U.S. Department of Energy, Office of Science

Program for Ecosystem Research

Research Project   Community and ecosystem response to global change: interactive effects of atmospheric carbon dioxide, temperature, and soil moisture

Principal investigators:   Richard J. Norby and Aimee Classen

Project goal

Investigate potential interactive effects of elevated carbon dioxide concentration, increased air temperature, and altered soil water availability on aboveground and belowground structure and processes in a constructed old-field ecosystem containing C3 and C4 grasses, forbs, and legumes.

Old-field plants in the experiment (below). Old-field plants

Ecosystem being studied

Old field, or abandoned agricultural land, in east Tennessee. Old-field ecosystems are common and widespread around much of the world. The plant community that characterizes these ecosystems is typically dominated by short-statured, relatively short-lived plants, which facilitates whole-system manipulation and analysis within short, but ecologically important, time frames.


Significant main effects of treatments were observed for many response variables, including biomass production, leaf area index, community composition and diversity, species reproductive phenology, plant demography, leaf-level gas exchange, fine root production. For example, total plant production was 60% greater in wet than in dry plots, though total plant production was unaffected by warming or [CO2] treatments. Production of Andropogon, Solidago, and Plantago were 540%, 170%, and 290% greater, respectively, in warmed than ambient temperature plots, although species-specific production was little affected by watering or [CO2] treatments. Treatments of temperature, [CO2], and soil moisture were expected to interact and thereby control processes at scales ranging from leaf to ecosystem. Most response variables, however, did not respond to interactive effects of the treatments; exceptions include community phenology, soil respiration, and decomposition.

Why this is important

Human-caused changes in atmospheric composition and climate are likely to alter how natural communities and ecosystems change through time (succession), and may reduce their capacity to provide essential goods and services to humans. This project seeks to understand how changes in [CO2], temperature, and water might affect a diverse old-field ecosystem. It is important to study these ecosystems because they are widespread and affect the quality of human life (e.g., by sequestering carbon or reverting to forested landscapes). In addition, the diverse species composition in this experiment enables an investigation of how different plant species can respond to different environmental drivers, and to consider how biotic interactions, such as interspecies competition or facilitation, might affect the response of plant communities to multiple changes in the environment associated with energy production.

Research site

An open-top chamber used in the study, covered to prevent ambient precipitation from entering the chamber so that soil moisture can be experimentally regulated.


Old-field plant communities were constructed within open-top chambers in which air temperature (ambient, ambient+3 C), atmospheric [CO2] (ambient, ambient+300 ppm), and soil moisture (dry, wet) are manipulated in a randomized complete block, split-plot design.

Rainout shelters permit two levels of soil moisture as split-plots within each chamber. Seedlings of seven species characteristic of local old-fields were planted in the plots prior to initiation of treatments in May 2003.

In addition to recording environmental variables, aboveground and belowground plant production, plant community composition, reproductive and community phenology, leaf-level and net ecosystem exchange of carbon, litter and soil organic matter decomposition, availability of soil nitrogen and phosphorus, and gross mineralization of soil nitrogen are measured.

Further information is available at the project's website.


Aimee Classen, University of Tennessee

Richard J. Norby, Oak Ridge National Laboratory

Charles T. Garten Jr., Oak Ridge National Laboratory

Funding period:   March 2002 to present