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Kim Eierman

Kim Eierman

Founder of EcoBeneficial!

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Our Allies in the Soil: Interview with Dr. Roger Koide on Mycorrhizal Fungi

Fungi are tremendously abundant organisms in our ecosystems, yet we often view them in a negative way or we don’t consider them at all.  Actually, many fungi are essential for nutrient cycling as they decompose organic matter.

A group of fungi with a daunting name, “mycorrhizal fungi,” are particularly valuable, as many can actually increase the nutrient and water uptake of plants.  For gardeners and landscape pros alike, mycorrhizal fungi are essential partners in maintaining healthy plants.

Dr. Roger Koide, Professor of Biology at Brigham Young University is one of the nation’s top experts on mycorrhizal fungi, having researched this subject for more than 25 years.   I recently interviewed Dr. Koide to learn from the master.

Dr. Koide explained that mycorrhizal fungi colonize plant roots in a symbiotic, and usually, but not always,  mutualistic relationship.   As these fungi consume carbohydrates from a plant’s roots, they often transfer mineral nutrients back to the plant.   In addition, they often increase uptake of water.  The term “mycorrhiza” refers to this symbiotic relationship between a plant’s roots and particular fungi in the soil.

Mycorrhizal fungi occur naturally in our soils, noted Dr. Koide, and 75% to 80% of all terrestrial plants are “mycorrhizal” having this important relationship with fungi.  Some studies have shown that mycorrhizal plants are often more resistant to diseases, especially those diseases caused by pathogens in the soil.

There are two main types of mycorrhizal fungi, said Dr. Koide,  ectomycorrhizal fungi which attach to plant roots and arbuscular mycorrhizal fungi which penetrate plant roots.  The vast majority are ectomycorrhizal.

Woodland soils are ectomycorrhizal.  Some of our “ecto” plants include:

  • Oaks
  • Birches
  • Beeches
  • Pines

Most herbaceous (non-woody) plants are arbuscular mycorrhizal, but there are some woody plants too, including:

  • Dogwoods
  • Redbuds
  • Tulip Poplars
  • Red Maples

You may have heard the term “endomycorrhiza” a term which is no longer used, according to Dr. Koide, now replaced by “arbuscular mycorrhiza.”  While there are other types of mycorrhizal fungi, these are less predominant.

Dr. Koide shared some key points to keep in mind:

  • Mycorrhizal fungi are important because they freqently increase plant nutrient uptake.
  • They can often increase the uptake of water, phosphorus and/or nitrogen to help plant growth.
  • Mycorrhizal fungi occur naturally in soils.  Where vegetation has been growing successfully, there will be mycorrhizal fungi in the soil.
  • They are living organisms native to specific locations – moving them around may not be the best idea.
  • Rototilling is very detrimental to mycorrhizal fungi, as it chops up the mycelium (the network of fine filaments of the fungus).
  • Most commercial mycorrhizal products (often sold as “mycorrhizal inoculant”) are not useful and will be outcompeted by existing native mycorrhizal fungi.
  • In many cases, commercial mycorrhizal products are nothing but fertilizer.
  • In areas where topsoil has been removed and there are no roots, an application of a commercial mycorrhizal inoculant may be useful.
  • Soiless mixes do not have mycorrhizal fungi (unless added in).
  • Compost will not have mycorrhizal fungi.  Even if there is soil and/or roots in the compost, the heat of the compost will kill the fungi.
  • Many edible mushrooms, such as Chanterelles and Truffles, are ectomycorrhizal fungi.
  • Arbuscular mycorrhizal fungi are not edible.
  • Some plants do not support mycorrhizal fungi, including plants in the mustard family.

Take advantage of this rare opportunity to hear Dr. Roger Koide discuss this fascinating subject on my video or podcast interview.

From Kim Eierman at EcoBeneficial!

Photo: A Truffle – a type of mycorrhizal fungi
Photo credit: Wikipedia




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