| 1. |
- Ellaway, R, et al.
(författare)
-
Building a virtual patient commons
- 2008
-
Ingår i: Medical teacher. - : Informa UK Limited. - 1466-187X .- 0142-159X. ; 30:2, s. 170-174
-
Tidskriftsartikel (refereegranskat)
|
|
| 2. |
- Poulton, Alex J., et al.
(författare)
-
Phytoplankton carbon fixation, chlorophyll-biomass and diagnostic pigments in the Atlantic Ocean
- 2006
-
Ingår i: Deep-sea research. Part II, Topical studies in oceanography. - : Elsevier BV. - 0967-0645 .- 1879-0100. ; 53:14-16, s. 1593-1610
-
Tidskriftsartikel (refereegranskat)abstract
- We have made daily measurements of phytoplankton pigments, size-fractionated (< 2 and > 2-mu m) carbon fixation and chlorophyll-a concentration during four Atlantic Meridional Transect (AMT) cruises in 2003-04. Surface rates of carbon fixation ranged from < 0.2-mmol C m(-3) d(-1) in the subtropical gyres to 0.2-0.5-mmol C m(-3) d(-1) in the tropical equatorial Atlantic. Significant intercruise variability was restricted to the subtropical gyres, with higher chlorophyll-a concentrations and carbon fixation in the subsurface chlorophyll maximum during spring in either hemisphere. In surface waters, although picoplankton (<-mu m) represented the dominant fraction in terms of both carbon fixation (50-70%) and chlorophyll-alpha (80-90%), nanoplankton (> 2-mu m) contributions to total carbon fixation (30-50%) were higher than to total chlorophyll-alpha (10-20%). However, in the subsurface chlorophyll maximum picoplankton dominated both carbon fixation (70-90%) and chlorophyll-alpha (70-90%). Thus, in surface waters chlorophyll-normalised carbon fixation was 2-3 times higher for nanoplankton and differences in picoplankton and nanoplankton carbon to chlorophyll-alpha ratios may lead to either higher or similar growth rates. These low chlorophyll-normalised carbon fixation rates for picoplankton may also reflect losses of fixed carbon (cell leakage or respiration), decreases in photosynthetic efficiency, grazing losses during the incubations, or some combination of all these. Comparison of nitrate concentrations in the subsurface chlorophyll maximum with estimates of those required to support the observed rates of carbon fixation (assuming Redfield stoichiometry) indicate that primary production in the chlorophyll maximum may be light rather than nutrient limited.
|
|
| 3. |
- Stapleton, L M, et al.
(författare)
-
Microbial carbon dynamics in nitrogen amended Arctic tundra soil: Measurement and model testing
- 2005
-
Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 37:11, s. 2088-2098
-
Tidskriftsartikel (refereegranskat)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).
|
|
