ABSTRACT
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 (μmol 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.
ACKNOWLEDGMENTS
The work was supported by the National Science Foundation of China (No. 30390082).