Redistribution of ¹⁴ C-Labeled Reserve Food in Young Red Pines During Shoot Elongation

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Abstract To study the role of food reserves in shoot elongation, we fed 14 CO2 photosynthetically to 1- and 2-year-old needles of young red pines late in the growing season and measured dry weight of plant parts and redistribution of 14 C during the next season's elongation growth. We also measured CO2 exchange during initial elongation growth. No massive movement of 14 C from either age class of needles into structural tissue of the developing shoot occurred under our conditions. However, 1-year-old needles appeared to be largely responsible for the initiation and maintenance of shoot elongation, and probably contributed in three ways: (1) by translocation of current photosynthate to the bud during the prior growing season, (2) by mobilization of reserves to meet immediate post-dormancy respiratory demands, and (3) by the provision of current photosynthate shortly after the beginning of bud extension. The relative importance of the three is probably heavily dependent on environmental

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