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Title: DOES LEAF POSITION WITHIN A CANOPY AFFECT ACCLIMATION OF PHOTOSYNTHESIS TO ELEVATED CO2? ANALYSIS OF A WHEAT CROP UNDER FREE-AIR CO2 ENRICHMENT.

Author
item OSBORNE, COLIN - JOHN TABOR LAB UK
item LAROCHE, JULIE - BROOKHAVEN NATL LAB NY
item GARCIA, RICHARD - USDA-ARS-USWCL PHOENIX AZ
item Kimball, Bruce
item Wall, Gerard - Gary
item Pinter Jr, Paul
item La Morte, Robert
item HENDREY, GEORGE - BROOKHAVEN NATL LAB NY
item LONG, STEVE - JOHN TABOR LAB UK

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: The CO2 concentration of the atmosphere is increasing, which will probably affect plant growth and water use in the future. Focusing on one aspect, an experiment was constructed to determined how elevated CO2 affects photosynthesis of wheat. The experiment was conducted using a relatively new approach called free-air CO2 enrichment (FACE), whereby the CO2 is increased in the air above plots in an open field with no walls or root growth restrictions. The results showed that net photosynthetic uptake of CO2 over the course of a day was higher in all the leaves at elevated CO2 concentration than in their counterparts at the current ambient CO2 concentration. These results indicate that wheat production will probably increase in the future due to the higher CO2 concentrations which will benefit both growers and consumers of wheat and wheat products.

Technical Abstract: Previous studies of photosynthetic acclimation to elevated CO2 have focused on the most recently expanded, sunlit leaves in the canopy. We examined acclimation of photosynthesis to elevated CO2 in a vertical profile of leaves through a wheat canopy. The crop was grown at an elevated CO2 partial pressure of 55 Pa within a replicated field experiment, using free-air CO2 enrichment (FACE). Gas exchange was used to estimate in vivo carboxylation capacity and the maximum rate of RubP- limited photosynthesis. Net photosynthetic CO2-uptake was measured for leaves in situ within the canopy. Leaf contents of Rubisco, light- harvesting complex proteins (LHC) and total nitrogen were determined. Elevated CO2 did not affect carboxylation capacity in the most recently expanded leaf, but led to a decrease in lower, shaded leaves during grain development. Despite this acclimation, in situ photosynthetic CO2-uptake remained higher under elevated CO2. Acclimation at elevated CO2 was accompanied by decreases in both Rubisco and leaf nitrogen and an increase in LHC content. Elevated CO2 led to a larger increase in LHC/Rubisco in lower canopy leaves than in the uppermost leaf. Acclimation of leaf photosynthesis to elevated CO2, therefore, depended on both vertical position within the canopy and developmental stage.