Seasonal Changes in Within-Canopy Allocation of 14C-Photosynthate by White Oak

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Seasonal changes in photosynthate translocation and allocation of two mature, co-dominant white oak trees were studied by following rates of movement of 14C-photosynthate from foliage labeled with 14CO2. Loss rates were determined by sampling foliage at 5 min and 1, 4, and 7 days after labeling on each of five dates (April 22-October 4). Incorporation of 14C-photosynthate into 1-, 3-, and 5-year-old branches was determined 7 days after tagging. Losses of 14C from leaves were rapid by day 1 (≤80 percent), greatly reduced by day 4, and ranged from 63 to 91 percent by day 7. Maximum retention of initial activity levels occurred in April for leaves (44 percent) and in October for branches (15 percent). Approximately equal apportionment of activity between leaves and branches did not occur until August. Highest total retention of photosynthate in the canopy occurred in April (due to high incorporation in leaves) and June (due to high retention in both leaves and branches). Based on measured retention and estimated respiration losses, translocation of the original 14C-photosynthate from the canopy was calculated to be approximately 0 percent in April, 30 percent in June, and 60 percent in October. These results indicate that canopy growth and maintenance impose a significant drain on availability of photosynthate throughout the growing season. Forest Sci. 25:361-370.

Keywords: Quercus alba; conversion kinetics; labile products; translocation

Document Type: Journal Article

Affiliations: University of Wisconsin at Stevens Point, Stevens Point, Wisconsin

Publication date: June 1, 1979

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