Mycorrhizal Fungi

What is it, and Why should I care?




I mentioned that in planting it's a good idea not to disturb the soil unduly. The reason for this, is that it is best not to disturb the Mycorrhizal Fungi in the soil.

The network that probably connects 90% of the earth's plants has existed for 460,000,000 year but it is only in about the last thirty years that it has become somewhat understood by scientists. They believe that it was the mycorrhizal fungi that enabled plants to adapt to land, and that this relationship began before there were any plants outside the oceans.

We do know that this fungi filaments attach to the roots of plants in a symboitic relationship providing access to additional water and nutrients. The network can connect one plant to another thus forming a network.¹ Scientists first discovered mycorrhizae observing plants grown in glass boxes. However, the strands of fungi are small and delicate and easily destroyed, and thus it was difficult to study in the wild. They have used core samples near plants and have used DNA testing to study plants in the same area, to determine if they are connected.²

It appears that the mycorrhizae function a bit like having an extra set of roots which are even more porous, and that also provide immune protection against airborne pathogens. New plants once they have been tapped into get extra help in getting established in the new location. In exchange for all the benefits to the plants, the fungi obtain glucose and sucrose. Mycorrhizal fungi can be either ecto- (that that contact the root system and keep an external link to the plant), and endo-mycorrhizal fungi (that actually enter the cell walls and form an internal link). Both kinds use the plant's sucrose to create an enzyme that breaks down minerals in the soil which are useful to both the fungi and the plant.

It's a wonderful relationship in nature, and one that is easy to promote, but also easy to disrupt. The fungi are very easily damaged by disruption of the soil, but also by the addition of fertilizer. The fertilizer overwhelms the fungi and in a sense gives it no reason to exist. Ironic isn't it? We added fertilizer to plants to make them grow better, not realizing that we were killing the very thing that could make them the strongest and healthiest. In fact, fertilizer while it greatly increases growth rate the cells in the stems, roots, and leaves are weaker and thus not as healthy.

What else happens when the soil is disturbed? In a native ecosystem the ratio of bacteria to fungi is about 1:10, when the network is broken the ratio changes in favor of bacteria, the water and minerals in the network is released and alien species such as weeds and rodents thrive.

In contrast, in the plant community linked by the mycorrhizae, the plants support each other. This is also the reason for learning about plant communities, and planting oaks with members of their plant community (Manzanita, Ceanothus, Ribes, Redberry, Coffeeberrry).³

Later: More about plant communities

¹N.A., "Mycorrhiza", February 11, 2010, http://en.wikipedia.org/wiki/Mycorrhiza, (12 February 2010)

²Peter Kennedy,November 2005, "Common Mycorrhizal Networks: An Important Ecological Phenomenon",http://www.mykoweb.com/articles/MycorrhizalNetworks.html, (12 February 2010)

³Celeste Wilson, "California Native Oaks and Mycorrhiza", May 13, 1995, http://www.laspilitas.com/classes/mycorrih.htm, (12 February 2010)