Soil Science
The living foundation beneath your feet — what soil is, how it works, how to improve it
Chapter 8: Mycorrhizal Fungi — The Underground Network
Why this matters: Mycorrhizal fungi are arguably the most important organisms in soil for plant establishment and long-term health. Understanding them explains why transplanted plants fail, why native plants thrive without fertilizer, and why disturbing soil biology can set a restoration project back by years.
8.1 What Mycorrhizae Are
MYCORRHIZA = "fungus root" (Greek)
From: 8.1 What Mycorrhizae Are
Image file: ../../../images/s01-foundation/c03-soil-science/ch08/c03-soil-science_ch08_mycorrhizal_fungi_fig01.png
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8.2 The Two Main Types
ECTOMYCORRHIZAE (ECM)
From: 8.2 The Two Main Types
Image file: ../../../images/s01-foundation/c03-soil-science/ch08/c03-soil-science_ch08_mycorrhizal_fungi_fig02.png
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8.3 The Hyphal Network
HOW FAR MYCORRHIZAL NETWORKS EXTEND
From: 8.3 The Hyphal Network
Image file: ../../../images/s01-foundation/c03-soil-science/ch08/c03-soil-science_ch08_mycorrhizal_fungi_fig03.png
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8.4 Mycorrhizae in Texas Native Plant Establishment
WHY NATIVE PLANTS ESTABLISH SLOWLY
From: 8.4 Mycorrhizae in Texas Native Plant Establishment
Image file: ../../../images/s01-foundation/c03-soil-science/ch08/c03-soil-science_ch08_mycorrhizal_fungi_fig04.png
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8.5 Practical Management for Mycorrhizae
✓ Inoculate transplants at planting
From: 8.5 Practical Management for Mycorrhizae
Image file: ../../../images/s01-foundation/c03-soil-science/ch08/c03-soil-science_ch08_mycorrhizal_fungi_fig05.png
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1. Mycorrhizal fungi form mutualistic relationships with the roots of most plant species.
2. Ectomycorrhizae surround roots in a sheath without penetrating cells.
3. Arbuscular mycorrhizae (AM) penetrate into root cells to exchange nutrients.
4. About 80-90% of all plant species form mycorrhizal associations.
5. Mycorrhizae can extend root effective absorbing surface by 100-1000x.
6. Phosphorus is the primary nutrient exchanged from fungi to plant.
7. The plant provides sugars to the fungus in exchange for nutrients.
8. Phosphorus fertilizer at high rates suppresses mycorrhizal colonization.
9. Glomalin is produced by mycorrhizal fungi and helps build soil aggregates.
10. Tillage significantly damages mycorrhizal networks.
11. Native plants typically have strong mycorrhizal associations.
12. Mycorrhizal fungi can transfer nutrients between plants of different species.
13. Mycorrhizal inoculants are never useful because fungi are already in soil.
14. Sterile potting mixes lack mycorrhizal fungi.
15. Mycorrhizae help plants resist drought by improving water uptake.
16. Some plants (brassicas, sedges) do not form mycorrhizal associations.
17. The "wood wide web" refers to mycorrhizal networks connecting trees.
18. Excessive fertilization reduces the need for mycorrhizal associations.
19. Mycorrhizal networks can transport carbon between neighboring plants.
20. Pesticides, especially fungicides, can reduce mycorrhizal colonization.
1. What is the difference between ectomycorrhizae and arbuscular (AM) mycorrhizae?
2. What is the nutrient exchange between a plant and its mycorrhizal fungi?
3. Why does high phosphorus fertilization reduce mycorrhizal colonization?
4. What is glomalin and why is it important?
5. Describe the "wood wide web" — what it is and what it does.
6. Which agricultural practices damage mycorrhizal networks?
7. Why are brassicas poor companion plants for mycorrhizal plant species?
8. How do mycorrhizae help plants survive drought?
9. What are mycorrhizal inoculants and when are they useful?
10. How do mycorrhizal networks benefit a forest ecosystem?
1. Mycorrhizal fungi that form a sheath around roots without entering cells are called .
2. Mycorrhizal fungi that penetrate root cells forming tree-like structures inside are called mycorrhizae.
3. The primary nutrient that AM fungi supply to plants is .
4. The sticky soil protein produced by mycorrhizal fungi is called .
5. The interconnected underground fungal network linking trees is called the web.
6. High fertilization suppresses mycorrhizal association because plants have no need to trade carbon for it.
7. Two plant families that do NOT form mycorrhizal associations are and Cyperaceae.
8. The proportion of plant species that form mycorrhizal associations is approximately .
9. Mycorrhizal are commercial products containing fungal spores for application at transplanting.
Complete in the field. Check each off as you go.
1. Mycorrhizal Observation: Carefully dig up roots of an established oak or native grass. Look for ectomycorrhizal sheaths (visible white/tan coating on root tips) or AM colonization (requires clearing/staining). Compare to roots of a recently transplanted plant.
2. Phosphorus Trade-off Test: Grow three identical tomato seedlings: (1) inoculated with mycorrhizae + no P fertilizer, (2) no inoculant + standard P fertilizer, (3) inoculated + standard P fertilizer. Measure growth and root development after 8 weeks.
3. Brassica vs Tomato Spacing: Plant tomatoes next to brassicas (cabbage, broccoli) and separately from brassicas. After 6 weeks, compare tomato growth. Brassicas may reduce mycorrhizal colonization of neighboring plants.
4. Glomalin Test: Collect soil from under an established native oak woodland and from a repeatedly tilled garden. Do a slake test on both. The woodland soil should have far more stable aggregates due to glomalin.
5. Network Transfer: In a forest, find two trees connected at the base by visible fungal structures. Research which tree species in Texas are known to share mycorrhizal networks. Note any nurse-seedling relationships you can observe.
Chapter Summary
MYCORRHIZAE: fungus-root symbiosis in 90%+ of plants
From: Chapter Summary
Image file: ../../../images/s01-foundation/c03-soil-science/ch08/c03-soil-science_ch08_mycorrhizal_fungi_fig06.png
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Next Chapter → Water Movement in Soil
Connections to Other Topics
→ C03 Ch07: Soil Biology — fungi in broader soil food web context
From: Connections to Other Topics
Image file: ../../../images/s01-foundation/c03-soil-science/ch08/c03-soil-science_ch08_mycorrhizal_fungi_fig07.png
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