Currently, beneath nearly every patch of soil on Earth, an astonishing living structure is thriving: a unique form of fungus, distinct from the mushrooms typically consumed. This fungus develops as microscopic threads, finer than cotton, weaving through the soil and extending into the roots of most plants.
Among the various types of root-dwelling fungi, the most prevalent are arbuscular mycorrhizal (AM) fungi, which have thrived for hundreds of millions of years, predating the first trees.
For over a century, scientists have understood that these fungi play a crucial role in sustaining ecosystems by transporting essential nutrients and water to plants. However, a fundamental question remained unanswered until now: How extensive is this hidden network lying underground?
The answer, revealed in a recent study by the Society for the Protection of Underground Networks (SPUN), is: an astonishing amount.
If laid end to end, the threads of Earth’s AM fungi would extend over 110 quadrillion kilometers—enough to span approximately one-tenth of the Milky Way or about 11,000 light-years. These threads also contain an estimated 300 megatonnes of carbon, equivalent to four to six times the combined weight of all humans on the planet.
Beyond presenting this incredible scale, the study raises significant questions: What role does this vast underground network play in our ecosystem, and what consequences might arise if it begins to fail?
Roots and All
Scientists often describe these fungal networks as Earth’s circulatory system, and the analogy is fitting.
Essentially, they integrate into plant roots, acting as an extension that reaches deeper into the soil than roots alone can. They gather water and nutrients, delivering them to the plant, while the plant reciprocates by providing sugars produced through photosynthesis.
This partnership is not limited to select species; AM fungi connect with approximately 70% of all plant species on Earth. Disrupt this underground network, and you jeopardize the supply lines for most of the planet’s vegetation—impacting crops, forests, and grazing lands upon which we all depend.
But these fungi do more than nourish plants; they also play a vital role in climate regulation. As plants absorb CO₂ from the atmosphere, they send some of that carbon underground to their fungal partners, aiding in carbon storage in the soil. Earlier studies estimated that about 4 billion tonnes of CO₂ enters the AM fungi ecosystem each year—almost equivalent to the annual emissions of the United States.
While considerable resources are allocated to planting and conserving forests, the extensive underground networks that capture much of this carbon have garnered significantly less attention.
“The importance and scale of these fungi cannot be overstated,” says lead author Dr. Justin Stewart, an evolutionary ecologist at SPUN. “In just a teaspoon of soil, there could be up to 10 meters of this network.”
Given this extensive system intertwined with life on Earth, one might assume its safety. Unfortunately, that’s not the case. The same study revealing its immense scale also highlighted a disturbing reality: we are rapidly destroying it.
Mowed Down
When people envision nature worth preserving, they typically think of rainforests and woodlands. Surprisingly, wild grasslands—often overlooked landscapes we tend to drive past—harbor an estimated 40% of the world’s AM fungi. Rich regions include the plains of South Sudan, Florida’s Everglades, and the Tibetan plateau.
“One of the major findings was the critical importance of grasslands, the often-overlooked ecosystems of Earth,” notes study contributor Katie Field, Professor of Plant Soil Processes at the University of Sheffield. Grasslands exhibit a remarkable diversity and density of fungi.
However, here’s where the issue arises. Grasslands are among the least protected ecosystems and are being converted into farmland four times faster than forests are being cleared. This accelerates the decline of these vital fungal networks.
Plowing disrupts the delicate threads of these networks, while chemical fertilizers diminish the plant’s incentive to nourish the fungi. Consequently, these vital connections weaken. Indeed, the study found that farmland contains only about half as much fungal network compared to wild land.
These networks are crucial, burying billions of tonnes of carbon annually. Thus, their deterioration has implications beyond mere soil.
“Fungi have been sidelined in discussions on climate change and conservation for too long,” asserts Dr. Toby Kiers, SPUN’s executive director and a professor of evolutionary biology at Vrije Universiteit Amsterdam. “Now is the time to shift this trajectory.”
The warning from outside the project is even more urgent. Professor Martin Bidartondo, a fungal ecologist at Imperial College London and Kew Gardens, emphasizes that two centuries of industrialization are pushing systems developed over hundreds of millions of years into unforeseen conditions.
“Humans have existed for around 300,000 years, and in the last 200, we’ve rapidly consumed that inheritance,” he states. “We are conducting a massive experiment without controls or replicates, rapidly creating conditions that flora and fungi have not evolved to withstand.”
If these networks face severe degradation, the repercussions will extend beyond the underground. Plants will struggle to establish and grow, causing downstream impacts on crops, timber resources, herbivores, soil’s capacity to store carbon and water, and its resistance to erosion.
Eliminating fungi, in essence, unwinds a significant part of the life that thrives above ground.
Into the Dark
The uncomfortable reality is that we are tasked with safeguarding something we barely comprehend. Even the scientists behind the measurements acknowledge gaps in their knowledge.
“We still know relatively little about their functions, effectiveness, and how their roles differ across environments and host plants,” Field admits. Her co-author, biologist Dr. Merlin Sheldrake, concurs: “We still lack a comprehensive understanding of how the infrastructure of these living transport systems is distributed globally.”
Typically, insufficient knowledge would justify a wait-and-see approach. However, here it compels urgency. We now understand that this vast network sustains much of the world’s plant life, yet we are rapidly depleting it.
Thus, the SPUN team isn’t awaiting a complete picture. Alongside the study, they have released a Mycorrhizal Infrastructure Map—the first comprehensive global guide to these networks—and are urging governments to integrate it into conservation strategies: safeguarding the richest grasslands, rethinking farmland management, and—most importantly—cultivating an approach that regards soil as a vital resource to preserve.
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Source: www.sciencefocus.com
