ALBERT

Description: The effect of pCO2 on carbon acquisition and intracellular assimilation was investigated in the three bloom-forming diatom species, Eucampia zodiacus (Ehrenberg), Skeletonema costatum (Greville) Cleve, Thalassionema nitzschioides (Grunow) Mereschkowsky and the non-bloom-forming Thalassiosira pseudonana (Hust.) Hasle and Heimdal. In vivo activities of carbonic anhydrase (CA), photosynthetic O2 evolution, CO2 and HCO3? uptake rates were measured by membrane-inlet mass spectrometry (MIMS) in cells acclimated to pCO2 levels of 370 and 800 ?atm. To investigate whether the cells operate a C4-like pathway, activities of ribulose-1,5-bisphosphate carboxylase (RubisCO) and phosphoenolpyruvate carboxylase (PEPC) were measured at the mentioned pCO2 levels and a lower pCO2 level of 50 ?atm. In the bloom-forming species, extracellular CA activities strongly increased with decreasing CO2 supply while constantly low activities were obtained for T. pseudonana. Half-saturation concentrations (K1/2) for photosynthetic O2 evolution decreased with decreasing CO2 supply in the two bloom-forming species S. costatum and T. nitzschioides, but not in T. pseudonana and E. zodiacus. With the exception of S. costatum, maximum rates (Vmax) of photosynthesis remained constant in all investigated diatom species. Independent of the pCO2 level, PEPC activities were significantly lower than those for RubisCO, averaging generally less than 3%. All examined diatom species operate highly efficient CCMs under ambient and high pCO2, but differ strongly in the degree of regulation of individual components of the CCM such as Ci uptake kinetics and extracellular CA activities. The present data do not suggest C4 metabolism in the investigated species.

Description: We investigated carbon acquisition by the N2-fixing cyanobacterium Trichodesmium IMS101 in response to CO2 levels of 15.1, 37.5, and 101.3 Pa (equivalent to 150, 370, and 1000 ppm). In these acclimations, growth rates as well as cellular C and N contents were measured. In vivo activities of carbonic anhydrase (CA), photosynthetic O2 evolution, and CO2 and HCO3- fluxes were measured using membrane inlet mass spectrometry and the 14C disequilibrium technique. While no differences in growth rates were observed, elevated CO2 levels caused higher C and N quotas and stimulated photosynthesis and N2 fixation. Minimal extracellular CA (eCA) activity was observed, indicating a minor role in carbon acquisition. Rates of CO2 uptake were small relative to total inorganic carbon (Ci) fixation, whereas HCO{3 contributed more than 90% and varied only slightly over the light period and between CO2 treatments. The low eCA activity and preference for HCO3- were verified by the 14C disequilibrium technique. Regarding apparent affinities, half-saturation concentrations (K1/2) for photosynthetic O2 evolution and HCO3- uptake changed markedly over the day and with CO2 concentration. Leakage (CO2 efflux : Ci uptake) showed pronounced diurnal changes. Our findings do not support a direct CO2 effect on the carboxylation efficiency of ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) but point to a shift in resource allocation among photosynthesis, carbon acquisition, and N2 fixation under elevated CO2 levels. The observed increase in photosynthesis and N2fixation could have potential biogeochemical implications, as it may stimulate productivity in N-limited oligotrophic regions and thus provide a negative feedback in rising atmospheric CO2 levels.

Description: The bacterial communities associated with the brown algae Laminaria saccharina were investigated. For characterization in different geographical settings, seasons and also on the morphologically different parts of the alga, denaturing gradient gel electrophoresis (DGGE), cloning and phylogenetic analysis of l 6S rDNA sequences were used. Biologically active bacteria, isolated from L. saccharina in an earlier study, were sequenced and phylogenetically analyzed. In addition an infected laboratory culture of Laminaria digitata was studied by scanning electron microscopy and DGGE. Infected L. digitata samples yielded DGGE banding patters that indicated a stable bacterial community. Scanning electron microcopy revealed blister like structures on the infected phylloid, containing morphologically different microorganisms not occurring on healthy L. digitata phylloids. The 16S rDNA DGGE banding pattems of L. saccharina from natural habitats indicated a specific bacterial community associated with the young and healthy algal tissues. Seasonal, geographical and algal-part specific differences were observed. Cloning experiments identified 18 phylotypes ( 6 in the Alphaproteobacteria, 8 in the Gammaproteobacteria and 4 in the Bacteroidetes group) derived only from Baltic L. saccharina, not shared by water-derived samples. This indicated a specific association of bacteria to L. saccharina. Furthermore sequence analysis of the L. saccharina-derived antimicrobially active isolates identified strain LD8 l to be a novel member of the Alphaproteobacteria with less than 96% sequence similarity to its closest relatives, Koprimonas byunsanensis (DQ 167245) and Rhodospirillum rubrum (X87278). These findings lead to the assumption, that L. saccharina provides a abitat for specifically associated bacteria and a source for the detection of novel bacterial species with antimicrobial activities.

Description: Aim of this study was the investigation of the vertical dis-tribution of N2O and the factors influencing this distribu-tion. Dissolved and atmospheric N2O was measured in the North Atlantic Ocean and the Baltic Sea. These data, in com-bination with physical and chemical parameters, were used to determine sources and sinks of N2O. Possible production pathways were investigated using the relationship between N2O and relevant production parameters, and their relation to physical processes in the oceans. The hypothesis whether N2O concentrations increased by oceanic iron fertilization via enhanced substrate supply for microbial respiration, was tested during the European Iron Fertilization Experi-ment (EIFEX) in the subpolar South Atlantic. The vertical structure of bacterial communities in the subtropical North Atlantic was investigated, with the intention to find corre-lations between the community structure of bacteria and the distribution of N2O. In summary, this study presents a de-tailed picture of the distribution of N2O in the North At-lantic Ocean and the Baltic Sea and adds 80 profiles of the Atlantic and 26 profiles of the Baltic Sea to the database.

Description: Die vorliegende Arbeit untersucht, inwieweit die Photonenweglängenverteilung der durch Wolken transmittierten solaren Strahlung Informationen über die Wolkeneigenschaften enthält und sich damit zur Wolkenfernerkundung eignet. Hierzu wurden Photonenweglängen (PPL) mit dem rückwärts rechnenden Monte-Carlo-Strahlungstransportmodell MC-UNIK-BW für dreidimensional inhomogene Wolkenfelder aus hydrodynamischen Modellläufen des mesoskaligen Atmosphärenmodells GESIMA simuliert. Die stärkste Korrelation der mittleren PPL mit den 13 untersuchten Wolkeneigenschaften liegt für die optische Dicke der Wolken vor. Relativ unabhängig von dieser Beziehung zeigt sich die Verbindung der PPL zur internen Wolkeninhomogenität. Der Einfluss der Inhomogenität zeigte sich auch in dem Vergleich zwischen einer gemessenen und einer modellierten PPL. Des Weiteren stellt sich heraus, dass ein existierender Zusammenhang zwischen der PPL und den Wolkeneigenschaften für einen größeren horizontalen Bereich der Wolken Gültigkeit behält. Durch die Aufspaltung des Datensatzes an PPL-Simulationen in unterschiedliche Messsituationen ergaben sich neue Korrelationen mit zum Teil deutlichen Verbesserungen der Korrelationen im Vergleich zum gesamten Datensatz. Daneben wurde auch der Einfluss der Gasabsorption auf die resultierende PPL und die Änderung der PPL mit der Variation des Messortes in einem Wolkenfeld untersucht.