Association between Soil Organic Carbon and Calcium in Acidic Grassland Soils

The Science

Understanding soil organic matter decomposition is crucial for predicting its behavior in a changing climate and land management. This project explored the role of calcium (Ca) in these dynamics. Researchers used synchrotron spectroscopy to study soils from Point Reyes National Seashore in California. Results showed a significant portion of organic matter was closely linked to Ca with distinct properties. Specifically, Ca-associated organic matter had more aromatic and phenolic carbon groups compared to iron-associated carbon. In areas with high Ca association, the spectra resembled lignin, indicating oxidative transformation. Thus, Ca appears to favor organic matter that has undergone some oxidative changes in California’s grassland soils.

The Impact

This work showed Ca is important in organic matter behavior even at sites with relatively low soil Ca concentrations. Knowing Ca is associated with the complexation, cycling, or stabilization of organic matter with a particular chemical composition will allow for better understanding and predictions of how soil organic matter stocks change over time and under changing conditions. The observation that Ca could be associating with plant-like organic matter and interrupting its decomposition pathway is a significant insight into the pathways of and controls on organic matter processes in soils.

Summary

Soils store a large amount of organic carbon, but it is not fully understood how quickly this carbon returns to the atmosphere as carbon dioxide (CO₂). It’s been suggested that Ca plays a key role in controlling the decomposition of organic matter. Most research has focused on soils with high Ca levels and significant amounts of calcium carbonate. This study shows Ca is also important in soils with lower calcium concentrations, suggesting its role in many types of soils. Compared to organic matter not linked with Ca, the organic matter associated with Ca was chemically different and more similar to lignin-like plant material. This likely indicates that Ca interrupts the normal decomposition process of plant matter. Identifying this new factor in organic matter cycling enhances the ability to predict how soil organic matter will respond to changes in climate and land management.

Principal Investigator

Peter S. Nico
Lawrence Berkeley National Laboratory
[email protected]

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

This research was supported by the Biological and Environmental Research program of the U.S. Department of Energy’s Office of Science under contract no. DE-AC02-05CH11231 as part of the Belowground Biogeochemistry Science Focus Area.

References