Written by Brianna Santamaria
From supporting plant growth to breaking down waste, fungi perform a large variety of important functions in our environment. We would need an entire library to discuss all the roles fungi play in the world around us. However, we are limited in time (and space on this website), so in line with the theme of this series, we will narrow our scope to mushroom-forming fungi and a few of the different ways they function in the world around us.
As a quick overview, mushroom-forming fungi make up only a fraction of all known fungi. Many fungi do not form a mushroom structure (known as a fruiting body, although many mycologists prefer the term sporocarp nowadays), and instead rely on other methods for spore dispersal. While mushroom formers account for a small proportion of fungi, they are the most visible, well-known, and attractive (according to some) members of the Fungal kingdom.
Mushrooms as homes
Fall conjures images of sculpted clay (Amanita) mushroom houses that are usually occupied by fairies and magical creatures alike. Unfortunately, fairies do not live in adorable mushroom homes but other small creatures do. Anyone who regularly forages for mushrooms every season will be well aware of the tiny surprises that sometimes hide inside their finds. These surprises are insects and arthropods and an astoundingly large diversity of them live in mushrooms. Various beetles, flies, mites, and others often burrow and nest inside mushrooms. A mushroom is an ideal habitat for these creatures to develop in because it is protected from the environment (meaning predators have less chance of finding them) and it is also a great source of nutrition.
This is not always a one-way relationship where one species uses the other for food and protection. The fungus can also benefit from having little guys living in its mushroom. How could having tiny creatures devouring a part of you be beneficial? If you recall from our introduction post, the primary function of a mushroom is to spread spores. As it turns out, insects and arthropods are great at transporting spores. Some mushroom species are even entirely reliant on this method of spore transportation. Truffles, for example, are thought to solely depend on beetles and other small animals to disperse their spores. Truffles develop under the soil and, as a result, cannot use wind for spore dispersal.
Some insects and arthropods rely so heavily on this interaction that they only breed in specific mushrooms. When a species preferentially chooses one mushroom over another, we call this interaction host-specific. Species that inhabit only one or two fungi are said to have a high degree of host specificity. In cases of high specificity, the species is so dependent on its fungal host that it would likely die without it. This is one of the reasons why many conservationists advocate for a diversity of species in protected forests. The disappearance of one fungal species could result in the disappearance of the insects and arthropods that depend on it and vice versa.
Mushrooms as friends
Outside of providing free affordable housing, mushrooms also form one of the most unique interconnecting networks found on Earth. We call this network the mycorrhizal network. We have referred to mycorrhizal fungi many times on this website, so now is a good time to go more in-depth. It is important to clarify that not all mycorrhizal fungi are mushroom formers, but many are. This function is crucial to the environment so we thought it was necessary to discuss it. One of the writers on this site has worked extensively with mycorrhizal fungi, so expect a more detailed blog post about them at some point in the future :).
Mycorrhizal fungi form close relationships with plants by connecting their hyphae (multiple hyphae form a mycelium) to the roots of plants. Through this connection, the plant and the fungus exchange nutrients in a beautiful symbiotic relationship that has persisted for millions of years. Nearly every plant species forms mycorrhizal connections which highlights how critical this interaction is in the environment. Some plants, such as orchids, are so dependent on these connections to obtain nutrients that they will die without them. Plants in environments with nutrient-poor soil, such as tropical rainforests, need this mycorrhizal web to survive. This is the reason why rainforests are very difficult to recover after being turned into farmlands. The mycorrhizal network disappears when the land is converted and plants that previously thrived in the environment cannot exist without them.
Mycorrhizal relationships are not limited to just a plant and a fungus. In 1994, researcher Jean Garbaye established the term ‘helper bacteria’ to describe bacteria that assist in the formation of mycorrhizal relationships. Since then, advances in technology have revealed a huge diversity of helper bacteria that are involved in these connections. These bacteria can help in establishing the connection between roots and hyphae, transferring nutrients, and protecting the fungus or plant in times of high stress. However, there is still much work to be done in untangling the complexity of these relationships.
Mushrooms as cleaner-uppers
One of my first introductions to mycology was in an elementary school lesson on food webs. The teacher gave us cards with the names of various creatures and we had to arrange ourselves by how we thought each creature would interact with each other (which I found out later were called trophic levels). One of the cards had the word ‘mushroom’ on it and the unfortunate kid who was given the card had to sit outside of the web we had created. The reason for this was that mushrooms were known as decomposers, meaning they were capable of ‘eating’ every creature in our imaginary food web. I am happy to report that this elementary science lesson was actually correct.
Mushrooms have the extremely important role of decomposing, or breaking down, all kinds of dead material that fall to the forest floor. To get an image of how key this process is, imagine the sidewalks in your neighborhood every fall before they are cleaned. Leaves, which are often wet and glued to the ground, are strewn everywhere. With every step you take you are met with an uncomfortable squish of dead leaves beneath your feet that also hitch a ride on your shoes and into your house. When leaf litter piles up on a forest floor it hinders the organisms that live on it. Plant seedlings that rely on light to grow are trapped beneath dead leaves. Creatures that hunt on the forest floor have difficulty finding food through the litter. In short, no one has a good time. This is why decomposers are so important to the environment.
In addition to clearing up the forest floor, mushrooms recycle nutrients back into the environment through decomposition. What does this mean exactly? Leaf litter contains essential nutrients that are difficult for most organisms to obtain. When we eat our body has the necessary tools needed to break down food and extract nutrients from it. However, we, and many other animals, do not have the tools to break apart leaves. Mushrooms do possess these tools so they can digest leaves and, through this process, make the nutrients trapped in the leaves available for other organisms to use. So, not only do mushrooms clean up the forest floor, but they also make life easier for the organisms around them.