Abstract:

The summer corn (Zea mays L.) in Huanghuaihai region of China grows under high temperature and low light in the season of the year, and there is a large area of corn intercropping with winter wheat in Shandong Province. With the change of ecological factors and productive conditions, corn is shaded by winter wheat at the seedling stage, and grow under high temperature and low light at grain forming stage, which decreased grain yield. However, there are few reports on the effects of shading on photosynthesis of corn. This research attempted to study the photosynthetic foundation for the effects of shading on grain yield of corn, and provide theoretical evidence to improve yield and quality of summer corn. Effects of different shading degrees and different shading stages in field on photosynthetic characteristics of summer corn were studied. The field was shaded by the nets with 50% and 90% shading over the plants. The positions of the nets were raised with the growth of corn plant, and the distance between the nets and the top of corn plants remained in about 2.5m. So that only the illumination intensity condition was changed, while the aeration condition and relative humidity were not changed. Other environmental changes might be due to the change of illumination intensity. The results showed that there were significant effects of shading in field on photosynthetic characteristics of summer corn, so that grain yield of corn were decreased significantly. When shaded by 50% and 90%, grain yield of ND108 decreased by 16.9% and 24.5% respectively from seedling to jointing stage, by 34.1% and 55.3% respectively from jointing to flowering stage, and by 67.5% and 79.4% respectively from flowering to maturity stage. Correspondently, leaf area index of corn were decreased by 53.6% and 64.3%, 22.1% and 23.0%, 66.2% and 79.4% respectively, net photosynthesis rate of corn were decreased by 28.6% and 49%, 36.6% and 59.6%, 43.9% and 64.7% respectively in three shading stage. Both ribulose-1,5-bisphosphate carboxylase (PEPCase) and phosphoenolpyruvate carboxylase (RuBPCase) activities of corn leaves were decreased significantly in different shading treatments. Effects of different shading stages on photosynthetic characteristics of corn were significantly higher than those of different shading degree.

Key words: Summer corn, Shading, Photosynthetic characteristics, Yield