CO2 in leaves

Bill Williams wewilliams at OSPREY.SMCM.EDU
Mon Mar 1 11:06:08 EST 1999

>Dear Colleagues,
>I'm preparing a lecture for first year students on photorespiration and C4
>carbon fixation.  I wanted to be able to tell the students what a typical
>C3 leaf might experience as its internal CO2 concentration on a hot
>afternoon when the stomata are closed.  I know the graphs that show
>internal CO2 vs. CO2 assimilation rates in C3 and C4 plants - the kind of
>thing every upper level plant phys book will have.  I know that in the lab
>you can create different gas compositions and so on to generate these
>graphs that carry the CO2 concentrations all the way down to zero.
>What I want to know is, what is the typical amount "in leafo" when stomata
>are closed for C3 plants out there in the world?  In the non-lab setting
>does the amount of CO2 inside a leaf really get down to zero?
>Thanks for any info you can provide.
>Kathleen Archer

Dear Kathleen,

Unfortunately, it is nearly impossible to get reliable measurements of Ci
in leaves when the stomata are closed, and I don't think it's ever been
done.  Calculated values from transpiration and photosynthesis rates can
vary apparently randomly  between thousands of ppm and very large negative
values (obviously impossible), because both transpiration and
photosynthesis are nearly zero and of course the Ci is calculated from the
ratio between the two.


William E. Williams
Biology Department, St. Mary's College of Maryland
St. Mary's City, MD 20686 USA
WEWilliams at

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