Root traits are strongly associated with nitrogen uptake efficiency in contrasting rapeseed genotypes.

Screening the higher nitrogen (N) uptake efficiency (NUpE) rapeseed (Brassica napus L.) genotype (N-efficient-genotype) and exploring the N efficient uptake mechanism could be an ideal way to meet the environmentally use of valuable N and the increasing demand for edible oils. In this study, we selected a N-efficient-genotype and a N-inefficient-genotype to dissect the differences in root physiological indexes under a pot experiment and a hydroponic culture. Results showed that during the high and low N levels, root biomass was the main factor affecting NUpE at the pot experiment. Compared to the N-inefficient-genotype, N-efficient-genotype displayed respectively 39.72%, 31.52%, 39.94%, 41.28% and 54.80% higher root biomass, N content, root length, root surface area and Vmax, along with 36.86%,48.68%, 134.14%, 72.71%, nitrate reductase (NR), glutamine synthetase (GS), catalase (CAT) and glutathione (GSH) activity. These were accompanied by a significant increase (P < 0.05) in BnNRT1.1 (7.04 fold), BnNRT1.5 (4.66 fold), BnNRT2.1 (8.63 fold) and BnNRT2.5 (12.13 fold), which may result in the greater N uptake ability than did the N-inefficient-genotype under the hydroponic culture. Our results indicate that higher root indexes for the N-efficient-genotype could uptake more N to support the photosynthesis sustained and seed development, and would achieve the larger NUpE and NUE in rapeseed genotypes.