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This subproject, "Effects of UV-B on birch: structural and phytochemical responses and herbivore susceptibility" was part of the project Herbivory in relation to variable defenses of woody plants lead by Asoc. Prof. Jorma Tahvanainen.
In silver birch tissue damage has been observed under very high doses of UV-B (Anu Wulff, pers. com.), but not under more realistic doses. Under these realistically increased doses no major effect was observed on growth and morphology or photosynthesis. However, our results indicate that realistically increased UV-B, both in growth chamber and greenhouse experiments, significantly alters the concentration of several phenolics in birch. We also observed that the feeding response of insects is different in UV-B treated birch seedlings to those from controls.
Although the recent surge in interest on UV-B research has been triggered by ongoing stratospheric ozone depletion, photomorphogenic responses to UV-B probably play an important role in the adjustment of plants to their environment in an undisturbed UV-B environment. Other, better studied, photoreceptors (e.g. phytochrome) are known to be required for normal plant growth, both within canopies and in plants growing without neighbours. Some of the light and UV radiation dependent adjustments are important for plant-plant interactions and, most probably, also for plant-herbivore interactions.
Our experiments aim to answer the following questions:
Outdoor experiments. In practice it is too expensive to irradiate with UV-B a large enough number of whole fully developed trees. Two feasible options are (1) to irradiate some branches in large trees, or (2) irradiate whole saplings. We have opted for the second approach because in a long term experiment some of the responses may depend on the status of whole plant rather than on localised effects.
Supplemental UV-B is provided by means of special fluorescent lamps filtered through cellulose acetate to remove radiation of shorter wavelengths. As this combination of lamp + filter emits some UV-A, the same lamps are used for the "UV-A" control, but filtered with polyester film which removes UV-B and radiation of shorter wavelengths. An additional control of non-energised lamps is also used. The output of the lamps is modulated using a datalogger and high frequency dimming ballasts so that the UV-B addition is a constant proportion of natural incoming UV-B. Seven replicate blocks were installed. (A detailed description of the irradiation system is available.)
Indoors experiments. Either clonal plantlets or seedlings are used. The experiments are short term (weeks to months) and are carried out in the new growth chambers and growth rooms of the Faculty of Forestry. UV-B, UV-A, and red light (R) is supplied by special fluorescent lamps. Far-red light is supplied either by special fluorescent lamps, or by incandescent lamps filtered with FR pass filters.
Aphalo, P J, Tegelberg, R, Julkunen-Tiitto, R (1999) The modulated UV-B system at the University of Joensuu. Biotronics 28, 109-120.
Tegelberg, R, Julkunen-Tiitto, R, Aphalo, P J (2001) The effects of long-term elevated UV-B on the growth and phenolics of field-grown silver birch (Betula pendula). Global Change Biology 7, 839-848.
Tegelberg, R, Julkunen-Tiitto, R, Aphalo, P J (2002) The effects of long-term elevated ultraviolet-B radiation on phytochemicals in the bark of silver birch (Betula pendula). Tree Physiology, 22, 1257–1263.
Tegelberg R, Veteli T, Aphalo P J, Julkunen-Tiitto R (2003) Clonal differences in growth and phenolics of willows exposed to elevated ultraviolet-B radiation. Basic and Applied Ecology, 4, 219-228.
Veteli T O, Tegelberg R, Sipura M, Tahvanainen J, Aphalo P J (2003) Interactions between willows and insect herbivores under enhanced ultraviolet-B radiation. Oecologia, 137, 312–320.
Julkunen-Tiitto R, Häggman H, Aphalo P J, Lavola A, Tegelberg R, Veteli T (2005) Growth and defense in deciduous trees and shrubs under UV-B. Environmental Pollution, 137, 404–414.
Tegelberg, R (2002) Impact of elevated ultraviolet-B radiation on three northern deciduous woody plants. PhD thesis. University of Joensuu. Department of Biology. ISBN 952-458-131-0.
Author: Pedro J. Aphalo.