A new finding explains how soil sequesters plant-based carbon from the atmosphere. The outcome should promote ideas to help tackle climate change, including strategies to prevent carbon release. With 2,500 billion tons of carbon, soil is one of Earth’s largest carbon sinks.
When carbon molecules from plants enter the soil, either the carbon gets 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 respire carbon dioxide into the ever-warming environment. Why and how does this distinction occur?
This has been the subject of Northwestern University research into the factors that could tip plant-based organic matter in one direction or the other. In terms of the significance, the amount of organic carbon stored in soil is about ten times the amount of carbon in the atmosphere.
For the research, scientists used experiments and computational modelling to study interactions between carbon molecules and clay minerals in soil. This reveals that electrostatic charges, structural features of carbon molecules, surrounding metal nutrients in soil and competition among molecules all play major roles in soil’s ability (or inability) to trap carbon.
This outcome provides clues to why some plant-based carbon molecules are sequestered in soils, but others are respired as carbon dioxide. For example, the findings could aid researchers in predicting which soil chemistries are most favourable for trapping carbon. This could potentially lead to soil-based solutions for slowing human-caused climate change.
In addition, the research shows that electrostatic charges, surrounding nutrients in soil and competition from other molecules all play roles in facilitating carbon trapping.
The study looked to smectite clay; a type of clay mineral known to sequester carbon in natural soils. The researchers focused on how the clay mineral’s surface bonded to ten different biomolecules — including amino acids, sugars related cellulose and phenolic acids related to lignin — with varying chemistry and structures.
Since clay minerals are negatively charged, biomolecules with positively charged components (lysine, histidine and threonine) experienced the strongest binding. Ass well as charge, the researchers additionally found that the structure of the biomolecules also played a role. Negatively charged biomolecules can also bind to the clay via positively charged metals, such as magnesium and calcium, forming a bridge between the negatively charged biomolecules and clay minerals to create a bond.
When studying interactions between individual biomolecules and clay minerals, the researchers found binding was predictable and straightforward. This offers a future model for understanding the release factors for carbon.
The research is published in Proceedings of the National Academy of Sciences, titled “Electrostatic coupling and water bridging in adsorption hierarchy of biomolecules at water-clay interfaces.”
