Maize (Zea mays L.) stands prominently as one of the major cereal crops in China as well as in the rest of the world.  Therefore, predicting the growth and yield of maize for large areas through yield components under high-yielding environments will help in understanding the process of yield formation and yield potential under different environmental conditions.  This accurate early assessment of yield requires accuracy in the formation process of yield components as well.  In order to formulate the quantitative design for high yields of maize in China, yield performance parameters of quantitative design for high grain yields were evaluated in this study, by utilizing the yield performance equation with normalization of planting density.  Planting density was evaluated by parameters including the maximum leaf area index and the maximum leaf area per plant.  Results showed that the variation of the maximum leaf area per plant with varying plant density conformed to the Reciprocal Model, which proved to have excellent prediction with root mean square error (RMSE) value of 5.95%.  Yield model estimation depicted that the best optimal maximum leaf area per plant was 0.63 times the potential maximum leaf area per plant of hybrids.  Yield performance parameters for different yield levels were quantitatively designed based on the yield performance equation.  Through validation of the yield performance model by simulating high yields of spring maize in the Inner Mongolia Autonomous Region and Jilin Province, China, and summer maize in Shandong Province, the yield performance equation showed excellent prediction with the satisfactory mean RMSE value (7.72%) of all the parameters.  The present study provides theoretical support for the formulation of quantitative design for sustainable high yield of maize in China, through consideration of planting density normalization in the yield prediction process, providing there is no water and nutrient limitation.

Over the past seven decades, the grain yield of maize (Zea mays L.) has increased continuously in China, mostly due to hybridization innovations, particularly recent genetic improvements in photosynthesis.  In order to reveal photosynthetic characters of elite inbred lines in different ears, a field experiment was conducted at the North China Plain of Shandong Province in China.  Six parental lines of maize introduced in three eras (the 1960s, 1980s, and 2000s) were investigated diurnal variation of gas exchange, chlorophyll fluorescence, and photosynthetic response characteristic at the grain filling stage.  Compared to earlier parental lines, the 2000s parental lines always had higher net photosynthetic rate (P_n) throughout the day, especially at noon, and a mid-day depression in Pn did not occur in all hybrids parental lines.  Moreover, the stomatal conductance (G_s) and water use efficiency (WUE) of the 2000s’ lines showed higher value than those of the 1960s’ and 1980s’ lines.  The inbred lines differences in photosynthetic parameters were partly owing to their different quantum carboxylation efficiencies and light synthase activities.  Simultaneously, the 2000s parental lines exhibited lower light and CO₂ compensation points, and their higher apparent quantum yield, and carboxylation efficiency.  These suggested that the modern parental lines required lower light intensity and less CO₂ to maintain a relatively high photosynthetic capacity, substantially increasing leaf physical quality and stress resistance.  It provided crucial information of high photo-efficiency and stress-resistance breeding in maize.