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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 ºÚÁϳԹÏÍø±¬ÍøÕ¾. 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 ºÚÁϳԹÏÍø±¬ÍøÕ¾ in 1999.

“That everything in ecology is happening as species are interacting with one another—Toby recognized that really early,” says Zoe Cardon, senior scientist with the University of Chicago’s Marine Biological Laboratory in Massachusetts and onetime assistant biology professor at ºÚÁϳԹÏÍø±¬ÍøÕ¾.

In the time they overlapped at the College, Cardon encouraged Kiers to take a year off and recommended the Smithsonian internship to her. “I could see she had the potential and the initiative—the drive—to really be able to make the most of opportunities that might be overwhelming to other people,” Cardon says. “You really got the sense that this was someone who was going to try very hard in their life to make a difference.”

Many are the parents of adult children who have said that the character, accomplishments, or interests of their offspring could be gleaned very early.

Soil scientist Kiers would seem to have been one of those children. “I was a very dirty kid,” she says, describing how she vehemently spurned shoes from an early age.

Often playing in the woods that bordered her home in northwest Connecticut, she and her sister became adept at hunting morels, the mushroom with a cap resembling a brain that is treasured by chefs. After a semester at the Mountain School in Vermont, Kiers graduated (barefoot) from Phillips Exeter Academy in New Hampshire in 1994 and started at ºÚÁϳԹÏÍø±¬ÍøÕ¾ the following fall.

The College supported her interests, she found, even if they weren’t widely shared. “It was very open,” she says, to unorthodox scholarly pursuits. “We did an independent study on homesteading in Maine,” which has long been a refuge for people who want to live off the land. “There were lots of outdoor programs. I wanted to open a toothbrush factory; I wanted to be a sheep farmer. I made a canoe!”

Classroom work, however, she found less thrilling. For someone interested in biology, that’s going to be frustrating, just because of the sheer volume of basic knowledge that must be acquired before one can literally get their hands dirty. “It’s a lot of lab work to be able to get a chance to go out into the field,” she says.

Fortunately for mycology, Cardon’s year at the College coincided with Kiers signing up for botany. “Toby was always asking good questions, very curious about the material and not just memorizing stuff,” Cardon recalls. But she could sense Kiers’s frustration with being stuck in the classroom, and she connected her with a colleague at the Smithsonian research station.

The institute maintains an island in the middle of the Panama Canal to study tropical forests as they existed before they were disturbed much by human presence. Of all terrestrial ecosystems, the tropical forest ecosystem hosts the greatest species diversity, but for all the bats, cats, birds, and trees that could be seen as she wandered through the dank terrain—as Kiers had explored the Connecticut woods by her home a decade earlier—it was the ground beneath her feet that captured her fascination.

“I was struck by the fact that there are these immensely diverse tropical ecosystems, and nobody was paying attention to what was happening under them,” Kiers recalls. Her supervisors at the institute encouraged her to develop her own research focus, and she decided to look at the fungi in the soils that formed the literal base of all the island’s biodiversity. Fungus was still a largely unexplored domain. “When I started in this field, it was sort of like, ‘What are they doing? Are they parasites?’” Kiers says. “Fungus still was kind of considered a pathogen. I mean, when you see something that’s penetrating into a cell, it’s not usually a good sign.”

Once she took a look at her research samples, she was hooked. “I think that what blew my mind is you could see them inside the root,” Kiers recalls. “I was really always into dirt, but I don’t think I thought of it intellectually until I went to Panama. You see these beautiful filament structures that are penetrating through the roots, and they make these structures that look like little mini trees inside the cells, which are the sites of nutrient transfer, and that was one of the most beautiful things I’d ever seen under the microscope.”

After graduating from ºÚÁϳԹÏÍø±¬ÍøÕ¾, Kiers embarked on a PhD path at the University of California, Davis—one of the top universities in the world for studying ecology and evolutionary biology. She became interested in the idea of cheating in nature and wrote her thesis on the give-and-take between partners in symbiotic relationships. Transactional relationships had been observed in nonhuman primates—chimps, bonobos, and gorillas trade grooming for food, and when food availability rises, less is required to “purchase” the same amount of grooming—but similar practices had never been established in organisms without a brain. “I’d read many of those biological market theory papers and wanted to try establishing that in the plant-mycorrhizal system,” Kiers says.

She designed an experiment to determine whether a plant with multiple colonies, which themselves have multiple colonizers, could sense whether certain partners were taking more resources and, if so, what, if anything, it would do about it. Kiers describes the essential question as, “Even if they don’t have cognition, can organisms sense and evaluate how good you are?” She found that fungi that were receiving carbon without delivering nitrogen in return were cut off: “When you have these two sides and they’ve each got multiple partnerships, you’ve got potential to trade with different partners so more of these market dynamics emerge.”

The dissertation—drawing on lab work conducted in part at ºÚÁϳԹÏÍø±¬ÍøÕ¾—was published in Nature in 2003; in the scientific world, this would be akin to a debut novel being nominated for the Pulitzer Prize.

At UC–Davis, Kiers began a relationship with a student in international development who is half Dutch, and as they neared the end of their studies, he encouraged her to apply for a grant from the Dutch Science Foundation so they could live together in the Netherlands. Later, they wed, and she accepted an offer from Free University.

The years since have seen a whirlwind of research expeditions: Corsica. Mongolia. Kazakhstan. Lesotho. “She’s like a tornado swallowing everything and integrating things, really crossing borders of disciplines very often, which is remarkable,” says Jan Jansa, group leader at the Institute for Microbiology at the Czech Academy of Science and a research partner of Kiers’s. Even on a paper with more than a dozen coauthors, says Jansa, “everyone has to contribute, which is really important and not that common. It tells something about her integrity and fairness. She’s not publishing hundreds of papers, but every one is a jewel.”

Much of the travel Kiers undertakes is to document the biodiversity of mycorrhizal networks while there’s still time. Deforestation, agriculture, and urbanization are destroying these networks before scientists can race to document them, or fully understand their significance. Cutting trees removes mycorrhizal network partners. Concrete severs their connections. Tilling introduces selection pressure for fast-growing fungi that don’t produce long-lived networks. This is doubly damaging because the mycorrhizal networks protect nutrients that crops need. Synthetic fertilizers, moreover, provide crops with what they had been getting from the fungi, enabling the plants—just as Kiers had shown in her PhD dissertation—to cut off the fungi’s carbon supply, dooming them to an early death. “What we’re worried about is the loss of unique communities associated with different ecosystem types,” Kiers says.

In 2023, Kiers was awarded the Spinoza Prize, sometimes referred to as the Dutch Nobel. The prize money will help her further develop, in concert with biophysicists at the Fundamental Research on Matter Institute for Atomic and Molecular Physics (known by its initials in Dutch, AMOLF), part of the Dutch government’s research council, an imaging robot to see how fungal networks change in response to different induced scenarios. She compares it to Google Maps for microbes: “You can see all the road systems, then you can zoom in and you can look at the traffic patterns inside the network.” When two streams were observed moving in opposite directions simultaneously inside the same tube, she says, the biophysicists were flummoxed. “They were like, ‘We have no idea how this is happening,’” Kiers recalls.

Machine learning is speeding these efforts. With 25,000 soil samples collected from around the world, a model is fed hundreds of geographic information system layers, such as temperature, altitude, and precipitation to predict where biodiverse fungal communities can be found.

It turns out the biodiverse communities belowground can be inversely correlated with species diversity above. “That’s what surprised us,” Kiers says. “The very rich places can be in almost any ecosystem.” Considering the enormous role these fungi have in sequestering carbon that Kiers established last year, the results could have huge implications for the global climate: “Can you use these maps to identify carbon drawdown hot spots? And can you protect those the way that we’re protecting the Amazon? What would it look like to manage an ecosystem for fungal biodiversity?”

Kiers’s career has provided what she longed for back at ºÚÁϳԹÏÍø±¬ÍøÕ¾, when she itched to get into the field, but collecting the samples necessary for her research can be perilous.

At the Palmyra Atoll, she waded among reef sharks and endured crabs that steal equipment and leeches that attach to your eyes. It’s one of the most remote patches of land in the world—in the event of an injury, no help can reach you for seventy-two hours. In Corsica she needed to lug coolers full of dry ice into the field.

But perhaps the biggest challenge has been to advance her work while maintaining a family. “It’s just very hard to be a field biologist with kids,” she says. So she and her husband, who has a somewhat portable career as a poet and IT professional, decided to just bring them along. Either that or she would need to be away from her family for weeks at a time, several times a year—a compromise she found unacceptable.

“It was both necessity, and then also: Is there a way to make it work? Is there a way to not be shy or somehow apologetic about it?” Initially, Kiers felt she needed to justify her children’s presence to the other scientists in order to overcome their apprehension that it would impede their work. But, considering the high rates of women dropping out of scientific professions after motherhood, she was determined to normalize the practice. Colleagues have become more welcoming; her children’s schools are less enthusiastic, however, about their being out of class for long periods. (Their grandparents, Kiers says, “are in a place of acceptance.”) She wrote about her “act of academic defiance” for The New York Times.

In 2021, Kiers and her colleagues launched the Society for the Protection of Underground Networks [SPUN] to expand Kiers’s mapping efforts and to advocate for fungal conservation. “One of the reasons that I started SPUN was frustration that scientists have been sounding the alarm on the destruction of underground ecosystems, and no one was listening,” Kiers says. The alarms had come in the form of academic research that wasn’t making its way into public awareness. “It’s hard to talk about those data with journalists or with policymakers because they want a very simple take-home message,” Kiers says.

But the comfort with uncertainty that scientific rigor requires isn’t widely shared outside the world of science. This has been the challenge facing climate scientists as well. “And so how do you distill that message while still staying true to the rigor of the science that you believe in? I think that’s the most difficult part,” says Kiers. “But I really felt that it was important to try to move between those two worlds.”

There remains much to determine. The currency used in the market transactions of nutrients for carbon—could it be chemical signals?—is still unknown more than ten years after Kiers first established their existence in 2011. But the fascination, and the urgency, drives her on, any eyeball leeches be damned.

“What’s so interesting about working with this particular symbiosis is that it affects climate, it affects agriculture, it affects restoration—and that’s mostly because of its ubiquity. If we really care about the Earth’s diversity, the places that house really important hot spots of underground biodiversity are not currently being protected. And we don’t even, in many cases, know where they are.”

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Paul Tullis is an Amsterdam-based freelancer whose work has appeared in many magazines, including The New Yorker, NYT Magazine, Businessweek, Scientific American, Nature, Wired, and others.

Sarah Sampson is a hand-lettering designer and illustrator who serves as senior designer at 2communiqué. She earned her BFA in graphic design at The College of Saint Rose.

 

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This story first appeared in the Fall 2024 issue of ºÚÁϳԹÏÍø±¬ÍøÕ¾ Magazine. Manage your subscription and see other stories from the magazine on the ºÚÁϳԹÏÍø±¬ÍøÕ¾ Magazine website.