Temperature and interspecific interactions drive differences in carbon use efficiencies and biomass stoichiometry among aquatic fungi

Saprotrophic fungi play important roles in transformations of carbon (C), nitrogen (N), and phosphorus (P) in aquatic environments. However, it is unclear how warming will alter fungal cycling of C, N, and P. We conducted an experiment with four aquatic hyphomycetes (Articulospora tetracladia, Hydrocina chaetocladia, Flagellospora sp., and Aquanectria penicillioides), and an assemblage of the same taxa, to test how temperature alters C and nutrient use. Specifically, we evaluated biomass accrual, C:N, C:P, delta C-13, and C use efficiency (CUE) over a 35-d experiment with temperatures ranging from 4oC to 20oC. Changes in biomass accrual and CUE were predominantly quadratic with peaks between 7oC and 15oC. The C:P of H. chaetocladia biomass increased 9x over the temperature gradient, though the C:P of other taxa was unaffected by temperature. Changes in C:N were relatively small across temperatures. Biomass delta C-13 of some taxa changed across temperatures, indicating differences in C isotope fractionation. Additionally, the 4-species assemblage differed from null expectations based on the monocultures in terms of biomass accrual, C:P, delta C-13, and CUE, suggesting that interactions among taxa altered C and nutrient use. These results highlight that temperature and interspecific interactions among fungi can alter traits affecting C and nutrient cycling. Temperature and interactions among different taxa drive differences in carbon and nutrient use of aquatic fungi.