Ramifications of varying atmospheric concentrations of reactive-odd nitrogen, ozone and carbon dioxide on the net ecosystem exchange of carbon in a northern deciduous forest: Human activities appear to be profoundly changing the chemical composition of the atmosphere. Partial pressures of carbon dioxide, odd-nitrogen oxides and ozone will most likely be higher in the future and will have both direct and indirect effects on plant performance. Past studies have suggested elevated CO2 stimulates growth in many plants, but this enhancement is often short-lived because of other limiting factors, most notably a lack of nitrogen for growth. The productivity of plants under elevated CO2 may also be influenced by other gases such as O3 and NOx. I propose to investigate the interrelationships among these gases using two approaches. First, by generating a descriptive model examining the relationship between NOx and O3 concentration on canopy-level uptake of CO2 at the University of Michigan Biological Station (UMBS). Second, by conducting fumigation experiments using varying concentrations of CO2, NOx, and ozone. Seedlings will be fumigated with varying partial pressures of NOx and CO2 to look for important threshold values and to develop a mechanistic model of plant carbon acquisition under fumigation. The assimilation rates observed in the fumigation experiment will be scaled up to the canopy level and compared to the observations made in the field.