Mycorrhiza - Wikipedia
A mycorrhiza is a symbiotic association between a fungus and the roots of a vascular host plant . When compared to non-mycorrhizal fine roots, ectomycorrhizae may contain very high concentrations of trace elements, including toxic Mycorrhizal fungi form a mutualistic relationship with the roots of most plant species. Mycorrhizae are considered to be a mutualistic relationship because both Numerous experiments have shown that plants without mycorrhizae cannot cope as well throughout the world, in spite of immense climatic and floristic differences. Over 35 years ago, it was hypothesized that mutualistic symbiotic soil fungi assisted land plants in their initial colonization of terrestrial.
Although a smaller number of species are involved, ectomycorrhizae dominate in the pine, oak, birch, willow, walnut and several other families. In the tropics these include the dipterocarps and large woody legumes. In New Brunswick our extensive forests of spruce, fir, white pine, birch and poplar support immense continuous networks of ectomycorrhizal fungi.
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Without these fungi our forests as we know them would not exist. 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.
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. However, in New Brunswick we are fortunate to have these other types of mycorrhizae and can observe them during the active growing season. The most widespread of the "minor" groups of mycorrhize are ericoid mycorrhizae, so named because they are restricted to the Ericaceae, the heath family, and some closely related families.
The Ericaceae are familiar to New Brunswickers in the form of blueberries, cranberries, sheep laurel, rhododendron, etc. Crowberries, in the related family Empetraceae, also have ericoid mycorrhizae.
The picture at right shows a root of Labrador tea, another member of the Ericaceae common throughout New Brunswick.
These plants are heterotrophic or mixotrophic and derive their carbon from the fungus partner. This is thus a non-mutualistic, parasitic type of mycorrhizal symbiosis. Orchid mycorrhiza All orchids are myco-heterotrophic at some stage during their lifecycle and form orchid mycorrhizas with a range of basidiomycete fungi.
Microbiologists unravel relationship among plants, mycorrhizal fungi
In such a relationship, both the plants themselves and those parts of the roots that host the fungi, are said to be mycorrhizal. The Orchidaceae are notorious as a family in which the absence of the correct mycorrhizae is fatal even to germinating seeds. This relationship was noted when mycorrhizal fungi were unexpectedly found to be hoarding nitrogen from plant roots in times of nitrogen scarcity. Researchers argue that some mycorrhizae distribute nutrients based upon the environment with surrounding plants and other mycorrhizae.
They go on to explain how this updated model could explain why mycorrhizae do not alleviate plant nitrogen limitation, and why plants can switch abruptly from a mixed strategy with both mycorrhizal and nonmycorrhizal roots to a purely mycorrhizal strategy as soil nitrogen availability declines.
On the right side of this diagram, the arbuscular mycorrhiza pathway, which branches off from the plant root, which is the brown cylinder-like figure in the image, provides the plant with nutrients, including, most importantly, phosphate and nitrogen. My reference source for this information is: 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. 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.