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Bacterial use of allochthonous organic carbon for respiration and growth in boreal freshwater systems

Berggren, Martin LU (2009)
Abstract (Swedish)
Popular Abstract in English

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Abstract
Aquatic systems worldwide receive large amounts of organic carbon from terrestrial sources. This ‘allochthonous’ organic carbon (AlloOC) affects critical physical and chemical properties of freshwater ecosystems, with consequences for food web structures and exchange of greenhouse gases with the atmosphere. In the boreal region, loadings of AlloOC are particularly high due to leaching from huge organic deposits in boreal forest, mire and tundra soils.



A main process of AlloOC turnover in aquatic systems is its use by heterotrophic bacteria. Applying a bioassay approach, I measured the respiration and growth (production) of bacteria in northern Sweden, in streams and lakes almost totally dominated by AlloOC. The objective... (More)
Aquatic systems worldwide receive large amounts of organic carbon from terrestrial sources. This ‘allochthonous’ organic carbon (AlloOC) affects critical physical and chemical properties of freshwater ecosystems, with consequences for food web structures and exchange of greenhouse gases with the atmosphere. In the boreal region, loadings of AlloOC are particularly high due to leaching from huge organic deposits in boreal forest, mire and tundra soils.



A main process of AlloOC turnover in aquatic systems is its use by heterotrophic bacteria. Applying a bioassay approach, I measured the respiration and growth (production) of bacteria in northern Sweden, in streams and lakes almost totally dominated by AlloOC. The objective was to elucidate how variations in AlloOC source, age, composition and concentration impact on its use by aquatic bacteria, and how AlloOC properties, in turn, are regulated by landscape composition and by hydrology.



The bacterial respiration (30-309 μg C L-1 d-1) was roughly proportional to the concentration of AlloOC (7-47 mg C L-1), but not significantly related to AlloOC source or character. Bacterial production (4-94 μg C L-1 d-1), on the other hand, was coupled to the AlloOC character, rather than concentration. A strong coupling to AlloOC character was also found for bacterial growth efficiency (0.06-0.51), i.e. production per unit of assimilated carbon. Bacterial production and growth efficiency increased with rising concentrations of low molecular weight AlloOC (carboxylic acids, free amino acids and simple carbohydrates). While the total AlloOC concentrations generally were the highest in mire-dominated catchments, low molecular weight AlloOC concentrations were much higher in forested catchments, compared to mire-dominated. These patterns were reflected in a strong landscape control of aquatic bacterial metabolism. Moreover, high flow episodes increased the export of organic carbon from forests, in relation to the export from mires, stimulating the bacterial production and growth efficiency in streams with mixed (forest and mire) catchments. The potential of AlloOC to support efficient bacterial growth decreased on time-scales of weeks to months, as the AlloOC was aged in laboratory or lake in situ conditions.



To conclude, landscape, hydrology and conditions which determine AlloOC age have large influence on bacterial metabolism in boreal aquatic systems. Considering the role of bacteria in heterotrophic food chains, these factors can have spin-off effects on the structure and function of boreal aquatic ecosystems. (Less)
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author
opponent
  • Pace, Michael L., Department of Environmental Sciences, University of Virginia, Clark Hall, Charlottesville, USA
publishing date
type
Thesis
publication status
published
subject
keywords
bacterial respiration, boreal, streams, lakes, bacterial production, bacterial growth efficiency, allochthonous organic carbon, low molecular weight compounds
pages
17 pages
publisher
Umeå University, Dept. of Ecology and Environmental Science
defense location
Stora hörsalen, KBC, Linnaeus väg 6, Universitetsområdet, Umeå
defense date
2010-01-15 10:00
language
English
LU publication?
no
id
aec3e84d-82d4-4d11-8819-0f5f5523cc83 (old id 3115736)
alternative location
http://umu.diva-portal.org/smash/record.jsf;jsessionid=2732f8c130dee2a89662e72d5d00?parentRecord=diva2:279148&pid=diva2:279150
date added to LUP
2012-09-26 15:11:39
date last changed
2016-09-19 08:45:07
@misc{aec3e84d-82d4-4d11-8819-0f5f5523cc83,
  abstract     = {Aquatic systems worldwide receive large amounts of organic carbon from terrestrial sources. This ‘allochthonous’ organic carbon (AlloOC) affects critical physical and chemical properties of freshwater ecosystems, with consequences for food web structures and exchange of greenhouse gases with the atmosphere. In the boreal region, loadings of AlloOC are particularly high due to leaching from huge organic deposits in boreal forest, mire and tundra soils.<br/><br>
<br/><br>
A main process of AlloOC turnover in aquatic systems is its use by heterotrophic bacteria. Applying a bioassay approach, I measured the respiration and growth (production) of bacteria in northern Sweden, in streams and lakes almost totally dominated by AlloOC. The objective was to elucidate how variations in AlloOC source, age, composition and concentration impact on its use by aquatic bacteria, and how AlloOC properties, in turn, are regulated by landscape composition and by hydrology.<br/><br>
<br/><br>
The bacterial respiration (30-309 μg C L-1 d-1) was roughly proportional to the concentration of AlloOC (7-47 mg C L-1), but not significantly related to AlloOC source or character. Bacterial production (4-94 μg C L-1 d-1), on the other hand, was coupled to the AlloOC character, rather than concentration. A strong coupling to AlloOC character was also found for bacterial growth efficiency (0.06-0.51), i.e. production per unit of assimilated carbon. Bacterial production and growth efficiency increased with rising concentrations of low molecular weight AlloOC (carboxylic acids, free amino acids and simple carbohydrates). While the total AlloOC concentrations generally were the highest in mire-dominated catchments, low molecular weight AlloOC concentrations were much higher in forested catchments, compared to mire-dominated. These patterns were reflected in a strong landscape control of aquatic bacterial metabolism. Moreover, high flow episodes increased the export of organic carbon from forests, in relation to the export from mires, stimulating the bacterial production and growth efficiency in streams with mixed (forest and mire) catchments. The potential of AlloOC to support efficient bacterial growth decreased on time-scales of weeks to months, as the AlloOC was aged in laboratory or lake in situ conditions.<br/><br>
<br/><br>
To conclude, landscape, hydrology and conditions which determine AlloOC age have large influence on bacterial metabolism in boreal aquatic systems. Considering the role of bacteria in heterotrophic food chains, these factors can have spin-off effects on the structure and function of boreal aquatic ecosystems.},
  author       = {Berggren, Martin},
  keyword      = {bacterial respiration,boreal,streams,lakes,bacterial production,bacterial growth efficiency,allochthonous organic carbon,low molecular weight compounds},
  language     = {eng},
  pages        = {17},
  publisher    = {ARRAY(0x87780f8)},
  title        = {Bacterial use of allochthonous organic carbon for respiration and growth in boreal freshwater systems},
  year         = {2009},
}