New findings explain how soil traps plant-based carbon | Top Vip News

When carbon molecules from plants enter the soil, they encounter a definitive fork in the road. Or the carbon is trapped in the soil for days or even years, where it is effectively sequestered from immediately entering the atmosphere. Or it feeds microbes, which then breathe carbon dioxide (CO₂) in the increasingly warm environment.

In a new study, researchers at Northwestern University determined the factors that could tilt plant-based organic matter in one direction or another.

Combining laboratory experiments and molecular modeling, the researchers examined interactions between organic carbon biomolecules and a type of clay minerals known to trap organic matter in soil. They found that electrostatic charges, structural characteristics of carbon molecules, surrounding metal nutrients in the soil, and competition between molecules play important roles in the soil’s ability (or inability) to trap carbon.

The new findings could help researchers predict which soil chemistries are most favorable for trapping carbon, which could lead to soil-based solutions to curb human-caused climate change.

The paper, titled “Electrostatic coupling and water bridging in the adsorption hierarchy of biomolecules at water-clay interfaces,” will be published Feb. 9 in the journal Proceedings of the National Academy of Sciences.

“The amount of organic carbon stored in soil is about 10 times the amount of carbon in the atmosphere,” said Ludmilla Aristilde, lead author of the Northwestern study. “If this huge reservoir is disturbed, it would have major ripple effects. There are many efforts to keep carbon trapped from entering the atmosphere. If we want to do that, we must first understand the mechanisms at play.”

An expert in the dynamics of organic compounds in environmental processes, Aristilde is an associate professor of civil and environmental engineering at Northwestern’s McCormick School of Engineering. Jiaxing Wang, Ph.D. student in Aristilde’s laboratory, is the first author of the article. Rebecca Wilson, a Northwestern undergraduate, is the second author of the paper.

common clay

Soil, containing 2.5 billion tonnes of sequestered carbon, is one of the largest carbon sinks on Earth, second only to the ocean. But although soil is all around us, researchers are only beginning to understand how it holds carbon to sequester it from the carbon cycle.

To investigate this process, Aristilde and her team looked for smectite clay, a type of clay mineral known to sequester carbon in natural soils. They then examined how the clay mineral surface bound ten different biomolecules, including amino acids, cellulose-related sugars, and lignin-related phenolic acids, with different chemistries and structures.

“We decided to study this clay mineral because it is everywhere,” Aristilde said. “Almost all soils have clay minerals. Additionally, clays are prevalent in semi-arid and temperate climates, regions that we know will be affected by climate change.”

Opposites attract

Aristilde and her team observed for the first time the interactions between clay minerals and individual biomolecules. Because clay minerals are negatively charged, biomolecules with positively charged components (lysine, histidine, and threonine) experienced the strongest binding. But, interestingly, this union was not determined solely by electrostatic charges. Using 3D computational models, the researchers found that the structure of the biomolecules also played a role.

“There are cases where two molecules are positively charged, but one has a better interaction with the clay than the other,” Aristilde said. “This is because the structural characteristics of the bond are also important. A molecule has to be flexible enough to adopt a structural arrangement that can be positioned in a way that aligns its positively charged components with the clay. Lysine, for example , has a long arm with a positive charge that it can use to anchor itself.”