Applications of Free-Air CO<sub>2</sub> Enrichment (FACE) Technology to a Forest Canopy

Forest ecosystems occupy an important fraction of the planet's land cover. Understanding their exchanges of carbon with the atmosphere is crucial in projecting future net atmospheric CO<sub>2</sub> increases. It is also important that experimental studies of these processes be performed under conditions which are as realistic as possible, particularly with respect to photosynthesis and evapotranspiration. New technology now exists which represents perhaps the best hope of studying an undisturbed forest canopy under long-term enriched CO<sub>2</sub> conditions. Brookhaven National Laboratory (BNL) has developed a system for exposing field-grown plants to controlled elevated concentrations of atmospheric gases, without use of confining exchange processes. This system, called FACE for Free Air CO<sub>2</sub> Enrichment, uses a 23-27 m and has been proven in over 8000 hours of testing at three locations (BNL; Yazoo City, MS; and Maricopa, AZ) mainly on cotton.