Photosynthetic acclimation to elevated CO2 in a sunflower canopy |
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Authors: | Sims D; Cheng W; Luo Y; Seemann J |
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Institution: | Department of Biology and Microbiology, California State University, Los Angeles, CA 90032, USA; Louisiana State University, Baton Rouge, LA, USA; University of Oklahoma, Norman, OK, USA; University of Nevada, Reno, NV, USA; Corresponding author; Fax: +1 323 343 6451; E-mail: dsim3@calstatela.edu |
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Abstract: | Sunflower canopies were grown in mesocosom gas exchange chambers at ambient
and elevated CO2 concentrations (360 and 700 ppm) and leaf photosynthetic
capacities measured at several depths within each canopy. Elevated CO2]
had little effect on whole-canopy photosynthetic capacity and total leaf
area, but had marked effects on the distribution of photosynthetic capacity
and leaf area within the canopy. Elevated CO2] did not significantly
reduce the photosynthetic capacities per unit leaf area of young leaves at
the top of the canopy, but it did reduce the photosynthetic capacities of
older leaves by as much as 40%. This effect was not dependent on the canopy
light environment since elevated CO2] also reduced the photosynthetic
capacities of older leaves exposed to full sun on the south edge of the
canopy. In addition to the effects on leaf photosynthetic capacity,
elevated CO2] shifted the distribution of leaf area within the canopy so
that more leaf area was concentrated near the top of the canopy. This
change resulted in as much as a 50% reduction in photon flux density in the
upper portions of the elevated CO2] canopy relative to the ambient CO2]
canopy, even though there was no significant difference in the total canopy
leaf area. This reduction in PFD appeared to account for leaf carbohydrate
contents that were actually lower for many of the shaded leaves in the
elevated as opposed to the ambient CO2] canopy. Photosynthetic capacities
were not significantly correlated with any of the individual leaf
carbohydrate contents. However, there was a strong negative correlation
between photosynthetic capacity and the ratio of hexose sugars to sucrose,
consistent with the hypothesis that sucrose cycling is a component of the
biochemical signalling pathway controlling photosynthetic acclimation to
elevated CO2]. |
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