Submitted to: Soybean Biotechnology Meeting
Publication Type: Proceedings
Publication Acceptance Date: 10/15/2003
Publication Date: 10/20/2004
Citation: Leakey, A., Bernacchi, C.J., Dohleman, F., Ort, D.R., Long, S. 2004. How Will Photosynthesis of Maize In The U.S. Corn Belt respond To Future CO2 Rich Atmospheres? Soybean Biotechnology Meeting. p. 951-962.
Technical Abstract: The C4 grass Z. mays (corn) is the third most important food crop globally in terms of production. Nonetheless, the effect of rising [CO2] upon corn is not sufficiently understood to allow accurate predictions of future crop production. A rainfed, field experiment, in the primary area of global corn production (U.S. Corn Belt), was undertaken to compare the in situ diurnal course of gas exchange of upper canopy leaves under ambient (370 ppm) and elevated [CO2] (550 ppm). FACE technology imposed the [CO2] treatments in 20-m diameter plots, from sowing to harvest with none of the effects of experimental enclosures on plant microclimate. Previous laboratory studies suggest that C4 photosynthesis is [CO2] saturated under ambient conditions and, therefore, should not respond to elevated [CO2]. However, stomatal conductance and transpiration are typically decreased, which can indirectly increase photosynthesis in dry climates. Given the deep soils and good rainfall of the Corn Belt, it was predicted that photosynthesis would not be enhanced by elevated [CO2]. However, growth at elevated [CO2] significantly increased leaf photosynthetic CO2 uptake rate (A) by 10% on average, and up to 41% at one stage of development. The increases in A were associated with greater intercellular [CO2] and water use efficiency. Summer rainfall during 2002 was very close to the 50-year average for this site, indicating that the year was typical and not a drought year. The results call for a reassessment of the established view that C4 photosynthesis is saturated at the current atmospheric [CO2] and that the production potential of corn in the US Corn Belt will not be affected by rising [CO2].