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| 2. |
- Högberg, Peter, et al.
(författare)
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Factors determining the 13C abundance of soil-respired CO2 in Boreal forests
- 2005
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Ingår i: Stable isotopes and biosphere-atmosphere interactions. - : Elsevier. - 9780120884476 ; , s. 47-68
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Bokkapitel (refereegranskat)abstract
- Analysis of the isotopic composition of the CO2 respired from soils may reveal information about the important component of the ecosystem C balance. This is crucial, since a large terrestrial sink for atmospheric CO2 has been located in the northern hemisphere, and the vast boreal forests may be largely responsible. At the same time, boreal and arctic ecosystems have large amounts of C stored in the soil, and could potentially become a source of CO2 in a warmer climate promoting more rapid decomposition of soil organic matter. Furthermore, the northern hemisphere has complex dynamics in terms of annual fluctuations in both the concentration of CO2 in the atmosphere and its δl3C. It is of utmost importance to understand the causes of this variability, since it interferes with the partitioning between the ocean and the terrestrial contributions in global models. This chapter aims to provide an update on the reviews by Flanagan and Ehleringer and Ehleringer et al. on the causation of the δ13C of the soil CO2 efflux and, in doing this, focuses on the boreal forests.
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| 3. |
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| 4. |
- Högberg, Mona N., et al.
(författare)
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Contrasting effects of nitrogen availability on plant carbon supply to mycorrhizal fungi and saprotrophs - a hypothesis based on field observations in boreal forest
- 2003
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Ingår i: New Phytologist. - : Wiley. - 1469-8137 .- 0028-646X. ; 160:1, s. 225-238
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Tidskriftsartikel (refereegranskat)abstract
- Soil microorganisms are considered C-limited, while plant productivity is frequently N-limited. Large stores of organic C in boreal forest soils are attributed to negative effects of low temperature, soil acidity and plant residue recalcitrance upon microbial activity. We examined microbial activity, biomass and community composition along a natural 90-m-long soil N supply gradient, where plant species composition varies profoundly, forest productivity three-fold and soil pH by three units. There was, however, no significant variation in soil respiration in the field across the gradient. Neither did microbial biomass C determined by fumigation-extraction vary, while other estimates of activity and biomass showed a weak increase with increasing N supply and soil pH. Simultaneously, a phospholipid fatty acid attributed mainly to mycorrhizal fungi declined drastically, while bacterial biomass increased. We hypothesize that low N supply and plant productivity, and hence low litter C supply to saprotrophs is associated with a high plant C supply to mycorrhizal fungi, while the reverse occurs under high N supply. This should mean that effects of N availability on C supply to these functional groups of microbes acts in opposing directions.
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| 5. |
- Högberg, Niclas, 1979-, et al.
(författare)
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Intestinal intraluminal glycerol and plasma I-FABP levels in preterm infants with necrotizing enterocolitis
- 2016
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Ingår i: Clinics in Surgery. ; 1:1085, s. 1-6
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Tidskriftsartikel (refereegranskat)abstract
- Background/Purpose: Necrotizing enterocolitis (NEC) is highly associated with prematurity and is characterized by bowel necrosis and multi-organ failure. There is a strong need for improved diagnostic methods to reduce the significant morbidity and mortality associated with NEC. The aim of this single centre prospective study was to investigate the possibility to detect early signs of NEC, by using rectal intraluminal microdialysis and plasma intestinal fatty acid binding protein (I-FABP) in preterm infants admitted to a level III neonatal intensive care unit.Methods: The study was performed on extremely preterm infants with a gestational age of less than 28 weeks. During a 4-week period after birth, rectal intraluminal microdialysate levels of glucose, lactate, pyruvate and glycerol were measured, and plasma was collected for I-FABP analysis. Infants not developing NEC served as controls. Results: Microdialysis revealed signs of intestinal hypoxic or ischemic damage and cell membrane degradation, with a marked increase of both intraluminal glycerol and plasma I-FABP in infants developing NEC, as well as in infants suffering from other complications. The microdialysate levels of glucose, lactate and pyruvate were too low to be evaluated in this setting. All infants tolerated the microdialysis well without any complications.Conclusion: Elevated levels of intraluminal glycerol and plasma I-FABP suggests mucosal cell membrane degradation and hypoxic or ischemic damage in preterm infants developing NEC, as well as in preterm infants suffering from other complications such as volvulus, sepsis or respiratory distress. However, it was not possible to predict development of NEC before clinical diagnosis using these markers.
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| 6. |
- Högberg, Peter, et al.
(författare)
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Large-scale forest girdling shows that current photosynthesis drives soil respiration
- 2001
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 411:6839, s. 789-792
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Tidskriftsartikel (refereegranskat)abstract
- The respiratory activities of plant roots, of their mycorrhizal fungi and of the free-living microbial heterotrophs (decomposers) in soils are significant components of the global carbon balance, but their relative contributions remain uncertain. To separate mycorrhizal root respiration from heterotrophic respiration in a boreal pine forest, we conducted a large-scale tree-girdling experiment, comprising 9 plots each containing about 120 trees. Tree-girdling involves stripping the stem bark to the depth of the current xylem at breast height terminating the supply of current photosynthates to roots and their mycorrhizal fungi without physically disturbing the delicate root-microbe-soil system. Here we report that girdling reduced soil respiration within 1-2 months by about 54% relative to respiration on ungirdled control plots, and that decreases of up to 37% were detected within 5 days. These values clearly show that the flux of current assimilates to roots is a key driver of soil respiration; they are conservative estimates of root respiration, however, because girdling increased the use of starch reserves in the roots. Our results indicate that models of soil respiration should incorporate measures of photosynthesis and of seasonal patterns of photosynthate allocation to roots.
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| 7. |
- Persson, Jörgen, et al.
(författare)
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Nitrogen acquisition from inorganic and organic sources by boreal forest plants in the field
- 2003
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Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 137:2, s. 252-257
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Tidskriftsartikel (refereegranskat)abstract
- A wide range of recent studies have indicated that organic nitrogen may be of great importance to plant nitrogen (N) nutrition. Most of these studies have, however, been conducted in laboratory settings, excluding important factors for actual plant uptake, such as competition, mycorrhizal associations and soil interactions. In order to accurately evaluate the importance of different N compounds to plant N nutrition, field studies are crucial. In this study, we investigated short- as well as long-term plant nitrogen uptake by Deschampsia flexuosa, Picea abies and Vaccinium myrtillus from 15NO3-, 15NH4+ and (U-13C, 15N) arginine, glycine or peptides. Root N uptake was analysed after 6 h and 64 days following injections. Our results show that all three species, irrespective of their type of associated mycorrhiza (arbuscular, ecto- or ericoid, respectively) rapidly acquired similar amounts of N from the entire range of added N sources. After 64 days, P. abies and V. myrtillus had acquired similar amounts of N from all N sources, while for D. flexuosa, the uptake from all N sources except ammonium was significantly lower than that from nitrate. Furthermore, soil analyses indicate that glycine was rapidly decarboxylated after injections, while other organic compounds exhibited slower turnover. In all, these results suggest that a wide range of N compounds may be of importance for the N nutrition of these boreal forest plants, and that the type of mycorrhiza may be of great importance for N scavenging, but less important to the N uptake capacity of plants.
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| 8. |
- Abdurahman, Samir, 1965-, et al.
(författare)
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Isolation and characterization of a small antiretroviral molecule affecting HIV-1 capsid morphology
- 2009
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Ingår i: Retrovirology. - : Springer Science and Business Media LLC. - 1742-4690. ; 6, s. 34-
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Tidskriftsartikel (refereegranskat)abstract
- Background: Formation of an HIV-1 particle with a conical core structure is a prerequisite for the subsequent infectivity of the virus particle. We have previously described that glycineamide (G-NH2) when added to the culture medium of infected cells induces non-infectious HIV-1 particles with aberrant core structures. Results: Here we demonstrate that it is not G-NH2 itself but a metabolite thereof that displays antiviral activity. We show that conversion of G-NH2 to its antiviral metabolite is catalyzed by an enzyme present in bovine and porcine but surprisingly not in human serum. Structure determination by NMR suggested that the active G-NH2 metabolite was alpha-hydroxy-glycineamide (alpha-HGA). Chemically synthesized alpha-HGA inhibited HIV-1 replication to the same degree as G-NH2, unlike a number of other synthesized analogues of G-NH2 which had no effect on HIV-1 replication. Comparisons by capillary electrophoresis and HPLC of the metabolite with the chemically synthesized alpha-HGA further confirmed that the antiviral G-NH2-metabolite indeed was alpha-HGA. Conclusion: alpha-HGA has an unusually simple structure and a novel mechanism of antiviral action. Thus, alpha-HGA could be a lead for new antiviral substances belonging to a new class of anti-HIV drugs, i.e. capsid assembly inhibitors.
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| 9. |
- Alfsdotter, Clara, 1988-
(författare)
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Bad Death at Sandby borg : A Bioarchaeological Analysis of Intergroup Violence and Postmortem Agency of Unburied Corpses
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The subject of corpses from mass violence is surprisingly unexplored, even though the materiality of the corpse carries strong symbolic capital in conflicts. The aim of my PhD research is to create new knowledge about the implications of unburied corpses that stem from intergroup conflicts, and subsequently to add knowledge concerning how intergroup violence is organised to achieve desired social agendas.In the licentiate thesis presented here, I research the conditions for postmortem agency and how treatment of corpses can be studied in prehistory, specifically through the material remains of unburied corpses from the Sandby borg massacre. The Sandby borg case study is explored through a bioarchaeological perspective. Inside the Iron Age ringfort, the remains of at least 26 individuals have been recovered hitherto. Several of the dead display traces of lethal intergroup violence. By integrating osteology, archaeology, taphonomy and social theories, I show how bioarchaeological research can contribute to the understanding of past postmortem agency in relation to intergroup violence as a social process. The thesis is comprised of four articles.
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| 10. |
- Ali, Imran, et al.
(författare)
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Exposure to polychlorinated biphenyls and prostate cancer : population-based prospective cohort and experimental studies
- 2016
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Ingår i: Carcinogenesis. - : Oxford University Press. - 0143-3334 .- 1460-2180. ; 37:12, s. 1144-1151
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Tidskriftsartikel (refereegranskat)abstract
- Polychlorinated biphenyls (PCBs) are highly persistent environmental pollutants and are undesirable components of our daily food. PCBs are classified as human carcinogens, but the evidence for prostate cancer is limited and available data are inconsistent. We explored the link between non-dioxin-like PCB and grade of prostate cancer in a prospective cohort as well as in cell experiments. A population-based cohort of 32496 Swedish men aged 45-79 years was followed prospectively through 1998-2011, to assess the association between validated estimates of dietary PCB exposure and incidence of prostate cancer by grade (2789 cases, whereof 1276 low grade, 756 intermediate grade, 450 high grade) and prostate cancer mortality (357 fatal cases). In addition, we investigated a non-dioxin-like PCB153-induced cell invasion and related markers in normal prostate stem cells (WPE-stem) and in three different prostate cancer cell lines (PC3, DU145 and 22RV1) at exposure levels relevant to humans. After multivariable-adjustment, dietary PCB exposure was positively associated with high-grade prostate cancer, relative risk (RR) 1.35 [95% confidence interval (CI): 1.03-1.76] and with fatal prostate cancer, RR 1.43 (95% CI: 1.05-1.95), comparing the highest tertile with the lowest. We observed no association with low or intermediate grade of prostate cancer. Cell invasion and related markers, including MMP9, MMP2, Slug and Snail, were significantly increased in human prostate cancer cells as well as in prostate stem cells after exposure to PCB153. Our findings both from the observational and experimental studies suggest a role of non-dioxin-like PCB153 in the development of high-grade and fatal prostate cancer.
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