| Heilongjiang province is the main producing area of japonica rice in China,it is of great significance to improve the yield per unit area of japonica rice for the food security of Heilongjiang province and even the whole country.There are differences in light energy utilization and carbon and nitrogen accumulation and transportation among different rice varieties,previous studies on light energy utilization and carbon and nitrogen accumulation and transportation of different varieties and different yield types of rice have been conducted,and most of them are single or small amount of experimental materials.however,under the condition of a large number of japonica rice varieties as experimental materials,there is still a lack of systematic research on this aspect.In this study,85 japonica rice varieties（lines）were used as experimental materials.The leaf area index,SPAD value,photosynthetic potential,net assimilation rate,specific leaf weight,canopy characteristics and other light energy utilization indexes of japonica rice varieties with different yield levels were systematically analyzed,the soluble sugar,nitrogen content,carbon and nitrogen transport distribution and carbon-nitrogen ratio in various organs were studied.The differences of light energy utilization,carbon and nitrogen accumulation and transport betw een japonica rice varieties with different yield levels were revealed,the formation mechanism of yield difference between japonica rice varieties was clarified,which provided theoretical basis for high-yield cultivation of japonica rice and breeding of excellent varieties.The main research results of this experiment are as follows:（1）The 85 japonica rice varieties were divided into 5 yield levels by cluster analysis,that is high yield level,middle-high yield level,middle yield level,middle-low yield level,low yield level.The high-yield level included 10 japonica rice varieties,with an average yield of 8559.67kg·hm-2.The middle-high yield level included 22 japonica rice varieties,with an average yield of7956.06kg·hm-2.The middle yield level included 30 japonica rice varieties,with an average yield of 7291.44kg·hm-2.The middle-low yield level included 17 japonica rice varieties,with an average yield of 6746.08kg·hm-2.The low yield level included 6 japonica rice varieties,with an average yield of 6055.56kg·hm-2.The difference in yield levels was extremely significant.（2）The leaf area index at heading stage,SPAD values at headi ng stage and filling stage（20d after heading）of japonica varieties at different yield levels increased with the increase of yield level.Leaf area index at high yield level was not significantl y different from that at middle-high yield level,but was significantly higher than that at middle,middle-low yield level and low yield level.The SPAD value at heading stage was higher than that at filling stage（20d after heading）.The SPAD value of upper three leaves at two growth stages was pour two leaves>sword leaf·inverted three leaves,and the SPAD value of upper three leaves at high y ield level was inverted three leaves more than sword leaf,and the SPAD value of upper three leaves at low-middle yield levels and low yield levels was inverted three leaves less than sword leaf.This indicated that SPAD value of upper three leaves could maintain high chlorophyll content after heading at high yield level.（3）The photosynthetic potential of japonica rice with different yield levels was the highest at middle yield level before heading stage,and there was no significan t difference between high yield、high-middle yield and middle yield levels.The net assimilation rate of high yield level from jointing to heading stage was significantly higher than that at middle-low yield and low yield.Photosynthetic potential and net assimilation rate increased with the increase of yield level from heading to maturity stage,and the high and middle-high yield levels were significantly higher than the other three yield levels.（4）The utilization rate of light energy increased with the increase of yield lev el,and the difference between yield levels was significant.The effects of photosynthetic potential and net assimilation rate from heading to maturity and light use efficiency,on yield of japonica rice were higher,and the correlation was net assimilation rate>photosynthetic potential>light use efficiency.The SPAD value of the upper three leaves was significantly positively correlated with the light energy utilization rate,and the effect of sword leaves on the light energy utilization rate was higher than that of the inverted two leaves and the inverted three leaves.Therefore,it is suitable to improve leaf area index,delay senescence and maintain high SPAD value,promote the increase of photosynthetic potential and net assimilation rate at heading stage to maturity stage.（5）The accumulation of soluble sugar in each organ and shoot（except mature stage）increased with the increase of yield level,and there were significant differences among yield levels.The peak value of soluble sugar content in each organ and the output of soluble sugar in stem and sheath of high yield japonica rice were always at a high level.There was a significant positive correlation between leaf soluble sugar accumulation and light energy utilization at heading stage.The content of soluble sugar in leaves at high yield level was higher,which promoted the increase of light energy utilization rate.At the same time,the organ soluble sugar decreased significantly,which was higher than the low yield level,and more sugar was transported to the grain,which was helpful for grain filling and reservoir filling.（6）There was no significant difference in nitrogen content among organs at different yield levels;The nitrogen accumulation in each organ and shoot increased with the increase of yield level,while the nitrogen distribution ratio between stem,sheath and leaf decreased with the increase of yield level at maturity stage,and the difference between yield levels was extremely significant.At the high yield level,the nitrogen accumulation in leaves at heading stage and milking stage was significantly higher than that at the middle and low yield stage,and the nitrogen distribution ratio between stems,sheaths and leaves at mature stage was significantly lower than that at the middle and low yield stage.At the high yield level,the nitrogen accumulation and distribution ratio of leaves at heading stage and maturity stage were high,but the nitrogen distribution ratio of leaves at maturity stage was low,and the light energy utilization ratio was negatively correlated with the nitrogen distribution ratio of leaves at maturity stage.In high yield level,the amount of nutrient organ transport was higher,which promoted the grain nitrogen accumulation,and made its contribution rate to grain significantly higher than that of low and middle yield levels,which was one of the important reasons for increasing grain yield.（7）The ratio of sugar to nitrogen in stem and sheath of japonica rice at different yield levels increased first and then decreased,with the lowest at maturity stage,while the low yield level had been increasing,and the difference in yield level at maturity stage was not significant.The ratio of sugar to nitrogen in leaves and grains peaked at milk stage.The ratio of sugar to nitrogen in stem-sheath,leaf and grain increased with the increase of yield level before heading.The leaf and grain milk stage at high yield level were at a high level,and the grain sugar-nitrogen ratio at low yield level at mature stage was higher than that at other yield levels.Nitrogen photosynthetic efficiency could promote the ratio of sugar to nitrogen in leaves after heading and grain at milk stage.There was a significant positive correlation between stem-sheath sugar-nitrogen ratio and yield at heading stage.Increasing stem-sheath sugar-nitrogen ratio at heading stage increased net assimilation rate and photosynthetic potential from heading stage to maturity stage,and then increased light utilization rate,which was beneficial to high yield of japonica rice. |
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