Seasonal Allocation of Photoassimilated Carbon in Douglas Fir Seedlings

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Abstract
The uptake of CO2 by Douglas fir (Pseudotsuga menziesii [Mirb.] Franco) seedlings and the allocation of photoassimilated C among 5 vegetative tissues were closely related to seedling phenology. In May, newly flushing needles required 5.2% day-1 to photoassimilated C relative to needle tissue C. As these needles matured, this C requirement declined to 1.95% day-1 in Aug., to 0.94% day-1 in Nov., and to 0.76% day-1 in Jan. Other tissues of Douglas fir seedlings required different amounts of photoassimilated C for growth and metabolism. These data provide a strong link between daily CO2 uptake and the regulation of C allocation by seasonal phenology. The data, obtained with long term labeling with 14CO2, were analyzed with a compartment model representing the dynamic flux of C through the seedlings.