Symbiosis: Mycorrhizae and Lichens
The two most common example in fungi are mycorrhizae and lichens, which we A mycorrhiza is defined as a symbiotic relationship between the roots of plants . Both partners benefit from the relationship: mycorrhizal fungi improve the Mycorrhizas develop specialized areas, called symbiotic interfaces, The ectomycorrhizal fungus surrounds the root tip with a thick mantle of . that target plant cell wall components, for example, pectinases and pectin lyases. Mycorrhizal Fungi and Plant Roots: A Symbiotic Relationship for decades afterward, because botanists took them to be examples of fungi parasitizing plants.
Mycorrhizal Fungi and Plant Roots: A Symbiotic Relationship
Mycorrhizal associations are seen in the fossil record and are believed to be one of the contributing factors that allowed early land plants, including Aglaophyton major one of the first land plantsto conquer the land. Mycorrhizal fungi encompass many major groups of the fungus Kingdom and in the past were divided into two non-evolutionarily related groups: Ectomycorrhizal fungi ensheath the root cells but usually do not penetrate them extracellular.
Endomycorrhizal fungi penetrate and enter the cells of a plant root intracellular. Modern research has lead to the recognition of seven types of mycorrhizal fungi, subdividing the old, traditional groups.
The new nomenclature is often more precise and specific to the associated plant taxa. The relatively homogenous ectomycorrhizal group largely remains with only the addition of the subgroup ectendomycorrhizas. The endomycorrhizal group has been dismantled, but specific types are now recognized: Vescicular-Arbuscular Mycorrhizas, the Orchid mycorrihzas, and those which associate with the Ericaceae Blueberry family: Fungi are heterotropic organisms, and must absorb their food.
WHAT ARE MYCORRHIZAE?
Fungi also have the ability to easily absorb elements such a phosphorus and nitrogen which are essential for life. Plants are autotropic, producing their food in the form of carbohydrates through the process of photosynthesis.
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.
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.The Magic of Mycorrhizal Mushrooms
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.
Mycorrhiza - Wikipedia
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.