Fungi: The worldwide web beneath our feet

Mycorrhizae on a plant root.

Mycorrhizae, a type of plant-fungal association, from the root of a Douglas fir tree. B. Zak, via Wikimedia Commons.

This article originally appeared in The Oxford Scientist’s Print edition in Trinity Term 2022.

To most, the word “biodiversity” conjures up images of rainforest flora, strange looking insects or famous endangered mammals like the panda. Even if some people think beyond these classic nature documentary images, biodiversity rarely makes us think of the ground beneath our feet. But despite its lack of recognition, the soil below is packed with life—it’s teeming with fungal networks.  

Mycelia are the root-like structures that make up the main body of a fungus. They comprise a mass of branching, thread-like hyphae that permeate through the soil, and this is what fungi look like for most of the year (rather than the mushroom fruiting bodies we are so familiar with). The mycelial networks might be hidden from the eye but they are by no means inconsequential: it’s estimated that each cubic centimetre of soil can contain enough hyphae to stretch a whole kilometre if laid out end to end. There are an estimated two to five million species of fungi worldwide and only a fraction of these have been classified. That compares to only 391,000 species of plants—fungi truly are symbols of biodiversity. 

Although they were once classified with land plants, the fungal kingdom is actually more closely related to animals. It includes budding and hyphal fungi, with the latter forming mycelial networks in soil. Soil fungi can make up to 30% of the soil rhizosphere (the soil surrounding plant roots), and play hugely important roles in their ecosystems.

Fungi are the decomposers of the natural world, recycling organic matter from dead plants and animals to release scarce but essential nutrients back into the food web and degrading material that would otherwise remain trapped in debris. They’re one of the only groups of organisms able to digest lignin, a tough compound found within plant cell walls that makes wood and bark particularly strong and resistant to degradation. Indeed, without fungal networks, dead plant matter would never be broken down and would remain inaccessible to other organisms in the ecosystem.  

Hyphal fungi also famously form associations with plant roots to form a mycorrhizal network. These networks can connect entire forests and recent studies have unveiled their incredible capacity to transmit resources through forest ecosystems, with trees sending carbon, water and trace nutrients through the mycelial links to nearby plants.

Trees have been found to send more resources to closely related individuals and so might be able to increase their indirect fitness through supporting the survival of plants that share more of their genes. Some studies have even suggested that trees send survival signals across the forest when they experience disease, allowing others to raise defence against incoming pathogens. The mycorrhizal networks do not just benefit plants: fungi receive carbon-rich sugars made by plants in exchange for phosphorus and nitrogen they scavenge from the soil. These extensive networks have promoted the survival of both groups through time and continue to play a vital role in shaping the above-ground diversity we see today. 

Fungi also very relevantly play a key role in carbon sequestration. An estimated five billion tonnes of carbon dioxide flow into fungal networks each year, equating to over 50% of the anthropogenic CO2 emissions in 2021. Though not all of this carbon is stored, a Swedish study found 50-70% carbon locked up in soil to be from tree roots and their associated mycorrhizal networks. This represents a significant sequestration capacity, something we know the importance of all too well given the increasing need for climate action across the globe. 

More recently, science has shown the power of fungal networks for biotechnology applications. The US company Ecovative was the first to produce composite material made of heat-treated mycelia to provide an alternative to polystyrene packaging. The so called ‘MycoComposite’ is produced by culturing hyphal fungi on farming and forestry by-products like sawdust and rice husks within a mould before heat treating it to kill the organism and leave behind a lightweight material that can be used to protect breakable goods in transport. The fungi can be cultured on locally available by-products to reduce transport costs, and has already been used by Dell and IKEA in place of polystyrene.

Fungi have also been used to produce vegan leather, mycoprotein meat alternatives and to clean up environmental toxins. Shiitake mushrooms are used for medicinal purposes in Asia, and provide an accessible source of protein due to their long shelf life and ability to be dehydrated for storage. The incredible diversity and utility of fungi and their networks offers humanity myriad opportunities for innovation, providing solutions to many of the pressing problems of the 21st century. 

Like most of the natural world, fungi are under threat. In 2015, Jacob Heilmann-Clausen and colleagues reported that fungi were threatened by habitat decline, overexploitation, land use change and climate change in the Anthropocene. Despite this, chronic underfunding of fungal research, lack of recognition and focus on more charismatic taxa mean they are routinely overlooked when it comes to conservation efforts.

The UN Framework Convention on Climate Change, Convention on Biological Diversity and International Union for Conservation of Nature, World Conservation Congress represent three of the leading initiatives on global conservation and are responsible for the global approach to the climate and biodiversity crises in coming decades. Yet none of these institutions recognise fungi in their scope of action, leaving a gaping hole in efforts for biodiversity conservation. Fungal networks are essential to the health of our planet, but there is very little data quantifying their impact so we often fail to include them in commitments to biodiversity goals. This represents a significant flaw in environmental legislation, which could be fatal to the millions of fungal species powering our planet. 

Nonetheless, several scientists are fighting to give fungi the recognition and protection they need. The Chilean mycologist Giuliana Furci made headlines in 2013 when her work led to Chile becoming the first country to include protection of fungi in environmental legislation. She founded the non-profit Fungi Foundation in 2012 to raise awareness of fungal uses and diversity worldwide, and works with communities in South America to document new species as well as promote sustainable foraging and markets for the mushrooms.

Recently the foundation collaborated with researchers at the University of Oxford to publish a paper outlining four key steps to bring fungi to the forefront of policy and society. These include acknowledging fungi as an independent kingdom of life; incorporating fungi into sustainable policy targets; monitoring the conservation status and trends of wild fungi; and promoting the responsible use of wild fungi as a livelihood opportunity for rural communities. The paper aims to inspire a fungal revolution, allowing us to better appreciate, use and conserve the fungal networks that lie beneath us. 

Whilst it might seem that the task ahead to document and protect such ubiquitous yet hidden beings is vast, the recent steps taken by international mycologists and community scientists are promising. Now more than ever do we need to safeguard these vital ecosystem engineers in ensuring a safe and equitable future for life on Earth, the many benefits of fungi could mean the shared need to conserve our fungal networks truly becomes the hypha to connect us.