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Photosynthetic and Stomatal Conductance Responses of Plants to Atmospheric CO2 Enrichment
Reference
Ainsworth, E.A. and Rogers, A. 2007. The response of photosynthesis and stomatal conductance to rising [CO2]: mechanisms and environmental interactions. Plant, Cell and Environment 30: 258-270.

What was done
The authors summarized results from a vast array of free-air CO2 enrichment (FACE) experiments via meta-analysis in order to quantify the mean responses of stomatal and photosynthetic parameters to an approximate 200-ppm increase in atmospheric CO2 concentration.

What was learned
As best we can determine from Ainsworth and Rogers' graphical presentations, the following plant types experienced the associated percentage decreases in stomatal conductance in response to an approximate 200-ppm increase in atmospheric CO2 concentration: trees (19%), shrubs (15%), forbs (19%), legumes (23%), C3 grasses (36%), C3 crops (25%), C4 grasses (27%), C4 crops (30%), all C3 plants (22%), all C4 plants (29%). Likewise, as best we can determine, the following plant types experienced the associated percentage increases in light-saturated CO2 uptake (net photosynthesis) in response to an approximate 200-ppm increase in atmospheric CO2 concentration: trees (46%), shrubs (21%), legumes (19%), C3 grasses (36%), C3 crops (13%), C4 grasses (-2%), C4 crops (11%).

Averaged over all C3 plants, the mean decrease in stomatal conductance was 22%, while the mean increase in net photosynthesis was 31%; and in comparing the latter results with those we have stored in our Photosynthesis Data Archives, it must be remembered that the numbers reported by Ainsworth and Rogers need to be boosted by approximately 50% in order to make them roughly comparable to our numbers, which pertain to a CO2 concentration increase of approximately 300 ppm, as opposed to their 200 ppm.

What it means
As Ainsworth and Rogers succinctly put it, with respect to the primary focus of their review, "rising carbon dioxide concentration will impact plants and ecosystems through two processes, reduced stomatal conductance and increased net rate of photosynthesis."

Reviewed 23 May 2007