Sink Strength in Relation to Allocation

Various centers of metabolic activity exhibit a high demand for photosynthates such that there is competition within the plant for available resources. Thus, during the development of the plant, at any moment in time, there exists a dominance hierarchy for photosynthates. In the Jerusalem artichoke, photosynthetically fixed carbon resources are allocated among maintenance reactions, production of additional structural components, and deposition within specialized storage sites within the plant. The allocation hierarchy shifts not only as the plant develops, but also in diurnal cycles. Therefore, photosynthate allocation depends upon both timing and assimilate availability. 

Sink strength is a measure of the sink s ability to accrue photosynthates, and the rate of change in dry weight of a particular sink is considered indicative of its competitive ability within the plant. 

Biology and Chemistry of Jerusalem Artichoke Helianthus tuberosus L. 

During initial development, structural growth generally has a higher priority in the hierarchical scheme of photosynthate distribution than stem and tuber storage sites. The relative importance of structural development is illustrated by the fact that after severe defoliation, the stem and leaves have the highest priority for assimilates as the plant reestablishes its carbon fixation intrastructure (Swanton and Cavers, 1989). 

It has been nearly a century and a half since Boussingault (1868) presented the hypothesis that the accumulation of assimilates in an illuminated leaf may be responsible for a reduction in the net photosynthetic rate of that leaf. According to the Munch hypothesis for phloem transport, the greater the sink strength, the greater the depression in solute concentration in the phloem at the sink. This increases the concentration differential between the source and sink, creating the hydrostatic pressure head that drives the system. 

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