Biostimulant Modulation of Soil Mycobiome Structure and Diversity and Amaranthus cruentus Growth Under Perfluorotetradecanoic Acid Stress

Perfluorotetradecanoic acid (PA) is a long-chain perfluorocarboxylic acid belonging to the group of per- and polyfluoroalkyl substances (PFASs), whose exceptional chemical stability promotes their persistence and accumulation in the environment. Despite the growing interest in PFASs, knowledge of the impact of PA on soil fungal communities and crop plants remains limited. The aim of this study was to evaluate the effects of PA and the biostimulants Shigeki and Aminoprim on the structure, diversity, and functional potential of the soil mycobiome, as well as on the growth and development of Amaranthus cruentus. A pot experiment was conducted under controlled greenhouse conditions using Eutric Cambisols soil. The structure of fungal communities was determined using high-throughput sequencing of the ITS region, while diversity was assessed based on alpha and beta diversity indices and trophic group analyses. In plants, stem length and the biomass of aboveground parts and roots were analyzed. PA significantly altered the composition and structure of soil fungal communities. Fungi belonging to the phylum Ascomycota were dominant in all samples, with their highest abundance observed in PA-contaminated soil. Contamination with this compound also reduced the abundance of the genera Penicillium and Talaromyces, while increasing the relative abundance of Humicola, Chaetomium, and Fusarium in soil treated with PA and biostimulants. Aminoprim promoted an increase in taxonomic richness and community evenness, whereas Shigeki enhanced the abundance of Chytridiomycota in PA-contaminated soil. Perfluorotetradecanoic acid inhibited the growth of A. cruentus; however, the applied biostimulants partially mitigated its adverse effects. The results indicate that PA affects both the structure and functioning of the soil mycobiome as well as plant development, while biostimulation may represent a potential strategy for supporting the biological stability of soils subjected to PFAS contamination.