O2, CO2 and trees?

Rod Savidge savidge at unb.ca
Fri Nov 17 13:21:37 EST 1995

Dear Henri,

Your questions are complex, so you must not expect
simple answers!   You might want to look at D. J. Avery (1977) Maximum
photosynthetic rate - a case study in apple.  New Phytol. 78:55-63.  Avery
examined data from other researchers and found widely different rates of
photosynthesis (CO2 fixation).  Differences also exist between species.
Thus, an "average" tree is very difficult to define.  A typical maximum
photosynthetic rate for trees under natural atmospheric and
optimal growth conditions would be about 20 micromoles (nearly 1
milligram) CO2 fixed per square metre of leaf surface per second, for
healthy recently matured leaves (lower for aged leaves).  As CO2 is
being fixed through photosynthesis, CO2 is also being evolved through
respiratory processes; hence, an accurate estimate of photosynthetic rate
is not necessarily an accurate estimate of atmospheric CO2 depletion.

The stoichiometry of photosynthesis has one mole of O2 generated for each
mole of CO2 fixed; however, that does not permit one to conclude that all
of the generated O2 makes it way back to the atmosphere.  Much of that O2
is utilized in metabolism (photorespiration, respiration, other oxidative
processes).  Most of that which does make its way out of the tree probably
is consumed by microbes in the breakdown of soil organic matter.

I haven't exactly given you the hard numbers you were looking for, but I
hope this analysis helps you to imagine the complexity associated with
getting accurate estimates.

Rod Savidge

In message 17 Nov 1995 16:43:19 GMT,
  cleanusa at ix.netcom.com (Henri D Harness )  writes:

> In <48bqob$bl0 at mark.ucdavis.edu> ez054530 at ucdavis.edu (Thomas Confal)
> writes:
>>  In article <488msj$fju at ixnews7.ix.netcom.com>, cleanusa at ix.netcom.com
> (Henri D Harness ) says:
>>>  OK, I know trees come in all shapes and sizes, but I'm looking for a
>>>  fair general answer or a range to the following related questions:
>>>  1.  How much oxygen does the average tree produce?
>>>  2.  How much carbon dioxide does the average tree produce?
>>>  The sad fact is, I've read these numbers somewhere, but for the life
>>>  of me, I don't recall.  I'd much appreciate answers and, if possible,
>>>  sources.  It's become one of those questions that incessantly pesters
>>>  the mind.
>>  I'm not sure you will find an exact answer for all trees. The amount
>>  of production depends on severl things: The type of tree (pine vs
>>  broad leaf), the amount of stomatas present, the amount of light the
>>  leaves are recieving for photosynthasis, if the tree is growing with
>>  out stress for best growth, etc. If  you do find a number, see if its
>>  for a given set of paramiters.
> The numbers I remember reading applied to broadleaf/deciduous
> trees and there was reference to an average period of sunlight.
> Regardless, any figures on O2 production/CO2 consumption would
> be appreciated.  I thought that, if nothing else, I would find
> such figures for an oak or a maple, but my search for answers
> has been bootless to date.
> I asked some friends and acquaintances in related fields --
> including a forester -- almost all said that they had read some
> such relevant figures somewhere, that the numbers were probably
> there in their offices, but that they were darned if they could
> find them.
> And that's just it.  I was sure I had a paper in my office
> that compared O2 production/CO2 consumption estimates of different
> trees and that _approximated_ the global O2 production/CO2 consumption
> of trees, but I can't find it.  And now that any real need for an
> answer has long passed, I'm still searching for answers, wondering
> where the blip I read such figures or if I dreamed I read it.
   Rod Savidge, PhD, Professor      |         E-mail: savidge at unb.ca
   Faculty of Forestry and         \|/
      Environmental Management  \   |   /     Phone:  (506) 453-4919
   University of New Brunswick  _\/ | \/_
   Fredericton, NB CANADA          \|/        Fax:    (506) 453-3538
   E3B 6C2                          |

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