What was done
Open-top chambers were erected within a natural scrub-oak community located in Florida, USA, and fumigated with 350 and 700 ppm CO2 to determine the effects of elevated CO2 on leaf senescence in Quercus myrtifolia.  Senescence was monitored by measuring leaf chlorophyll content, nitrogen content, and rubisco activity over a four-month winter season when leaf abscission naturally occurs for year-old leaves in this perennial species.

What was learned
Elevated CO2 clearly delayed the onset of leaf senescence in this species.  Year-old leaves on trees growing in ambient air that were monitored during the four-month period displayed 75, 52, and 82% reductions in leaf chlorophyll content, nitrogen content and rubisco activity, respectively, relative to newly expanded leaves on the same trees.  In contrast, leaf chlorophyll content, nitrogen content and rubisco activity in year-old leaves of CO2-enriched trees were not significantly different from those of newly expanded leaves on the same trees, except for nitrogen content, which was only reduced by 25% in year-old leaves.

These phenomena allowed leaves of the CO2-enriched trees to photosynthesize at much higher rates than leaves of trees growing in ambient air.  At the end of the four-month period when senescence was close to complete in the ambient CO2 treatment, for example, CO2-enriched leaves exhibited photosynthetic rates that were 97% greater than leaves of trees growing in ambient air.

What it means
As the atmospheric CO2 concentration continues to rise, it is likely that Quercus myrtifolia trees will exhibit slower rates of leaf senescence, thereby extending the amount of time that leaves can actively engage in carbon fixation.  As a direct consequence of this phenomenon, scrub-oak communities dominated by this species should exhibit increasing rates of carbon sequestration with continuing increases in the air's CO2 concentration.