Characterisation of a deep-water moss from the perennially ice-covered Lake Vanda, Antarctica

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Bryophytes from submerged habitats are particularly difficult to identify because developmental plasticity obscures their characteristic features. A deep-water moss population of uncertain identity was found isolated at a depth of 31 m within the perennially ice-covered Lake Vanda, Wright Valley, Antarctica. Through phylogenetic analysis of the chloroplast region, ribosomal subunit 4 gene, nuclear ribosomal DNA region, and the internal transcribed spacer region, the Lake Vanda moss was identified as the cosmopolitan species Bryum pseudotriquetrum and resolved to a clade containing exclusively specimens from Antarctica, specifically those from the neighbouring Taylor Valley and Granite Harbour. The close genetic similarity of the Lake Vanda population to other populations of B. pseudotriquetrum in Southern Victoria Land suggests that colonisation was likely to have been from local sources, and colonisation likely occurred at least 80–100 years ago, given the position of mosses in the deeper of two convection cells in the lake. Light and scanning electron microscopy of in vitro cultured specimens revealed adaptations to permanent submersion, including very thin cell walls, which may increase CO2 absorption under water. The production of rhizoidal knots in contaminated, low-nutrient media, but not in axenic cultures, might result from interactions between the moss and organisms in the microbial mat from which it was isolated. The absence of mosses around the lake margin or elsewhere in Wright Valley highlights the importance of freshwater ecosystems as refugia for biodiversity in Antarctica.