| Maize is one of the important crops in China, especially on the cereal production. Nitrogen fertilizer application is one of the necessary measures for increasing maize production. However, recently, the unreasonable application of nitrogen fertilizer causes the decreasing of nitrogen use efficiency as well as contamination of ecological environment. So it has important significant to use nitrogen fertilizer reasonably according to the characteristic of nitrogen use of maize. The study was carried out on three locations in Jilin province and two years experiments were conducted for nitrogen uptake characteristic research of maize. Our objective was to find the critical nitrogen uptake curve adapting to spring maize in China, and provide useful method for nitrogen nutrition diagnosis basing on plant.In addition, leaf senescence is the major obstacle for high yield of maize. The scientists both from domestic and abroad agree that the yield can be improved by keeping green leaf, extending the photosynthesis and delaying leaf senescence. Although there is very close relationship between nitrogen metabolism and leaf senescence, the mechanism still lack research deeply. In the study, the stay-green maize and early-senescence maize were used to discover the relationship between nitrogen metabolism and senescence and provide theoretical foundation for adjusting to leaf senescence and optimizing the variety characteristic of stray-green maize. The main results are as follows:1) In Jilin province, the optimum application rate of nitrogen was154kg/hm2, the optimum yield was9764.5kg/hm2. The index of nitrogen efficiency existed big different in different years and locations. The average agronomy efficiency of nitrogen was9.3kg/kg, the average recovery efficiency was31.7%, the average partial productivity was64.1kg/kg, and the average physiological use efficiency was30.2kg/kg. According to the nitrogen content and dry matter weight in different seasons and locations, a critical nitrogen uptake curve was fitted out adapting to the spring maize in Northeast China.(Nc=36.5W0.48). The curve can provide a new nitrogen diagnosis method for us and help us to diagnose the status of maize nitrogen nutrition correctly.2) In the late growing season (from tasseling stage to maturity stage), the rate of green leaf of Xianyu335(stay-green) was higher than in Sidan19(early-senescence), which display the character of'stay green'. In the same nitrogen application treatment, the nitrogen absorption, dry matter accumulation and nitrogen efficiency were higher than in Sidian19. Especially in the later growing season, the dry matter accumulation rate was higher than in Sidan19significantly, which leading the yield increasing. Moreover, nitrogen application can also adjust the activity of active oxygen scavenging enzymes, as well as decrease the content of MDA and H2O2, suppress the expression of seel gene. The high expression of seel gene may be one of the reasons for early senescence of Sidan19.3) After treating with ABA, the contents of MDA and H2O2in maize leaves were increased, but the contents were decreased in6-BA treatment. The activity of oxygen scavenging enzymes was increased after treated by exogenous hormone. And the increasing rate of the activity was higher by treating with6-BA than with ABA. So the capacity of scavenging active oxygen was more improved by6-BA. Nitrogen application can suppress leaf senescence by increasing the accumulation of ZR, DHZR and iPA, and decreasing ABA. The content of ABA was lower in the leaf of Xianyu335than in the leaf of Sidan19, which indicated Xianyun335was a senescence resistant variety. |
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