| 1. |
- Walker, M. D., et al.
(författare)
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Plant community responses to experimental warming across the tundra biome
- 2006
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 103:5, s. 1342-1346
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Tidskriftsartikel (refereegranskat)abstract
- Recent observations of changes in some tundra ecosystems appear to be responses to a warming climate. Several experimental studies have shown that tundra plants and ecosystems can respond strongly to environmental change, including warming; however, most studies were limited to a single location and were of short duration and based on a variety of experimental designs. In addition, comparisons among studies are difficult because a variety of techniques have been used to achieve experimental warming and different measurements have been used to assess responses. We used metaanalysis on plant community measurements from standardized warming experiments at 11 locations across the tundra biome involved in the International Tundra Experiment. The passive warming treatment increased plant-level air temperature by 1-3 degrees C, which is in the range of predicted and observed warming for tundra regions. Responses were rapid and detected in whole plant communities after only two growing seasons. Overall, warming increased height and cover of deciduous shrubs and graminoids, decreased cover of mosses and lichens, and decreased species diversity and evenness. These results predict that warming will cause a decline in biodiversity across a wide variety of tundra, at least in the short term. They also provide rigorous experimental evidence that recently observed increases in shrub cover in many tundra regions are in response to climate warming. These changes have important implications for processes and interactions within tundra ecosystems and between tundra and the atmosphere.
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| 2. |
- Post, Eric, et al.
(författare)
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Ecological Dynamics Across the Arctic Associated with Recent Climate Change
- 2009
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 325:5946, s. 1355-1358
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Forskningsöversikt (refereegranskat)abstract
- At the close of the Fourth International Polar Year, we take stock of the ecological consequences of recent climate change in the Arctic, focusing on effects at population, community, and ecosystem scales. Despite the buffering effect of landscape heterogeneity, Arctic ecosystems and the trophic relationships that structure them have been severely perturbed. These rapid changes may be a bellwether of changes to come at lower latitudes and have the potential to affect ecosystem services related to natural resources, food production, climate regulation, and cultural integrity. We highlight areas of ecological research that deserve priority as the Arctic continues to warm.
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| 3. |
- Björk, Robert G., 1974, et al.
(författare)
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Effect of reduced below-ground C sequestration on greenhouse gas fluxes within dry tundra ecosystems along an altitudinal gradient
- 2008
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Ingår i: The 15th ITEX workshop, Reykjavik, Iceland, 9–12 October 2008..
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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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| 4. |
- Sjögersten, Sofie, et al.
(författare)
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Depth distribution of net methanotrophic activity at a mountain birch forest-tundra heath ecotone, northern Sweden
- 2007
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Ingår i: Arctic, Antarctic and Alpine research. - 1523-0430 .- 1938-4246. ; 39:3, s. 477-480
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Tidskriftsartikel (refereegranskat)abstract
- Methanotrophy (the bacterial oxidation of CH4) in soils is the major biological sink for atmospheric CH4. Here we present results from a study designed to quantify the role of the physical diffusion barrier to CH4, through surface soils, as a factor affecting methanotrophy. We used the mountain birch forest-tundra heath ecotone in subarctic northern Sweden as our study system. Our results show that, although CH4 fluxes were generally low (around -20 mu mol m(-2) h(-1); a net flux from atmosphere to soil), the two adjacent communities responded in contrasting ways to in situ experimental reduction of the diffusion barrier (removal of the top 50 mm of soil): Uptake increased by 40% in forest soil in association with the removal, whereas it decreased marginally (by 10%) in tundra heath. Investigations of the depth-distribution of CH4 oxidation in vitro revealed maximum rates at the top of the mineral soil for the forest site, whereas at the tundra heath this was more evenly spread throughout the organic horizon. The contrasting physicochemical properties and methanotroph activity in the organic horizons together explain the contrasting responses to the removal treatment. They also illustrate the potential role of vegetation for methane oxidation around this ecotone, exerted through its influence on the depth and properties of the organic horizons in these subarctic soils.
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