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Effects of Reducing the Ambient UV-B Radiation in the High Arctic on Salix arctica and Vaccinium uliginosum.

Effects of reducing the ambient UV-B radiation on gas exchange and chlorophyll fluorescence of two dwarf shrub species, Salix arctica and Vaccinium uliginosum, was studied in a high arctic heath in North East Greenland during two growing seasons. Films (Mylar, transmitting A > 320 nm, and Lexan, transmitting A > 400 nm) were used to reduce UV-B radiation and UV-B+A respectively. A UV transparent film (Teflon, transmitting A > 280 nm) and no film were used as controls. Field measurements showed that the plants under Teflon, Mylar and Lexan received app. 91%, 39% and 17% of the ambient UV-B irradiance, respectively. UV radiation decreased the maximal photochemical efficiency (F v /F m ) and other fast fluorescence transient derived parameters in both species, despite an increased level of leaf flavonoid content. The responses varied in significance according to species and site. The relation of these effects to a significantly decreased stomatal conductance (g s ) and intercellular CO 2 concentration (C i ) pointed to respiration as an important factor in the interpretation of the observed unaffected net CO 2 assimilation (P n ) in UV- reduced treatments. It is concluded that the studied species have not fully acclimatized to the level of ambient UV-B radiation, and that ambient UV-B level is an important stress factor for the investigated plants in High Arctic.