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  • Ecology
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  • 1
    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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  • 2
    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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  • 3
    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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  • 4
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 28 October 2003, Vol.100(22), pp.12776-81
    Description: The majority of organisms can be grouped into those relying solely on photosynthesis (phototrophy) or those relying solely on the assimilation of organic substances (heterotrophy) to meet their requirements for energy and carbon. However, a special life history trait exists in which organisms combine both phototrophy and heterotrophy. Such "mixotrophy" is a widespread phenomenon in aquatic habitats and is observed in many protozoan and metazoan organisms. The strategy requires investment in both photosynthetic and heterotrophic cellular apparatus, and the benefits must outweigh these costs. In accordance with mechanistic resource competition theory, laboratory experiments revealed that pigmented mixotrophs combined light, mineral nutrients, and prey as substitutable resources. Thereby, they reduced prey abundance below the critical food concentration of competing specialist grazers [Rothhaupt, K. O. (1996) Ecology 77, 716-724]. Here, we demonstrate the important consequences of this strategy for an aquatic community. In the illuminated surface strata of a lake, mixotrophs reduced prey abundance steeply. The data suggest that, as a consequence, grazers from higher trophic levels, consuming both the mixotrophs and their prey, could not persist. Thus, the mixotrophs escaped from competition with and losses to higher grazers. Furthermore, the mixotrophs structured prey abundance along the vertical light gradient, creating low densities near the surface and a pronounced maximum of their algal prey at depth. Such deep algal accumulations are typical features of nutrient-poor aquatic habitats, previously explained by resource availability. We hypothesize instead that the mixotrophic grazing strategy is responsible for deep algal accumulations in many aquatic environments.
    Keywords: Food Chain ; Chlamydomonas -- Physiology
    ISSN: 0027-8424
    E-ISSN: 10916490
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  • 5
    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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  • 6
    In: Journal of Plankton Research, 2012, Vol. 34(10), pp.922-927
    Description: Ingestion of the large pelagic ciliates Stentor araucanus and S. amethystinus by the cyclopoid copepod Mesocyclops araucanus was independent of light conditions and copepod sex, but rates were twice as high on S. araucanus as on S. amethystinus . Copepods consumed 44–183% of their biomass daily. Absorption efficiency was 5–40%, while 20–30% of the ingested food was found in the faeces. In field samples, 32–93% of Mesocyclops had ingested Stentor, indicating the importance of this food source.
    Keywords: Predation ; Cyclopoid Copepods ; Mixotrophic Ciliates ; 〈Kwd〉〈Italic〉Stentor〈/Italic〉〈/Kwd〉 ; North Patagonian Lakes
    ISSN: 0142-7873
    E-ISSN: 1464-3774
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  • 7
    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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  • 8
    Language: English
    In: Microbial Ecology, 2010, Vol.60(3), pp.618-627
    Description: As extreme environmental conditions strongly affect bacterial community composition (BCC), we examined whether differences in pH—even at low pH—and in iron and sulfate concentrations lead to changes in BCC of acidic mining lakes. Thereby, we tested the following hypotheses: (1) diversity of the bacterial community in acidic lakes decreases with reducing pH, (2) BCC differs between epilimnion and hypolimnion, and (3) BCC in extremely acidic environments does not vary much over time. Therefore, we investigated the BCC of three acidic lakes with different pH values (2.3, 2.7, and 3.2) by denaturing gradient gel electrophoresis (DGGE) and subsequent sequencing of DGGE bands as well as catalyzed reporter deposition-FISH (CARD-FISH). BCC did not significantly vary among the studied lakes nor differ much between water layers. In contrast, BCC significantly changed over time, which is contradictory to our hypotheses. Bacterial communities were dominated by Alpha-, Beta-, and Gammaproteobacteria, whereas Actino- and Acidobacteria rarely occurred. Cell numbers of both free and attached bacteria were positively related to DOC concentration. Overall, low pH and extreme chemical conditions of the studied lakes led to similar assemblages of bacteria with pronounced temporal differences. This notion indicates that temporal changes in environmental conditions including food web structure also affect unique communities of bacteria thriving at low pH.
    Keywords: Limnology ; Aquatic Ecological Zones ; Ph ; Mining Industry ; Universities And Colleges ; Sulfates;
    ISSN: 0095-3628
    E-ISSN: 1432-184X
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  • 9
    Language: English
    In: Environmental Monitoring and Assessment, 2015, Vol.187(7), pp.1-13
    Description: As benthic biofilms mediate essential functions in stream ecosystems (e.g., carbon flux, storage of nutrients and other substances), the element-specific regulation of the biofilm composition is of great interest. We tested whether (1) the elemental composition of biofilms is related to that of the water column and (2) there are different accumulation patterns from the dissolved phase (adsorption) and the particulate phase (incorporation of suspended matter). We analysed biomass parameters, nutrients and metals in biofilms and surface waters at 28 sites within a stream network (Bode catchment, Germany). Algal biomass in biofilms was dominated by diatoms. The P/C ratio in biofilms was positively related to total phosphorus of surface water (and to the proportion of agricultural area in the catchment) indicating phosphorus limitation of biofilms, whereas the N/C ratio was not related to nitrate levels of surface water, and neither the P/C nor the N/C ratio to the concentration of dissolved organic carbon (DOC) of surface water. Biofilms were enriched in metals compared to their concentrations in water. The metals in biofilms were positively related to the concentration of dissolved metals in surface water for iron and strontium (but not for manganese, copper, zinc, arsenic or lead) and to the concentrations of particle-associated metals of surface waters for strontium and lead. Manganese and arsenic were the metals with a negative effect on the biomasses of biofilm diatoms and cyanobacteria. Overall, we observed element-specific accumulation patterns in biofilms with selected elements being related to the water column while others were probably subject to biofilm-internal processes.
    Keywords: Nutrients ; Stoichiometry ; Heavy metals ; Total reflection X-ray fluorescence spectrometry (TXRF) ; Stream biofilms ; River Bode
    ISSN: 0167-6369
    E-ISSN: 1573-2959
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  • 10
    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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