WHOLE-PLANT C-14 PHOTOSYNTHATE ALLOCATION IN PINUS-TAEDA - SEASONAL PATTERNS AT AMBIENT AND ELEVATED OZONE LEVELS

Seedlings were grown in either ambient air or air enriched with ozone at twice-ambient levels. On 5 sampling dates during the 1987 growing season, seedlings were labeled with 14CO2, and whole-plant carbon budgets were constructed. Rate of assimilation of CO2 varied by a factor of 2 during the growing season, with a late spring maximum during the 1st growth flush. Respiratory losses were highest in spring, then declined sharply during summer when photosynthate allocation to the foliage increased rapidly. A 2nd major shift in the carbon budget occurred in the autumn when allocation to the fine roots increased at the expense of the foliage. No statistically significant effects of elevated ozone on either carbon gain or photosynthate allocation were detected at any specific time during the growing season, but seedlings grown at twice-ambient ozone levels consistently exhibited lower rates of CO2 assimilation, greater allocation of photosynthate to respiration, and corresponding reduction in photosynthate allocation to fine roots. An individual-fascicle 14C-labeling technique reflected seasonal patterns of carbon import and export by foliage and thus may serve as an acceptable surrogate for whole-tree tagging. -from Authors