The Ground Beneath Her Feet
By Paul Tullis for ÁñÁ«ÊÓƵ MagazineThe video shows what looks like a close-up of veins or arteries—something carrying blood—or maybe a computer simulation of bad highway traffic. There’s a lot of red. The strands form a rough triangle, and the red patches move along the sides of the triangle—now speeding, now slowing.
It looks pretty normal for something organic and alive.
But then the red patches in the strand on the right behave unlike either blood in a body or cars on a highway: They suddenly reverse direction. They were going down; now they quickly travel upward. Then they reverse direction again.
The video is part of and comes from a paper published the previous year in Current Biology—one of the most influential peer-reviewed scientific journals—that came out of her lab at the Free University of Amsterdam (Vrije Universiteit). The strands are half a millimeter or so of a mycorrhizal network, systems of fungi that make associations with plants, often connecting roots underground. It is no exaggeration to say that they underpin all life on Earth.
Using high-resolution cameras, Kiers’s team showed how these fungi move resources across their networks to their host plants according to cues received. It was a groundbreaking demonstration of the complexity of mutualism and symbiosis among species, bolstering recent developments showing how life on Earth is interconnected and interdependent and establishing that a species without a brain has evolved “trading strategies” on par with sophisticated market economics in order to maximize its resources and get by with providing as little as possible to its trading partners.
“You’re watching them calculate and make decisions,” Kiers tells me with excitement in her apartment on the top floor of a nineteenth-century tenement building in Amsterdam, just outside the canal ring. Collecting samples for her studies has taken Kiers to some of the most remote places on Earth, from the Gobi Desert to the South Pacific to the rainforests of Ecuador. “It’s like studying a primate, [because] you can watch its behavior in real time and you can do all these things to it, and it reacts. We’re trying to understand how fungi regulate those flows and how they use that to process information about their environment.”
This might sound like the acute, immaterial inquiries of an obscure corner of biology. Far from it. Fungal-plant symbiosis has existed for 450 million years; the two evolved together, each providing the other with something it could not produce itself but needed to survive.
Between 70 and 90 percent of all plant species are now interacting with mycorrhizal fungi, making the symbiosis among the planet’s most ubiquitous, and underlying the food webs that are the basis for much of the planet’s life. Largely invisible—when we hear “fungi,” we think “mushrooms,” but mushrooms are just the fruiting bodies of these organisms, and the majority of fungal species do not produce them—they are essential ecosystem engineers comprising up to 30 percent of soil; if all the mycorrhizal fungi in just the top ten centimeters of soil worldwide were laid end to end, they would stretch half the width of our galaxy. They have evolved the capability to reshape themselves as needed, foraging for nutrients essential to plants—up to 80 percent of the phosphorus in plants goes through fungal networks—which they deliver to the plants in exchange for carbon. This they deploy to build their networks, which then act as a scaffolding, holding soil together, fighting erosion, and retaining water.
The carbon they contain and transport adds up to about 75 percent of all the carbon in the ground—far more than is aboveground in all the rainforests in all the world—making soils an essential carbon sink without which the planet would heat to unthinkable levels. “It’s just a major component of the carbon cycle that had been ignored,” Kiers says, until she and colleagues quantified it in a second paper for Current Biology, published in 2023.
Since around the turn of the century, the field of biology has undergone a revolution as scientists learn more and more about the relationships between species—how they influence and interact with one another—and study these relationships per se, instead of just looking at a plant, animal, or microbial species independently. One of the sparks that ignited this fire was a paper concerning mycorrhizal fungi published in 1997, when Kiers was about to embark on a semester at the Smithsonian Tropical Research Institute in Panama during a gap year from ÁñÁ«ÊÓƵ. But she hadn’t heard of the paper when she decided, at nineteen, to try to find out whether certain tropical trees on the institute grounds preferred their own soils (and, by extension, their own fungi) or whether they grew just as well with soil and fungi that had developed beneath a different species of tree. The result: There’s no place like home. The research she conducted in Panama was accepted for publication a few months after Kiers graduated from ÁñÁ«ÊÓƵ in 1999.