Shading post flowering, caused by cloudy weather and the surrounding protective trees, often occurs in some wheat ( Triticum aestivum L.) area in north China. In general, wheat yield is negatively influenced by shading post flowering, but the effect on grain quality is reported discrepantly. This study aimed at disclosing the effects of post-flowering shading on photosynthesis of leaf and yield and quality of grain in wheat, accordingly, giving suggestions to wheat production. Three treatments were designed with shading of 20%, 50%, and 80% for 30 d, respectively. The normal condition was taken as the control. The results showed that shading treatments had significant influences on photosynthetic characteristics of flag leaf. The shading treatments increased the number of sterile spikelet and reduced the grain weight per spike and the 1000-grain weight. As a result, the grain yield of the three shading treatments significantly decreased by 27.6%, 49.0%, and 60.2% compared with the control. In the shading treatments, the contents of the chlorophylls a and b increased, whereas the ratio of chlorophyll a to chlorophyll b decreased. Moreover, the net photosynthetic rate, the stomatal conductance, and the transpiration rate were also significantly reduced, but the intercellular CO 2 concentration was promoted. The shading depression on net photosynthetic rate became smaller in the process of grain filling, with the largest effect at early stage of grain filling and the smallest effect at late stage of grain filling stage. The contents of protein, wet gluten, glutenin, gliadin and the ratio of glutenin to gliadin in grains increased significantly with the increase of shading. The shading influence on glutenin was greater than that on gliadin. Although the shading treatments decreased grain yield obviously, it raised some quality parameters, such as extensibility, development time, stability time, and water absorption of dough. The responses of yield and quality of wheat grain to shading were different because of the discrepant synthesis mechanisms of starch and protein under weak light condition. In wheat protective areas, yield is a priority factor and the tree-wheat intercropping mode should be avoided.
