Effects of Temperature on Activity of Aquatic Hyphomycetes: A Microcosm Study

Predicted increases in temperature under climate change scenarios are expected to affect not only atmospheric and water temperatures, but also the rate of heterotrophic activity and carbon dynamics and retention in ecosystems. The magnitude of the increase in metabolic activity of living organisms with increased temperature can be predicted by the Metabolic Theory of Ecology, however, multiple factors can cause deviations from simple predictions. The goal of this study is to assess the temperature sensitivity of aquatic hyphomycetes and fungi-mediated leaf litter decomposition by following responses to temperature of fungal biomass accrual, respiration and decomposition rates in laboratory microcosms simulating stream conditions. We found that fungal parameters and leaf litter decomposition rates often do not follow simple predictions of the MTE. We observed much greater temperature sensitivity of microbial parameters at low temperatures (5-1 0° C interval) and more moderate sensitivity at higher temperatures (15-200 C interval). These trends may have important implications for stream ecosystems under climate change scenarios since the bulk leaf litter input and the highest microbial activity coincide with the coldest season (autumn-winter) in temperate streams