Across the globe, just a handful of common bacteria taxa account for the use of carbon in the soil.

According to a new survey, published Monday in the journal Nature Communications, the soil carbon cycle in a variety of ecosystems is dominated by just three to six common bacteria groups.

Thousands of studies have examined the flow of carbon in and out of forests and wetlands, but scientists have only recently started to play closer attention to carbon pathways in the soil.

The planet's soil hosts twice as much carbon as its vegetation. As such, understanding the soil carbon cycle is key to modeling the planet's broader carbon cycle and predicting how it will be affected by climate change.

"We found that carbon cycling is really controlled by a few groups of common bacteria," lead author Bram Stone, who conducted the study while a postdoctoral researcher at the Center for Ecosystem Science and Society at Northern Arizona University, said in a press release. "The sequencing era has delivered incredible insight into how diverse the microbial world is."

"But our data suggest that when it comes to important functions like soil respiration, there might be a lot of redundancy built into the soil community," said Stone, now at the Pacific Northwest National Laboratory. "It's a few common, abundant actors who are making the most difference."

Sampling efforts across four different ecosystems revealed the presence of hundreds of distinct bacteria genera. Different genera can contain dozens of closely related species.

When researchers analyzed the rates of carbon consumption by the different genera, they found just six groups were need to account for more than 50 percent of carbon use.

When they added excess carbon and nutrients to the soil, they found just three dominant groups -- Bradyrhizobium, the Acidobacteria RB41 and Streptomyces -- accounted for more than 50 percent of carbon use.

For the study, scientists deployed water with different isotopes of oxygen in various soil samples. These signature isotopes become incorporated into different bacteria taxa as they proliferate, allowing scientists to estimate growth rates among the different groups -- a technique called quantitative stable isotope probing, or qSIP.

The researchers then used models to predict how efficiently these taxa were able to use the available carbon.

"Better understanding how individual organisms contribute to carbon cycling has important implications for managing soil fertility and reducing uncertainty in climate change projections," said study co-author Kirsten Hofmockel, head of the Microbiome Science Team at Pacific Northwest National Laboratory.

"This research teases apart taxonomic and functional diversity of soil microorganisms and asks us to consider biodiversity in a new way," Hofmockel said.

Previously, scientists were only able to make general assumptions about how communities of soil bacteria were behaving -- the equivalent, according to Hofmockel, of reporting that a state went red or blue in an election.

"Now, with qSIP, we can see who is driving that larger pattern -- the 'election results,' if you will -- at the level of individual microbial neighborhoods, city blocks," Hofmockel said. "In this way, we can start to identify which soil organisms are performing important functions, like carbon sequestration, and study those more closely."

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