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Response of a C3 and C4 Forage Crop to Elevated CO2
Fritschi, F.B., Boote, K.J., Sollenberger, L.E., Allen, Jr. L.H. and Sinclair, T.R. 1999. Carbon dioxide and temperature effects on forage establishment: photosynthesis and biomass production. Global Change Biology 5: 441-453.

What was done
The authors grew the C3 nitrogen-fixing rhizoma peanut and the C4 non-nitrogen-fixing bahiagrass along a temperature gradient of 4.5C within greenhouses that received atmospheric CO2 concentrations of 365 and 640 ppm for seven months to determine the effects of temperature and elevated CO2 on the early establishment of these perennial forage species.

What was learned
Growth temperature did not significantly effect seasonal photosynthetic rates or whole-plot forage harvests in rhizoma peanut and bahiagrass. Elevated CO2, however, increased seasonal photosynthetic rates in these C3 and C4 species by 37 and 22%, respectively. These photosynthetic increases likely contributed to greater biomass production in both forage crops, enhancing total biomass by 52% for rhizoma peanut and 9% for bahiagrass. More importantly, at the end of the season, elevated CO2 had increased the whole-plot forage harvest by 21 and 17% for rhizoma peanut and bahiagrass, respectively.

What it means
As the CO2 content and temperature of the air continue to rise, these two perennial forage crops will likely exhibit significant increases in photosynthesis, thus providing greater carbohydrates to enhance their growth and establishment under the humid tropical conditions to which they are already adapted. In fact, the authors stated that "an increase in global temperature of 4.5C above conditions at Gainesville, FL, (where both species are important forage crops, and where the experiment was conducted) will not adversely affect photosynthesis or biomass production of these two species when well watered." Thus, increased temperature should pose no threat to the productivity of these crops, while atmospheric CO2 enrichment should improve them.

Reviewed 1 August 1999