Study On Characteristics Of Post-anthesis Matter Production And Translocation Of Carbon And Nitrogen In Indica And Japonica Hybrid Rice

The utilization of the heterosis between indica and japonica has been considered as an effective method to further improving the rice yield.Compared with other types of rice,indica-japonica hybrid rice,which has the characteristics of long grain-filling period,post-anthesis photosynthetic production advantages,the higher post-anthesis nitrogen demand and huge yield improving potential,has been widely cultivated in many provinces.However,the mechanism of nitrogen to maintain highly efficient photosynthetic function and long grain filling period,carbon and nitroge n translocation and‘flow’patency,grain filling and yield formation in indica-japonica hybrid rice after anthesis is not clear.Panicle fertilizer N is the key method of increasing yield,and it needs further study on the difference of accumulation and transport in the two stages of spike differentiation-anthesis and anthesis-maturity.To understand the post-anthesis N uptake characteristics of indica-japonica hybrid rice and its effects on leaf N output,maintenance of long grain-filling period and high-efficient photosynthetic function,assimilation and translocation of carbon and nitrogen during ripening and yield formation,a field experiment with four N application levels,a pot test with ¹⁵N labled panicle fertilizer application and a pot test with soil nitrogen leaching after anthesis were conducted respectively.The representative variety of indica-japonica hybrid rice Yongyou 12（YY12）and indica hybrid rice Zhongzheyou 1（ZZY1）were selected as the test material in this study.It will provide a theoretical basis for the regulation of nitrogen and the rational application of nitrogen fertilizer in indica-japonica hybrid rice.The main results are as follows:（1）After the compariation of different nitrogen application during the whole growth period,we found that the output of nitrogen in rice leaves during ripening was accompanied by a rapid decline in photosynthetic function,excessive transport of dry matter and sugar,and aggravation of leaf senescence.The increase of N application could significantly increase the activity of nitrogen assimilation enzymes in the leaves of indica-japonica hybrid rice YY12,promote nitrogen uptake after anthesis,and the contribute of post-anthesis N uptake to grain N（Post-NC）of YY12（15.0%-27.6%）was significantly higher than that of ZZY1（8.5%-14.8%）.At the same N applicaiton,YY12leaves could maintain the higher N levels,which contributed significantly to high efficient photosynthetic function,long leaf stay-green duration,carbon and nitrogen accumulation after anthesis and its contribution to grain yield.As a result,the yield of YY12 was significantly increased by 12.7%-21.8%compared with ZZY1（P<0.05）.（2）There was obvious difference in grain filling per hill between the two types of rice.The growth of ZZY grain weight per hill mainly depended on the early and middle stage,while the grain filling at early stage was dependent on the higher grain filling rate.The N accumulation rate and the accumulation of N at early stage played an important role in promoting grain filling of ZZY1.The increase of grain weight per hill in YY12depended mainly on the middle and late stage,while grain filling in the middle and late stage mainly depended on the longer filling duration,and grain N accumulation played an important role in adjusting the grain filling days and the grain filling accumulation at the middle and late stage.The relationship among grain N accumulation（x）,nitrogen application（y）and grain weight growth dynamics（z）could be described by z=-0.172+0.103x-0.013y-1.067×10^-5x²+2.931×10^-55 y²-5.524×10^-55 xy;the relationship among grain N accumulation（x）,grain-filling days（y）and grain weight growth dynamics（z）could be described by z=0.679+0.062 x+0.688 y-9.917×10^-6x²-4.390×10^-3y²-7.512×10^-6xy;the relationship among N application（x）,grain-filling days（y）and grain weight growth dynamics（z）could be described by z=2.272+0.074x+2.003y-2.145×10^-4x²-1.739×10^-2y²+7.526×10^-44 xy.（3）With the increase of nitrogen application,the number and area of large vascular bundles and the bleeding intensity in the neck-panicle node were significantly increased.Meanwhile,the transport rate of free amino acids,ammonium nitrogen,nitrate nitrogen and other nitrogen compounds,sucrose and soluble sugars in the bleeding fluids increased significantly,which accelerated the transport of sugar and nitrogen substances into the grain.Slow output rate of leaf N after anthesis maintained high photosynthetic ability,strong long-term sucrose synthesis capacity and increased transfer amount,which not only sufficient starch synthesize substrate in grain suppled,b ut also N assimilation during ripening promoted.（4）Soil N deficiency after anthesis resulted in a significant decrease of the avtivity of nitrogen assimilation enzymes and photosynthetic function in YY12 leaves.The translocation of dry matter accumulated before anthesis was reduced too.The decrease of antioxidant enzyme activity in leaves also accelerated leaf senescence,shortened leaf stay-green period,which led to the decrease of post-anthesis accumulation of dry matter,and the decline of grain plumpness and yield.Soil nitrogen supply after anthesis could be effectively reduced by soil nitrogen leaching method designed by ourselves.The results showed that the content of available N in YY12 pot soil decreased significantly during ripening,the post-anthesis N uptake reached 2.0-3.4 folds of that of ZZY1.The activity of nitrogen assimilation enzymes and antioxidant enzymes,photosynthetic rate and dry matter accumulation during ripening were significantly higher than those in ZZY1.（5）Through ¹⁵N labled panicle fertilizer application,the pre-anthesis and post-anthesis accumulation of panicle fertilizer N were distinguished.The results showed that 75.3%-75.8%and 77.5%-83.6%of the accumulated panicle fertilizer N were accumulated before anthesis in ZZY1 and YY12 respectively,and less than 25%were absorbed after anthesis.Pre-anthesis accumulation of panicle fertilizer N was mainly stored in leaves,followed by stem and sheath,post-anthesis accumulation of panicle fertilizer N on the contrary.The translocation of panicle fertilizer ¹⁵N to grain was dominated by panicle-fertilizer ¹⁵N accumulated before anthesis,and the output of leaf N was the main source,while the post-anthesis stage was mainly from ¹⁵N in stem and sheath.At the same time,52.9%-76.1%of the panicle fertilizer ¹⁵N was absorbed by the plants,10.1%-18.5%remained in the soil,and up to 13.8%-28.6%of the panicle fertilizer was lost through various ways.In the indica-japonica hybrid rice YY12,the N utilization rate,the amount and distribution to leaves of panicle-fertilizer ¹⁵N accumulated after anthesis were higher than those of ZZY1,and more attention should be paid to the post-anthesis N supply.In summary,the higher N assimilation capacity in indica-japonica hybrid rice YY12after anthesis was beneficial to maintain high N level and high photosynthetic function of leaves,promote the accumulation of carbon and nitrogen substance during super-long grain filling period.The increase of N application could not only improve vascular traits in the neck-panicle node,but also accelerate carbon and nitrogen transport from stems and leaves to panicles.Long grain-filling period,high-efficiency photosynthetic carbon assimilation,and unobstructed carbon-nitrogen substance transport,jointly met the huge demand for carbon and nitrogen substance formed by large spikelet number and sink potential,making it easier to develop its production potential.Panicle fertilizer N played an important role in ensuring post-anthesis high nitrogen uptake and the retard of the output of leaf N in YY12.On the basis of reducing the loss of panicle fertilizer,the post-anthesis nitrogen supply for indica-japonica hybrid rice should be increased through appropriate cultivation measures.