Plastic is exceedingly abundant in soils, but little is known about its ecological consequences for soil microbiome functioning. Here we report the impacts of polyethylene and biodegradable Ecovio and BI-OPL plastic films buried in alpine soils for 5 months on the genetic potential of the soil microbiome using shotgun metagenomics. The microbiome was more affected by Ecovio and BI-OPL than by polyethylene. Fungi, α- and β-Proteobacteria dominated on the biodegradable films. Ecovio and BI-OPL showed signs of degradation after the incubation, whereas polyethylene did not. Genes involved in cellular processes and signaling (intracellular trafficking, secretion, vesicular transport), as well as metabolism (carbohydrate, lipid and secondary metabolism), were enriched in the plastisphere. Several α/β-hydrolase gene families (cutinase_like, polyesterase-lipase-cutinase, carboxylesterase), which encode enzymes essential to plastic degradation, and carbohydrate-active genes involved in lignin and murein degradation increased on Ecovio and BI-OPL films. Enriched nitrogen fixation and organic N degradation and synthesis genes and decreased nitrification genes on Ecovio altered the biogeochemical cycling, leading to higher ammonium concentrations and depletion of nitrite and nitrate in the soil. Our results indicate that plastics affect the alpine soil microbiome and its functions and suggest that the plastisphere has an untapped microbial potential for plastic biodegradation.