Ecological importance of ambient solar ultraviolet radiation to a sub-arctic heath community

While there is considerable knowledge of the effects of enhanced levelsof ultraviolet radiation (UV) on plant species, much less is known of theimportance of ambient levels of solar UV, particularly on natural plantcommunities. Effects of ambient solar UV radiation on a natural sub-Arcticheathcommunity were investigated in a three year UV exclusion experiment in northernSweden (68° N). UV transparent and UV opaque (excluding< 400 nm) plexiglas screens were placed over vegetation forthree years to determine ambient solar UV effects on growth, reproduction andphenology of the three dominant dwarf shrub species, Vacciniumuliginosum, V. vitis-idaea andEmpetrum hermaphroditum. Additionally, effects of ambientsolar UV radiation on leaf protection from UV-B were assessed throughmeasurements of leaf UV-B absorbing compounds. Flowering and berry productionbyV. uliginosum were greatly increased (by five and 15 fold)in plots receiving ambient solar UV compared to those where solar UV had beenexcluded for three years. However, solar UV had no effect on stem growth,senescence and cover of the dwarf shrub species studied. It was thereforeconcluded that sub-Arctic dwarf shrubs are generally tolerant of ambient solarUV. Counterintuitively, ambient solar UV radiation reduced the levels of UV-Babsorbing compounds in both Vaccinium species suggesting areduction in protection provided. This indicates that measurements of leaf UV-Babsorbing compounds do not necessarily provide a good indicator of planttolerance to UV.