Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/6/1999
Publication Date: N/A
Citation: N/A Interpretive Summary: The atmospheric carbon dioxide concentration has risen nearly 20 percent in this century and is expected to reach a doubling of pre-industrial revolution levels by the middle of the next century. Carbon dioxide, as the essential substrate for photosynthetic carbon reduction, is the fundamental building block of carbon-based life on this planet. With a future that portends such dramatic and rapid changes in atmospheric carbon dioxide, it is vital that we understand the differential response of photosynthesis across species as these changes are expected to differentially advantage certain species. Thus, the rapid increase in carbon dioxide may drive profound changes in the composition of natural plant communities that would in turn have far reaching effects on natural resources, land use and conservation biology. The work reported here was conducted in the Free Air Carbon Enrichment facility currently operating in the Duke Forest. We have investigated the effect of a doubling of carbon dioxide on the photosynthetic efficiency of forest understory trees as a predictor of differential competitiveness. These results form the basis for further work culminating in a quantitative assessment of elevated carbon dioxide on forest floor productivity.
Technical Abstract: Chlorophyll fluorescence and leaf gas analysis measurements were conducted in FACE rings on understory woody species in order to evaluate the effects of carbon dioxide enrichment on perennial deciduous plants growing in a limited light environment. Eastern redbud (Cercis canadensis) was qualitatively representative of the behavior that we observed for all understory woody perennials that we investigated. The operational quantum efficiency in the control FACE rings, peaked in late morning, declined through the afternoon and recovered during the early evening. Although a decline in leaf stomatal conductance was observed to qualitatively mimic the decline in photosynthetic efficiency, undiminished Ci values revealed that the decline in stomatal conductance could not directly explain the diurnal decline in photosynthetic efficiency. Chlorophyll fluorescence measurements revealed that changes in antenna quenching paralleled diurnal changes in the operational quantum efficiency. Thus, while it is clear that the supply of carbon dioxide to the intercellular air spaces of the leaf and the biochemical demand for carbon dioxide remained metabolically balanced throughout the day, it is not known which is driving the decline in efficiency and which is adjusting to reestablish the balance. Measurements taken in the carbon dioxide enriched rings showed that the daily decline in photosynthetic efficiency was not as severe and the onset of the decline was delayed until later in the day.