| 1. |
- Berggren, Martin, 1981-, et al.
(författare)
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Aging of allochthonous organic carbon regulates bacterial production in unproductive boreal lakes
- 2009
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 54:4, s. 1333-1342
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
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| 3. |
- Berggren, Martin, 1981-, et al.
(författare)
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Efficient aquatic bacterial metabolism of dissolved low-molecular-weight compounds from terrestrial sources
- 2010
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Ingår i: The ISME Journal. - London : Nature Publishing Group. - 1751-7362 .- 1751-7370. ; 4:3, s. 408-416
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Berggren, Martin, 1981-, et al.
(författare)
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Hydrological control of organic carbon support for bacterial growth in boreal headwater streams
- 2009
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Ingår i: Microbial Ecology. - : Springer Science and Business Media LLC. - 0095-3628 .- 1432-184X. ; 57:1, s. 170-178
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Berggren, Martin, et al.
(författare)
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Lake secondary production fueled by rapid transfer of low molecular weight organic carbon from terrestrial sources to aquatic consumers
- 2010
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 13:7, s. 870-880
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Tidskriftsartikel (refereegranskat)abstract
- P>Carbon of terrestrial origin often makes up a significant share of consumer biomass in unproductive lake ecosystems. However, the mechanisms for terrestrial support of lake secondary production are largely unclear. By using a modelling approach, we show that terrestrial export of dissolved labile low molecular weight carbon (LMWC) compounds supported 80% (34-95%), 54% (19-90%) and 23% (7-45%) of the secondary production by bacteria, protozoa and metazoa, respectively, in a 7-km2 boreal lake (conservative to liberal estimates in brackets). Bacterial growth on LMWC was of similar magnitude as that of primary production (PP), and grazing on bacteria effectively channelled the LMWC carbon to higher trophic levels. We suggest that rapid turnover of forest LMWC pools enables continuous export of fresh photosynthates and other labile metabolites to aquatic systems, and that substantial transfer of LMWC from terrestrial sources to lake consumers can occur within a few days. Sequestration of LMWC of terrestrial origin, thus, helps explain high shares of terrestrial carbon in lake organisms and implies that lake food webs can be closely dependent on recent terrestrial PP.
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| 6. |
- Berggren, Martin, 1981-, et al.
(författare)
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Landscape regulation of bacterial growth efficiency in boreal freshwaters
- 2007
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Ingår i: Global Biogeochemical Cycles. - : American Geophysical Union. - 0886-6236 .- 1944-9224. ; 21
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Berggren, Martin, 1981-, et al.
(författare)
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Nutrient constraints on metabolism affect the temperature regulation of aquatic bacterial growth efficiency
- 2010
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Ingår i: Microbial Ecology. - : Springer. - 0095-3628 .- 1432-184X. ; 60:4, s. 894-902
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Tidskriftsartikel (refereegranskat)abstract
- Inorganic nutrient availability and temperature are recognized as major regulators of organic carbon processing by aquatic bacteria, but little is known about how these two factors interact to control bacterial metabolic processes. We manipulated the temperature of boreal humic stream water samples within 0–25°C and measured bacterial production (BP) and respiration (BR) with and without inorganic nitrogen + phosphorus addition. Both BP and BR increased exponentially with temperature in all experiments, with Q 10 values varying between 1.2 and 2.4. The bacterial growth efficiency (BGE) showed strong negative relationships with temperature in nutrient-enriched samples and in natural stream water where community-level BP and BR were not limited by nutrients. However, there were no relationships between BGE and temperature in samples where BP and BR were significantly constrained by the inorganic nutrient availability. The results suggest that metabolic responses of aquatic bacterial communities to temperature variations can be strongly dependent on whether the bacterial metabolism is limited by inorganic nutrients or not. Such responses can have consequences for both the carbon flux through aquatic food webs and for the flux of CO2 from aquatic systems to the atmosphere.
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| 8. |
- Berggren, Martin, et al.
(författare)
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Quality transformation of dissolved organic carbon during water transit through lakes : contrasting controls by photochemical and biological processes
- 2018
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Ingår i: Biogeosciences. - : European Geosciences Union (EGU). - 1726-4170 .- 1726-4189. ; 15:2, s. 457-470
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Tidskriftsartikel (refereegranskat)abstract
- Dissolved organic carbon (DOC) may be removed, transformed, or added during water transit through lakes, resulting in changes in DOC composition and pigmentation (color). However, the process-based understanding of these changes is incomplete, especially for headwater lakes. We hypothesized that because heterotrophic bacteria preferentially consume noncolored DOC, while photochemical processing removes colored fractions, the overall changes in DOC color upon water passage through a lake depend on the relative importance of these two processes, accordingly. To test this hypothesis we combined laboratory experiments with field studies in nine boreal lakes, assessing both the relative importance of different DOC decay processes (biological or photochemical) and the loss of color during water transit time (WTT) through the lakes. We found that influence from photo-decay dominated changes in DOC quality in the epilimnia of relatively clear headwater lakes, resulting in systematic and selective net losses of colored DOC. However, in highly pigmented brown-water lakes (absorbance at 420 nm > 7 m(-1)) biological processes dominated, and there was no systematic relationship between color loss and WTT. Moreover, in situ data and dark experiments supported our hypothesis on the selective microbial removal of nonpigmented DOC, mainly of low molecular weight, leading to persistent water color in these highly colored lakes. Our study shows that brown headwater lakes may not conform to the commonly reported pattern of the selective removal of colored constituents in freshwaters, as DOC can show a sustained degree of pigmentation upon transit through these lakes.
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| 9. |
- Jansson, Mats, et al.
(författare)
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Bioavailable phosphorus in humic headwater streams in boreal Sweden
- 2012
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Ingår i: Limnology and Oceanography. - : Wiley. - 1939-5590 .- 0024-3590. ; 57:4, s. 1161-1170
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Tidskriftsartikel (refereegranskat)abstract
- Bioavailable phosphorus (BAP) concentrations were determined nine times between April and October 2010 in two humic boreal headwater streams draining forest-and mire-dominated catchments. BAP was analyzed in a bioassay in which natural P-limited bacterioplankton grew with natural P as the sole P source. In both streams, approximately 90% of the BAP occurred as dissolved species (passing a 0.2-mu m filter), consisting partly of low-molecular-weight forms (passing a filter with nominal cutoff at 1 kDa) and partly of high-molecular-weight forms (passing a 0.2-mu m filter but not a 1-kDa filter). Concentrations of total dissolved BAP varied between 1 mu g L-1 and 14 mu g L-1, with the highest values in the middle of the summer. Compared to the forest stream, BAP concentrations were generally higher in the mire stream, where it occasionally amounted to nearly 50% of total P. Molybdate reactive phosphorus overestimated BAP considerably. Most of the BAP was in forms other than free orthophosphate. Temporal BAP variations showed no relationships with dissolved organic carbon (C) or iron but were positively related to air temperature and negatively related to the absorbance ratio (a254 : a365) of organic compounds in the water, indicating connections between terrestrial export of BAP and temperature-dependent terrestrial C metabolism. Concentrations of BAP can relieve stream bacteria from P limitation, and a significant share of BAP exported to streams can reach and be used in downstream lakes.
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| 10. |
- Karlsson, Jan, et al.
(författare)
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Response to Comment: Terrestrial support of pelagic consumers in unproductive lakes : uncertainty and potential in assessments using stable isotopes
- 2014
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Ingår i: Limnology and Oceanography. - : Wiley. - 1939-5590 .- 0024-3590. ; 59:5, s. 1800-1803
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Tidskriftsartikel (refereegranskat)abstract
- The use of stable carbon isotopes (d13C) has played a key role in estimation of the proportion of aquatic consumer biomass derived from terrestrial organic matter (OM; i.e., allochthony; Meili et al. 1996; Grey et al. 2001; Pace et al. 2004). However, the use of d13C for assessing allochthony has shortcomings because of the small natural separation between terrestrial and aquatic isotopic end members and the difficulty in physically separating autotrophic phytoplankton for d13C analysis from other components of particulate organic carbon (POC). These shortcomings are especially problematic in unproductive lakes where the phytoplankton are dominated by small and mixotrophic species, and where the internal photosynthesis is low compared to the input of terrestrial OM (Algesten et al. 2004; Jansson et al. 2008). Several alternative analyses and approaches have been tested to overcome these methodological limitations, including compound-specific analyses of phytoplankton biomarkers (Pace et al. 2007; Van Den Meersche et al. 2009; Berggren et al. 2014), manipulation of phytoplankton d13C by addition of 13C-labeled dissolved inorganic carbon (Pace et al. 2004; Taipale et al. 2008), addition of 13C-enriched OM (Karlsson et al. 2007; Bartels et al. 2012), and various mass balance and modeling approaches (Marty and Planas 2008; Mohamed and Taylor 2009; Berggren et al. 2010). Still, a generally applicable method is lacking, implying that the problems with assessing d13C of phytoplankton is a major limitation in the use of d13C for estimating allochthony with the accuracy needed for detailed understanding of food web dynamics.
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