November 1, 2013
Demise Of Tallgrass Prairies Was Due To Extremely Fertile Soil
April Flowers for redOrbit.com - Your Universe Online
They have all but disappeared, but America's once-abundant tallgrass prairies were home to dozens of species of grasses that could grow to the height of a man, hundreds of species of flowers, and herds of roaming bison.Now, a team of researchers from the University of Colorado Boulder (CU-Boulder) has gotten a peek at a vitally important, yet rarely studied community of those tallgrass prairies. The study, published in Science, examined the diverse assortment of microbes that thrived in the dark, rich soils beneath the grass.
"These soils played a huge role in American history because they were so fertile and so incredibly productive," said Noah Fierer, a fellow at CU-Boulder's Cooperative Institute for Research in Environmental Sciences (CIRES) - a joint institute of CU-Boulder and the National Oceanic and Atmospheric Administration (NOAA). "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 tallgrass prairies once covered more than 150 million acres from Minnesota to Texas and from Illinois to Nebraska. The amazing fertility of the soils beneath the prairie was also the prairie's undoing. Settlers, attracted by the richness of the dirt, began to plow up the prairie more than 150 years ago. These settlers replaced the native plants with corn, wheat, soybeans and other crops. Today, only remnants of the tallgrass prairie remain, covering a small fraction of the original ecosystem's range.
Fierer, an associate professor of microbial ecology, and a team of researchers used soil samples collected by Rebecca McCulley, a grassland ecologist at the University of Kentucky, from 31 sites spread out across the prairie's historical range. The majority of these sites were nature preserves or old cemeteries.
"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."
To characterize the microbial community living in each soil sample, the team used DNA sequencing, which showed that a poorly understood phylum of bacteria, Verrucomicrobia, dominated the microbial communities in the soil.
"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."
The microbial makeup of each particular soil sample was unique, despite the fact that Verrucomicrobia were dominant across all samples. To understand how soil microbial diversity might have varied across the tallgrass prairie when it was still an intact ecosystem, the scientists created a model based on climate data and the data from the samples.
"I am thrilled that we were able to accurately reconstruct the microbial component of prairie soils using statistical modeling and data from the few remaining snippets of this vanishing ecosystem," said Katherine Pollard, an investigator at the Gladstone Institutes in San Francisco.
The research team is currently working to grow Verrucomicrobia in the lab to understand what it does and the conditions it favors. They expect their current findings to bolster tallgrass prairie restoration efforts in the future, with or without a full understanding of the microbes.
"Here's a group that's really critical in the functioning of these 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.