Formation and distribution of food reserves during autumn and their subsequent utilization in jack pine

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Abstract
Five Pinus banksiana (Lamb.) seedlings were fed 50 μCi of 14CO2 (1 Ci = 37 GBq) per seedling in August and at 2-week intervals another set of five trees was fed until December for a total of 10 feedings. Trees of each set were sampled from January to June, in their dormant frost hardy phase and in their growing phase. Sampled trees were separated into needles, bark, xylem, and roots, freeze-dried, and ground. Samples of ground tissues were extracted sequentially for saponifiable and nonsaponifiable lipids, starch, lignin, hemicelluloses, and cellulose. Some protein, amino acids, and sugars were also extracted.In the dormant trees the total amount of 14C in the tissues decreased from August to December except for the needles where it increased towards December. Considerable amounts of 14C occurred in the structural components of the early feedings. The 14C distribution among the chemical components within the tissues was fairly similar over the entire feeding period except for an increase in root starch, xylem lipids, and sugars. No 14C occurred in the amino acids. A drastic reduction in 14C occurred with the onset of growth from all chemical components and little 14C occurred in the new growth.The photosynthate produced during the autumn contributes substantially more to respiration than to the buildup of reserves. In conifers the important forms of food reserves are carbohydrates and lipids. There is an increase in lipid synthesis in early fall which is chiefly restricted to the xylem. All tissue components of the tree are important for storage of food reserves but they are not of equal importance simultaneously. Food reserves do not play a direct role in wood formation of the secondary meristem which is dependent on current photosynthate. Some hemicelluloses appear to be a form of food reserve in trees.