9652581 Norby The response of natural ecosystems to an increasing concentration of CO2 in the atmosphere is a key component of analyses of the current and potential impact of global change. Efforts to understand how eastern deciduous forests will be affected by CO2 enrichment of the atmosphere have heretofore been addressed by studying components of the forest system (individual small trees, specific processes), but it is now time to take the critical leap to measuring the integrated response of an intact forest ecosystem with a focus on stand-level mechanisms. A free-air CO2 exposure (FACE) facility being assembled on the Oak Ridge National Environmental Research Park provides a mechanism for studying stand-level responses. The facility in a closed-canopy, 11m tall sweetgum monoculture will expose trees continuously to CO2 concentrations 200 PPM above ambient. The scientific tasks are organized around an interconnected set of hypotheses that address the essential features of a forest stand and how these features could influence responses to CO2. The objectives of these tasks are to characterize aboveground tree growth and leaf area in relation to CO2 concentration and interannual variation in other environmental factors; determine physiological mechanisms of response, including foliar gas exchange, plant water relations, respiration and tissue biochemistry; quantify fine root density and turnover and other components of soil carbon cycling; quantify the critical components of the nitrogen cycle and their response to CO2 enrichment; and use a mechanistic, process-based, soil-plant ecosystem model to develop and refine hypotheses of ecosystem response to elevated CO2. The results of these analyses will be used for modeling and assessment of potential global change impacts. The Oak Ridge FACE facility will be a user facility, open to researchers from universities and other research laboratories who are interested in pursuing other questions relevant to forest response to elevated C O2.
