The Science

Land use changes, nutrient depletion, and drought can make plant roots grow deeper into the soil, but scientists question how that growth affects carbon in the soil. More roots reaching deep soil layers could result in more carbon being sequestered, or roots may unlock older carbon in deep soils. By combining advanced imaging techniques, this study examined how root activity impacts organic carbon compounds and their association with minerals in soil. The findings show that the amount of time deep soil has been subjected to root activity dictates whether roots promote the storage or loss of carbon.

The Impact

Soils contain more than twice the amount of carbon stored in the atmosphere. Most of this carbon resides in deep soils, where it can be stored for millennia. This study showed that root activity in relatively young soils could result in carbon storage by forming new associations between organic carbon compounds and minerals. In contrast, continued root activity in older soils may disrupt existing associations and cause carbon to be released as climate-active carbon dioxide. The results of this study will help scientists determine which soils can better store carbon at depth and which may be vulnerable to carbon loss.

Summary

Scientists from the University of Massachusetts, University of Arizona, and U.S. Geological Survey teamed with scientists from two U.S. Department of Energy (DOE) Office of Science user facilities, the Stanford Synchrotron Radiation Lightsource (SSRL) and Environmental Molecular Sciences Laboratory (EMSL), to examine deep soils that were 3 to more than 5 feet underground. These soils ranged in age from 65,000 to 226,000 years, and all had portions that had been impacted by the repeated growth of roots. A multi-institutional team of scientists used a suite of solid-phase analyses, including EMSL’s high-resolution Fourier-transform ion cyclotron resonance mass spectrometry and Mössbauer spectroscopy capabilities, other capabilities at SSRL, and scanning transmission X-ray microscopy at the Canadian Light Source. When combined, these techniques gave the team unique insights into the nature of associations between minerals and organic carbon compounds in the soil, including their specificity, particle size, and molecular composition. The patterns of root-driven weathering are in excellent agreement with the conditions found at locations with different soil types, climate, and vegetation. The fundamental processes discovered in this study may therefore be useful for modeling the impact of root activity on carbon storage in soils globally.

Principal Investigator

Marco Keiluweit
University of Lausanne, Switzerland
marco.keiluweit@unil.ch

Program Manager

Paul Bayer
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
paul.bayer@science.doe.gov

Funding

This work was supported by the Environmental System Science program within the U.S. Department of Energy’s (DOE) Biological and Environmental Research (BER) program under Award no. DE-SC0019477. A portion of this research was performed using the Environmental Molecular Sciences Laboratory (EMSL), a DOE Office of Science User Facility.

Related Links

• Getting to the Root of Carbon Storage in Deep Soils
• Using Soil to Combat Climate Change
• Deep Soils Have Dual Role in Global Carbon Cycle, New Study Shows

References