Five decades of selection for yield reduced root length density and increased nitrogen uptake per unit root length in Australian wheat varieties.

Background and aims: Given the worldwide effort to improve the nitrogen (N) economy of crops, it is critical to understand the mechanisms of improved N uptake which have resulted from selection pressure for grain yield in Australian wheat ( Triticum aestivum L.). Changes in root system traits and N uptake were examined in nine Australian wheat varieties released between 1958 and 2007. Methods: Wheat varieties were grown in rhizo-boxes in a glasshouse. We measured nitrogen uptake and mapped root growth and proliferation to quantify root length density (RLD), root length per plant, root biomass, specific root length, and plant nitrogen uptake per unit root length. Results: Selection for yield reduced total RLD and total root length, and increased N uptake per unit root length that overrode the reduction in root system size, effectively explaining the increase in N uptake. Importantly, N uptake in our experiment under controlled conditions matched field measurements, reinforcing the agronomic significance of the present study. Conclusions: Wheat varieties released in Australia between 1958 and 2007 increased their N uptake, not because of increasing their root length and RLD, but for progressively increasing the efficiency of their root system in capturing N. Our collection of varieties is therefore an interesting model to probe for variation in the affinity of the root system for nitrate. [ABSTRACT FROM AUTHOR]