Streamside mesocosm experiments were conducted in a low-order forest watershed to directly examine responses by microbial communities on standardized substrates to different terrestrial and aquatic sources of dissolved organic matter (DOM). Community respiration (oxygen uptake), microbial density (colony-forming units on agar plates), leaf decomposition, and community metabolic profiles (metabolism patterns in sole carbon source utilization assays) were measured. Stream benthic microbial communities responded immediately and positively to increases in terrestrially derived DOM. Respiration activity and density estimates increased significantly, but there was no significant change in community metabolic profile. Responses were greater to DOM extracted from upper soil horizons than from deeper soils. Community respiration and bacterial abundance also increased in response to an aquatic DOM source, but were accompanied by a significant change in community metabolic profiles. Results provide direct experimental evidence that benthic microbial communities of forest headwater streams are able to rapidly utilize terrestrial DOM.
Sediment microbial communities rely on different dissolved organic matter sources along a Mediterranean river continuum
