9317019 Day The presence of well-documented stratospheric "ozone hole" events and enhanced ultraviolet-B radiation levels in Antarctica provide a unique opportunity to assess the effects of ultraviolet-B radiation on plant performance. There are several reasons to expect the ultraviolet-B radiation may be a significant, and increasingly important limitation to the performance of Antarctic vascular plants: Levels of terrestrial ultraviolet-B radiation in Antarctica have increased considerably in recent years, and are likely to continue increasing, particularly in austral spring; Recent research on marine phytoplankton in Antarctic waters has found that enhanced ultraviolet-B radiation levels associated with ozone hole events are responsible for significant reductions in phytoplankton productivity; Research on vascular plants in other regions has shown that supplemental ultraviolet-B radiation levels can limit the performance of many plant species; and Recent investigations have show that the leaves of many grasses and forbs from other regions are particularly ineffective at screening ultraviolet-B radiation before it reaches potentially-sensitive mesophyll tissue in the leaf interior. Thus, one would suspect that the grass Deschampsia antarctica and the forb Colobanthus quitensis, which are the only two vascular plants native to Antarctica, are likely to be relatively ineffective at screening ultraviolet-B radiation. Surprisingly, apparently no research has addressed the impacts of ultraviolet-B radiation on Antarctic vascular plants. The proposed research attempts to answer the question of whether ultraviolet-B, particularly ultraviolet-B radiation associated with ozone hole events, affects photosynthesis, growth, and reproductive performance of D. antarctica and C. quitensis. The relative magnitude of this limitation will be assessed by using experimental field treatments to compare ultraviolet-B radiation to other potential limitations. Selective filte rs will be used to remove UV components from sunlight over naturally-growing plants, while additional water or nutrients will be supplied to other plants. These field experiments will be complemented with more detailed investigations using supplemental ultraviolet-B radiation treatments in West Virginia. Recently developed techniques such as fiber-optic microprobes will be used to examine the UV/visible optical properties of leaves and reproductive structures in D. antarctica and C. quitensis, and assess how these change in response to enhanced ultraviolet-B radiation levels. This approach will elucidate some of the underlying mechanisms responsible for Antarctic plant responses to ultraviolet-B radiation in the field.
