Target Grade Level / Age Range:

Grades 9-12

Estimated Time:

50 minutes

Purpose:

Students will identify characteristics of a healthy soil and how fungi help build healthy soil.

Materials:

  • Variety of soil samples
  • Two large clear jars, vases, or pitchers
  • Two pieces of ¼” wire mesh
  • Optional: poster paper, markers
  • 2 different soil samples – conventionally tilled field and one soil under natural growth
  • 3 or more screens of different sized mesh (window screen or other insect screen). Suggested sizes:
    • 5mm opening
    • 2mm opening
    • 1mm opening
    • .5mm opening
    • .25mm opening
    • .125mm opening
  • Spray water bottle
  • Glass dishes – 6 or more

Essential Files (maps, charts, pictures, or documents)

Vocabulary (with definitions)

  • Mycorrhizal fungi – symbiotic relationships that form between fungi and plants. The fungi colonize the root system of a host plant, providing increased water and nutrient absorption capabilities while the plant provides the fungus with carbohydrates formed from photosynthesis
  • Hyphae – interconnected network of root-like tubes of a fungus. A mushroom is the fruiting body of this fungus.
    • Size: 1/10 to 1/50 the width of a human hair
  • Arbuscules – branched finger-like hyphae

Background – Agricultural Connections (what would a teacher need to know to be able to teach this content)

By weight, fungi are the dominate soil microbe biota. Their cells contain nuclei and are therefore eukaryotic, although some are unicellular with multiple nuclei. They reproduce both asexually and sexually by producing spores which are capable of surviving prolonged periods of nutrient deprivation. Because of their larger size, they are found in larger spaces between clumps of soil particles.

Their appearance is similar to that of the actinomycete bacteria, but they are much larger, with a diameter of 2-10 µm and a length of up to 50-100 µm. In one extreme exception, researchers in northern Michigan discovered a fungus estimated to be 21,000 pounds, 30 acres wide, and 1500 years old; other similarly large soil fungi have since been discovered. Though not as large as giant redwoods, these discoveries make fungi among the largest and oldest living things on earth.

Fungi are obligate aerobes, unable to survive in anoxic conditions. They have a variety of life history strategies, but their most important ecological role is that of decomposer. They can break down very tough molecules such as lignin and soil humic acids. They can tolerate acidic conditions better than bacteria, and in extremely acidic forest soils (such as in coniferous forests) they perform a task usually restricted to bacteria, that of fixing nitrogen.

Interest Approach – Engagement (what will you do to engage students at the beginning of the lesson)

Repeat the Slake test demonstration from Lesson #3, How Soil Behaves. Take your two-contrasting soil peds and explain to the classroom how their sources differ. One should have a strong structure from a largely undisturbed soil (pasture or forest), and one should have poorer structure from a more disturbed soil (field or garden).

Have two large, clear containers filled with water at the front of the room. Each should have large mesh baskets at the top to hold the soil peds in the water. Place the two contrasting peds into the jars at the same time. Consider setting a digital timer or stopwatch so students can record times of their observations.

What is providing the soil its structure? How are the soil particles being held together? Why does the undisturbed soil withstand the water breaking it apart? Explain that in today’s lesson we will be answering these questions.

Procedures

  1. Present the content in the PowerPoint slide deck titled Fungi in Soil.pptx.
    1. Types of fungi
      1. Saprophytes – feed on organic matter that is difficult to break down such as crop residue
        1. Decomposers and nutrient transporters. Store nitrogen in hyphal bodies and release nitrogen by decomposing.
      2. Parasites – attach foliar and root plant material, other fungi, nematodes, and micro and macroarthropods
      3. Mutualists – trade nutrients with plants
    2. Microorganisms - fungi
      1. Habitat characteristics
        1. Aerobic only
        2. Tolerant of acidic soil
        3. Moderately dry
        4. Forest, compost, garden/field, or prairie
      2. Role in food chain and ecosystem
        1. Decomposers – consume lignin and soil humic acids, and others
        2. Occasionally nitrogen fixation
    3. Symbiosis           
      1. Plants and fungi are symbiotic – because of this, fallow fields lose their fungi (no plants to interact with)
      2. 80-95% of land plants benefit from a mycorrhizal fungus.
      3. Fungi inserts hyphae into the plant root for exchange of nutrients
    4. Symbiotic Relationships – Plant, Fungus, Bacterium
      1. Bacteria live on or near the hyphae.
      2. Fungus takes carbon from the plant and gives carbon to phosphate-solubilizing bacteria.
      3. Phosphate-solubilizing bacteria create enzymes to solubilize phosphorus.
      4. Fungus takes up phosphorus and gives it to the plant.
      5. Fungus can obtain and provide the plant up to 90% of the nitrogen and phosphorus needs of the plant.
      6. The fungus requires 4-30% of the plant’s carbon.
      7. Healthy fungal communities could help farmers reduce their need to apply fertilizer.
      8. Fertilizer application on crops can have a negative impact on mycorrhizal fungi development because it could inhibit this natural exchange if nutrients are already readily available.
      9. Any N or P that the plant can’t get from this symbiotic relationship has to be added in a plant-available form like fertilizer.
    5. Fungi – Building Soil Structure
      1. Fungal hyphae create a net that holds soil particles and soil aggregates together.
      2. Think of it as a hair net in the soil.
      3. Aggregations is largely a biological process
      4. Arbuscular mycorrhizal fungi connect plant roots to minerals in the soil.
      5. The arbuscules help transport the minerals into the plant.
      6. Fungi produce a biomolecule – a protein called glomalin – making a waxy seal on the surface of the soil aggregate.
      7. This waxy coating minimizes the water’s ability to break apart the soil aggregate
  2. Ensure that everyone has a solid understanding of the information that was presented by reviewing the material (slides 11-12) and asking students questions to gauge their comprehension. Ensure that the students have captured key information through appropriate note-taking techniques.
  3. Maps can be a visual representation of information and the relationships among pieces of information. Have students represent the information they just learned using a map style of their choice. Have them capture the maps in their notebooks or provide paper, markers, and other material to make larger, more visual maps. This activity can also work well in partners or teams.
  4. Measure aggregate stability.

Did You Know? (Ag facts)

  • 80-95% of land plants benefit from a mycorrhizal fungus
  • Fungus can obtain and provide the plant up to 90% of the nitrogen and phosphorus needs of the plant

Extension Activities (how students can carry this beyond the classroom)

  • Have students interview a no-till farmer about why they choose no-till. Have students interview a farmer that does till about why they choose tillage.

Suggested Companion Resources (books and websites)

Sources/Credits

Author(s)

Will Fett

Organization Affiliation

Iowa Agriculture Literacy Foundation

Agriculture Literacy Outcomes

T1.9-12.b. Describe resource and conservation management practices used in agricultural systems (e.g., riparian management, rotational grazing, no-till farming, crop and variety selection, wildlife management, timber harvesting techniques).

Iowa Core Standards

  • HS-LS2-6. Evaluate the claims, evidence, and reasoning that the complex interactions in ecosystems maintain relatively consistent numbers and types of organisms in stable conditions, but changing conditions may result in a new ecosystem.
  • HS-LS2-7. Design, evaluate, and refine a solution for reducing the impacts of human activities on the environment and biodiversity.*

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