Neighbourly Dispute at the Edge of Life: Species Interactions Among Antarctic Mosses

Question: The stress gradient hypothesis predicts that extreme environments favour positive over negative species interactions, that is, facilitation over competition. However, along the Antarctic Peninsula (maritime Antarctic), we observed indirect evidence of competitive interactions among moss species, leading to the question of whether mosses compete even under harsh abiotic conditions for plant growth. Location: Lagoon Island and Anchorage Island, northern Marguerite Bay, Antarctic Peninsula (67° S 68° W). Methods: In a laboratory experiment based on simulated Antarctic field conditions, we used the locally dominant moss, Sanionia uncinata, in combination with three other native moss species to compare lateral growth rates between individual clumps and species combinations. The experiment included species associations collected directly from the field as well as experimentally assembled combinations. Results: After one simulated growing season, S. uncinata showed increased growth in all combinations, whereas all other species decreased in surface area, demonstrating contramensalism—an interaction in which one species is positively and the other negatively affected. Conclusions: While the underlying mechanisms cannot be confirmed, the results indicate that significant interactions do occur between moss species under simulated Antarctic conditions and should therefore be taken into account, alongside strong abiotic drivers, to understand moss community assembly in extreme environments such as those of the Antarctic.