Photosynthetic Capacity and Nitrogen Use Efficiency of Maize, Wheat, and Rice: A Comparison Between C3and C4Photosynthesis

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Abstract
The C3 species wheat and rice and the C4 species maize were grown for 2–3 weeks in controlled environment growth chambers at 20 or 30 °C day and 15 °C night temperatures. CO2 assimilation rates (at 20 and 30 °C) and several leaf parameters including total nitrogen, soluble protein, and RuBP carboxylase protein were determined. When the assimilation rates under atmospheric CO2 and O2 levels were expressed on a total nitrogen basis (= nitrogen use efficiency), the C4 species maize had a greater nitrogen use efficiency than either of the two C3 species examined, regardless of the combination of temperatures used for growth or measurement of CO2 assimilation. Maize is also shown to make more efficient use of its soluble protein and RuBP carboxylase protein than either wheat or rice when measurements are made at 320 parts 10−6 CO2 and 21% O2. Atmospheric CO2 enrichment during CO2 assimilation measurements increased the nitrogen use efficiency in the C3 species. In one treatment (wheat grown and measured at 20 °C), CO2 assimilation under saturating CO2 showed nitrogen, soluble protein, and RuBP carboxylase protein use efficiencies equal to or greater than that of the C4 species. These data indicate that C4 species may make more efficient use of their nitrogen, soluble protein, and RuBP carboxylase protein than C3 species under atmospheric CO2 conditions. This may be due in part to the C4 cycle and CO2-concentrating mechanism in C4 photosynthesis.