| 31. |
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| 32. |
- 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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| 33. |
- Björk, Robert G., 1974, et al.
(författare)
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Long-term warming effects on root morphology, root mass distribution, and microbial activity in two dry tundra plant communities in northern Sweden
- 2007
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Ingår i: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 176:4, s. 862-873
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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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| 34. |
- 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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| 35. |
- 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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| 36. |
- Björk, Robert G., 1974, et al.
(författare)
-
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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| 37. |
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| 38. |
- 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.
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| 39. |
- Björk, Robert G., 1974, et al.
(författare)
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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..
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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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| 40. |
- Björkman, Anne, 1981, et al.
(författare)
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Plant functional trait change across a warming tundra biome
- 2018
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 562:7725, s. 57-62
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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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