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  • 1. Degerman, Rickard
    et al.
    Dinasquet, Julie
    Linnéuniversitetet, Fakulteten för Hälso- och livsvetenskap (FHL), Institutionen för biologi och miljö (BOM).
    Riemann, Lasse
    Linnéuniversitetet, Fakulteten för Hälso- och livsvetenskap (FHL), Institutionen för biologi och miljö (BOM).
    de Luna, Sara Sjostedt
    Andersson, Agneta
    Effect of resource availability on bacterial community responses to increased temperature2013Ingår i: Aquatic Microbial Ecology, ISSN 0948-3055, E-ISSN 1616-1564, Vol. 68, nr 2, s. 131-142Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Climate change is predicted to cause higher temperatures and increased precipitation, resulting in increased inflow of nutrients to coastal waters in northern Europe. This has been assumed to increase the overall heterotrophy, including enhanced bacterial growth. However, the relative importance of temperature, resource availability and bacterial community composition for the bacterial growth response is poorly understood. In the present study, we investigated effects of increased temperature on bacterial growth in waters supplemented with different nutrient concentrations and inoculated with microbial communities from distinct seasonal periods. Seven experiments were performed in the northern Baltic Sea spanning an entire annual cycle. In each experiment, bacterioplankton were exposed to 2 temperature regimes (in situ and in situ + 4 degrees C) and 5 nutrient concentrations. Generally, elevated temperature and higher nutrient levels caused an increase in the bacterial growth rate and a shortening of the response time (lag phase). However, at the lowest nutrient concentration, bacterial growth was low at all tested temperatures, implying a stronger dependence on resource availability than on temperature for bacterial growth. Furthermore, data indicated that different bacterial assemblages had varying temperature responses and that community composition was strongly affected by the combination of high nutrient addition and high temperature. These results support the concern that climate change will promote heterotrophy in aquatic systems, where nutrient levels will increase considerably. In such environments, the bacterial community composition will change, their growth rates will increase, and their response time will be shortened compared to the present situation.

  • 2.
    Dinasquet, Julie
    Linnéuniversitetet, Fakulteten för Hälso- och livsvetenskap (FHL), Institutionen för biologi och miljö (BOM).
    Substrate control of community composition and functional adaptation in marine bacterioplankton2013Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    A drop of sea-water is teeming with a million of bacteria, on which pelagic food-webs and biogeochemical cycles depend. These bacteria thrive on a wide range of dissolved organic carbon (DOC) compounds produced through biotic and abiotic processes. Molecular analyses have over the past decades shown that specific bacterial taxa differ in their capacity to exploit DOC, suggesting a tight link between bacterial community composition (BCC) and ocean biogeo-chemistry. Therefore, an understanding of how resource availability and mortality agents drive BCC and bacterial functional adaptation is a prerequisit for predictions of how marine ecosystems will respond to future global change.

    In this thesis, I have studied BCC and bacterial functionality in response to various controlling factors relevant in an environmental changes perspective. For instance, the extensive regional warming in Antarctica induces the proliferation of icebergs. By investigating the bacterioplankton in the surrounding of a drifting iceberg, hydrographical perturbations driven by the iceberg were found to affect BCC, functionality and the capacity of indigenous taxa to utilize specific DOC compounds. Furthermore, a study of community succession during DOC utilization assays demonstrated that bacterial assemblages adapt to the gradual exhaustion of available DOC through community compositional succession. In addition, the variation in substrate availability and temperature may also affect BCC in eutrophic systems.

    While substrate availability can have an important impact on BCC and bacterial functionality, it is also important to study the cascading effects of higher trophic levels on bacteria. During a mesocosm experiment, the presence of an invasive gelatinous top-predator was shown to have only limited effects on the structure and function of the bacterial community in the Baltic Sea due to nutrient limiting conditions and to the overall complexity of the food-web. However, this top-predator may have direct bottom-up impact on bacteria in its close surrounding.

    The results presented in this thesis show that the bacterioplankton is sensitive to the availability of substrates and that bacterial community composition responds to contemporary environmental conditions. These results contribute to our understanding of how ecosystem disturbances affect marine bacterioplankton; insights of relevance to biogeochemistry and food-webs in the oceans.

  • 3.
    Dinasquet, Julie
    et al.
    Linnéuniversitetet, Fakultetsnämnden för naturvetenskap och teknik, Institutionen för naturvetenskap, NV. University of Copenhagen, Denmark.
    Granhag, Lena
    University of Gothenburg ; Chalmers University of Technology.
    Riemann, Lasse
    Linnéuniversitetet, Fakultetsnämnden för naturvetenskap och teknik, Institutionen för naturvetenskap, NV.
    Stimulated bacterioplankton growth and selection for certain bacterial taxa in the vicinity of the ctenophore Mnemiopsis leidyi2012Ingår i: Frontiers in Microbiology, ISSN 1664-302X, E-ISSN 1664-302X, Vol. 3, artikel-id 302Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Episodic blooms of voracious gelatinous zooplankton, such as the ctenophore Mnemiopsis leidyi, affect pools of inorganic nutrients and dissolved organic carbon by intensive grazing activities and mucus release. This will potentially influence bacterioplankton activity and community composition, at least at local scales; however, available studies on this are scarce. In the present study we examined effects of M. leidyi on bacterioplankton growth and composition in incubation experiments. Moreover, we examined community composition of bacteria associated with the surface and gut of M. leidyi. High release of ammonium and high bacterial growth was observed in the treatments with M. leidyi relative to controls. Deep 454 pyrosequencing of 16 S rRNA genes showed specific bacterial communities in treatments with M. leidyi as well as specific communities associated with M. leidyi tissue and gut. In particular, members of Flavobacteriaceae were associated with M. leidyi. Our study shows that M. leidyi influences bacterioplankton activity and community composition in the vicinity of the jellyfish. In particular during temporary aggregations of jellyfish, these local zones of high bacterial growth may contribute significantly to the spatial heterogeneity of bacterioplankton activity and community composition in the sea.

  • 4.
    Dinasquet, Julie
    et al.
    Linnéuniversitetet, Fakulteten för Hälso- och livsvetenskap (FHL), Institutionen för biologi och miljö (BOM). Univ Copenhagen, Marine Biol Sect, DK-3000 Helsingor, Denmark.
    Kragh, Theis
    Schroter, Marie-Louise
    Linnéuniversitetet, Fakulteten för Hälso- och livsvetenskap (FHL), Institutionen för biologi och miljö (BOM).
    Sondergaard, Morten
    Riemann, Lasse
    Linnéuniversitetet, Fakulteten för Hälso- och livsvetenskap (FHL), Institutionen för biologi och miljö (BOM). Univ Copenhagen, Marine Biol Sect, DK-3000 Helsingor, Denmark.
    Functional and compositional succession of bacterioplankton in response to a gradient in bioavailable dissolved organic carbon2013Ingår i: Environmental Microbiology, ISSN 1462-2912, E-ISSN 1462-2920, Vol. 15, nr 9, s. 2616-2628Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Studies indicate that bacterial taxa utilize different fractions of the dissolved organic carbon (DOC) pool, while others suggest functional redundancy among constituents of bacterioplankton, implying only a weak coupling between community structure and function. We examined bacterial compositional and functional [ectoenzymatic activities and growth efficiency; bacterial growth efficiency (BGE)] responses to a gradient in bioavailable DOC (bDOC). This was achieved over 10 days in DOC utilization assays containing Baltic Sea water with variable amounts of natural bDOC. Measurements of bacterial growth, O-2 and DOC consumption in the assays using non-invasive sampling showed that BGE changed over time and that the bDOC utilized accounted for 4-13% of the DOC pool. Pyrosequencing of 16S rRNA genes demonstrated minor differences at the phylum level between samples, whereas larger successional differences were discernible at lower phylogenetic levels. Our study suggests that changes in concentrations of bDOC affect bacterioplankton BGE and community structure by selecting for some taxa while the relative abundance of most taxa remained unaffected. Ectoenzymes activities suggested preferential degradation of protein-rich compounds by bacteria, switching to carbohydrate-rich DOC when proteins were depleted. Hence, there was a fairly weak linkage between bacterial community composition and DOC utilization suggesting that overall bacterioplankton community structure only to some extent has predictive power for processing of the DOC pool.

  • 5.
    Dinasquet, Julie
    et al.
    Linnéuniversitetet, Fakulteten för Hälso- och livsvetenskap (FHL), Institutionen för biologi och miljö (BOM). Univ Copenhagen, Denmark ; Scripps Inst Oceanography, USA.
    Richert, Inga
    Uppsala University ; UFZ Helmholtz Ctr Environm Res, Germany.
    Logares, Ramiro
    CSIC, Spain.
    Yager, Patricia
    Univ Georgia, USA.
    Bertilsson, Stefan
    Uppsala University.
    Riemann, Lasse
    Univ Copenhagen, Denmark.
    Mixing of water masses caused by a drifting iceberg affects bacterial activity, community composition and substrate utilization capability in the Southern Ocean2017Ingår i: Environmental Microbiology, ISSN 1462-2912, E-ISSN 1462-2920, Vol. 19, nr 6, s. 2453-2467Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The number of icebergs produced from ice-shelf disintegration has increased over the past decade in Antarctica. These drifting icebergs mix the water column, influence stratification and nutrient condition, and can affect local productivity and food web composition. Data on whether icebergs affect bacterioplankton function and composition are scarce, however. We assessed the influence of iceberg drift on bacterial community composition and on their ability to exploit carbon substrates during summer in the coastal Southern Ocean. An elevated bacterial production and a different community composition were observed in iceberg-influenced waters relative to the undisturbed water column nearby. These major differences were confirmed in short-term incubations with bromodeoxyuridine followed by CARD-FISH. Furthermore, one-week bottle incubations amended with inorganic nutrients and carbon substrates (a mix of substrates, glutamine, Nacetylglucosamine, or pyruvate) revealed contrasting capacity of bacterioplankton to utilize specific carbon substrates in the iceberg-influenced waters compared with the undisturbed site. Our study demonstrates that the hydrographical perturbations introduced by a drifting iceberg can affect activity, composition, and substrate utilization capability of marine bacterioplankton. Consequently, in a context of global warming, increased frequency of drifting icebergs in polar regions holds the potential to affect carbon and nutrient biogeochemistry at local and possibly regional scales.

  • 6.
    Rowe, Owen F.
    et al.
    Umeå University;Umeå Marine Sci Ctr;Univ Helsinki, Finland;Balt Marine Environm Protect Commiss, Finland.
    Dinasquet, Julie
    Linnéuniversitetet, Fakulteten för Hälso- och livsvetenskap (FHL), Institutionen för biologi och miljö (BOM). Univ Copenhagen, Denmark;Scripps Inst Oceanog, USA.
    Paczkowska, Joanna
    Umeå University;Umeå Marine Sci Ctr.
    Figueroa, Daniela
    Umeå University;Umeå Marine Sci Ctr.
    Riemann, Lasse
    Linnéuniversitetet, Fakulteten för Hälso- och livsvetenskap (FHL), Institutionen för biologi och miljö (BOM). Univ Copenhagen, Denmark.
    Andersson, Agneta
    Umeå University;Umeå Marine Sci Ctr.
    Major differences in dissolved organic matter characteristics and bacterial processing over an extensive brackish water gradient, the Baltic Sea2018Ingår i: Marine Chemistry, ISSN 0304-4203, E-ISSN 1872-7581, Vol. 202, s. 27-36Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dissolved organic matter (DOM) in marine waters is a complex mixture of compounds and elements that contribute substantially to the global carbon cycle. The large reservoir of dissolved organic carbon (DOC) represents a vital resource for heterotrophic bacteria. Bacteria can utilise, produce, recycle and transform components of the DOM pool, and the physicochemical characteristics of this pool can directly influence bacterial activity; with consequences for nutrient cycling and primary productivity. In the present study we explored bacterial transformation of naturally occurring DOM across an extensive brackish water gradient in the Baltic Sea. Highest DOC utilisation (indicated by decreased DOC concentration) was recorded in the more saline southerly region where waters are characterised by more autochthonous DOM. These sites expressed the lowest bacterial growth efficiency (BGE), whereas in northerly regions, characterised by higher terrestrial and allochthonous DOM, the DOC utilisation was low and BGE was highest. Bacterial processing of the DOM pool in the south resulted in larger molecular weight compounds and compounds associated with secondary terrestrial humic matter being degraded, and a processed DOM pool that was more aromatic in nature and contributed more strongly to water colour; while the opposite was true in the north. Nutrient concentration and stoichiometry and DOM characteristics affected bacterial activity, including metabolic status (BGE), which influenced DOM transformations. Our study highlights dramatic differences in DOM characteristics and microbial carbon cycling in sub-basins of the Baltic Sea. These findings are critical for our understanding of carbon and nutrient biogeochemistry, particularly in light of climate change scenarios.

  • 7.
    Swalethorp, Rasmus
    et al.
    Univ Calif San Diego, USA;University of Gothenburg.
    Dinasquet, Julie
    Linnéuniversitetet, Fakulteten för Hälso- och livsvetenskap (FHL), Institutionen för biologi och miljö (BOM). Univ Calif San Diego, USA;Tech Univ Denmark, Denmark;Univ Copenhagen, Denmark.
    Logares, Ramiro
    CSIC, Spain.
    Bertilsson, Stefan
    Uppsala University.
    Kjellerup, Sanne
    Tech Univ Denmark, Denmark;University of Gothenburg.
    Krabberod, Anders K.
    Univ Oslo, Norway.
    Moksnes, Per-Olav
    University of Gothenburg.
    Nielsen, Torkel G.
    Tech Univ Denmark, Denmark.
    Riemann, Lasse
    Univ Copenhagen, Denmark.
    Microzooplankton distribution in the Amundsen Sea Polynya (Antarctica) during an extensive Phaeocystis antarctica bloom2019Ingår i: Progress in Oceanography, ISSN 0079-6611, E-ISSN 1873-4472, Vol. 170, s. 1-10Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In Antarctica, summer is a time of extreme environmental shifts resulting in large coastal phytoplankton blooms fueling the food web. Despite the importance of the microbial loop in remineralizing biomass from primary production, studies of how microzooplankton communities respond to such blooms in the Southern Ocean are rather scarce. Microzooplankton (ciliate and dinoflagellate) communities were investigated combining microscopy and 18S rRNA sequencing analyses in the Amundsen Sea Polynya during an extensive summer bloom of Phaeocystis antarctica. The succession of microzooplankton was further assessed during a 15-day induced bloom microcosm experiment. Dinoflagellates accounted for up to 59 % of the microzooplankton biomass in situ with Gymnodinium spp., Protoperidiwn spp. and Gyrodinium spp. constituting 89 % of the dinoflagellate biomass. Strobilidium spp., Strombidium spp. and tintinids represented 90 % of the ciliate biomass. Gymnodiniwn, Gyrodinium and tintinnids are known grazers of Phaeocystis, suggesting that this prymnesiophyte selected for the key microzooplankton taxa. Availability of other potential prey, such as diatoms, heterotrophic nanoflagellates and bacteria, also correlated to changes in microzooplankton community structure. Overall, both heterotrophy and mixotrophy appeared to be key trophic strategies of the dominant microzooplankton observed, suggesting that they influence carbon flow in the microbial food web through top-down control on the phytoplankton community.

  • 8.
    Williams, C. M.
    et al.
    Univ Georgia, USA.
    Dupont, A. M.
    Univ Georgia, USA.
    Loevenich, J.
    Univ Georgia, USA.
    Post, A. F.
    URI, USA.
    Dinasquet, Julie
    Linnéuniversitetet, Fakulteten för Hälso- och livsvetenskap (FHL), Institutionen för biologi och miljö (BOM). Univ Copenhagen, Denmark.
    Yager, P. L.
    Univ Georgia, USA.
    Pelagic microbial heterotrophy in response to a highly productive bloom of Phaeocystis antarctica in the Amundsen Sea Polynya, Antarctica2016Ingår i: Elementa: Science of the Anthropocene, E-ISSN 2325-1026, Vol. 4, s. 1-18, artikel-id 000102Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Heterotrophic bacteria play a key role in marine carbon cycling, and understanding their activities in polar systems is important for considering climate change impacts there. One goal of the ASPIRE project was to examine the relationship between the phytoplankton bloom and bacterial heterotrophy in the Amundsen Sea Polynya (ASP). Bacterial abundance, production (BP), respiration, growth efficiency, and extracellular enzyme activity (EEA) were compared to nutrient and organic matter inventories, chlorophyll a (Chl a), viral and microzooplankton abundance, and net primary production (NPP). Bacterial production and respiration clearly responded (0.04-4.0 and 10-53 mu g C L-1 d(-1), respectively) to the buildup of a massive Phaeocystis antarctica bloom (Chl a: 0.2-22 mu g L-1), with highest rates observed in the central polynya where Chl a and particulate organic carbon (POC) were greatest. The highest BP rates exceeded those reported for the Ross Sea or any other Antarctic coastal system, yet the BP: NPP ratio (2.1-9.4%) was relatively low. Bacterial respiration was also high, and growth efficiency (2-27%; median = 10%) was similar to oligotrophic systems. Thus, the integrated bacterial carbon demand (0.8-2.8 g C m(-2) d(-1)) was a high fraction (25-128%; median = 43%) of NPP during bloom development. During peak bloom, activity was particle-associated: BP and EEA correlated well with POC, and size fractionation experiments showed that the larger size fraction (> 3 mu m) accounted for a majority (similar to 75%) of the BP. The community was psychrophilic, with a 5x reduction in BP when warmed to 20 degrees C. In deeper waters, respiration remained relatively high, likely fueled by the significant downward particle flux in the region. A highly active, particle-associated, heterotrophic microbial community clearly responded to the extraordinary phytoplankton bloom in the ASP, likely limiting biological pump efficiency during the early season.

  • 9.
    Yager, P. L.
    et al.
    Univ Georgia, USA.
    Sherrell, R. M.
    Rutgers State Univ, USA.
    Stammerjohn, S. E.
    Univ Colorado, USA.
    Ducklow, H. W.
    Columbia Univ, USA.
    Schofield, O. M. E.
    Rutgers State Univ, USA.
    Ingall, E. D.
    Georgia Inst Technol, USA.
    Wilson, S. E.
    Bangor Univ, UK.
    Lowry, K. E.
    Stanford Univ, USA.
    Williams, C. M.
    Univ Georgia, USA.
    Riemann, Lasse
    Univ Copenhagen, Denmark.
    Bertilsson, S.
    Uppsala University.
    Alderkamp, A-C
    Stanford Univ, USA.
    Dinasquet, Julie
    Linnéuniversitetet, Fakulteten för Hälso- och livsvetenskap (FHL), Institutionen för biologi och miljö (BOM). Univ Copenhagen, Denmark.
    Logares, R.
    CSIC, Spain.
    Richert, I.
    Uppsala University.
    Sipler, R. E.
    Coll William & Mary, USA.
    Melara, A. J.
    Univ Georgia, USA.
    Mu, L.
    Univ Georgia, USA.
    Newstead, R. G.
    Bangor Univ, UK.
    Post, A. F.
    Florida Atlantic Univ, USA.
    Swalethorp, R.
    Tech Univ Denmark, Denmark;University of Gothenburg.
    van Dijken, G. L.
    Stanford Univ, USA.
    A carbon budget for the Amundsen Sea Polynya, Antarctica: Estimating net community production and export in a highly productive polar ecosystem2016Ingår i: Elementa: Science of the Anthropocene, E-ISSN 2325-1026, Vol. 4, artikel-id 000140Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Polynyas, or recurring areas of seasonally open water surrounded by sea ice, are foci for energy and material transfer between the atmosphere and the polar ocean. They are also climate sensitive, with both sea ice extent and glacial melt influencing their productivity. The Amundsen Sea Polynya (ASP) is the greenest polynya in the Southern Ocean, with summertime chlorophyll a concentrations exceeding 20 mu g L-1. During the Amundsen Sea Polynya International Research Expedition (ASPIRE) in austral summer 2010-11, we aimed to determine the fate of this high algal productivity. We collected water column profiles for total dissolved inorganic carbon (DIC) and nutrients, particulate and dissolved organic matter, chlorophyll a, mesozoo-plankton, and microbial biomass to make a carbon budget for this ecosystem. We also measured primary and secondary production, community respiration rates, vertical particle flux and fecal pellet production and grazing. With observations arranged along a gradient of increasing integrated dissolved inorganic nitrogen drawdown (Delta DIN; 0.027-0.74 mol N m(-2)), changes in DIC in the upper water column (ranging from 0.2 to 4.7 mol C m(-2)) and gas exchange (0-1.7 mol C m(-2)) were combined to estimate early season net community production (sNCP; 0.2-5.9 mol C m(-2)) and then compared to organic matter inventories to estimate export. From a phytoplankton bloom dominated by Phaeocystis antarctica, a high fraction (up to similar to 60%) of sNCP was exported to sub-euphotic depths. Microbial respiration remineralized much of this export in the mid waters. Comparisons to short-term (2-3 days) drifting traps and a year-long moored sediment trap capturing the downward flux confirmed that a relatively high fraction (3-6%) of the export from similar to 100 m made it through the mid waters to depth. We discuss the climate-sensitive nature of these carbon fluxes, in light of the changing sea ice cover and melting ice sheets in the region.

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