Mycorrhizae: Types and Benefits

May 20, 2019

The mutualistic association of plant roots and fungi is known as mycorrhizae.
There are generally two types of mycorrhizae. They are:

A) Ecto-mycorrhizae

In this type, fungal cells form an extensive sheath around the outside of the root and there is only a little penetration into the root tissue itself.
These are found mostly in forest trees, especially conifers, beeches, and oaks.
These are most developed in boreal and temperate forests.
Almost every root of every tree is mycorrhizal in this type of forests.
The root system of mycorrhizal tree such as pine (genus Pinus) is composed of both long and short roots.
The short roots of Pinus are dichotomously branched which show typical fungal colonization and long roots are also frequently colonized.

B)Endo-mycorrhizae

The fungal mycelium becomes deeply embedded within the root tissue in this type.
These are more common than ecto-mycorrhizae.
Arbuscular mycorrhizae is one of the type of endomycorrhizae that are found in the roots of over 80% of all terrestrial plant species so far examined.
Most mycorrhizal fungi do not catabolize cellulose and other leaf litter polymers.
They only catabolize simple carbohydrates and typically have one or more vitamins requirements.
They obtain their carbon from secretions of the roots and get inorganic mineral from the soil.
They are rarely found in nature except in association with the roots.
Many of them are obligate symbionts as well.
They produce plant growth substances that induce morphological alterations in the roots which stimulate the formation of mycorrhizal state.
Despite the close relationship between fungus and root, a single species of Pine can form a mycorrhizal association with over 40 species of fungi.

Benefits

The benefits of mycorrhizal fungus can be best observed in poor soils where trees that are mycorrhizal thrive but non-mycorrhizal ones do not.
Trees planted in prairie soils which ordinarily lack a suitable fungal inoculum grow much more rapidly when artificially inoculated at the time of planting than un-inoculated trees.
The mycorrhizal plant can absorb nutrients from its environment more efficiently and thus have a competitive advantage.
For example, in the pine seedling, the overwhelming part of the absorptive capacity of the plant root system is due to ecto-mycorrhizal fungal mycelium.
In addition to helping the plants absorb nutrients, they have also a significant role in supporting plant diversity.
A positive correlation between the abundance and diversity of mycorrhizae in a soil has clearly been shown by field experiments.
The experiments have also shown the extent of the plant diversity that develops in such environment.
Thus, mycorrhizae are considered to be a true mutualistic symbiosis.
The mycorrhizal plants are better able to function physiologically and compete successfully in a species rich plant community where the fungus benefits from a steady supply of organic nutrients.