| 1. |
- Kritzberg, Emma, et al.
(författare)
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Autochthonous versus allochthonous carbon sources of bacteria: Results from whole-lake C-13 addition experiments
- 2004
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Ingår i: Limnology and Oceanography. - 1939-5590. ; 49:2, s. 588-596
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Tidskriftsartikel (refereegranskat)abstract
- Organic substrates for pelagic bacteria are derived from dissolved organic carbon (DOC) in the water column. DOC is a heterogeneous mixture of molecules, some of which are imported from the watershed (allochthonous DOC) and others that are produced by autotrophs within the system (autochthonous DOC). We examined the importance of autochthonous versus allochthonous DOC in supporting the growth of pelagic bacteria by manipulating the C-13 content of autochthonous sources in a whole-lake experiment. (NaHCO3)-C-13 was added daily to two small forested lakes for a period of 42 d, thereby strongly labeling autochthonous primary production. To obtain bacterial carbon isotopes, bacteria were regrown in vitro in particle-free lake water and in situ in dialysis tubes; little difference was found between the two methods. The contribution of autochthonous versus allochthonous carbon to the bacterial biomass was estimated by applying a two-member mixing model using a C-13 of -28parts per thousand as the allochthonous end member. The autochthonous end member, which varied over time, was estimated indirectly by several approaches. The bacterial biomass consisted of 35-70% allochthonous carbon. This result confirms the often-stated hypothesis that autochthonous carbon alone does not support bacterial production. On the other hand, autochthonous DOC was preferentially utilized relative to terrestrial DOC. On the basis of C-13 measurements, only 13% of the DOC standing stock was of recent autochthonous origin, but it supported 30-65% of bacterial production.
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| 2. |
- Kritzberg, Emma, et al.
(författare)
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Bacterial growth on allochthonous carbon in humic and nutrient-enriched lakes: Results from whole-lake C-13 addition experiments
- 2006
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Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 9:3, s. 489-499
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Tidskriftsartikel (refereegranskat)abstract
- Organic carbon (C) in lakes originates from two distinct sources-primary production from within the lake itself (autochthonous supply) and importation of organic matter from the terrestrial watershed (allochthonous supply). By manipulating the C-13 of dissolved inorganic C, thereby labeling within-lake primary production, we examined the relative importance of autochthonous and allochthonous C in supporting bacterial production. For 35 days, (NaHCO3)-C-13 was added daily to two small, forested lakes. One of the lakes (Peter) was fertilized so that primary production exceeded total respiration in the epilimnion. The other lake (Tuesday), in contrast, was low in productivity and had high levels of colored dissolved organic C (DOC). To obtain bacterial C isotopes, bacteria were regrown in situ in particle-free lake water in dialysis tubes. The contribution of allochthonous C to bacterial biomass was calculated by applying a two-member mixing model. In the absence of a direct measurement, the isotopic signature of the autochthonous end-member was estimated indirectly by three different approaches. Although there was excess primary production in Peter Lake, bacterial biomass consisted of 43-46% allochthonous C. In Tuesday Lake more than 75% of bacterial growth was supported by allochthonous C. Although bacteria used autochthonous C preferentially over allochthonous C, DOC from the watershed contributed significantly to bacterial production. In combination with results from similar experiments in different lakes, our findings suggest that the contribution of allochthonous C to bacterial production can be predicted from ratios of chromophoric dissolved organic matter (a surrogate for allochthonous supply) and chlorophyll a (a surrogate for autochthonous supply).
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| 3. |
- Kritzberg, Emma, et al.
(författare)
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Does autochthonous primary production drive variability in bacterial metabolism and growth efficiency in lakes dominated by terrestrial C inputs?
- 2005
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Ingår i: Aquatic Microbial Ecology. - 0948-3055. ; 38:2, s. 103-111
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Tidskriftsartikel (refereegranskat)abstract
- During the past 20 yr, aquatic microbiologists have reported 2 strong patterns which initially appear contradictory. In pelagic systems, bacterial growth and biomass is well correlated with the growth and biomass of primary producers. However, bacterial respiration often exceeds net primary production, which suggests that bacteria are subsidized by external inputs of organic matter. We hypothesize that bacterial growth efficiency (BGE) varies systematically between autochthonous and allochthonous carbon (C) sources and that this variation resolves the above conundrum. To test these ideas, we examined the ecological regulation of bacterial secondary production (BP), bacterial respiration (BR) and BGE in a series of lakes dominated by terrestrial (allochthonous) C inputs. BP was correlated with autochthonous C sources (chlorophyll a) even though the lakes were net heterotrophic (i.e. heterotrophic respiration consistently exceeded primary production). The results were simulated by a simple steady-state model of bacterial utilization of autochthonous and allochthonous dissolved organic C. A higher preference and greater growth efficiency of bacteria on autochthonous C may explain why BP is coupled to autochthonous production also in net heterotrophic ecosystems where the use of allochthonous C by bacteria is high. These results suggest that little of the allochthonous C assimilated by bacteria is likely to reach higher consumers.
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| 4. |
- Bade, Darren L., et al.
(författare)
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Sources and fates of dissolved organic carbon in lakes as determined by whole-lake carbon isotope additions
- 2007
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 1573-515X .- 0168-2563. ; 84:2, s. 115-129
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Tidskriftsartikel (refereegranskat)abstract
- Four whole- lake inorganic C-13 addition experiments were conducted in lakes of differing trophic status. Inorganic C-13 addition enriched algal carbon in C-13 and changed the delta C-13- DOC by + 1.5 parts per thousand to + 9.5 parts per thousand, depending on the specific lake. This change in delta C-13- DOC represented a significant input of algal DOC that was not completely consumed by bacteria. We modeled the dynamics in delta C-13- DOC to estimate the fluxes of algal and terrestrial carbon to and from the DOC pool, and determine the composition of the standing stock. Two experiments in lightly stained, oligotrophic lakes indicated that algal production was the source of about 20% of the DOC pool. In the following year, the experiment was repeated in one of these lakes under conditions of nutrient enrichment, and in a third, more humic lake. Algal contributions to the DOC pool were 40% in the nutrient enriched lake and 5% in the more humic lake. Spectroscopic and elemental analyses corroborated the presence of increased algal DOC in the nutrient enriched lake. Natural abundance measurements of the delta C-13 of DOC in 32 lakes also revealed the dual contributions of both terrestrial and algal carbon to DOC. From these results, we suggest an approach for inferring the contribution of algal and terrestrial DOC using easily measurable parameters.
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| 5. |
- Carpenter, Stephen R., et al.
(författare)
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Ecosystem subsidies : Terrestrial support of aquatic food webs from C-13 addition to contrasting lakes
- 2005
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Ingår i: Ecology. - : John Wiley & Sons. - 0012-9658 .- 1939-9170. ; 86:10, s. 2737-2750
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Tidskriftsartikel (refereegranskat)abstract
- Whole-lake additions of dissolved inorganic C-13 were used to measure allochthony (the terrestrial contribution of organic carbon to aquatic consumers) in two unproductive lakes (Paul and Peter Lakes in 2001), a nutrient-enriched lake (Peter Lake in 2002), and a dystrophic lake (Tuesday Lake in 2002). Three kinds of dynamic models were used to estimate allochthony: a process-rich, dual-isotope flow model based on mass balances of two carbon isotopes in 12 carbon pools; simple univariate time-series models driven by observed time courses of delta(13)CO(2); and multivariate autoregression models that combined information from time series of delta(13)C in several interacting carbon pools. All three models gave similar estimates of allochthony. In the three experiments without nutrient enrichment, flows of terrestrial carbon to dissolved and particulate organic carbon, zooplankton, Chaoborus, and fishes were substantial. For example, terrestrial sources accounted for more than half the carbon flow to juvenile and adult largemouth bass, pumpkinseed sunfish, golden shiners, brook sticklebacks, and fathead minnows in the unenriched experiments. Allochthony was highest in the dystrophic lake and lowest in the nutrient-enriched lake. Nutrient enrichment of Peter Lake decreased allochthony of zooplankton from 0.34-0.48 to 0-0.12, and of fishes from 0.51-0.80 to 0.25-0.55. These experiments show that lake ecosystem carbon cycles, including carbon flows to consumers, are heavily subsidized by organic carbon from the surrounding landscape.
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| 6. |
- Pace, Michael L., et al.
(författare)
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Whole-lake carbon-13 additions reveal terrestrial support of aquatic food webs
- 2004
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Ingår i: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 427:6971, s. 240-243
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Tidskriftsartikel (refereegranskat)abstract
- Ecosystems are supported by organic carbon from two distinct sources. Endogenous carbon is produced by photosynthesis within an ecosystem by autotrophic organisms. Exogenous carbon is produced elsewhere and transported into ecosystems. Consumers may use exogenous carbon with consequent influences on population dynamics, predator-prey relationships and ecosystem processes(1). For example, exogenous inputs provide resources that may enhance consumer abundance beyond levels supported by within-system primary production(2). Exogenous fluxes of organic carbon to ecosystems are often large, but this material is recalcitrant and difficult to assimilate, in contrast to endogenously produced organic matter, which is used more easily(3,4). Here we show, by the experimental manipulation of dissolved inorganic C-13 in two lakes, that internal primary production is insufficient to support the food webs of these ecosystems. Additions of NaH (CO3)-C-13 enriched the C-13 content of dissolved inorganic carbon, particulate organic carbon, zooplankton and fish. Dynamics of C-13 indicate that 40-55% of particulate organic carbon and 22-50% of zooplankton carbon are derived from terrestrial sources, showing that there is significant subsidy of these ecosystems by organic carbon produced outside their boundaries.
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