DE LA ROSA, T.M., M. LAHTI, T. LEHTO & P.J. APHALO.
University of Joensuu, Faculty of Forestry, P.O. Box 111, 80101 Joensuu, FINLAND.
Increasing ultraviolet-B (UV-B) radiation may be expected
to affect mycorrhizas either through changes in carbon allocation, or through
changes in plant secondary metabolism. Our objective was to assess the effects
of increased UV-B radiation on growth and ectomycorrhizas of silver birch (Betula
pendula) and Norway spruce (Picea abies) seedlings. The seedlings
were grown in a greenhouse, in a substrate containing forest soil (humus from
birch and spruce forest respectively). In the birch experiment, the increased
UV-B regime (2 h daily) corresponds to 25 % ozone depletion under a clear sky
on a summer solstice day in Finland. In the spruce experiment, there were five
doses ranging from 0 to a dose equivalent to 55% ozone depletion. The plants
were exposed to these treatments for eight weeks. Short roots were classified
based on morphology.
UV-B radiation did not affect the growth of the plants in either species. In
birch, there was no treatment effect on the frequency of the different mycorrhiza
morphotypes. In spruce, there was a small but significant shift from types without
a fully developed mantle to fully developed mycorrhizas. As a whole, the changes
in the formation of mycorrhizas were small, and even the highest doses of UV-B
were not detrimental.
Key words: Betula pendula, ectomycorrhizas, Picea abies, ultraviolet-B