About Understanding how soil traps carbon
The process by which soil absorbs atmospheric carbon derived from plants is clarified by recent research.
Either way, the carbon is effectively sequestered in the soil for days or even years, preventing it from entering the atmosphere right away. Alternatively, it provides food for microorganisms, which release carbon dioxide (CO2) into the atmosphere when it warms.
Researchers from Northwestern University identified the variables that might tip plant-based organic matter in one way or another in a recent study.
Researchers studied interactions between organic carbon biomolecules and a kind of clay mineral that is known to retain organic matter in soil by combining laboratory studies with molecular modeling. They discovered that the capacity (or inability) of soil to trap carbon is largely determined by electrostatic charges, the structural characteristics of carbon molecules, surrounding metal nutrients in soil, and competition among molecules.
The new discovery may make it easier for scientists to forecast which soil chemistries are best for storing carbon, which might result in soil-based strategies to mitigate climate change brought on by humans.
The study will appear in the Proceedings of the National Academy of Sciences on Friday, February 9.
The study’s principal author, Ludmilla Aristilde of Northwestern University, stated that “the amount of organic carbon stored in soil is about ten times the amount of carbon in the atmosphere.” “This massive reservoir would have significant knock-on effects if it were to get disturbed. To stop carbon from entering the atmosphere, a lot of work is done to capture it. We must first comprehend the underlying mechanics if we wish to achieve it.
Aristilde is an associate professor of civil and environmental engineering at Northwestern’s McCormick School of Engineering and a specialist in the dynamics of organics in environmental systems. The first author of the study is Jiaxing Wang, a Ph.D. candidate in Aristilde’s group. The second author of the study is Rebecca Wilson, a Northwestern undergraduate.
Common clay
Soil is one of Earth’s greatest carbon sinks, second only to the ocean, with 2,500 billion tons of trapped carbon. However, despite the fact that soil is all around us, our knowledge of how it sequesters carbon from the carbon cycle is still developing.
Aristilde and her colleagues looked at smectite clay, a kind of clay mineral that is known to trap carbon in natural soils, to learn more about this process. Then, they looked at the surface bonds of 10 distinct biomolecules with various chemistry and structures, such as amino acids, sugars linked to cellulose, and phenolic acids associated to lignin.
“We chose to investigate this clay mineral due to its widespread presence,” stated Aristilde. Clay minerals are present in almost all soils. Furthermore, clays are common in temperate and semi-arid climates, which are areas that will undoubtedly be impacted by climate change.
Opposites attract
Initially, Aristilde and her colleagues examined the relationships between certain proteins and clay minerals. The biomolecules containing positively charged components (lysine, histidine, and threonine) exhibited the greatest binding since clay minerals are negatively charged. It’s noteworthy to note, though, that electrostatic charges were not the only factor in this binding. Through the use of 3D computer modeling, the researchers discovered that the biomolecules’ structure also mattered.
According to Aristilde, there are situations in which two positively charged molecules interact with clay more effectively than one another. It’s because the binding’s structural elements are equally crucial. A molecule must possess sufficient flexibility to assume a structural configuration that enables it to align its positively charged constituents with the clay. For instance, the lysine may anchor itself with its long, positively charged arm.
A little help from friends
By this reasoning, one may conclude that biomolecules with negative charges couldn’t attach to the clay. However, Aristilde and her colleagues found that natural metal nutrients in the environment might step in. The negatively charged proteins and clay minerals created a link through the formation of a bridge by positively charged metals like calcium and magnesium.
According to Aristilde, “we saw a significant increase in binding when magnesium was there, even with a biomolecule that wouldn’t normally bind to the clay.” Thus, soil-based natural metal components may aid in the sequestration of carbon. Despite the fact that this phenomena has been extensively documented, we clarify the structures and processes.
Mix and mingle
The researchers observed that binding was simple and predictable when examining the interactions between individual proteins and clay minerals. Aristilde and her team blended the various biomolecules to obtain data that was more in line with real-world settings.
“We are aware that various biomolecule types coexist in the environment,” stated Aristilde. Thus, we also worked with a variety of biomolecules in our research.
Despite their initial assumption that the biomolecules would vie with one another for clay interaction, the researchers found unanticipated responses. Unexpectedly, even biomolecules with flexible architectures and a positive charge were unable to adhere to the clay particles. The biomolecules’ needs to bond with each other seem to outweigh their attraction to the clay, even though they linked to it quickly when they were alone themselves.
“This has never been demonstrated before,” stated Aristilde. In actuality, the attraction between two biomolecules was greater than the attraction between a biomolecule and the clay. As a result, there was less adsorption. It modifies our understanding of how molecules compete with one another on the surface. They are in competition for more than simply surface-level binding sites. They are really drawn to one another.
What’s next
Aristilde and her colleagues will next investigate the interactions between biomolecules and minerals in soils found in tropical and other warmer climes. They want to investigate the movement of biological materials in rivers and other water systems in a similar study.
“We want to understand other types of minerals now that we have studied clay minerals, which are mostly found in temperate zones,” stated Aristilde. “How do they capture living things? Do the procedures vary or remain the same? We must comprehend how soil is put together and how this influences microbial accessibility if we are to maintain soil’s ability to hold carbon.