9524144 Stratospheric ozone loss, resulting primarily from chemicals generated by human activities, results in an increased amount of solar ultraviolet-B radiation reaching the earth. Ultraviolet-B radiation is capable of damaging biological systems, including DNA. Only a modest amount of research, however, has been directed toward the potential biological consequences of stratospheric ozone depletion, and virtually nothing has been done at the level of terrestrial ecosystems. This research is an ecosystem-level study of the responses to elevated solar ultraviolet-B resulting near Ushuaia, Argentina. The site is on the southern tip of South America across the Drake Passage from the Antarctic Peninsula. This location experiences more pronounced ozone reduction than at anywhere else in the world where terrestrial ecosystems with appreciable plant cover occur. Three phenomena contribute to this: The so-called "ozone hole" can pass directly overhead, parcels of ozone-depleted air can float northward from the ozone hole, and a general erosion of the ozone layer is most prominent at high latitudes and in the Southern Hemisphere. At the study site, extremely high fluxes of ultraviolet-B can occur when skies are clear and, when cloudy, there can be very high ultraviolet-B relative to total solar radiation. Thus, this will be an extreme case study to determine ecosystem-level effects of ozone reduction. A three-year, on-site field study of a shrub-grass community will be conducted. Effects of elevated ultraviolet-B will assessed for both acute exposures, such as when the ozone hole passes overhead and as chronic, growing-season and multi-season exposures to elevated ultraviolet-B. For responses to acute exposures to high ultraviolet-B and high ultraviolet-B/(total solar radiation) ratios, damage to DNA and photosynthesis will be determined. Acute exposures will be studied both as natural events (tracking the precession of the ozone hole by downloading satellite-based images and anticipating overhead passage) and by simulating such occurrences with special UV lamp systems. Most of the effort will be directed to effects of chronic exposures at the population level (e.g., reproduction and expansion or contraction of plant populations) and at the ecosystem level. Researchers will determine changes in competitive balance among species, timing of annual biological events, plant consumption by insects, and decomposition of plant litter. If solar ultraviolet-B affects such ecosystem-level processes, there are many implications for the function and integrity of these systems. Preliminary evidence collected recently in Argentina shows large effects of sunlight ultraviolet-B on DNA damage, plant growth and insect herbivory. Changes in litter decomposition may affect ecosystem carbon balance and atmospheric carbon dioxide concentrations. Knowledge of the direction and magnitude of such changes is essential if we are to predict the biological consequences of changing atmospheric chemistry and develop rational management strategies.
