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Effects of leaf age on the photosynthetic capacity of sweetgum after 5 years CO2 enrichment.
HERRICK, JEFFREY*,1, THOMAS, RICHARD1, 1 West Virginia University, Morgantown, West Virginia
ABSTRACT- We have been monitoring the effects of CO2 enrichment on photosynthetic capacity of sun and shade leaves of overstory sweetgum (Liquidambar styraciflua) trees for the past five years. Previously (1997-1999), we found no effect of CO2 on photosynthetic capacity of sun or shade leaves. In this study, we examined whether CO2 enrichment affected photosynthetic capacity of sweetgum trees differentially in younger and older leaves. The Duke Forest FACE experiment consists of three control plots and three plots that have been fumigated with elevated CO2 (ambient plus 200 l l-1) since August 1996. During June and September of 2000-2001, we measured A (net photosynthetic rate) versus Ci (calculated intercellular CO2) on sun and shade leaves as well as the oldest sun leaves. Elevated CO2 stimulated net photosynthesis (A) in young shade and sun leaves and the oldest sun leaves (P <0.05). The maximum rate of carboxylation (Vcmax, from A-Ci curves) and electron transport (Jmax) were not significantly affected by CO2 enrichment for all leaf types examined during 2000 and 2001. Young sun leaves had approximately 30% higher A, Vcmax and Jmax than the oldest sun leaves during September of 2000 and 2001 (P <0.05). Thus, we found no evidence of photosynthetic acclimation in sweetgum leaves after 5 years of treatment and, despite a decline in photosynthetic capacity with age, old sun leaves also did not acclimate to CO2 enrichment.
KEY WORDS: FACE, CO2, Photosynthesis