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

Abstract

The C<inf>3</inf> species wheat and rice and the C<inf>4</inf> species maize were grown for 2–3 weeks in controlled environment growth chambers at 20 or 30 °C day and 15 °C night temperatures. CO<inf>2</inf> 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 CO<inf>2</inf> and O<inf>2</inf> levels were expressed on a total nitrogen basis (= nitrogen use efficiency), the C<inf>4</inf> species maize had a greater nitrogen use efficiency than either of the two C<inf>3</inf> species examined, regardless of the combination of temperatures used for growth or measurement of CO<inf>2</inf> 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 CO<inf>2</inf> and 21% O<inf>2</inf>. Atmospheric CO<inf>2</inf> enrichment during CO<inf>2</inf> assimilation measurements increased the nitrogen use efficiency in the C<inf>3</inf> species. In one treatment (wheat grown and measured at 20 °C), CO<inf>2</inf> assimilation under saturating CO<inf>2</inf> showed nitrogen, soluble protein, and RuBP carboxylase protein use efficiencies equal to or greater than that of the C<inf>4</inf> species. These data indicate that C4 species may make more efficient use of their nitrogen, soluble protein, and RuBP carboxylase protein than C<inf>3</inf> species under atmospheric CO<inf>2</inf> conditions. This may be due in part to the C<inf>4</inf> cycle and CO<inf>2</inf>-concentrating mechanism in C<inf>4</inf> photosynthesis.