PHOTOSYNTHETIC AND STOMATAL RESPONSES OF GINKGO BILOBA TO HIGHLY ENRICHED ATMOSPHERIC CARBON DIOXIDE AND OXYGEN

Recent experimental studies on the photosynthetic rate, stomatal density and stomatal index of Ginkgo biloba have been effective in reconstructing paleo-CO₂ levels. However, few experimental studies have examined other environmental factors that can affect photosynthesis and stomatal frequency. Photosynthetic rate, stomatal index, and stomatal density data were collected from plants after experimental exposure to atmospheric content treatments within hyperbaric chambers at Duke University Medical Center (Durham, NC). Treatments include:

1. Control: no atmospheric alteration
2. Pressure: atmospheric pressure increased to 1.25 atm, but gas mix unaltered
3. CO₂: atmospheric pressure increased to 1.25 atm, CO₂ increased to 2000 ppm
4. O₂: atmospheric pressure increased to 1.25 atm, O₂ increased to 30%
5. CO₂&O₂: atmospheric pressure increased to 1.25 atm, CO₂ increased to 2000 ppm, and O₂ increased to 30%

Photosynthetic rate data were collected after a 24-hour acclimation period in all treatments, and after 1 month of acclimation for treatments A, C, and E. Stomatal density and stomatal index were measured from leaves formed under exposure to treatments A, C, and E.

Preliminary photosynthetic rate data indicate two interesting results: (1) increased CO₂ increased photosynthetic rate by a factor of 2 to 3, and (2) elevated oxygen, contrary to previous research, did not significantly inhibit photosynthesis at ambient CO₂. Both long and short acclimation periods gave similar gas exchange results. Stomatal density and index showed an unexpected positive relationship with CO₂, as well as a lack of significant oxygen effect. Future studies will examine additional replications of the gas composition treatments to verify gas exchange and stomatal results and will examine the effects of these treatments on the chemical composition of leaves produced under the different gas conditions.