Effects of enhanced ultraviolet-B radiation on subarctic ecosystems

Biologically harmful ultraviolet-B radiation (UV-B, 280-320 nm) is increasing at the Earth´s surface owing to stratospheric ozone depletion. This is of global concern due to potential impacts of enhanced UV-B radiation on the biosphere. The aim of this thesis was to investigate effects of enhanced UV-B radiation on components (bryophytes) and processes (decomposition, productivity, species interactions) in ecosystems. In the Subarctic, a bog and a birch-heath ecosystem were exposed to enhanced UV-B radiation for two and three growing seasons, respectively. A 15% ozone depletion was simulated. Bryophytes (Sphagnum fuscum, Hylocomium splendens, Polytrichum commune), representing different morphological ?types? and growth strategies, responded to UV-B enhancement with altered shoot morphology and reduced stem increment. Changed growth was not clearly linked to alterations in pigmentation, maximum net photosynthesis or dark respiration. Feedbacks of growth alterations on intra- and interspecific interactions are discussed. Productivity per unit area was not affected in S. fuscum. The main variables determining productivity (length increment, shoot mass relations, spatial shoot density) were affected although in opposite directions. UV-B-induced changes in shoot biometry and reduced spatial shoot density imply long-term effects on peat structure with possible feedback on productivity and decomposition. In H. splendens, enhanced UV-B radiation reduced current year´s shoot biomass production by 25% and tended to decrease spatial shoot density. The effect on these variables caused an amplified effect at the community level as productivity per unit area was reduced by 34%. Decomposition studies were done with dwarf shrub litter in the laboratory and in the heath. Altered leaf litter quality, which was induced during leaf growth under enhanced UV-B radiation, caused a decrease in microbial decomposer activity and delayed litter turnover. UV-B radiation applied during decomposition reduced microbial decomposer activity and decreased the abundance of fungi in the decomposer community but did not delay litter turnover. The potential delay was possibly offset by photodegradation of litter. Changes in species composition in the heath (including phanerogams and cryptogams) were not detectable after four growing seasons. Because of differences in UV-B responsiveness between species with different growth strategies, a shift in species composition could occur over the long-term perspective

Ecotypical differentiation in bipolar lichens.

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Effects of ozone depletion and increased ultraviolet-B radiation on northern vegetation

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 UV-B radiation in field experiments extending over several years. Our experimental sites are located at Abisko, in northern Sweden (68°N), and Adventdalen, on the island of Spitsbergen (78°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

Effects of ozone depletion and increased ultraviolet-B radiation on northern vegetation

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