The Hidden World of Fungi

The underground network that made us and keeps us going

All mushrooms are magic. That’s a statement that you probably won’t find in the textbooks, but it’s a fact that goes without saying. When you look at all that these organisms do, from being the second-best pizza topping to supporting the foundations of entire ecosystems, it’s hard to argue. But just in case you're still unconvinced, we turned to an expert to help get the point across: Dr. Bryn Dentinger, Curator of Mycology at the Natural History Museum of Utah and former Head of Mycology at the Royal Botanic Gardens in London. Dr. Dentinger has dedicated the better part of his career to studying the weird and wonderful world of fungi. But for him, one group stands out in particular: mycorrhizal fungi, which are fungi that have a symbiotic relationship with the roots of a plant, keeping both alive and well. Since “myco” means fungi and “rhiza” means root, this checks out. Dr. Dentinger did us the honor of putting his thoughts to paper on this global connection of root-fungi networks, their role as major players in making the world go round, and what we can learn from their secret universe. 

Words by Dr. Bryn Dentinger

I was a junior in high school when I discovered the faint apricot scent of dreamsicle-orange chanterelle mushrooms growing wild in the forests of northern Minnesota. In 1995 I could not have predicted that three decades later I would have captured this scent on every continent except Antarctica. In 1995 I didn’t know there was an entire discipline of science dedicated to the study of mushrooms (and their relatives) called mycology. I have been part of that discipline now for over 20 years, though most people in the world have never heard of it. Which is a shame because the organisms at the center of it, fungi*, made our world habitable and keep it that way.

That’s not to say they do it alone, of course. For example, the oxygen in our atmosphere that enables us to live is the byproduct of photosynthesis, the process of converting sunlight and carbon dioxide into energy, a function exclusive to plants and photosynthetic microorganisms. We are just starting to understand the importance of fungi in aquatic ecosystems, but on land, we know that fungi make it possible for plants to photosynthesize. While it may not be so obvious when looking at a forest, soil fungi are the support network that forests depend on.

Fungi in the soil recycle dead organisms, breaking down and releasing their parts as nutrients to support new growth. Without this service, ecosystems would collapse because all of the energy would eventually be locked up in dead things. Fungi in soils also have a more mysterious and intriguing role: They partner with plants through a transactional agreement in which they provision plants with nutrients and water, and in return plants pay for this service with sugar they make through photosynthesis. In my scientific discipline, this partnership is called “mycorrhizae,” which translates as “fungus roots.”

Mycorrhizae made it possible for aquatic plants to colonize land for the first time about 450 million years ago. We know this because the fossilized roots of the first land plants preserved the hallmark structures of mycorrhizal fungi in their cells. Early land plants didn’t have the root structures to acquire enough water and nutrients on their own, so fungi were essential to their survival. Fungi are far more efficient than plants at obtaining water and nutrients because they have much smaller cells that can spread over vast areas, creating networks of filaments exceptional at moving resources around. But it wasn’t a one-and-done event. For decades now, mycologists have documented mycorrhizae in land plants living today — some appear unchanged from the way they looked 450 million years ago. And the relationship is found not just in some plants, but in most plants. This partnership is so ubiquitous that all vegetated habitats have always depended on it and still do.

How much oxygen a plant produces, and in turn how much carbon is sequestered from the air, is dependent to a large degree on how much water and nutrients it gets from its mycorrhizal fungal partners. The more nutrients and water a plant receives, the more a plant can photosynthesize. This has global implications for the regulation of carbon in our atmosphere. This also introduces a parameter to the equation of terrestrial ecosystems that has largely been underappreciated until recently: Our forests are not just trees, but complex and intimate partnerships above- and belowground.

It is difficult to overstate the importance of mycorrhizal fungi to life on land. Soils can no longer be seen as inert material that plants root in. Instead, they are dynamic life support systems that enable the planet to breathe. These systems are far from simplistic, capable of forming extensive networks over vast areas, persisting for hundreds and possibly thousands of years, interconnecting hundreds and thousands of living plants. Through these networks, mycorrhizal fungi can move resources around, maintaining forest health at a landscape scale. This “wood-wide web” can consist of hundreds of different species, interacting and communicating in ways we are just beginning to understand. Some evidence even suggests that neighboring plants can use this network to communicate with each other. Far from a mere transactional relationship, these so-called “common mycorrhizal networks” have been shown to transfer energy from one plant to another via the shared fungal mycelium. The prevalence and importance of such capability requires further study, but it does present the possibility of plant altruism: If your neighbor needs a little help, send over some nutrients by way of the fungus courier. 

But in a world where it is well-documented that plants compete for light and soil resources, is this altruism real or is our understanding of common mycorrhizal networks only superficial? From the plants’ perspectives, it is counterintuitive to explain resource sharing through fungal intermediates as altruistic given what we understand about how natural selection works. But consider the fungus’s perspective: maximizing the collective productivity of all of your partners maximizes your payment of sugar. So, perhaps it takes a soil-born perspective to understand common mycorrhizal networks and the wood-wide web not as servants to plant needs, but as gardeners of a vast aboveground farm.

*I use this term to refer exclusively to organisms in kingdom Fungi, which does not include fungal-like organisms such as slime molds (myxomycetes) and water molds (oomycetes). Fungi encompass a wide range of life forms, from single-celled yeasts to the world’s largest individual organism composed of a vast network of minute threadlike filaments (hyphae) that collectively (mycelium) span over three square miles of forest. Mushrooms are the reproductive structures produced by mycelia, organisms that make up around one-fifth of all Fungi.