What was done
Twenty-one representative species from the Panicum and Flaveria genera, which exhibit C3, C3-C4 intermediate, and C4 photosynthetic physiologies, were grown from seed in greenhouses at ambient CO2 concentrations.  The plants were then periodically exposed to elevated CO2 concentrations of 900 ppm during gas exchange measurements to study the short-term effects of atmospheric CO2 enrichment on photosynthesis in these species.

What was learned
On average, elevated CO2 stimulated photosynthetic rates in C3, C3-C4 intermediate, and C4 Panicum species by 41, 34, and 13%, respectively.  Similarly, within the Flaveria genus, atmospheric CO2 enrichment enhanced photosynthetic rates of C3, C3-C4 intermediate, and C4 species by 53, 46, and 13%, respectively.  Thus, the greatest CO2-induced photosynthetic stimulations occurred in C3 species, followed by C3-C4 intermediates, and finally C4 species, as anticipated from previous studies.

What it means
As the air's CO2 content increases, all species within the Panicum and Flaveria genera will likely exhibit enhanced rates of photosynthesis that should lead to greater biomass production, regardless of the photosynthetic physiology they utilize.  C3 species are expected to exhibit the greatest CO2-induced photosynthetic increases, followed by C3-C4 intermediates, and then C4 species.