Symbiosis: Mycorrhizae and Lichens
A mycorrhiza is a symbiotic association between a fungus and the roots of a vascular host plant . Mycorrhizal fungi form a mutualistic relationship with the roots of most plant species. In such a relationship, both the plants themselves and. Plant Mutualism: Mycorrhizae What are mycorrhizae? Mycorrhizae (mahy-kuh- rahy-zee), mycorrhiza singular, refers to the symbiotic interaction. A mycorrhiza is defined as a symbiotic relationship between the roots of plants and fungi. The term mycorrhiza literally means root fungus, but in the broad sense.
They also draw water from within the soil's micropores, which would otherwise be inaccessible by the root. Thus, roots colonized by mycorrhizae enables the plant to be better protected and to resist the stress caused by transplanting, drought and heat, while maintaining an optimal growth rate.
Mycorrhizal fungi also receive benefit from symbiosis with the plant. Due to the plants ability to photosynthesize, the plant synthesizes carbon-based substances sugarswhich feeds the fungi.
You may say there is an exchange of services between the fungus and the plant. Soils disturbed by urbanization Urban landscaping in recent years, is challenged by climate change and urban heat islands that are generated with the use of concrete surfaces in city environments.
This means that the plants selected for these locations must be reviewed periodically to ensure they can survive in these landscaped areas with extreme temperatures, drought, human activity, etc.
The soil must also be considered when it comes to plant survival, as it plays a crucial part in the retention of water and health of plants, especially for trees and shrubs, whose life cycle is longer than annuals. The organic matter, microflora and other organisms, such as earthworms, are essential factors in soil fertility and play a major role in the plant establishment success.
Without these fungi our forests as we know them would not exist.
Mycorrhizal Fungi and Plant Roots | MOTHER EARTH NEWS
Thus the ecological and economic importance of ectomycorrhizae cannot be overestimated. Many biologists have noted the major differences between tropical and temperate forests and have attempted to relate these to dominance by certain mycorrhizal types. The pictures above illustrate two such forests; at left a tropical rain forest in northern Costa Rica and at right a forest near Schefferville, Quebec.
The Costa Rican forest is dense and made up of a great variety of tree species. You might walk some distance through this forest before encountering two individual trees of the same species. Biodiversity here, including the trees, seems to be high.
On the other hand the Quebec forest appears to have only one kind of tree.
Closer examination would reveal some four or five species but hardly more. If you started walking away from the base of a spruce tree it wouldn't be long before you encountered another.The relationship between insects and plants
Biodiversity here seems to be very low. Curiously, fungal biodiversity in these forests takes another form, at least when it comes to mushrooms.
Few trees in the Costa Rican forest are able to form ectomycorrhizae while in the Quebec forest all the trees form ectomycorrhizae. As a result of this the Quebec forest will have a great variety of large mushrooms while the tropical one will support a lessor variety of mostly small mushrooms.
Other kinds of mycorrhizae Although arbuscular and ectomycorrhizae account for most instances of mycorrhizae there are some other more specialized types. These are all restricted to a single plant family, or a closely related group of families, and are not as commonly encountered as the two main types.
In return, the plant gains the benefits of the mycelium 's higher absorptive capacity for water and mineral nutrients, partly because of the large surface area of fungal hyphae, which are much longer and finer than plant root hairsand partly because some such fungi can mobilize soil minerals unavailable to the plants' roots.
The effect is thus to improve the plant's mineral absorption capabilities.
- Mycorrhizal Fungi and Plant Roots: A Symbiotic Relationship
- Plant Mutualism: the connection between fungi and plants
One form of such immobilization occurs in soil with high clay content, or soils with a strongly basic pH. The mycelium of the mycorrhizal fungus can, however, access many such nutrient sources, and make them available to the plants they colonize.
Another form of immobilisation is when nutrients are locked up in organic matter that is slow to decay, such as wood, and some mycorrhizal fungi act directly as decay organisms, mobilising the nutrients and passing some onto the host plants; for example, in some dystrophic forests, large amounts of phosphate and other nutrients are taken up by mycorrhizal hyphae acting directly on leaf litter, bypassing the need for soil uptake.
These structures have been shown to host nitrogen fixing bacteria which contribute a significant amount of nitrogen and allow the pines to colonize nutrient-poor sites. Physically, most mycorrhizal mycelia are much smaller in diameter than the smallest root or root hair, and thus can explore soil material that roots and root hairs cannot reach, and provide a larger surface area for absorption.
Chemically, the cell membrane chemistry of fungi differs from that of plants. For example, they may secrete organic acid that dissolve or chelate many ions, or release them from minerals by ion exchange.
These associations have been found to assist in plant defense both above and belowground. Mycorrhizas have been found to excrete enzymes that are toxic to soil borne organisms such as nematodes. When this association is formed a defense response is activated similarly to the response that occurs when the plant is under attack.