SHORT-TERM EFFECTS OF ENHANCED UV-B AND CO2 ON LICHENS AT DIFFERENT LATITUDES

Interaction effects of UV-B and CO2 on three lichens species, Cladonia arbuscula, Cetraria islandica and Stereocaulon paschale, from two lat itudinal sites, 68 degrees N and 56 degrees N, were studied in a labor atory experiment. The response of the plants was recorded by measuring their chlorophyll fluorescence. All species had a similar response to enhanced UV-B depending on the latitude from which the population cam e and the time of the season when they were sampled. Overall, there wa s a significant increase in photosystem II yield (as measured by a flu orescence technique) due to UV-B and no separate effect due to enhance d CO2, although there was a significant interaction between CO2 and UV -B. The increase due to UV-B was at the low CO2 level. There were also significant differences in response due to latitude. The results cont radict our hypotheses that negative effects of UV-B would be larger in the North than in the South and that a negative response should be es pecially large during the early season. (C) 1995 The British Lichen So ciety