Dynamics of Photoassimilated Carbon in Douglas Fir Seedlings

The relations between CO(2) uptake, translocation, and carbon accumulation in several vegetative components of Douglas fir seedlings (Pseudotsuga menziesii [Mirb.] Franco) have been quantified using (14)CO(2). Seedlings were exposed to a constant specific radioactivity of (14)CO(2) and a repeating daily pattern of temperature and light for 4 consecutive days. Results of (14)C analysis, which indicated a transitory pattern of photoassimilated carbon movement, were extrapolated to a "steady rate" using a compartment analysis. Accumulation rates of photoassimilated carbon, relative to tissue carbon, were new needles, 0.94%/day, old needles, 1.14%/day, new shoots 0.38%/day, stem, 0.16%/day, and roots, 0.50%/day. Therefore, the source of carbon, the needles, is also the strongest sink.