How Underground Fungal Networks Help Keep Planet Earth Healthy

In short: Evolutionary biologist Toby Kiers describes how mycorrhizal fungi trade minerals with plant roots and handle huge amounts of carbon. This is a podcast interview summarising her lab's work and published estimates, not a new study, and most of the trading experiments were done in simplified lab dishes.

The soil under a forest or a city park is not just dirt. It is laced with fungal threads thinner than a human hair, running a trade network older than roots.

What happened, in plain words

In an episode of Quanta Magazine's podcast The Joy of Why, co-host Steven Strogatz interviewed Toby Kiers, an evolutionary biologist at Vrije Universiteit Amsterdam. She explained how mycorrhizal fungi partner with most plants, delivering minerals such as phosphorus and nitrogen in exchange for sugars and fats. Her lab uses tools such as imaging robots and fluorescent quantum dots, along with ideas from economics, to study how these brainless networks decide where to send resources.

Key points

An ancient partnership: Over 80% of plant species form these partnerships, which evolved some 450 million years ago and helped plants move from water onto land, before true roots existed.
Carbon on a large scale: Work published by her group in 2023 estimated that plants send about 13 billion tons of carbon dioxide to these networks each year, roughly a third of fossil-fuel emissions.
Feeding plants: Up to 80% of a plant's phosphorus first passes through a fungal network, and the fungi also help with nitrogen and water.
Picky trading partners: In lab dishes, plants gave more carbon to fungi that supplied more phosphorus, and fungi gave more phosphorus to plants that supplied more carbon.
Moving resources to a better price: Using quantum dots attached to phosphorus, her team saw a fungus move phosphorus from a rich side of its network to a side where a plant gave more carbon in return.

Terms explained

Mycorrhizal fungi — Fungi that live in close partnership with plant roots, trading soil minerals for the plant's carbon. Example: Fine threads around the roots of a tree that bring it phosphorus from the surrounding soil.
Symbiosis — A close, long-term relationship between two different kinds of living things. Example: Bees getting nectar from flowers while carrying pollen between them.
Quantum dots — Tiny glowing particles that can be attached to a substance so scientists can follow where it goes. Example: Tagging a parcel with a tracker so you can watch its route on a map.

Critical analysis

What is encouraging. Kiers backs her claims with concrete experiments, from tracking about half a million points in growing networks to following tagged phosphorus. She is also careful about language, preferring "information processing" and "discriminate" over words that suggest fungi have intentions.

What deserves caution:

An interview, not a paper. The episode gives broad summaries in conversation. Listeners do not get the data, methods or uncertainty behind each finding.
Lab dishes are simple. Many trading experiments took place in Petri dishes, and Kiers herself says that what happens in nature is very different and shaped by many other organisms.
Carbon sent is not carbon stored. The 13 billion tons is carbon that plants send to the networks. Kiers notes that the fungi breathe some of it back out, so the amount kept in the soil long term is smaller and not given.
Economic words are a shortcut. Terms like trading, price and strategy make the behaviour easy to picture, but they can suggest choices that fungi do not make in a human sense.

Bottom line: A vivid, expert account of a hidden system that matters for soil, food and climate, best taken as an introduction rather than as new evidence.

What we still don't know

How fungi process information without a brain is still an open question in her lab, as is how the two-way flows inside the networks work. The episode also does not say how much of the carbon stays underground over decades.

Based on reporting from Quanta Magazine. This is an independent explainer, written in our own words with AI assistance; Quanta Magazine has not reviewed or endorsed it. Read the original for the full details.