Photosynthetic nitrogen- and water-use efficiencies in C₃ and C₄ subtype grasses grown under two nitrogen supply levels
2022
Togawa-Urakoshi, Yuko | Ueno, Osamu
C₄ plants have higher photosynthetic nitrogen- and water-use efficiencies (PNUE and PWUE) than C₃ plants. Some studies on C₄ grasses have reported that NADP-malic enzyme (NADP-ME) grasses have higher PNUE than NAD-malic enzyme (NAD-ME) grasses, whereas other studies have suggested that this difference is caused by the traits of phylogenetic lineage. Further extensive studies are required to properly understand the PNUE and PWUE of C₄ grasses. We investigated the PNUE and PWUE for 22 grass species of four photosynthetic types [4 NADP-ME, 6 NAD-ME, 6 phosphoenolpyruvate carboxykinase (PCK), and 6 C₃ species] grown under two N supply levels. Under the same N level, the three C₄ types showed higher photosynthetic rate and lower stomatal conductance and transpiration rate than the C₃ type, but these parameters were similar in the C₄ types. Although there were no significant differences in leaf mass per area and N content per leaf area among the four types, these traits tended to be somewhat lower in the NADP-ME type than in other types. As a result, PNUE was highest in the NADP-ME type, lowest in the C₃ type, and intermediate in the NAD-ME and PCK types. PWUE was much higher in the C₄ types than in the C₃ type but similar in the C₄ types. The N supply level did not greatly affect the trends of PNUE and PWUE. This study suggests that the NAD-ME and PCK grasses have the N-related physiological traits similar to each other but differing from the NADP-ME grasses.
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