Translocation of 14C in ponderosa pine seedlings
The movement of 14C from the old needles to the roots, and later to the new needles, was measured in 2-year-old ponderosa pine seedlings. The seedlings were in one of three growth stages at the time of the feeding of 14CO2: 9 days before spring bud break with no root activity; 7 days before spring bud break with high root activity; and 7 days after spring bud break with moderate root activity. The form of the curves of count rate plotted against time are similar for a given plant part. Immediately after being fed 14CO2, year-old needles had high 14C count rates which dropped rapidly, leveled out within 7 to 10 days, and reached a steady state residual count rate after 10 to 20 days. The decrease in count rate from the old needles was followed by an increase in count rate by the root tip and (or) the new needles. The count rate of the root tips increased from background to a peak within 3 to 7 days, then decreased for the duration of the study. The details and timing of movement of 14C to and from plant parts was a function of the growth state at the time of 14CO2 feeding.