Carbon “Fertilization” Limited by Nitrogen Availability


DOE’s investments in a long-term Free-Air CO2 Enrichment (FACE) experiment at the Oak Ridge National Laboratory are providing important insights into the role of terrestrial ecosystems in climate change. Increasing atmospheric carbon dioxide levels have been predicted to result in enhanced plant uptake and growth, providing a dampening influence on climate change. This negative feedback process is represented in most coupled Earth system models and has been shown to be an area of sensitivity for future climate projections. While the ORNL FACE experiment showed strong CO2 “fertilization” effects for the first five years of the experiment, in subsequent years that effect declined dramatically. Results suggest that this decline was the result of nitrogen limitation. This finding reinforces the need to include nitrogen cycles in Earth system models and a revision of our expectations for ability of plants to take up additional atmospheric CO2.


Norby, R. J., J. M. Warren, C. M. Iversen, B. E. Medlyn, and R. E. McMurtrie. 2010. “CO2 Enhancement of Forest Productivity Constrained by Limited Nitrogen Availability,” Proceedings of the National Academy of Sciences 107(45), 19368–73. DOI: 10.1073/pnas.1006463107 PNAS.