Study On The Source-Sink Characteristics Of Super Hybrid Rice And The Grain Yield Response To Planting Regions And Nitrogen Fertilizer Level

China’s super hybrid rice breeding program has achieved a continuous span of rice yield from 10.5 t ha^-1 to 15.0 t ha^-1.However,the yield difference of super hybrid rice in large area was significant,and the super high yield could not be equalized.In this paper,the source-sink characteristics of five super hybrid rice varieties were compared,and the yield performance and yield component factors of the yield of four super hybrid rice varieties in different ecological zones were studied.The influence mechanism of ecological environment and fertility level on the formation of yield difference was explored,and the high yield potential of the varieties was further explored through the study of precise application of nitrogen fertilizer in the differentiation stage of young panicle.It provides technical support for the realization of large area high and stable yield of super hybrid rice.From the first stage to the fifth stage of super hybrid rice varieties,the population storage capacity of increased significantly under the nitrogen application level of 210 kg ha^-1.The effective panicle number of the fifth variety stage Xiangliangyou 900 was decreased by 9.6%compared with the first stage variety Liangyoupeijiu.However,because the grain number per panicle increased from 192.7 grains/panicle to 286.1 grains/panicle,the population total spikelet number of Xiangliangyou 900 was up to 581.1×106 ha^-1 at full-heading stage,which was 34.3%higher than that of Liangyoupeijiu.In terms of population source characteristics,functional leaves of the fourth and fifth stage varieties had longer duration of high light efficiency.The photosynthetic rate was still as high as 20.0μmol·m^-2·s^-1 after wax ripening.The accumulation of source matter in stem and leaf at full heading stage was 9.2-12.7%and 13.0-22.1%higher than that of the previous three stages,respectively.In addition,the output of stem and leaf matter of the fourth and fifth stage cultivars with higher yield potential was not conducive to the accumulation of panicle matter,and there was a significant negative correlation between them.With the increase of yield potential of super hybrid rice varieties,the yield difference of1-5 stage varieties in the five ecological regions did not increase,and the yield difference of different ecological regions was up to 3.17 t ha^-1.Under the condition of no fertilizer,the yield difference between regions increased significantly with the increase of the variation of effective panicles and grain number per panicle,and the correlation coefficients were r=0.5678*and r=0.6183*,respectively.Under the nitrogen application rate of 210 and 300kg ha^-1,the yield difference was positively correlated with the grain number per spike,and the correlation coefficients were r=0.6884** and r=0.6303**,respectively.Reasonable fertilizer control can significantly reduce the yield difference between regions.Under the nitrogen application rate of 300 kg ha^-1,the yield variation of Yliangyou 1,Yliangyou 2 and Yliangyou 900 in five ecological regions decreased from 23.72%,26.00%and 26.60%to12.43%,12.04%and 19.52%,respectively.As the variation of seed setting rate in Liangyoupeijiu increased with the increase of nitrogen application rate,the yield difference between regions showed an increasing trend.Increasing nitrogen application significantly increased the yield of super hybrid rice varieties,but the yield increase factors were different under different fertility levels.From no fertilizer application to N application at 210 kg ha^-1,the increase of rice yield was the result of the interaction between population panicle increment and grain number per panicle increment,but had no significant correlation with single factor increment.From N application of 210 to 270 kg ha^-1,the increase of rice yield was significantly related to the increase of panicle number（r=0.7690**）.From N application level of 270 to 330 kg ha^-1,rice yield continued to increase,which was mainly dependent on the increase of grain number per panicle under high N application level,and the correlation between the two was significant（r=0.6644*）.In this process,the grain number per panicle of super hybrid rice varieties decreased,leading to a downward trend in rice yield.In addition,the yield difference among the five cultivars increased with the increase of fertilizer application rate,from about 2.50 t ha^-1 under low fertilizer to more than 4.00 t ha^-1under high fertilizer.The rice yield of super hybrid rice was increased by 4.3%～18.5%through the improvement of population structure in the middle and late growth stage of super hybrid rice by applying nitrogen fertilizer at the right time and proper amount in the differentiation stage of young panicle.Nitrogen supplementation at the early stage of young panicle differentiation promoted panicle formation and increased the effective panicle number of population by more than 10.0%.Nitrogen supplementation in the middle and late stages of young panicle differentiation effectively extended the duration of high light efficiency of the population at grain filling stage.Compared with no nitrogen supplementation,the SPAD value of functional leaves increased by nearly 20.0%30 days after full heading,and the net photosynthetic rate was maintained above 13.0μmol·m^-2·s^-1,which significantly increased the grain yield（r=0.5640*）.In addition,Under the condition of nitrogen fertilizer at the differentiation stage of young panicle,the outward source material from leaf sheath significantly promoted the matter accumulation in the grain sink（r=0.5782*）.