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1.
  • Lembrechts, Jonas J., et al. (författare)
  • SoilTemp : A global database of near-surface temperature
  • 2020
  • Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 26:11, s. 6616-6629
  • Tidskriftsartikel (refereegranskat)abstract
    • Current analyses and predictions of spatially explicit patterns and processes in ecology most often rely on climate data interpolated from standardized weather stations. This interpolated climate data represents long-term average thermal conditions at coarse spatial resolutions only. Hence, many climate-forcing factors that operate at fine spatiotemporal resolutions are overlooked. This is particularly important in relation to effects of observation height (e.g. vegetation, snow and soil characteristics) and in habitats varying in their exposure to radiation, moisture and wind (e.g. topography, radiative forcing or cold-air pooling). Since organisms living close to the ground relate more strongly to these microclimatic conditions than to free-air temperatures, microclimatic ground and near-surface data are needed to provide realistic forecasts of the fate of such organisms under anthropogenic climate change, as well as of the functioning of the ecosystems they live in. To fill this critical gap, we highlight a call for temperature time series submissions to SoilTemp, a geospatial database initiative compiling soil and near-surface temperature data from all over the world. Currently, this database contains time series from 7,538 temperature sensors from 51 countries across all key biomes. The database will pave the way toward an improved global understanding of microclimate and bridge the gap between the available climate data and the climate at fine spatiotemporal resolutions relevant to most organisms and ecosystem processes.
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2.
  • Björkman, Anne, 1981, et al. (författare)
  • Plant functional trait change across a warming tundra biome
  • 2018
  • Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 562:7725, s. 57-62
  • Tidskriftsartikel (refereegranskat)abstract
    • The tundra is warming more rapidly than any other biome on Earth, and the potential ramifications are far-reaching because of global feedback effects between vegetation and climate. A better understanding of how environmental factors shape plant structure and function is crucial for predicting the consequences of environmental change for ecosystem functioning. Here we explore the biome-wide relationships between temperature, moisture and seven key plant functional traits both across space and over three decades of warming at 117 tundra locations. Spatial temperature–trait relationships were generally strong but soil moisture had a marked influence on the strength and direction of these relationships, highlighting the potentially important influence of changes in water availability on future trait shifts in tundra plant communities. Community height increased with warming across all sites over the past three decades, but other traits lagged far behind predicted rates of change. Our findings highlight the challenge of using space-for-time substitution to predict the functional consequences of future warming and suggest that functions that are tied closely to plant height will experience the most rapid change. They also reveal the strength with which environmental factors shape biotic communities at the coldest extremes of the planet and will help to improve projections of functional changes in tundra ecosystems with climate warming.
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3.
  • Björkman, Anne, 1981, et al. (författare)
  • Tundra Trait Team: A database of plant traits spanning the tundra biome
  • 2018
  • Ingår i: Global Ecology and Biogeography. - : Wiley. - 1466-822X .- 1466-8238. ; 27:12, s. 1402-1411
  • Tidskriftsartikel (refereegranskat)abstract
    • © 2018 The Authors Global Ecology and Biogeography Published by John Wiley & Sons Ltd Motivation: The Tundra Trait Team (TTT) database includes field-based measurements of key traits related to plant form and function at multiple sites across the tundra biome. This dataset can be used to address theoretical questions about plant strategy and trade-offs, trait–environment relationships and environmental filtering, and trait variation across spatial scales, to validate satellite data, and to inform Earth system model parameters. Main types of variable contained: The database contains 91,970 measurements of 18 plant traits. The most frequently measured traits (>1,000 observations each) include plant height, leaf area, specific leaf area, leaf fresh and dry mass, leaf dry matter content, leaf nitrogen, carbon and phosphorus content, leaf C:N and N:P, seed mass, and stem specific density. Spatial location and grain: Measurements were collected in tundra habitats in both the Northern and Southern Hemispheres, including Arctic sites in Alaska, Canada, Greenland, Fennoscandia and Siberia, alpine sites in the European Alps, Colorado Rockies, Caucasus, Ural Mountains, Pyrenees, Australian Alps, and Central Otago Mountains (New Zealand), and sub-Antarctic Marion Island. More than 99% of observations are georeferenced. Time period and grain: All data were collected between 1964 and 2018. A small number of sites have repeated trait measurements at two or more time periods. Major taxa and level of measurement: Trait measurements were made on 978 terrestrial vascular plant species growing in tundra habitats. Most observations are on individuals (86%), while the remainder represent plot or site means or maximums per species. Software format: csv file and GitHub repository with data cleaning scripts in R; contribution to TRY plant trait database (www.try-db.org) to be included in the next version release.
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4.
  • Cavieres, Lohengrin A., et al. (författare)
  • Facilitative plant interactions and climate simultaneously drive alpine plant diversity
  • 2014
  • Ingår i: Ecology Letters. - : Wiley. - 1461-0248 .- 1461-023X. ; 17:2, s. 193-202
  • Tidskriftsartikel (refereegranskat)abstract
    • Interactions among species determine local-scale diversity, but local interactions are thought to have minor effects at larger scales. However, quantitative comparisons of the importance of biotic interactions relative to other drivers are rarely made at larger scales. Using a data set spanning 78 sites and five continents, we assessed the relative importance of biotic interactions and climate in determining plant diversity in alpine ecosystems dominated by nurse-plant cushion species. Climate variables related with water balance showed the highest correlation with richness at the global scale. Strikingly, although the effect of cushion species on diversity was lower than that of climate, its contribution was still substantial. In particular, cushion species enhanced species richness more in systems with inherently impoverished local diversity. Nurse species appear to act as a ‘safety net’ sustaining diversity under harsh conditions, demonstrating that climate and species interactions should be integrated when predicting future biodiversity effects of climate change.
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5.
  • Elmendorf, Sarah C., et al. (författare)
  • Global assessment of experimental climate warming on tundra vegetation : heterogeneity over space and time
  • 2012
  • Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 15:2, s. 164-175
  • Forskningsöversikt (refereegranskat)abstract
    • Understanding the sensitivity of tundra vegetation to climate warming is critical to forecasting future biodiversity and vegetation feedbacks to climate. In situ warming experiments accelerate climate change on a small scale to forecast responses of local plant communities. Limitations of this approach include the apparent site-specificity of results and uncertainty about the power of short-term studies to anticipate longer term change. We address these issues with a synthesis of 61 experimental warming studies, of up to 20 years duration, in tundra sites worldwide. The response of plant groups to warming often differed with ambient summer temperature, soil moisture and experimental duration. Shrubs increased with warming only where ambient temperature was high, whereas graminoids increased primarily in the coldest study sites. Linear increases in effect size over time were frequently observed. There was little indication of saturating or accelerating effects, as would be predicted if negative or positive vegetation feedbacks were common. These results indicate that tundra vegetation exhibits strong regional variation in response to warming, and that in vulnerable regions, cumulative effects of long-term warming on tundra vegetation and associated ecosystem consequences have the potential to be much greater than we have observed to date.
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6.
  • Elmendorf, Sarah C., et al. (författare)
  • Plot-scale evidence of tundra vegetation change and links to recent summer warming
  • 2012
  • Ingår i: Nature Climate Change. - : Nature Publishing Group. - 1758-678X .- 1758-6798. ; 2:6, s. 453-457
  • Tidskriftsartikel (refereegranskat)abstract
    • Temperature is increasing at unprecedented rates across most of the tundra biome. Remote-sensing data indicate that contemporary climate warming has already resulted in increased productivity over much of the Arctic, but plot-based evidence for vegetation transformation is not widespread. We analysed change in tundra vegetation surveyed between 1980 and 2010 in 158 plant communities spread across 46 locations.We found biome-wide trends of increased height of the plant canopy and maximum observed plant height for most vascular growth forms; increased abundance of litter; increased abundance of evergreen, low-growing and tall shrubs; and decreased abundance of bare ground. Intersite comparisons indicated an association between the degree of summer warming and change in vascular plant abundance, with shrubs, forbs and rushes increasing with warming. However, the association was dependent on the climate zone, the moisture regime and the presence of permafrost. Our data provide plot-scale evidence linking changes in vascular plant abundance to local summer warming in widely dispersed tundra locations across the globe.
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7.
  • Elphinstone, Cassandra, et al. (författare)
  • Multiple Pleistocene refugia for Arctic Bell-Heather revealed with genomic analyses of modern and historic plants
  • 2024
  • Ingår i: Journal of Biogeography. - 0305-0270 .- 1365-2699.
  • Tidskriftsartikel (refereegranskat)abstract
    • Aim: Arctic plants survived the Pleistocene glaciations in unglaciated refugia. The number, ages, and locations of these refugia are often unclear. We use high-resolution genomic data from present-day and Little-Ice-Age populations of Arctic Bell-Heather to re-evaluate the biogeography of this species and determine whether it had multiple independent refugia or a single refugium in Beringia. Location: Circumpolar Arctic and Coastal British Columbia (BC) alpine. Taxon: Cassiope tetragona L., subspecies saximontana and tetragona, outgroup C. mertensiana (Ericaceae). Methods: We built genotyping-by-sequencing (GBS) libraries using Cassiope tetragona tissue from 36 Arctic locations, including two ~250- to 500-year-old populations collected under glacial ice on Ellesmere Island, Canada. We assembled a de novo GBS reference to call variants. Population structure, genetic diversity and demography were inferred from PCA, ADMIXTURE, fastsimcoal2, SplitsTree, and several population genomics statistics. Results: Population structure analyses identified 4–5 clusters that align with geographic locations. Nucleotide diversity was highest in Beringia and decreased eastwards across Canada. Demographic coalescent analyses dated the following splits with Alaska: BC subspecies saximontana (5 mya), Russia (~1.4 mya), Europe (>200–600 kya), and Greenland (~60 kya). Northern Canada populations appear to have formed during the current interglacial (7–9 kya). Admixture analyses show genetic variants from Alaska appear more frequently in present-day than historic plants on Ellesmere Island. Conclusions: Population and demographic analyses support BC, Alaska, Russia, Europe and Greenland as all having had independent Pleistocene refugia. Northern Canadian populations appear to be founded during the current interglacial with genetic contributions from Alaska, Europe and Greenland. We found evidence, on Ellesmere Island, for continued recent gene flow in the last 250–500 years. These results suggest that a re-analysis of other Arctic species with shallow population structure using higher resolution genomic markers and demographic analyses may help reveal deeper structure and other circumpolar glacial refugia.
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8.
  • Hasselmann, Julien, et al. (författare)
  • Inguinal Vascular Surgical Wound Protection by Incisional Negative Pressure Wound Therapy : A Randomized Controlled Trial-INVIPS Trial
  • 2020
  • Ingår i: Annals of Surgery. - 1528-1140. ; 271:1, s. 48-53
  • Tidskriftsartikel (refereegranskat)abstract
    • OBJECTIVE: A randomized controlled trial (RCT) was undertaken to determine the effect of negative pressure wound therapy (NPWT) on closed incisions after inguinal vascular surgery regarding surgical site infections (SSIs) and other wound complications. BACKGROUND: SSIs are a major concern in open vascular procedures involving the inguinal region. Prophylactic NPWT on closed incisions has shown promising results, but the quality of evidence can be debated. This study aims to objectively evaluate whether NPWT on sutured inguinal incisions after elective vascular surgery can decrease the incidence of surgical site complications. METHODS: One hundred thirty-nine patients undergoing elective open vascular surgery with inguinal incisions received either NPWT or a standard dressing. Patients with bilateral incisions randomly received a dressing on one incision and the opposite dressing on the other. The primary endpoints were SSI or other wound complications at 3 months, assessed by wound care experts blinded to the treatment arm and using objective wound assessment criteria (ASEPSIS-score). Statistical analysis was performed on an intention-to-treat basis and obtained P values from analyses in the uni- and bilateral groups were combined to an overall P value using Fisher's method for combining P values. RESULTS: The incidence of SSI was reduced in the NPWT group compared with the control group [11.9% vs 29.5% in the unilateral group (n = 120), 5.3% vs 26.3% in the bilateral group (n = 19), respectively; combined P = 0.02]. No differences regarding other surgical site complications were observed between the groups. CONCLUSION: NPWT on closed inguinal vascular surgical incisions in elective patients reduces the incidence of SSI.
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9.
  • Hasselmann, Julien, et al. (författare)
  • Proposed Classification of Incision Complications: Analysis of a Prospective Study on Elective Open Lower - Limb Revascularization.
  • 2020
  • Ingår i: Surgical Infections. - : Mary Ann Liebert Inc. - 1557-8674 .- 1096-2964. ; 21:4, s. 384-390
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: Incision complications (IC) have a significant impact on procedure-related morbidity after lower-limb revascularization. One of the most studied IC is surgical site infection (SSI). Reporting these complications in a uniform way is crucial to evaluate treatment approaches. The aim of this study was to propose a comprehensive classification of IC and apply it to compare SSI with other IC in a trial on elective open lower-limb revascularization procedures. Methods: Two hundred twenty-three eligible patients undergoing elective unilateral inguinal and infra-inguinal arterial vascular surgery were extracted from a randomized controlled trial on incisional negative-pressure wound therapy (NPWT) on inguinal vascular surgical incisions. The IC were classified by grades of severity (grade 0-6) that focused on IC-related consequences such as out-patient treatment (grade 1), prolonged in-patient treatment (grade 2), re-admission (grade 3), and re-operation (grade ≥4). An SSI was defined by the ASEPSIS score criteria. Results: An SSI was diagnosed in 63 patients (28.3%). Thirty-five of 160 patients (21.8%) not suffering from SSI underwent IC treatment. Treatment for IC was recorded for 25/144 patients (17.4%) with satisfactory site healing as judged by the ASEPSIS score. The median incision-related in-hospital stay in those with SSI (n = 79) and disturbed healing (n = 16) according to the ASEPSIS score was 13 days in both groups (p = 0.53). Five patients had peri-vascular SSI (IC grade 4 n = 4; grade 5 n = 1). The proposed classification of IC and the ASEPSIS score correlated highly (r = 0.77; p < 0.001). Inter-rater reliability for IC grading was substantial for three investigators with different levels of experience (k = 0.81, 0.71, and 0.70). Conclusions: The proposed incision classification suggests a comparable clinical significance of vascular IC in terms of IC-related in-patient stay, whether there was a surgical site infection or not. This classification system requires external validation.
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10.
  • Henry, Greg H.R., et al. (författare)
  • The International Tundra Experiment (ITEX): 30 years of research on tundra ecosystems
  • 2022
  • Ingår i: Arctic Science. - : Canadian Science Publishing. - 2368-7460. ; 8:3, s. 550-571
  • Tidskriftsartikel (refereegranskat)abstract
    • The International Tundra Experiment (ITEX) was founded in 1990 as a network of scientists studying responses of tundra ecosystems to ambient and experimental climate change at Arctic and alpine sites across the globe. Common measurement and experimental design protocols have facilitated synthesis of results across sites to gain biome-wide insights of climate change impacts on tundra. This special issue presents results from more than 30 years of ITEX research. The importance of snow regimes, bryophytes, and herbivory are highlighted, with new protocols and studies proposed. The increasing frequency and magnitude of extreme climate events is shown to have strong effects on plant reproduction. The most consistent plant trait response across sites is an increase in vegetation height, especially for shrubs. This will affect surface energy balance, carbon and nutrient dynamics and trophic level interactions. Common garden studies show adaptation responses in tundra species to climate change but they are species and regionally specific. Recommendations are made including establishing sites near northern communities to increase reciprocal engagement with local knowledge holders and establishing multi-factor experiments. The success of ITEX is based on collegial cooperation among researchers and the network remains focused on documenting and understanding impacts of environmental change on tundra ecosystems.
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11.
  • Kikvidze, Zaal, et al. (författare)
  • The effects of foundation species on community assembly: a global study on alpine cushion plant communities
  • 2015
  • Ingår i: Ecology. - : Ecological Society of America. - 0012-9658. ; 96:8, s. 2064-2069
  • Tidskriftsartikel (refereegranskat)abstract
    • Foundation species can change plant community structure by modulating important ecological processes such as community assembly, yet this topic is poorly understood. In alpine systems, cushion plants commonly act as foundation species by ameliorating local conditions. Here, we analyze diversity patterns of species' assembly within cushions and in adjacent surrounding open substrates (83 sites across five continents) calculating floristic dissimilarity between replicate plots, and using linear models to analyze relationships between microhabitats and species diversity. Floristic dissimilarity did not change across biogeographic regions, but was consistently lower in the cushions than in the open microhabitat. Cushion plants appear to enable recruitment of many relatively stress-intolerant species that otherwise would not establish in these communities, yet the niche space constructed by cushion plants supports a more homogeneous composition of species than the niche space beyond the cushion's influence. As a result, cushion plants support higher α-diversity and a larger species pool, but harbor assemblies with lower ?-diversity than open microhabitats. We conclude that habitats with and without dominant foundation species can strongly differ in the processes that drive species recruitment, and thus the relationship between local and regional species diversity.
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12.
  • Prevéy, Janet S., et al. (författare)
  • The tundra phenology database: more than two decades of tundra phenology responses to climate change
  • 2022
  • Ingår i: Arctic Science. - : Canadian Science Publishing. - 2368-7460. ; 8:3, s. 1026-1039
  • Tidskriftsartikel (refereegranskat)abstract
    • Observations of changes in phenology have provided some of the strongest signals of the effects of climate change on terrestrial ecosystems. The International Tundra Experiment (ITEX), initiated in the early 1990s, established a common protocol to measure plant phenology in tundra study areas across the globe. Today, this valuable collec-tion of phenology measurements depicts the responses of plants at the colder extremes of our planet to experimental and ambient changes in temperature over the past decades. The database contains 150 434 phenology observations of 278 plant species taken at 28 study areas for periods of 1–26 years. Here we describe the full data set to increase the visibility and use of these data in global analyses and to invite phenology data contributions from underrepresented tundra locations. Portions of this tundra phenology database have been used in three recent syntheses, some data sets are expanded, others are from entirely new study areas, and the entirety of these data are now available at the Polar Data Catalogue (https://doi.org/10.21963/13215).
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13.
  • Svensson Björk, Robert, et al. (författare)
  • Negative Pressure Wound Therapy for the Prevention of Surgical Site Infections Using Fascia Closure After EVAR-A Randomized Trial
  • 2022
  • Ingår i: World Journal of Surgery. - : Springer. - 0364-2313 .- 1432-2323. ; 46:12, s. 3111-3120
  • Tidskriftsartikel (refereegranskat)abstract
    • Background Surgical site infections (SSI) in the groin after vascular surgery are common. The aim of the study was to evaluate the effect of negative pressure wound therapy (NPWT) on SSI incidence when applied on closed inguinal incisions after endovascular aneurysm repair (EVAR). Methods A multicenter randomized controlled trial (RCT). Between November 2013 and December 2020, 377 incisions (336 bilateral and 41 unilateral) from elective EVAR procedures with the primary intent of fascia closure were randomized and included, receiving either NPWT or a standard dressing. In bilateral incisions, each incision randomly received the opposite dressing of the other side, thereby becoming each others control. The primary endpoint was SSI incidence at 90 days postoperatively, analyzed on an intention-to-treat basis. Uni and bilaterally operated incisions were analyzed separately, and their respective p-values combined using Fishers method for combining P-values. Study protocol (NCT01913132). Results The SSI incidence at 90 days postoperatively in bilateral incisions was 1.8% (n = 3/168) in the NPWT and 4.8% (n = 8/168) in the standard dressing group, and in unilateral incisions 13.3% (n = 2/15) and 11.5% (n = 3/26), respectively (combined p = 0.49). In all SSIs, bacteria were isolated from incisional wound cultures. No additional SSIs were diagnosed between 90 days and 1 year follow-up. Conclusions No evidence of difference in SSI incidence was seen in these low-risk inguinal incisions when comparing NPWT with standard dressings after EVAR with the primary intent of fascia closure.
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14.
  • Ahlberg, Erik, et al. (författare)
  • "Vi klimatforskare stödjer Greta och skolungdomarna"
  • 2019
  • Ingår i: Dagens nyheter (DN debatt). - 1101-2447.
  • Tidskriftsartikel (populärvet., debatt m.m.)abstract
    • DN DEBATT 15/3. Sedan industrialiseringens början har vi använt omkring fyra femtedelar av den mängd fossilt kol som får förbrännas för att vi ska klara Parisavtalet. Vi har bara en femtedel kvar och det är bråttom att kraftigt reducera utsläppen. Det har Greta Thunberg och de strejkande ungdomarna förstått. Därför stödjer vi deras krav, skriver 270 klimatforskare.
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15.
  • Andresen, Louise C., 1974, et al. (författare)
  • Free amino acids in the rhizosphere
  • 2014
  • Ingår i: 19th European Nitrogen Cycle Meeting. September 10-12th 2014, Gent, Belgium.
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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16.
  • Andresen, Louise C., 1974, et al. (författare)
  • Patterns of free amino acids in tundra soils reflect mycorrhizal type, shrubification, and warming
  • 2022
  • Ingår i: Mycorrhiza. - : Springer Science and Business Media LLC. - 0940-6360 .- 1432-1890. ; 32:3-4, s. 305-313
  • Tidskriftsartikel (refereegranskat)abstract
    • The soil nitrogen (N) cycle in cold terrestrial ecosystems is slow and organically bound N is an important source of N for plants in these ecosystems. Many plant species can take up free amino acids from these infertile soils, either directly or indirectly via their mycorrhizal fungi. We hypothesized that plant community changes and local plant community differences will alter the soil free amino acid pool and composition; and that long-term warming could enhance this effect. To test this, we studied the composition of extractable free amino acids at five separate heath, meadow, and bog locations in subarctic and alpine Scandinavia, with long-term (13 to 24 years) warming manipulations. The plant communities all included a mixture of ecto-, ericoid-, and arbuscular mycorrhizal plant species. Vegetation dominated by grasses and forbs with arbuscular and non-mycorrhizal associations showed highest soil free amino acid content, distinguishing them from the sites dominated by shrubs with ecto- and ericoid-mycorrhizal associations. Warming increased shrub and decreased moss cover at two sites, and by using redundancy analysis, we found that altered soil free amino acid composition was related to this plant cover change. From this, we conclude that the mycorrhizal type is important in controlling soil N cycling and that expansion of shrubs with ectomycorrhiza (and to some extent ericoid mycorrhiza) can help retain N within the ecosystems by tightening the N cycle.
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17.
  • Antonsson, Henrik, 1976, et al. (författare)
  • Nurse plant effect of the cushion plant Silene acaulis (L.) Jacq. in an alpine environment in the subarctic Scandes, Sweden
  • 2009
  • Ingår i: Plant Ecology & Diversity. - : Informa UK Limited. - 1755-0874 .- 1755-1668. ; 2:1, s. 17-25
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: Facilitation plays important roles in the structuring of plant communities and several studies have found that it tends to increase with environmental severity in alpine plant communities. In addition, cushion plants have been shown to act as nurse plants, moderating extreme environmental conditions, and providing resources for other species, with substantial effects on local plant diversity. Aims: This study addresses the nurse plant effects of Silene acaulis – a common, circumpolar alpine plant species with a compact cushion-forming growth form – along an altitude transect in the mid- to high-alpine zones in northern Sweden. Methods: The numbers of species in paired S. acaulis cushions and identical-sized control plots along an altitude transect between 1150 m and 1450 m above sea level were compared, and differences in species composition were analysed. Results: At altitudes above c. 1280 m, but not at lower altitudes, more species were found inside the cushions than in their paired control plots. Species composition was similar inside cushions and in control plots. Conclusions: Our results suggest that S. acaulis acts as a nurse plant at altitudes higher than a certain threshold (c. 1280 m at the investigated site). It appears to play an important role in creating focal points for local vascular plant diversity in highalpine environments, where vegetation is open and occurs in small patches. Keywords: facilitation; plant-to-plant interactions; Silene acaulis; species richness; stress
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18.
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19.
  • Beylich, Achim A., et al. (författare)
  • Selection of critical key test catchments
  • 2007
  • Ingår i: In: Beylich AA and Warburton J, eds. Analysis of Source-to-Sink-Fluxes and Sediment Budgets in Changing High-Latitude and High-Altitude Cold Environments: SEDIFLUX Manual, First Edition.. - Trondheim : Geological Survey of Norway.
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)
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20.
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21.
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22.
  • Björk, Joakim, et al. (författare)
  • Analysis of Coordinated HVDC Control for Power Oscillation Damping
  • 2018
  • Ingår i: Conference Record of the 3rd IEEE International Workshop on Electronic Power Grid, eGrid 2018. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781538676653 ; , s. 19-24
  • Konferensbidrag (refereegranskat)abstract
    • Controlling the active power of high-voltage de (HVDC) transmission that interconnects two asynchronous ac grids can be used to improve the power oscillation damping in both of the interconnected ac systems. Using one HVDC link, achievable performance are limited since control actions may excite modes of similar frequencies in the assisting network. However, with coordinated control of two or more HVDC links, the limitations can be circumvented. With decoupling control the system interactions can be avoided all together. This paper investigates the conditions suitable for decoupling control. It is also shown that decoupling between system modes can be achieved using a proportional controller. The control method is compared to decentralized and H-2 optimal control. The best control method for different system topologies is investigated by looking on input usage and stability following dc link failure.
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23.
  • Björk, Linnea, et al. (författare)
  • Amino-Acid Side-Chain Nanoarchitectonics for Tuning the Chiroptical Properties and Supramolecular Structure of Pentameric Oligothiophenes
  • 2024
  • Ingår i: ChemPhotoChem. - : WILEY-V C H VERLAG GMBH. - 2367-0932.
  • Tidskriftsartikel (refereegranskat)abstract
    • Oligothiophenes with specific photophysical properties and molecular organization are of great interest, since this class of materials are used in organic electronics and bioelectronics, as well as biosensing. Herein, 8 different pentameric oligothiophenes, denoted proteophenes, with different amino acid substitution patterns at distinct positions along the thiophene backbone were investigated. Spectroscopic and microscopic studies of the ligands revealed the formation of optically active self-assembled materials under acidic or basic conditions. The distinct photophysical characteristics, including induced circular dichroism, as well as the supramolecular structures of the assemblies deduced from light scattering and transmission electron microscopy, were highly influenced by the positioning of distinct amino acid moieties along the thiophene backbone. Proteophenes functionalized with only glutamate residues or these functionalities in combination with hydrophobic valine moieties formed fibrillar structures with excellent chiroptical properties under acidic conditions. In addition, the amino acid functionality at the beta-position of distinct thiophene moieties influenced the induced circular dichroism pattern observed from the proteophenes. Overall, the obtained results demonstrate how changes in the position of various amino acid functionalities, as well as the chemical nature of the amino acid side chain functionality greatly affect the optical properties as well as the architecture of the self-assembled materials. Self-assembled Proteophenes. Oligothiophenes with distinct amino acid side-chain functionalities along the conjugated backbone displayed distinct chiroptical and structural properties in acidic or alkaline solutions. The distinct photophysical characteristics, as well as the supramolecular structures of the assemblies were highly influenced by the chemical nature of the amino acid, as well as the positioning of distinct amino acid moieties along the thiophene backbone.image
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24.
  • Björk, Robert G., 1974, et al. (författare)
  • A Climate Change aspect on root dynamics and nitrogen partitioning in a tundra landscape
  • 2005
  • Ingår i: Sediment budgets and rates of sediment transfer across cold environments in Europe. 3rd Workshop of the ESF Network SEDIFLUX, Durham, UK, 15 – 19 December 2005..
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • The Arctic Climate Impact Assessment (ACIA) recently reported that Arctic is rapidly changing due to Climate Change. Likewise, the mountains of Europe are going to experience large shifts in plant composition and 41-56% of the alpine species might be on the edge of extinction according to the 1st synthesis of the Global Observation Research Initiative in Alpine Environments (GLORIA). Although the tundra ecosystems are subjected to dramatical changes as a result of Climate Change, there is little knowledge of the effect on root dynamics and its implication on the nitrifying and denitrifying microbial community. Here, we compare nitrification enzyme activity (NEA) and denitrification enzyme activity (DEA) rates along an altitudinal gradient with the effects of climatic warming using Open Top Chambers (OTCs) in consideration with root dynamics and architecture. This study was conducted at Latnjajaure Field Station (LFS) located in the midalpine region in northern Sweden. LFS is the Swedish field site for the International Tundra Experiment (ITEX), established in 1993. This gives an opportunity to investigate long-term effects of climatic warming by OTCs and an altitudinal gradient (1000m to 1365m), both within a very small geographical range. The OTCs used at LFS increases the soil surface temperature by approximately 1.5ºC whereas air temperatures normally falls with 0.6ºC with every hundred meter of increased altitude. To analyse the NEA and DEA we used an anaerobic incubation technique, based on acetylene inhibition technique, resulting in N2O as the only end product, which then were analysed by gas chromatography. Soil cores were additionally sampled in the OTCs to study the effects of climatic warming on the root system. The specific root length, root length density and root biomass were determined for the different root fractions. The results from NEA and DEA contradict each other. The gradient study show decreased NEA and DEA rates with falling altitude, whereas the warming experiment show a slight non significant increase due to the temperature enhancement by OTCs. The preliminary results from the root sampling indicate that there is a plant community specific response in root architecture, which has an output on root biomass and particularly in the fraction of fine roots, although, climatic warming did not have any significant affect on the root biomass. The fact that altitudinal temperature decline did not reduce NEA and DEA rates might in part be explained of the variables measured here, although they are not conclusive.
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25.
  • Björk, Robert G., 1974, et al. (författare)
  • Biocomplexity and biogeochemical cycling in terrestrial ecosystems
  • 2008
  • Ingår i: 1st Workshop and planning meeting ‘Winter processes in arctic tundra ecosystems’, Longyearbyen, Svalbard, 9-11 June 2008..
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • The activities concerted within Tellus are aiming at adding essential knowledge to the system scale aspects of fluxes and transformation of carbon (C) in the terrestrial domain. The systems studied are the Arctic, the alpine area of the Scandes, and organic soils in southern Sweden (including both forest and agricultural systems). The main research sites are Skogaryd, in the boreal forest, and Latnjajaure Field Station in the western Abisko Mountains. The overall aim with the present work at Skogaryd is to increase our fundamental understanding of process involved in cycling of C and nitrogen (N) in forest ecosystems, and generate high quality data on C/N cycle from drained forested organic soils using micrometeorological methods, laser and automatic chambers techniques. Skogaryd is also included in NitroEurope, an EU project focusing on modelling and up-scaling of greenhouse gas fluxes, and is incorporated in two interdisciplinary research centres at University of Gothenburg, Tellus (http://www.tellus.science.gu.se/english/) and Gothenburg Atmospheric Science Centre (GAC; http://www.chalmers.se/gmv/gac-en/). Furthermore, our research group has been instrumental in the establishment of the International Tundra Experiment (ITEX) network by Professor Ulf Molau who chaired ITEX 1992-1996 and Latnjajaure Field Station have been a master site within the network since 1992. As an outcome, much of the research in Latnjajaure during the 90ies was focused plant responsiveness to global change. However, since 2002 the research has expanded and projects are now running that are dealing with snow-vegetation-soil interactions. Recently, a collaboration with Dr. Elisabeth J. Cooper, of the University Centre in Svalbard (UNIS), and Prof. Bo Elberling, University of Copenhagen, was initiated focusing on winter soil respiration and comparing sub-arctic and high-arctic trace gas fluxes. Currently, we have these projects running in tundra ecosystems: 1.Climate-related changes in tundra ecosystems – An IPY project (PIs Björk and Molau with others). 2.Temporal pattern of CO2, CH4 and N2O fluxes and soil microbial structure in snow-covered ecosystems (PIs Björk, Elberling, Klemedtsson, and Cooper). 3.The responsiveness of tundra ecosystems to warming: linking above- and below-ground components (PI Björk). There is also a project under evaluation by the Swedish Research Council, which are entitled ‘The fate of carbon in high-arctic tundra ecosystems under changing snow cover conditions’. The research questions that we want to address within this winter ecology network are 1) to increase our understand of the C dynamics (thus explicitly linking ecosystem C sequestration pattern and soil microbial dynamics) in tundra ecosystems, and, particularly, (2) to improve the winter resolution of carbon dioxide (and other greenhouse gases) effluxes to the atmosphere. Furthermore, (3) to understand the influence of changing snow cover, both in depth and duration, for the C dynamics in tundra ecosystems.
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26.
  • Björk, Robert G., 1974, et al. (författare)
  • Can present melt-out patterns identify snowbed plant species vulnerable to climate change?
  • 2005
  • Ingår i: Second International Conference on Arctic Research Planning – ICARP II, Copenhagen, Denmark, 10 – 12 November 2005..
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Snowbeds form in topographic depressions which accumulate high amounts of snow during the winter months and the final snowmelt does not occur until late in the growing season. Many species preferentially grow in snowbed habitats and some of these are even limited to habitats in which winter snow accumulates. In connection with the Global Warming forecast, snowbed ecosystems of alpine Europe are regarded as particularly vulnerable in IPCC’s 2001 assessment report. This study is running at Latnjajaure Field Station, in northern Swedish Lapland, where four snowbed plant communi¬ties are studied. The snowbeds are of the “moderate type”, which means that they are melting out before the end of July, and they are situated in both heath and meadow sites. In this study we try to identify vulnerable plant species by the use of snow dynamics and plant community structure. Snowbed plant communi¬ties have high abundances of bryophytes along with high bryophyte diversity, 55 identified bryophytes within the snowbeds. The dominant bryophytes (e.g. Kiaeria stakei, Polytrichastrum sexangulare, Sanionia nivalis, Anthelia juratzkana, Scapania obcordata) are also snowbed specialist. The preliminary results show that earlier melt-out day will increase the vascular plant cover by 0.8 percent per day as well as increase in lichen cover by 0.5 percent per day. Bryophytes will suffer the most by decreasing in abundance by 1.7 percent per day of earlier melt-out day. Although, the response among bryophyte species is not uniform with Kiaeria stakei having the large decrease followed by Anthelia juratzkana, whereas Polytrichastrum sexangulare does not respond at all. There is also interaction among bryophyte species.
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27.
  • Björk, Robert G., 1974, et al. (författare)
  • Climate-related soil changes in tundra ecosystems at Latnjajaure, northern Sweden – an ITEX-IPY project
  • 2010
  • Ingår i: International Polar Year Oslo Science Conference.
  • Konferensbidrag (refereegranskat)abstract
    • During the 90'ies, the International Tundra Experiment (ITEX) was established as a leading project in arctic and alpine ecology, and has become a model for many later network establishments. The present study capitalizes on the early efforts of ITEX and aims at assessing ecosystem changes in the alpine areas of northern Sweden above timberline, i.e. the tundra, in relation to global change. By using the "old" ITEX plots established during the early years of the program we have measured ecosystem respiration (ER), the Normalized Difference Vegetation Index, and nitrogen (N) mineralization over the growing season. In addition, have soil samples been taken to quantify changes in the carbon (C) and N pool, including 13C and 15N. After 12 to 15 years of open top chamber (OTC) treatment no statistical effect was found on the soil temperature (10 cm soil depth), although the was an overall increase in all OTC by +0.2°C. However, the soil moisture decreased significantly by 3-14%, depending on plant community, in the OTCs compared to ambient conditions. Preliminary, there was a 20-37% non-significant higher mean ER in the OTC compared to the ambient plots over the growing season. Furthermore, the OTC treatment did not affect the growing season mineralization of inorganic N, or total C and N content of the soil. The stable isotope data showed both enrichment and depletion as a consequence of the OTC treatment, but no general pattern was discerned. Thus, this non-significant higher ER is most likely of plant origin than soil, as the plant standing biomass has increased in the OTCs. This study does not support the current consensus that tundra soils will alter their C and N dynamics in response to climate change.
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28.
  • Björk, Robert G., 1974, et al. (författare)
  • Contrasting effects of wood ash application on microbial community structure, biomass and processes in drained forested peatlands
  • 2010
  • Ingår i: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 73:3, s. 550-562
  • Tidskriftsartikel (refereegranskat)abstract
    • The effects of wood ash application on soil microbial processes were investigated in three drained forested peatlands, which differed in nutrient status and time since application. Measured variables included concentrations of soil elements and phospholipid fatty acids (PLFAs), net nitrogen mineralisation, nitrification and denitrification enzyme activity, potential methane oxidation, methane production and microbial respiration kinetics. Wood ash application had a considerable influence on soil element concentrations. This mirrored a decrease in the majority of the microbial biomarkers by more than one-third in the two oligotrophic peatlands, although microbial community composition was not altered. The decreases in PLFAs coincided with reduced net ammonification and net nitrogen mineralisation. Other measured variables did not change systematically as a result of wood ash application. No significant changes in microbial biomass or processes were found in the mesotrophic peatland, possibly because too little time (1 year) had elapsed since the wood ash application. This study suggests that oligotrophic peatlands can be substantially affected by wood ash for a period of at least four years after application. However, within 25 years of the wood ash application, the microbial biomass seemed to have recovered or adapted to enhanced element concentrations in the soil.
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29.
  • Björk, Robert G., 1974, et al. (författare)
  • Ecology of Alpine Snowbeds and the Impact of Global Change
  • 2007
  • Ingår i: Arctic, Antarctic, and Alpine Research. ; 39:1
  • Recension (övrigt vetenskapligt/konstnärligt)abstract
    • The ecosystems of alpine snowbed habitats are reviewed with emphasis on ecosystem functioning and capability to adapt to current and predicted global change. Snowbeds form in topographic depressions that accumulate large amounts of snow during the winter months, and the final snowmelt does not occur until late in the growing season. Many species preferentially grow in snowbed habitats and some of these are even restricted to these habitats. In this review we identify several ecosystem services which snowbeds provide to the alpine landscape. For instance, snowbeds provide a steady water and nutrient supply to adjacent plant communities and offer newly emerged high-quality food for herbivores late in the growing season. We also propose that alpine snowbeds are much more productive than earlier thought, especially when the very short growing season and often high grazing pressure are taken fully into account. Furthermore, we propose that bryophytes and graminoids (grasses, sedges, and rushes) probably will be most negatively impacted by global change, and the snowbed plant communities will be invaded by species from adjacent plant communities, especially by shrubs and boreal species. As snowbed plants have special growth conditions, their sensitivity and ability to respond rapidly to changes in annual snowfall patterns make snowbed communities particularly vulnerable in a warmer climate, and thereby sensitive indicators of global change
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30.
  • Björk, Robert G., 1974 (författare)
  • Ectomycorrhizal mycelia production in a forested peatland: effects on greenhouse gas fluxes
  • 2012
  • Ingår i: 4th COST meeting ‘Belowground carbon in European forest’, Antalya, Turkey, 28–31 October 2012.
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • The role of ectomycorrhizal fungi in key ecosystem processes such as C sequestration and greenhouse gas (GHG) fluxes is surprisingly poorly understood, even though they are undoubtedly of major significance. In this study we have measured the production and isotopic signature of extramatrical mycelium (EMM) of mycorrhizal fungi since 2007 using in-growth mesh bags. We also conducted a trenching experiment, where 50 µm (permit EMM but not roots) or 1 µm (excludes both EMM and roots) mesh was used. Soil respiration was measured using an automatic chamber system, and nitrous oxide (N2O) and methane (CH4) using a closed chamber technique. In general, the EMM production in the peat soil was low compared to other soils, but also varied much between years (from 0.03 to 4.09 g C m-2). The EMM production was also 2 to 6 times higher in the top 10 cm compared to 10-20 cm soil depth depending of year. Over the growing season the EMM production peaked in August, a few weeks before the main sporocarp season. The mycelial delta values also varied with several ‰ within season as well as between years. Interestingly, the δ15N but not the δ13C of the mycelia changed with depth and the differences relative to the SOM were inconsistent. Although the EMM production in the peat soil is low it had a major impact on GHG emissions from the soil. In 2009, the contribution from autotrophic mycelia respiration was 10% of the annual CO2 emissions, while autotrophic root respiration contributed with 23%. This means that 2/3 of the annual CO2 emissions are originated from heterotrophic respiration at this site. For N2O, the exclusion of roots alone did not affect N2O emissions, the simultaneous exclusion of roots and mycorrhizal mycelia doubled N2O emissions, compared to the control plots. The results of the study emphasize the importance of ectomycorrhiza in regulating GHG emissions from forested organic soils.
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31.
  • Björk, Robert G., 1974, et al. (författare)
  • Effect of reduced below-ground C sequestration on greenhouse gas fluxes within dry tundra ecosystems along an altitudinal gradient
  • 2008
  • Ingår i: Mountain soils under a changing climate and land-use, Birmensdorf, Switzerland, 6–8 March 2008..
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • It has been suggested that global climate change will have a great impact on arctic and alpine areas, affecting the carbon and nitrogen dynamics in these ecosystems. Temperature are widely thought to be the main limiting factors for plants and microorganisms in these tundra ecosystem, and warming the soil in high latitude tundra have been shown to change trace gas (CO2, CH4, and N2O) exchange rates and increase N availability. However, little attention has been paid, to date, to variations in trace gas fluxes with altitude, although it is a key determinant of temperature and should therefore be strongly correlated with these fluxes if temperature is the main variable affecting these processes. The objectives of this study were, therefore, to measure growing season variation in carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes from heath plant communities along an altitudinal gradient ranging from mid alpine (~950 m a.s.l) to high alpine (~1,365 m a.s.l) zones within an alpine tundra landscape in the subarctic region of Sweden. Furthermore, by reducing the C supply to the root system and mycorrhizal fungi (achieved by clipping the above-ground plant parts) we wanted to decrease the rhizosphere priming effect and thereby change the C sequestration pattern within the ecosystem to be able to separate heterotrophic and root respiration. The study was conducted on the slopes of Mt. Latnjatjårro (1,447 m; 68°21’N, 18°31’E), near Latnjajaure Field Station, 16 km west of Abisko in Northern Sweden. Flux measurements of CO2 were analysed using a portable infra red gas analyser (IRGA) based on the SBA-4 OEM CO2 Analyzer (PP System). Fluxes of CH4 and N2O were sampled using a closed chamber system, where chambers were placed at collars, which were gently pressed into the ground. Air from the chamber was circulated into a headspace bottle and analysed by gas chromatograph. A two-step incubation technique was also used to determine Nitrification Enzyme Activity (NEA) for analysing nitrification in acid soils with low activities, and for Denitrification Enzyme Activity (DEA) an anaerobic incubation technique, based on acetylene inhibition of the N2O-reductase, was used. Preliminary, our results show a decrease in average growing season CO2 efflux with altitude, but not constantly, and although soil temperature in general decreased with altitude there were no perfect fit between soil temperature and average growing season CO2 efflux. Furthermore, the clipping of the above-ground plant parts reduced the CO2 efflux at all altitudes, except at 1,225 m a.s.l., and in August the reduction in CO2 efflux was largest at 950 m a.s.l. (231 mg CO2 m-2 h-1) and decreased with altitude (to 33 mg CO2 m-2 h-1 at 1,365 m a.s.l). However, the proportion of the reduced CO2 efflux, corresponding to root respiration, was relatively constant with altitude (28-43% of total respiration), except at 1,365 m a.s.l where the root respiration only contributed with 12%. The fluxes of CH4 and N2O was very low with poor resolution of the fluxes due to many samples had a flux lower than the limit of detection for the gas chromatograph, thus no particularly pattern was discerned. However, to try to improve the resolution along the altitudinal gradient the NEA and DEA was used and give a potential measure on the nitrification and denitrification rates, which goes back to the actual populations of nitrifiers and denitrifiers in the soil. The results shows that there were a substantial increases with altitude in the activities of nitrifying and denitrifying microbes, this is contrary to expectations and the average growing season CO2 efflux if the decline in mean annual temperature with altitude is the main driver for nitrification and denitrification. Thus, our results are just indicative for the complex interaction that may occur along altitudinal gradients. But, clearly, there is a need for further studies to assess the effects of altitude and temperature on carbon and nitrogen dynamics in high alpine and arctic ecosystems across wide altitudinal ranges.
  •  
32.
  • Björk, Robert G., 1974, et al. (författare)
  • Effect of reduced below-ground C sequestration on greenhouse gas fluxes within dry tundra ecosystems along an altitudinal gradient
  • 2008
  • Ingår i: The 15th ITEX workshop, Reykjavik, Iceland, 9–12 October 2008..
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • It has been suggested that global climate change will have a great impact on arctic and alpine areas, affecting the carbon and nitrogen dynamics in these ecosystems. Temperature is widely thought to be the main limiting factor for plants and microorganisms in these tundra ecosystems, and warming the soil in high latitude tundra has been shown to change trace gas (CO2, CH4, and N2O) exchange rates and increase N availability. However, little attention has been paid, to date, to variations in trace gas fluxes with altitude, although altitude is a key determinant of temperature and should therefore be strongly correlated with these fluxes if temperature is a major variable affecting these processes. The objectives of this study were, therefore, to measure growing season variation in carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes from heath plant communities along an altitudinal gradient ranging from mid alpine (~950 m a.s.l) to high alpine (~1,365 m a.s.l) zones within an alpine tundra landscape in the subarctic region of Sweden. Furthermore, by reducing the C supply to the root system and mycorrhizal fungi (achieved by clipping the above-ground plant parts) we wanted to decrease the rhizosphere priming effect and thereby change the C sequestration pattern within the ecosystem to be able to separate heterotrophic and autotrophic respiration. The study was conducted on the slopes of Mt. Latnjatjårro (1,447 m a.s.l.; 68°21’N, 18°31’E), near Latnjajaure Field Station, 16 km west of Abisko in Northern Sweden. Flux measurements of CO2 were analysed using a portable infra red gas analyser (IRGA) based on the SBA-4 OEM CO2 Analyzer (PP System). Fluxes of CH4 and N2O were sampled using a closed chamber system, where chambers were placed on collars, which were gently pressed into the ground. Air from the chamber was circulated into a headspace bottle and analysed by gas chromatograph. A two-step incubation technique was also used to determine Nitrification Enzyme Activity (NEA) for analysing nitrification in acid soils with low activities, and for Denitrification Enzyme Activity (DEA) an anaerobic incubation technique, based on acetylene inhibition of the N2O-reductase, was used. Our results show a decrease in average growing season CO2 efflux with altitude, but not consistently, and although soil temperature in general decreased with altitude there was only a loose association between soil temperature and average growing season CO2 efflux. Furthermore, the clipping of the above-ground plant parts reduced the CO2 efflux at all altitudes, except at 1,225 m a.s.l., and in August the reduction in CO2 efflux was largest at 950 m a.s.l. (231 mg CO2 m-2 h-1) and decreased with altitude (to 33 mg CO2 m-2 h-1 at 1,365 m a.s.l.). However, the proportion of the reduced CO2 efflux, corresponding to autotrophic respiration, was relatively constant with altitude (28-43% of total respiration), except at 1,365 m a.s.l. where the autotrophic respiration only contributed 12%. The fluxes of CH4 and N2O were very low, and resolution was constrained by the large number of samples with apparent fluxes below the limit of detection for the gas chromatograph, thus no particular pattern could be identified. However, to try to improve the resolution along the altitudinal gradient, the NEA and DEA were used, and give a potential measure of the nitrification and denitrification rates, which goes back to the actual populations of nitrifiers and denitrifiers in the soil. The results show that there were a substantial increases with altitude in the activities of nitrifying and denitrifying microbes; this is contrary to expectations and the average growing season CO2 efflux if the decline in mean annual temperature with altitude is the main driver for nitrification and denitrification. Thus, our results are indicative of the complex interaction that may occur along altitudinal gradients. But, clearly, there is a need for further studies to assess the effects of altitude and temperature on carbon and nitrogen dynamics in high alpine and arctic ecosystems across wide altitudinal ranges.
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33.
  • Björk, Robert G., 1974, et al. (författare)
  • Extramatrical mycelia production and turnover in two drained Norway spruce forests
  • 2010
  • Ingår i: 1st COST meeting ‘Belowground carbon in Europeanforest’, Birmensdorf, Switzerland, 26–28 January 2010..
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Root systems form important associations with fungi, so called mycorrhiza, which in spruce forests are dominated by ectomycorrhiza. Ectomycorrhizal fungi is functionally important in water and nutrient capture, and therefore probably have major influence on the overall ecosystem functioning. In addition to transferring water and nutrient to its host plant the fungus receive photosynthetic C. The extramatrical mycelium (EMM) is thereby an important sink for carbon in boreal forests, but estimation of the actual EMM production is rare. The objective was to quantify the annual and seasonal production and turnover of EMM in two drained coniferous soils. The study was conducted in two Norway spruce stands at Skogaryd Research Forest, southwest Sweden. One of the sites was a mineral soil (“the mineral site”), with high organic content, and affor-ested in 1962. The other site was a peat soil of minerotrophic origin (“the peat site”), drained in the 1870s and afforested in 1951. In-growth tubes (10-20 cm long) were used to estimate EMM production and turnover through sequential harvesting during 2007-2009. Preliminary results show a higher EMM production at the mineral site than at the peat site. At the peat site the annual EMM production varied largely between years, 0.1-10.1 gdw m-2 (no annual data are currently available for the mineral site). Interestingly, a significant EMM production from December to 15th of June at the mineral site was found, most likely occurring during late May-early June. How-ever, the major EMM production (21-53 mg m-2 d-1) occurred mid-August to mid-September at both sites. It was not possible to calculate an EMM turnover the first two years due to the large spatial vari-ability. Our study suggests that high EMM production coincides with fine root production, and can equal one-fourth of belowground production. However, the large spatial variability in EMM production accentuates the need to increase within sub-site replication.
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34.
  • Björk, Robert G., 1974, et al. (författare)
  • ITEX at Latnjajaure
  • 2007
  • Ingår i: The 14th ITEX workshop, Falls Creek, Victoria, Australia, 2–6 February 2007..
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • ITEX and ITEX-related research at Latnjajaure in northern Swedish Lapland has been quite diverse during the past few years, with most emphasis at the ecosystem and landscape scales. The basic warming experiment with open-top chambers and control plots is still running in a variety of ecosystems since 1993. During 2006, a re-inventory of OTCs and controls in Eriophorum vaginatum (cottongrass) dominated tussock tundra at the outlet of the lake showed significant changes since the last point-framing in 1995, not only in the OTCs but also in the control plots. No species were lost but dominance relationships among species had changed dramatically. The underlying permafrost had degraded substantially; it was continuous here in the early 1990ies but could not be detected in 2006. Already in 2003, a geo-radar transect showed no indication of remaining permafrost at the site (Else Kohlstrup et al., Uppsala University). The ecosystem had undergone a clear desiccation, and formerly water-filled boulder pits were now invaded by moss-dominated pioneer vegetation. The cottongrass tussocks had become less dense and more "fluffy" and had gradually been invaded by lingonberry (Vaccinium vitis-idaea), the most expansive species in the community. The effect size was about twice as high in OTCs as in controls. The cottongrass tussock tundra is one of a handful of vegetation types pointed out as particularly sensitive to Climate Change, based on the listing in IPCC's Third Assessment Report 2001. Our team is undertaking a longer-term project including four of these systems, i.e., snowbeds, tussock tundra, high alpine fellfields, and mesic alpine heath (being invaded by mountain birch). A helicopter inventory of possible sites for tussock tundra in the region in August 2005 revealed a total stock of ca 2 km2 in Sweden (compared with the circum-arctic total of 336,000 km2). As a further outcome of the project on indicator ecosystems, new project, Alpine Cliff Ecology (ACE) was initiated at Latnjajaure in 2006 (see separate presentation). In the snowbed project, initiated in 2002, four snowbed plant communi¬ties are studied. The snowbeds are of the “moderate" class (melting out before the end of July), and they are situated in both heath and meadow sites. Our current studies encompass plant community scale to landscape scale, and include, e.g., monitoring of snow dynamics, microbial and plant community structure in fertilized and control plots, lemming population dynamics, nitrogen and debris deposition, and soil processes (for microbial studies see separate abstract/presentation). Interestingly, our preliminary data suggests that the plant community structure does not change due to fertilization. In 2004 we sampled the OTCs, established in 1993, in dry meadow and dry heath for root morphology characteristics, root biomass distribution, and microbial activity. This study shows that tundra plants may respond to climate change by increasing their specific root length (SRL; m gDM-1) and specific root area (SRA; m2 kgDM -1), whilst the microbial activity may remain unaffected. Furthermore, this study suggests that there might be incorporation of C in tundra soils partly as a result of increased turnover of the finer roots produced within the OTCs. However, the response across plant communities is not consistent. The "Meeting of Litters" experiment headed by Hans Cornelissen, Vrije Universiteit Amsterdam (Holland) was finalized in 2004, with a multi-authored paper in review at present. The project focused on comparative decomposition studies on litter samples from a large number of ITEX sites gathered at two experimental outdoor facilities in Sweden: Latnjajaure (mid alpine) and Abisko (sub-alpine). Other international within-ITEX activities at Latnja include a field research campaign by Catharine Copass Thompson and Carrie McCalley from the Marine Biological Laboratory, Woods Hole, and Robert Bell and Kerry Dinsmore from the University of Edinburgh. They visited the Latnjajaure Field Station between August 2 and August 9, 2004. Their research in the Abisko area entailed linking measurements of carbon fluxes to the Normalized Difference Vegetation Index (NDVI), an index of greenness which can be measured on multiple scales, including from satellites. The goal for the 2004 summer was to cover as many different kinds of vegetation types in the region as possible, given the constraints of their sampling protocol. The up-scaling to the landscape level was manifested by the final publication of the GIS-based vegetation map over the Latnjajaure catchment (12 km2, 1 m2 pixel resolution) by Lindblad et al. (Pirineos 161: 3-32, 2006). This work is part of Karin Lindblad's Ph.D. thesis for her dissertation 26 January 2007.
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35.
  • Björk, Robert G., 1974, et al. (författare)
  • Linkages between N turnover and plant community structure in a tundra landscape
  • 2007
  • Ingår i: Plant and Soil. - : Springer Science and Business Media LLC. - 0032-079X .- 1573-5036. ; 294:1-2, s. 247-261
  • Tidskriftsartikel (refereegranskat)abstract
    • The spatial distribution of organic soil nitrogen (N) in alpine tundra was studied along a natural environmental gradient, covering five plant communities, at the Latnjajaure Field Station, northern Swedish Lapland. The five communities (mesic meadow, meadow snowbed, dry heath, mesic heath, and heath snowbed) are the dominant types in this region and are differentiated by soil pH. Net N mineralization, net ammonification, and net nitrification were measured using 40-day laboratory incubations based on extractable NH4+ and NO3-. Nitrification enzyme activity (NEA), denitrification enzyme activity (DEA), amino acid concentrations, and microbial respiration were measured for soils from each plant community. The results show that net N mineralization rates were more than three times higher in the meadow ecosystems (mesic meadow 0.7 mu g N g(-1) OM day(-1) and meadow snowbed 0.6 mu g N g(-1) OM day(-1)) than the heath ecosystems (dry heath 0.2 mu g N g(-1) OM day(-1), mesic heath 0.1 mu g N g(-1) OM day(-1) and heath snowbed 0.2 mu g N g(-1) OM day(-1)). The net N mineralization rates were negatively correlated to organic soil C/N ratio (r = -0.652, P < 0.001) and positively correlated to soil pH (r = 0.701, P < 0.001). Net nitrification, inorganic N concentrations, and NEA rates also differed between plant communities; the values for the mesic meadow were at least four times higher than the other plant communities, and the snowbeds formed an intermediate group. Moreover, the results show a different pattern of distribution for individual amino acids across the plant communities, with snowbeds tending to have the highest amino acid N concentrations. The differences between plant communities along this natural gradient also illustrate variations between the dominant mycorrhizal associations in facilitating N capture by the characteristic functional groups of plants.
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36.
  • Björk, Robert G., 1974, et al. (författare)
  • Long-term warming effects on carbon and nitrogen dynamics in tundra soils
  • 2012
  • Ingår i: 20th Anniversary ITEX Workshop, El Paso, USA, 17–21 January 2012.
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • During IPY 2008 we used the ITEX experiment in Latnjajaure (northern Sweden), established during the early years of the program, to investigate long-term warming effects on ecosystem respiration (ER), carbon (C) and nitrogen (N) pool (including d13C and d15N), soil organic C (SOC) chemical composition, and N mineralization among plant communities. After 12 to 15 years of open top chamber (OTC) treatment no statistical effect was found on the soil temperature (10 cm soil depth), although the was an overall increase in all OTC by +0.2°C. However, the soil moisture decreased significantly by 3-14%, depending on plant community, in the OTCs compared to ambient conditions. Preliminary, there was a 19-61% non-significant increase in annual growing season ER in the OTC compared to the ambient plots over the growing season. The were distinct differences in the SOM functional composition among plant communities with c 10% more O-alkyls stored in tussock tundra than in dry meadow. The OTCs did not consistently alter the SOM composition among the vegetation types but clearly showed a trend for reduced aliphatic and O-alkyl C in the OTCs suggesting increased decomposition (or reduced inputs) of these compounds. Thus, the non-significantly higher ER may in some communities be of plant origin linked to greater plant biomass in the OTCs, and in other (e.g. tussock tundra) from increased decomposition rates. In conclusion, this study showed that 12-15 years of OTC treatment had a modest effects impact C and N dynamics in tundra soils specific to distinct plant communities.
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37.
  • Björk, Robert G., 1974, et al. (författare)
  • Long-term warming effects on root morphology, root mass distribution, and microbial activity in two dry tundra plant communities in northern Sweden
  • 2007
  • Ingår i: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 176:4, s. 862-873
  • Tidskriftsartikel (refereegranskat)abstract
    • center dot Effects of warming on root morphology, root mass distribution and microbial activity were studied in organic and mineral soil layers in two alpine ecosystems over > 10 yr, using open-top chambers, in Swedish Lapland. center dot Root mass was estimated using soil cores. Washed roots were scanned and sorted into four diameter classes, for which variables including root mass (g dry matter (g DM) m(-2)), root length density (RLD; cm cm(-3) soil), specific root length (SRL; m g DM-1), specific root area (SRA; m(2) kg DM-1), and number of root tips m(-2) were determined. Nitrification (NEA) and denitrification enzyme activity (DEA) in the top 10 cm of soil were measured. center dot Soil warming shifted the rooting zone towards the upper soil organic layer in both plant communities. In the dry heath, warming increased SRL and SRA of the finest roots in both soil layers, whereas the dry meadow was unaffected. Neither NEA nor DEA exhibited differences attributable to warming. center dot Tundra plants may respond to climate change by altering their root morphology and mass while microbial activity may be unaffected. This suggests that carbon may be incorporated in tundra soils partly as a result of increases in the mass of the finer roots if temperatures rise.
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38.
  • Björk, Robert G., 1974, et al. (författare)
  • Nitrification and Denitrification Enzyme Activity: a successful tool in Arctic and Alpine soil ecology
  • 2007
  • Ingår i: The 14th ITEX workshop, Falls Creek, Victoria, Australia, 2–6 February 2007..
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Nitrogen is consideration to be a limiting factor for plants and microbes in arctic and alpine ecosystems and the rates of mineralization, nitrification, and denitrifi¬cation are known to be generally low. However, Climate Change is expected to alter the nitrogen availability and dynamics and, as a consequence, affect plant community composition and production. The general consensus today is that increased temperature will lead to greater microbial activity and more plant-available nitrogen. Nevertheless, nitrification and denitrification are restricted by a number of environmental factors such as low tem¬perature and low pH. The C/N ratio and the water content of the soils also play an important role in determining the rates of nitrification and denitrification. Since 2002 microbial studies has been undertaken at Latnjajure, and comprise several microbial techniques, e.g. Nitrification Enzyme Activity (NEA), Denitrification Enzyme Activity (DEA), Phospholipid fatty acid analysis (PFLA), and Temperature Gradient Gel Electrophoresis (TGGE). These studies focuses on the interaction between plants and microbes along natural environmental gradients, both within plant communities and within the landscape, but also entails the OTCs used in the ITEX studies at Latnjajaure. Here we present the techniques NEA and DEA and give some brief results from how these have been successfully applied at Latnjajaure. In ecosystems with low nitrification activity, small amounts of NO3-/NO2- will be formed and it is thus difficult to measure low fluxes. However, NO3-/NO2- can be converted to N2O and then analysed by gas chromatography, whereby the detection limit is increased at least 1000 times compared to the spectroscopical technique. These techniques are referred to Nitrification (NEA) and Denitrification Enzyme Activity (DEA) and give a potential measure on the nitrification and denitrification rates, which goes back to the actual populations of nitrifiers and denitrifiers in the soil. For instance, NEA has been proved to better correlate with extractable NH4+ concentration than net nitrification does, and still after twelve weeks show a strong correlation with the initial extractable NH4+ concentration. Therefore, these variables, in particular NEA, have the advantage of being a much more stable variable than, for instance, extractable N concentrations and net nitrification, and NEA and DEA are therefore suitable when working in fringe environments with restricted logistics like the Latnjajaure catchment. NEA is measured using a two-step incubation technique; first by incubate the soil with a nutrient solution for 24 hours in darkness, at room temperature on a rotary shaker. Sub-samples are then withdrawn after a specified time schedule. The second step allows NO3- to be reduced to N2O by adding a modified denitrifying bacterium, Pseudomonas chlororaphis ATCC 43928, together with a carbon source. This strain of bacteria lacks the enzyme to reduce N2O to N2. The samples are then again incubated in darkness, at room temperature for 24 hours, and analysed by gas chromatography. This method was first used by Lensi et al. (1985, 1986), to study nitrification potentials in forest soils. Furthermore, the method has been developed for soils with low pH and small amounts of NO3- and the analysis makes the quantification without interference of organic matter, which makes it suitable for arctic and alpine ecosystems. To analyse DEA an anaerobic incubation technique is used, based on acetylene inhibition of the N2O-reductase resulting in N2O as the only end product. The soil sample is evacuated and flushed with N2. Thereafter acetylene is inserted to a final acetylene concentration of 10%, and the samples are shaken continuously and gas samples are withdrawn after a specified time schedule, which is then analysed by gas chromatography. This provides an estimate of the maximum concentration of functional denitrifying enzymes in the soil. Denitrifiers, in contrast to nitrifiers, are heterotrophs and can switch from using NO3- as an alternative electron acceptor to O2 under aerobic conditions. This makes other factors in the soil important determinants of DEA, e.g. availability of oxygen and C. Hence, the presence of denitrifiers is rarely a limitation for denitrification and they usually make up a reasonably large fraction of the soil bacteria. At Latnjajaure NEA shows a larger differentiation across plant communities than DEA. However, the spatial variability in the landscape, at the meso-scale, was in the same range in both variables and increased with altitude from 1000 to 1365 m a.s.l, particularly in heath plant communities. This result suggests that the decrease in mean annual temperature with altitude (0.6ºC with every one hundred meters) did not reduce nitrification and denitrification rates, as one might have expected. None of the other variable studied could explain the altitudinal increase in all cases, and the factors controlling the nitrification and denitrification rates seem to vary with the vegetation type. Furthermore, neither NEA nor DEA exhibited any changes between the ambient and warmed plots in the warming experiments. However, the warming experiment in the dry heath exhibited a change in root morphology via increased specific root length (SRL; m gDM-1) and specific root area (SRA; m2 kgDM -1). As both heterotrophic microbes and plants out-compete nitrifiers for NH4+, a change in root morphology, as seen in the warming experiment, may also explain the increased activity of nitrifying and denitrifying microbes with altitude.
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39.
  • Björk, Robert G., 1974, et al. (författare)
  • Root architecture and nutrient allocation in tundra plants
  • 2005
  • Ingår i: ESA-INTECOL 2005 Joint Meeting – Ecology at multiple scales, Montreal, Canada, 7 – 12 August 2005..
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • The Arctic Climate Impact Assessment (ACIA) recently reported that the Arctic is rapidly changing due to Climate Change. Likewise, the mountains of Europe are going to experience large shifts in plant composition and 41-56% of the alpine species might be on the edge of extinction according to the 1st synthesis of the Global Observation Research Initiative in Alpine Environments (GLORIA). Although the tundra ecosystems are subjected to dramatical changes as a result of Climate Change, there is little knowledge of the effect on root dynamics. Roots are crucial for soil development and nutrient cycling in most ecosystems. The further out in the root system a single root is located, the faster the root turns over. The fine roots are also having a lower C:N ratio than more developed and supporting roots. The aim of this study is to investigate the dynamic of root architecture and how tundra plants allocate carbon and nitrogen between root and shoot biomass and, moreover, how the plants respond to climatic warming. The dominant plant species (e.g. Cassiope tetragona, Vaccinium vitis-idaea and Diapensia lapponica for the dry heath) within each of four plant communities at Latnjajaure Field Station, in northern Swedish Scandes, were sampled and divided into shoot and root. To study the effects of climatic warming on the root system, soil cores were as well sampled in Open Top Chambers (OTCs) that was established in 1993. The root architecture was analysed by observing the degree of branching, colour, consistency etc. of the roots, which then were cut and sorted by diameter. To determine the C and N allocation within the plants we also quantified the shoot:root ratio. The preliminary results indicate that there is a difference between plant species in root biomass and particularly in the fraction of fine roots. As a result of a greater amount of root exudates from fine roots, these results imply that plant distribution has a great impact on the soil microbial community and activity. The large spatial variability often seen in microbial measurement within plant communities may be due to a sampling procedure, in that samples are taken from different plants’ root systems.
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40.
  • Björk, Robert G., 1974, et al. (författare)
  • Root biomass distribution and morphology in Norway spruce forests on drained organic soils: root system variation in d13C and d15N
  • 2010
  • Ingår i: 1st COST meeting ‘Belowground carbon in Europeanforest’, Birmensdorf, Switzerland, 26–28 January 2010..
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Little is known about the distribution and morphology of fine roots in organic soils. Organic soils are typical features of northern Europe, covering over 250 000 km2, and in the recent century, 1/3 of the pristine peatlands have been drained for forestry and large areas of peatlands used for agriculture have been afforested. The aim of the present study was to investigate how fine root distribution, mor-phology, and 13C/15N differed between two fertile drained and forested organic soils. The study was conducted in two Norway spruce stands at the Skogaryd Research Forest, in south-west Sweden. One of the sites was a mineral soil (“the mineral site”) with high organic content that had been under agricultural use since the 15th century, and was afforested in 1962. The other site was a peat soil of minerotrophic origin (“the peat site”) that was used for extensive grazing from the 1800s to the 1870s, used for crop production after the drainage in the 1870s and afforested in 1951. Root biomass and necromass were estimated using soil cores, to a depth of 40 cm. Washed roots were scanned and sorted into five diameter classes, and analysed for 13C and 15N. There was a distinct difference in fine root morphology between the two sites, with longer and thinner roots at the peat site. Despite this, no significant differences in total root biomass or biomass-to-necromass ratio between the sites were found. At the peat site, the fine roots were en-riched in 15N by 1-1.5‰ compared to the mineral site, and had consistently lower C/N within the root classes. The mineral site, which is the less fertile of the sites, produced shorter and thicker roots, and more extensive extramatrical mycelia. Thus, one possibility is that the trees at the mineral site invest more in their mycorrhizal symbiont instead of exploring the soil environment themselves.
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41.
  • Björk, Robert G., 1974, et al. (författare)
  • Snow distribution and biocomplexity in alpine landscapes: a progress report
  • 2005
  • Ingår i: ESF – SEDIFLUX Network, Second Workshop, Clermont-Ferrand, France, 20 – 22 January 2005.
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Snowbed ecosystems make up a pronounced component throughout the tundra biome, particularly in alpine areas due to the ragged topography and wind re-distribution of snow. As there are species and communities restricted to the snowbed habitat, they make a unique com-ponent in the alpine biodiversity at scales from species to landscapes. In connection with the Global Warming forecast, snowbed ecosystems of alpine Europe are regarded as particularly vulnerable in IPCC's 2001 assessment report. Snowbeds also provide important ecosystem services to the landscape such as maintaining the adjacent earlier-thawing ecosystems by steady water and nutrient supply, and by ensuring good winter conditions for lemmings. During years of low density the lemming preferentially grazes in snowbeds. Furthermore, snowbeds is the plant community of utmost importance for reindeers, and the availability of snowbeds in the landscape can influence the well-being of reindeers by having the possibility to offer nutrient rich food late in the growing season when the food supply have started to run short. The winter weather conditions are those that are primarily responsible for the variability in the snowbed morphology, while the local topography sets the general snowbed pattern. However, the summer weather conditions are also implicated in the variation of rate and pattern of snowmelt between years, though the general snowbed outline remains consistent among years. As tundra ecosystems are typically limited by nitrogen availability as well as temperature, Climate Change and a likely exponentially increasing deposition of plant-available nitrogen with the precipitation are inevitably accelerating processes that will alter the structure and extent of this key ecosystem. The project “Snow Distribution and Biocomplexity in Alpine Landscapes” is running at Latnjajaure Field Station, in northern Swedish Lapland, where four snowbed plant communi-ties are studied. The snowbeds are of the “moderate type”, which means that they are melting out before the end of July, and they are situated in both heath and meadow sites. Our current studies include, e.g., monitoring of snow dynamics, plant community structure in fertilized and control plots, lemming population dynamics, nitrogen and debris deposition, and soil processes. We will report on the progress of this ongoing project.
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42.
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43.
  • Björk, Robert G., 1974, et al. (författare)
  • Temporal pattern of CO2, CH4 and N2O fluxes and soil microbial structure from snow-covered Alpine plant communities
  • 2006
  • Ingår i: Abstracts and Proceedings of the Geological Society of Norway. ; :4
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Global warming is expected to have large effects on carbon exchange between the biosphere and the atmosphere in the Arctic. Arctic ecosystems, which can be a net sink in the summer, are often a net source of CO2 to the atmosphere on an annual basis. Few studies on winter CO2 and CH4 efflux have been conducted in the subarctic part of Sweden. So far, no integrated estimates of winter fluxes of CO2, CH4 or N2O has been reported from the alpine areas in the Scandinavian mountains. As much as 44 to 53% of the northern hemispheres landmass may be snow covered for parts of the year. The depth and spatial spread of snow cover is a result of moisture availability, duration of temperatures bellow 0ºC, storm frequency and the more local factors such as wind redistribution and compaction. In future climate scenarios, predictions of warmer climate and increased precipitations are often mentioned, but to which extent is more uncertain. However, the major changes in precipitation will occur over the North Pacific, North Atlantic and Scandinavia. The controlling factor for microbial activity in the organic layer during winter in alpine areas is the development of a consistent snow cover, which effectively decouples the soil from the atmospheric temperature. The air and soil temperature the days before snow cover development is important, as it sets the temperature conditions for the whole winter period. Soil microbial activity is markedly reduced below temperatures of 0 to -5°C, when the soil starts to freeze and free water becomes limited. Nitrogen mineralisation, nitrification and denitrification can, however, be maintained down to -4°C, and N2O production (from denitrification) in frozen soils has potential to affect annual dynamics and budgets of N (although the soil pore water content prior to freezing is an important regulating factor for winter N2O production). Snowbed communities are rarely, if ever, subjected to temperatures as low as -5°C, which implies that they may be favourable for microbial activity during the winter. Furthermore, tundra soil microbial biomass reaches its annual peak under snow, and fungi account for most of the biomass. However, how the microbial community changes during winter and snowmelt are poorly know and, in particular, in relation to trace gas fluxes. Flux of CO2, CH4 and N2O through a seasonal snowpack, using Fick’s law, from four plant communities with different snow regime and how it changes during snowmelt in the subarctic-alpine part of Sweden will be presented. We will also try to relate the trace gas fluxes to the soil microbial community composition using phospholipid fatty acid analysis.
  •  
44.
  • Björk, Robert G., 1974, et al. (författare)
  • Temporal variation in soil microbial communities and the influence of snow cover
  • 2007
  • Ingår i: The 14th ITEX workshop, Falls Creek, Victoria, Australia, 2–6 February 2007..
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Global climate change is projected to have a large impact in arctic and alpine areas. Future projections with increased temperature also include increased precipitation, but to which extent is uncertain. However, the major changes in precipitation will occur over the North Pacific, North Atlantic and Scandinavia. As much as 44 to 53% of the northern hemispheres landmass may be snow covered for parts of the year and in higher alpine terrain the increased precipitation will lead to a greater snow accumulation. The controlling factor for microbial activity in the organic layer during winter in alpine areas is the development of a consistent snow cover, which effectively decouples the soil from the atmospheric temperature. The air and soil temperature the days before snow cover development is important, as it sets the temperature conditions for the whole winter period. Soil microbial activity is markedly reduced below temperatures of 0 to -5°C, when the soil starts to freeze and free water becomes limited. Nitrogen mineralisation, nitrification and denitrification can, however, be maintained down to -4°C, and N2O production (from denitrification) in frozen soils could potentially affect the annual dynamics and budgets of N. Snowbed communities are rarely, if ever, subjected to temperatures as low as -5°C, which implies that they may be favourable for microbial activity during the winter. Furthermore, tundra soil microbial biomass reaches its annual peak under snow, and fungi account for most of the biomass. However, how the microbial community changes during winter and snowmelt is poorly known and, in particular, in relation to trace gas fluxes. The objective of our study was, therefore, to investigate the temporal pattern of soil microbial structure in four plant communities with contrasting snow cover and nitrogen turnover. This study was conducted at Latnjajaure Field Station (LFS) located in the midalpine region in northern Sweden. The study includes four different plant communities, heath snowbed, heath meadow, meadow snowbed, and mesic meadow. To characterize the soil microbial community we used phospholipid fatty acid analysis (PLFA), which is a method targeting the fatty acid profiles of membrane phospholipids microorganisms. The results show that at each individual sampling occasion the four plant communities’ exhibits different soil microbial structure. However, the temporal variation is larger than the difference across plant communities. This temporal shift in microbial structure seems to be partially related to the fatty acid 18:2ω6, indicative of fungi, which show a high proportion in soils protected by snow and decreases after snow melt. Furthermore, the shift in microbial structure during the season is more modest in snowbeds than the mesic heath and meadow.
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45.
  • Björk, Robert G., 1974, et al. (författare)
  • Temporal variation in soil microbial communities in Alpine tundra
  • 2008
  • Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 40:1, s. 266-268
  • Tidskriftsartikel (refereegranskat)abstract
    • Temporal variation in soil microbial communities was studied at a mid-alpine environment in Latnjajaure, northern Sweden, using phospholipid fatty acid (PLFA) analysis. The results show two seasonal shifts in microbial composition. The first shift was associated with snowmelt and mainly related to a decrease in fungal PLFAs, accompanied by an increase in branched 17:0 and methylated PLFAs (biomarkers for Gram-positive- and actinobacteria, respectively), resulting in a decrease in the ratio of fungi-to-bacteria. The second shift occurred across the growing, season, and was associated with a switch from shorter to longer PLFAs and an increase in 18:1 omega 7 (biomarker for Gram-negative bacteria). Vegetation, snow cover dynamics, and N turnover seem to be of minor importance to broadscale microbial community structure in this area. (c) 2007 Elsevier Ltd. All rights reserved.
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46.
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47.
  • Björk, Robert G., 1974, et al. (författare)
  • The effect of long-term temperature enhancement on the subarctic-alpine biocomplexity
  • 2004
  • Ingår i: International Conference on Arctic Microbiology.
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Climate change is expected to alter the nitrogen availability and soil carbon dynamics and, as a consequence, affect plant community composition and production and thereby ecosystem gas flux rates. The International Tundra Experiment (ITEX) was established at Latnjajaure Field Station (LFS), in northern Swedish Lapland, in 1993 and gives a great opportunity to investigate the long-term effect of climatic warming on the soil ecosystem. The Open Top Chambers (OTCs) used within ITEX are located in five different plant communities, which covers both heaths and meadows and the gradient from dry to moist plant communities. The ITEX species Cassiope tetragona, Dryas octopetala, Eriophorum vaginatum, Polygonum viviparum and Ranunculus nivalis, studied at LFS, are all showing positive responses to phenology, growth and reproduction to the warming treatment. The temperature enhancement on the plant community level seems to lead to changes in the dominance of species, especially by shrubs and bryophytes. However, the overall plant community pattern also appears to depend much on changes in the nitrogen availability, where their combined effects are multiplicative rather than additive with a rapidly decrease in species diversity. In this newly started study we are adopting the results from the ITEX study and try to relate them to the soil processes and properties such as potential nitrification and denitrification, soil organic matter, C:N ratio and ecosystem respiration. Thus, we make an effort to amalgamate plant community changes with changes in the subarctic-alpine soil ecosystem.
  •  
48.
  • Björk, Robert G., 1974, et al. (författare)
  • Two aspects on soil nitrogen dynamics in a climate change context
  • 2005
  • Ingår i: Second International Conference on Arctic Research Planning – ICARP II, Copenhagen, Denmark, 10 – 12 November 2005..
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Climate change is expected to alter the nitrogen availability and dynamics and, as a consequence, affect plant community composition and production. The general consensus today is that increased temperature will lead to greater microbial activity and more plant-available nitrogen Although, there are hardly any studies on how nitrification and denitrification varies with altitude, and no previous studies in high arctic-alpine tundra landscapes. If temperature is an important factor limiting microbes in tundra areas, and the mean annual temperature falls with increasing altitude, it would be expected that nitrification and denitrification rates also would decrease with increasing altitude and thereby reflect a reverse Climate Change gradient. Here, we compare nitrification enzyme activity (NEA) and denitrification enzyme activity (DEA) rates in dry heaths a along an altitudinal gradient with the effects of climatic warming using Open Top Chambers (OTCs). This study was conducted at Latnjajaure Field Station (LFS) located in the midalpine region in northern Sweden. LFS is also the Swedish field site for the International Tundra Experiment (ITEX), established in 1993. This gives an opportunity to investigate long-term effect of climatic warming on as well as an altitudinal gradient (1000m to 1365m) within a very small geographical range. The OTCs used at LFS increases the soil surface temperature by approximately 1.5ºC whereas air temperature falls with 1ºC for every hundred meter of increased altitude. To analyse the NEA and DEA we used an anaerobic incubation technique, based on acetylene inhibition technique, resulting in N2O as the only end product, which is then analysed by gas chromatography. The results contradict each other. The gradient study showed a decreased NEA and DEA rates with falling altitude, whereas the warming experiment show a slight increase due to the temperature enhancement by OTCs, although, there is no significant OTC effect. DEA was correlated with NEA and SOM, explaining part of the altitudinal variation. The results indicate that the altitudinal temperature decline did not reduce NEA and DEA rates, and although some of the variables measured here might explain part of the results in this study, they are not conclusive.
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49.
  • Björk-Åman, Camilla, et al. (författare)
  • Nordic research on special needs education in upper secondary vocational education and training: A review
  • 2021
  • Ingår i: Nordic Journal of Vocational Education and Training. - Linköping : Linköping University Electronic Press. - 2242-458X. ; 11:1, s. 97-123
  • Tidskriftsartikel (refereegranskat)abstract
    • The purpose of this article is to describe and analyse the state of the art of research on special needs education (SNE) in the context of the Nordic countries’ vocational education and training (VET) systems during the period January 2010 to September 2018.  Twenty studies remained after the search procedure and thematic analysis, 15 of which deal with the practice level and five with the organisation level. No studies were identified as belonging to the policy level. The following themes were found at the practice level: teachers’ work and role, teaching and learning, student transition and student dropout. Themes identified at the organisation level were changes to vocational policy documents and educational practices, and school organisation and its implementation. Finland dominates in terms of number of studies. Furthermore, the review shows that there were few studies in the area of SNE in VET. The results show that further studies are needed to acquire more knowledge about SNE in vocational education.
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50.
  • Björkman, Mats P., 1978, et al. (författare)
  • A comparison of annual and seasonal carbon dioxide effluxes between sub-Arctic Sweden and High-Arctic Svalbard
  • 2010
  • Ingår i: Polar Research. - : Norwegian Polar Institute. - 1751-8369. ; 29:1, s. 75-84
  • Tidskriftsartikel (refereegranskat)abstract
    • Recent climate change predictions suggest altered patterns of winter precipitation across the Arctic. It has been suggested that the presence, timing and amount of snow all affect microbial activity, thus influencing CO2 production in soil. In this study annual and seasonal emissions of CO2 were estimated in High-Arctic Adventdalen, Svalbard, and sub-Arctic Latnjajaure, Sweden, using a new trace gas-based method to track real time diffusion rates through the snow. Summer measurements from snow-free soils were made using a chamber-based method. Measurements were obtained at different snow regimes in order to evaluate the effect of snow depth on winter CO2 effluxes. Total annual emissions of CO2 from the sub-Arctic site (0.662–1.487 kg CO2 m-2 yr-1) were found to be more than double the emissions from the High-Arctic site (0.369–0.591 kg CO2 m-2 yr-1). There were no significant differences in winter effluxes between snow regimes or vegetation types, indicating that spatial variability in winter soil CO2 effluxes are not directly linked to snow cover thickness or soil temperatures. Total winter emissions (0.004–0.248 kg CO2 m-2) were found to be in the lower range of those previously described in the literature. Winter emissions varied in their contribution to total annual production between 1 and 18%. Artificial snow drifts shortened the snow-free period by two weeks and decreased annual CO2 emission by up to 20%. This study suggests that future shifts in vegetation zones may increase soil respiration from Arctic tundra regions.
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