| The experiment was carried out in Rice Research Institute of Shenyang Agricultural University from2011to2012. In the first year, the japonica rice variety, Akihikari, was used to research the effects of shading on the yield and quality of japonica rice within different growth stages such as tillering stage (TS), jointing stage (JS), heading stage (HS) and10days after heading stage (10DAH) which are the critical stages of that, and find out the regularity of effects of shading on the yield and quality of japonica rice in northern China. Based on the results of2011, three different panicle types japonica rice cultivars including erect panicle rice Shennong9741, half-erect panicle rice Yanfeng47and curved panicle rice Liaoyanl6were used in2012, and further some major development of japonica rice were investigated with shading at heading stage under field conditions, such as photosynthetic physiological characteristics, carbon and nitrogen metabolism and grain yield and its physiological mechanism. The mainly results were as follows:1. The leaf area per plant and dry matter weight of each part aboveground were reduced by shading at different stages; the largest reduction of leaves weight per plant,26.77%, was got at tillering stage under shading treatment, while shading treatment mainly decreased the weight of stem per plant that there was a46.02%decrease at jointing stage. The weight of panicle was mainly decreased by shading after heading stage and the biggest drop of that was about45%. Studying on dry matter distribution of each part, it showed that there has been increased in the dry matter partition of leaf weight per plant under shading treatment at tillering stage and jointing stage, but decreased in dry matter partition of panicle per plant under shading treatment after heading stage. It was no obvious changes in dry matter partition of each part with shading treatment at different growth stages, however, shading just retarded the development of leaf or panicle (sink) at each growth stage. The influence of shading on yield of japonica rice was different at different stages, which indicated that the yield after shading within TS and JS was reduced from about9t·hm-2to8t·hm-2and7t·hm-2respectively, and the drop of yield was more than40%in HS and10DAH which was significant reduced from about9t·hm-2to approximately6t·hm-2under shading stress. The effects of shading on spikelets per panicle, seed setting rate,1000-grains weight and grain yield were significant (P<0.05), however there was no obvious effects of shading on effective panicles. Shading mainly led to the decrease of spikelets per panicle in the TS and JS and decrease of seed setting rate and1000-grains weight in HS and10DAH. That might be the reason for the marked reduction of grain of yield of rice under shading treatment. The yield of the top and middle of panicle which had the most contribution to the grain of yield was reduced evidently with shading treatment at heading stage.2. Studying on the effects of shading on quality of japonica rice at different stages, it showed that there were no obvious changes in quality of rice under shading treatment during TS and JS. With the increase of shading degree, the milling quality, appearance quality and nutrient quality were decreased in different degrees after HS. Shading mainly resulted in significant increase of chalkiness rate and chalkiness degree (P<0.05), however there was no significant influence on milled rice rate (P>0.05). With the increase of the days for shading, the quality of rice was decreased slightly but was not significant. This study also indicated that the quality of rice wasn’t changed evidently before heading. The changes in the quality of rice mainly happened at grain-filling stage after heading, which was a more advance explanation that the reason why the quality of rice was reduced by shading treatment was the poor grain plumpness.3. Studying on the changes in yield of japonica rice with different panicle types under shading treatment, it showed that the yield was decreased with increase of shading days significantly. The reduction in the yield of Shennong9741was the most, which was up to45.49%, while the drop of Liaoyan16and Yanfeng47were almost the same, which was40.07%and39.29%, respectively. The analysis of yield components indicated that there was no obvious influence on spikelets per panicle of rice with different panicle types under shading treatment at heading stage, and it was not up to a significant level. But both1000-grains weight and the rate of fructification were decreased markedly. Overall, the changes in Shennong9741from the aspect of1000-grains weight and the rate of fructification were the biggest under shading treatment.4. The chlorophyll content of flag-leaf was increased, and the increase of chlorophyll content in Shennong9741was most, which were resulted from studying on the photosynthetic characteristics of flag-leaf in japonica rice with different panicle types with shading treatment. Meanwhile, the net photosynthesis rate (Pn) of flag-leaf was decreased that the drop of Shennong9741was the biggest (49.87%) and the drop of Liaoyanl6was the smallest (31.78%). The transpiration rate (Tr) and apparent mesophyll conductance (Gs) of flag-leaf were also reduced with shading treatment, but CO2concentration intercellular (Ci) of flag-leaf was increased, and the difference among the photosynthetic characteristics of japonica rice with different panicle types was not significant. It was increased in Fv/Fm of flag-leaf in japonica rice with different panicle types under shading, but the Yield of flag-leaf was significantly decreased under shading within6days after heading. That suggested that shading led mainly to reduce the proportion of visible light for photochemical reaction, while increased the proportion of light energy conversion for heat dissipation. The results aslo indicated that shading could result in decrease of SOD、POD and CAT activity of flag-leaf in japonica rice, which did not reach a significant level, but it increased the MDA contents in cultivars at the same time. That suggests that50%shading constrained the activity of antioxidant enzymes in flag-leaf severely, which was resulted in the generation of active oxygen exceeding the scavenging ability of antioxidant enzymes, and then the membrane system was damaged eventually. It also might be one of the main reasons for the reduction of leaf photosynthetic capacity in japonica rice cultivars with different panicle types. The Chloroplast structure of japonica rice with different panicle types was strongly influenced under shading, and specific performance in the shape of chloroplast was swelled slightly. Meanwhile, there has more numbers of osmphore, fewer numbers of starch granule and higher of thylakoids stacking in chloroplast. There was a certain degree of concentration and periphery in cytoplasmic of chloroplast cell under shading, but thylakoid and lamella structure of grana were almost complete. Our studies indicated that there had different degrees of shading tolerance in japonica rice with different panicle types under shading stress, but the influences of shading on Shennong9741were greater than that of Yanfeng47and Liaoyanl6. The ability to absorb light energy was improved increasing chlorophyll content in Shennong9741, but the most of the light energy was converted into heat and dissipated, which was resulted in the actual photochemical efficiency decreasing significantly.5. The accumulation of dry weight was decreased under shading, while the effects on leaf weight per plant and the weight of stem and sheath per plant were complex, which was different with different panicle types. Generally, the effects of shading on the weight of leaf and stem per plant of Shennong9741were smaller than those of Yanfeng47and Liaoyanl6. The reduction of panicle weight per plant of Yanfeng47was the smallest under shading, and panicle weight per plant of Shennong9741and Liaoyanl6were decreased significantly within8days after shading. Further analysis on the change of dry matter distribution of each part within shading after heading10days showed that, dry matter distribution of panicle were all reduced. As dry matter distribution of panicle was decreased, dry matter distribution of leaves in Shennong9741and Yanfeng47was increased slightly, while those of stem in Liaoyan16were increased slimly.6. Analyzing the changes in enzymes of carbon and nitrogen metabolism in leaf and grain of rice with different panicle types, it indicated that the activity of SS and SBS was declined under shading treatment, which was resulted in the decrease of sucrose contents. That had limited output of photosynthetic products and delayed starch synthesis in panicle indirectly. The influence on enzymes of nitrogen metabolism in leaf was larger than those in grain with shading treatment. Meanwhile, the comparison among rice with different panicle types showed that the effects of shading on enzymes of nitrogen metabolism in Shennong9741were larger than others. The activity of GS and GOGAT of different panicle types was decreased by shading, but the activity of GDH was increased. |
PDF Full Text Request