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

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.