The root nodules of the Podocarpaceae harbour arbuscular mycorrhizal fungi

•  Here we present the ultrastructure and molecular identification of the fungi in the mycorrhizal nodules of four species of Podocarpaceae endemic to New Zealand. Podocarps form a major component of the rain forest of New Zealand, where they grow on soils poor in extractable phosphate and high in organic matter. •  Histological studies showed that the mycorrhizal nodules develop as modified lateral roots, and are colonised by an endophytic fungus. Scanning and transmission electron microscopy showed the fungus to contain intracellular coils and arbuscules typical of the order Glomales. •  DNA was extracted and amplified using PCR to identify mycorrhizal fungi. Several different lineages of arbuscular mycorrhizal fungi colonising the nodules were identified. Individual nodules contained more than one fungal lineage. •  This study is the first to indicate species of Glomales present in the New Zealand rain forest. It is likely that many of the taxa sampled are new to science because there has been little taxonomic work on Australasian Glomales.

Angiosperm Gymnostoma trees produce root nodules colonized by arbuscular mycorrhizal fungi related to Glomus

•  Structure and fungal composition is presented here for 'mycorrhizal' nodules of two angiosperms of the genus Gymnostoma (Casuarinaceae), G. deplancheanum and G. nodiflorum. These species are endemic to New Caledonia, where they grow on ultramafic soils. The mycorrhizal nodules, which are modified lateral roots invaded by an arbuscular mycorrhizal fungus, occur in addition to N₂ -fixing nodules. •  Techniques included PCR amplification of extracted DNA, for species identification, and histological studies to compare the developmental pathway of Gymnostoma mycorrhizal nodules with that of actinorhizal nodules. •  The fungal DNA suggested that the strain belongs to the genus Glomus (Glomales). The endophytic mycelium also contained typical Glomus arbuscules and hyphal coils. Structurally, Gymnostoma mycorrhizal nodules are similar to those described in some Coniferales and in Caesalpinioideae trees of French Guyana. •  The mycorrhizal nodules of G. deplancheanum and G. nodiflorum contain a fungus belonging to the Glomales. The role of the nodules might be linked to the ecological situation of the host plants, which are pioneers in exposed and rocky habitats.