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The flux of ultraviolet-B radiation (UV-B) at the earth surface has increased in recent years and it is expected to continue increasing. The increase in the UV-B flux is caused by the depletion of the ozone layer in the stratosphere, mainly as a consequence of the release of chlorofluorocarbons (CFCs). As these compounds have a long half life, their effect will persist for many years even if their use is drastically reduced.
Plants are sensitive to UV-B: damage to cells and chloroplasts has been observed, especially with high doses, but UV-B can also alter the morphology of plants and regulate the synthesis of chemical compounds. The latter responses are photomorphogenic, and there is evidence of the existence of a photoreceptor of UV-B, distinct from the UV-A and blue light photoreceptor(s) and phytochromes. All the effects of UV-B mentioned above can directly or indirectly affect the growth of trees, and could consequently also affect forest primary production and timber yield.
The objective of this project is to get integrated knowledge of how UV-B radiation affects the growth of silver birch (Betula pendula) and other tree species from high latitudes (Pinus sylvestris, Picea abies and Nothofagus pumilio). Experiments consist (a) in growing seedlings under current and increased levels of UV-B. We measure in seedlings: (1) growth and morphology of shoots and roots, (2) leaf gas-exchange and water use efficiency, (3) epidermal optical properties as affected by the accumulation of UV-B absorbing compounds, (4) ultrastructure of mesophyll and stomatal cells and chloroplasts, and (5) function of the photosynthetic apparatus (Rubisco, Photosystem II).
Aphalo P J, Ballaré C L, Díaz S (1996) Possible effects of increased UV-B on the vegetation of Tierra del Fuego. Ecodecision (Montreal) 19, 71– 73.
Lavola A, Julkunen-Tiitto R, Aphalo P, de la Rosa T, Lehto T (1997) The effect of u. v.-B radiation on u. v.-screening secondary metabolites in birch seedlings grown in simulated forest soil conditions. New Phytologist 137, 617– 621.
Lavola A., Julkunen-Tiitto R, Aphalo P J (1998) Host-plant preference of an in-sect herbivore mediated by UV-B and CO2 in relation to plant secondary metabolites. Biochemical Systematics and Ecology 26, 1-12.
Lavola A, Julkunen-Tiitto R, de la Rosa T, Lehto T, Aphalo P J. (2000) Allocation of carbon to growth and secondary metabolites in birch seedlings under UV-B and CO2 exposure. Physiologia Plantarum, 109, 260–267.
de la Rosa T M, Julkunen-Tiitto R, Aphalo PJ and Lehto T. (2001) Secondary metabolites and nutrient concentrations in silver birch seedlings under five levels of daily UV-B exposure and two relative nutrient addition rates. New Phytologist, 150, 121-131.
de la Rosa T M, Aphalo P J, Lehto T (2003) Effects of ultraviolet-B radiation on growth, mycorrhizas and mineral nutrition of silver birch (Betula pendula) seedlings grown in low-nutrient conditions. Global Change Biology, 9, 65-73.
Lavola A, Aphalo P J, Lahti M, Julkunen-Tiitto R (2003) Nutrient availability and the effect of increasing UV-B radiation on Scots pine. Environmental and Experimental Botany, 49, 49-60.
Aphalo P J (2003) Do current levels of UV-B radiation affect vegetation? The importance of long-term experiments. New Phytologist, 160, 273–276. (Invited commentary.)
Rousseaux M C, Julkunen-Tiitto R, Searles P S, Scopel A L, Aphalo P J, Ballaré C L. (2004) Solar UV-B radiation affects leaf quality and insect herbivory in the southern beech tree Nothofagus antarctica. Oecologia, 138, 505–512.
Tegelberg R, Julkunen-Tiitto R, Aphalo P J (2004) R:FR light ratio and UV-B radiation: their effects on leaf phenolics and growth of silver birch seedlings. Plant Cell and Environment, 27, 1005–1013.
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.
de la Rosa, T M (2002) Responses of forest tree seedlings to far-red and ultraviolet-B signals. PhD thesis. University of Joensuu, Faculty of Forestry. Joensuu. ISBN 952-458-121-3.
Anu Lavola (1997) PhD thesis, University of Joensuu.
T. Matthew Robson (1997) MSc thesis, University of Edinburgh.
Johanna Riikonen (1998) MSc thesis, University of Joensuu.
Markku Lahti (1999) MSc thesis, University of Joensuu.
Author: Pedro J. Aphalo.