Root mass density is responsible for nitrogen use efficiency in wheat during the early vegetative stage in low nitrogen conditions

Crop nitrogen use efficiency (NUE) decreases as the N supply increases, leading to wasted resources. Genetic variations that alter root morphological traits may be useful for developing crops able to explore the deep soil strata to enhance their N acquisition and NUE. The objective of this study was to examine the relationship between root functional traits and NUE on the basis of a large set of wheat genotypes. A total of 126 genetically diverse wheat genotypes from major wheat-growing regions worldwide were grown for 2 months to compare root morphological traits, photosynthetic traits, biomass, N accumulation, and NUE under low N conditions. There were large genotypic variations in dry biomass accumulation, N accumulation, N concentration, and NUE in response to low N supply. An analysis of specific low N stress-induced phenotypic changes revealed the examined root morphological traits were closely associated with N accumulation, NUE, and biomass accumulation. A high root mass density (RMD) was conducive to improving NUE in response to the limited availability of N. Photosynthesis had little effect on NUE in wheat during the early stage under low N conditions. In wheat, compared with photosynthetic activities, root system development, especially in terms of RMD, has a greater effect on N acquisition and use for biomass production during the initial stage under low N conditions.