Intraspecific variation for nitrate uptake and nitrogen utilization in wheat (T. Aestivum L.) grown under nitrogen stress

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Abstract
Twenty four wheat lines representative of varieties developed over the last eighty years were evaluated for differences in short term nitrate uptake and nitrogen utilization at the vegetative stage under conditions of nitrogen limitation. Net nitrate fluxes in three‐week‐old plants were determined by the depletion method and nitrogen utilization was expressed as both the efficiency ratio and utilization efficiency, In addition the kinetic parameters Vmax and Km were obtained for eight of these varieties. Considerable differences were observed for all attributes examined although variation in efficiency ratio was characteristically small and substantially lower than that in utilization efficiency. The tall traditional varieties generally exhibited higher uptake rates and nitrogen utilization than most of the fertilizer responsive dwarf types. However they were no better than the triple dwarfs in nitrate uptake. Differences in affinity for nitrate as measured by the apparent Km were also substantial, of particular interest being the low affinity exhibited by one of the triple dwarf varieties. The findings made in this study are discussed in relation to their bearing on performance under nutrient‐limiting conditions, the likely consequences of selection under different fertilizer regimes and the prospects for genetic improvement of fertilizer use efficiency.