Riitta Tegelberg (2002) Impact of elevated ultraviolet-B radiation on three northern deciduous woody plants PhD Thesis. Faculty of Science, University of Joensuu Joensuu: Abstract: The aim of this thesis was to assess the impact of elevated ultraviolet-B radiation (UV-B, 280-320 nm) on growth and phytochemicals of three northern deciduous woody species. Therefore, silver birch (Betula pendula Roth) seedlings were exposed for three growing seasons and clonal shoots of dark-leaved willow (Salix myrsinifolia Salisb.) and tea-leaved willow (Salix phylicifolia L.) for one growing season to elevated UV-B radiation in a modulated irradiation system outdoors. In addition, clonal plantlets of dark-leaved willow were exposed to short-term elevated UV-B radiation in a growth chamber.
Elevated UV-B radiation significantly increased the concentrations of UV-B-absorbing flavonoids, such as quercetin-3-arabinoside, quercetin-3-glucose+glucuronide and kaempferol-3-rhamnoside, and a few phenolic acids in silver birch leaves during the first and second growing seasons of the field study. During the third growing season, the contents of phenolics in leaves were not affected by the treatments; but compared with the controls, the stem diameter growth of the saplings treated with elevated UV-B radiation was significantly reduced. It was also found that with long-term elevated UV-B treatment the concentrations of a phenolic acid, 3,4’-dihydroxypropiophenone-3-glucopyranoside, and two soluble sugars, sucrose and glucose, increased in the bark of silver birch saplings. These results indicate that if exposure is long-term, the growth of field-grown silver birch saplings is affected by elevated UV-B radiation. The symptoms of UV-B stress also included changes in the metabolism of carbohydrates and phenolic compounds.
Indoors, with elevated UV-B treatment the leaves of dark-leaved willow clones accumulated UV-B-screening luteolin glycosides, myricetin glycoside and a hydroxycinnamic acid derivative, while the low-UV-B-absorbing salicylates, salicin and saligenin, decreased in concentration. Similarly, in the field, with elevated UV-B radiation certain flavonoids and phenolic acids accumulated in the leaves of dark-leaved willow clones and tea-leaved willow clones, while the low-UV-B-absorbing phenolics, i.e. condensed tannins, gallic acid derivatives and salicylates, either decreased or remained unaffected. These results show that under higher UV-B exposure, willow leaves accumulated only those phenolics that screen UV-B radiation efficiently. The results also indicate that the chemical responses in willows were more clone-specific than species-specific.
Despite high constitutive concentrations of UV-B-protective flavonoids in the leaves, both growth and biomass of one field-grown tea-leaved willow clone were sensitive to elevated levels of UV-B radiation. In contrast, the growth of dark-leaved willows grown outdoors or indoors was not affected by elevated UV-B radiation, even though the concentrations of UV-B-screening flavonoids in the leaves were low. Consequently, the secondary chemical background of a native willow species or clone does not necessarily predict its sensitivity to elevated UV-B radiation.
Notes: University of Joensuu, PhD Dissertations in Biology, No. 11. ISBN 952-458-131-0
