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Effects of Elevated CO2 on an Important C4 Crop: Maize
Maroco, J.P., Edwards, G.E. and Ku, M.S.B.  1999.  Photosynthetic acclimation of maize to growth under elevated levels of carbon dioxide.  Planta 210: 115-125.

What was done
The authors grew maize (Zea mays) for 30 days in Plexiglass chambers receiving ambient or triple-ambient concentrations of atmospheric CO2 to determine the effects of elevated CO2 on growth in this important agricultural C4 species.

What was learned
Elevated CO2 (1100 ppm) increased photosynthesis in maize by about 15% relative to that measured in plants grown at 350 ppm CO2, in spite of the fact that photosynthetic down-regulation occurred for both rubisco and PEP-carboxylase.  This increase in carbon fixation likely contributed to the 20% greater biomass accumulation in CO2-enriched plants.  In addition, leaves of CO2-enriched plants contained approximately 10% fewer stomata per unit leaf area than leaves of control plants.  Moreover, atmospheric CO2 enrichment reduced stomatal conductance by as much as 71% in elevated-CO2-grown plants.  Consequently, the higher atmospheric CO2 concentration increased the intrinsic water-use efficiency of the CO2-enriched plants by over 225% relative to plants grown at ambient CO2.

What it means
As the CO2 content of the air rises, it is likely that C4 maize crops will exhibit significant increases in photosynthesis and biomass production, while increasing the efficiency at which they use water to produce that biomass.  Thus, the rising atmospheric CO2 concentration will likely have a very positive impact on maize production, particularly in arid regions where soil moisture may not be optimal for C3 crop production.

Reviewed 1 June 2000