Seasonal allocation of photoassimilated carbon in douglas fir seedlings.

The uptake of CO(2) by Douglas fir (Pseudotsuga menziesii [Mirb.] Franco) seedlings and the allocation of photoassimilated carbon among five vegetative tissues were closely related to seedling phenology. In May, newly flushing needles required 5.2% day(-1) of photoassimilated carbon relative to needle tissue carbon. As these needles matured, this carbon requirement declined to 1.95% day(-1) in August, to 0.94% day(-1) in November, and to 0.76% day(-1) in January. Other tissues of Douglas fir seedlings required different amounts of photoassimilated carbon for growth and metabolism. These data provide a strong link between daily CO(2) uptake and the regulation of carbon allocation by seasonal phenology.The data, obtained with long term labeling with (14)CO(2), were analyzed with a compartment model representing the dynamic flux of carbon through the seedlings.