Partitioning of current photosynthate to different chemical fractions in leaves, stems, and roots of northern red oak seedlings during episodic growth

The episodic or flushing growth habit of northern red oak (Quercus rubra L. ) has a significant influence on carbon fixation, carbon transport from sou rce leaves, and carbon allocation within the plant; however, the impact of episodic growth on carbon partitioning among chemical fractions is unknown. Median-flush leaves of the first and second flush were photosynthetically labeled with (CO2)-C-14, and partitioning of C-14 into lipids and pigments, sugars, amino acids, organic acids, protein, starch, and structural carboh ydrates of source leaves, stem, and roots was determined. In addition, four chemical fractions (sugars, starch, amino acids, and total structural carb ohydrates) were quantitatively analyzed in leaves, stems, and roots. Chemic al changes in source leaves reflected leaf maturation, changing sink demand during a growth cycle, and leaf senescence. Starch and sugar storage in le aves, stems, and roots during lag and bud growth stages indicate a feedback response of these tissues to decreasing sink strength and temporary storag e of both starch and sugar in these plant tissues. Northern red oak, with e pisodic shoot growth patterns, provides an experimental system in which lar ge changes in sink strength occur naturally and require no plant manipulati on. Metabolic changes in leaf, stem, and root tissue of red oak have broad application for other oak species and for both temperate and tropical tree species with cyclic growth habits.