Nitrogen fertilizer accelerated silk growth and increased grain yield of maize under low light stress

Context

Low light stress has become a major limiting factor for maize yield, with particularly detrimental effects during the flowering stage. As an essential nutrient, nitrogen not only enhances photosynthetic efficiency but also plays a key role in regulating plant physiological processes and alleviating abiotic stress. However, the mechanism by which nitrogen topdressing alleviates low light stress during maize flowering remains unclear.

Objectives

This study aims to investigate the physiological mechanism of nitrogen topdressing in alleviating the adverse effects of low light stress during the flowering stage on maize growth, development, and yield formation under different densities.

Methods

A split-plot experimental design was employed, with planting density as the main plot factor (45,000, 67,500, and 90,000 plants per hectare; D1, D2, and D3). Normal light and shading (75 ± 5 % light-blocking started at the tasseling stage and lasted for 6 days) were set as the subplot factor. Nitrogen fertilizer level served as the sub-subplot factor, including normal base fertilization (180 kg ha⁻¹) and increased nitrogen application (240 kg ha⁻¹) with 60 kg ha⁻¹ of nitrogen topdressed at the V14 stage (14th leaf was fully expended).

Results

The results showed that shading significantly inhibited net photosynthetic rate, dry matter accumulation, silk number, and kernel number per ear, especially under high density. The application of nitrogen topdressing, however, enhanced dry matter accumulation and its allocation to the ear, improved carbohydrate availability, and increased the contents of sucrose, fructose, glucose, and cellulose of silks. Additionally, nitrogen topdressing stimulated the activities of sucrose synthase and soluble acid invertase enzymes, maintained hormonal balance, and elevated levels of Zeatin and Gibberellin A3, thereby increasing the length and number of silks and enhancing vitality and length of trichomes on silks. These showed significant positive correlation with kernel number per ear. Finally, nitrogen topdressing increased kernel number per ear and yield by 18.1 %, 31.8 %, 51.9 % and 24.2 %, 36.6 %, 58.1 % under D1, D2, and D3, respectively, under shading conditions.

Conclusion

Nitrogen topdressing mitigated the yield loss caused by low light stress during flowering by promoting silk growth and increasing kernel number per ear. This study provided a valuable management strategy for maize production under low light conditions, especially in high-density planting systems.