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Endomycorrhizae, also called arbuscular mycorrhizae, do not form a dense sheath over the root. Instead, the fungal mycelium is embedded within the root tissue. Endomycorrhizae are found in the roots of more than 80 percent of terrestrial plants. Learning Objectives Describe the symbiotic relationship of mycorrhizae and plant roots.
The relationship between plants and fungi is symbiotic because the plant obtains phosphate and other minerals through the fungus, while the fungus obtains sugars from the plant root. The long extensions of the fungus, called hyphae, help increase the surface area of the plant root system so that it can extend beyond the area of nutrient depletion.
April Plant Health. Incorporate these beneficial organisms into your production, and you may see improved plant growth and reduced nutritional deficiencies, as well as benefits to the end user.
Figure 1 top. Magnification detail of root cell containing an arbuscule little tree endomycorrhizal structure. Figure 2 bottom. Magnification of vesicles round balloon-like structures found between plant root cells.
What are Mychorrhizae? What is the Difference? Endomycorrhizal Structures The most common type of endomycorrhizae is arbuscular endomycorrhizae. Colonization of roots begins by the secretion of enzymes by arbuscular endomycorrhizae allowing hyphae to penetrate the epidermal and fleshy cortical cells of plant roots.
Two to three days after colonizing the cell, the hyphae form structures within plant cells called arbuscules Latin for tree which resemble tiny trees and serve to facilitate the transfer of nutrients within the cortical cells Figure 1. Arbuscular endomycorrhizae provide the plant with certain fertilizer elements and water from the soil, and in turn, the plant provides sugars and other carbohydrates for the fungus.
Between the cells, sac like structures, called vesicles means little sac , form midway or at the terminal ends of the hyphae Figure 2. Vesicles contain lipids and serve primarily as storage organs for the fungus. Vesicles can also serve as propagules that can colonize other parts of the plant root. Arbuscular endomycorrhizae hyphae also will give rise to spores, which serve the same function as seeds do to plants.
Spores have very thick walls, which makes them very resistant to freezing and intense heat so they can survive for long periods of time. For this reason, spores are ideal for incorporating into growing media and for use as inoculants.
Figure 3. Plant root without mycorrhizae on left, plant root with mycorrhizae on right. Benefits for the Grower and the End User Intensely farmed land, new housing developments where the topsoil has been stripped away, landfills and mine sites can benefit greatly from endomycorrhizal fungi since the combination of chemical fertilizer applications and the lack of organic matter replenishment has left much of our soils almost void of beneficial organisms.
These benefits include: Reduced nutritional deficiencies. Endomycorrhizae mine out the growing medium to efficiently bring nutrients particularly phosphorus, copper, manganese and zinc to the plant where plant roots are not present. This delays nutrient deficiencies and their visual symptoms from appearing. Potential reduction in fertilizer use.
Disease resistance Mycorrhizae also help the plant resist infection by other fungi and even bacteria. This may be because the plant, being better nourished, is healthier and has better resistance to the invader. It may also be that the large physical presence of one fungus impedes infection by others. Another possibility is that either the plant or the fungus produces compounds that prevent infection by pathogens.
Interaction with other soil microbes — a cycle of benefit. Desert plants interact with other organisms in the soil. Many of these microorganisms fertilize plants by "fixing" nitrogen, which is then available for plant growth. When mycorrhizae are present, the number and vitality of these nitrogen fixers increase. Many fungi will form associations with plants, and many plants will form mycorrhizal associations.
These interactions appear to be plant- and fungus-specific. Not all mycorrhizae-forming fungi will work with all desert plants. There are research reports which show that association with the "wrong" fungus actually decreases the health and vigor of the plant. Because there is a requirement for specific plant-fungus association, mycorrhizae can be important in reestablishing native species in areas where they have been lost.
Mycorrhizal fungi are available for sale from several sources. Introducing mycorrhizal fungal spores inoculation is sometimes suggested to improve yields and plant vigor, particularly for container and landscape ornamentals. Inoculation with mycorrhizal fungi may not be a benefit unless it is specific to the plant, because there is a requirement for a specific fungus-plant interaction for optimum benefit.
It would also be counterproductive to inoculate with a fungus that could strongly benefit a weedy species. Many desert soils already have mycorrhizal fungi present, at least in small amounts. Even without inoculation, spores can be found in many desert locations. If host plants are grown where there are spores of these fungi, then both thrive.
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