text: Elevated CO 2 increased the average steady-state photosynthetic rates of four hardwood understory saplings by 60 and 40% under high and low light conditions, respectively. In going from shaded to lighted conditions, elevated CO 2 had no effect on photosynthetic induction, with ambient and CO 2 -enriched species both reaching 90% of their maximal transient photosynthetic rates at approximately the same time. However, in going from lighted to shaded conditions, elevated CO 2 extended the time during which maximal rates of photosynthesis were maintained. Thus, elevated CO 2 slowed the rate of photosynthetic decline caused by the onset of shading. Consequently, shaded leaves of CO 2 -enriched saplings maintained greater rates of photosynthesis for longer periods of time than did shaded leaves of saplings growing in ambient air, which allowed the CO 2 -enriched leaves to sequester greater amounts of carbon than was expected from photosynthetic measurements made under steady-state conditions.