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Berlin Brandenburg


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  • JSTOR Current Journals  (3)
Type of Medium
  • 1
    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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  • 2
    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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  • 3
    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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