Differences in shoot and root physiological indexes of the rapeseed (Brassica napus L.) genotypes with contrasting nitrogen uptake efficiency

Screening the higher nitrogen (N) uptake efficiency (NUpE) rapeseed (Brassica napus L.) genotypes and exploring the N efficient uptake mechanism could be an ideal way to meet the environmentally efficient use of N and the increasing demand for edible oils. Before conducting this study, we screened two higher (efficient genotypes) and two lower (inefficient genotypes) NUpE rapeseed genotypes according to their NUpE ranking. In this study, a field experiment and a hydroponic culture with the two efficient and the two inefficient rapeseed genotypes were conducted to dissect the differences in shoot and root physiological indexes at the vegetative stage. Results showed that the efficient rapeseed genotypes displayed significantly higher root indices (root length, root surface area, root diameter and root volume), along with greater root characteristics, root N metabolism enzyme activity, nitrate uptake kinetic parameters and root relative RNA expression than the inefficient genotypes. The larger N uptake ability of the efficient rapeseed genotypes led to the higher shoot indexes, leaf photosynthetic characteristics and leaf N metabolism enzyme activity, compared to the inefficient rapeseed genotypes. Our results indicate that the higher root indexes could uptake more N to support the shoot growth, resulting in the greater shoot indexes, ultimately achieve the larger NUpE, NUE and seed yield to meet the requirement for environmentally friendly agriculture systems.