Effects of Nitrogen Allocation Mode on Physiological Parameters Related to Nitrogen Utilization and Yield of Winter Wheat/Summer Maize

Abstract

In this study, according to the issue that the nitrogen supply response characteristics of winter wheat/summer maize across whole year in Hebei plain is needed to be further clarified, the effects of different nitrogen distribution modes on nitrogen uptake, related physiological parameters and yield traits of these crops were investigated. The results showed that compared with control (CK, the ratio of basal application to topdressing 5:5), the population leaf area index (LAI) and dry mass of wheat and maize increased in treatment 1 (T1, the ratio of basal application to topdressing 6:4) at early growth stage (jointing stage). In addition, the photosynthetic parameters (Chl content, Pn and gs), nitrogen content and nitrogen accumulation, nitrate reductase (NR) and glutamine synthase (GS) activities were also increased. However, the above population traits, plant photosynthetic parameters, nitrogen uptake and accumulation, and nitrogen assimilation enzyme activities during the late growth stages of this treatment were worse than those of CK. In contrast to T1, the above traits of wheat and maize in treatment 2 (T2, the ratio of basal application and topdressing 4:6) were worse than CK at early growth stage, but significantly better than CK at the late growth stages (flowering to maturity). According to the yield behavior at maturity stage, the ranking of the treatments was shown to be T2>CK>T1. Gene expression analysis showed that the expression levels of NRT genes <i>TaNRT1.1</i> and <i>TaNRT2.1</i> in wheat and NRT genes <i>ZmNRT1.2</i> and <i>ZmNRT2.1</i> in maize were involved in nitrogen uptake at flowering stage; those of wheat NR gene <i>TaNR3</i> and maize NR gene <i>ZmNR3.1 </i>were tightly associated with nitrate reductase (NR) activities; the wheat GS gene <i>TaGS2.2 </i>and the maize GS gene <i>ZmGS2</i> were related to the activities of glutamine synthetase (GS). These results indicated that the expression levels of these genes had crucial effects on the nitrogen uptake and assimilation characteristics of wheat and maize plants. Our investigation suggested that T2 treatment significantly enhanced the expression levels of specific genes associated with nitrogen uptake and assimilation. It improves the nitrogen utilization and related physiological parameters during the late growth stages by which to enhance the nitrogen efficiency and yield formation ability of the winter wheat/summer maize plants.