Wohlers, Julia (2005) Effect of temperature on the production and fate of dissolved organic matter in a microalgal culture. (Diploma thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 55 pp.

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Abstract

The goal of the here presented study was to elucidate the effect of temperature on the production and lass mechanisms of dissolved organic matter in a microalgal culture. For this purpose, an axenic diatom culture was grown in North Sea water containing a natural bacterial community and exposed to three different temperatures (17°C, 21°C and 26°C). During the following 25 days the development of algal growth and bacterial activities as weil as changes in the concentration of DOC, carbohydrates and TEP were closely followed. The here obtained results show a clear dependence of the autotrophic and heterotrophic processes on temperature. At the highest temperature, algae grew about two times faster than those incubated at the lowest temperature. The overall produced amount of algal biomass did not differ between the three temperature incubations as indicated by the concentration of POC. Contrary to this, algae growing at the lowest temperature produced considerably less Chi a than those at the highest temperature. lt is suggested that cells growing at their lower temperature limit cannot efficiently use large amounts of light energy captured by photosynthesis, because their intracellular processes are considerably slowed down. Thus, by producing less Chi a they absorbed less light energy at a time, but used it efficiently to build up biomass over a langer period of time. All cultures reached a situation of nutrient depletion in the course of the experiment. The ratio of C: N rase up to values of ~20:1. Thus, the extracellular release of carbon-rich dissolved organic compounds was highly probable. Astonishingly, no effect of temperature on the pools of DOC and carbohydrates could be observed. Interestingly, the production of TEP was influenced by temperature. An increase by 9°C led to a more than two-fold increase in the amount of TEP produced. Based on this finding it is suggested that the production of TEP exhibits a temperature-sensitivity that is on the same scale as heterotrophic processes. Thus, the hypothesis that the production of TEP could be reduced at elevated temperatures due to a faster uptake of DOM by bacterial processes, has to be rejected. A decrease in POC and TEP at the highest temperature was observed in the second half of the experiment, whereas bacterial activities increased. High activities of bacterial a-Dglucosidase and ß-D-glucosidase suggest that a considerable amount of carbon-rich DOM was exuded in the course of the experiment. In summary, the data of DOC cannot be explained to this point of time. An increase in temperature clearly affected the dynamics in the autotrophic and the heterotrophic processes. Since even the pool of TEP was positively influenced, it seems likely that temperature has an effect on the pool of DOM.

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