Seasonal Pathways of 14 C-Photosynthate In Red Pine Labeled in May, July, and October

The seasonal pathways of 14 C-photosynthate were followed in the major organs and constituents of 4-year-old red pine seedlings labeled in May, July, and October. The distribution of 14 C-labeled assimilates among plant parts was related to the intensity of tissue development in those parts at exposure time. A relatively large proportion of May- 14 C was channeled into the cell wall fraction of elongating shoots and needles while a large proportion of October- 14 C was channeled to growing roots. Individual plant organs retained a large percentage of assimilates once they obtained them. Redistribution of October- 14 C was more active than May- 14 C or July- 14 C since a large proportion of October- 14 C was fixed in reserves. Regardless of exposure date, 70 percent or more of the activity in the noncell wall fraction was in constituents other than carbohydrates, primarily lipids and nitrogenous compounds. Relative counts in the sugar fraction remained about the same for all exposures at all times of the year since sugars are probably the central metabolic pool in the redistribution of 14 C. Forest Sci. 16:1-13.