How does rising atmospheric CO2 affect marine organisms?

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Effects of Elevated CO2 on Transpiration in a Mature Sweetgum Stand
Wullschleger, S.D., Gunderson, C.A., Hanson, P.J., Wilson. K.B. and Norby, R.J.  2002.  Sensitivity of stomatal and canopy conductance to elevated CO2 concentration - interacting variables and perspectives of scale.  New Phytologist 153: 485-496.

What was done
A FACE study was established within a twelve-year-old stand of sweetgum (Liquidambar styraciflua L.) trees growing in a forest plantation on nutrient-rich soils in Tennessee, USA.  The trees, which were in a linear growth phase at the onset of the experiment, were exposed to atmospheric CO2 concentrations of 390 and 540 ppm.  This paper reports the effects of elevated CO2 on leaf and canopy stomatal conductance and stand evapotranspiration.  Measurements were made during the five-month growing season common to this species.

What was learned
Elevated CO2 reduced the stomatal conductances of individual leaves of mature sweetgum trees by 23% across the growing season.  When extrapolated to the entire canopy, however, the CO2-induced reduction in stomatal conductance declined to 14%.  The bottom line was a 7% reduction in stand evapotranspiration.

What it means
As the air's CO2 concentration increases, leaf stomatal conductances of mature sweetgum trees will likely decline.  At the canopy level, these reductions - though much less dramatic - should help trees conserve water via reduced transpiration and, therefore, enable them to better deal with drought.

Reviewed 3 April 2002