The influence of shoot and root size on nitrogen uptake in wheat is affected by nitrate affinity in the roots during early growth

Shoot and root system size influences N uptake in wheat (Triticum aestivum L.). Previously, we showed that four wheat genotypes with different biomass had similar N uptake at tillering. In the present study, we determined whether the similarity in N uptake in these genotypes was associated with genotypic differences in the affinity of the root system for NO3– uptake. Kinetic parameters of NO3– uptake were measured in hydroponic seedlings of vigorous and nonvigorous early growth wheat genotypes by exposing them to solutions with differing concentrations of K15NO3 for 15 min. In the low concentration range, the high-affinity transport system of the nonvigorous cultivar Janz showed a higher maximum influx rate than the three vigorous lines and a higher affinity than two of the three vigorous lines. At high NO3– concentrations, where the low-affinity transport system was functional, the responsiveness of NO3– uptake to external concentrations was greater in Janz than in the vigorous lines. Both the high- and low-affinity transport systems were inducible. The genotypic variation in the kinetic parameters of NO3– uptake was large enough to offset differences in morphological traits and should be considered in efforts to improve N uptake. In a field trial, the growth and N uptake performance of the four wheat genotypes was investigated over the winter–spring growing season (June–November of 2010). The field trial showed that although early N uptake was disproportionately large relative to biomass accumulation, the differences in uptake at tillering can be changed by subsequent patterns of uptake.