The Intensity of the Interaction Between Native and Non-native Antarctic Plants Depends on the Non-native Plant, Water Availability and Temperature.

Abstract Anthropogenic pressure and climate change have generated important changes in the environmental conditions of Antarctic ecosystems (e.g., arrival of non-native species, increase in temperature, precipitation, and ice-free areas), which can generate negative impacts on the native flora. Thus, we evaluated how the presence of the non-native plants Poa annua and Juncus bufonius could impact the native species Colobanthus quitensis and Deschampsia antarctica under climate change scenarios. Individuals of C quitensis/D. antarctica and J. bufonius/P. annua were subjected to four growth conditions: 6°C/low water availability (LW); 8°C/LW and 6°C/high water availability (HW) and 8°C/HW. We hypothesize that competition will be more intense at 8°C/HW, while at 6°C/LW the predominant interaction will be facilitation. Under 8°C/HW conditions all species significantly increase biomass production, but mortality of native species tends to increase. The relative interaction index (RII) showed a competitive effect of both non-native species on D. antarctica, independent of temperature and water availability, while for C. quitensis competition is more intense at LW. These results show that the effect of climate change could enhance the impact of non-native species on native species in Antarctic ecosystems, including non-native species that have been reported but do not have stable populations in the Antarctic Peninsula.