Studies on the physiological parameters related to nitrogen use efficiency in wheat cultivars with different nitrogen utilization

The physiological parameters related to grain yield, nitrogen (N) content and N accumulation in plant, and N use efficiency were studied using wheat cultivars with different N use efficiency capabilities. Under deficient-N (LN) condition, Canghe036, a wheat cultivar with typical high-N use efficiency, had higher yield, plant nitrogen concentration, and N accumulation than Heng6599(H6599), a wheat cultivar with typical low-N use efficiency. The yield decrease more in LN condition for Canghe036(CH036) compared to Heng6599, which was mainly attributed to the significant decrease of spike number per plant area in Heng6599. At the stages of flag leaf expansion, flowering and grain filling, the activities of nitrate reductase (NR), nitrite reductase (NIR), and glutamine synthetase (GS), as well as photosynthetic pigments and soluble protein content in the top three unfolded leaves of Canghe036 were all higher than Heng6599 under deficient-N condition. The stomatal conductance and photosynthetic rate (Pn) were also higher in Canghe036 at late growth stage than in Heng6599, but the soluble sugar content and proline content was lower in Changhe036. There were no significant differences on superoxide dismutase (SOD) activities between these two cultivars, but the MDA contents were significantly lower in Canghe036 than in Heng6599. Therefore, the high-N efficiency in Canghe036 under deficient-N condition was resulted from integrated effects of the stronger capabilities in nitrogen acquisition and assimilation, higher over-oxidation degree of the cytoplasm, and stronger carbon assimilation functions.