Impacts of Climate Change on Antarctic Vascular Plants: Warming and UV-B Radiation

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9615268 Day There is strong evidence that the climate of the Antarctic Peninsula has changed appreciably in this century. Weather records indicate that mean summer air temperatures have risen 1oC over the past 45 yr at some Peninsula locations. In addition to this warming trend, springtime ozone depletion events have resulted in well-documented increases in UV-B radiation levels. These rapid changes in regional climate provide a unique opportunity to assess the impacts of climate change on vascular plants. While the presence of only two native vascular plant species (Deschampsia antarctica and Colobanthus quitensis) and their sparse distribution in Antarctica attest to the severe conditions for plant survival, there are already indications that climate changes are exerting a strong influence on these species. Regional warming appears to be leading to rapid increases in populations of these species, based on censuses along the Peninsula. The influence of enhanced UV-B levels on these species is less clear. An experiment has been initiated in which temperature and UV radiation levels are manipulated around naturally growing Deschampsia and Colobanthus plants on the Antarctic Peninsula to assess their response to these factors. Assessment involves examining changes in photosynthesis, growth and reproduction of these plants following warming or exclusion of different UV components. During the first field season growth significantly improved under warming treatments. Exclusion of UV did not have any significant effects, although conclusions from this short-term assessment would be premature. Field manipulations will be continued, and expanded in the current assessment of plant responses in four key areas: (1) photosynthesis, (2) general thermal adaptations, (3) reproduction, and (4) soils. These areas are critical to understanding plant responses to climate change in Antarctica. (1) Photosynthesis - Antarctic plants have unique photosynthetic charact eristics including the ability to photosynthesize at near freezing temperatures and a high sensitivity to moderate temperatures. Using in vitro and in vivo techniques including gas exchange, chlorophyll fluorescence and enzyme assays, the mechanisms responsible for these unique photosynthetic traits will be examined. It will also be determined whether these species can alter these traits in response to changes in climate. (2) General thermal adaptations - These plants must also possess well-developed thermal adaptations that allow them to survive in the Antarctic. Cell membrane stability, osmotic potentials and supercooling characteristics of these plants will be noted to determine how these characteristics change in response to our field manipulations. (3) Reproduction - Warming appears to substantially improve sexual reproduction in these plants. However, high levels of UV-B may reduce reproductive success by damaging pollen. The influence of these opposing factors will be observed by examining the production and viability of pollen and seeds under field manipulations. (4) Soils - Nutrient cycling plays an important role in controlling plant responses to changes in climate. Baseline information will be collected on pools of nutrients (C, N, P) in soils and plants under our field manipulations, which will be complimented with measurements of soil respiration.