The Mysterious World of Mycorrhizas

Sometimes when you need help doing something, you get a new app on your phone. Did you know that other living things do something similar? Plants cannot absorb all the nutrients they need from soil without help. And fungi cannot get the energy they need without help. So, these two types of organisms have developed a unique symbiotic partnership to help each other out. We call this mycorrhiza.

In this article, we will explain what mycorrhizas are, how they benefit plants and fungi, how they affect soils, and how they benefit us.

What is a mycorrhiza?

When certain groups of fungi grow around or inside the fine roots of plants, a mycorrhiza is formed. Fine roots, or feeder roots, are the smallest roots at the end of the root systems.

Some mycorrhizas are visible to the human eye. But a microscope is needed to see the fungal filaments, or hyphae.

Image - Text Version

Shown is a colour photograph of long, thin, tangled strands of fungal hyphae. The hyphae resemble tubes. Some tubes are a translucent brown colour, some are dark brown and some are colourless. The tubes are layered on a light grey background. This looks as if the camera is peering through long vines.

Mycorrhizas come in different forms. This depends on the fungi they partner with. Some fungi make the tips of roots look swollen. Some make the root tips look branched or fluffy. Others have long hyphae that create web-like patterns in the soil. These forms increase their surface area so they can better absorb water and nutrients.

Image - Text Version

Shown is a colour, close-up photograph of thin beige filaments curving out from a brown root. The root comes in from the top right of the photograph. Near the end, it appears thicker, with a beige, bark-like texture. Thin beige filaments curve out from this part of the root. They have even thinner, cloud-like filaments growing out around them.

Image - Text Version

Shown is a colour, close-up photograph of thick, white filaments branching out from a root. The filaments are thick and straight, like small tree branches. Much shorter, thinner filaments branch out from them. These look a little like white insect legs.

Image - Text Version

Shown is a colour, close-up photograph of thin, web-like filaments around a light brown root. The root has thick, tubular branches growing off the main root. These are surrounded by a mesh of very thin white filaments. Two long, thin strands, that look like hairs, reach out toward the left and right edges of the image.

How do plants and fungi benefit by forming mycorrhizas?

Plants provide the mycorrhizal fungi with the energy they need to grow and reproduce. They do this through photosynthesis. This is when plants take carbon and oxygen from the air and use energy from the Sun to form sugars. They release some of these sugars to the mycorrhizal fungi growing on their roots. This way, the mycorrhizal fungi have a steady supply of energy.

Did you know?

From one to 13% of the carbon photosynthesized by plants is sent to mycorrhizal fungi.

Nutrients and water are found in the tiny spaces between soil particles. But most plant roots are too large to reach into these tiny spaces. To solve this problem, they partner with mycorrhizal fungi. The narrow hyphae of fungi can reach places that roots cannot.

Image - Text Version

Shown is a colour, close-up photograph of a cross-section of soil with thin, white fungal hyphae. The soil is light brown and has many air spaces between the soil particles. Filling some of the spaces are long, intertwined white strands. These grow from the centre top of the photograph, down toward the bottom edge. Three thick, short, white tubes branch out to either side. In the nearby soil are globs of filaments that resemble clouds or spiders’ webs.

Also, roots can’t take up some nutrients on their own. This includes important things they need to grow, like nitrogen and phosphorus. But again, their partner fungi can help. Many mycorrhizal hyphae make enzymes that break down dead material to release these nutrients.

In some cases, hyphae also act as highways to move bacteria around. These bacteria also break down dead material, releasing nutrients to the fungi. The fungi then pass these nutrients on to their partner plants. Because of this exchange of sugars and nutrients between the partners, mycorrhizas are an example of mutualism.

Sometimes, one mycorrhizal fungus can grow on the roots of more than one plant at the same time. This physically connects the roots of the plants. Scientists call this connection a common mycorrhizal network.

These networks can even form between plants of different species. Scientists are not sure whether these fungal networks move resources between plants. But this is a question many are researching.

Image - Text Version

Shown is a colour photograph of two sets of plant roots behind a glass frame. The frame is about the size of a piece of printer paper. It is made of two flat sheets of clear glass, taped together, with light brown soil sandwiched between them. At the top of the frame, two small seedlings grow up from the edge of the soil. The left one has thin green needles and a brown stem. The right one has a fuzzy pinkish stem and four wide, green heart-shaped leaves. The roots of both plants take up almost all the frame. The left seedling has long, thin brown roots that branch and spread wide and deep. The right seedling has thin, light brown roots that are curlier than the left, but stretch wide and deep. They are dotted with large patches of dark and light brown. About a third of the way down the frame, both sets of roots are sprinkled with short beige structures. These look a bit like cake sprinkles. About halfway down, the two sets of roots connect, and seem to grow down further as one.

How do mycorrhizas affect soils?

Not only do mycorrhizas increase the nutrients available to plants, they also impact soil. The networks of hyphae help to bind small particles of soil together. This gives the soil structure. Soil structure allows water to move more easily through soils. 

Did you know?

One cubic centimetre of forest soil has up to 1 km of fungal hyphae!

Also, when mycorrhizal fungi die, other fungi and microbes decompose them. This adds even more organic matter to soils, improving soil nutrients and structure.

In both life and death, mycorrhizal fungi cycle nutrients and carbon. These processes give both plants and fungi the nutrients they need to survive and grow.

How do mycorrhizas benefit us? 

Most plants depend on mycorrhizal fungi to grow and develop normally. These include plants we use as crops and trees we use for wood and paper products. As people manage these types of plants, they should be thinking about the role of mycorrhizas. For example, scientists are trying to find out if farmers can reduce their use of fertilizer by encouraging the growth of mycorrhizal fungi and bacteria.

People also eat some types of mycorrhizal fungi. These include truffles, chanterelles, and matsutake mushrooms.

As with all wild mushrooms, it is important to have an expert identify what is safe to eat. Otherwise you could become very sick or even die.

Image - Text Version

Shown is a colour, close-up photograph of a light brown mushroom with a round cap. The mushroom is growing in rocky, greyish-brown soil, at the base of a tree with reddish-brown bark. The mushroom has a short, tubular, light brown stem. The cap is round, reddish gold and domed. Its edge is rounded and curled under.

Conclusion 

Mycorrhizas are such successful partnerships that they are found with most plant species in the world. For plants, having help from fungi is like having a nutrient ‘app’. For fungi, having help from plants is like having an energy ‘app’. Fungi extend what plants can do, and plants extend what fungi can do.

So, if you walk through a forest or a park, think about the network of fungi quietly working away, supporting most of the plants you see!