What benefit do mycorrhizal fungi receive in their symbiotic relationship with plants?
Mycorrhizae play an important role in plant nutrition. Because they are unseen, they are often disregarded when it comes to deciding upon a cause for decline in a particular planting. Just what are mycorrhizae and why are they so important in plant production? The word “mycorrhiza”
means fungal root. To be more specific, mycorrhizae are fungi that have a symbiotic relationship with the roots of many plants. The fungi which commonly form mycorrhizal relationships with plants are ubiquitous in the soil. Many mycorrhizal fungi are obligately symbiotic and therefore are unable to survive in nature for extended periods of time without their host. Because the relationship between the fungus and the plant is symbiotic, both members of the relationship obtain a benefit from each
other. Neither the host plant nor the fungus suffer any ill effects as a result of the relationship. The fungus, because it does not photosynthesize, cannot fix its own carbon. Consequently, it receives all of its necessary carbohydrates from the host plant. In return, the mycorrhiza absorbs nutrients from the soil which are passed along to the plant. There are two main classes of mycorrhizae: ectomycorrhizae and endomycorrhizae. The ectomycorrhizae are also know as sheathing mycorhizae. They are found on many evergreen trees and shrubs. Deciduous trees are also colonized and include plants in the genera Fagus, Betula, Quercus, Tilia, Populus, Salix and Castanea. The fungus covers the ends of young roots and only penetrates the cell wall of the cortex; no further cellular penetration occurs. The ectomycorrhizal
fungi belong to the class of fungi called Basidiomycetes. Basidiomycetes are fungi that commonly produce mushrooms as their fruiting structures. This explains the occurrence of mushrooms in the root zone beneath the dripline of a tree. Ectomycorrhizae not only absorb phosphate from the soil but they also are important in ammonium and zinc uptake as well. The fungi that form a symbiotic relationship with the plant are relatively host-specific. However, some fungal species may be more generalized
and will colonize several species of plants. Ectomycorrhizal fungi are dispersed either by airborne spores or through the transfer of infected plant tissue. In addition to increasing the uptake of nutrients, mycorrhizae often provide some protection against soil-borne diseases. They may also increase a plant’s tolerance to adverse conditions. Drought, high temperatures, salinity, and acidity, or a build-up of toxic elements in the soil are some of
the effects on host plants that mycorrhizae reduce. This aspect may be important to a tree’s survival in landscape plantings. Additional Information
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