BER launches Environmental System Science Program. Visit our new website under construction!

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

BER Research Highlights

Carbon Release from Roots to Microbes Prevents Nitrogen Limitation Under CO2 Enrichment
Published: March 21, 2011
Posted: April 06, 2011

A forest’s ability to store carbon depends on resource limitations, such as nitrogen. The Progressive Nitrogen Limitation (PNL) theory suggests that under elevated CO2, a forest will immobilize nitrogen in biomass, limiting nitrogen needed for enhanced growth. DOE scientists show, for the first time, that mature trees exposed to CO2 enrichment increase the release of soluble carbon from roots to soil, and that such increases are coupled to the accelerated turnover of nitrogen pools in the rhizosphere. Over the course of three years, the team measured in situ rates of root exudation from intact loblolly pine (Pinus taeda L.) roots at the Duke Forest, near Chapel Hill, North Carolina. Trees fumigated with elevated CO2 increased exudation rates by 55% during the primary growing season, leading to a 50% annual increase in dissolved organic inputs to fumigated forest soils. These increases in root-derived carbon were positively correlated with microbial release of extracellular enzymes involved in breakdown of organic nitrogen in the rhizosphere, indicating that exudation stimulated microbial activity and accelerated the rate of soil organic matter turnover. Trees exposed to both elevated CO2 and nitrogen fertilization did not increase exudation rates and had reduced enzyme activities in the rhizosphere. These results provide field-based empirical support suggesting that sustained growth responses of forests to elevated CO2 in low fertility soils are maintained by enhanced rates of microbial activity and nitrogen cycling fuelled by inputs of root-derived carbon. However, the decomposition of soil organic matter by the stimulated microbes may prevent a large soil carbon pool from accumulating in forest soils.

References: Phillips, R. P, A. C. Finzi, and E. S. Bernhardt. 2011. “Enhanced Root Exudation Induces Microbial Feedbacks to N Cycling in a Pine Forest Under Long-Term CO2 Fumigation,” Ecology Letters 14, 187–94.

Drake, J. E, A. Gallet-Budynek, K. S. Hofmockel, E. S. Bernhardt, S. A. Billings, R. B. Jackson, K. S. Johnsen, J. Lichter, H. R. McCarthy, M. L. McCormack, D. J. P. Moore, R. Oren, S. Palmroth, R. P. Phillips, J. S. Pippen, S. G. Pritchard, K. K. Treseder, W. H. Schlesinger, E. H. DeLucia, and A. C. Finzi. 2011. “Increases in the Flux of Carbon Belowground Stimulate Nitrogen Uptake and Sustain the Long-Term Enhancement of Forest Productivity Under Elevated CO2,” Ecology Letters 14, 349–57.

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

  • Research Area: Terrestrial Ecosystem Science
  • Research Area: Carbon Cycle, Nutrient Cycling
  • Research Area: Free Air CO2 Enrichment (FACE)

Division: SC-33.1 Earth and Environmental Sciences Division, BER


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

Recent Highlights

Mar 23, 2021
Molecular Connections from Plants to Fungi to Ants
Lipids transfer energy and serve as an inter-kingdom communication tool in leaf-cutter ants&rsqu [more...]

Mar 19, 2021
Microbes Use Ancient Metabolism to Cycle Phosphorus
Microbial cycling of phosphorus through reduction-oxidation reactions is older and more widespre [more...]

Feb 22, 2021
Warming Soil Means Stronger Microbe Networks
Soil warming leads to more complex, larger, and more connected networks of microbes in those soi [more...]

Jan 27, 2021
Labeling the Thale Cress Metabolites
New data pipeline identifies metabolites following heavy isotope labeling.

Analysis [more...]

Aug 31, 2020
Novel Bacterial Clade Reveals Origin of Form I Rubisco

  • All plant biomass is sourced from the carbon-fixing enzyme Rub [more...]

List all highlights (possible long download time)