Abstract
Maize (Zea mays L.) is the important crop over the world. Nitrogen (N) as necessary element affects photosynthetic characteristics and grain yield of summer maize. In this study, N0 (0 kg N ha-1), N1 (129 kg N ha-1), N2 (185 kg N ha-1), and N3 (300 kg N ha-1) was conducted using hybrid ‘ZhengDan958’ at Dawenkou research field (36°11′N, 117°06′E, 178 m altitude) in the North China Plain to explore the effects of N rate on photosynthetic characteristics and chloroplast ultrastructure. Gas exchange parameters, chlorophyll fluorescence parameters, leaf area index (LAI), chlorophyll SPAD value, chloroplast ultrastructure, dry matter weight and grain yield were measured. At physiological maturity stage, dry matter weight and grain yield of N2 increased by 33–52% (P ≤ 0.05) and 6–32% (P ≤ 0.05), respectively, compared with other treatments. During the growing from silking (R1) to milk (R3) stage, LAI of N0 and N1 were 35–38% (P ≤ 0.05) and 9–23% (P ≤ 0.05) less than that of N2, respectively. Chlorophyll SPAD value of N0 and N1 were 13–22% (P ≤ 0.05) and 5–11% (P ≤ 0.05) lower than that of N2. There was no significant difference in LAI and chlorophyll SPAD value between N2 and N3 during the period from R1 to R3 (P > 0.05). The net photosynthetic rate (Pn), maximal quantum efficiency of PSII (Fv/Fm) and quantum efficiency of PSII (ΦPSII) were higher with the increase of N rate up to N2 (P ≤ 0.05), and those of N3 were significantly less than N2 (P ≤ 0.05). In compared with N2, the chloroplast configuration of N0 and N1 became elliptical, almost circular or irregular. The membrane of chloroplast and thylakoid resolved with growing stage, and the number of chloroplast per cell and lamellae per grana decreased under N0 and N1 treatment (P ≤ 0.05). Under N0 and N1 treatments, summer maize had more negative photosynthetic characteristics. The more number of osmium granule and vesicle and the larger gap between lamellae were shown in N3. Therefore, N2 treatment, 185 kg N ha-1, is the appropriate application rate for grain yield, photosynthesis and chloroplast ultrastructure.
Highlights
Nitrogen (N) is necessary element and the limiting factor for grain yield of summer maize (Zea mays L.)
Grain yield increased with the increase of N rate up to N2, and no greater yield was obtained in N3
The kernels per ear of N0 was significantly lower than others (P ≤ 0.05) and no significant difference was obtained among N ha−1 (N1), N2, and N3 (P > 0.05)
Summary
Nitrogen (N) is necessary element and the limiting factor for grain yield of summer maize (Zea mays L.). Nitrogen Rate Influence Chloroplast Ultrastructure that the recommended N rate (185 kg N ha−1), and the continued increases in N rate have not resulted in the commensurate increases in summer maize yield (Jin et al, 2012; Zhu et al, 2014; Liu et al, 2017). N application significantly increase dry matter weight, but excessive N rate would delay crops maturity and inhibit N translocation from vegetative organs to grain which is not conductive to crop production (Fang et al, 2006; Zhao et al, 2006). Excessive N rate make vegetative organs vigorously grow resulting in self-shade within the population, which have a negative effect on crop production. The chlorophyll SPAD value is used to determine the effect of N rate on leaf chlorophyll concentration since there is a non-linear relationship between them (Richardson et al, 2002). The changes in photosynthetic characteristics and chloroplast ultrastructure of field-grown summer maize would be responsible for the decreased yield with inaptitude N supply
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