The cooler the better: Increased aquatic hyphomycete diversity in subtropical streams along a neotropical latitudinal gradient

Aquatic hyphomycetes are microbial decomposers in freshwater environments that, together with detritivores, play an essential role in the functioning of low-order streams. Here, we evaluated aquatic hyphomycetes communities associated with decomposing leaves of Nectandra megapotamica, a common Neotropical riparian tree, along a subtropical-tropical latitudinal gradient. Two forest streams located in subtropical regions and 3 in tropical regions were selected. We identified 29 species of aquatic hyphomycetes, 22 (75.8%) in subtropical streams and 15 (51.7%) in tropical streams. We also found a higher fungal biomass in subtropical streams. However, the amounts of leaf mass loss did not differ between regions, but the values were higher in summer than in winter. High temperature, pH and electrical conductivity values, as well as low dissolved oxygen levels, negatively affected spore production. These results suggest that the subtropical-tropical gradient is an important predictor of aquatic hyphomycete diversity; however, the observed species had different sensitivities to local environmental factors.