Virtual Museum of Canada
Jardin botanique de Montréal 
Centre for Forest Research

Transcription of video clip The tree and its nutrients

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Source/Sink Relationships: From the producer (the leaves) to the consumer (the trunk and branches)

Sugars produced by the leaves are transferred by the tree to all its growing tissues. 90% of those sugars are directed towards the ground.
The basis behind that ratio, called the Pressler Law, becomes obvious if we modify it.

Graphic representation of a tree, based upon a source/sink mathematical model

© Philippe DeReffye, MengZhen Kang
The trunk and branches use the sugars produced by the leaves.

If you transfer more sugars towards the ground, the leaves and branches, malnourished, pay the price.

If you transfer fewer sugars towards the ground, now the trunk does not receive enough. It is not big enough to support the foliage's weight.

Graphic representation of a tree with a diminishing trunk

© Philippe DeReffye, MengZhen Kang
Less sugars, the trunk's width diminishes.

When it grows larger, the trunk must follow the source/sink relationship.

If the trunk doesn't ask for enough resources, the tree will be tall and lean, but will not hold upright.

If the trunk takes too many sugars the upwards growth of the tree is stopped, by lack of resources.

Fruits are another sink in which the tree invests resources. The more fruit it bears, the less resources this poplar will have spent for its growth.

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