Distributional and ecophysiological study on the Antarctic lichens species pair Usnea antarctica/Usnea aurantiaco-atra

The factors that control lichen distribution in Antarctica are still not well understood, and in this investigation we focused on the distribution, local and continental, and gas exchange of a species pair, closely related lichens with differing reproductive strategies, Usnea aurantiaco - atra (fertile) and Usnea antarctica (sterile, sorediate). The local distributions of these species were recorded along an altitudinal gradient of nearly 300 m at South Bay, Livingston Island, and microclimate was also recorded over 1 year. The photosynthetic responses to temperature, light and thallus water content were determined under controlled conditions in the laboratory. The species were almost identical in their photosynthetic profiles. Locally, on Livingston Island, U. antarctica was confined to low altitude sites which were warmer and drier, whilst U. aurantiaco - atra was present at all altitudes. This contrasts with its distribution across Antarctica where U. antarctica grows 9° latitude further south than U. aurantiaco - atra . Temperature appears not to be the main controller of distribution in these species, but dryness of habitat, which will influence length of activity periods, may be important.