Photosynthesis and photosynthate distribution in Douglas-fir strobili grafted to young seedlings

In Douglas fir, scions bearing female strobilus buds were grafted to young seedlings. As the strobili developed, examination was made of the effect of their presence on photosynthesis and photosynthate distribution within the plant. At different times, the conelets constituted between 7% and 21% of the total dry weight of the plants.The presence of conelets did not significantly affect the photosynthetic rate of the leaves. It did, however, significantly alter the proportionate distribution of assimilates by restricting the amount of 14 C photosynthate available for vegetative growth, particularly that of the roots and the current season's shoots.The conelets themselves had an appreciable rate of photosynthesis as shown by infrared gas analysis, 14-carbon labeling, and autoradiography. Per unit of chlorophyll, conelets were apparently some six times as efficient photosynthetically as leaves; per unit of dry weight, however, they were slightly less efficient than leaves.