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The below mentioned article provides a paragraph on Mycorrhizae.
The mutually beneficial or symbiotic association of a fungus with the root of a higher plant is known as mycorrhiza. Mycorrhizal roots often show a wooly covering of fungal hyphae. The shape is different from normal root— tuberous, nodulated, coralloid. Root cap and root hairs are absent.
Mycorrhizal roots often remain in the upper layers of the soil where organic matter is abundant. Mycorrhizal association is not very specific. A plant can form association with several fungi. A birch tree is found to have mycorrhizal association with 13 species of fungi.
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The fungus is able to break the cell walls of the root cells to only a limited extent. As a result the fungus remains restricted to cortical region of the root. The vascular strand and growing point are not affected. Depending upon the residence of the fungus, mycorrhizae are of two types ectomycorrhizae (= ectotrophic mycorrhizae) and endomycorrhizae (= endotrophic mycorrhizae).
In ectomycorrhizae the bulk of the fungus lies on the surface of the root while a part of it lives in the intercellular spaces of the cortex. In endomycorrhizae only a little of the fungus lies on the root surface. It resides mostly inside the cortex of the root with some hyphal tips passing into the cortical cells.
The fungus is dependent upon the higher plant for shelter and food. It obtains its nourishment from the cortical cells of the root. The fungal hyphae are intercellular where the root cells excrete sugars and other soluble food ingredients.
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Intracellular hyphae develop where the root cells do not excrete food materials. Such hyphae obtain nourishment directly from inside the cells. The fungus seems to be essential for proper growth of the plant having mycorrhiza. Many orchids do not survive without mycorrhiza.
Several forest plants show stunted growth if they are deprived of root association with the fungus, e.g., Birch, Pine. The plant is immensely benefitted from the association with the fungus. Fungal hyphae are spread in the soil over a large area.
They take part in:
(a) Absorption of water,
(b) Dissolving essential minerals present in the organic debris and handing over the same to the plant. This allows the plant to grow in areas deficient in inorganic minerals,
(c) Absorbing inorganic salts present in the soil from over a large area. The forest trees like pines and birches are known to absorb 2-3 times more of potassium, nitrogen and phosphorus in the presence of mycorrhiza than in its absence,
(d) The fungus produces various growth promoting substances, and
(e) It secretes antimicrobial substances which protect the young roots from attack of pathogens.
