Microbial Underside of Rare Tallgrass Prairie Ecosystem Revealed in New Study

The historic soil composition of America's tallgrass prairies has been given a fresh analysis by a team of scientists who used bacteria samples and weather data to recreate the Midwestern soil conditions of more than 100 years ago.

America's tallgrass prairies, which once dominated huge swaths of the American Midwest, have been reduced to almost nothing. With their disappearance, hundreds of species of flowers, herds of roaming bison and dozens of species of grass that could grow as tall as a man have also vanished.

But now, a team of scientists have taken a look at part of the ecosystem that was unseen even when it was thriving: tiny microbes that lived amid the rich soils.

"These soils played a huge role in American history because they were so fertile and so incredibly productive," said Noah Fierer, a fellow at Colorado University-Boulder's Cooperative Institute for Research in Environmental Sciences and lead author of a new study in the journal Science. "They don't exist anymore except in really small parcels. This is our first glimpse into what might have existed across the whole range."

The whole range was immense. The full extent of the tallgrass prairie system covered more than 150 million acres, from Minnesota in the north, all the way south to Texas, and from Illinois westward across the vast expanse of Nebraska.

But the rich soils proved lucrative to farmers, who plowed down the tallgrass to plant crops in the fertile soil. Over the course of a century and half, the tallgrasses and flowers were replaced with fields of corn, soy and wheat. Today, only small patches of tallgrass prairie remains, mostly in reserves and conservation sites where the ecosystem has been corralled into small patches.

"It was very hard to find sites that we knew had never been tilled," Fierer said. "As soon as you till a soil, it's totally different. Most gardeners are familiar with that."

Fierer and his colleagues were able to find some undisturbed sites, collecting soil samples from 31 sites spread out across the prairie's historical range. When the team conducted tests on the soil samples, they found an abundance of a poorly understood phylum of bacteria known as Verrucomicrobia.

"We have these soils that are dominated by this one group that we really don't know anything about," Fierer said. "Why is it so abundant in these soils? We don't know."

By using soil samples and historical climate data, the researchers modeled what the soil's microbial structure would have looked like when the tallgrass prairie range was still an intact ecosystem.

Katherine Pollard, an investigator at the Gladstone Institutes in San Francisco and a co-author of the paper, said the team was able to accurately reconstruct the microbial components of prairie soils "using statistical modeling and data from the few remaining snippets of this vanishing ecosystem."

Fierer said the Verrucomicrobia are "critical" to the functioning of these tallgrass prairie soils.

"So if you're trying to have effective prairie restoration, it may be useful to try and restore the below-ground diversity as well," Fierer said.