If you’re like me, you may have thought “mycorrhizal fungi” described a specific fungi, which isn’t quite accurate. It’s actually descriptive of a process or system wherein fungi interact with plant roots. The mycelium of the fungus radiate out into the soil to enhance phosphate uptake, with the host root providing carbohydrates to the fungus.
Mycorrhizae’s literal translation is “fungus-root”, which is the mutually beneficial relationship between the colonizing fungus and the plant root. These fungi can grow on the surface or within the plant root. The fungi facilitates water and nutrient uptake and the plant provides food and nutrients to the fungi.
Types of Mycorrhizae
This type of fungi tend to grow on woody plants, including oak, spruce, fir, willow, pine, beech and birch trees. This fungi forms a dence hyphal sheath or mantle around the outside of the root. Five to ten percent of terrestial plant species have ectomycorrhiza.
Eighty percent of extant plant species, including crops and greenhouse plants, most vegetables, grasses, flowers, and fruit trees, have endomycorrhizal relationships wherein the fungi penetrate the cortical cells. The exchange mechanism between the fungi and root system is internal, inside the root, but the fungi’s hyphae extend outside the root. This makes for a much more invasive relationship compared to ectomycorrhiza.
Orchid Mycorrhiza – Orchid seeds require fungal invasion to germinate because the seeds lack necessary nutrients to grow. Once the seed sprouts and roots emerge, the hyphae of orchidaceous mycorrhiza penetrate the root’s cells and create hyphal coils or pelatons, which are where nutrients are exchanged.
Arbuscular Mycorrhiza – The most widespread mycorrhiza which are obligate symbionts; they cannot grow without a plant host.
Ericaceous Mycorrhiza – Generally found on plants in the order Ericales. Inhospitable, acid environments where these fungi help regulate the plant’s uptake of minerals including iron, manganese, and aluminum. They form hyphal coils outside of the root cells significantly increasing root size.
Ectotrophic Mycorrhiza – Associate with Ascomyota and Basidiomyota families. They are found in cooler environments around tree roots. They derive their nutrients from the living plant exclusively.
Arbutoid Mycorrhiza – Similar to ectomycorrhizal fungi with the exception they are nonpenatrative. Instead they encompass the roots of the plant.
How do Plants Benefit from Mycorrhizae?
- Increase available water and nutrients to the plant through their finer hairs, mycelia, which increase surface area and act as a second set of roots for the host plant.
- Studies have shown that mycorrhizal fungi can be an effective disease control creating a physical barrier between pathogens and plant roots.
- In addition to this, mycorrhizal fungi can also impart to the host plant resistance to toxicity and resistance to insects.
- Improve soil structure and quality. Mcorrhizal fungi create humic compounds, polysaccharides, and glycoproteins that increase soil porosity, bind and promote aeration and water movement in the soil.
- Some ectomycorrhizal associations create structures that host nitrogen-fixing bacteria. Mycorrhizal fungi do not fix nitrogen themselves.
What’s in it For the Fungi?
- Sugar – glucose and sucrose.
- Photosynthetically fixed carbon – which triggers nitrogen uptake and transport.