The diffusion resistance of the leaf boundary layer is different locally with the individual leaves, and it has an effect on the photosynthetic rate (
P). Therefore, it is expected that the local difference of the boundary layer resistance makes individual leaves produce the distribution patterns of
P. Then, bush beans were used as an example crop and experiments were carried out under various air flow conditions.
The distribution patterns of
P were determined by the difference of concentration of assimilatory starch in leaves. Starch was made to appear brown color by means of the iodine test method, and its concentration was quantitatively measured by means of Photo-Pattern Analyzer and divided into 4 levels. The results are as follows;
1) When the attack angle of air to a leaf (α) is 0°, higher parts of
P are distributed at both the leading edge and side tip of leaves.
2) The distribution patterns of
P are almost uniform when α is positive, in other words when the air flow runs against the leaf's abaxial surface.
3) When α is negative, higher parts of
P are distributed around the course of the air flow which turns around slant leading edges of the delta shaped leaves, while for rectangular shaped leaves they distributed around the side and trailing edges like a horseshoe shape.
4) When α is ±60°, distribution of
P is low at the center of leaves.
5) When the leaves vibrate freely in the turbulent air flow, higher parts of
P are distributed at the front margine of leaves, which correspond to the thinner parts of equivalent viscous sublayers.
As mentioned above, the distribution of
P of a single leaf agrees well with that expected from the detailed analysis of the boundary layer structure for model leaves. From these results it has been confirmed that the slight difference of the leaf-boundary layer produces a great effect on the photo-synthetic rate of a single leaf.
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