A powerful and underrated ally in the climate crisis? Mushrooms | Toby Kiers and Merlin Sheldrake

If we are to tackle the climate crisis, we must tackle a global blind spot: the vast underground fungal networks that sequester carbon and sustain much of life on Earth.

Fungi are largely invisible ecosystem engineers. Most live as branching, fusing networks of tubular cells called mycelia. Overall, the total length of fungal mycelium in the top 10 centimeters of the soil is more than 450 quadrillion km: about half the width of our galaxy. These symbiotic networks include an ancient survival system that easily qualifies as one of the wonders of the living world.

Through fungal activity, carbon seeps into the soil, where it supports complex food webs – about 25% of all species on the planet live underground. A large part stay in the ground, making underground ecosystems the stable reserve of 75% of all terrestrial carbon. But climate change strategies, conservation programs and restoration efforts neglect fungi and focus heavily on aerial ecosystems. It’s a problem: Destruction of underground fungal networks accelerates both climate change and biodiversity loss, and interrupts the life cycles of global nutrients. These networks must be seen as a global public good to be urgently mapped, protected and restored.

Fungi are found at the base of food webs that support much of life on Earth. Around 500 million years ago, fungi facilitated the movement of aquatic plants on dry land, with the fungal mycelium serving as a plant root systems for tens of millions of years until plants can evolve on their own. This association transformed the planet and its atmosphere – the evolution of plant-fungal partnerships coincided with a 90% reduction in the level of atmospheric carbon dioxide. Today most plants to depend about mycorrhizal fungi – Greek words for fungus (mykes) and root (rhiza) – which weave through the roots, supply plants with essential nutrients, defend them against disease and connect them in shared networks sometimes called “wood wide web”. These fungi are a more basic part of the vegetation than the leaves, wood, fruits, flowers or even the roots.

We are destroying the planet’s fungal networks at an alarming rate. According to current trends, more than 90% of the Earth’s soil will be degraded by 2050. Modern industries, from agriculture to forestry, have not taken the life of the soil into account. Despite the fact that mycorrhizal fungi provide up to 80% of a plant’s nutrients, intensive agricultural practices – through a combination of plowing and the application of chemical fertilizers, pesticides and fungicides – significantly reduce the abundance, diversity and physical integrity of fungal networks. Registration wreaks havoc underground, reducing the abundance of mycorrhizal fungi by up to 95% and the diversity of fungal communities by up to 75%. A large study published in 2018 suggested that the “alarming deterioration” in tree health across Europe has been caused by a disruption in their mycorrhizal relationships, caused by nitrogen pollution from the burning of fossil fuels and agricultural fertilizers.

Mycorrhizal fungal networks reconcile between one third and one half of the living mass of soils and constitute a major global carbon sink. When we destroy them, we sabotage our efforts to limit global warming. Plants provide carbon to their fungal partners in exchange for nutrients like nitrogen and phosphorus – much of the phosphorus that makes up your own body’s DNA will have passed through a mycorrhizal fungus. In their exchange, plants and fungi engage in sophisticated business strategies, finding compromises and solving compromises of dizzying complexity. The influence of these quadrillions of microscopic business decisions spans entire continents.

Globally, at least 5 billion tonnes of carbon dioxide are held captive within mycorrhizal networks each year, an amount roughly equivalent to the amount of carbon dioxide emitted annually by the United States (unpublished data suggests this figure is closer to 17 billion tonnes). Even small reductions in the prevalence of fungal networks have important consequences: a release of only 0.1% of the carbon now stored in European soils is equivalent to the annual emissions of 100 million cars.

Mycorrhizal fungi are key organisms that support planetary biodiversity; when we disrupt them, we jeopardize the health and resilience of the organisms on which we depend. Fungal networks form a sticky living layer that holds the soil together; remove the mushrooms, and the soil is washed away. Mycorrhizal networks increase the volume of water that the soil can absorb, reduce the amount of nutrients leached from the soil by precipitation by up to 50%. They make plants less sensitive to drought and more resistant to salinity and heavy metals. They even increase the ability of plants to repel pest attacks by stimulating the production of defensive chemicals. The current focus on aerial biodiversity neglects more than half of the most biodiverse underground ecosystems, as the areas with the highest aerial biodiversity are not always those with the highest soil biodiversity.

Mycorrhizal fungal networks and the nutrient flows and processes they manage should be viewed as a global public good, analogous to clean air and water. For millennia in many parts of the world, traditional farming and land management practices have ensured soil health and therefore have implicitly supported the fungal relationships of plants. But during the 20th century, our behavior got us into trouble.

Organizations like the Society for the Protection of Underground Networks (Spun), the Mushroom Foundation and Global mushrooms defend soil ecosystems and lead a massive global sampling effort to create open source maps of Earth’s fungal networks. These maps will help map the properties of underground ecosystems, such as carbon sequestration hotspots, and document new fungal species capable of withstanding drought and high temperatures. Researchers will be able to track the distribution of fungal networks as they evolve in response to climate change and land use patterns, just as they already do with global vegetation, climates and ocean currents.

A deeper understanding of these dynamic living systems will support conservation projects and policies that aim to stop their destruction and encourage their recovery, in addition to stimulating much needed innovation in the science and technology of underground ecosystems.

Networks of mycorrhizal fungi have long supported and enriched life on our planet. It’s time they got the attention they deserve.

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