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  • Phytoplankton
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  • 1
    In: Limnology and Oceanography, May 2000, Vol.45(3), pp.741-743
    Description: In experiments with axenic cultures of , we tested whether this cyanobacterium incorporates leucine, a compound that is often used for the measurement of heterotrophic bacterioplankton production. showed significant leucine incorporation, and the uptake of exponentially growing cells was higher than the uptake of cells in stationary growth phase. Therefore, the leucine method may not be suitable for measuring bacterial production in highly eutrophic waters with a dominance of cyanobacteria.
    Keywords: Oceanography;
    ISSN: 0024-3590
    E-ISSN: 1939-5590
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  • 2
    Language: English
    In: Hydrobiologia, 2001, Vol.442(1), pp.165-176
    Description: The filtration rate of Daphnia galeata was determined in in situ experiments in Bautzen Reservoir and in laboratory experiments, where daphnids were exposed to filtrates that previously contained either natural phytoplankton or cultured eukaryotic algae ( Scenedesmus obliquus or Asterionella formosa ), respectively. Individual filtration rate (FR) was measured using fluorescent beads, taking into account ingested beads in the gut only. Compared to heated control treatments (100 °C), dissolved compounds released by the nutritious cultured algae during the preconditioning phase or by the natural phytoplankton assemblages from Bautzen Reservoir strongly reduced the filtration rate of D. galeata (down to 60%). Heating deactivated these dissolved compounds. A significant correlation was found between primary production measured in situ and the reduction of FR in the filtrate of reservoir water, indicating that extra-cellular products released during photosynthesis triggered the reduction of the filtration rate. The ratio of ingested to collected beads was used to quantify the proportion of food, which was not only collected but passed the mouth of D. galeata . The ratio of ingestion to collection was compared between filtered and unfiltered reservoir water both media identical with respect to the concentration of dissolved compounds, whereas other factors (e.g. food concentration, temperature, filtration rate) were different. The changes in this ratio between filtered and unfiltered reservoir water suggest that D. galeata is capable of a chemosensory control of the ingestion behaviour by detecting external metabolites.
    Keywords: grazing experiments ; Daphnia ; filtration rate ; phytoplankton ; primary production
    ISSN: 0018-8158
    E-ISSN: 1573-5117
    Source: Springer Science & Business Media B.V.
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  • 3
    In: Journal of Plankton Research, 2012, Vol. 34(2), pp.102-112
    Description: Aquatic bacteria are considered to exhibit a paradoxical behaviour. They luxuriously consume phosphorus, the element often restricting the abundance of algae, which provide the organic substrates maintaining bacterial growth. Here, we test the hypothesis that bacteria can limit their uptake of phosphorus and increase the availability of phosphorus to algae. The physiological costs for bacteria must be compensated for by a surplus of photosynthetic exudates facilitating higher biomass production. To test the potential of such an economic behaviour, we used a new differential equation model that was parameterized by independent experiments. Model results indicate that this potential does exist. As a consequence, we conducted continuous growth chemostat experiments. Bacteria did not leave more phosphorus to, “high exudation” algae compared with algae with low release. Therefore, the hypothesis was not supported by the experiments. However, bacteria significantly increased production 1.4–1.8-fold in cultures with “high exudation” algae. This was explained by an increase in conversion of organic carbon from growth medium into bacteria biomass. Algal exudates were quantitatively negligible but could act as growth factors. The results show that biomass of algae and bacteria cannot be predicted solely by mineral nutrients and carbon as assumed by the classical theory.
    Keywords: Bacteria ; Phytoplankton ; Exudation ; Phosphorus ; Differential Equation Model
    ISSN: 0142-7873
    E-ISSN: 1464-3774
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  • 4
    In: Freshwater Biology, August 2004, Vol.49(8), pp.1062-1071
    Description: 1. Lakes formed in mining pits often contain high concentrations of dissolved ferric iron and sulphate (e.g. 2 and 16 mmol L, respectively) and the pH is buffered between 2.5 and 3.5. Efforts to neutralise their water are based on the stimulation of lake internal, bacterial iron‐ and sulphate reduction. Electron donors may be supplied by organic carbon compounds or indirectly by enhancement of primary production. Here, we investigated the function of mixotrophic algae, which can potentially supplement or deplete the organic carbon pool, in the carbon metabolism and alkalinity budget of an acidic mining lake. 2. Two weeks after organic substrates had been added in a large mesocosm of 30 m diameter, a bloom of occurred, reaching a biovolume of 80 mm L. Growth experiments using filtered lake water showed that the alga reduced the overall dissolved organic carbon (DOC) concentration despite significant photosynthetic activity. However, when were grown together with natural bacterioplankton, net DOC consumption did not increase. 3. Uptake experiments using [C]‐glucose indicated that bacteria dominated glucose uptake and remineralisation. Therefore, the DOC leached in the water column was processed mainly by planktonic bacteria. Leached DOC must be regarded as loss, not transferred by larger organisms to the sediment, where reduction processes take place. 4. From phytoplankton biomass and production 2 years after fertilisation we estimated that pelagic photosynthesis does not supply an electron donor capacity capable of reducing more than 2% of actual stock of acidity per year. We estimated that only the benthic primary production was in a range to compensate for ongoing inputs of iron and sulphate.
    Keywords: Acidic ; Chlamydomonas ; Mining Lakes ; Mixotrophic ; Organic Carbon
    ISSN: 0046-5070
    E-ISSN: 1365-2427
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  • 5
    Language: English
    In: Microbial Ecology, 2017, Vol.74(3), pp.534-549
    Description: Microbial decomposition of terrestrial carbon may be enhanced by the addition of easily decomposable compounds, a phenomenon referred to as priming effect. We investigated the microbial decomposition of terrestrial dissolved organic carbon (DOC) in one-stage and two-stage flow-through cultures (chemostats) in the absence and presence of growing phytoplankton as phytoplankton-derived organic matter might facilitate the mineralization of more refractory terrestrial compounds. Peat water and soil leachate were used as terrestrial substrates, and only slight DOC decomposition was observed in the absence of phytoplankton for both substrates. A priming effect was revealed via 14 C data. Priming was more pronounced for the peat water substrate than for the soil leachate. The total DOC concentrations increased for both substrates in the presence of phytoplankton due to exudation and cell lysis. Samples from the soil leachate experiments were analyzed using ultra-high-resolution mass spectrometry (FT-ICR MS). Predominantly, the same saturated, aliphatic molecules with H/C ratios 〉1.5 were completely decomposed in the absence and in the presence of phytoplankton. The decomposition of more stable molecules differed in their intensity. Oxidized and unsaturated molecules with H/C ratios 〈1.0 and O/C ratios 〉0.4 were more strongly decomposed in phytoplankton presence (i.e., under priming). We conclude that an aquatic priming effect is not easily detectable via net concentration changes alone, and that qualitative investigations of the DOC processed by bacterial decomposition are necessary to detect aquatic priming.
    Keywords: Radiocarbon ; C ; Ultra-high-resolution mass spectrometry ; FT-ICR MS ; DOM quality
    ISSN: 0095-3628
    E-ISSN: 1432-184X
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  • 6
    Language: English
    In: Limnologica, 2008, Vol.38(3), pp.360-366
    Description: Since amino acids represent an important component of dissolved organic carbon in lakes, we investigated the uptake and consumption of leucine by several phytoplankton species. Firstly, we measured the leucine uptake of 28 phytoplankton species (several cyanobacteria and chlorophytes, one diatom, and one euglenophyte) and the uptake kinetics by a chlorophyte ( ) compared to that of heterotrophic bacteria. Furthermore, we tested whether the algae can decrease the concentration of leucine in the light to lower levels than in darkness (hypothesis 1), and whether algae with high minimum substrate requirements exhibit higher consumption rates at plentiful concentrations compared to algae with high substrate reduction capability but low maximum consumption rate (hypothesis 2). Thirteen species of cyanobacteria and chlorophytes showed leucine uptake. Specific uptake rates by were lower in the light than in the dark and much lower than that of heterotrophic bacteria. In the consumption experiments, several algae consumed leucine with higher rates and to lower residual concentrations in the dark than in the light, but with lower rates and not to lower concentrations than heterotrophic bacteria. Residual concentrations and consumption rates were not related to algal cell volume and chlorophyll content. Consumption rates were negatively related to residual concentrations, i.e. algae with higher consumption rates also depleted leucine to lower concentrations. Although the hypotheses were not supported, several algae were capable of removing leucine to equally low concentrations as bacteria so that algal uptake of amino acids is potentially important in natural waters.
    Keywords: Algae ; Amino Acids ; Bacteria ; Competition ; Cyanobacteria ; Doc ; Leucine ; Mixotrophy ; Oceanography ; Ecology
    ISSN: 0075-9511
    E-ISSN: 1873-5851
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  • 7
    In: Limnology and Oceanography, November 2003, Vol.48(6), pp.2392-2396
    Description: Herbivorous fish feed on cyanobacteria. Digestability differs, however, between cyanobacteria species without mucous cover and mucilaginous genera such as . The latter can pass fish guts almost undamaged, and it has been hypothesized that they can take up nutrients during gut passage. Here we tested whether live , as food for juvenile roach labeled with P, indeed showed higher radioactivity after gut passage as compared to gut contents in control experiments with fish fed heated . showed high viability after passage through roach guts, and live colonies had a significantly higher radioactivity than dead ones. We conclude that is protected against digestion in roach guts and can directly use the phosphorus supplied in the fish guts during passage.
    Keywords: Oceanography;
    ISSN: 0024-3590
    E-ISSN: 1939-5590
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  • 8
    Language: English
    In: Microbial Ecology, 2015, Vol.69(2), pp.361-371
    Description: The fate of allochthonous dissolved organic carbon (DOC) in aquatic systems is primarily controlled by the turnover of heterotrophic bacteria. However, the roles that abiotic and biotic factors such as light and DOC release by aquatic primary producers play in the microbial decomposition of allochthonous DOC is not well understood. We therefore tested if light and autochthonous DOC additions would increase allochthonous DOC decomposition rates and change bacterial growth efficiencies and community composition (BCC). We established continuous growth cultures with different inocula of natural bacterial communities and alder leaf leachates (DOC leaf ) with and without light exposure before amendment. Furthermore, we incubated DOC leaf together with autochthonous DOC from lysed phytoplankton cultures (DOC phyto ). Our results revealed that pretreatments of DOC leaf with light resulted in a doubling of bacterial growth efficiency (BGE), whereas additions of DOC phyto or combined additions of DOC phyto and light had no effect on BGE. The change in BGE was not accompanied by shifts in the phylogenetic structure of the BCC, but BCC was influenced by the DOC source. Our results highlight that a doubling of BGE is not necessarily accompanied by a shift in BCC and that BCC is more strongly affected by resource properties.
    Keywords: Bacterial growth efficiency ; Continuous cultures ; Carbon decomposition ; Leaf litter ; Photolysis
    ISSN: 0095-3628
    E-ISSN: 1432-184X
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  • 9
    Language: English
    In: Protist, 2005, Vol.156(1), pp.63-75
    Description: Plankton communities in acidic mining lakes (pH 2.5–3.3) are species-poor because they face extreme environmental conditions, e.g. 150 mg l Fe +Fe . We investigated the growth characteristics of the dominant pigmented species, the flagellate , in semi-continuous culture experiments under in situ conditions. The following hypotheses were tested: (1) Low inorganic carbon (IC) concentrations in the epilimnion (e.g. 0.3 mg l ) arising from the low pH limit phototrophic growth (H-1); (2) the additional use of dissolved organic carbon (mixotrophy) leads to higher growth rates under IC-limitation (H-2), and (3) phagotrophy is not relevant (H-3). H-1 was supported as the culture experiments, in situ PAR and IC concentrations indicated that IC potentially limited phototrophic growth in the mixed surface layers. H-2 was also supported: mixotrophic growth always exceeded pure phototrophic growth even when photosynthesis was saturated. Dark growth in filtered lake water illuminated prior to inoculation provided evidence that was able to use the natural DOC. The alga did not grow on bacteria, thus confirming H-3. exhibited a remarkable resistance to starvation in the dark. The compensation light intensity (ca. 20 μmol photons m s ) and the maximum phototrophic growth (1.50 d ) fell within the range of algae from non-acidic waters. Overall, , a typical -strategist in circum-neutral systems, showed characteristics of a -strategist in the stable, acidic lake environment in achieving moderate growth rates and minimizing metabolic losses.
    Keywords: Mixotroph ; Osmotroph ; Chlamydomonas ; CO 2 Limitation ; Acidic Mining Lake ; Doc ; Biology ; Zoology
    ISSN: 1434-4610
    E-ISSN: 1618-0941
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  • 10
    Language: English
    In: Hydrobiologia, 1999, Vol.403, pp.109-121
    Description: We determined clearance rates and ingestion rates of Daphnia galeata on bacteria and phytoplankton in order to test if bacteria are an important alternative food resource for daphnids during periods of low phytoplankton biomass in the biomanipulated Bautzen reservoir (Germany). D. galeata was able to feed on bacteria with the same efficiency as on algae during most of the time. In spite of similar clearance rates, bacteria ingestion was usually lower than phytoplankton ingestion due to lower bacterial biomass. Only at low biomass of algae in late fall and during the clear water phase, bacteria contributed up to 87% and 42%, respectively, to total carbon ingestion of D. galeata. However, even a short period of relatively high bacteria grazing by daphnids may be important for biomanipulation. Bacteria might bridge over periods of food limitation of daphnids thus promoting the maintenance of high Daphnia biomass. Therefore, ingestion of bacteria by daphnids is thought to stabilize biomanipulation and may hold a key position in the food web of biomanipulated lakes.
    Keywords: bacteria ; phytoplankton ; daphnids ; clearance rate ; ingestion ; biomanipulation
    ISSN: 0018-8158
    E-ISSN: 1573-5117
    Source: Springer Science & Business Media B.V.
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