Land-use categories shape aquatic conidial fungal communities in Atlantic Forest streams: the roles of water chemistry and substrate quality.

The intensification of land use, driven by urbanization and agriculture, threatens the integrity of tropical aquatic ecosystems, impacting key processes such as organic matter decomposition. However, the effects of these pressures on the diversity of aquatic conidial fungi, that are essential fungal decomposers in nutrient cycling, remain largely unexplored. In this study, we evaluated how the diversity of fungi in submerged leaf litter varies along a land-use gradient (forested, rural, and urban areas) in two tropical river basins in Brazil. We conducted morphological identification of the fungal community and analyzed water physicochemical variables as well as the nutrient composition of the leaf litter. We identified 22 taxa, with richness and occurrence significantly higher in forested areas. Marginal multivariate analyses (PERMANOVA) confirmed that land use is a significant, independent predictor of fungal community composition, even when accounting for river identity. These compositional shifts were mediated by simultaneous alterations in limnological variables (e.g., pH, conductivity, dissolved oxygen) and the nutrient quality of the substrate. Our results suggest that the preservation of riparian vegetation supports diverse fungal decomposer communities in these tropical streams. These findings highlight the potential of conidial fungi as indicators of water quality and underscore the importance of watershed conservation for maintaining local aquatic biodiversity.