Maintenance and Constructive Respiration, Photosynthesis, and Net Assimilation Rate in Seedlings of Pitch Pine (Pinus rigida Mill.)

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Abstract
Pitch pine seedlings were grown at constant temperature and photoperiod. Net CO2-uptake h−1 g−1 leaves decreased steadily during ontogeny until leaf production ceased. Thereafter, there was no change or a slight increase. Though the ontogenetic pattern was the same in populations native to different geographic areas, there were differences among populations in the rate of CO2-uptake. Root respiration, calculated from the difference between CO2-uptake and net assimilation rate, accounted for 6 to 69 per cent of diurnal assimilation. Growth of shoots and roots was episodic and out of phase. Spurts of growth could be forecast by high rates of respiration 4 weeks earlier, probably because high-energy syntheses precede the processes of cell elongation and cell wall formation. Maintenance and constructive respiration were substantially higher for the shoots (85 per cent leaf tissue) than for the roots. Constructive respiration was proportional to photosynthesis.