Effects Of Irrigation Practices On Carbohydrate Accumulation And Translocation And Grain Filling In Rice

Rice is one of the most important food crops in China.As the population grows and the area of cultivated land decreases,the output of grain needs to be continuously increased.The process of yield formation is essentially the process of nutrient accumulation during grain filling.The accumulation of carbohydrates before heading,the transport of carbohydrates after heading,and the photosynthetic productivity of leaves after heading are important factors that affect rice grain filling and increase yield.The increase in output often requires a large amount of water and fertilizer input,which not only causes waste of resources,but also pollutes the environment.Therefore,promoting the high-yield and high-efficiency coordinated development of rice through the comprehensive application of cultivation measures is of great significance to increase grain yield.In this study,Yongyou 2640 and Wuyunjing 24 were used as experimental materials.Eight different cultivation methods were set up to analyze their effects on rice yield and its constituent factors,growth and development,and population quality.Two conventional and precise irrigation methods were selected to analyze the effects of comprehensive cultivation methods on carbohydrate accumulation and transportation and grain filling and their physiological mechanisms.The main results and conclusions are as follows:1.Rice yield and its constituent factorsYields of Yongyou 2640 were 6.98,10.59,11.26,12.29 t hm-2 and Wuyunjing 24 were 5.75,9.52,10.06,10.81 t hm-2 under the conditions of High yield cultivation(HYC),Precision irrigation(PI),respectively.Compared with the Local farmer’s practice(LFP,control),the yield of Yongyou 2640 and Wuyunjing 24 increased by 6.33%～16.05%and 5.67%～13.49%.The main reason for the increase in yield under IDRN,PI was the increase in the total amount of glumes(number of spikes x number of grain per spike).Secondly,the seed setting rate and thousand-grain weight have also increased,further increasing the yield.It shows that the optimization of cultivation measures is conducive to the increase of yield2.Population growth and development qualityCompared with the LFP,HYC,PI of Youyou 2640 and Wuyunjing 24 had higher number of stems and panicle formation rate at heading stage and mature stage.Among them,the panicle rate increased by 7.91%～14.83%and 3.97%～11.68%respectively compared with the control.From heading to maturity,the accumulation of dry matter above ground increased by 3.11%～7.67%and 3.54%～6.61%,and the harvest index increased by 3.13%～7.80%and 2.05%～6.52%.At the same time,increasing the leaf area index at the panicle initiation stage and the heading stage,the oxidative activity of the root system,and the photosynthetic rate and SPAD value also increased,increasing the production of photosynthetic materials and delaying the senescence of leaves and root systems.It shows that the optimization of cultivation measures can promote individual growth and development to build a good group structure,improve the relationship between source and sink and then increase yield.3.Carbohydrate accumulation and transportCompared with the Conventional irrigation,the Precision irrigation treatment increased the activities of starch-associated enzymes AGP,StS and SBE in the stems before heading,increased the rate of starch synthesis in the stems,and increased the content of starch and NSC in the stems.The precise irrigation treatment did not increase the dry matter weight of the stem and sheath at the heading stage,indicating that the increase in the NSC content of the stem and sheath caused the carbohydrate accumulation at the heading stage.At the heading stage,Yongyou 2640 and Wuyunjing 24 increased 11.04%and 10.83%of NSC accumulation in stem-sheath under precise irrigation treatment than conventional irrigation.In addition,the scanning electron micrograph also showed that the starch granule accumulation in the stalk was larger and denser under Precision irrigation treatment.After heading,precision irrigation treatment enhanced the activities of stems starch hydrolase a-amylase and β-amylase and sucrose synthesis-related enzymes SPS and SSs,promoted the rapid hydrolysis of starch and the synthesis of sucrose after starch hydrolysis,and promoted the NSC transport.The transport volume of Yongyou 2640 and Wuyunjing 24 increased by 26.86%and 22.38%respectively.It shows that the Water regulation can promote the accumulation and transport of carbohydrates.The number and area of large and small vascular bundles and the phloem area of rice stem internode were smaller in Precision irrigation treatment.The rice vascular bundle system is the necessary channel for nutrients to flow to the panicle and enter the grain Although the characteristics of vascular bundles in Precision irrigation treatment are not better than the Conventional irrigation,the NSC transfer efficiency and the rate of grain filling are still high.This shows that the size of the channel of the vascular bundle system is not the main influencing factor of material transport and grain filling.4.Rice grain filling characteristicsCompared with the Conventional irrigation,Precision irrigation treatment promotes the filling of weak grains,increases the grain filling rate,and increases the grain weight.The reason is that the Precision irrigation treatment has a higher photosynthetic rate to synthesize photosynthetic products and temporarily stored NSC in the stems are delivered to the grains in the form of sucrose.At the same time,the activities of sucrose hydrolysis-related enzymes SSc in the grain are increased,and the utilization rate of sucrose in the grain and the enzyme activities of starch synthesis-related enzymes AGP,StS,and SBE are increased.The grain filling increases grain weight and yield.