In 1997, at age 19, Toby Kiers talked her way into the Smithsonian’s renowned tropical research institute on Barro Colorado, an island in the middle of the Panama Canal. The scientists studied the many species of local bats, the monkeys they outfitted with radio or GPS collars, and the towering rainforest canopy.

There, during a year-long fellowship, Kiers learned about a type of fungi known as mycorrhizae that formed intimate associations with the tropical trees and grew in sprawling, underground networks. Found all over the world, mycorrhizae are microscopic. But if you stretched out all the mycorrhizae present in a hectare of grassland, end to end, they would be the length of many, many Amazon Rivers.

“It seemed like the most sort of frontier world at that time,” she says, “because you just couldn’t see it.”

It became her life’s work. The fungi would penetrate the roots of nearby plants, so some scientists suspected they were parasites. But over the following years, as Kiers earned her PhD and became an evolutionary biologist, she and other researchers showed that mycorrhizae were exchanging resources: They gave the plants phosphorus and nitrogen in exchange for sugars and fats that plants made from carbon in the air.

This led Kiers to the defining question of her career: Were plants and fungi canny economic actors? Was there a market price—a fluctuating exchange rate—between phosphorus and carbon?

Her goal is not to figure out whether fungi can trade and make economic decisions as well as us brainy humans. Instead, she suspects that by some measures fungi are better at economics than us—and some of the world’s most powerful corporations seem to think she might be right.

Dr. Toby Kiers takes a soil core in the Gobi desert, Mongolia. Tomás Munita/SPUN

Tomás Munita/SPUN

Markets in Nature

Over the past few decades, scientists have come to increasingly appreciate plant intelligence. Plants communicate and alert each other to predators. They mount defenses, such as releasing toxic or unpleasant chemicals when animals munch on their greenery, and learn to ignore harmless stimuli. They may even form memories.

Some 70 to 90% of plants engage in symbiotic exchanges like those between mycorrhizae and their plant partners. Many scientists view this cooperation as akin to sharing. In 2016, ecologist Suzanne Simard memorably called a forest “a cooperative system.”

To Kiers, though, the idea that plants and fungi shared resources like well-behaved kindergarteners seemed to underestimate them. Why wouldn’t these amazing organisms, these survivors of millions of years of evolution and resource competition, try to cheat each other? Why not take their partners’ resources and offer nothing in return?

Nature is full of literal parasites. So if plants and fungi had been exchanging resources for millions of years, they must have strategies to prevent freeloading. It seemed like an economic problem.