Format: ORAL

Ana Aramburu1, Jos Raggio1, David S. Pescador1, Nria Beltrn-Sanz1, Ana Pintado1, Leopoldo G. Sancho1

1 Section of Botany, Faculty of Pharmacy, Complutense University of Madrid, plaza Ramón y Cajal s/n, 28040 Madrid (Spain)

Understanding the environmental responses of the polar cryptogamic flora and determining its ecological boundaries is a useful tool to evaluate the impact of ongoing global change on Antarctic regions. In maritime Antarctica, ice-free rocks on coastal areas and on nunataks within mountain systems offer suitable niches for cryptogams, particularly for lichens able to survive in severe environmental conditions. Due to their poikylohydric nature, these photosynthetic lithobionts are strongly tied to the local climatic conditions. The present study focuses on the fruticulose lichen Usnea aurantiaco-atra (Jacq.) Bory, an Antarctic endemism vastly spread throughout maritime Antarctica. The aim of the research is to assess the ecophysiological optimums and ranges of tolerance of U. aurantiaco-atra to environmental change. Two sites were chosen across an altitudinal gradient within the South Bay on Livingston Island (South Shetland Islands) with intent to cover an environmental-pressure range of the subject species: Punta Polaca (50 m a.s.l.) and El Castillo Nunatak (449 m a.s.l.). The photosynthetic and respiratory rates of thalli collected from each site were measured in relation to key drivers such as water content, temperature, and light under controlled laboratory conditions. Metabolic performance was analysed in situ for both locations through continuous chlorophyll a fluorescence monitoring paired with simultaneous recording of microclimatic conditions. To further understand potential acclimation or adaptation mechanisms adopted by the photobionts of U. aurantiaco-atra, induction-recovery curves were conducted. Additionally, an extensive network of temperature and relative humidity microsensors was deployed throughout multiple lithic niches at both sites and kept recording for over a year. Preliminary results suggest that the coastal population achieves significantly greater photosynthetic activity at higher temperatures. No dissimilarities have been found in the performance of coastal and mountainous individuals at lower temperatures. There seems to be strong environmental filtering in the nunatak, which points to greater ambient stress.