The impacts of UV-B radiation on the regeneration of a sub-arctic heath community

The effects of ultraviolet-B radiation on regeneration after disturbance of a natural sub-arctic heathland have been investigated. Areas of pristine d warf shrub heath were denuded of all above ground biomass in 1992 and expos ed to enhanced UV-B (simulating a 15% depletion of the ozone layer). The re sulting regenerated stem and leaf growth parameters were measured after fou r years on three dwarf shrubs, Vaccinium myrtillus, V. uliginosum and V. vi tis-idaea and the grass Calamagrostis lapponica; leaves of the three dwarf shrubs were also analysed for UV-absorbing compounds and carbohydrates. Reg eneration irrespective of treatment was slow, with Empetrum hermaphroditum failing to regenerate at all. Vaccinium myrtillus showed the most rapid reg eneration attaining much of its original biomass in four years. There was a significant interaction between UV-B and year of regeneration in V. myrtil lus; annual stem length increment showed an initial stimulation of 75% unde r enhanced UV-B in the first year of regeneration while a reduction of 16% was observed in the fourth year. Both V. uliginosum and V. vitis-idaea show ed a reduction in annual stem length increment as regeneration progressed w ith a greater than 50% reduction in stem increment in the fourth year of re generation compared to the first. Vaccinium uliginosum also showed an initi al reduction in stem length increment of 40% under enhanced UV-B. None of t he species were affected by enhanced UV-B in terms of total regenerated ste m and leaf biomass or UV-absorbing compounds in regenerated leaf tissue. To tal leaf carbohydrate and the ethanol/water soluble fraction in V. uliginos um were significantly increased by 29% and 31% respectively under enhanced UV-B. This suggests either a stimulation of photosynthesis or a reduction i n sink size for photo-assimilates. Results are discussed in the context of the extremely slow regeneration of sub-arctic heath communities and the imp lications of contrasting UV-B effects on the regenerative ability of differ ent species.