Skip to main content
Science Areas
Environmental Transformations and Interactions

Soil Depth Plays Role in Decomposition of Soil Organic Matter

A study of soil organic matter mineralization from more than two dozen locations across the United States reveals details about potential for decomposition and release of carbon dioxide. 

soil samples
A variety of factors were shown to affect soil organic matter decomposition at different soil depths as part of a recent study. (Image courtesy of Adrian Gallo, Oregon State University)

The Science 


Soil organic matter is composed of the remnants of plant and animal tissues. Its decomposition, also known as mineralization, provides beneficial nutrients for plant health and ecosystem vitality. However, decomposition also releases carbon dioxide into the atmosphere, potentially contributing to climate change. Scientists don’t yet have a complete understanding of what controls the decomposition of soil organic matter. To gain a better understanding, a multi-institutional team of scientists analyzed carbon dioxide release and other soil properties at different depths from more than two dozen locations from across the United States. Their results showed that controls on soil organic matter mineralization are not only more complex than originally thought, but that soil depth also plays an important role. 

 

Impact 


Soil organic matter (SOM) comprises the largest terrestrial pool of organic carbon on Earth, and a significant portion of that pool lies below the immediate surface of the soil. However, the impact of temperature increases and the availability of water on the release of carbon dioxide and other greenhouse gases from decomposing SOM is not well understood. By analyzing soil samples from a variety of soil depths and from across the United States in a laboratory setting, and using simulated climate conditions that mimic the samples’ origin, a multi-institutional team of scientists pieced together the puzzle of how much carbon dioxide could be released from SOM, and how that might change from one U.S. location and soil type to another. 

 

Summary 


SOM consists of remnants of plant and animal tissues that decompose further to provide nutrients for plant health and ecosystem vitality. However, the additional decomposition of SOM also releases carbon dioxide into the atmosphere. To gain a better understanding of what controls the decomposition of SOM, a multi-institutional team of scientists analyzed carbon dioxide release and other soil properties at different depths from more than two dozen locations from across the United States. As part of the study, the team used soil samples collected from 26 National Ecological Observatory Network (NEON) sites spanning the United States, which were incubated for 52 weeks at mean summer temperatures that corresponded to their region of origin and sample-specific field capacity moisture content. Cumulative carbon dioxide respired was periodically measured and normalized by soil organic carbon content to calculate the cumulative specific respiration, which is one measure of SOM vulnerability to mineralization under optimal field conditions. The team extracted and analyzed sequential water, methanol, and chloroform from soil samples, and completed their analysis of the samples using the Fourier transform ion cyclotron resonance mass spectrometer at EMSL, a DOE Office of Science User Facility. Among their findings, the team found that the relationship among soil properties, soil organic matter chemistry, and cumulative specific respiration was complex. Very few soil properties were consistently useful at predicting SOM decomposition, showing how important local soil properties and environments are in the soil carbon cycle. What was particularly surprising was that the controls on mineralization not only changed from site to site, but also with depth within a site. These findings highlight the limitations of assuming all SOM will respond similarly to future changes in climate and the need to understand this variability in space and time. 

Contacts 

Brian Strahm, Virginia Tech, brian.strahm@vt.edu 

Maggie Bowman, Environmental Molecular Sciences Laboratory, maggie.bowman@pnnl.gov 

 

Funding 

This study was funded by the U.S. National Science Foundation (NSF). NEON is sponsored by NSF and operated under cooperative agreement by Battelle. This study is based in part upon work supported by NSF through the NEON program. The work at EMSL was carried out as part of a DOE rapid access user proposal. 

 

Publication 

Weiglein, T.L., Strahm, B.D., Bowman, M.M. et al. “Key predictors of soil organic matter vulnerability to mineralization differ with depth at a continental scale.” Biogeochemistry 157, 87–107 (2022). [DOI: 10.1007/s10533-021-00856-x]