There Is a Whole World Inside Every Plant

Author: Sarah Laskow / Source: Atlas Obscura

In Corvallis, Oregon, Posy Busby works in a garden planted with 3,000 black cottonwood trees that represent 1,000 unique genetic specimens, each originally found somewhere on the West Coast of North America, from California to Canada.

Cottonwoods are some of the fastest-growing trees in the world, and the garden looks a lot like a timber company plantation. But Busby, an ecologist at Oregon State University, studies something on a much smaller scale than trees—the microbes that live inside their leaves.

Busby started paying attention to microbes because she wanted to understand why wild plants plagued by a disease, such as leaf rust, fall ill in one place and not another. Genetics and environment could explain only part of this puzzle. But inside a plant is a whole world of microorganisms, and some of the cottonwoods’ resident microbes seemed to have an impact on the severity of the leaf rust.

At first Busby thought of these bacteria and fungi as individuals that could be either troublesome or beneficial to the plants, like the fungus that causes leaf rust. But as she read up on the human microbiome, she realized that the microbial communities within plants were as complex as those within us. “We’re really dealing with the same thing,” she says.

Scientists have known for centuries that soil is packed with microscopic organisms and, since the late 1800s, that some plants form symbiotic relationships with fungi.

But now they are finding that microorganisms live not just around but inside plants—in their roots, stems, and leaves—in greater numbers and with more diversity than anyone realized.

Busby’s cottonwood trees, for instance, were known to have a handful of microbial pathogens. “But when we looked at the overall diversity of the fungi in the leaves, it was more like a thousand or 1,500 different fungi living in and on these leaves,” across the tree’s range, she says. “So that was an astounding number.”

Just as we have learned that the human microbiome has a greater influence on human health than anyone imagined, there’s an emerging understanding that the plant microbiome could be the key to floral health. One initial goal of exploring the plant microbiome has been to determine who’s part of this community and what they’re doing for the plant. The answer, it turns out, depends on location. If you’re a plant, the place you live changes the ecosystem inside you, and that can…

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