The Dirt on Mycorrhizae

The dirt on mycorrhizae

What is mycorrhizae?

Myco-what? mycorrhizae fungi, pronounced my-coh-RYE-zay, scientists and gardeners both have been learning more in recent years about these mycorrhizal fungi and how they benefit the garden and ecosystem. But just what is it, and why do your plants need it?

Tiny plant helpers

Mycorrhizae, a term derived from the Greek words 'mykos', meaning fungus, and 'rhiza', meaning root, refer to a type of fungi that form symbiotic associations with plant root systems. This symbiotic relationship is widespread, encompassing approximately 95% of plant species worldwide, excluding certain families such as Brassicaceae, which includes vegetables like cabbage, broccoli, and radish.

The symbiosis between mycorrhizae and plant roots is primarily beneficial for nutrient acquisition. Plants provide the fungi with carbohydrates, products of photosynthesis, and in return, the mycorrhizae enhance the plant's access to soil nutrients, particularly those that are less mobile or in limited supply, such as phosphorus, nitrogen, and micronutrients. This mutualistic relationship is crucial for many plants, especially in nutrient-poor soils.

Mycorrhizae extend far beyond the root’s physical reach by forming extensive networks known as mycelium. These networks increase the root's surface area for absorption, thereby facilitating greater uptake of water and nutrients. This mechanism is particularly advantageous in environments where these resources are scarce or sporadically available.

In leguminous plants, the role of mycorrhizae is even more pronounced due to their interaction with nitrogen-fixing bacteria. These bacteria, housed in root nodules, convert atmospheric nitrogen into forms usable by the plant. Mycorrhizae assist in this process by enhancing the overall nutrient and water uptake efficiency of the plant, thus supporting the energy-intensive nitrogen fixation process.

Furthermore, mycorrhizae contribute to soil health by improving soil structure. Their mycelial networks help in aggregating soil particles, which enhances soil porosity and aeration. This improvement in soil structure facilitates root growth and microbial activity, leading to a more dynamic and healthy soil ecosystem.

Mycorrhizae also play a role in plant health beyond nutrition. They can suppress soil-borne pathogens either by outcompeting them for resources or by inducing systemic resistance in the plant. This biocontrol aspect is crucial in sustainable agriculture, reducing the need for chemical fungicides and pesticides.

Additionally, mycorrhizal fungi can act as a bridge between different plants, creating a network through which nutrients and signals can be exchanged. This interconnected network, often referred to as the "wood wide web," allows plants to share resources and communicate, thereby enhancing the resilience of the plant community to environmental stresses.

Endo or Ecto?

There are two kinds of mycorrhizae: endomycorrhizae and ectomycorrhizae. Both live partially within the roots of their host plants, and also spread fungal hyphae away from the plant roots into the soil. Arbuscular mycorrhizae or Endo (meaning “in”) mycorrhizae penetrate into the cells of the roots of plants with which it forms relationships. The fungal hyphae deliver nutrients directly into the plant cells. A wide range of plants can live symbiotically with endomycorrhizae including most vegetables, grasses, flowers, shrubs and fruit trees.

Ecto (“out”) mycorrhizae live in between the cells of roots forming a “net” through the root, and also coat the outside of the root. This mycelial network delivers nutrients to the outside of plant cells with which they are in direct contact, but the plant must absorb the nutrients into the cells itself. Ectomycorrhizae form relationships with only a few kinds of trees including oaks and conifers.

Improving your soil with fungi!

There are many species of mycorrhizae, which typically can form relationships with multiple species of trees, flowers and garden veggies. Scientists have even discovered that one mycorrhizal fungus can simultaneously inhabit the roots of two or more different species of plants, and this connection is so strong that the health of one plant directly affects the other.

Mycorrhizae is present in most soils, and it can be encouraged to grow and flourish by caring for your soil with mulching, cover cropping, adding organic matter, and by not making rapid changes to the soil nutrient levels or pH. Low or no-till farming and gardening is better for mycorrhizae than conventional tillage. To add more mycorrhizae to your soil, you can inoculate your garden with Chappy’s Root Booster or Granular Root Growth Enhancer, or select potting soils or fertilizers with this ingredient. Some mycorrhizae also produce edible “fruiting bodies”: growing your own morel mushrooms is a delicious way to help your garden at the same time! Check out the book Mycelium Running by Paul Stamets for in depth and practical information on these and other fungi.

Additional Resources

  1. "Mycorrhizae — Worth the Investment?" by Judy Kunz, Colorado Master Gardener, from Arapahoe County Extension. This article discusses the role of mycorrhizae in soil health and questions the effectiveness of commercial mycorrhizae additives in garden soils. It also advises on practices that can enhance or harm mycorrhizae populations in soil​.

  2. "A Gardener’s Primer to Mycorrhizae: Understanding How They Work and Learning How To Protect Them," a publication from the WSU Extension, which explains the symbiotic relationships between mycorrhizae and plant roots, and provides guidance on how gardeners can protect these beneficial fungi.

  3. "Mycorrhizae: Nature's Gift to Plant Health" from the University of Missouri's Integrated Pest Management program. This article discusses different types of mycorrhizal relationships, the benefits they provide to plant growth, and the use of mycorrhizal supplements in agriculture.

  4. "The Effects of Mycorrhizal Fungi Inoculum on Vegetables" by the Master Gardeners of San Mateo & San Francisco Counties. This study compares the yield and vigor of vegetables grown with and without mycorrhizal fungi plant inoculum, providing practical insights for home gardeners​.

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Goodspeed, here is a section in our biochar article that answers your question, “Biochar Benefits Soil Biology-The porous structure also creates the perfect habitat for soil microbes and beneficial fungi to flourish. Although the microorganisms will eventually move into the biochar, you will see an even bigger benefit if you “pre-charge” or “activate” your biochar (this process is also sometimes called inoculating, maturing, culturing, or charging the biochar). This optional step is done prior to incorporating the biochar into your garden, and has the added benefit of preventing excessive nutrient binding (where so many nutrients become bound up with the biochar in the soil that not enough are available to the plants for a short time. Eventually the biochar will effect a nutrient gain, once the binding evens out).”


Do mycorrhizae perform well in soils that have been enhanced or amended with biochar, or does one hinder the performance of the other?


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