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Transpiration and CO2 conversion

Jeffrey Kirby ez043438 at dilbert.ucdavis.edu
Sat Apr 4 04:55:02 EST 1998

Kevin Telmer (ktelmer at gsc.NRCan.gc.ca) wrote:
: Are any of you aware of any relationship between rates of transpiration
: and rates of conversion of CO2 in plants to C?

That'd be water use efficiency (WUE) or its reciprocol, transpiration

WUE = (moles of CO2 fixed)/(moles of H2O transpired)

trans ratio = (moles of H2O transpired)/(moles of CO2 fixed)

And to give you rough numbers: According to Taiz and Zeiger (Plant
Physiology text), C3 plants generally lose 400-500g H2O per g CO2, C4
plants generally lose 250-300g H2O per g CO2, and CAM plants generally
lose 50-100g H2O per g CO2 (although that is speculated by some people
to drop as low as 5g H20 per g CO2 in some CAM plants).

These numbers will of course change with differing relative humidity and
differing atmospheric CO2 concentrations, and you can probably get funding
to study it by using the words "elevated CO2 conditions" repeatedly in
grant applications. 


-----------------------------                                      -----
        Jeffrey A. Kirby                         jakirby at ucdavis.edu


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