Effects of N input level on the N-associated traits and physiological processes of winter wheat cultivated under water-saving condition

Enhancing nitrogen (N) use efficiency (NUE) of cereal crops contribute largely to the sustainable agriculture worldwide. In this study, the effects of N input level on the N-associated and agronomic traits of winter wheat cultivated under deficit irrigation were investigated, using two contrasting NUE cultivars. Under sufficient-N treatment (SN, N240), the two cultivars including the high NUE Shinong 086 and the N deprivation sensitive Jimai 325 both displayed higher N concentrations, biomass, N accumulative amounts, and photosynthetic function at various growth stages and yields at maturity than those obtained under deficient-N treatment (DN, N120). For two cultivars examined, Shinong 086 showed profound improvement on the N-associated traits, photosynthetic function, and the agronomic traits with respect to Jimai 325 under both SN and ND treatments. These results were in consistent with the N supply responses of the tested wheat cultivars. Expression levels of TaNRT1, a nitrate transporter (NRT) family gene mediating N uptake and TaNR5/6, TaNIR6/7, and TaGS3/4, the genes in nitrate reductase (NR), nitrite reductase (NIR), and glutamine synthetase (GS) families, respectively, were significantly upregulated in both N-deprived cultivars, with more transcripts in Shinong 086 plants than the Jimai 325 ones. Transgene analysis on TaNRT1 and TaGS3 validated their functions in positively regulating the plant N uptake and GS activity under DN conditions, respectively. Thus, distinct N uptake- and N assimilation-associated genes contributes to the plant adaptation of wheat plants to low-N stress given the enhanced transcription efficiency.