Researchers identified key factors that determine if soil traps carbon or releases it as CO2, highlighting the role of molecular interactions and soil chemistry, potentially aiding climate change mitigation efforts. Smectite clay holds clay minerals known to sequester carbon in natural soils. Credit: Francesco UngaroWhen carbon molecules from plants make their way into the soil, they hit a definitive fork in the road.
An expert in the dynamics of organics in environmental processes, Aristilde is an associate professor of civil and environmental engineering at Northwestern’s McCormick School of Engineering. Jiaxing Wang, a Ph.D. student in Aristilde’s laboratory, is the paper’s first author. Rebecca Wilson, an undergraduate student at Northwestern, is the paper’s second author.Holding 2,500 billion tons of sequestered carbon, soil is one of Earth’s largest carbon sinks — second only to the ocean.
“There are instances where two molecules are both positively charged, yet one has a better interaction with the clay than the other,” Aristilde said. “It’s because the structural features of the binding are also important. A molecule has to be flexible enough to adopt a structural arrangement that can position itself in a way that aligns its positively charged components with the clay. The lysine, for example, has a long arm with a positive charge that it can use to anchor itself.
Although the researchers initially thought the biomolecules would compete with one another to interact with the clay, they instead discovered unexpected behaviors. In a surprising twist, even positively charged biomolecules with flexible structures were inhibited from binding to the clay minerals. While they easily bonded to the clay when alone, the biomolecules’ urges to bond with one another appears to supersede their attraction to the clay.