Symbiotic Relationships of
Fungi
Douglas Wilkin, Ph.D.
Jean Brainard, Ph.D.
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Printed: December 22, 2015
AUTHORS
Douglas Wilkin, Ph.D.
Jean Brainard, Ph.D.
www.ck12.org
C HAPTER
Chapter 1. Symbiotic Relationships of Fungi
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Symbiotic Relationships of
Fungi
• Define parasitism and mutualism.
• Identify symbiotic relationships of fungi.
• Distinguish between a mycorrhiza and a lichen.
Do all fungi feed only on dead organisms?
Not all. This fungus is a lichen, providing nutrients to the tree. The lichen gets sugars from the plant. Both benefit
from this relationship.
Symbiotic Relationships of Fungi
Not all fungi feed on dead organisms. Many are involved in symbiotic relationships, including parasitism and
mutualism.
Fungi as Parasites
In a parasitic relationship, the parasite benefits while the host is harmed. Parasitic fungi live in or on other organisms
and get their nutrients from them. Fungi have special structures for penetrating a host. They also produce enzymes
that break down the host’s tissues.
Parasitic fungi often cause illness and may eventually kill their host. They are the major cause of disease in
agricultural plants. Fungi also parasitize animals, such as the insect pictured in Figure 1.1. Fungi even parasitize
humans. Did you ever have athelete’s foot? If so, you were the host of a parasitic fungus.
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FIGURE 1.1
Parasitic Fungus and Insect Host. The
white parasitic fungus named Cordyceps
is shown here growing on its host—a dark
brown moth.
Mutualism in Fungi
Fungi have several mutualistic relationships with other organisms. In mutualism, both organisms benefit from the
relationship. Two common mutualistic relationships involving fungi are mycorrhiza and lichen.
• A mycorrhiza is a mutualistic relationship between a fungus and a plant. The fungus grows in or on the plant
roots. The fungus benefits from the easy access to food made by the plant. The plant benefits because the
fungus puts out mycelia that help absorb water and nutrients. Scientists think that a symbiotic relationship
such as this may have allowed plants to first colonize the land.
• A lichen is an organism that results from a mutualistic relationship between a fungus and a photosynthetic
organism. The other organism is usually a cyanobacterium or green alga. The fungus grows around the
bacterial or algal cells. The fungus benefits from the constant supply of food produced by the photosynthesizer.
The photosynthesizer benefits from the water and nutrients absorbed by the fungus. Figure 1.2 shows lichen
growing on a rock.
Some fungi have mutualistic relationships with insects. For example:
• Leafcutter ants grow fungi on beds of leaves in their nests. The fungi get a protected place to live. The ants
feed the fungi to their larvae.
• Ambrosia beetles bore holes in tree bark and “plant” fungal spores in the holes. The holes in the bark give the
fungi an ideal place to grow. The beetles harvest fungi from their “garden.”
Summary
• Many fungi are involved in symbiotic relationships.
• Some fungi are parasites. They are specialized to penetrate a host and break down the host’s tissues. Parasitic
fungi often cause illness and may eventually kill their host.
• Two common mutualistic relationships involving fungi are mycorrhiza (fungi and plant roots) and lichen (fungi
and either cyanobacteria or green algae).
• Some fungi also have mutualistic relationships with insects.
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Chapter 1. Symbiotic Relationships of Fungi
FIGURE 1.2
Lichen Growing on Rock. Unlike plants,
lichen can grow on bare rocks because
they don’t have roots. That’s why lichens
are often pioneer species in primary ecological succession.
How do lichen get
water and nutrients without roots?
Explore More
Use this resource to answer the questions that follow.
• Symbiotic Fungi at http://www.clarku.edu/faculty/dhibbett/tftol/content/3folder/symbiotic.html .
1.
2.
3.
4.
5.
What is symbioses?
Give an example of a fungal parasite.
Why are many fungi involved in mutualism?
What are lichen and mycorrhizae?
Give an example of fungal commensalism.
Review
1. How significant are fungi as plant parasites?
2. Describe an example of a mutualistic relationship between fungi and insects.
3. Assume that you notice a fungus growing on a plant. What possible relationships might exist between the
fungus and the plant? What type of evidence might help you identify which is the correct relationship?
4. Compare and contrast mycorrhiza and lichen.
References
1. Image copyright Dr. Morley Read, 2014. Parasitic fungus and insect host . Used under license from
Shutterstock.com
2. User:Hardyplants/Wikipedia. Lichen growing on rock . Public Domain
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