What are Mycorrhizae Fungi?

The word Mycorrhizae literally means ‘Fungus Root’ coming from the Greek words ‘mycos’ meaning fungus, and ‘rhiza’ meaning root.  Mycorrhizae are special soil fungi that form a symbiotic relationship with plant roots. In this association both organisms’ benefit. The fungi attach themselves to the roots and feed on the sugars (carbon) produced by the plant during photosynthesis. In exchange the fungi branch out and act as an extension of the plants root system. It is estimated that mycorrhizae can extend the surface area of the roots by as much as 400 times (Canadian Organic Growers Inc., 1992). This assists the plant with the absorption of water and nutrients (especially immobile nutrients like phosphorus), and also plays a role in disease protection, and overall soil quality. It is estimated that between 80% and 90% of all known species of plants form mycorrhizal relationships (Australian National Botanic Gardens, 2012).

Their Importance in Plant Health
While mineral nutrient acquisition from soil is considered to be the primary function of mycorrhizae there are many other benefits to this association such as:

•  Reduced water requirements and increased drought resistance. With a more expansive root network in place the roots are able to explore more soil in search of water.
•   Improved soil structure. Endotrophic* mycorrhizae, commonly called arbuscular mycorrhizae (AM), make a protein called glomalin. This sticky substance (which does not dissolve in water and is resistant to decay), helps to bind soil particles together into aggregates. This aggregation results in increased soil porosity, improved water infiltration and percolation, and reduces soil erosion.
•   Enhanced plant health and vigor. Through this association with mycorrhizae, plants are able to extract soil nutrients and water that otherwise would have been inaccessible to them.  Glomalin further helps out the situation by coating the hyphae (the thread like extensions) preventing water and nutrients from getting lost on their way. This improved nutrition enhances the plants health and makes them more resistant to disease.
•   Increased fruit and flowering.
•   Plants establish faster.

Building Mycorrhizae Populations in your Soil
These ancient microorganisms have evolved with plants for millions of years, but their populations may be greatly reduced or even eliminated from soils where severe soil disturbances have occurred. Some examples include removal or erosion of topsoil, increased soil salinity, overly dry or overly wet soils, compaction, tillage, fertilization, road and home construction, leaving soils bare and fumigation.
Reintroducing mycorrhizal fungi into areas where they have been depleted can dramatically improve plant establishment and growth.
To re-establish or build native mycorrhizal populations sustainable farming practices such as growing cover crops, adding compost, minimizing tillage, rotating crops, mulching and eliminating synthetic chemicals can be implemented.
Another means of establishing mycorrhizal populations is through inoculation. Mycorrhizal spores, pieces of colonized plant roots or viable mycorrhizal hyphae can be used to inoculate seed or applied directly to the roots or the soil directly around young seedlings (mycorrhizae prefer to colonize young feeder roots).  Be sure you are introducing the right mycorrhizae. 

Note:
* There are seven types of mycorrhizae described in current scientific literature (arbuscular, ecto, ectendo, arbutoid, monotropoid, ericoid and orchidaceous mycorrhizae), (Springer, 2008). The arbuscular (also known as endotrophic mycorrhizae) and ectomycorrhizae are the most abundant and widespread.

Photo credit: the author

References:

1. Canadian Organic Growers. Inc. (1992). Cognition. COG Organic Field Crop Handbook Retrieved Feb. 4, 2014 from http://eap.mcgill.ca/MagRack/COG/COGHandbook/COGHandbook_1_3.htm 
2. Australian National Botanic Gardens and Australian National Herbarium (2012); Australian Fungi; Retrieved Feb. 4, 2014 from https://www.anbg.gov.au/fungi/mycorrhiza.html
3.  Springer (2008), MYCORRHIZAE: SUSTAINABLE AGRICULTURE AND FORESTRY; Retrieved Feb. 4, 2014 from http://www.krishibid.com/ebook/Mycorrhizae%20-%20Sustainable%20Agriculture%20and%20Forestry%20%28Springer,%202008%29.pdf 

Suggested Reading:

1. MYCORRHIZAE: SUSTAINABLE AGRICULTURE AND FORESTRY; by Springer (2008), http://www.krishibid.com/ebook/Mycorrhizae%20-%20Sustainable%20Agriculture%20and%20Forestry%20%28Springer,%202008%29.pdf 
2. Complete How-To: On-farm AM fungus inoculum production http://rodaleinstitute.org/2010/a-complete-how-to-on-farm-am-fungus-inoculum-production 
3. Science Daily (January 8, 2014); Fungi may determine the future of soil carbon http://www.sciencedaily.com/releases/2014/01/140108133303.htm 
4. WORKING WITH MYCORRHIZAS IN FORESTRY AND AGRICULTURE, by Mark Brundrett, Neale Bougher, Bernie Dell, Tim Grove and Nick Malajczuk (1996).  Published by the Australian Centre for International Agricultural Research.

Suggested Videos:

1.  Michael Martin Melendrez  (uploaded, Feb 27, 2011);  Ecoversity; Soil Humus Mycorrhizae Glomalin  http://www.youtube.com/watch?v=WmBL6PI-vYY 
2. Mycorrhizae from the History Channel http://www.youtube.com/watch?feature=player_embedded&v=AEI41JyKu6g 

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