Genotypic difference in nitrogen acquisition ability in maize plants is related to the coordination of leaf and root growth

The capacity of a plant to take up nitrate is a function of the activity of its nitrate-transporter systems and the size and architecture of its root system. It is unclear which of the two components, root system or nitrate-uptake system, is more important in nitrogen (N) acquisition under nitrogen-sufficiency conditions. Two maize (Zea mays L.) inbred lines (478 and Wu312) grown in nutrient solution in a controlled environment were compared for their N acquisition at 0.1, 0.5, 2.5, 5, and 10 mmol L-1 nitrate supply. Genotype 478 could take up more N than Wu312 at all nitrate concentrations, though the shoot biomass of the two genotypes was similar. Genotype 478 had a larger leaf area and longer root length. The specific N uptake rate of 478 (mu mol N g(-1) root. d(-1)) was lower than that of Wu312. In an independent nitrate-depletion experiment, the potential nitrate uptake rate of 478 was also lower than that of Wu312. No genotypic difference was found in photosynthesis rate. It was concluded that the greater N acquisition ability in 478 involves the coordination of leaf and root growth. Vigorous leaf growth caused a large demand for N. This demand was met by the genotype's large root system. Besides providing a strong sink for N uptake, the larger leaf area of 478 might also guarantee the carbohydrate supply necessary for its greater root growth.