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Sökning: WFRF:(Kritzberg Emma)

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  • Lebret, Karen, et al. (författare)
  • Genetic diversity within and genetic differentiation between blooms of a microalgal species
  • 2012
  • Ingår i: Environmental Microbiology. - : Wiley-Blackwell. - 1462-2912 .- 1462-2920. ; 14:9, s. 2395-2404
  • Tidskriftsartikel (refereegranskat)abstract
    • The field of genetic diversity in protists, particularly phytoplankton, is under expansion. However, little is known regarding variation in genetic diversity within populations over time. The aim of our study was to investigate intrapopulation genetic diversity and genetic differentiation in the freshwater bloom-forming microalga Gonyostomum semen (Raphidophyceae). The study covered a 2-year period including all phases of the bloom. Amplified fragment length polymorphism (AFLP) was used to determine the genetic structure and diversity of the population. Our results showed a significant differentiation between samples collected during the two blooms from consecutive years. Also, an increase of gene diversity and a loss of differentiation among sampling dates were observed over time within a single bloom. The latter observations may reflect the continuous germination of cysts from the sediment. The life cycle characteristics of G. semen, particularly reproduction and recruitment, most likely explain a high proportion of the observed variation. This study highlights the importance of the life cycle for the intraspecific genetic diversity of microbial species, which alternates between sexual and asexual reproduction.
  • Lebret, Karen, et al. (författare)
  • Phylogeography of the freshwater raphidophyte Gonyostomum semen confirms a recent expansion in northern Europe by a single haplotype
  • 2015
  • Ingår i: Journal of Phycology. - : Wiley-Blackwell. - 0022-3646 .- 1529-8817. ; 51:4, s. 768-781
  • Tidskriftsartikel (refereegranskat)abstract
    • Gonyostmum semen is a freshwater raphidophyte that has increased in occurrence and abundance in several countries in northern Europe since the 1980s. More recently, the species has expanded rapidly also in north-eastern Europe, and it is frequently referred to as invasive. To better understand the species history, we have explored the phylogeography of G. semen using strains from northern Europe, United States, and Japan. Three regions of the ribosomal RNA gene (small subunit [SSU], internal transcribed spacer [ITS] and large subunit [LSU]) and one mitochondrial DNA marker (cox1) were analyzed. The SSU and partial LSU sequences were identical in all strains, confirming that they belong to the same species. The ITS region differentiated the American from the other strains, but showed high intra-strain variability. In contrast, the mitochondrial marker cox1 showed distinct differences between the European, American, and Japanese strains. Interestingly, only one cox1 haplotype was detected in European strains. The overall low diversity and weak geographic structure within northern European strains supported the hypothesis of a recent invasion of new lakes by G. semen. Our data also show that the invasive northern European lineage is genetically distinct from the lineages from the other continents. Finally, we concluded that the mitochondrial cox1 was the most useful marker in determining large-scale biogeographic patterns in this species.
  • Lebret, Karen, et al. (författare)
  • Population Genetic Structure of a Microalgal Species under Expansion
  • 2013
  • Ingår i: PLoS ONE. - : Public Library of Science. - 1932-6203 .- 1932-6203. ; 8:12, s. e82510-
  • Tidskriftsartikel (refereegranskat)abstract
    • Biological invasions often cause major perturbations in the environment and are well studied among macroorganisms. Less is known about invasion by free-living microbes. Gonyostomum semen (Raphidophyceae) is a freshwater phytoplankton species that has increased in abundance in Northern Europe since the 1980's and has expanded its habitat range. In this study, we aimed to determine the genetic population structure of G. semen in Northern Europe and to what extent it reflects the species' recent expansion. We sampled lakes from 12 locations (11 lakes) in Norway, Sweden and Finland. Multiple strains from each location were genotyped using Amplified Fragment Length Polymorphism (AFLP). We found low differentiation between locations, and low gene diversity within each location. Moreover, there was an absence of genetic isolation with distance (Mantel test, p = 0.50). According to a Bayesian clustering method all the isolates belonged to the same genetic population. Together our data suggest the presence of one metapopulation and an overall low diversity, which is coherent with a recent expansion of G. semen.
  • Lindstrom, Eva S., et al. (författare)
  • The interplay between bacterial community composition and the environment determining function of inland water bacteria
  • 2010
  • Ingår i: Limnology and Oceanography. - : ASLO. - 1939-5590 .- 0024-3590. ; 55:5, s. 2052-2060
  • Tidskriftsartikel (refereegranskat)abstract
    • We hypothesized that habitats differing in water flow regime would differ in bacterial function either because of differences in the local environment, in bacterial community composition (BCC), or in the mechanism shaping BCC (community assembly). In 20 lakes and 17 inlet streams BCC was analyzed by terminal restriction fragment length polymorphism of the gene coding for 16S ribosomal RNA, and bacterial function was estimated as bacterial production rate (BP, measured as leucine incorporation) per content of dissolved organic carbon (DOC) (BP : DOC). BCC in both lakes and streams appeared to be shaped by local environmental forces (i.e., species sorting according to metacommunity theory), but not by massive introduction of cells from the drainage area (mass effect). BP : DOC was lower in streams than in lakes, which appeared to be both because of differences in BCC and environment between lakes and streams, independent of each other. We found no support for an effect of water flow regime in itself (i.e., cell dispersal rate) causing the lower functionality of the streams. In streams, BP : DOC was correlated to both BCC and environment, independent of each other, while in lakes function could not be explained by either BCC or environment. The greater environmental variability among our streams than among our lakes may be the cause for the stronger BCC-function coupling in our streams, since smaller environmental variation among our lakes would allow a greater functional redundancy.
  • Logue, Jurg B., et al. (författare)
  • Experimental insights into the importance of aquatic bacterial community composition to the degradation of dissolved organic matter
  • 2016
  • Ingår i: The ISME Journal. - : Nature Publishing Group. - 1751-7362 .- 1751-7370. ; 10:3, s. 533-545
  • Tidskriftsartikel (refereegranskat)abstract
    • Bacteria play a central role in the cycling of carbon, yet our understanding of the relationship between the taxonomic composition and the degradation of dissolved organic matter (DOM) is still poor. In this experimental study, we were able to demonstrate a direct link between community composition and ecosystem functioning in that differently structured aquatic bacterial communities differed in their degradation of terrestrially derived DOM. Although the same amount of carbon was processed, both the temporal pattern of degradation and the compounds degraded differed among communities. We, moreover, uncovered that low-molecular-weight carbon was available to all communities for utilisation, whereas the ability to degrade carbon of greater molecular weight was a trait less widely distributed. Finally, whereas the degradation of either low-or high-molecular-weight carbon was not restricted to a single phylogenetic clade, our results illustrate that bacterial taxa of similar phylogenetic classification differed substantially in their association with the degradation of DOM compounds. Applying techniques that capture the diversity and complexity of both bacterial communities and DOM, our study provides new insight into how the structure of bacterial communities may affect processes of biogeochemical significance.
  • Ostman, Orjan, et al. (författare)
  • Importance of space and the local environment for linking local and regional abundances of microbes
  • 2012
  • Ingår i: Aquatic Microbial Ecology. - : Inter-Research. - 0948-3055 .- 1616-1564. ; 67:1, s. 35-158
  • Tidskriftsartikel (refereegranskat)abstract
    • It is frequently observed that the local relative abundances of aquatic microbial taxa are correlated with their average relative abundance at the regional scale, which results in the composition of different communities being more similar than expected by chance or invariant. The degree to which communities within a region match the regional average community is variable and likely depends on several different mechanisms that control the process of microbial community assembly. Here, we show that environmental variables were associated with the community specific degree of regional invariance in 9 of 10 datasets of microbial communities in aquatic systems, being the main set of variables explaining differences in regional invariance in 5 of them. This indicates that variation in local environmental conditions across a region reduces the degree of regional invariance amongst communities. Spatial distances between communities were not related to the degrees of regional invariance, but in 7 of the datasets, regional invariance differed among different parts of the regions, particularly for phytoplankton communities. This suggests an influence of spatial or historical processes on the community specific degree of regional invariance. We conclude that both local environmental conditions and spatial/historical processes cause between-site differences in the degree of invariance between local and regional abundances in aquatic microbial metacommunities. We argue that studies of regional invariance can be an important complement to other statistical methods due to its propensity to detect variation in stochastic processes along gradients.
  • Ostman, Orjan, et al. (författare)
  • Regional invariance among microbial communities
  • 2010
  • Ingår i: Ecology Letters. - : Wiley-Blackwell. - 1461-023X .- 1461-0248. ; 13:1, s. 118-127
  • Tidskriftsartikel (refereegranskat)abstract
    • Microbial ecology has focused much on causes of between-site variation in community composition. By analysing five data-sets each of aquatic bacteria and phytoplankton, we demonstrated that microbial communities show a large degree of similarity in community composition and that abundant taxa were widespread, a typical pattern for many metazoan metacommunities. The regional abundance of taxa explained on average 85 and 41% of variation in detection frequency and 58 and 31% of variation in local abundances for bacteria and phytoplankton, respectively. However, regional abundance explained less variation in local abundances with increasing environmental variation between sites within data-sets. These findings indicate that the studies of microbial assemblages need to consider similarities between communities to better understand the processes underlying the assembly of microbial communities. Finally, we propose that the degree of regional invariance can be linked to the evolution of microbes and the variation in ecosystem functions performed by microbial communities. Ecology Letters (2010) 13: 118-127.
  • Pace, Michael L., et al. (författare)
  • Whole-lake carbon-13 additions reveal terrestrial support of aquatic food webs
  • 2004
  • Ingår i: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 427:6971, s. 240-243
  • Tidskriftsartikel (refereegranskat)abstract
    • Ecosystems are supported by organic carbon from two distinct sources. Endogenous carbon is produced by photosynthesis within an ecosystem by autotrophic organisms. Exogenous carbon is produced elsewhere and transported into ecosystems. Consumers may use exogenous carbon with consequent influences on population dynamics, predator-prey relationships and ecosystem processes(1). For example, exogenous inputs provide resources that may enhance consumer abundance beyond levels supported by within-system primary production(2). Exogenous fluxes of organic carbon to ecosystems are often large, but this material is recalcitrant and difficult to assimilate, in contrast to endogenously produced organic matter, which is used more easily(3,4). Here we show, by the experimental manipulation of dissolved inorganic C-13 in two lakes, that internal primary production is insufficient to support the food webs of these ecosystems. Additions of NaH (CO3)-C-13 enriched the C-13 content of dissolved inorganic carbon, particulate organic carbon, zooplankton and fish. Dynamics of C-13 indicate that 40-55% of particulate organic carbon and 22-50% of zooplankton carbon are derived from terrestrial sources, showing that there is significant subsidy of these ecosystems by organic carbon produced outside their boundaries.
  • Soares, Ana R. A., et al. (författare)
  • New insights on resource stoichiometry : assessing availability of carbon, nitrogen, and phosphorus to bacterioplankton
  • 2017
  • Ingår i: Biogeosciences. - : Copernicus Publications. - 1726-4170 .- 1726-4189. ; 14:6, s. 1527-1539
  • Tidskriftsartikel (refereegranskat)abstract
    • Boreal lake and river ecosystems receive large quantities of organic nutrients and carbon (C) from their catchments. How bacterioplankton respond to these inputs is not well understood, in part because we base our understanding and predictions on "total pools", yet we know little about the stoichiometry of bioavailable elements within organic matter. We designed bioassays with the purpose of exhausting the pools of readily bioavailable dissolved organic carbon (BDOC), bioavailable dissolved nitrogen (BDN), and bioavailable dissolved phosphorus (BDP) as fast as possible. Applying the method in four boreal lakes at base-flow conditions yielded concentrations of bioavailable resources in the range 105-693 mu g CL-1 for BDOC (2% of initial total DOC), 24-288 mu g NL-1 for BDN (31% of initial total dissolved nitrogen), and 0.2-17 mu g PL-1 for BDP (49% of initial total dissolved phosphorus). Thus, relative bioavailability increased from carbon (C) to nitrogen (N) to phosphorus (P). We show that the main fraction of bioavailable nutrients is organic, representing 80% of BDN and 61% of BDP. In addition, we demonstrate that total C : N and C: P ratios are as much as 13-fold higher than C : N and C: P ratios for bioavailable resource fractions. Further, by applying additional bioavailability measurements to seven widely distributed rivers, we provide support for a general pattern of relatively high bioavailability of P and N in relation to C. Altogether, our findings underscore the poor availability of C for support of bacterial metabolism in boreal C-rich fresh-waters, and suggest that these ecosystems are very sensitive to increased input of bioavailable DOC.
  • Vaquer-Sunyer, Raquel, et al. (författare)
  • Dissolved Organic Nitrogen Inputs from Wastewater Treatment Plant Effluents Increase Responses of Planktonic Metabolic Rates to Warming
  • 2015
  • Ingår i: Environmental Science and Technology. - : The American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 49:19, s. 11411-11420
  • Tidskriftsartikel (refereegranskat)abstract
    • Increased anthropogenic pressures on coastal marine ecosystems in the last century are threatening their biodiversity and functioning. Global warming and increases in nutrient loadings are two major stressors affecting these systems. Global warming is expected to increase both atmospheric and water temperatures and increase precipitation and terrestrial runoff, further increasing organic matter and nutrient inputs to coastal areas. Dissolved organic nitrogen (DON) concentrations frequently exceed those of dissolved inorganic nitrogen in aquatic systems. Many components of the DON pool have been shown to supply nitrogen nutrition to phytoplankton and bacteria. Predictions of how global warming and eutrophication will affect metabolic rates and dissolved oxygen dynamics in the future are needed to elucidate their impacts on biodiversity and ecosystem functioning. Here, we experimentally determine simultaneous DON additions and warming on planktonic community metabolism in the Baltic Sea, the largest coastal area suffering from eutrophication-driven hypoxia. Both bacterioplankton community composition and metabolic rates changed in relation to temperature. DON additions from wastewater treatment plant effluents significantly increased the activation energies for community respiration and gross primary production. Activation energies for community respiration were higher than those for gross primary production. Results support the prediction that warming of the Baltic Sea will enhance planktonic respiration rates faster than it will for planktonic primary production. Higher increases in respiration rates than in production may lead to the depletion of the oxygen pool, further aggravating hypoxia in the Baltic Sea.
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