A physiological and mathematical study of the growth and productivity of a Calluna-Sphagnum community. 3. Distribution of photosynthate in Calluna vulgaris L. Hull.
The time course of changes in the quantity of Calluna leaves and wood were measured during 1971 and an analysis of the data used to derive the seasonal pattern of photosynthate utilization. Budbreak began when the (max. + min.)/2 temperature reached 7.2 deg C. The early part of the season was associated with leaf growth, accompanied by a fall in the sugar reserves of the plant. The middle of the season was devoted to the formation of the wood increment, and the end of the season was dominated by leaf growth, which ceased when the temperature had fallen to 7.4 deg C. Total leaf production (6.5 g/plant) was considerably greater than wood production (2.8 g/plant). A laboratory experiment involving 14CO2 demonstrated that the photosynthate pool sizes in Calluna were large in relation to the C throughput rate, as suggested from analysis of leaf sugar content. The pattern of labelling in the ethanol-soluble fraction suggested that the metabolite pools in the leaf do not equilibrate rapidly with those in the wood. A tentative scheme of the relationship between photosynthate production and utilization is proposed.