@inproceedings{RueckerKnieNixdorfetal.2015, author = {R{\"u}cker, Jacqueline and Knie, Matthias and Nixdorf, Brigitte and Kolzau, Sebastian and Voss, Maren and Wiedner, Claudia}, title = {Nitrogen fixation in two polymictic lakes}, series = {Aquatic Sciences Meeting of the Association for the Sciences of Limnology and Oceanography (ASLO) held in Granada, Spain, 22-27 February 2015}, booktitle = {Aquatic Sciences Meeting of the Association for the Sciences of Limnology and Oceanography (ASLO) held in Granada, Spain, 22-27 February 2015}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-37082}, year = {2015}, abstract = {The ability to fix molecular nitrogen is considered to be a competitive advantage of Nostocales to overcome periods of nitrogen shortage but it is unclear to what extend these cyanobacteria import nitrogen into freshwaters and if they are able to compensate the efforts of reducing anthropogenic nitrogen input. We studied nitrogen fixation, cyanobacterial biovolume and species composition and abiotic parameters in two polymictic lakes (Germany) over three years. Although Nostocales were present from April to November N2-fixation was found only from June/July to September. In the summer months, it amounted up to 40 mgN m-²d-¹ or up to 500 mgN m-²d-¹ resulting in rather low annual N-inputs between 0.1 and 8 gN m-²a-¹. We found a high variation in N2-fixation rates between the two lakes and the years, which could neither be explained by total Nostocales biovolume nor heterocyte numbers. N2-fixation rates measured in the field will be analyzed on Nostocales species level, be compared to those of laboratory cultures and be discussed in the context of possible phosphorus or light limitation of Nostocales.}, subject = {Nostocales; Nitrogen fixation; Cyanobacteria; Light; Nitrogen input in lakes; Cyanobakterien; Nostocales; Stickstofffixierung; Lichtabsorption}, language = {en} } @phdthesis{Ramm2014, author = {Ramm, Jessica}, title = {Occurrence and life-cycle strategies of bloom-forming Nostocales (cyanobacteria) in deep lakes in Northern Germany and in Lake Kinneret, Israel}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-31729}, school = {BTU Cottbus - Senftenberg}, year = {2014}, abstract = {Nostocalean cyanobacteria differentiate heterocysts to fix dissolved nitrogen (N2) and dormant cells (akinetes) to survive harsh environmental conditions. The distribution and proliferation of Nostocales and their hibernation strategies in deep stratified lakes of different trophic states and climate zones were investigated. Studies were carried out in the meso-eutrophic Lake Kinneret (Israel) and in the mesotrophic Lake Scharm{\"u}tzelsee and the oligo-mesotrophic Lake Stechlinsee (Germany). The spatio-temporal distribution of akinetes in sediments was analysed. The abundance in the sediment surface increased with water depth and differed due to basin morphometry. Light and temperature distribution revealed shallow areas of sedimentary akinete pool as a potential inoculum to contribute to the formation of a pelagic population. Hence, a small viable akinete pool was deposited in shallow sediments. A CARD-FISH protocol was implemented to identify and quantify the akinetes in sediments. Tested Nostocales strains and akinetes in sediment samples were successfully labelled with 16S rRNA targeted probes and microscopically detected by their fluorescence signal. Akinete enumeration in field samples confirmed the suitability of the CARD-FISH approach. Species- or genus-specific differences in the overwintering strategies of Nostocales were observed. Akinetes were the only overwintering form of Anabaena spp. On the other hand, Aphanizomenon flos-aquae overwintered as vegetative filaments in the pelagial of Lake Stechlinsee. In the other lakes studied, Aphanizomenon spp. performed an intermediate life cycle, with akinetes and a small pelagic population in winter. This suggested that Aphanizomenon spp. had another overwintering strategy contrary to the exclusively dormant strategy of Anabaena spp. Putative strains of cylindrospermopsin (CYN)-producing Aphanizomenon ovalisporum were isolated from Lake Kinneret. Their morphologic and phylogenetic diversity, as well as the presence of CYN-encoding gene cluster and CYN production, were analysed. Four of the six strains were assigned to Anabaena bergii. Although all the isolated strains possess at least fragments of CYN gene cluster, no CYN production was detected. Non-CYN-producing Aphanizomenon ovalisporum strains and the presence of non-toxic Anabaena bergii in Lake Kinneret have not been reported before. This suggested that toxic and non-toxic Nostocales strains can coexist in lakes.}, subject = {Cyanobacteria; Cylindrospermopsin (CYN); Lake sediment; Akinetes; Cyanobakterien; Lebenszyklusstrategien; Akineten; Seesediment; Cylindrospermopsin (CYN); Life-cycle strategies; Brandenburg; Israel; Seesediment; Cyanobakterien; Klimazone; Lebensdauer}, language = {en} } @inproceedings{Ramm2015, author = {Ramm, Jessica}, title = {Spatial variability and germination potential of cyanobacterial akinetes in sediments of deep dimictic lakes}, series = {PLANKTON RESTING STAGES 2015 WORKSHOP: Geological, Ecological and Evolutionary Perspectives, held in Hanko (Tv{\"a}rminne Zoological Station), Finnland, 5-8 October 2015}, booktitle = {PLANKTON RESTING STAGES 2015 WORKSHOP: Geological, Ecological and Evolutionary Perspectives, held in Hanko (Tv{\"a}rminne Zoological Station), Finnland, 5-8 October 2015}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-41552}, year = {2015}, abstract = {Nostocales form thick-walled, resting cells (akinetes) for overwintering in lake sediments of Central Europe. The pelagic Nostocales population recruits after the germination of akinetes, which mainly takes place in the spring with increasing temperatures and light intensities. The study aimed to i) characterize the sediment surfaces inhabited by viable akinetes that potentially contribute to the formation of a pelagic population, and ii) estimate the inoculum size of the available sedimentary akinete pool. We investigated the horizontal distribution of akinetes in sediments and the seasonal course of light and temperature in two deep dimictic lakes (Lake Stechlinsee, max. depth 69 m and Lake Scharm{\"u}tzelsee, max. depth 29.5 m; NE Germany). The akinete pool was calculated and the potential inoculum was estimated using assumed light and temperature data for akinete germination. The akinete abundance in sediments depended on the basin morphometry and increased with water depth. Only a small proportion of the viable akinete pool in shallow water areas contributed as inoculum to pelagic population. The potential inoculum size in Lake Scharm{\"u}tzelsee was larger than in Lake Stechlinsee.}, subject = {Cyanobacteria; Dimitic lakes; Akinetes; Sediments; Cyanobakterien; Limnobakteriologie; Seesediment}, language = {en} }