| 1. |
- Stapleton, L M, et al.
(author)
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Microbial carbon dynamics in nitrogen amended Arctic tundra soil: Measurement and model testing
- 2005
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In: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 37:11, s. 2088-2098
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Journal article (peer-reviewed)abstract
- We examined the responses of grazers (protozoa and nematodes) and their main food sources to low levels of nitrogen (N) fertilisation and applied carbon (C) flux models to our data. Replicate plots of tundra soil adjacent to the Kongsfjorden (Svalbard 78°N) were amended with ammonium and nitrate at concentrations of 1 and 5 kg N ha−1 to assess the impact of anthropogenic N deposition over three summers. Bacterial abundance as determined using the fluorochrome SYBR Green and epifluorescence microscopy ranged between 9.73×108 and 102.49×108 cells/g dry wt of soil, with a significant response to N addition occurring only during the second sampling in 2001. Despite little change in bacterial biomass, bacterial production (measured by the incorporation of 3H thymidine into DNA) during the second sampling in 2002, increased in NH4 enriched plots compared to control and NO3 amended plots, indicating that NH4 was the preferred source of inorganic N. The main bacterial predators were heterotrophic flagellates (HNAN) and naked amoebae, which showed no significant response to the N addition. HNAN showed a correlation with bacterial abundance suggesting a dependence on bacteria as a food source. The inability of a microbial C flux model to fit our data (RWSS/data=18.6, r2=0.088) was at least partly due to insufficient bacterial production to meet the C demands of predator taxa, and high variability in the data over time. This is reflected in the performance statistics for model variants where select microbial taxa and data were removed. The optimal model in terms of predictive utility was a model with data from 2002 only, minus naked amoebae (RWSS/data=2.45, r2=0.806).
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| 2. |
- Carvalho, A., et al.
(author)
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Identification of the local vibrational modes of small nitrogen clusters in dilute GaAsN
- 2007
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In: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 401-402, s. 339-342
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Journal article (peer-reviewed)abstract
- Ultra-high-resolution infra-red local vibrational mode (IR LVM) spectroscopy measurements together with density-functional calculations have been used to identify the signatures of close substitutional nitrogen (NAs) pairs in GaAs1 - x Nx alloys with concentrations of x < 0.025. We show that the presence of sub-peaks close to the NAs absorption band can be attributed to nitrogen pairs up to fourth neighbor position. Additionally, we suggest that the nitrogen pairs which give rise to the deepest levels below the conduction band edge are the first to be removed upon annealing
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| 3. |
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| 4. |
- Sawstrom, C., et al.
(author)
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Heterotrophic bacterial and viral dynamics in Arctic freshwaters: results from a field study and nutrient-temperature manipulation experiments
- 2007
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In: Polar Biology. - : Springer Science and Business Media LLC. - 1432-2056 .- 0722-4060. ; 30:11, s. 1407-1415
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Journal article (peer-reviewed)abstract
- Heterotrophic bacterial and viral concentrations (range, 0.7 x 10(4) to 206.2 x 10(4) ml(-1) and 0.05 x 10(6) to 128.9 x 10(6) ml(-1), respectively) were determined in several Arctic freshwater environments, including lakes and glacial ecosystems (78.55 degrees N, 11.56 degrees E). Our bacteria and virus results mirrored trends seen in temperate lakes, with an average virus-to-bacteria ratio (VBR) of 13 (range, 7.3-25.2) and viral concentrations and DOC positively correlated with bacterial concentrations (R = 0.964, P < 0.01 and R = 0.813, P < 0.05, respectively). Lysogenic bacteria, determined by induction with Mitomycin C, were not detected in any of the investigated Arctic freshwater environments. Nutrient-addition experiments at in situ and at elevated temperatures were performed to elucidate the factors which influenced the bacterial growth and the virus-bacteria interactions in Arctic freshwaters. Our results suggest that multiple limiting factors interacted and constrained bacterial growth. Bacterial concentrations and doubling times increased at elevated temperatures and appeared to be co-stimulated by phosphorus and carbon. However, viral concentrations showed a lack of response to nutrient addition thus indicating an uncoupling between bacteria and viruses in the experiment.
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| 5. |
- Säwström, Christin, et al.
(author)
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Bacteriophage in polar inland waters.
- 2008
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In: Extremophiles. - : Springer Science and Business Media LLC. - 1431-0651 .- 1433-4909. ; 12:2, s. 167-175
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Journal article (peer-reviewed)abstract
- Bacteriophages are found wherever microbial life is present and play a significant role in aquatic ecosystems. They mediate microbial abundance, production, respiration, diversity, genetic transfer, nutrient cycling and particle size distribution. Most studies of bacteriophage ecology have been undertaken at temperate latitudes. Data on bacteriophages in polar inland waters are scant but the indications are that they play an active and dynamic role in these microbially dominated polar ecosystems. This review summarises what is presently known about polar inland bacteriophages, ranging from subglacial Antarctic lakes to glacial ecosystems in the Arctic. The review examines interactions between bacteriophages and their hosts and the abiotic and biotic variables that influence these interactions in polar inland waters. In addition, we consider the proportion of the bacteria in Arctic and Antarctic lake and glacial waters that are lysogenic and visibly infected with viruses. We assess the relevance of bacteriophages in the microbial loop in the extreme environments of Antarctic and Arctic inland waters with an emphasis on carbon cycling.
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