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

The stratospheric ozone layer has been depleted at high and mid-latitudes a s a consequence of man's pollution of the atmosphere, and this results in i ncreasing ultraviolet-B radiation at ground level. We investigate the effec ts of further radiation increases on plants and ecosystems by irradiating n atural sub-Arctic and Arctic vegetation with artificial W-B radiation in fi eld experiments extending over several years. Our experimental sites are lo cated at Abisko, in northern Sweden (68 degrees N), and Adventdalen, on the island of Spitsbergen (78 degrees N). Additional UV-B induced interspecifi c differences in plant response in terms of reduced (or, in one case, incre ased) growth, changed morphology and changed pigment content. In some cases effects seem to be accumulated from one year to another. Plant litter deco mposition is retarded. We are also studying how UV-B enhancement may affect the interaction between species. In some experiments we combine UV-B enhan cement with changes in other factors: carbon dioxide concentration, water a vailability, and temperature. In some cases the effect of radiation enhance ment is modified, or even reversed, by such changes. Over a four year perio d we did not find any significant radiation induced change in species compo sition, but based on the effects on individual plant species, such changes can be expected to take place over a longer time.