Impact of land use intensification on soil fungal communities in the Argentine Pampas

In the Argentine Pampas, intensive land use has degraded soils, but the relationships among organic matter composition, enzyme activity, and fungal communities remain unclear. To address this gap, this study was conducted across contrasting ecoregions, including an undisturbed environment (pristine, PI), pasture (PA), crop rotation with cover crops (RO), and monoculture (MO), integrating chemical, biochemical, and molecular analyses. Infrared analysis of soil organic matter (SOM) under PI land uses showed that in Anguil, the upper bands (3400 to 1646 cm-1), linked to hydroxyl and amine groups, aliphatic methyl and methylene structures, carbonyls, and conjugated aromatic groups, had higher intensities, indicating greater functional diversity of SOM. In Pergamino, these variations were smaller or constant, reflecting the influence of location. Overall, enzyme activities were higher under PA and PI, especially in the semi-arid Anguil site, indicating that less disturbed soils support enhanced microbial functionality. Both land use and location also influenced the relative abundance of key fungal classes, with Mortierellomycetes more abundant in Pergamino, and Leotiomycetes and Agaricomycetes favored in PI or PA. Dothideomycetes increased under intensive agricultural land uses (MO and RO), likely related to plant residue inputs and soil disturbance. Despite these shifts, fungal diversity indices showed slight differences between treatments. Finally, key microbes closely related to land use and location were identified using the linear discriminant analysis (LDA) effect size (LEfSe) after fungal ITS sequencing. These results emphasize the importance of combining chemical, biochemical, and molecular approaches to evaluate soil health and support sustainable practices that preserve microbial processes and ecosystem resilience.