Linking wheat nitrogen use to root traits: Shallow and thin embryonic roots enhance uptake but reduce conversion efficiency of nitrogen

Nitrogen (N) is considered quantitatively most important for crop growth and productivity. The improvement of crop N use efficiency is economically beneficial to farmers and reduces the negative environmental impact of agriculture. Root traits are promising, yet underexploited breeding targets to improve N use efficiency. We aimed to evaluate (1) the effects of genotype and environment on N use efficiency and various root architectural and anatomical traits; and (2) the relationships between root traits, N uptake and conversion efficiency. Nine spring wheat genotypes were grown on compacted and non-compacted soil during two years with contrasting weather conditions in Central Sweden. Wheat genotype and year caused considerable variation in several root and N use efficiency traits. Negative correlations were found between N uptake efficiency and N conversion efficiency; root number and diameter; root number and angle; and metaxylem number and diameter. The N uptake efficiency increased with shallower root angle, higher root number, smaller root diameter, higher metaxylem number and smaller metaxylem diameter; whilst N conversion efficiency showed the opposite pattern. We conclude that a negative relationship observed between N uptake efficiency and N conversion efficiency can be linked to tradeoffs between embryonic root traits.

Automated summary

Nitrogen is crucial for crop growth and productivity. Enhancing nitrogen use efficiency can benefit farmers economically and reduce environmental impact. This study examined the effects of genotype and environment on nitrogen use efficiency and root traits in wheat, and found correlations between these traits.