A cosmopolitan Serendipita forms mycothalli with sub-Antarctic leafy liverworts

The occurrence of mycothalli, symbioses between liverworts and fungi bearing similarities to mycorrhizas, is poorly documented in sub-Antarctica, and biogeographical patterns in Serendipita, one of the main fungal genera forming the symbiosis, remain understudied. Here, 83 specimens of 16 leafy liverwort species in eight families were hence sampled from 12 sites on the Thatcher Peninsula on sub-Antarctic South Georgia and were examined for mycothalli. Staining and epifluorescence microscopy were used to enumerate fungal structures in liverwort tissues, and PCR amplification and sequencing of fungal ribosomal DNA were used to determine the taxonomic and biogeographical affinities of the fungi present in plants. Stained hyphal coils, a defining feature of the symbiosis, were found to be frequent (>40 % of stem length colonised) in Barbilophozia hatcheri (Anastrophyllaceae), Cephaloziella varians (Cephaloziellaceae) and Lophoziopsis excisa (Lophoziaceae). Analyses of fungal ITS2 region sequences showed that a single species of Serendipita, based on a 3 % cut-off for sequence divergence, was a frequent colonist of B. hatcheri, C. varians and L. excisa, and that a further 18 basidiomycete and ascomycete taxa colonised other liverwort species. Principal component analysis and analysis of variance indicated that the presence of the Serendipita species was positively associated with the occurrence of stained hyphal coils in stem epidermal cells. Phylogenetic analyses, incorporating worldwide accessions from leafy liverwort-associated Serendipita, showed that the same species, which also occurs in Chile, mainland Europe and on Svalbard, is apparently the sole symbiont of sub- and maritime Antarctic leafy liverworts, and indicated much higher species richness of the genus outside Antarctica.

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