Carbon dioxide assimilation efficiency of four spring wheat cultivars grown under low and high nitrogen

Little is known about varietal differences in carbon dioxide (CO2) assimilation efficiency of leaves during the gain filling period under nitrogen (N) stress. The objective of this study was to compare four cultivars of spring wheat (Triticum aestivum L.) grown in the growth chamber under high and low soil N regimes for their CO2 assimilation efficiency indices (AEI), CO2 exchange rate (CER), leaf N concentration (NL) and spike grain yield and its components. The cutivars used in the study had different characteristics. Nesma is an older cultivar, but adapted to a large range of environments in northern Africa, Merchouch 8 is a newer cultivar adapted to the semi arid and arid areas, 5/70-32 is adapted to more favorable conditions (high moisture), and Saada was used because it has high tillering capacity and resists Hessian fly (Maeytiola destructor Say.). Measurements were taken at stem elongation, boot and dough stages on the last well developed leaf for AEI, CER, and NL and at physiological maturity for grain yield and its components. This study showed that increased N supply improved the values of CER, AEI, and grain yield and its components. Cultivars differed under both high and low N conditions for all the variables measured. Merchouch 8 had the highest AEI and NL at all stages, and its seed number/head and seed weight were less affected by N stress. Saada had higher values of CER, especially at stem elongation, while 5/70-32 had the lowest values for the parameters measured. Nesma was intermediate for AEI. From this study, we concluded that Merchouch 8 was the most stable cultivar under different soil N environments and can tolerate low N regimes. Although the number of cultivars in the test was small, they represented a wide range of adaptation and/or use. On this basis, it appears that physiological measures of AEI and CER may assist in identifying wheat cultivars which are superior for use in reduced N environments.