B: Mycorrhizae: The Symbiotic Relationship between Fungi and Roots - Biology LibreTexts
Discusses parasitic and mutualistic relationships of fungi. This fungus is a lichen, providing nutrients to the tree. The white parasitic fungus named Cordyceps is shown here growing on its host—a dark brown moth. Two common mutualistic relationships involving fungi are mycorrhiza and lichen. Oak trees live in association with usually two kinds of fungi called mycorrhiza. The association that oaks have with these types of mycorrhiza is called symbiotic. This is a relationship where each partner shares something it possesses with. Describe the symbiotic relationship of mycorrhizae and plant roots Hyphae proliferate within the mycorrhizae, which appears as off-white fuzz in this This type of mycorrhizae is found in forest trees, especially conifers, birches, and oaks.
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. Ectomycorrhizae are a type of mycorrhizae that form a dense sheath around the plant roots, called a mantle, from which the hyphae grow; in endomycorrhizae, mycelium is embedded within the root tissue, as opposed to forming a sheath around it.
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In endomycorrhizae, mycelium is embedded within the root tissue, as opposed to forming a sheath around it; these are found in the roots of most terrestrial plants. The Symbiotic Relationship between Fungi and Roots A nutrient depletion zone can develop when there is rapid soil solution uptake, low nutrient concentration, low diffusion rate, or low soil moisture. These conditions are very common; therefore, most plants rely on fungi to facilitate the uptake of minerals from the soil. Mycorrhizae, known as root fungi, form symbiotic associations with plant roots.
In these associations, the fungi are actually integrated into the physical structure of the root. The fungi colonize the living root tissue during active plant growth. Through mycorrhization, the plant obtains phosphate and other minerals, such as zinc and copper, from the soil. The fungus obtains nutrients, such as sugars, from the plant root. Mycorrhizae help increase the surface area of the plant root system because hyphae, which are narrow, can spread beyond the nutrient depletion zone.
Hyphae are long extensions of the fungus, which can grow into small soil pores that allow access to phosphorus otherwise unavailable to the plant.
The beneficial effect on the plant is best observed in poor soils. Oaks in Chaparral, Oak Woodland, etc. Oak trees live in association with usually two kinds of fungi called mycorrhiza. These fungi live on or in their roots. The fungi also extend beyond the oak trees roots to collect nutrients and water for themselves and the oak trees as well as other plants hooked up to this mycorrhizal grid. One kind of this mycorrhizal fungi is called Ectomycorrhiza, as these live on the outside of the oak root, and you can see them with the naked eye.
They extract nutrients from the oak leaf litter, as they break it down, and share some of these nutrients with the oak tree.
The Relationship Between Mycorrhiza & Trees | Home Guides | SF Gate
They live in the top four inches of soil under the canopy of the oak tree. For someone who has never seen Ectomycorrhiza you might think it was dry rot, or the roots had knobs instead of root hairs.
This kind lives inside the oaks roots and are microscopic. They live in the soil zone below the ectomycorrhizal fungi, from four inches below the soil surface to 20 feet down into the ground. What does the mycorrhizal fungi do? Oaks need these fungi to live; that is, oaks are obligately mycorrhizal. The association that oaks have with these types of mycorrhiza is called symbiotic. This is a relationship where each partner shares something it possesses with the other partner.
In the case of the oak and the mycorrhizae mycorrhizas: The mycorrhizal fungi provide nutrients and water to the oak. Mycorrhiza can be a thousand times more efficient than root hairs at extracting minerals and moisture. The fungi also protect the oak from diseases, that is, they are like the oak tree's immune system. The fungi produce chemicals that inhibit pathogenic bacteria, fungi and herbivores.
In return, the oak provides carbohydrates, food the fungi cannot make because they do not contain chlorophyll, Only green plants such as the oak contain chlorophyll, and can make food from the sun's energy. Oaks also bring up deep water that the fungus can't get to.
Another critical function of these fungi is erosion control. The tiny strands hyphae of the body of the fungus wrap around individual particles of sand or clay and, in addition produce a glue, that helps hold soil particles together, thereby controlling erosion. Sharon Rose's photo is a good illustration see reference section, Rose, Sharon. These fungi form connections underground from oak tree to oak tree and to other plants in the community, thereby interconnecting most of the plants of the plant community.
If one area of the forest has excess nutrition or moisture the fungi will attempt to balance the forest. Oak trees have sideways roots and a few vertical tap roots. What happens if the mycorrhizal grid is disturbed? In California native ecosystems there are many more fungi in the soil than bacteria; the numbers are usually 10 fungi to 1 bacterium. This is a critical point because, if the native ecosystem is broken down, such as when a disturbance occurs, and there is a mass invasion of alien plants, the numbers change.
In these situations, where alien plants are now the dominant species, and there are more bacteria than there are fungi. This phenomenon is called an ecological switch. It is as if all the numbers are automatically changed, just as if a light switch is turned on or off.
The change in the ratio of fungi to bacteria demonstrates that the change in the ecosystem occurs from the microscopic level up to the level of the massive oak trees.
The Relationship Between Mycorrhiza & Trees
This is very bad news for the oak tree because, remember, its immune system, its water, and its nutrients, depend upon the dominance and integrity of the fungi. For example, think of a small section of oak woodland, a lovely hill covered with oaks and pines and their associated plants.
Then imagine a soil disturbance, such as a caterpillar tractor climbing this hill, turning this way and that to avoid the trees. The result is gashes of bare soil, where the associated plants were torn up. When the associated plants were torn up and the bare soil was exposed, the threads or hyphae of the mycorrhizal fungi that are attached to the roots of those plants were also broken. These threads are the body of the fungus. Within this body nutrients and water are held.
Guess what leaks out all over the ground and is now available for any enterprising weed to pick up? Yeah, nutrients and water. What do weeds dearly love? Lots of nutrients and water! Limited soil disturbance does occur naturally such as rodent activity, but this is very minor if the habitat is undisturbed, and has a healthy plant community. When an area becomes disturbed and has an influx of alien species, usually lots of grasses certain rodent populations explode.
How does ecological succession apply to mycorrhizal fungi? As the oak tree grows, different species of fungi live with it. Also, more species live with it as it grows. On an old oak tree, there may be species living in symbiosis with the oak. Also, as the season changes from winter to spring, for example, the dominant species of fungi living on the oak change. More water is tolerated when the oak tree is young because the species of fungi that live in association with the oak tolerate more water.
Remember, though, this relationship between the oak and the fungi is bases on stress.
This means the fungi will only live with the oak if the oak is under slight water or nutrient stress. How does the plant community use mycorrhizal fungi?