| 1. |
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| 2. |
- Björk, Robert G., 1974, et al.
(författare)
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A Climate Change aspect on root dynamics and nitrogen partitioning in a tundra landscape
- 2005
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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..
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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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| 3. |
- Björk, Robert G., 1974, et al.
(författare)
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Can present melt-out patterns identify snowbed plant species vulnerable to climate change?
- 2005
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Ingår i: Second International Conference on Arctic Research Planning – ICARP II, Copenhagen, Denmark, 10 – 12 November 2005..
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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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| 4. |
- Björk, Robert G., 1974, et al.
(författare)
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Climate-related soil changes in tundra ecosystems at Latnjajaure, northern Sweden – an ITEX-IPY project
- 2010
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Ingår i: International Polar Year Oslo Science Conference.
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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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| 5. |
- Björk, Robert G., 1974, et al.
(författare)
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ITEX at Latnjajaure
- 2007
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Ingår i: The 14th ITEX workshop, Falls Creek, Victoria, Australia, 2–6 February 2007..
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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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| 6. |
- Björk, Robert G., 1974, et al.
(författare)
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Long-term warming effects on carbon and nitrogen dynamics in tundra soils
- 2012
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Ingår i: 20th Anniversary ITEX Workshop, El Paso, USA, 17–21 January 2012.
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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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| 7. |
- Björk, Robert G., 1974, et al.
(författare)
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Nitrification and Denitrification Enzyme Activity: a successful tool in Arctic and Alpine soil ecology
- 2007
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Ingår i: The 14th ITEX workshop, Falls Creek, Victoria, Australia, 2–6 February 2007..
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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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| 8. |
- Björk, Robert G., 1974, et al.
(författare)
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Root architecture and nutrient allocation in tundra plants
- 2005
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Ingår i: ESA-INTECOL 2005 Joint Meeting – Ecology at multiple scales, Montreal, Canada, 7 – 12 August 2005..
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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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| 9. |
- Björk, Robert G., 1974, et al.
(författare)
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Snow distribution and biocomplexity in alpine landscapes: a progress report
- 2005
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Ingår i: ESF – SEDIFLUX Network, Second Workshop, Clermont-Ferrand, France, 20 – 22 January 2005.
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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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| 10. |
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