Abstract:

Improvement in nitrogen use efficiency (NUE) in crop plants is significant in the view of economic efficiency and environment friendly. A better understanding of the physiological mechanism underlying nitrogen use efficiency is necessary for genotype screening and breeding rice cultivar with high NUE. In present study, four rice genotypes identified as high and low nitrogen use efficiency (NUE) were used to investigate their responses of physio-biochemical properties to N-fertilizer and its relationship with NUE at the rate of 0, 0.51, 1.02, 1.53, and 2.04 g N pot^-1 (equivalent to 0, 75, 150, 225, 300 kg N ha^-1, respectively) under pot-grown conditions. The results showed that the soluble protein content in leaves was relatively lower in high-NUE genotypes than that in low-NUE genotypes at panicle initiation stage, while the glutamine synthetase (GS) activity was higher significantly. Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) content in leaves appeared to be no significant difference between two NUE types of rice. The net photosynthetic rate (P_n) in the low-NUE genotypes was significantly lower by 28.66% in comparison with that in high-NUE genotypes at full heading stage, regardless of no significant difference at panicle initiation stage. Interestingly, P_n per chlorophyll unit (P_n/Chl) was lower in low-NUE genotypes than in high-NUE genotypes at both two stages by about 18.51% and 29.67%, respectively. Total aboveground biomass and grain yield at five nitrogen levels were significantly higher in high-NUE genotypes than those in low-NUE genotypes. It was observed GS activity was significantly correlated with biomass at harvest stage at the rate of 0, 0.5, 1.0, and 1.5 g N pot^-1. P_n at full heading stage, GS activity, and P_n/Chl were all significantly and positively correlated with agronomy efficiency (AE), partial factor production of applied N (PFP), and nitrogen physiology efficiency (NUEb), respectively. However, PFP, AE, and NUEb were negatively correlated with soluble protein content in leaves, respectively. Additionally, no significant correlation was observed between nitrogen recovery efficiency (RE) and the physiological parameters mentioned above. The results presented in the paper suggest the important contributions of Pn and GS to NUE. According to the relationships among NUE, GS and soluble protein content, GS activity and soluble protein content in leaves might be candidate indicators for NUE evaluation in rice.

Key words: Nitrogen use efficiency (NUE), Glutamine synthetase (GS), Photosynthetic properties, Rubisco content, Rice