[VIPS] Ideotype question (fwd)

'Toby' H D Bradshaw toby at u.washington.edu
Wed Oct 11 15:56:03 EST 1995

Forwarded from Rongling Wu, University of Washington

-Toby Bradshaw
toby at u.washington.edu

---------- Forwarded message ----------
Date: Tue, 3 Oct 1995 12:43:14 -0700 (PDT)
From: Rongling Wu <nfl at u.washington.edu>
> Reinhart and Siguo, your models seek to maximize light interception at the
> canopy level, if I'm reading the papers correctly.  Don tells me that, on
> a per-leaf basis, photosynthesis is light-saturated at levels quite a bit
> below full sun.  I have a couple of questions: 
> 1) Is there a way for your models to maximize net photosynthesis at
> 	the canopy level, instead of light interception, by tailoring
> 	leaf orientation to capture only the amount of light necessary
> 	to saturate photosynthesis, and letting the rest through to
> 	the leaves lower in the crown?  I realize that this would
> 	take some tinkering since you'd be trying to optimize over
> 	days and seasons when the angle/intensity of the sun is
> 	also changing, but you seem to be able to do this for
> 	light interception already.
	- My model was just based on maximum net photosynthesis at the canopy
	  level.  We tried to find optimal distribution patterns with a 
          canopy for key physiological processes, such as photosynthetic 
	  capacity and nitrogen content per unit of leaf area, given maximum
	  photosynthetic production.  These distrubition patterns were 
          surprisingly relied on how light radiation declines from the 
	  top to bottom of the canopy.  If photosynthetic capacity (and 
	  therefore nitrogen content) decreases exponentially with depth 
          of the canopy as light and the coefficient of light extinction 
          is small, we can expect the maximization of the whole canopy 
          photosynthesis.  This finding can be intepretted in terms of 
	  leaf display with the canopy (Don Dickmann et al. 1990, in Tree 
	  Physiol.).  Vertical leaves in th top, in conjunction with horizontal 
	  leaves in the bottom, allow for more light to go through the entire 
	  canopy, and such structure has a low coefficient of light extinction.
	  Our results derived from modelling have been empirically observed in 
	  annual plants (e.g., Field, Hirose, and others) but not forest 
          trees yet.

> 2) Would it make sense to even try to optimize photosynthesis
> 	rather than just light interception?

	- Yes. See above.

> 3) Don tells me that a generalized leaf ideotype would have
> 	more vertically-oriented leaves in the upper crown
> 	(to let "excess" light penetrate into the lower
> 	crown), but more horizontal leaves in the lower
> 	crown to capture increasingly attenuated light.
> 	In "real life" do you see variation of leaf orientation
> 	in different positions within the crown?  That is, can
> 	we expect to have genetic variation for differences
> 	in leaf orientation among crown positions?

	- Our F2/B1 poplar plantation in Puyallup domenstrated remarkable 
          variation in leaf orientations and also in their change pattern 
	  within a canopy.  For example, some clones have leaves that are 
	  horizontally or vertically oriented in the whole crown, whereas some 
	  clones may follow the Dickmann model of ideotype.

R. Wu

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