NON-DAMAGING AND POSITIVE EFFECTS OF UV RADIATION ON HIGHER PLANTS - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 164

in northern Sweden. They observed contrasting responses in which UV-B
supplementation resulted in increased insect herbivory in the dwarf shrub Vaccinium
myrtillus L. but reduced herbivory in Vaccinium uliginosum L. Contrasting responses
were observed by Lindroth et al 89 .
Salt et al 90 also used supplementary UV-B radiation to simulate a 15% ozone
depletion (seasonally adjusted) to study psyllid ( Strophingia ericae (Curtis))
populations on heather ( Calluna vulgaris L.). They found that enhanced UV-B caused a
gradual reduction in S. ericae populations compared with controls over 27 months.
They tentatively proposed that reduced levels of the amino acid isoleucine in the plants
exposed to supplementary UV-B radiation may have caused the lower psyllid
population.
From the examples reported here, it can be concluded that exposure of plants to
UV-B radiation, or to more UV-B radiation than the control plants, reduces insect
herbivory in 8 cases, but increases it in 2 examples. However, the interactions are
notably complex 91 .
11. Leaf litter decomposition
Leaf litter decomposition has an important influence on plant growth 92 because it
results in the production of soil organic matter and the mineralization of elements.
Studies on the effect of UV-B radiation on leaf litter decomposition have been
somewhat contradictory. Two outdoor studies have shown that UV-B radiation added to
backgound daylight decreases the rate of litter decomposition ( Vaccinium 93 ;
Calamagrostis 94 ); by contrast, two studies reported that UV-B radiation added to
backgound daylight increases the rate of litter decomposition ( Triticum 95 ; Quercus 96 ).
Newsham et al 97 point out that the above were relatively short-tem studies (between
0.15 and 1.33 years). In a relatively long-term (4.08 y) experiment they have clearly
demonstrated that, at least for Quercus robur L., elevated UV-B levels accelerated the
rate of decomposition of leaf litter produced by the plants when the litter was placed in
a fully randomised design in the litter layer of a Quercus/Fraxinus woodland. Bearing
in mind the important role of litter decomposition in ecosystems, it is clear that further
studies are necessary if we are to understand the apparently important role of UV-B
radiation in modulating the decomposition of leaf litter.
Further recent and relevant review reading in the general subject area of UV-B
radiation effects on ecosystems at various trophic levels including insects, pathogens,
symbionts and decomposers can be found in Ballaré et al 98 , Paul et al 99,100 and van de
Staaij et al 101 .
12. The UV-B photoreceptor
Evidence for a specific UV-B photoreceptor has been mentioned in passing on
several occasions in this article. Action spectroscopy is a useful tool for indicating the
absorptive properties of functional photoreceptors. Under ideal conditions, the action
spectrum would show close spectral similarity to the absorption spectrum of the target
photoreceptor. In practice, the similarity is often distorted because the target
photoreceptor is usually surrounded by tissue with selective absorptive and scattering
properties so the measured action spectrum can be distorted. This can be a particular