The effects of altered levels of UV-B radiation on an Antarctic grass and lichen

We report a long-term experiment on the photosynthetic response of natural vegetation of Deschampsia antarctica (Poaceae) and Turgidosculum complicatulum (Lichenes) to altered UV-B levels on Leonie Island, Antarctica. UV-B above the vegetation was reduced by filter screens during two seasons. Half of the screens were transparent to UV-A and UV-B (ambient treatment) or absorbing UV-B and part of the UV-A (below-ambient treatment). Half of the wedge- shaped filters had side walls leading to an enhancement of the daily mean temperature in summer by 2-4 degreesC, simulating rising mean air temperature on the Antarctic Peninsula. The other half of the filters were without side walls resulting in close-to-ambient temperature underneath. Plots without filters served as controls. UV-B supplementation of an extra 1.3 kJ UV-B(BE) was achieved using UV-mini-lamp systems during 15 days in the second season. We found no evidence that altered incident UV-B levels and temperature had an effect on maximum photosystem II efficiency (F(v)/F(m)) and effective photosystem II efficiency (DeltaF/F(m)') in both species. UV-B reduction did not influence contents of chlorophyll, carotenoids and methanol-soluble UV absorbing compounds in D. antarctica. Flowering shoot length of D. antarctica was not affected by UV-B reduction. Temperature enhancement tended to result in longer inflorescence axes. Results of two austral summer seasons of UV- reduction in natural stands of D. antarctica and T. complicatulum suggest that current ambient levels of UV-B do not have a direct effect on the photosynthetic performance and pigment contents of these species. Cumulative effects on growth have not been recorded after two years but can not be excluded on a longer term.