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- Arft, M, et al.
(författare)
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Responses of tundra plants to experimental warming : Meta-analysis of the international tundra experiment
- 1999
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Ingår i: Ecological Monographs. - 0012-9615 .- 1557-7015. ; 69:4, s. 491-511
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Tidskriftsartikel (refereegranskat)abstract
- The International Tundra Experiment (ITEX) is a collaborative, multisite experiment using a common temperature manipulation to examine variability in species response across climatic and geographic gradients of tundra ecosystems. ITEX was designed specifically to examine variability in arctic and alpine species response to increased temperature. We compiled from one to four years of experimental data from 13 different ITEX sites and used meta-analysis to analyze responses of plant phenology, growth, and reproduction to experimental warming. Results indicate that key phenological events such as leaf bud burst and flowering occurred earlier in warmed plots throughout the study period; however, there was little impact on growth cessation at the end of the season. Quantitative measures of vegetative growth were greatest in warmed plots in the early years of the experiment, whereas reproductive effort and success increased in later years. A shift away from vegetative growth and toward reproductive effort and success in the fourth treatment year suggests a shift from the initial response to a secondary response. The change in vegetative response may be due to depletion of stored plant reserves, whereas the lag in reproductive response may be due to the formation of flower buds one to several seasons prior to flowering. Both vegetative and reproductive responses varied among life-forms; herbaceous forms had stronger and more consistent vegetative growth responses than did woody forms. The greater responsiveness of the herbaceous forms may be attributed to their more flexible morphology and to their relatively greater proportion of stored plant reserves. Finally, warmer, low arctic sites produced the strongest growth responses, but colder sites produced a greater reproductive response. Greater resource investment in vegetative growth may be a conservative strategy in the Low Arctic, where there is more competition for light, nutrients, or water, and there may be little opportunity for successful germination or seedling development. In contrast, in the High Arctic, heavy investment in producing seed under a higher temperature scenario may provide an opportunity for species to colonize patches of unvegetated ground. The observed differential response to warming suggests that the primary forces driving the response vary across climatic zones, functional groups, and through time.
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| 2. |
- Andrés, E. C., et al.
(författare)
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The AMANDA neutrino telescope
- 1999
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Ingår i: Nuclear physics B, Proceedings supplements. - 0920-5632 .- 1873-3832. ; 77:1-3, s. 474-485
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Tidskriftsartikel (refereegranskat)abstract
- With an effective telescope area of order 104 m2 for TeV neutrinos, a threshold near ∼50 GeV and a pointing accuracy of 2.5 degrees per muon track, the AMANDA detector represents the first of a new generation of high energy neutrino telescopes, reaching a scale envisaged over 25 years ago. We describe early results on the calibration of natural deep ice as a particle detector as well as on AMANDA's performance as a neutrino telescope.
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| 3. |
- Björn, Lars Olof, et al.
(författare)
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Effects of ozone depletion and increased ultraviolet-B radiation on northern vegetation
- 1999
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Ingår i: Polar Research. - : Norwegian Polar Institute. - 0800-0395 .- 1751-8369. ; 18:2, s. 331-337
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Tidskriftsartikel (refereegranskat)abstract
- The stratospheric ozone layer has been depleted at high and mid-latitudes as a consequence of man's pollution of the atmosphere, and this results in increasing ultraviolet-B radiation at ground level. We investigate the effects of further radiation increases on plants and ecosystems by irradiating natural sub-Arctic and Arctic vegetation with artificial W-B radiation in field experiments extending over several years. Our experimental sites are located at Abisko, in northern Sweden (68 degrees N), and Adventdalen, on the island of Spitsbergen (78 degrees N). Additional UV-B induced interspecific differences in plant response in terms of reduced (or, in one case, increased) growth, changed morphology and changed pigment content. In some cases effects seem to be accumulated from one year to another. Plant litter decomposition is retarded. We are also studying how UV-B enhancement may affect the interaction between species. In some experiments we combine UV-B enhancement with changes in other factors: carbon dioxide concentration, water availability, and temperature. In some cases the effect of radiation enhancement is modified, or even reversed, by such changes. Over a four year period we did not find any significant radiation induced change in species composition, but based on the effects on individual plant species, such changes can be expected to take place over a longer time.
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| 4. |
- Björn, Lars Olof, et al.
(författare)
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The problem of ozone depletion in northern Europe
- 1998
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Ingår i: Ambio: a Journal of Human Environment. - 0044-7447. ; 27:4, s. 275-279
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Tidskriftsartikel (refereegranskat)abstract
- Ozone in the atmosphere, mainly in the stratosphere, absorbs most of the ultraviolet-B (wavelength 280-315 nm) radiation from the sun, which can destroy DNA and other biologically important molecules and, thereby, damage living organisms. Due to the pollution of the atmosphere by humans, the ozone layer is presently being depleted, more rapidly at higher latitudes than at lower, and more rapidly over Scandinavia than over most geographical regions at corresponding latitudes. Ultraviolet-B radiation is generally more intense in mountain regions than at sea level. We have experiments in progress in which we simulate the effects of further ozone depletion on terrestrial ecosystems (mountain heaths, bogs, tundra) by irradiating them with artificial ultraviolet-B radiation. Effects on the growth of dwarf-shrubs and mosses and on plant litter decomposition are described.
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| 8. |
- Taulavuori, E, et al.
(författare)
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Long-term exposure to enhanced ultraviolet-B radiation in the sub-arctic does not cause oxidative stress in Vaccinium myrtillus
- 1998
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Ingår i: New Phytologist. - : Wiley. - 1469-8137 .- 0028-646X. ; 140:4, s. 691-697
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this work was to assess whether or not oxidative stress had developed in a dwarf shrub bilberry (Vaccinium myrtillus L.) under long-term exposure to enhanced levels of ultraviolet-B (u.v.-B) radiation. The bilberry plants were exposed to increased u.v.-B representing a 15 stratospheric ozone depletion for seven full growing seasons (19911997) at Abisko, Swedish Lapland (68N). The oxidative stress was assessed on leaves and stems by analysing ascorbate and glutathione concentrations, and activities of the closely related enzymes ascorbate peroxidase (EC 1.11.1.11) and glutathione reductase (EC 1.6.4.2). The affects of autumnal leaf senescence and stem cold hardening on these variables were also considered. The results showed that the treatment caused scarcely any response in the studied variables, indicating that u.v.-B flux representing a 15 ozone depletion under clear sky conditions is not sufficient to cause oxidative stress in the bilberry. It is suggested that no strain was evoked since adaptation was possible under such u.v.-B increases. The studied variables did, however, respond significantly to leaf senescence and especially to stem cold hardening.
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