The cryptogamic cover in the Antarctica: the response to temperature discriminates endemic and cosmopolitan species

Abstract

The cryptogamic tundra in maritime Antarctica is composed of lichens and mosses of diverse phylogeographic origins. Around half of the total cryptogamic flora is made up of species that are either endemic or cosmopolitan, yet these two groups are at opposite poles of the phylogeographic classification. For cosmopolitan species the maritime Antarctic represents a small part of their global distribution whereas, for endemic species, it constitutes their only available location. The two groups have evolved under dissimilar geographic and environmental conditions and might be expected to show different adaptive potential, having been selected to meet distinct limiting factors. For instance, under a warming scenario, it might be expected that cosmopolitan species will have adaptive advantages compared to the endemic ones. To test this hypothesis, we investigated the response of net photosynthesis to light intensity and temperature for some of the most abundant species of lichens (Himantormia lugubris, Usnea antarctica, Sphaerophorus globosus, Stereocaulon alpinum) and mosses (Andreaea gainii, Sanionia uncinata) belonging to different phylogeographic categories. We used standard CO2-exchange techniques under fully controlled measurement conditions to generate response curves of net photosynthesis to light and temperature. From these, we determined the respective optima obtaining significantly higher values of optimal temperature for the cosmopolitan species. In addition, we recorded the microclimatic conditions when selected species of each phylogeographic category were active in their natural habitats on Livingston Island (South Shetland Islands), using dataloggers and chlorophyll fluorescence monitoring. Both endemic and cosmopolitan species where most of the time active at around 4 ºC but while endemics were active always below 13 ºC, the cosmopolitans showed activity at temperatures up to 25 ºC. In conclusion, although growing well under present environmental conditions, cosmopolitan species (both lichen and mosses) showed a positive response to warmer temperatures that was not detected in the endemics.