungal richness and diversity declined with increasing abundance of fibrous MPs, PVC, and small particles. At the phylum level, fungal groups responded selectively to MPs' traits, suggesting that MPs act as environmental filters. These findings reveal the widespread presence of MPs in alpine soils and their trait-specific impacts on fungal communities, emphasizing the need to account for MP heterogeneity in ecological risk assessments.