The distribution and evolution of fungal symbioses in ancient lineages of land plants

Abstract

An accurate understanding of the diversity and distribution of fungal symbioses in land plants is essential for mycorrhizal research. Here we update the seminal work of Wang and Qiu (Mycorrhiza 16:299-363, 2006) with a long-overdue focus on early-diverging land plant lineages, which were considerably under-represented in their survey, by examining the published literature to compile data on the status of fungal symbioses in liverworts, hornworts and lycophytes. Our survey combines data from 84 publications, including recent, post-2006, reports of Mucoromycotina associations in these lineages, to produce a list of at least 591 species with known fungal symbiosis status, 180 of which were included in Wang and Qiu (Mycorrhiza 16:299-363, 2006). Using this up-to-date compilation, we estimate that fewer than 30% of liverwort species engage in symbiosis with fungi belonging to all three mycorrhizal phyla, Mucoromycota, Basidiomycota and Ascomycota, with the last being the most widespread (17%). Fungal symbioses in hornworts (78%) and lycophytes (up to 100%) appear to be more common but involve only members of the two Mucoromycota subphyla Mucoromycotina and Glomeromycotina, with Glomeromycotina prevailing in both plant groups. Our fungal symbiosis occurrence estimates are considerably more conservative than those published previously, but they too may represent overestimates due to currently unavoidable assumptions.

Keywords: Arbuscular mycorrhizas; Ericoid mycorrhizas; Hornworts; Liverworts; Lycophytes; Mucoromycota.

Fig. 1

The phylogenetic position and fungal symbiosis status of early-diverging plant families. Branch lengths have no value and only show how the families are currently considered to be related. Initials in the table denote: M Mucoromycotina, G Glomeromycotina, A Ascomycota, B Basidiomycota. A check indicates presence, a cross absence, and a question mark indicates an unknown identity reported only as ‘fungal association’. Checks highlighted in grey are likely accurate reports and were used for occurrence rate estimations, whereas the mutualistic status of un-highlighted checks remains unknown (only relevant for Ascomycota and Basidiomycota symbioses in liverworts). An asterisk indicates a likely incorrect report of symbiosis