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UV -screening in Arctic and alpine vascular plants and lichens

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With depletion of the stratospheric ozone layer over arctic regions, ecosystems at arctic Svalbard will experience enhanced UV-B irradiation. This thesis deals with vascular plants and lichens, which may protect themselves against the possibly damaging irradiation by screening compounds located in the epidermis and in the cortex, respectively. For vascular plants it is well established that the screening compounds are induced by UV-B, while the induction mechanisms for lichen compounds have not been studied in detail. Through exclusion studies in the field and in a growth chamber we have investigated the significance of PAR and UVR separately for the induction of the lichen compounds melanin and parietin. Synthesis of both parietin and melanin seem to be dependent on UV-light.

We present a survey of the present screening capacity of twelve vascular plants and two lichens from Svalbard. The acclimation potential of selected Svalbard vascular plants (Bistorta vivipara, Dryas octopetala, Oxyria digyna, Salix reticulata, Saxifraga oppositifolia, Silene acaulis) and lichens (Cetraria islandica, Xanthoria elegans) to enhanced UV-B was investigated by comparing their screening capacity with that of ecotypes from the mountains of southern Norway and the Alps, where UV-B exposure is higher by a factor of 3 to 5. In a second experiment, natural Svalbard-vegetation was exposed to artificially raised UV-B irradiation corresponding to a 15% reduction in the ozone column. We have also looked for possible effects of a future climatic warming on UV-B acclimation by enhancing the temperature using Open Top Chambers (OTCs).

We conclude that the Svalbard species studied are in general well protected against UV-B. It may be that UV-B is only one of the environmental factors inducing epidermal UV-B compound screening in vascular plants or, alternatively, that ambient UV-levels are already high enough to saturate synthesis of absorbing compounds. This suggestion is based on the relatively low transmittance in most plants, the failure to induce higher screening by artificial UV-B radiation, and the high variability from year to year. Artificially enhanced temperature did not influence the epidermal UV-screening.

 

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