Exploit Genotypic Difference in Root Plasticity to Increase Nitrogen Use Efficiency in Maize

Increased nitrogen use efficiency (NUE) has been an essential step in sustainable agriculture. Root architecture and its plasticity can play a fundamental role in N acquisition. In this review, we discussed the plasticity of maize root growth to short and long term of low N input and the possibility to utilize genotypic difference in root plasticity to low-N stress to increase NUE of field-grown maize genetically. The response of root architecture to low N input is different with the degree of low-N stress. In maize, short-term low-N stress (or mild N stress) increased both root elongation and lateral root growth. with sustained low-N stress (or severe N stress), lateral root growth is inhibited while root elongation is still enhanced. In field conditions, root plasticity to N supply is complicated with soil properties, soil N heterogeneity, and climate conditions. Nevertheless, root size (as indicated root length density) is maximized under optimized N supply, and there is a general correlation between root size and grain yield when N is not overused. The degree of the root responsiveness to low-N stress is genotype dependent. The genotypes with stronger root plasticity to low-N supply seems grow better and get higher grain in low-N field. A case study indicated that the genotypic difference in root plasticity can be used to improve root architecture and grain yield via QTL-based genetic approach.