Objectives This study aimed to explore the characteristics of nitrogen (N) uptake, transport and utilization of different maize inbred lines from anthesis to maturity, to reveal their related physiological and inherited mechanisms in N efficiencies.
Methods Pot experiment method was used in this research. The tested materials included the parent inbred lines of high-N-efficiency maize hybrid cultivar Ludan818 (female parent Qx508 and male parent Qxh0121), and the inbred lines of low-N-efficiency maize hybrid cultivar Ludan981 (female parent Q319, male parent Lx9801). The four inbred lines were grown in N application rates of 0, 7.1 and 14.2 g/pot, denoted by N0, N1 and N2 treatments in turn. The accumulation and distribution of dry matter and N were investigated, and the N utilization efficiency were calculated. The nitrate reductase (NR) activity and the soluble protein contents were determined.
Results Since starting of anthesis stage, the accumulation of dry matter and N were significantly decreased in the stems and leaves but significantly increased in spikes and grains, these variations in Qxh0121 and Q319 were higher than their corresponding parent inbred lines. During the grain-filling period, the post-anthesis N uptake for Qxh0121 was higher than that for Qx508, and that for Q319 was higher than for Lx9801. Under the low N (N1) and high N (N2) treatments, the N transport efficiency of male parent Qxh0121 was 29.2% and 14.3% higher than the female parent Qx508, and the contribution rate to grain was 74.0% and 17.4% higher, respectively. Likewise, the N transport efficiency in female parent lines Q319 were 43.4% and 24.7% higher, and the contribution rate to grain was 75.3% and 39. 6% higher than in the male parent Lx9801, respectively. In each pair of inbred lines, the Qxh0121 and Q319 had relatively high yield and N use efficiency. In N1 and N2 treatments, the yield of Qxh0121 was 43.3% and 42.5% respectively higher than that of Qx508, and yied of Q319 was 20.2% and 10.5% higher than that of Lx9801. The changes of leaf NR activity and soluble protein contents from anthesis to maturity showed a single peak curve with the peak value being around 10 days after anthesis. The leaf NR activity and soluble protein contents of Qxh0121 and Q319 were higher than those of their paired parent at all times, showing a higher ability for N uptake and assimilation.
Conclusions Among the two pair of inbred lines, the male parent Qxh0121 and the female parent Q319 show high N efficiency. Therefore, using the two inbred lines to breed new cultivar should be attempted for full use of their advantages in N translocation and allocation to grain with high N efficiency to achieve both high yield and grain N concentration while decreasing N residual in stems in their corresponding hybrids.
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