Do Antarctic lichens modify microclimate and facilitate vascular plants in the maritime Antarctic? A comment to Molina-Montenegro et al. (2014)

摘要

A recent article published by Molina-Montenegro etal. (Journal of Vegetation Science24: 463) examines the association of Antarctic native plant and lichen species to the lichen Usnea antarctica on Fildes Peninsula, King George Island, maritime Antarctica. The authors report that on two sites, five out of 13 and four out of 11 species of lichens and mosses were spatially associated with U.antarctica, suggesting positive interactions between them. Although Deschampsia antarctica does not grow naturally associated with U.antarctica, Molina-Montenegro etal. carried out a transplantation experiment to demonstrate that the macrolichen acts as a nurse plant, improving the survival of the grass. Serious conceptual and methodological discrepancies emerge from a critical evaluation of this study, challenging their conclusions. First, we suspect that the author confused some lichen taxa, and we also disagree with macrolichens being treated as cushion plants, because rootless, poikilohydric and poikilothermic thallophytes such as lichens are unable to create a stable, enclave-like microhabitat as vascular cushion plants do. Indeed, a critical evaluation of some of the micro-environmental parameters measured indicates that there are no biologically meaningful differences between the U.antarctica thalli and surrounding open areas. Second, the lack of consideration of the life history of the species under study leads to confusion when (a) referring to the succession sequence of species that colonize the studied area and (b) interpreting the putative distribution patterns promoted by Usnea versus the substrate preferences of associated species. Third, the authors intend to demonstrate experimentally that Usnea can facilitate the survival of D.antarctica plants, transplanting adult plants and not seedlings between the lichen thalli, and it is not clear how the grass was planted - between or within the lichens - as at both experimental sites the lichens grow on stones or rocks. Facilitative interactions are present in the Antarctic and may play a pivotal role in the structure and functioning of the fragile Antarctic ecosystems. However, more rigorous and well-planned research is needed to assess its presence, importance and involved mechanisms.