What was done
One-year old Ginkgo saplings were grown in greenhouses with atmospheric CO2 concentrations of 350 and 560 ppm for three years to study the effects of elevated CO2 on stomatal responses and photosynthesis in this species.

What was learned
After three years of atmospheric CO2 enrichment, leaves of plants grown at 560 ppm CO2 exhibited significant reductions in stomatal density and stomatal index, compared to leaves of plants grown at ambient CO2.  In fact, the stomatal density of CO2-enriched leaves was similar to that measured on fossilized Ginkgo leaves dating back to the Triassic and Jurassic time periods.

After analyzing various photosynthetic characteristics, the authors determined that no significant differences in photosynthesis existed between plants of either CO2 regime.  Rubisco activity, for example, was similar in all plants regardless of growth CO2 concentration, suggesting that down regulation does not occur in this Gingko species.  However, because the CO2-induced reductions in stomatal density and index did not impact rates of photosynthesis, it can be inferred that the water-use efficiencies of ancient Ginkgo species living in the Triassic and Jurassic were much higher than those of their modern counterparts of this dispensation.  And as the CO2 concentration of the air continues to increase, it may, in the words of the authors, "contribute to restoring the function of this 'living fossil' species back to that more representative of its long geological history."

What it means
As the air's CO2 content continues to rise, it is likely that Ginkgo biloba will experience decreased leaf stomatal density and index, much as its ancient relatives did in the high CO2 greenhouse world that once existed.  The induction of these phenomena will likely increase the water-use efficiency of this species and allow it to grow larger and perhaps withstand drought conditions better than it currently does under present atmospheric CO2 concentrations.