U.S. Department of Energy, Office of Science

Program for Ecosystem Research

Research Project   The interaction of carbon sequestration and water availability along a subambient to elevated CO2 gradient

Principal investigator:   Robert B. Jackson

Project goal

Determine, by direct experiment, how the combination of increasing atmospheric carbon dioxide concentration and drought may affect several aspects of the functioning of U.S. southcentral grasslands, with a focus on soil microbial communities and changes in nutrient availability and cycling.


Part of the experimental tunnel system [photo: Andrew Procter].

Ecosystem being studied

Texas grasslands.


The experiments are underway.

Why this is important

The potential interactive effects of elevated atmospheric carbon dioxide concentration and altered availability of soil moisture on the structure and functioning of terrestrial ecosystems is one of the most important aspects of ongoing environmental changes associated with energy production. While the effects of elevated carbon dioxide concentration and the effects of limited water availability on terrestrial ecosystems are each well understood as single factors, the potential effects of the combination of elevated carbon dioxide concentration and limited soil moisture is more of an open question. Climate models predict that drying is likely to occur in the southcentral United States in the next several decades as a result of increasing atmospheric greenhouse gas concentrations (most notably, the increasing concentration of carbon dioxide associated with energy production), so the uncertainty about possible interactive effects of changes in carbon dioxide concentration and reduced soil moisture on terrestrial ecosystems is important in that region of the country.


The project will use the well-characterized experimental carbon-dioxide-concentration-gradient tunnel system at the USDA-ARS Blackland Prairie Research Center in Temple, Texas, to expose grassland mesocosms to carbon dioxide concentrations from about 200 to 560 ppm (the present mean global atmospheric carbon dioxide concentration is about 380-400 ppm, which is about 70 ppm, or more than 20%, greater than it was 50 years ago).

Three soil types are contained in the various experimental mesocosms so that interactions between carbon dioxide concentration, soil moisture, and soil type can be identified. The project uses a combination of well established, widely used techniques along with newer, advanced approaches to studying soil microbial population dynamics and nutrient cycling processes. Plant physiology and ecosystem net primary production are assessed with appropriate standard approaches.


Robert B. Jackson, Duke University

Noah Fierer, Duke University

Dafeng Hui, Duke University (now at Tennessee State University)

Richard A. Gill, Washington State University (subaward)

H. Wayne Pooley, USDA ARS (unfunded collaborator)

Hyrum B. Johnson, USDA ARS (unfunded collaborator)

P. Fay, USDA ARS (unfunded collaborator)

Chris Schadt, Oak Ridge National Laboratory (unfunded collaborator)

Funding period:   June 2006 to present