What is Mycorrhizae?
Most of us think of mycorrhizae as a fungus, but really, it is the beneficial symbiotic relationship between a fungus and a plant. This relationship benefits both the plant and the fungus. With the plants above ground, it is easier to see the benefits the plants receive from this, but the fungus also takes advantage of this partnership. The mycorrhizae aid the plant with growth, improved strength, increased root absorption area, while the fungus receives carbon from the plant. This interaction is more important for the plant because of the benefits that it receives.
Below I hope to be able to explain how these benefits and functions of mycorrhizae help our bonsai.
Benefits for Plants
Mycorrhizae create a large network of the roots of a plant and the soil around them. This allows for the fungus to absorb nutrients such as nitrogen and phosphorus for the plant. At the same time, this increases the surface area of the roots. With this increased absorption area, we can easily see the many benefits that the plant will receive. A couple of the benefits include an increase in the availability of nutrients and water for the plants’ consumption. Since nutrients and water are needed in order for plant growth, this mycorrhizal interaction can lead to an increase in the growth of the plant.
This increased availability of nutrients for the plant leads to more advantages. A plant with a mycorrhizae interaction will increase its nutrient and water uptake, whereas a plant without this partnership will have to rely on just its roots for the uptake of materials. If a plant with this symbiotic relationship is in an area with plants who do not have a mycorrhizae partnership, the fungi and plant partnership can give the plant the ability to out-compete other plants. Plants with mycorrhizal interactions can lead to changes in the plant composition of an area.
Benefits for the Fungi
Because Mycorrhizae is a symbiotic relationship, the fungus benefits from the partnership as well. While helping plants with the uptake of nutrients and water, the plants will give somewhere between 10% and 20% of the carbon they obtain from photosynthesis to the fungus.
What are the Functions of Mycorrhizae?
One function of mycorrhizae is its ability to exchange nutrients with their surroundings and their host plant. The increased surface area of the roots allows the fungus to absorb more nutrients for its host. Mycorrhizae are able to absorb water, inorganic phosphorus, mineral or organic nitrogen, and amino acids through transport cells located on their membrane. Once the water and nutrients are absorbed, they can then be transferred to the plant, who in return supplies carbon.
Mycorrhizal relationships help increase plant growth and therefore yield. An increase in yield for farmers would mean an increase in income. With this relationship in agricultural fields, you would see an increase in crop production followed by an increase in food output.
The mycorrhizal fungi help with soil aggregation. This can increase water filtration and gas exchange within the soil. An increase in gas exchange can aid in the aeration of agricultural fields. Along with the other benefits of mycorrhizae, you can see an increase crop yield.
This symbiotic relationship can be helpful in restoration areas. The fungus helps certain plants to be greater competitors and can allow them to prosper in areas low in nutrients and water. This relationship would be very useful in restoration efforts. This important partnership can increase a plant’s ability to colonize an area by having a greater capacity to out-compete invasive species.
How does this Relate to Bonsai?
The Bonsai Pot and Roots
The goal for the roots of a bonsai is to have a mat of fine feeder roots that are able to absorb water and nutrients throughout the whole pot. But some species have thicker roots than others and this makes it more difficult to form the fine mat that we look for. If we are unable to fill the pot with fine feeder roots, it’s more difficult to absorb enough water and nutrients and the plants will suffer. This is where mycorrhizae have a role with our bonsai. One way to look at this relationship between the plant and the fungus is that the fungus almost acts as fine feeder roots. By colonizing the areas between the roots, it increases the absorption area. With this relationship, we increase the health of the plant and roots. This increased health will increase the number of fine feeder roots.
Bare Rooting Conifers
One reason we do not bare root conifer bonsai is because of this symbiotic relationship. If you remove all of the soil, you are also removing the mycorrhizae. Conifers, in particular, rely heavily on mycorrhizae to transform nutrients into a form that they can use. By removing the fungus, you are removing a vital part of the root zone. In some cases, it is enough to kill a tree. I like the half bare root method to repotting conifers. Repotting black pine in nursery soil
Healthy Roots, Healthy Bonsai
I have always said that if you can’t grow roots, then you can’t grow bonsai. Of course, it is more than that, but it’s true. If the root zone is healthy then you will have a healthy bonsai. If the root zone is unhealthy and dies then the bonsai dies.
Especially in conifers, you want to see the fuzz in your soil. This is the mycorrhizae growing and this indicates a healthy root zone. This is going to do a couple things. 1) It will increase the absorption area of the roots. This allows the roots to absorb more water and nutrients to transport to the bonsai. 2) With the increase in nutrients to the bonsai, the plant will respond with healthier growth. This growth will be in the form of more back buds, shorter internodes, and increased ramification. This increased ramification will also increase the ramification of the roots, meaning finer roots. This circles us back to the “The Bonsai Pot and Roots” section.
Fertilizing to Promote Mycorrhizae
You will hear some people say that some plants don’t need mycorrhizae to survive. This is true to some degree. If you are providing enough nitrogen and phosphorus in forms that are easily used by the
bonsai, mycorrhizae will not grow. This usually happens in bonsai when we use inorganic fertilizers. These fertilizers are fast acting, can burn the root hairs, and harm the fungus because they are chemicals.
What happens is that you make that plant “dependent” on a steady stream of fertilizer and you will always have to keep fertilizing. The fertilizer runs right through our “soil”.
Organic fertilizers provide enough nutrients for the plant to grow, however, they are slower acting. Also, mycorrhizae are needed to break down those nutrients into a form that the bonsai can absorb. The organic fertilizer promotes or “feeds” the fungus and the fungus feeds the bonsai. The organic fertilizer should break down slowly over time (usually 4-6 weeks). This network of fuzz in our soil slowly breaks down the nutrients in the organic fertilizer so the bonsai has a steady food source that promotes healthy roots.
To wrap up this article, I want to reiterate that mycorrhizae are important for plant health. Especially in conifers. This symbiotic relationship is one of the most important things we can cultivate for a healthy root zone along with a healthy bonsai. If you are using an inorganic fertilizer and then paying money for a mycorrhizae product, you are wasting your money. Switch over to an organic fertilizer that promotes the root zone, like Sumo Cakes does. In the end, your bonsai will be happier.
To read more about fertilizers, I recommend this page.