Benefits of Mycorrhiza

More on the benefits of Mycorrhiza

The Living Soil

During your favorite hike, have you ever wondered which fertilizer or pesticide was used to create and maintain such lush, healthy vegetation? Probably not. That's because in nature, plants are growing in a living soil. In just one handful of soil there are more than 100 million bacteria, several miles of fungal filaments, and another million of algae, protozoa, and nematodes combined. This diverse community is responsible for nutrient cycling and storage and provides competition for disease causing organisms. Soil fungi are the dominant residents of this community, contributing over 50% of the soil biomass. The obvious stars of this living soil are a specialized group of beneficial soil fungi that form an intimate relationship with plant roots. This relationship is called mycorrhiza. Mycorrhiza plays a key role in plant-soil health and functioning.

Myco-What?

First things first... the terms. Thankfully biological terms are mostly descriptive, noting a structure or function of a biological system. "Mycorrhiza" is no different. It is simply describes a fungus (myco) - root (rhiza) association. More specifically we are talking about a distinct type of mycorrhiza in which the fungus is found inside of the root, termed "endomycorrhiza". This MYCORRHIZA type of mycorrhiza is found in most "Myco" = fungus plants and we will be referring to this "Rhiza" = root type from here on out. Looking at internal structures, particularly the arbuscule or "tree-like" structure, Fungus insideroot we can narrow the term even further to "Arbuscular" Mycorrhiza or "AM" (preferred over VAM or vesicular "AM" fungi arbuscular mycorrhiza). To summarize, "mycorrhiza" is the general term used for the association. "Endomycorrhiza" is a specific type of mycorrhiza, and "arbuscular mycorrhiza" is just a more specific name for endomycorrhiza.

AM Symbiosis

Arbuscular mycorrhiza is a mutually beneficial symbiosis or partnership between beneficial soil fungi and plants. The symbiosis works much like the cartoon - the plant gets something it needs from the fungus (mostly soil nutrients) and in exchange the fungus gets sugar or carbon. This symbiosis is ancient. It has been found in plant fossils dating back to 400 million years ago, which is approximately when plants first colonized the land. Scientists believe that this partnership with soil fungi was essential to the plants ability to establish on land. This simple but important relationship has changed little over the past 400 million years and remains a significant part of plant ecology. Mycorrhiza is the natural state of most plants with an estimated 90% of all plant species belonging to plant families that form mycorrhiza. There are four major plant families that characteristically do not form mycorrhiza: Amaranthaceae or Pigweed family, Brassicaceae or Mustard family, Chenopodiaceae or Goosefoot family, and the Zygophyllaceae or Caltrop family. These plant families are well known as weeds.

How Does It Work?

A plants root system - finely branched with many root hairs or coarse with few root hairs - determines the amount of soil the plant can "mine" for nutrients. When AM fungi colonize the "host" plant root system it spreads out thin fungal filaments or hyphae from the root surface into the surrounding soil. These hyphae can spread out past the root hairs and access larger amounts of soil, thereby retrieving otherwise inaccessible pools of nutrients and water. Therefore, for plants with coarse root systems, partnering with an AM fungus greatly increases their ability to absorb and compete for precious soil nutrients.

AM Plant Benefits

  • Enhanced Soil Nutrient Uptake -Phosphorus,Calcium, Sulfur, Ammonium, Zinc
    The AM fungal hyphae increase the amount of soil that the plant roots can "mine" for nutrients and thus increases the soil nutrient uptake. This works most effectively on nutrients that are poorly mobile in the soil. Phosphorus is a particularly "sticky" nutrient, extremely important in plant nutrition and the increased Phosphorous uptake by mycorrhiza is very well documented but mycorrhiza has also been shown to increase the uptake of other poorly mobile nutrients.
  • Increased Drought and Pest Tolerance
    Along with accessing more nutrients, the hyphae also allow greater access to water. In addition, the extensive hyphal network block pest access to roots. The increased tolerance to drought and pests has also been related directly to the improved plant nutrition of mycorrhizal plants.
  • Increased Tolerance to Toxic Heavy Metals
    Mycorrhiza alleviates root stunting typically caused by toxic metals, thereby increasing nutrient uptake. AM fungi may also bind metals in the root zone and alter the plant cells ability to capture the metals.
  • Improved Soil Aggregation
    The AM fungal hyphae has also been shown to excrete gluey sugar based compounds termed "Glomalin" which helps to bind soil particles and create stable soil aggregates, which gives the soil structure and improves water and air infiltration as well as enhance carbon and nutrient storage.
  • Enhance Biodiversity of Soil Microorganisms
    The presence of mycorrhiza also increases the biodiversity of soil microbe populations, which creates a healthy soil ecosystem. What a healthy soil ecosystem means to plants is improved nutrient cycling and retention, improved air and water relations, and importantly resistance to invasion and establishment of disease causing organisms.
  • BOOST PLANT "IMMUNE SYSTEM"
    All of these benefits are actually interrelated and all work together to make the plant healthy by recreating a "Living Soil".

Got Mycorrhiza?

Mycorrhizal fungi, while naturally occurring, can be lessened to an inadequate level or even eliminated by certain land practices:

  • Eroded?
  • Graded?
  • Excavated?
  • Occupied with Non-mycorrhizal Plants?
  • Little Original Topsoil?

YES - Need to inoculate NO - Should be native AM fungi present

AM Inoculum

If you answered "yes" to any of the questions above, there may be a need to reintroduce AM fungi with inoculum in order to reestablish mycorrhiza. Inoculum contains fungal propagules or "seeds" of the fungus, which are live fungal structures that have the ability to initiate colonization of plant roots. Care must be taken with the inoculum in order to maintain viable propagules.

  • AM Fungal Propagules
    • Spores, colonized roots, hyphae
    • Sand, calcined clay, or peat carriers
      • Requires Plant Host
      • Application
    • Seeding
    • Seed Drilling
    • Hydroseeding
    • Broadcast and Till
    • Planting
    • Nursery Medium

AM Production Benefits

All of the plant benefits associated with a well functioning mycorrhiza can lead to these practical production benefits:

  • Increase Plant Establishment
  • Sustain Plant Production and Productivity
  • Reduce Soil Erosion
  • Reduce Transplant Shock
  • Reduced Use of Fertilizers and Pesticides
  • Lower Water Requirement
  • Increased Soil Aeration and Drainage
  • Increase Resistance to Invasive Weeds
  • Increased Pathogen Resistance

Necessary for Successful AM Inoculum Use

Care must be taken in order to maximize plant benefit to inoculation. AM inoculum is like no other soil amendment. The purpose behind inoculating with AM fungi is to establish a functioning healthy biological symbiosis. A beneficial symbiosis is dependent upon the right balance between the needs of the plant and that of the fungus.

  • Watch Phosphorus Fertilization
    Phosphorus plays a major role in the establishment and functioning of the symbiosis. High phosphorus fertilization limits mycorrhiza effectiveness, but low to moderate levels of phosphorus or the use of slow release forms such as rock phosphate maximize plant benefits from mycorrhiza.

  • Limit Use of Fungicides
    Benlate, Aliette, Phaltan, Diazinon
    These are some of the fungicides that have been found to damage AM fungi.

  • Limit Soil Disturbance
    Severe disruption of the soil hyphae limits nutrient and water movement into the plant root.

  • Match AM fungi with Host and Soil
    While AM fungi are not host-specific, there are some associations that are more effective than others in benefiting the plant. AM fungi also differ in their tolerance of different soil factors. Therefore it will be a future priority to match AM fungi with host and soil in order to optimize the use of inoculum and maximize the plant benefit.