So what are mycorrhizal fungi??
In the most basic sense, these fungi live in the soil and beneficially associate with plants. These fungi have what is called a "mutualistic relationship" with the plant they inhabit. Each player gives a little to the benefit of the other. Depending on the feeding strategy organisms receive carbon (essential ingredient of our metabolic processes) from various sources. Plants take up carbon in the form of carbon dioxide from the air, decomposer fungi receive carbon from wooden logs by excreting enzymes. Mycorrhizal fungi need carbon as well, but they often get this from their "hosts" or in other words the plant shares the carbon (sugars) it produces with the fungi! So what does the plant get out of this? Well, quite a bit actually. Plants receive nutrients, a larger area to access nutrients from, disease protection, and even assistance with drought tolerance. Nice deal for both parties!
The quintessential mycorrhiza on pine tree cover photo on Smith and Read's, Mycorrhizal Symbiosis.
They are several groups of mycorrhizal fungi, but the two main are arbuscular mycorrhizal fungi or AMF (formally known as vesicular-arbscular mycorrhizas or VAM), which grow into the plant cells. This makes them endomycorrhizal. The AMF fungi have a "tree-like" structure that can be seen inside the cells where nutrient exchange takes place. The other main group is ectomycorrhizal fungi (EMF). These fungi grow into the plant, but grow around the cells.
Arbuscule inside a plant cell. Photo credit - Shachar-Hill Lab MSU (http://shachar-hill.plantbiology.msu.edu/?page_id=44)
Ok, so here we go back to the main point of this blog entry. The two main groups AMF (endos) and EMF (ectos) are associated with different types of plants. Over 80% of Earth's plants have a mycorrhizal association. However, AMF's association is only with certain plants (typically herbaceous/non-woody) and EMF's associate with the other plants (usually woody plants). Note: Every now and then there is some cross-over, but I'll go over that in a future posting. Ok with the concept of host-specificity in mind (certain mycorrhizae associating with certain plants) we start to look at what certain products are providing to you as the consumer.
Ectomycorrhiza on a root. Photo credit: Mycorrhizal Associations (http://mycorrhizas.info/ecm.html)
I have seen these biological products that are designed for specific plants (citrus, turf, roses, etc). These products are providing both AMF and EMF in these products when in actuality only AMF fungi are appropriate. The addition of both of these types of fungi will not hurt your plants and if the company supplying the product wants to provide both then fine. However, what is not helpful to you the consumer is that these companies are making you think that more organisms = better product. In actuality, adding proper organisms, not more, may be a better approach!
If you are interested in which mycorrhizal group your plants fall into, please click on the following link: http://californiamycorrhiza.com/lists.html
There is a lot to be learned about microorganisms in soil, but hopefully what we do know (as in the case of mycorrhizas) can be applied in more of a scientific approach to help you grow the best plants possible! What are your thoughts on biological products with mycorrhizas that you have used? Yea or nay?