Endomycorrhizal fungi (more commonly referred to as endomycorrhizae) is one of the major types of known mycorrhizae which differs from the another type of mycorrhizae, ectomycorrhizae, in structure. Unlike ectomycorrhizae which form a system of hyphae that grow around the cells of the root, the hyphae of the endomycorrhizae not only grow inside the root of the plant but penetrate the root cell walls and become enclosed in the cell membrane as well (1). This makes for a more invasive symbiotic relationship between the fungi and the plant. The penetrating hyphae create a greater contact surface area between the hyphae of the fungi and the plant. This heightened contact facilitates a greater transfer of nutrients between the two. Endomycorrhizae have further been classified into five major groups: arbuscular, ericoid, arbutoid, monotropoid, and orchid mycorrhizae (2).
Ectomycorrhiza[edit]
Beech is
ectomycorrhizal
Main article:
Ectomycorrhiza
Ectomycorrhizas, or EcM, are typically formed between the roots of around 10% of plant families, mostly woody plants including the
birch,
dipterocarp,
eucalyptus,
oak,
pine, and
rose[26] families,
orchids,
[32] and fungi belonging to the
Basidiomycota,
Ascomycota, and
Zygomycota. Some EcM fungi, such as many
Leccinum and
Suillus, are symbiotic with only one particular genus of plant, while other fungi, such as the
Amanita, are generalists that form mycorrhizas with many different plants.
[33] An individual tree may have 15 or more different fungal EcM partners at one time.
[34] Thousands of ectomycorrhizal fungal species exist, hosted in over 200 genera. A recent study has conservatively estimated global ectomycorrhizal fungal species richness at approximately 7750 species, although, on the basis of estimates of knowns and unknowns in macromycete diversity, a final estimate of ECM species richness would probably be between 20000 and 25000.
[35]
Ectomycorrhizas consist of a hyphal sheath, or mantle, covering the root tip and a
Hartig net of hyphae surrounding the plant cells within the root
cortex. In some cases the hyphae may also penetrate the plant cells, in which case the mycorrhiza is called an ectendomycorrhiza. Outside the root,
Ectomycorrhizal extramatrical mycelium forms an extensive network within the soil and leaf litter.
Nutrients can be shown to move between different plants through the fungal network. Carbon has been shown to move from
paper birch trees into
Douglas-fir trees thereby promoting
succession in
ecosystems.
[36] The ectomycorrhizal fungus
Laccaria bicolor has been found to lure and kill
springtails to obtain nitrogen, some of which may then be transferred to the mycorrhizal host plant. In a study by Klironomos and Hart,
Eastern White Pine inoculated with
L. bicolor was able to derive up to 25% of its nitrogen from springtails.
[37][38]
The first genomic sequence for a representative of symbiotic fungi, the ectomycorrhizal basidiomycete
Laccaria bicolor, has been published.
[39] An expansion of several multigene families occurred in this fungus, suggesting that adaptation to symbiosis proceeded by gene duplication. Within lineage-specific genes those coding for symbiosis-regulated secreted proteins showed an up-regulated expression in ectomycorrhizal root tips suggesting a role in the partner communication.
Laccaria bicolor is lacking enzymes involved in the degradation of plant cell wall components (cellulose, hemicellulose, pectins and pectates), preventing the symbiont from degrading host cells during the root colonisation. By contrast,
Laccaria bicolor possesses expanded multigene families associated with hydrolysis of bacterial and microfauna polysaccharides and proteins. This genome analysis revealed the dual
saprotrophic and
biotrophic lifestyle of the mycorrhizal fungus that enables it to grow within both soil and living plant roots.
