The importance of facilitative interactions on the performance of Colobanthus quitensis in an Antarctic tundra

Aims: The sign of interactions among plants in very harsh environments is under debate. The Antarctic tundra is one of the harshest environments on Earth and only two vascular plants (Deschampsia antarctica and Colobanthus quitensis) have successfully established natural populations. D.antarctica mostly establishes facilitative interactions with other species (mosses), but there is no information about the inter-specific interactions established by C.quitensis. We assessed whether C.quitensis grows frequently associated with D.antarctica, and if D.antarctica neighbours have a positive effect on the survival, growth and photochemical efficiency of C.quitensis individuals. Location: King George Island, Antarctic Peninsula. Methods: To assess the spatial association among the two Antarctic vascular plants fifty 50mx50cm quadrats were sampled on each of four different substrates: moss carpet areas; dead moss carpet areas dominated by D. antarctica; a transition zone between dead moss carpets and fellfields; and fellfields characterized by very poor vegetation cover. Infrared thermal images were taken to estimate whether growth associated with D. antarctica affected the foliar temperature of C. quitensis. The importance of D.antarctica neighbours on the growth, survival and photochemical efficiency of C.quitensis was evaluated with a neighbour removal experiment. Results: The number of C. quitensis individuals associated with D. antarctica was significantly higher than when growing alone in the moss carpet and the dead moss carpet, while in the transition zone there was a trend in that direction. C. quitensis individuals growing associated with D. antarctica were bigger than those growing alone in these three substrate types. In the fellfield site there were no significant differences, neither in the number nor the size of individuals when growing alone or associated with D. antarctica. Foliar temperature of C. quitensis individuals associated with D. antarctica was slightly (1.1 degrees C) but significantly higher than in those growing alone. The growth, survival and photochemical efficiency of C. quitensis individuals with neighbours were higher than in individuals with neighbours removed. Conclusions: Our results indicate that D. antarctica has a facilitative effect on the growth, survival and photochemical efficiency of C. quitensis. Thus, facilitative interactions are present and are important in one of the harshest environments on Earth, although results from the fellfield site indicate that further research is needed.