U.S. Department of Energy Office of Biological and Environmental Research

BER Research Highlights

The Priming Effect: How Plant Root Exudates Make Soil Carbon More Susceptible to Microbial Degradation
Published: March 30, 2015
Posted: April 07, 2015

Rates of decompositional processes performed by soil microbes are influenced by a variety of factors including temperature, water availability, and the presence of minerals. As plant materials are broken down by microbes, released organic carbon compounds can bind to soil minerals, becoming much less accessible to further decomposition. These bound pools of organic carbon can be stored in soils for years, decades, or centuries depending on local site conditions. However, microbiologists have long observed a phenomenon known as “the priming effect,” in which the addition of small amounts of unbound organic carbon results in microbial degradation of older pools of mineral-bound soil carbon. Elevated atmospheric CO2 levels recently have been shown to cause plant roots to increase their secretion of small carbon molecules (“exudates”), which has significantly increased the importance of understanding how the priming effect works. In a recent study, a team of scientists co-led by Lawrence Livermore National Laboratory and Oregon State University used a combination of microbial community analysis and high-resolution mass spectrometry (NanoSIMS) to examine the mechanistic basis of the priming effect in soil microcosms. When a variety of different carbon compounds associated with root exudates were added to the soils via an artificial root system, they were shown to directly disrupt associations between older carbon and soil minerals. Liberated carbon was rapidly consumed by soil microbes, and the team was able to follow correlated shifts in microbial community composition and elevated CO2 production. Different types of exudate compounds had varying degrees of ability to strip stored carbon from minerals, a particularly significant observation since elevated atmospheric CO2 shifts both the amounts and types of exudates that plants produce. These results represent a new breakthrough in understanding the molecular-scale mechanisms underlying the priming effect and could significantly advance our ability to predict impacts of climate change on carbon cycling in terrestrial ecosystems.

Reference: Keiluweit, M., J. J. Bougoure, P. S. Nico, J. Pett-Ridge, P. K. Weber, and M. Kleber. 2015. “Mineral Protection of Soil Carbon Counteracted by Root Exudates,” Nature Climate Change, DOI: 10.1038/NCLIMATE2580. (Reference link)

Contact: Joseph Graber, SC-23.2, (301) 903-1239
Topic Areas:

  • Research Area: Subsurface Biogeochemical Research
  • Research Area: Carbon Cycle, Nutrient Cycling
  • Research Area: Microbes and Communities
  • Research Area: Structural Biology, Biomolecular Characterization and Imaging

Division: SC-23.2 Biological Systems Science Division, BER


BER supports basic research and scientific user facilities to advance DOE missions in energy and environment. More about BER

Recent Highlights

Aug 24, 2019
New Approach for Studying How Microbes Influence Their Environment
A diverse group of scientists suggests a common framework and targeting of known microbial processes [more...]

Aug 08, 2019
Nutrient-Hungry Peatland Microbes Reduce Carbon Loss Under Warmer Conditions
Enzyme production in peatlands reduces carbon lost to respiration under future high temperatures. [more...]

Aug 05, 2019
Amazon Forest Response to CO2 Fertilization Dependent on Plant Phosphorus Acquisition
AmazonFACE Model Intercomparison. The Science Plant growth is dependent on the availabi [more...]

Jul 29, 2019
A Slippery Slope: Soil Carbon Destabilization
Carbon gain or loss depends on the balance between competing biological, chemical, and physical reac [more...]

Jul 15, 2019
Field Evaluation of Gas Analyzers for Measuring Ecosystem Fluxes
How gas analyzer type and correction method impact measured fluxes. The Science A side- [more...]

List all highlights (possible long download time)