Part 4: Water and assimilate movement

5. Sink strength

Each organ which acts as a sink in a plant has a different sink strength. Organs can have different strengths at different points in their lives depending on how active they are, or how quickly they are growing.

The high investment of a plant putting its resources into a sink pays back when that sink then provides an important function for the plant such as becoming a source (a leaf photosynthesising), or carrying out reproduction (producing flowers, seeds and fruit), providing stability and structure (roots and stems) or storing energy for the following year (tuber).

Sinks compete for assimilates. When a young plant is developing, the sinks which are the growing shoot and growing root compete for sugars for growth. The development of both of these is important, as the shoot will photosynthesise to produce more assimilates, and the root will uptake water and nutrients, which is essential for the photosynthesis. It is important that neither of the organs takes too large a proportion of the assimilates, otherwise the other organs will suffer and the plant will not be successful.