The new imaging method observes carbon in the soil at approximately atomic proportions

Earth’s soils contain more than three times the amount of carbon than is found in the atmosphere, but the processes that bind carbon in the soil are still not well understood.

Improving such an understanding can help researchers develop strategies to separate more carbon in the soil, keeping it out of the atmosphere where it combines with oxygen and acts as a greenhouse gas.

New research describes a revolutionary method for showing the physical and chemical interactions that separate carbon in soil close to atomic proportions, with some surprising results.

The study “Organo-organic and organic-mineral bonds in the soil on a nanometer scale” was published on November 30 in Nature Communications.

At that resolution, researchers showed for the first time that soil carbon interacts with minerals and other forms of carbon from organic materials, such as bacterial cell walls and microbial by-products. Previous research has only indicated layered interactions between carbon and minerals in the soil.

“If there is a neglected mechanism that can help us retain more carbon in soils, then it will help our climate,” said senior author Johannes Lehmann, professor of Liberty Hyde Bailey at the School of Integrative Plant Science, Department of Soil and Plant Sciences, at College of Agriculture and Natural Sciences. Angela Possinger Ph.D. ’19, who was a graduate student in Lehmann’s laboratory and is currently a postdoctoral researcher at Virginia Tech University, is the first work of this paper.

Because the resolution of the new technique is close to atomic scale, researchers are not sure which compounds they are looking at, but suspect that the carbon found in the soil is probably from metabolites produced by microbes in the soil and from microbial cell walls. “In all likelihood, this is a microbial graveyard,” Lehmann said.

“We had an unexpected discovery where we could see connections between different forms of carbon, not just between carbon and minerals,” Possinger said. “We could start looking at those interfaces and try to understand something about those interactions.”

The technique revealed carbon layers around these organic surfaces. Nitrogen has also been shown to be an important player in facilitating chemical interactions between organic and mineral surfaces, Possinger said.

As a result, farmers can improve soil health and mitigate climate change through carbon sequestration by taking into account the form of nitrogen in soil changes, she said.

During her doctorate, Possinger collaborated for years with Cornell physicists – including co-authors Lena Kourkoutis, associate professor of applied and engineering physics, and David Muller, professor of applied and engineering physics Samuel B. Eckert and associates director of the Cowley Institute at Cornell for nanoraz nanoraz helped develop the multistage method.

The researchers planned to use powerful electron microscopes to focus electron beams to subatomic proportions, but found that electrons modify and damage loose and complex soil samples. As a result, they had to freeze the samples to about minus 180 degrees Celsius, which reduced the harmful effects of the air.

“We had to develop a technique that basically retains soil particles during the process of making very thin slices to look at these small areas,” Possinger said.

The beams can then be scanned over the sample to create images of the structure and chemistry of the soil sample and its complex interfaces, Kourkoutis said.

“Our physics colleagues are leading a global path to improving our ability to carefully observe the properties of materials,” Lehmann said. “Without such interdisciplinary collaboration, these discoveries are not possible.”

The new cryogenic electron microscopy and spectroscopy technique will allow researchers to examine a whole range of interfaces between soft and hard materials, including those that play a role in the function of batteries, fuel cells and electrolyzers, Kourkoutis said.