Document: JEF-3-34-36

Late season photosynthesis, chemistry and phenology of sun and shade leaves of sweetgum (Liquidambar styraciflua L.) trees after two years of CO₂ enrichment.

HERRICK, J.D.* and R.B.THOMAS

West Virginia University, Morgantown, WV 26506 ¹

Abstract:
The objective of this study was to determine whether elevated CO₂ affected leaf senescence of sweetgum (Liquidambar styraciflua L.) trees at the Duke/Brookhaven FACE experiment. A change in late season leaf phenology due to CO₂ enrichment, either accelerating or retarding senescence, could substantially affect seasonal carbon gain by these trees. In this study, experimental plots have been fumigated with elevated CO₂ (ambient plus 200 ml l^-1) since August 1996. During September, October and November of 1998, we measured light-saturated photosynthesis and chlorophyll content on the youngest and oldest leaves of four sun and shade shoots from six trees per CO₂ treatment. Older leaves had lower photosynthetic rates, chlorophyll content and senesced earlier than young leaves. Elevated CO₂ enhanced net photosynthesis at growth CO₂ concentration by 74% in the sun leaves and 35% in the shade leaves through the senescent period. The timing of decline of photosynthesis was not affected by CO₂ enrichment. Leaf chlorophyll content was not different between the elevated and ambient CO₂ treatments at any time during the experiment. Elevated CO₂ did not change the timing or rate of senescence in sun leaves. However, shade leaves appeared to initiate senescence slightly earlier under elevated CO₂, but the rate of senescence was not changed. In summary, we found very little CO₂ induced change in late season leaf characteristics of sweetgum trees in the Duke FACE experiment.

Keywords: FACE, senescence, gas exchange

This abstract is being presented at: 9:45 AM in session:
Oral Session #40: Elevated CO₂ In Forest Systems.