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  • 1
    In: Journal of Phycology, August 2009, Vol.45(4), pp.807-811
    Description: Algae of various taxonomic groups are capable of assimilating dissolved organic carbon (DOC) from their environments (mixotrophy). Recently, we reported that, with increasing biomass of mixotrophs, heterotrophic bacteria did not increase. We hypothesized that algal uptake of external DOC may outweigh their release of DOC by exudation (H1). Here, we addressed an alternative hypothesis that algae did not assimilate external DOC but constrained the release of DOC (H2). In chemostat experiments, we cultured the mixotrophic Negoro together with heterotrophic bacteria. As external substrates, we used glucose, which was potentially available for both bacteria and algae, or fructose, which was available only for bacteria. We increased the biomass of algae by the stepwise addition of phosphorus. Bacterial biomass did not increase in experiments using glucose or when fructose was offered, suggesting that mechanisms other than algal mixotrophy (H1) kept concentrations of bacteria low. Measured exudation rates (percent extracellular release, PER) of mixotrophic algae ( W. Krüger) were very low and ranged between 1.0% and 3.5% at low and moderately high phosphorus concentrations. In contrast, an obligately phototrophic alga ( H. Ettl) showed higher exudation rates, particularly under phosphorus limitation (70%). The results support H2. If mixotrophy is considered as a mechanism to recycle organic exudates from near the cell surface, this would explain why algae retained mixotrophic capabilities although they cannot compete with bacteria for external organic carbon.
    Keywords: Algae ; Bacteria ; Chemostat ; Competition ; Doc ; Exudation ; Mixotroph
    ISSN: 0022-3646
    E-ISSN: 1529-8817
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  • 2
    Language: English
    In: Science of the Total Environment, 01 April 2016, Vol.548-549, pp.51-59
    Description: Enhanced concentrations of dissolved organic matter (DOM) in freshwaters are an increasing problem in drinking water reservoirs. In this study we investigated bacterial DOM degradation rates in the tributaries of the reservoirs and tested the hypotheses that (1) DOM degradation is high enough to decrease DOM loads to reservoirs considerably, (2) DOM degradation is affected by stream hydrology, and (3) phosphorus addition may stimulate bacterial DOM degradation. Bacterial biomass production, which was used as a measure of DOM degradation, was highest in summer, and was usually lower at upstream than at downstream sites. An important proportion of bacterial production was realized in epilithic biofilms. Production of planktonic and biofilm bacteria was related to water temperature. Planktonic production weakly correlated to DOM quality and to total phosphorus concentration. Addition of soluble reactive phosphorus did not stimulate bacterial DOM degradation. Overall, DOM was considerably degraded in summer at low discharge levels, whereas degradation was negligible during flood events (when DOM load in reservoirs was high). The ratio of DOM degradation to total DOM release was negatively related to discharge. On annual average, only 0.6–12% of total DOM released by the catchments was degraded within the tributaries.
    Keywords: Bacterial Production ; Doc ; Freshness Index ; Humification Index ; Phosphorus ; Environmental Sciences ; Biology ; Public Health
    ISSN: 0048-9697
    E-ISSN: 1879-1026
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  • 3
    Language: English
    In: Science of the Total Environment, 15 February 2015, Vol.506-507, pp.353-360
    Description: Streams and rivers are important sites of organic carbon mineralization which is dependent on the land use within river catchments. Here we tested whether planktonic and epilithic biofilm bacteria differ in their response to the quality of dissolved organic carbon (DOC). Thus, planktonic and biofilm bacterial production was compared with patterns of DOC along a land-use gradient in the Bode catchment area (Germany). The freshness index of DOC was positively related to the proportion of agricultural area in the catchment. The humification index correlated with the proportion of forest area. Abundance and production of planktonic bacteria were lower in headwaters than at downstream sites. Planktonic production was weakly correlated to the total concentration of DOC but more strongly to quality-measures as revealed by spectra indexes, i.e. positively to the freshness index and negatively to the humification index. In contrast to planktonic bacteria, abundance and production of biofilm bacteria were independent of DOC quality. This finding may be explained by the association of biofilm bacteria with benthic algae and an extracellular matrix which represent additional substrate sources. The data show that planktonic bacteria seem to be regulated at a landscape scale controlled by land use, whereas biofilm bacteria are regulated at a biofilm matrix scale controlled by autochthonous production. Thus, the effects of catchment-scale land use changes on ecosystem processes are likely lower in small streams dominated by biofilm bacteria than in larger streams dominated by planktonic bacteria.
    Keywords: Bacterial Production ; Doc ; Freshness Index ; Humification Index ; Biofilm ; Confocal Laser Scanning Microscopy (Clsm) ; Environmental Sciences ; Biology ; Public Health
    ISSN: 0048-9697
    E-ISSN: 1879-1026
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  • 4
    Language: English
    In: Environmental Monitoring and Assessment, 2013, Vol.185(11), pp.9221-9236
    Description: The Bode catchment (Germany) shows strong land use gradients from forested parts of the National Park (23 % of total land cover) to agricultural (70 %) and urbanised areas (7 %). It is part of the Terrestrial Environmental Observatories of the German Helmholtz association. We performed a biogeochemical analysis of the entire river network. Surface water was sampled at 21 headwaters and at ten downstream sites, before (in early spring) and during the growing season (in late summer). Many parameters showed lower concentrations in headwaters than in downstream reaches, among them nutrients (ammonium, nitrate and phosphorus), dissolved copper and seston dry mass. Nitrate and phosphorus concentrations were positively related to the proportion of agricultural area within the catchment. Punctual anthropogenic loads affected some parameters such as chloride and arsenic. Chlorophyll a concentration and total phosphorus in surface waters were positively related. The concentration of dissolved organic carbon (DOC) was higher in summer than in spring, whereas the molecular size of DOC was lower in summer. The specific UV absorption at 254 nm, indicating the content of humic substances, was higher in headwaters than in downstream reaches and was positively related to the proportion of forest within the catchment. CO 2 oversaturation of the water was higher downstream compared with headwaters and was higher in summer than in spring. It was correlated negatively with oxygen saturation and positively with DOC concentration but negatively with DOC quality (molecular size and humic content). A principle component analysis clearly separated the effects of site (44 %) and season (15 %), demonstrating the strong effect of land use on biogeochemical parameters.
    Keywords: TERENO ; Land use ; Nutrients ; Heavy metals ; DOC ; Bode
    ISSN: 0167-6369
    E-ISSN: 1573-2959
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  • 5
    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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  • 6
    Language: English
    In: Journal of phycology, 2008, Vol.44(3), pp.616-623
    Description: Dissolved organic carbon (DOC) constitutes the bulk of organic carbon in aquatic environments. The importance of DOC utilization by mixotrophic algae is unclear since heterotrophic bacteria are regarded as more efficient users. We tested the hypothesis that algae decrease the DOC concentration in the light to lower levels than in darkness resulting in competitive exclusion of heterotrophic bacteria according to the mechanistic competition theory. We investigated (a) the uptake kinetics of glucose as a model substrate by two cultured algae and mixed bacteria populations, (b) the competition for glucose between algae and bacteria in chemostats, (c) the effect of discontinuous glucose supply in chemostats, and (d) the minimum glucose concentrations achieved in cultures of algae and bacteria. Bacteria showed higher specific-glucose-uptake rates than algae. In chemostats, algae became extinct in the dark and coexisted in the light where they decreased bacteria to lower densities. Discontinuous glucose supply promoted the algae compared to continuous substrate addition. Several algae consumed glucose to lower concentrations in the dark than in the light and showed lower or equal residual glucose concentrations than bacteria. Residual concentrations were not related to allometric traits (cell volume) and photosynthetic potential (chl content). Overall, the hypothesis was not supported, and mechanisms of competition for DOC obviously differed from those for particulate prey. However, since some algae showed lower or equal residual glucose concentrations than bacteria, algal dark uptake of DOC may be important in deep layers of many waters. ; Includes references ; p. 616-623.
    Keywords: Bacteria ; Algae ; Mixotrophy ; Doc ; Competition
    ISSN: 0022-3646
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  • 7
    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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  • 8
    Language: English
    Keywords: Ddc:550 ; 550 Earth Sciences ; 550 Geowissenschaften ; 570 Life Sciences ; Ddc:570 ; 570 Biowissenschaften; Biologie ; Dissolved Organic Material ; Agricultural Land Use ; Parafac ; Doc ; Don
    Source: Freie Universitat Berlin
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  • 9
    Language: English
    In: 2015
    Keywords: Confocal Laser Scanning Microscopy (Clsm) ; Forests ; Land Use Change ; Dissolved Organic Carbon ; Watersheds ; Doc ; Ecosystems ; Rivers ; Plankton ; Algae ; Humification ; Bacterial Production ; Extracellular Matrix ; Freshness Index ; Benthic Organisms ; Biofilm ; Biofilm ; Carbon ; Bacteria ; Mineralization ; Streams ; Freshness ; Humification Index ; Landscapes
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 10
    Language: English
    In: Archiv für Hydrobiologie, 03/01/2006, Vol.165(3), pp.355-364
    Description: We compared growth rates and efficiencies of pelagic bacteria from an extremely acidic mining lake (pH 2.6, mean depth 4.6 m) supplied with different sources of carbon: (1) excreted by phytoplankton, (2) derived from benthic algae, (3) entering the lake via ground water, and (4) leached from leaf litter. Bacteria exhibited high growth rate and efficiency on exudates of pelagic and benthic algae. In contrast, they showed a lower growth rate and efficiency with organic carbon from ground water, and grew at a very high rate but a very low efficiency on leaf leachate. Results from stable isotope analyses indicate a greater importance of benthic exudates and leaf leachate for bacteria in the epilimnion, and a higher impact of ground water sources in the hypolimnion. Given the magnitude of differential source inputs into the lake, we suggest that benthic primary production was the most important carbon source for pelagic bacteria. The benthic-pelagic coupling seems to be more relevant in this shallow acidic lake with low pelagic carbon dioxide concentrations than in neutral lakes.
    Keywords: Scientific Research ; Growth Rate ; Isotopes ; Leaves ; Phytoplankton ; Carbon Sources ; Primary Production ; Leaf Litter ; Lakes ; Exudates ; Carbon ; Ground Water ; Mining ; Dissolved Organic Carbon ; Carbon Dioxide ; Ph Effects ; Leachates ; Algae ; Isotopes ; Acidic Wastes ; Leaching ; Epilimnion ; Organic Carbon ; Water Quality ; Primary Production ; Lakes ; Mining ; Leaf Litter ; Dissolved Organic Carbon ; Groundwater ; Carbon Dioxide ; Leachates ; Ph ; Bacteria ; Litter ; Lakes ; Carbon ; Organic Carbon ; Growth Rates ; Groundwater ; Leachates ; Algae ; Bacteria ; Litter ; Lakes ; Carbon ; Organic Carbon ; Growth Rates ; Groundwater ; Leachates ; Algae ; Ecosystem and Ecology Studies ; Water Resources and Supplies ; Lakes ; Freshwater Pollution ; Ecology ; Cell Biology ; Plant Diseases ; General;
    ISSN: 00039136
    E-ISSN: 00000000
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