The Fantastic World of the Underground: How Mycorrhizae Fungi Makes Us Understand Interconnected Life

We neither see nor hear them, yet they exist.

Mycorrhiza fungi colonising a host plant’s root tissues. Photo courtesy of NewScientist

When I was in college studying Biology, I had zero interest in things that weren’t related to animals (especially the Order Carnivora). Taking courses in Botany, systematics, or plant morphology felt like torture to me, although as with everything in this field of study, it has its intriguing aspects.

However, luckily I believe, my university offered something that is not typical among biology courses in my country: a specific course about Fungi. During this course, I learned the importance and relevance that Fungi can and will have in our daily lives, as crazy as that sounds.

Why did this strike me? Let me explain.

The Science of Fungi

Fungal biologists have debated for over 200 years about which organisms should be counted as Fungi. Before the 1960s, fungi were categorized within the Plantae kingdom, because of shared similarities with plants: they are immobile, have cell walls, and reproduce through spores.

But, everything changed with the technological advances in molecular and cell biology, which permitted the development of more precise techniques that allowed researchers to dive into finer detail into the Fungi world by studying their taxonomic and phylogenetic characteristics.

All of these frontiers tackled by science led to the proposal of a new categorization of kingdoms by Robert Whittaker in 1969, adding Fungi as a monophyletic kingdom. As time went by, the field expanded, until in the 1990s, with the development of the polymerase chain reaction (PCR), the “universal primers” — short sequences of RNA that are shared among most known species — were designed especially for fungi. In conclusion, Fungi were and are incredibly relevant to science.

Fungi’s vegetative structure is called the mycelium. It’s a network of fine white elements (hyphae) that extend plant root systems, aiding in the absortion of water and hard-to-reach nutrients.

Mycelium; various examples of mycelium in different sizes, environments and species (source).

Fungi and the Biosphere

The concept of Biosphere was proposed by Soviet scientists in the late 1920s. Essentially, the Biosphere is composed of the parts of Earth in which life exists. This extends from the deepest root systems (spoiler) of trees to the dark environment of ocean trenches, to lush rainforests and high mountaintops.

What does the Biosphere have to do with the Fungi kingdom, you would be asking? Well, there are an estimated 5.1 million species of Fungi on Earth, out of which we have only found 150,000…

They interact with everything that you can imagine: soil, water, and any kind of organism. That’s because Fungi have the property to interact with eukaryotic cells in three types of fashion: neutral (with minimal interaction with the other organism), pathogenic (fungi act as parasites, living out of the host's internal resources), and beneficial (where host-Fungi interaction has a net benefit for both).

Fungi are among the most important and beautiful soil organisms (source).

This last one is predominantly represented by what are called Mycorrhizae Fungi. This is a type of symbiotic relationship between plants and fungi, where the fungi species take up water, nitrogen, phosphorus, and other nutrients directly from the soil and transfer them to the plant roots, while the plant provides sugars as a byproduct of photosynthesis. Arbuscular mycorrhizae (AM) associations are more common and occur with up to 80% of all plant species and 92% of all plant families.

Flax root cortical cells containing paired arbuscules (source).

Bidirectional root carbon transfer between mature forest trees. Isotope mixing signals indicate that the interspecific, bidirectional transfer, assisted by common ectomycorrhiza networks, accounted for 40% of the fine root carbon (about 280 kilograms per hectare per year tree-to-tree transfer). Estimation of the magnitude of the interspecific root carbon exchange in the studied mixed forest stand based on the observed δ¹³C values. An isotope mixing ratio of 60% self and 40% exchanged carbon between fine roots of labeled and unlabeled trees satisfies the ¹³C signals in both. Although competition for resources is commonly considered as the dominant tree-to-tree interaction in forests, trees may interact in more complex ways, including substantial carbon exchange (source).

An example of this relationship was found in 1999 (see figure above) by a group of researchers, who were trying to study the effect of atmospheric carbon dioxide on trees, and found that trees couldn’t be isolated as a single organism in their area of study. The reason? The traced effects extended to all surrounding trees, implying a Web connecting them. To their surprise, this web consisted of Mycorrhizae Fungi that were exchanging nutrients with all the surrounding trees, of multiple species, in an interconnected way. This was called the Wood Wide Web.

The Wood Wide Web. Photo courtesy of woodwidewebstories.

Mycorrhiza and Agriculture

As previously mentioned, this type of Fungi has a remarkable capacity to interact with a large part of plant species on Earth. How is this relevant to our modern day agriculture?

Food safety and security for the global population have always been crucial challenges for our species. Our current system of industrial agriculture has enabled us to feed a big chunk of the population, however, in a non-sustainable manner.

Industrial agriculture uses a wide variety of agrochemicals (such as pesticides, insecticides, and herbicides) that generate an accumulation of toxic metals and biocide residues in soils, harming soil productivity, and human and ecosystem health.

Nonetheless, in the last four decades, research and literature considering the use of AM for farming (AMF) has expanded dramatically, to achieve higher crop yield and productivity, while simultaneously solving soil degradation and water shortage.

Multiple studies have experimented with AMF in the context of Organic Agriculture, where the use of agrochemicals is none and crop yield and productivity depend solely on the type of species and interactions that you use. This is where AMF plays a key role.

“Organic agriculture is a production system that sustains the health of soils, ecosystems and people. It relies on ecological processes, biodiversity and cycles adapted to local conditions, rather than the use of inputs with adverse effects. Organic agriculture combines tradition, innovation and science to benefit the shared environment and promote fair relationships and a good quality of life for all involved…”— International Federation of Organic Agriculture Movements

Roles of AMF in soil health (source).

Research proves that AMF can increase soil restoration, productivity, quality of plant food, carbon sequestration, and carbon stabilization in soil. AM productivity can be enhanced by the combined use of selected native crops in land previously used for intensive agrochemical agriculture, as well as in untouched land. Consequently, an increase in Mycorrhizae fungi proliferation allows the soil to recover, and therefore, obtain high-quality crop yields.

But, here’s where it gets tricky. Organic Agriculture is a small-scale type of farming. As such, is still at its experimental stages in most parts of the world and doesn’t seem to be replacing industrial agriculture anytime soon.

“Everything is theoretically impossible, until is done” — Robert A. Heinlein

However, there’s still hope. As was described at the beginning of this article, science has this particular characteristic: the current paradigm can be shaken and changed for good with the uprising of new scientific/technological breakthroughs.

Technologies in Organic Farming at present are being focussed on increasing precision agriculture by the implementation of data-driven mechanisms. These should help develop the quality and quantity of collected information about crops and land.

This, in turn, can elevate the productivity of crop yields in organic farms, and allow producing more and higher quality food, satisfying customers and reaching bigger markets. An increase in supply versus demand could result in a price decrease, and a preference for products coming from Organic farms could be achieved. That’s the current road map.

In order to accomplish this, organic farming, with the implementation of AMF, can benefit from technology and science to become the future standard way of agricultural practices.

The use of drones in Organic Farming increases detection and control of pest or diseases to crops (source)

With the increasing rate of heat waves, floods, droughts, and many more natural causes triggered by our changing climate, industrial agriculture, if it continues as it stands, we will not be able to satisfy consumer demands without increasing pressure over cultivable land. We as a species will have to adapt and generate new and innovative ways to confront this planetary challenge.

In this context, Mycorrhizae Fungi may serve as a prime example to start a new symbiotic interaction with humans by helping to overcome our current flawed system of agriculture and make this place called Earth a better place to live. However, the stakes are high.