Journal
JOURNAL OF ECOLOGY
Volume 103, Issue 5, Pages 1165-1171Publisher
WILEY
DOI: 10.1111/1365-2745.12455
Keywords
Alaska; algal-bacterial interactions; aquatic plant ecology; climate change; decomposition; dissolved organic carbon; nutrients; priming effect; resource subsidies; wetland
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Funding
- ASPiRE Junior Faculty Research programme at Ball State University
- National Science Foundation [DEB 0425328, DEB-0080609]
- Bonanza Creek Long Term Ecological Research Program (US Forest Service) [PNW01-JV11261952-231]
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In most high-latitude wetlands, carbon accumulation as peat represents a balance between plant net primary productivity and heterotrophic decomposition. We hypothesized that this assessment of ecosystem metabolism is incomplete as it does not include information on energy inputs from microalgae, which form complex biofilms with heterotrophic micro-organisms on the peat surface. To investigate the potential for algae (and associated exudates) to support heterotrophic metabolism under ambient and elevated nutrient levels, we conducted a factorial enrichment of nutrients (nitrogen and phosphorus) and carbon (glucose) in mesocosms with and without the presence of algae (using light-transparent and dark treatments, respectively) in an Alaskan fen. We measured respiration rates and changes in bacterial biomass to characterize the response of heterotrophic bacteria to our experimental treatments. During incubation assays, algae released up to 38% of their net productivity as exudates and there was a positive relationship between algal production and concentrations of dissolved organic carbon inside mesocosms. Elevated algal productivity in the presence of nutrient enrichment stimulated heterotrophic bacterial respiration and biomass. These responses did not occur with nutrient enrichment in the dark (without algae). The response of bacteria to algae was similar in magnitude to bacterial responses to glucose enrichment.Synthesis. We conclude that bacteria in this boreal fen were primarily limited by labile carbon, and this constraint was alleviated in the presence of elevated algal production. Consequently, algae may facilitate hotspots of microbial activity in northern peatlands, especially in conditions of greater nutrient availability associated with more variable hydrology expected for this region with ongoing climate change.
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