| Pot-cultivation experiment was conducted to explore effects of shading on growth, photosynthesis characteristics, and yield of different genotype corns. This experiment included two factors: variety and shading. There were 4 corn varieties selected in this experiment: Yedan 22, Yedan 6, Yuyu 2, and Danyu 13. Shading was respectively performed at three growth stages: seedling stage (from germination to 6th leaf full expansion), ear stage (from 6th leaf full expansion to silking), and grain stage (from silking to maturity). The main results were as follows:1. Corn growth and development was significantly affected by shading, and there was a significant difference caused by shading in corn growth and development among different varieties. Shading slowed leaf appearance, thinned leaves, postponed the senescence of leaves, and prolonged the functional period of leaves when shading treatment was ended, however, the functional period of leaves experienced shading in early stage became shorter than that of leaves continuously growing under normal light. Shading at various stages had different effects on corn leaf area index (LAI). LAI decreased because of seedling and ear shading, but increased due to grain shading. Plant height increased compared with control during the shading period, but it was gradually lower than control after regaining normal light. The weight of dry matter was reduced by shading, and larger reduction range in root than that in stem and leaves was observed. Shading postponed tasseling and silking period, especially silking stage. Therefore, the anthesis-silking interval (AS1) was prolonged, which caused asynchrony between pollen shed and silking. Different sensitivity to weak light stress existed among four varieties applied in this experiment. Both Yedan 22 and Yuyu 2 were affected slightly by shading in terms of growth and development, while larger for Yedan 6 and Danyu 13.2. Shading decreased the corn's light saturation point and CO2 saturation point. The result showed influences of shading on Pn- PFD curve were larger than on Pn- Ca curve, and effects of shading on Pn response curve was different in different varieties.3. Shading reduced chlorophyll content in leaves, especially the content of chlorophyll a. Net photosynthesis rate (Pn) also decreased under shading. After light transfer at the stage of 6th leaf full expansion, Pn declined quickly, and began to recover after 4-5 days, but it couldn't regained the normal lever. When the corn growing in normal light was transferredto shading condition, PSII, Fv/Fm and qP increased soon, while NPQ and ETR decreased; when the corn growing in shading condition was transferred to normal light, all the chlorophyll fluorescence parameters changed oppositely. There was significant difference caused by light-transferring in photosynthetic parameters among different varieties. Yandan 22 had a good light adaptation, because it could maintain a higher photosynthesis rate both in normal light and shading condition.4. Shading also played an important role on photosynthesis efficiency diurnal changes. Shading lowered the peak of Pn in daily change, but let it appeared earlier. PS II and Fv/Fm also declined by shading treatment. ETR showed one two-peak diurnal changes curve, falling at noon. There was significant difference caused by shading in parameter stated above among different varieties. Effects of shading on Pn and chlorophyll fluorescence parameters in Yedan 6 and Danyu 13 were larger than those in Yedan 22 and Yuyu 2.5. The activities of SOD and content of MDA in corn leaves were affected by shading dramatically. The results indicated that activities of SOD under shading increased compared with control, the longer shading, the larger difference between shading and control. In contrast, the content of MDA reduced under shading. Effects of shading on the activities of SOD and the content of MDA were different among different genotype maizes, these difference became larger when the time of shading was extended.6. Shadin...
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