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Bacterial use of allochthonous organic carbon for respiration and growth in boreal freshwater systems
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science. (Naturgeografi)
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, Institutionen för ekologi, miljö och geovetenskap , 2009. , 17 + 4 papers p.
Keyword [en]
lakes, streams, boreal, bacterial respiration, bacterial production, bacterial growth efficiency, allochthonous organic carbon, low molecular weight compounds
Research subject
Physical Geography
URN: urn:nbn:se:umu:diva-30051ISBN: 978-91-7264-870-8OAI: diva2:279150
Public defence
2010-01-15, Stora hörsalen, KBC, Linnaeus väg 6, Universitetsområdet, Umeå, 10:00 (English)
Available from: 2009-12-04 Created: 2009-12-01 Last updated: 2009-12-04Bibliographically approved
List of papers
1. Landscape regulation of bacterial growth efficiency in boreal freshwaters
Open this publication in new window or tab >>Landscape regulation of bacterial growth efficiency in boreal freshwaters
2007 (English)In: Global Biogeochemical Cycles, ISSN 0886-6236, Vol. 21Article in journal (Refereed) Published
Abstract [en]

Allochthonous organic carbon in aquatic systems is metabolized by heterotrophic bacteria, with significant consequences for the biostructure and energy pathways of freshwater ecosystems. The degree to which allochthonous substrates support growth of bacteria is largely dependent on bacterial growth efficiency (BGE), i.e., bacterial production (BP) per unit of assimilated carbon. Here we show how the spatial variability of BGE in the boreal region can be mediated by the distribution of the two dominating landscape elements forest and mires. Using an 11 days bioassay approach, the production and respiration of bacteria were measured in water samples from nine small Swedish streams (64°N 19°E), representing a gradient ranging from organic carbon supplied mainly from peat mires to carbon supplied mainly from coniferous forests. BP was positively correlated to forest coverage (%) of the catchment, while bacterial respiration was similar in all streams. Consequently, BGE showed a strong positive correlation with forest coverage. Partial least square regression showed that BGE was chiefly regulated by qualitative properties of the organic material, indicated by the absorbance ratio a254/a365 plus C/N and C/P ratios. The data suggest that a share of the organic carbon pool, drained mainly from forest soils, had a potential of being incorporated into bacterial biomass with great efficiency. Its potential for supporting growth was probably nutrient regulated as indicated by inorganic nutrient enrichment experiments.

Place, publisher, year, edition, pages
American Geophysical Union, 2007
urn:nbn:se:umu:diva-17348 (URN)10.1029/2006GB002844 (DOI)
Available from: 2007-11-08 Created: 2007-11-08 Last updated: 2009-12-02Bibliographically approved
2. Hydrological control of organic carbon support for bacterial growth in boreal headwater streams
Open this publication in new window or tab >>Hydrological control of organic carbon support for bacterial growth in boreal headwater streams
2009 (English)In: Microbial Ecology, ISSN 0095-3628, Vol. 57, no 1, 170-178 p.Article in journal (Refereed) Published
Abstract [en]

Terrestrial organic carbon is exported to freshwater systems where it serves as substrate for bacterial growth. Temporal variations in the terrigenous organic carbon support for aquatic bacteria are not well understood. In this paper, we demonstrate how the combined influence of landscape characteristics and hydrology can shape such variations. Using a 13-day bioassay approach, the production and respiration of bacteria were measured in water samples from six small Swedish streams (64° N, 19° E), draining coniferous forests, peat mires, and mixed catchments with typical boreal proportions between forest and mire coverage. Forest drainage supported higher bacterial production and higher bacterial growth efficiency than drainage from mires. The areal export of organic carbon was several times higher from mire than from forest at low runoff, while there was no difference at high flow. As a consequence, mixed streams (catchments including both mire and forest) were dominated by mire organic carbon with low support of bacterial production at low discharge situations but dominated by forest carbon supporting higher bacterial production at high flow. The stimulation of bacterial growth during high-flow episodes was a result of higher relative export of organic carbon via forest drainage rather than increased drainage of specific “high-quality” carbon pools in mire or forest soils.

urn:nbn:se:umu:diva-23276 (URN)10.1007/s00248-008-9423-6 (DOI)
Available from: 2009-06-09 Created: 2009-06-09 Last updated: 2009-12-02
3. Aging of allochthonous organic carbon regulates bacterial production in unproductive boreal lakes
Open this publication in new window or tab >>Aging of allochthonous organic carbon regulates bacterial production in unproductive boreal lakes
2009 (English)In: Limnology and Oceanography, ISSN 0024-3590, Vol. 54, no 4, 1333-1342 p.Article in journal (Refereed) Published
Abstract [en]

We calculated average aquatic dissolved organic carbon (DOC) age (the time span from soil discharge to observation) in water from the inlets and outlets of two unproductive Swedish lakes at different times during an annual cycle. Bacterial production (BP) and bacterial growth efficiency (BGE) determined during 7-d bioassays decreased with increasing average aquatic DOC age. Parallel to the declines in BP and BGE there was a rise in specific ultraviolet absorbance at the wavelength of 254 nm (SUVA254), which indicates that decreasing BP and BGE were connected to a shift to a more aromatic and recalcitrant DOC pool. The relationships between bacterial metabolism and DOC age were stronger after a Q10 correction of the DOC age, showing that temperature affected rates of DOC quality changes over time and should be taken into account when relating lake bacterial growth to substrate aging in natural environments. We propose that hydrological variability in combination with lake size (water renewal time) have a large influence on pelagic BP in lakes with high input of terrigenous DOC.

urn:nbn:se:umu:diva-23250 (URN)
Available from: 2009-06-08 Created: 2009-06-08 Last updated: 2009-12-02
4. Efficient aquatic bacterial metabolism of dissolved low-molecular-weight compounds from terrestrial sources
Open this publication in new window or tab >>Efficient aquatic bacterial metabolism of dissolved low-molecular-weight compounds from terrestrial sources
Show others...
2010 (English)In: The ISME Journal, ISSN 1751-7362, Vol. 4, no 3, 408-416 p.Article in journal (Refereed) Published
Abstract [en]

Carboxylic acids (CAs), amino acids (AAs) and carbohydrates (CHs) in dissolved free forms can be readily assimilated by aquatic bacteria and metabolized at high growth efficiencies. Previous studies have shown that these low-molecular-weight (LMW) substrates are released by phytoplankton but also that unidentified LMW compounds of terrestrial origin is a subsidy for bacterial metabolism in unproductive freshwater systems. We tested the hypothesis that different terrestrially derived CA, AA and CH compounds can offer substantial support for aquatic bacterial metabolism in fresh waters that are dominated by allochthonous dissolved organic matter (DOM). Drainage water from three catchments of different characters in the Krycklan experimental area in Northern Sweden were studied at the rising and falling limb of the spring flood, using a 2-week bioassay approach. A variety of CA, AA and CH compounds were significantly assimilated by bacteria, meeting 15–100% of the bacterial carbon demand and explaining most of the observed variation in bacterial growth efficiency (BGE; R2=0.66). Of the 29 chemical species that was detected, acetate was the most important, representing 45% of the total bacterial consumption of all LMW compounds. We suggest that LMW organic compounds in boreal spring flood drainage could potentially support all in situ bacterial production in receiving lake waters during periods of weeks to months after the spring flood.

Place, publisher, year, edition, pages
London: Nature Publishing Group, 2010
freshwater, growth efficiency, heterotrophic bacteria, low-molecular-weight DOM
National Category
Research subject
Physical Geography
urn:nbn:se:umu:diva-30050 (URN)10.1038/ismej.2009.120 (DOI)000274800100010 ()
Available from: 2009-12-01 Created: 2009-12-01 Last updated: 2011-04-26Bibliographically approved

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