RUSSELL, ANGELA J.*, RIADH FRANCIS, ROBERTO LIGRONE, JEFFREY G. DUCKETT, AND DAVID READ. School of Biological Sciences, Queen Mary and Westfield College, Mile End Road, London., E1 4NS, UK. - Symbiotic fungal associations in liverworts.
Three fungal phyla, which form mycorrhizas in higher plants, also form
symbiotic fungal associations in liverworts. Zygomycetous fungi
colonise a range of thalloid liverworts where they produce structures
analogous to those seen in the vesicular-arbuscular (VA) mycorrhizas
of higher plants. Experiments reveal that glomalean fungi forming
typical VA mycorrhizas with a higher plant (Plantago
lanceolata) can colonise a thalloid liverwort (Pellia
fabroniana) producing arbuscules and vesicles in the thallus.
Some members of the Jungermanniales and Metzgeriales form associations
with basidiomycetous fungi, which produce intracellular hyphal coils
similar to the pelotons seen in orchid mycorrhizas. The fungal
associates of the autotrophic Aneura pinguis and its
heterotrophic relative Cryptothallus mirabilis have been
isolated. Resynthesis experiments have shown that the fungal symbiont
of Cryptothallus is an ectomycorrhizal associate of
Betula suggesting an explanation for the apparently obligate
nature of the association between the two. Ascomycetous associations
are found in the Cephaloziaceae and Lepidoziaceae. Cross-inoculation
experiments have shown that a typical mycorrhizal endophyte of
ericaceous plants, Hymenoscyphus ericae will colonise the
rhizoids and underground axes of these plants. Ascomycete-containing
hepatics are particularly conspicuous associates of the Ericaceae and
Epacridaceae. Metzgeralean genera with VA-fungi are most diverse in
the podocarp forests of New Zealand. Nutrient exchange between these
hepatics and seed plants via common mycobionts is currently under
investigation.
Key words: ascomycete, basidiomycete, liverwort, mycorrhiza, symbiosis, vesicular-arbuscular (VA)