Abstract

Fungi are important decomposers of leaf litter in streams with possible knock-on effects on other stream microbes and carbon cycling. We designed an experiment in outdoor experimental flumes simulating sand-bed streams in an early successional state. We expected an overall enhanced microbial activity in the presence of fungi. Fifteen experimental channels were inoculated with stream water containing: 1) bacteria and fungi 2) bacteria only, 3) no microorganisms, and 4) killed bacteria and fungi. The experiment runs for 5 weeks. Whole-stream metabolism and microbial respiration associated with leaf litter and sediment microbial respiration at the last sampling date were higher in experimental streams inoculated with fungi. Similarly, increases in net primary production and chlorophyll-a content were greatest in the streams inoculated with fungi. These results point to a major role of fungal communities in stream ecosystems, well beyond the direct involvement in leaf litter decomposition.