OF INCREASED SOLAR ULTRAVIOLET RADIATION ON TERRESTRIAL ECOSYSTEMS
M.M. Caldwell, L.O. Björn, J. F. Bornman, S.D.
Flint, G. Kulandaivelu, A.H. Teramura and M. Tevini
Elevated solar UV-B radiation associated with stratospheric
ozone reduction may exert effects on terrestrial ecosystems through actions
on plants, microbes, and perhaps on some animals. At the ecosystem level,
the effects are less well understood than at the molecular and organismal
levels. Many of the most important, yet less predictable, consequences
will be indirect effects of elevated UV-B acting through changes in the
chemical composition and form of plants and through changes in the abiotic
environment. These indirect effects include changes in the susceptibility
of plants to attack by insects and pathogens in both agricultural and natural
ecosystems; the direction of these changes can result in either a decrease
or an increase in susceptibility. Other indirect effects of elevated UV-B
include changes in competitive balance of plants and nutrient cycling.
The direct UV-B action on plants that results in changes in form or function
of plants appears to occur more often through altered gene activity rather
than damage. The yield of some crop varieties can be decreased by elevated
UV-B, but other varieties are not affected. Plant breeding and genetic
engineering efforts should be able to cope with the potential threats to
crop productivity due to elevated UV-B. For forest trees, this may be more
difficult if effects of elevated UV-B accumulate over several years. All
effects of elevated UV-B radiation must be considered in the context of
other climate changes such as increased temperature and levels of carbon
dioxide, which may alter the UV-B responses, especially for plants. The
actions of elevated carbon dioxide and UV-B appear to be largely independent,
but interactions occur between changes in UV-B and other factors. Other
ecosystem-level consequences of elevated UV-B radiation are emerging and
their magnitude and direction will not be easily predicted.
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