| 1. |
- Andresen, Louise C., et al.
(författare)
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Seasonal changes in nitrogen availability, and root and microbial uptake of (15)N(13)C(9)-phenylalanine and (15)N-ammonium in situ at a temperate heath
- 2011
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Ingår i: Applied Soil Ecology. - : Elsevier BV. - 0929-1393. ; 51, s. 94-101
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Tidskriftsartikel (refereegranskat)abstract
- In the plant biosynthesis of secondary compounds, phenylalanine is a precursor of condensed tannins. Tannins are deposited into the soil in plant root exudates and dead plant material and have been suggested to precipitate some soil nutrients and hence reduce nutrient availability for plants. Free amino acid, inorganic and microbial N concentration during the growing season was investigated in an ecosystem with a natural tannin chemosphere. The influence of tannins on the uptake of nitrogen in plants and microbes was followed by injecting tannic acid (TA), ammonium-(15)N and phenylalanine-(15)N/(13)C(9). Plants preferred ammonium over phenylalanine, while microbes had no preference. Soil microbes had a 77% uptake of intact phenylalanine. Phenylalanine was acquired intact by both grasses and Calluna, with 63% and 38% uptake of intact phenylalanine in grass fine roots and Calluna roots, respectively. Inorganic N and amino acid concentrations were lowest in the period with highest plant activity and grass root biomass but were unaffected by TA addition. (C) 2011 Elsevier B.V. All rights reserved.
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| 2. |
- Andresen, Louise C., et al.
(författare)
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Uptake of pulse injected nitrogen by soil microbes and mycorrhizal and non-mycorrhizal plants in a species-diverse subarctic heath ecosystem
- 2008
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Ingår i: Plant and Soil. - : Springer Science and Business Media LLC. - 0032-079X .- 1573-5036. ; 313:1-2, s. 283-295
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Tidskriftsartikel (refereegranskat)abstract
- N-15 labeled ammonium, glycine or glutamic acid was injected into subarctic heath soil in situ, with the purpose of investigating how the nitrogen added in these pulses was subsequently utilized and cycled in the ecosystem. We analyzed the acquisition of N-15 label in mycorrhizal and non-mycorrhizal plants and in soil microorganisms, in order to reveal probable differences in acquisition patterns between the two functional plant types and between plants and soil microorganisms. Three weeks after the label addition, with the N-15-forms added with same amount of nitrogen per square meter, we analyzed the N-15-enrichment in total soil, in soil K2SO4 (0.5 M) extracts and in the microbial biomass after vacuum-incubation of soil in chloroform and subsequent K2SO4 extraction. Furthermore the N-15-enrichment was analyzed in current years leaves of the dominant plant species sampled three, five and 21 days after label addition. The soil microorganisms had very high N-15 recovery from all the N sources compared to plants. Microorganisms incorporated most N-15 from the glutamic acid source, intermediate amounts of N-15 from the glycine source and least N-15 from the NH4+ source. In contrast to microorganisms, all ten investigated plant species generally acquired more N-15 label from the NH4+ source than from the amino acid sources. Non-mycorrhizal plant species showed higher concentration of N-15 label than mycorrhizal plant species 3 days after labeling, while 21 days after labeling their acquisition of N-15 label from amino acid injection was lower than, and the acquisition of N-15 label from NH4 injection was similar to that of the mycorrhizal species. We conclude that the soil microorganisms were more efficient than plants in acquiring pulses of nutrients which, under natural conditions, occur after e. g. freeze-thaw and dry rewet events, although of smaller size. It also appears that the mycorrhizal plants in the short term may be less efficient than non-mycorrhizal plants in nitrogen acquisition, but in a longer term show larger nitrogen acquisition than non-mycorrhizal plants. However, the differences in N-15 uptake patterns may also be due to differences in leaf longevity and woodiness between plant functional groups.
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| 3. |
- Callaghan, Terry V., et al.
(författare)
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Biodiversity, distributions and adaptations of arctic species in the context of environmental change
- 2004
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Ingår i: Ambio: a Journal of Human Environment. - : Royal Swedish Academy of Sciences. - 0044-7447. ; 33:7, s. 404-417
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Forskningsöversikt (refereegranskat)abstract
- The individual of a species is the basic unit which responds to climate and UV-B changes, and it responds over a wide range of time scales. The diversity of animal, plant and microbial species appears to be low in the Arctic, and decreases from the boreal forests to the polar deserts of the extreme North but primitive species are particularly abundant. This latitudinal decline is associated with an increase in super-dominant species that occupy a wide range of habitats. Climate warming is expected to reduce the abundance and restrict the ranges of such species and to affect species at their northern range boundaries more than in the South: some Arctic animal and plant specialists could face extinction. Species most likely to expand into tundra are boreal species that currently exist as outlier populations in the Arctic. Many plant species have characteristics that allow them to survive short snow-free growing seasons, low solar angles, permafrost and low soil temperatures, low nutrient availability and physical disturbance. Many of these characteristics are likely to limit species responses to climate warming, but mainly because of poor competitive ability compared with potential immigrant species. Terrestrial Arctic animals possess many adaptations that enable them to persist under a wide range of temperatures in the Arctic. Many escape unfavorable weather and resource shortage by winter dormancy or by migration. The biotic environment of Arctic animal species is relatively simple with few enemies, competitors, diseases, parasites and available food resources. Terrestrial Arctic animals are likely to be most vulnerable to warmer and drier summers, climatic changes that interfere with migration routes and staging areas, altered snow conditions and freeze-thaw cycles in winter, climate-induced disruption of the seasonal timing of reproduction and development, and influx of new competitors, predators, parasites and diseases. Arctic microorganisms are also well adapted to the Arctics climate: some can metabolize at temperatures down to -39degreesC. Cyanobacteria and algae have a wide range of adaptive strategies that allow them to avoid, or at least minimize UV injury. Microorganisms can tolerate most environmental conditions and they have short generation times which can facilitate rapid adaptation to new environments. In contrast, Arctic plant and animal species are very likely to change their distributions rather than evolve significantly in response to warming.
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| 4. |
- Callaghan, Terry V., et al.
(författare)
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Climate Change and UV-B Impacts on Arctic Tundra and Polar Desert Ecosystems: Key Findings and Extended Summaries
- 2004
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Ingår i: Ambio: a Journal of Human Environment. - 0044-7447. ; 33:7, s. 386-392
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Tidskriftsartikel (refereegranskat)abstract
- The Arctic has become an important region in which to assess the impacts of current climate variability and amplification of projected global warming. This is because i) the Arctic has experienced considerable warming in recent decades (an average of about 3°C and between 4° and 5°C over much of the landmass); i) climate projections suggest a continuation of the warming trend with an increase in mean annual temperatures of 4–5°C by 2080; ii) recent warming is already impacting the environment and economy of the Arctic and these impacts are expected to increase and affect also life style, culture and ecosystems; and iv) changes occurring in the Arctic are likely to affect other regions of the Earth, for example changes in snow, vegetation and sea ice are likely to affect the energy balance and ocean circulation at regional and even global scales (Chapter 1 in ref. 1). Responding to the urgent need to understand and project impacts of changes in climate and UV-B radiation on many facets of the Arctic, the Arctic Climate Impact Assessment (ACIA) (1) undertook a four-year study. Part of this study (1–10) assessed the impacts of changes in climate and UV-B radiation on Arctic terrestrial ecosystems, both those changes already occurring and those likely to occur in the future. Here, we present the key findings of the assessment of climate change impacts on tundra and polar desert ecosystems, and xtended summaries of its components.
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| 5. |
- Callaghan, Terry V., et al.
(författare)
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Effects of changes in climate on landscape and regional processes, and feedbacks to the climate system
- 2004
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Ingår i: Ambio: a Journal of Human Environment. - 0044-7447. ; 33:7, s. 459-468
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Forskningsöversikt (refereegranskat)abstract
- Biological and physical processes in the Arctic system operate at various temporal and spatial scales to impact large-scale feedbacks and interactions with the earth system. There are four main potential feedback mechanisms between the impacts of climate change on the Arctic and the global climate system: albedo, greenhouse gas emissions or uptake by ecosystems, greenhouse gas emissions from methane hydrates, and increased freshwater fluxes that could affect the thermohaline circulation. All these feedbacks are controlled to some extent by changes in ecosystem distribution and character and particularly by large-scale movement of vegetation zones. Indications from a few, full annual measurements of CO2 fluxes are that currently the source areas exceed sink areas in geographical distribution. The little available information on CH4 sources indicates that emissions at the landscape level are of great importance for the total greenhouse balance of the circumpolar North. Energy and water balances of Arctic landscapes are also important feedback mechanisms in a changing climate. Increasing density and spatial expansion of vegetation will cause a lowering of the albedo and more energy to be absorbed on the ground. This effect is likely to exceed the negative feedback of increased C sequestration in greater primary productivity resulting from the displacements of areas of polar desert by tundra, and areas of tundra by forest. The degradation of permafrost has complex consequences for trace gas dynamics. In areas of discontinuous permafrost, warming, will lead to a complete loss of the permafrost. Depending on local hydrological conditions this may in turn lead to a wetting or drying of the environment with subsequent implications for greenhouse gas fluxes. Overall, the complex interactions between processes contributing to feedbacks, variability over time and space in these processes, and insufficient data have generated considerable uncertainties in estimating the net effects of climate change on terrestrial feedbacks to the climate system. This uncertainty applies to magnitude, and even direction of some of the feedbacks.
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| 6. |
- Callaghan, Terry V., et al.
(författare)
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Effects on the structure of arctic ecosystems in the short- and long-term perspectives
- 2004
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Ingår i: Ambio: a Journal of Human Environment. - : Royal Swedish Academy of Sciences. - 0044-7447. ; 33:7, s. 436-447
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Forskningsöversikt (refereegranskat)abstract
- Species individualistic responses to warming and increased UV-B radiation are moderated by the responses of neighbors within communities, and trophic interactions within ecosystems. All of these responses lead to changes in ecosystem structure. Experimental manipulation of environmental factors expected to change at high latitudes showed that summer warming of tundra vegetation has generally led to smaller changes than fertilizer addition. Some of the factors manipulated have strong effects on the structure of Arctic ecosystems but the effects vary regionally, with the greatest response of plant and invertebrate communities being observed at the coldest locations. Arctic invertebrate communities are very likely to respond rapidly to warming whereas microbial biomass and nutrient stocks are more stable. Experimentally enhanced UV-B radiation altered the community composition of gram-negative bacteria and fungi, but not that of plants. Increased plant productivity due to warmer summers may dominate food-web dynamics. Trophic interactions of tundra and sub-Arctic forest plant-based food webs are centered on a few dominant animal species which often have cyclic population fluctuations that lead to extremely high peak abundances in some years. Population cycles of small rodents and insect defoliators such as the autumn moth affect the structure and diversity of tundra and forest-tundra vegetation and the viability of a number of specialist predators and parasites. Ice crusting in warmer winters is likely to reduce the accessibility of plant food to lemmings, while deep snow may protect them from snow-surface predators. In Fennoscandia, there is evidence already for a pronounced shift in small rodent community structure and dynamics that have resulted in a decline of predators that specialize in feeding on small rodents. Climate is also likely to alter the role of insect pests in the birch forest system: warmer winters may increase survival of eggs and expand the range of the insects. Insects that harass reindeer in the summer are also likely to become more widespread, abundant and active during warmer summers while refuges for reindeer/caribou on glaciers and late snow patches will probably disappear.
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| 7. |
- Callaghan, Terry V., et al.
(författare)
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Past changes in arctic terrestrial ecosystems, climate and UV radiation
- 2004
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Ingår i: Ambio: a Journal of Human Environment. - 0044-7447. ; 33:7, s. 398-403
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Tidskriftsartikel (refereegranskat)abstract
- At the last glacial maximum, vast ice sheets covered many continental areas. The beds of some shallow seas were exposed thereby connecting previously separated landmasses. Although some areas were ice-free and supported a flora and fauna, mean annual temperatures were 10-13degreesC colder than during the Holocene. Within a few millennia of the glacial maximum, deglaciation started, characterized by a series of climatic fluctuations between about 18 000 and 11 400 years ago. Following the general thermal maximum in the Holocene, there has been a modest overall cooling trend, superimposed upon which have been a series of millennial and centennial fluctuations in climate such as the "Little Ice Age spanning approximately the late 13th to early 19th centuries. Throughout the climatic fluctuations of the last 150 000 years, Arctic ecosystems and biota have been close to their minimum extent within the most recent 10 000 years. They suffered loss of diversity as a result of extinctions during the most recent large-magnitude rapid global warming at the end of the last glacial stage. Consequently, Arctic ecosystems and biota such as large vertebrates are already under pressure and are particularly vulnerable to current and projected future global warming. Evidence from the past indicates that the treeline will very as it probably advance, perhaps rapidly, into tundra areas, a it did during the early Holocene, reducing the extent of tundra and increasing the risk of species extinction. Species will very probably extend their ranges northwards, displacing Arctic species as in the past. However, unlike the early Holocene, when lower relative sea level allowed a belt of tundra to persist around at least some parts of the Arctic basin when treelines advanced to the present coast, sea level is very likely to rise in future, further restricting the area of tundra and other treeless Arctic ecosystems. The negative response of current Arctic ecosystems to global climatic conditions that are apparently without precedent during the Pleistocene is likely to be considerable, particularly as their exposure to co-occurring environmental changes (such as enhanced levels of UV-B, deposition of nitrogen compounds from the atmosphere, heavy metal and acidic pollution, radioactive contamination, increased habitat fragmentation) is also without precedent.
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| 8. |
- Callaghan, Terry V., et al.
(författare)
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Rationale, concepts and approach to the assessment
- 2004
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Ingår i: Ambio: a Journal of Human Environment. - 0044-7447. ; 33:7, s. 393-397
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Tidskriftsartikel (refereegranskat)abstract
- A general recognition that the Arctic will amplify global climate warming, that UV-B radiation may continue to increase there because of possible delays in the repair of stratospheric ozone, and that the Arctic environment and its peoples are likely to be particularly susceptible to such environmental changes stimulated an international assessment of climate change impacts. The Arctic Climate Impacts Assessment (ACIA) is a four-year study, culminating in publication of a major scientific report (1) as well as other products. In this paper and those following in this Ambio Special Issue, we present the findings of the section of the report that focuses on terrestrial ecosystems of the Arctic, from the treeline ecotone to the polar deserts. The Arctic is generally recognized as a treeless wilderness with cold winters and cool summers. However, definitions of the southern boundary vary according to environmental, geographical or political biases. This paper and the assessment in the following papers of this Ambio Special Issue focus on biota (plants, animals and microorganisms) and processes in the region beyond the northern limit of the closed forest (the taiga), but we also include processes south of this boundary that affect ecosystems in the Arctic. Examples are overwintering periods of migratory animals spent in the south and the regulation of the latitudinal treeline. The geographical area we have defined as the current Arctic is the area we use for developing scenarios of future impacts: Our geographical area of interest will not decrease under a scenario of the replacement of current Arctic tundra by boreal forests.
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| 9. |
- Callaghan, Terry V., et al.
(författare)
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Responses to projected changes in climate and UV-B at the species level
- 2004
-
Ingår i: Ambio: a Journal of Human Environment. - : Royal Swedish Academy of Sciences. - 0044-7447. ; 33:7, s. 418-435
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Forskningsöversikt (refereegranskat)abstract
- Environmental manipulation experiments showed that species respond individualistically to each environmental-change variable. The greatest responses of plants were generally to nutrient, particularly nitrogen, addition. Summer warming experiments showed that woody plant responses were dominant and that mosses and lichens became less abundant. Responses to warming were controlled by moisture availability and snow cover. Many invertebrates increased population growth in response to summer warming, as long as desiccation was not induced. CO2 and UV-B enrichment experiments showed that plant and animal responses were small. However, some microorganisms and species of fungi were sensitive to increased UV-B and some intensive mutagenic actions could, perhaps, lead to unexpected epidemic outbreaks. Tundra soil heating, CO 2 enrichment and amendment with mineral nutrients generally accelerated microbial activity. Algae are likely to dominate cyanobacteria in milder climates. Expected increases in winter freeze-thaw cycles leading to ice-crust formation are likely to severely reduce winter survival rate and disrupt the population dynamics of many terrestrial animals. A deeper snow cover is likely to restrict access to winter pastures by reindeer/caribou and their ability to flee from predators while any earlier onset of the snow-free period is likely to stimulate increased plant growth. Initial species responses to climate change might occur at the sub-species level: an Arctic plant or animal species with high genetic/racial diversity has proved an ability to adapt to different environmental conditions in the past and is likely to do so also in the future. Indigenous knowledge, air photographs, satellite images and monitoring show that changes in the distributions of some species are already occurring: Arctic vegetation is becoming more shrubby and more productive, there have been recent changes in the ranges of caribou, and "new" species of insects and birds previously associated with areas south of the treeline have been recorded. In contrast, almost all Arctic breeding bird species are declining and models predict further quite dramatic reductions of the populations of tundra birds due to warming. Species-climate response surface models predict potential future ranges of current Arctic species that are often markedly reduced and displaced northwards in response to warming. In contrast, invertebrates and microorganisms are very likely to quickly expand their ranges northwards into the Arctic.
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| 10. |
- Callaghan, Terry V., et al.
(författare)
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Synthesis of effects in four Arctic subregions
- 2004
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Ingår i: Ambio: a Journal of Human Environment. - : Royal Swedish Academy of Sciences. - 0044-7447. ; 33:7, s. 469-473
-
Tidskriftsartikel (refereegranskat)abstract
- An assessment of impacts on Arctic terrestrial ecosystems has emphasized geographical variability in responses of species and ecosystems to environmental change. This variability is usually associated with north-south gradients in climate, biodiversity, vegetation zones, and ecosystem structure and function. It is clear, however, that significant east-west variability in environment, ecosystem structure and function, environmental history, and recent climate variability is also important. Some areas have cooled while others have become warmer. Also, east-west differences between geographical barriers of oceans, archipelagos and mountains have contributed significantly in the past to the ability of species and vegetation zones to relocate in response to climate changes, and they have created the isolation necessary for genetic differentiation of populations and biodiversity hot-spots to occur. These barriers will also affect the ability of species to relocate during projected future warming. To include this east-west variability and also to strike a balance between overgeneralization and overspecialization, the ACIA identified four major sub regions based on large-scale differences in weather and climate-shaping factors. Drawing on information, mostly model output that can be related to the four ACIA subregions, it is evident that geographical barriers to species re-location, particularly the distribution of landmasses and separation by seas, will affect the northwards shift in vegetation zones. The geographical constraints-or facilitation-of northward movement of vegetation zones will affect the future storage and release of carbon, and the exchange of energy and water between biosphere and atmosphere. In addition, differences in the ability of vegetation zones to re-locate will affect the biodiversity associated with each zone while the number of species threatened by climate change varies greatly between subregions with a significant hot-spot in Beringia. Overall, the subregional synthesis demonstrates the difficulty of generalizing projections of responses of ecosystem structure and function species loss, and biospheric feedbacks to the climate system for the whole Arctic region and implies a need for a far greater understanding of the spatial variability in the responses of terrestrial arctic ecosystems to climate change.
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| 11. |
- Callaghan, Terry V., et al.
(författare)
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Uncertainties and recommendations
- 2004
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Ingår i: Ambio: a Journal of Human Environment. - : Royal Swedish Academy of Sciences. - 0044-7447. ; 33:7, s. 474-479
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Tidskriftsartikel (refereegranskat)abstract
- An assessment of the impacts of changes in climate and UV-B radiation on Arctic terrestrial ecosystems, made within the Arctic Climate Impacts Assessment (ACIA), highlighted the profound implications of projected warming in particular for future ecosystem services, biodiversity and feedbacks to climate. However, although our current understanding of ecological processes and changes driven by climate and UV-B is strong in some geographical areas and in some disciplines, it is weak in others. Even though recently the strength of our predictions has increased dramatically with increased research effort in the Arctic and the introduction of new technologies, our current understanding is still constrained by various uncertainties. The assessment is based on a range of approaches that each have uncertainties, and on data sets that are often far from complete. Uncertainties arise from methodologies and conceptual frameworks, from unpredictable surprises, from lack of validation of models, and from the use of particular scenarios, rather than predictions, of future greenhouse gas emissions and climates. Recommendations to reduce the uncertainties are wide-ranging and relate to all disciplines within the assessment. However, a repeated theme is the critical importance of achieving an adequate spatial and long-term coverage of experiments, observations and monitoring of environmental changes and their impacts throughout the sparsely populated and remote region that is the Arctic.
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| 12. |
- Cornelissen, Johannes H C, et al.
(författare)
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Global negative vegetation feedback to climate warming responses of leaf litter decomposition rates in cold biomes
- 2007
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 10:7, s. 619-627
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Tidskriftsartikel (refereegranskat)abstract
- Whether climate change will turn cold biomes from large long-term carbon sinks into sources is hotly debated because of the great potential for ecosystem-mediated feedbacks to global climate. Critical are the direction, magnitude and generality of climate responses of plant litter decomposition. Here, we present the first quantitative analysis of the major climate-change-related drivers of litter decomposition rates in cold northern biomes worldwide.Leaf litters collected from the predominant species in 33 global change manipulation experiments in circum-arctic-alpine ecosystems were incubated simultaneously in two contrasting arctic life zones. We demonstrate that longer-term, large-scale changes to leaf litter decomposition will be driven primarily by both direct warming effects and concomitant shifts in plant growth form composition, with a much smaller role for changes in litter quality within species. Specifically, the ongoing warming-induced expansion of shrubs with recalcitrant leaf litter across cold biomes would constitute a negative feedback to global warming. Depending on the strength of other (previously reported) positive feedbacks of shrub expansion on soil carbon turnover, this may partly counteract direct warming enhancement of litter decomposition.
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| 13. |
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| 14. |
- Engelbrecht Clemmensen, Karina, et al.
(författare)
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Site-dependent N uptake from N-form mixtures by arctic plants, soil microbes and ectomycorrhizal fungi
- 2008
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Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 1432-1939 .- 0029-8549. ; 155:4, s. 771-783
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedSoil microbes constitute an important control on nitrogen (N) turnover and retention in arctic ecosystems where N availability is the main constraint on primary production. Ectomycorrhizal (ECM) symbioses may facilitate plant competition for the specific N pools available in various arctic ecosystems. We report here our study on the N uptake patterns of coexisting plants and microbes at two tundra sites with contrasting dominance of the circumpolar ECM shrub Betula nana. We added equimolar mixtures of glycine-N, NH4+-N and NO3--N, with one N form labelled with N-15 at a time, and in the case of glycine, also labelled with C-13, either directly to the soil or to ECM fungal ingrowth bags. After 2 days, the vegetation contained 5.6, 7.7 and 9.1% (heath tundra) and 7.1, 14.3 and 12.5% (shrub tundra) of the glycine-, NH4+- and NO3--N-15, respectively, recovered in the plant-soil system, and the major part of N-15 in the soil was immobilized by microbes (chloroform fumigation-extraction). In the subsequent 24 days, microbial N turnover transferred about half of the immobilized N-15 to the non-extractable soil organic N pool, demonstrating that soil microbes played a major role in N turnover and retention in both tundra types. The ECM mycelial communities at the two tundras differed in N-form preferences, with a higher contribution of glycine to total N uptake at the heath tundra; however, the ECM mycelial communities at both sites strongly discriminated against NO3-. Betula nana did not directly reflect ECM mycelial N uptake, and we conclude that N uptake by ECM plants is modulated by the N uptake patterns of both fungal and plant components of the symbiosis and by competitive interactions in the soil. Our field study furthermore showed that intact free amino acids are potentially important N sources for arctic ECM fungi and plants as well as for soil microorganisms.
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| 15. |
- Guo, Yanfei, 1984, et al.
(författare)
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Frailty Trajectories in Chinese Older Adults : Evidence From the China Health and Retirement Longitudinal Study
- 2024
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Ingår i: Innovation in Aging. - : Oxford University Press. - 2399-5300. ; 8:1, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- Background and Objectives The individual heterogeneity in the progression of frailty has not been fully disclosed. Studies on frailty trajectories in Chinese older adults are rare and lack evidence suggesting that the frailty trajectories follow similar patterns to those in other countries. This study aims to identify distinct frailty trajectories in a nationwide cohort of community-dwelling older adults in China and explore the relationship between demographic, socioeconomic, and behavioral factors, and frailty trajectories.Research Design and Methods We included an analytical sample of 8,993 individuals aged 50 and older from the China Health and Retirement Longitudinal Study. We used group-based trajectory models to identify patterns of frailty trajectories over time. Multinomial logistic regression was used to estimate the relationship between demographic, socioeconomic, and behavioral factors, and group membership.Results Three frailty trajectories were identified: "Low and stable trajectory" (56.8% of the respondents), "Moderate and increasing trajectory" (34.4%), and "High and increasing trajectory" (8.8%). Older age (odds ratio [OR] = 7.37, 95% confidence interval [CI]: 5.90-9.20), being female (OR = 1.79, 95% CI: 1.42-2.27), no formal education (OR = 4.91, 95% CI: 2.33-10.36), living in rural areas (OR = 1.22, 95% CI: 1.01-1.47), low level of physical activity (OR = 2.65, 95% CI: 1.94-3.62), and residing in Northeast China (OR = 3.53, 95% CI: 2.56-4.88) were associated with the rapid progression of frailty, whereas moderate alcohol consumption appears to be associated with low and stable frailty trajectory (OR = 0.45, 95% CI: 0.35-0.58).Discussion and Implications The findings of the study emphasize a significant number of older adults with moderate and increasing as well as high and increasing frailty trajectories in China, which is cause for concern.
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| 16. |
- Hatem, Mohammed, et al.
(författare)
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Design of concrete mixes by systematic steps and ANN
- 2012
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Ingår i: Journal of Advanced Science and Engineering Research. - 2231-8844. ; 2:4, s. 232-251
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Tidskriftsartikel (refereegranskat)abstract
- The current research caters for the possibility of arriving at a system for designing concrete mixeseasily using available materials locally by specified wide ranges of pre-requisites of three mainprescribed properties to cover a good variety of practical mixes, which are water, water-cement ratioand total aggregate-cement ratio. Using these three properties, a tri-linear form was constructed bygraphical technique manner based on absolute volume approach. This approach defines as asummation of absolute volume for each of these three materials individually water, cement andaggregate should be equal to the absolute volume of whole concrete mixture based on thesealtogether. A quad-form area which includes a wide range of mixes can be formed from thisrepresentation. This area should achieve all the prescribed properties aforementioned. Artificial neuralnetwork concept used in this study also to build easily and quickly system which can be translatedinto Excel sheet. This system predict proportions of concrete mixture and the compressive strengthusing the results designed by the quad-form area method in addition to the data from literature around500 mixes based on local materials used in Iraq. Six input parameters (water to cement ratio, theslump, % of fine to total aggregate content, maximum aggregate size, fineness modulus of fineaggregate and the compressive strength) were used in this system to get the outputs. In addition, nineinput parameters ((water, cement, sand and gravel contents) and the properties of the mix (Finenessmodulus, W/C ratio, the slump, % of fine to total aggregate and the M.A.S)) were used as basis ofcompressive strength model. The algorithm of this system aimed to reduce the high number of trailmixes error as well as saving the labors, cost and time. Results indicated that the concrete mix designand the compressive strength model can be predicted accurately by using graphical perspective andthe ANN approach.
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| 17. |
- Hatem, Mohammed, et al.
(författare)
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Performance of Cement-poor Concrete with Different Superplasticizers
- 2014
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Ingår i: International Journal of Research and Reviews in Applied Sciences. - 2076-734X .- 2076-7366. ; 18:2, s. 163-172
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Tidskriftsartikel (refereegranskat)abstract
- Concrete can be used for casting plugs in deep boreholes where fracture zones are intersected. They will be exposed to flowing groundwater and be in contact with very tight seals of smectite clay installed where the surrounding rock is tight. The cast concrete must be able to carry the clay segments placed over it after a few days. Its bearing capacity does not have to be very high after that since the clay soon adheres to the rock and carries itself. The concrete must be poor in cement for minimizing the risk of creation of voids caused by dissolution of the cement and it should have “inert” aggregate of quartz-rich material. Inorganic superplasticizers instead of conventional organic ones should be used for eliminating the risk of degradation and loss by formation of colloids that can carry radionuclides to the biosphere from holes bored in repository rock. The two concrete types discussed in the present study had Portland and Merit 5000 low pH cement as binders and crushed quartzite as aggregate. Talc mineral powder and ordinary organic Glenium 51 were used as superplasticizers for comparing their impact on the physical properties. The matrix of the cement-poor talc concrete gave ductile behaviour during initial hardening. The very dense matrix of either of the concretes would not lead to compression of the system even after complete loss of cement, which will happen over a longer period of time. The overall conclusion was that talc as superplasticizer and conditioner of the concrete can make the concrete sufficiently fluid for constructing seals at depth in boreholes, and react with cement to provide high strength with some delay. pH is much lower in Merit than in Portland concrete, which causes less impact on the clay seals. Portland concrete has five times higher strength than Merit concrete after a week but three times lower strength after 28 days.
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| 18. |
- Hatem, Mohammed, et al.
(författare)
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Proportioning of cement-based grout for sealing fractured rock-use of packing models
- 2013
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Ingår i: Engineering. - : Scientific Research Publishing, Inc.. - 1947-3931 .- 1947-394X. ; 5:10, s. 765-774
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Tidskriftsartikel (refereegranskat)abstract
- Fractured, very permeable rock hosting repositories for radioactive waste will require grouting. New grout types of possible use where long-term performance is needed should have a small amount of cement for minimizing the increase in porosity that will follow from the ultimate dissolution and erosion of this component. They have to be low-viscous and gain strength early after injection and packing theory can assist designers in selecting suitable proportions of various grout components. Optimum particle packing means that the porosity is at minimum and that the amount of cement paste needed to fill the voids between aggregate particles is very small. Low porosity and microstructural stability must be guaranteed for long periods of time. Organic additives for reaching high fluidity cannot be used since they can give off colloids that carry released radionuclides and talc can be an alternative superplasticizer. Low-pH cement reacts with talc to give high strength with time while Portland cement gives early but limited strengthening. The clay mineral palygorskite can be used for early gelation because of its thixotropic properties. Once forced into the rock fractures or channels in soil it stiffens and serves as a filter that prevents fine particles to migrate through it be lost. However, its hydrophilic potential is too high to give the grout a high density and high strength. According to the experiments carried out most of the investigated grouts are injectable in fractures with apertures down to 100 μm.
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| 19. |
- Hatem, Mohammed, et al.
(författare)
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Rheological properties of low pH cement-palygorskite injection grout
- 2013
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Ingår i: Journal of Advanced Science and Engineering Research. - 2231-8844. ; 3:3, s. 167-192
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Tidskriftsartikel (refereegranskat)abstract
- The rheological properties of cementitious materials containing fine particles, such as mineral admixture were investigated using a Viso Star-L rheometer with cylindrical spindles. Selected features of the behavior of these materials are evaluated from a rheological perspective through literatures results for the past 30 years. One of the important factors that governs the ability of grout to penetrate fractures, channels and porous material is the rheology. The mineral admixture was clay palygorskite which can be used for early gelation because of its thixotropic properties as well as the powder quartz used as aggregate. The cementitious materials were designed and three recipes (MPG1, MPG2 and MPG3) were examined in this research by changing the mix proportions of the mineral admixture palygorskite and water content. For ensuring the accuracy of rheological measurement for the candidate’s grouts, necessary verification was been evaluated such as, influence of mixing time, stability and “time effect” to the accuracy of viscosity measurement, and yield stress as well as the physical properties at 3, 7 and 28 days. The results showed that grouts recipes with quartzite aggregate of different granulometry, are chemically compatible and fulfill the requirement of containing no organic matter. Candidate’s grouts found to satisfy the stable sedimentation criteria with sedimentation rates less than 5% after 2 hours. Furthermore, it was found that the grout recipe 3 followed by 1 showed lower yield stress and plastic viscosity which are (0.1 Pa and 0.269 Pas) and (0.288 Pa and 0.531 Pas) respectively.
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| 20. |
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| 21. |
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| 22. |
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| 23. |
- Jonasson, Sofia, et al.
(författare)
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Different effects of deep inspirations on central and peripheral airways in healthy and allergen-challenged mice
- 2008
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Ingår i: Respiratory Research. - : Springer Science and Business Media LLC. - 1465-9921 .- 1465-993X. ; 9:23
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Deep inspirations (DI) have bronchodilatory and bronchoprotective effects in healthy human subjects, but these effects appear to be absent in asthmatic lungs. We have characterized the effects of DI on lung mechanics during mechanical ventilation in healthy mice and in a murine model of acute and chronic airway inflammation. METHODS: Balb/c mice were sensitized to ovalbumin (OVA) and challenged with nebulized OVA for 1 week or 12 weeks. Control mice were challenged with PBS. Mice were randomly selected to receive DI, which was given twice during the minute before assessment of lung mechanics. RESULTS: DI protected against bronchoconstriction of central airways in healthy mice and in mice with acute airway inflammation, but not when OVA-induced chronic inflammation was present. DI reduced lung resistance induced by methacholine from 3.8+/-0.3 to 2.8+/-0.1 cmH2O*s*mL-1 in healthy mice and 5.1+/-0.3 to 3.5+/-0.3 cmH2O*s*mL-1 in acute airway inflammation (both P < 0.001). In healthy mice, DI reduced the maximum decrease in lung compliance from 15.9+/-1.5% to 5.6+/-0.6% (P < 0.0001). This protective effect was even more pronounced in mice with chronic inflammation where DI attenuated maximum decrease in compliance from 44.1+/-6.6% to 14.3+/-1.3% (P < 0.001). DI largely prevented increased peripheral tissue damping (G) and tissue elastance (H) in both healthy (G and H both P < 0.0001) and chronic allergen-treated animals (G and H both P < 0.0001). CONCLUSIONS: We have tested a mouse model of potential value for defining mechanisms and sites of action of DI in healthy and asthmatic human subjects. Our current results point to potent protective effects of DI on peripheral parts of chronically inflamed murine lungs and that presence of DI may blunt airway hyperreactivity.
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| 24. |
- Jonasson, Sven, et al.
(författare)
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Modeller för transport och spridning av föroreningar fas 2
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Grundvattenmodeller kan vara mycket kraftfulla verktyg för att beräkna och visualisera grundvattenflöde och föroreningstransport. I rätt sammanhang och rätt använda är grundvattenmodeller viktiga och kostnadseffektiva verktyg för att ta fram beslutsunderlag för riskbedömningar, åtgärdsförslag, projektering av efterbehandlingsåtgärder, etc. Föreliggande handledning syftar till att underlätta användning av modellverktyg för beskrivning av föroreningstransport med grundvatten, samt medverka till att höja kunskapsnivån så att dessa verktyg används på ett lämpligt sätt. Handledningen är programoberoende och har tagits fram för att ge handfasta råd för upprättande av modeller för simulering av föroreningstransport. Handledningen omfattar hela modelleringsprocessen, från de förberedande arbetena, själva upprättandet av modellen till avrapporteringen. Modelleringsprocessen tar sin början i problemformuleringen. Sedan följer upprättandet en konceptuell hydrogeologisk modell över det aktuella området. Den konceptuella modellen används som underlag vid skapande av den numeriska modellen. För detta arbete krävs en god förståelse geologiska förhållanden, anläggningar som ändrar de naturliga grundvattenflödena, områdets vattenbalans, grundvattennivåer, grundvattenflöden och vattenstånd i vattendrag och grundvattenkemisk karaktärisering. Numeriska beräkningsmodeller för beräkning av föroreningstransport kan göras på många olika sätt alltifrån relativt enkla till mycket komplexa modeller. Den numeriska flödesmodellen upprättas sedan i en programvara/-kod. Modellen lagerindelas på lämpligt sätt utifrån de geologiska förutsättningarna och avgränsas geografiskt utifrån de hydrauliska förutsättningarna genom ansättande av s k randvillkor. Baserat på vilken flödesmodell som utnyttjas kan sedan olika moduler kopplas på för att beräkna masstransporten av föroreningar som tar hänsyn till diffusion och dispersion, nedbrytning, kemiska reaktioner, avångning, sorptionsprocesser etc. Det är viktigt att modellen inte blir mer komplex än att den ger de svar som vi är ute efter. För att modellera och simulera ämnestransport i grundvatten krävs ett antal nödvändiga indata och kvalitet. Mängd och typ styr hur komplex modellen kan vara samt vilka resultat som kan förväntas från modelleringsarbetet. När modellen har upprättats skall den kalibreras och valideras. Kalibrering i egentlig betydelse innebär att man på ett objektivt sätt justerar modellen till dess att överensstämmelse mellan konstaterade förhållanden och av modellen predikterade förhållanden erhålls. För att värdera hur bra modellen är kalibrerad och överensstämmer med verkligheten bör den testas mot oberoende data. Det kan t ex vara från en annan tidsperiod eller från uppmätta nivåer eller flöden som ej använts för kalibreringen. Detta kallas validering. När väl detta är genomfört kan modellen användas för att beräkna föroreningstransport för olika scenarion och som beslutsunderlag för att miljökonsekvenser, åtgärdsförslag, kontrollprogram, etc.
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| 25. |
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| 26. |
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| 27. |
- Rinnan, Riikka, et al.
(författare)
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Effects of litter addition and warming on soil carbon, nutrient pools and microbial communities in a subarctic heath ecosystem
- 2008
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Ingår i: Applied Soil Ecology. - : Elsevier BV. - 0929-1393. ; 39:3, s. 271-281
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Tidskriftsartikel (refereegranskat)abstract
- Climatic warming leads to the expansion of deciduous shrubs and trees in the Arctic. This leads to higher leaf litter inputs, which together with warming may alter the rate of carbon and nutrient cycling in the arctic ecosystems. We assessed effects of factorial warming and additional litter on the soil ecosystem of a subarctic heath in a 7-year-long field experiment. Fine root biomass, dissolved organic carbon (DOC) and total C concentration increased in response to warming, which probably was a result of the increased vegetation cover. Litter addition increased the concentration of inorganic P in the uppermost 5 cm soil, while decreasing the pool of total P per unit area of the organic profile and having no significant effects on N concentrations or pools. Microbial biomass C and N were unaffected by the treatments, while the microbial biomass P increased significantly with litter addition. Soil ergosterol concentration was also slightly increased by the added litter in the uppermost soil, although not statistically significantly. According to a principal component analysis of the phospholipid fatty acid profiles, litter addition differed from the other treatments by increasing the relative proportion of biomarkers for Gram-positive bacteria. The combined warming plus litter addition treatment decreased the soil water content in the uppermost 5 cm soil, which was a likely reason for many interactions between the effects of warming and litter addition. The soil organic matter quality of the combined treatment was also clearly different from the control based on a near-infrared reflectance (NIR) spectroscopic analysis, implying that the treatment altered the composition of soil organic matter. However, it appears that the biological processes and the microbial community composition responded more to the soil and litter moisture conditions than to the change in the quality of the organic matter.
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| 28. |
- Rinnan, Riikka, et al.
(författare)
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Mineralization and carbon turnover in subarctic heath soil as affected by warming and additional litter
- 2007
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 39:12, s. 3014-3023
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Tidskriftsartikel (refereegranskat)abstract
- Arctic soil carbon (C) stocks are threatened by the rapidly advancing global warming. In addition to temperature, increasing amounts of leaf litter fall following from the expansion of deciduous shrubs and trees in northern ecosystems may alter biogeochemical cycling of C and nutrients. Our aim was to assess how factorial warming and litter addition in a long-term field experiment on a subarctic heath affect resource limitation of soil microbial communities (measured by thymidine and leucine incorporation techniques), net growing-season mineralization of nitrogen (N) and phosphorus (P), and carbon turnover (measured as changes in the pools during a growing-season-long field incubation of soil cores in situ). The mainly N limited bacterial communities had shifted slightly towards limitation by C and P in response to seven growing seasons of warming. This and the significantly increased bacterial growth rate under warming may partly explain the observed higher C loss from the warmed soil. This is furthermore consistent with the less dramatic increase in the contents of dissolved organic carbon (DOC) and dissolved organic N (DON) in the warmed soil than in the soil from ambient temperature during the field incubation. The added litter did not affect the carbon content, but it was a source of nutrients to the soil, and it also tended to increase bacterial growth rate and net mineralization of P. The inorganic N pool decreased during the field incubation of soil cores, especially in the separate warming and litter addition treatments, while gross mineralized N was immobilized in the biomass of microbes and plants transplanted into the incubates soil cores, but without any significant effect of the treatments. The effects of warming plus litter addition on bacterial growth rates and of warming on C and N transformations during field incubation suggest that microbial activity is an important control on the carbon balance of arctic soils under climate change.
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| 29. |
- Swedin, Linda, et al.
(författare)
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Dissociation of airway inflammation and hyperresponsiveness by cyxloogynease inhibition in allergen challenged mice
- 2009
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Ingår i: European Respiratory Journal. - : European Respiratory Society (ERS). - 0903-1936 .- 1399-3003. ; 34:1, s. 200-208
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the current study was to define how cyclooxygenase (COX)-activity affects airway hyperresponsiveness (AHR) and inflammation using interventions with COX inhibitors at different time points during allergen challenge and/or prior to measurement of AHR in an eosinophil-driven allergic mouse model. Inflammatory cells were assessed in bronchioalveolar lavage (BAL) and AHR was evaluated as the total lung resistance to methacholine (MCh) challenge. Administration of FR122047 (COX-1 inhibitor) during ovalbumin (OVA) challenge and prior to MCh challenge enhanced AHR without affecting the inflammatory cell response. In contrast, administration of lumiracoxib (COX-2 inhibitor) during the same time period had no effect on AHR but reduced the inflammatory cells in BAL. Nonselective COX inhibition with diclofenac both enhanced the AHR and reduced the inflammatory cells. Administration of diclofenac only during OVA challenge reduced the cells in BAL without any changes in AHR, whereas administration of diclofenac only prior to MCh challenge enhanced AHR but did not affect the cells in BAL. The present study implicates distinct roles of prostanoids generated along the COX-1 and COX-2 pathways and, furthermore, that inflammatory cells in BAL do not change in parallel with AHR. These findings support the fact that AHR and the inflammatory response are distinct and, at least in part, uncoupled events.
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| 30. |
- Tiveljung, Annika, et al.
(författare)
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Identification of Helicobacter in gastric biopsies by PCR based on 16S rDNA sequences: a matter of little significance for the prediction of H. pylori-associated gastritis?
- 1998
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Ingår i: Journal of Medical Microbiology. - : Microbiology Society. - 0022-2615 .- 1473-5644. ; 47:8, s. 695-704
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the present study was to correlate molecular evidence of the presence of Helicobacter pylori in gastric biopsy samples, based on analysis of 16S rDNA, vacuolating toxin (vacA), urease A (ureA) and cagA genes, with the clinical, histological and serological findings in patients with H. pylori-associated gastritis. Fresh biopsy samples were collected from the gastric antrum and corpus of 22 asymptomatic volunteers with or without H. pylori-associated gastritis. Total DNA was extracted from the biopsy material and subjected to 16S rDNA PCR amplification, Southern blotting and 16S rDNA sequence analysis of the PCR products. The vacA, ureA and cagA genes were characterised by PCR amplification and Southern blot analysis. Based on partial 16S rDNA sequence analysis, DNA belonging to the genus Helicobacter was detected in gastric biopsy samples from 20 of 22 subjects, including seven of nine histologically and serologically normal controls. Six of 20 partial 16S rDNA sequences revealed variations within variable regions V3 and V4 that deviated from those of the H. pylori type strain ATCC 4350T and, therefore, possibly represented other species of Helicobacter. VacA genes identical with those of the type strain were found predominantly in the subjects with H. pylori gastritis, and all the patients except one were found to be cagA-positive. There was no evidence of false positive PCR reactions. In conclusion, the PCR-based molecular typing methods used here were apparently too sensitive when applied to the detection of H. pylori in human gastric tissues. The lack of quantitative analysis makes them inappropriate as clinical tools for the diagnosis of H. pylori-associated gastritis, despite the fact that they provide a qualitative and sensitive tool for the detection and characterisation of H. pylori in the gastrointestinal tract.
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| 31. |
- von Brömssen, Mattias, et al.
(författare)
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Modeller för transport och spridning av föroreningar – fas 1 : Förstudie – Användning av numeriska beräkningsmodeller för beskrivning av transport och spridning av föroreningar i grundvatten
- 2006
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- rundvattenmodeller kan vara mycket kraftfulla verktyg att beräkna och visualisera grundvattenflöde och föroreningstransport, speciellt vid akvifärer med komplicerad geometri. I rätt sammanhang och rätt använda är grundvattenmodeller viktiga och kostnadseffektiva verktyg för att ta fram beslutsunderlag beträffande olika grundvatten- och föroreningsfrågor. Detta gäller särskilt där skyddsobjekten är stora, tydliga och värdefulla. Idag saknas emellertid kunskap och indata för att allmänt i Sverige med hjälp av befintliga numeriska beräkningsmodeller, med precision kvantifiera och prediktera transport av föroreningar i grundvatten. Föreliggande rapport syftar till att beskriva den erfarenhet och kunskap om sådan modellering, för svenska förhållanden, som finns i ”branschen” och vid universiteten. Dessutom föreslås en metodik för användningen av dessa modeller i samband med miljöriskbedömningar för förorenade områden samt så redovisas ett protokoll för hur osäkerheter kan beskrivas. Vidare föreslås ett antal rekommendationer för fortsatta arbeten inom ämnesområdet i Sverige. För att få en bild av statusläget i Sverige utfördes intervjuer med ca 25 nyckelpersoner med direkt erfarenhet i ämnet. Ett mindre antal aktörer i Danmark, Finland och Norge kontaktades även för att erhålla underlag för en syntes av statusen i respektive land. Utöver detta genomfördes en litteratursökning av svenska erfarenheter av modellering av föroreningsspridning med grundvatten under svenska förhållanden.Sammanfattningsvis kan sägas att många aktörer använder grundvattenmodeller vid projekt med anknytning till förorenad mark. Detta sker dock oftast på ett kraftigt förenklat sätt. Det är vanligt att använda enbart en flödesmodell, samt partikelspårning. Masstransportmodeller används i princip bara i FoU-projekt och för hypotetiska scenarion (där man inte behöver eller kan kalibrera) eller alternativt mycket stora projekt. Oftast tvingas man bortse från heterogeniteter i förenklade modeller. Osäkerheter hanteras sällan systematiskt men ofta genom en förenklad känslighetsanalys. Sveriges geologi med tämligen små avrinningsområden och akvifärer, begränsad användning av grundvatten för kommunalt dricksvatten, liksom svårigheter att kommunicera mervärden med uppdragsgivare synes vara orsaker till en begränsad användning av grundvattenmodeller i Sverige. Olika mervärden är förknippade med grundvattenmodeller såsom att man kan pröva hypoteser samt att man tvingas skapa en vattenbalans för systemet. Oväntade simuleringsresultat erhålls relativt frekvent. Detta torde vara ett mervärde då detta tyder på att utan användning av modellen skulle relevant information ha förbigåtts. Modeller anses även vara mycket pedagogiska för redovisning av resultat. I andra länder (t.ex. Danmark) har nyttan av modeller varit mer uppenbar och därför har modeller kommit mer till användning. Erfarenhetsvärden på de olika parametrar som behövs vid masstransportmodellering efterfrågas av många aktörer. Även baskunskaper om dessa processer samt hantering av heterogeniteter och parameterisering efterfrågas. Det finns även ett stort behov av erfarenhetsspridning och – återföring beträffande grundvattenmodellering i allmänhet och transportmodellering i synnerhet. Vidare saknas lättanvänt kalibreringsverktyg eller protokoll. Protokollet bör innehålla information om vad man behöver för typ av information i relation till olika osäkerheter. Det bedöms inte nödvändigt att utveckla (särskild) generell programkod i Sverige för de vanliga tillämpningarna i branschen.
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