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- Daniel, Cesar Bolivar
(författare)
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The importance of terrestrial carbon in plankton food webs
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Allochthonous substances, i.e. produced in terrestrial ecosystems, are known to fuel bacterial production in humic lakes. I observed that allochthonous carbon subsidizes bacteria even at high levels of phytoplankton biomass. In line with that, my results also show that dissolved organic carbon is largely constituted of terrestrial substances irrespective of lake characteristics. Since bacteria constitute a quantitatively important food source for lake zooplankton, zooplankton growth can be subsidized by allochthonous carbon. Moreover, in the absence of phytoplankton derived substances I observed bacteria to grow and sustain the microbial food web. This was demonstrated by increasing populations of copepods in the absence of any input of newly produced algal carbon after a period of 1.5 years. Photochemical breakdown of organic substances, affects utilization of detrital carbon by bacteria and consequently the contribution of terrestrial carbon to food webs in humic lakes. Increase of bacterial production following abiotic cleavage of dissolved organic matter stimulated biomass production of lake zooplankton. Stimulation of zooplankton may depend on a direct trophic coupling to bacteria and flagellates, which is probably stronger in rotifers and cladocerans than in copepods. Mixotrophic flagellates can feed large zooplankton as much as heterotrophic flagellates. The flux of allochthonous substances and photosynthetic production to zooplankton is strongly coupled when bacterivorous algae dominates the flagellated community. I observed that ingestion rates of bacteria by the mixotrophic chrysophyte Poterioochromonas malhamensis is as high as for the heterotrophic Spumella elongata, whereas photosynthesis plays an important role on P. malhamensis nutrition. I conclude that allochthonous energy sources have great ecological relevance in terms of zooplankton nutrition, not only in special circumstances found in humic lakes.
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| 2. |
- Anesio, Alexandre Magno
(författare)
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Effects of solar radiation on the abiotic and bacterially mediated carbon flux in aquatic ecosystems
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this Thesis, I studied some of the current aspects of organic matter photochemistry. I analyzed abiotic phototransformations of several types of dissolved (DOM) and particulate organic matter (POM). I also evaluated the effects of phototransformation of several types of DOM on bacteria. Finally, in a field experiment, I analyzed net effects of solar radiation on organic matter decomposition. DOM undergoes several transformations due to solar irradiation. One such transformation is photooxidation of organic matter into inorganic carbon. Results of this Thesis show that photooxidation is ubiquitous to all kinds of organic matter in both dissolved and particulate forms. The intensity of this process depends on several factors, including DOM composition, radiation type and time of exposure. Besides mineralization to inorganic carbon, DOM undergoes other chemical transformations due to UV radiation, with profound consequences to DOM availability for bacteria. Bioavailability was tested by measuring bacterial growth and respiration on irradiated and non-irradiated DOM from several types of humic matter and plant leachates. Irradiation of freshly-leached DOM often produced negative effects on bacteria, whereas irradiation of humic material was followed by stimulation of bacterial growth. The degree of stimulation seems to be related to the initial bioavailability of the DOM and to the capability of the DOM to produce hydrogen peroxide upon irradiation. Other factors also accounted for differences in bacterial response to photochemical modification of DOM, including length and type of irradiation exposure. The effects of solar radiation on litter decomposition were also evaluated using experiments that more closely mimic natural conditions. I could not observe differences between dry weight loss of leaves and culms exposed to solar radiation or kept in darkness, which may be explained by the fact that abiotic decomposition under solar radiation is counterbalanced by negative effects of solar radiation on decomposers.
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