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Aquatic Microbial Ecology

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AME 68:171-184 (2013)  -  DOI:

Responses of microbial food web to increased allochthonous DOM in an oligotrophic subarctic lake

Laura Forsström1,3,*, Toni Roiha1,2, Milla Rautio1,2

1Department of Biological and Environmental Science, 40014 University of Jyväskylä, Finland
2Département des sciences fondamentales and Centre for Northern Studies (CEN), Université du Québec à Chicoutimi, Québec G7H 2B1, Canada
3Present address: Department of Environmental Sciences, 00014 University of Helsinki, Finland

ABSTRACT: Climate-induced changes in catchment area vegetation and runoff alter the quality and quantity of carbon that enters lakes, with implications for food webs in recipient water bodies. The effect of dissolved organic matter (DOM) on the ratio between heterotrophic and autotrophic biomass and productivity was studied in a subarctic, clear water lake in northern Finland. In a mesocosm experiment, natural DOM from a subarctic bog and a boreal lake was added to the lake water, doubling the initial dissolved organic carbon (DOC) concentration. Optical indices suggested that the subarctic DOM addition was more bioavailable, which was in line with the greater increase in bacterial biomass and production observed in this treatment. Both DOM additions increased the abundance of heterotrophic nanoflagellates (HNF) and decreased primary productivity. They also led to lower ratios of primary to bacterial production, autotrophic to mixotrophic algae and pigmented nanoflagellates (PNF) to HNF relative to the control samples, indicating a shift from a primary production-based food web towards one based on bacterial production. A comparable increase in DOM in the natural environment would lead to a considerable decrease in the euphotic layer and loss of areas available for primary production, resulting in a shift towards a heterotrophic production based food web.

KEY WORDS: Dissolved organic matter · Dissolved organic carbon · Subarctic · Microbial food web

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Cite this article as: Forsström L, Roiha T, Rautio M (2013) Responses of microbial food web to increased allochthonous DOM in an oligotrophic subarctic lake. Aquat Microb Ecol 68:171-184.

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