Light interception vs. total net photosynthesis

R. Ceulemans rceulem at
Thu Oct 12 14:53:07 EST 1995

(1) Chen has built a photosynthesis sub-model to our
FRACPO and CANLIP models which allows us to calculate
gross photosynthesis for different cells (clusters of
leaves at different depths in the canopy) in the canopy.
We are able to estimate whether these cells are
saturated or over-saturated with light for optimal 
photosynthesis. However, whether we can backwards try
to optimize photosynthesis is a different and more
difficult question.

(2) Our starting point has been the very close
relation between light interception and crop productivity
of most crops, incl. tree stands. See many papers on
agricultural crops and papers by Linder et al. on 
woody plants and trees. Therefor we have been primarily 
looking to light interception since it should determine
the overall potential productivity. From an ecophysiological
point of view and try to improve our understanding of the
tree functioning, photosynthesis might indeed be better.
However, from an overall yield standpoint, I think total
light interception is more logical.

(3) Yes, we have collected some data in the past that
show a trend of more vertically oriented leaves in the
upper toward more horizontal leaves in the lower part of
the canopy. This has been published by Lemeur, Impens et
al. in some IUFRO proceedings only. I could look it up
and send you a copy if you like. My own data from Puyallup
are less straightforward however, but the trend seems to
be there for the hybrid clones.

Reinhart Ceulemans

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