Effects-Terrestrial Plants-L3

Effects/Terrestrial Plants-L3From Roger
 CIESIN Thematic Guides
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Ultraviolet-B Effects on Terrestrial Plants
Effects of elevated ultraviolet-B (UV-B) on terrestrial plants vary widely
among species and even among cultivars of the same species. These effects
range from the molecular scale, such as DNA damage, to tissue and whole plant
effects, including a decrease in photosynthetic activity and changes in plant
structure and biomass. In "The Changing Solar Ultraviolet Climate and the
Ecological Consequences for Higher Plants," Caldwell, Teramura, and Tevini
(1989) discuss a range of potential consequences from the molecular scale up
to ecosystem levels and illustrate these in a flowchart. Large-scale results
include a possible shift in competitive balance and species population within
communities and ecosystems.
The majority of research on elevated UV-B impacts has been carried out in
laboratory settings where climatic conditions can be controlled. Notable
exceptions to this include field studies of certain agriculturally important
species and coniferous trees. Teramura et al. (1991) outline both types of
studies in the chapter "Terrestrial Plants" of the United Nations Environment
Programme's (UNEP) Effects of Ozone Depletion.

Several studies have investigated the effects on agricultural crops. In a
six-year field study at the University of Maryland, Teramura, Sullivan, and
Lydon (1990) describe significant yield reductions of soybean under simulated
ozone-depletion scenarios for one species, while another species appeared
tolerant, in "Effects of UV-B Radiation on Soybean Yield and Seed Quality."
Conversely, in "Growth and Yield of Field-grown Soybean in Response to
Enhanced Exposure to UV-B Radiation," Sinclair, N'Diaye, and Biggs (1990)
indicate no effect of enhanced UV-B on soybeans in a study conducted at the
University of Florida. Teramura, Ziska, and Sztein (1991) report sensitivity
of rice cultivars to UV-B was exhibited in certain species in "Changes in
Growth and Photosynthetic Capacity of Rice with Increased UV-B Radiation."
These studies also emphasize the impact that local microclimatic conditions
can have on plant sensitivity to increased UV-B.

Indirect effects of UV-B on agricultural and other plant species have also
been observed. Barnes, Flint, and Caldwell (1990) describe changes in
morphology of wheat and wild oat species exposed to enhanced UV-B in
"Morphological Responses of Crop and Weed Species of Different Growth Forms to
Ultraviolet-B Radiation." These results suggest that UV-B enhancement may lead
to a shift in competitive balance among certain species. Field studies with
loblolly pine trees show decreased photosynthetic activity under simulated
ozone depletion scenarios. Reductions in productivity ranged from 0 to 40
percent depending on seed sources and the age of tree needles. Other
conclusions drawn from this study suggest UV-B may have a cumulative effect in
the loblolly pine, resulting in reduced growth over the lifetime of the tree.
Teramura and Sullivan (1991) review these effects in "Potential Impacts of
Increased Solar UV-B on Global Plant Productivity." Rupert (1986) discusses
plants' natural photorepair mechanisms, which could mitigate UV-B damage, in
"Cellular Repair and Assessment of UV-B Radiation Damage."> These mechanisms,
along with other factors such as temperature, precipitation, and availability
of nutrients, are likely to modify the impacts of ozone depletion. As with
many biological systems, further studies are required to gain a better
understanding of all processes involved.

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