中文摘要：

在大田条件下研究不同时期和不同程度遮荫对夏玉米光合特性及其产量的影响。结果表明，遮荫对玉米叶片的光合特性有显著影响，导致玉米籽粒产量显著降低，农大108（ND108）苗期遮荫50％和90％的籽粒产量分别比对照降低16．9％和24．5％，穗期遮荫分别降低34．1％和55．3％，花粒期遮荫分别降低67．5％和79．4％。遮荫后玉米的叶面积指数、叶绿素含量和净光合速率等都显著降低。不同生育时期对遮荫的响应不同，苗期遮荫50％和90％处理的叶面积指数分别较对照降低53．6％和64．3％，穗期分别降低22．1％和23．0％，花粒期分别降低66．2％和79．4％。遮荫50％和90％处理叶片的光合速率苗期分别较对照降低28．6％和49．0％，穗期分别降低36．6％和59．6％。花粒期分别降低43．9％和64．7％。遮荫使玉米叶片的磷酸烯醇式丙酮酸羧化酶（PEPCase）和核酮糖二磷酸羧化酶（RuBPCase）活性显著降低，不同遮荫时期对其影响不同，花粒期遮荫影响最显著。遮荫时期对玉米光合特性的影响大于遮荫程度对其影响。

英文摘要：

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 intereropping 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. Therefore, 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 hy 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 carb