H2O/CO2 diffusion rates

MEK104 at psuvm.psu.edu MEK104 at psuvm.psu.edu
Wed Nov 11 12:34:44 EST 1992

bwilliam at oyster.smcm.edu (Bill Williams) in article <16925 at umd5.umd.edu>

>In article <92311.111507MEK104 at psuvm.psu.edu> , MEK104 at psuvm.psu.edu

>>I tend to agree in that I'm skeptical, but I think an important factor
>>that may not be included in some of the theoretical and experimental work
>>is the heat exchange that occurrs from leaf to atmosphere.  To take the
>>debate full circle, could the relative size of individual stomata have an
>>effect on heat exchange?  This could also be way out of whack since I'm
>>not familiar enough with the literature.

>Since the relevance of stomata to heat exchange is entirely through
>transpiration, I don't see how this could be the case unless data for
>transpiration were estimated from direct microscopic measurements of
>stomatal aperture, distribution, pore length, and so on.  As far as I know,

Good point, I suppose thats the basis of this discussion: Does stomatal size
(ie guard cell length) as it relates to sun versus shade leaves have an
influence on transpiration rate and/or water use efficiency?  I was simply
raising the question, "do models of molecular diffusion across porous
membranes, meant to simulate CO2/H2O exchange through leaf epidermis,
consider the temperature differential between air and leaf"?  If not, a
major aspect of leaf gas exchange is ignored.

>no one has successfully modeled the biophysics of transpiration at that
>level.  There is someone in Germany (name forgotten) who has recently set
>up a gas-exchange apparatus with a transparent cuvette and a long-distance
>microscope, so the dimensions of the pores and the gross leaf conductance
>can be compared.  I haven't seen any results yet, but they should be

This definately sounds exciting.  If you recall who is doing this, I'd sure
appreciate the info.

Mark Kubiske                < MEK104 at PSUVM.PSU.EDU >
School of Forest Resources
Penn State University

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