The Role of Fungi in the Ecosystem
When you say “fungi,” the vast majority of people would think mushrooms that they associate with rot, mould, blight and disease. Fungi are in fact a diverse group of organisms that form an essential component of many ecosystems on Earth. They encompass a wide range of life forms, from microscopic single-celled spores to showy fruity bodies that have extensive underground systems. There are approximately 3 to 13 million species of fungi! This includes yeast, which contributes to the production of beer, wine, and bread - but it also comprises fungi that can lead to diseases such as Athlete’s foot and potentially deadly histoplasmosis.
Fungi are globally distributed, but different species inhabit distinct geographical domains due to their vast functional diversity. Their success as organisms of ecological influence is attributed to their ability to span multiple dimensions of time, space, and biological interactions. They are unrivalled in this ability, allowing them to act as core mediators between organisms. They feast on the deceased remains of almost all organisms on the planet. Thus, they convert the organic matter that we’re all made of back into soil- from which new life will spring. They thrive on death, and in the process, make all life possible. This is facilitated via a number of roles: decomposition, nutrient cycling, carbon cycling, and symbiosis.
Fungi play a crucial role in the process of decomposition; wherein complex organic matter is broken down into simple molecular forms. This process is begun by bacteria, invertebrates, and other organisms when they physically breakdown organic matter into smaller pieces. Any organic matter, including dead, waste or excreta is acted upon.
Fungi are heterotrophs like us, meaning they need to intake nutrition from their surroundings in order to survive. Thereby, fungi have an important function as they colonise the surface of the matter and release powerful enzymes into the environment. The enzymatic secretion by the fungi metabolises the dead matter in the process of decomposing it, which is eventually taken up as nutrients for the fungi to feed, grow and reproduce.
Fungi is able to decompose almost any type of organism material. Some species of fungi are better at breaking down certain types of materials than others, and some can metabolise materials that other decomposers cannot. For example, some fungi can break down lignin, which is a complex polymer found in wood, and is difficult for many other organisms to decompose.
Decomposition facilitates the movement and recycling of nutrients through the ecosystem. No energy in the world is created or destroyed, it is simply taken into different states and forms. When organisms die, their nutrients can be locked up in insoluble compounds or in forms that are inaccessible for plants. Fungi have the ability to transform these nutrients and increase their availability in soil.
Plants require two important nutrients: nitrogen and phosphorous. Fungi engage in processes to propel this availability and facilitate plant development.
Nitrogen fixation is the process by which inorganic forms of nitrogen is converted into a useable form. While fungi do not directly fixate the nitrogen gas into ammonia, they form a relationship with nitrogen-fixing bacteria and create an optimal environment for this bacterial growth. We’ll explore more about this type of relationship in the symbiosis section! But essentially, this also allows for nitrogen locked up in proteins of dead matter to decomposed and converted from amino acids into the useable nitrate.
In a similar example, fungi engage in phosphorous mobilisation which allows phosphorous to become readily available for use by plants in the soluble form of phosphate. Another way that this mineral can be mobilised is through the action of mycorrhizal fungi. These fungi form mutualistic associations with the roots of many plant species, and they are able to extract phosphorous from the soil and transfer it to the plant!
Carbon Cycling and Sequestration:
Carbon cycling is a process by which carbon moves through the Earth’s biosphere, geosphere, hydrosphere and atmosphere. Carbon is an essential element for life on Earth, and it plays a crucial role in the global climate system.
Fungi decompose complex materials and release carbon back into the soil in the form of simpler compounds such as glucose and other sugars. This helps the carbon that fixed by photosynthesis to be released back into the environment. They also release carbon dioxide back into the atmosphere during this process, regulating atmospheric carbon dioxide concentrations.
Plants and fungi also form a combined process called soil carbon sequestration. This captures carbon from the atmosphere and stores it in the form of fungal biomass in the soil for decades, acting as a sink for atmospheric carbon. This helps improve soil fertility, as well as reduce the excess carbon production by human activity.
Fungi can form symbiotic relationship with a wide variety of organisms, including pants, animals, and even other fungi. Symbiosis refers to a close interaction between two dissimilar organisms, in which both parties benefit from the relationship. Fungi can provide a range of services to its host including increased nutrient uptake and disease protection.
One of the most well-known examples of fungi symbiosis is the mycorrhizal associations between fungi and plants. These fungi form a mutualistic relationship with the roots of many plant species, in which the fungus provides the plant with increased access to nutrients such as phosphorous and nitrogen, while the plant provides the fungus photosynthetically-derived carbon compounds.
The role of fungi across Earth’s ecosystems is mediated through their complex and dynamic ecological interactions. Fungi are also used in pharmaceutical, chemical, food, drink, contamination, biorefinery and biofuel applications, which originate from the intricate functions that fungi have evolved to perform. However, fungi are being threatened by global changes, including climate change, land use change, pollution, pesticides and fertilisers. This will have implications for agriculture and human health - without the contribution of fungi, life as we know it would cease to exist.