Effect Of Foliar Application Of Patassium Fertilizer On Quality Formation Of Winter Wheat And Its Mechanism

Potassium fertilizer has a significant effect on wheat yield and quality.However,influenced by the traditional concept of“rich K”in soil in the northwest,more nitrogen and phosphorus fertilizers are used in wheat production,while potassium input is ignored.However,with the application of high biomass wheat varieties and the improvement of crop yield,the consumption of potassium fertilizer in soil is accelerated,and the potassium supply capacity of soil is decreasing day by day.In the later stage of wheat growth,the root system is prone to senescence,which will weaken the potassium absorption capacity and thus lead to the occurrence of potassium deficiency.Therefore,the reasonable potassium application is of great significance to wheat production in northwest China.Foliar fertilizer spraying has the advantages of easy absorption and fast fertilizer effect,which is an important supplementary measure for soil fertilization.In addition,most of the wheat flour in China is consumed by wheat grain processing,and the changes of nutrients in wheat flour can better reflect the application effect of potassium fertilizer.At present,there are few studies on the effect of foliar spraying potassium fertilizer on quality indexes in flour at the late growth stage.Therefore,it is of great significance to explore the effects of potassium fertilizer foliar spraying on wheat flour processing quality and nutritional quality and its physiological mechanism.In this study,different potassium fertilizer spraying periods,concentrations and methods were set up to determine the changes of wet gluten,protein and protein components,high molecular weight glutenin subunit(HMW-GS)content,microelements and phytic acid content,sedimentation value,dough stability time and formation time in different types of flour,so as to clarify the effects of potassium fertilizer on wheat nutritional quality and processing quality.At the same time,combined with the changes of key enzyme activities in leaves and RNA-Seq analysis results after potassium fertilizer spraying,the physiological mechanism of potassium fertilizer affecting grain quality was revealed.The main conclusions of this study were as follows:(1)Potassium fertilizer foliar spraying had a certain improvement effect on the quality indexes of the three types of flour,but the effect was less than that of milling treatment.After the grains were processed into flour,the contents of wet gluten,total protein,albumin,globulin,iron(Fe),manganese(Mn),zinc(Zn),phytic acid and sedimentation value changed.In the three kinds of flour,the overall performance was whole flour>85%whole flour>70%whole flour.However,the contents of gliadin,glutenin and HMW-GS,the formation time and stability time of dough showed different trends,which were 85%whole powder>70%whole powder.The molar ratio of phytic acid to trace elements(Fe,Mn,Zn)was expressed as whole flour<85%whole flour<70%whole flour.Potassium fertilizer spraying significantly reduced the albumin content of the two varieties,but had no significant effect on the globulin content.Compared with the other two periods,the K₂ concentration of potassium fertilizer spraying at flowering stage significantly increased the contents of protein,wet gluten,sedimentation value and gluten in Xinong 20,and reduced the molar ratio of phytic acid and microelements,but spraying K₂ concentration 10 days after flowering was more conducive to the prolongation of dough stability time.For Xiaoyan 22,the formation time of protein,wet gluten and gluten increased significantly under K₂concentration at flowering stage,and the molar ratio of phytic acid to trace elements decreased significantly.There were significant genotypic differences in the composition and content of HMW-GS between the two varieties.Spraying K₂ concentration significantly increased the content of each subunit of the two varieties,but the optimum periods were slightly different,and the increase of subunit content of Xinong 20 was more obviously.The effect of foliar application of potassium fertilizer on yield had genotype difference,which was only beneficial to the increase of Xiaoyan 22 yield.Compared with foliar application of potassium fertilizer,grain milling had more significant effect on wheat quality indexes.(2)Foliar application of potassium fertilizer could promote the increase of grain filling rate and grain weight of xiaoyan 22,but the effect of dominant seed weight and grain filling rate was not significant,and there was no significant effect on grain weight and grain filling rate of Xinong 20.Potassium foliar spraying decreased the activity of antioxidant enzymes and increased the content of malondialdehyde(MDA)in the upper three leaves,and also increased the contents of key enzymes and free amino acids(FAA)in the upper three leaves and grains.These data revealed that foliar application of potassium fertilizer regulates the filling of vulnerable grains by improving the processing efficiency of genetic information in grains,such as regulating the processes of"membrane transport","amino acid metabolism"and"carbohydrate metabolism",and also affects the activity of related enzymes and MDA content in the upper three leaves.The changes of related enzyme activities combined with transcriptome analysis revealed the mechanism of potassium fertilizer affecting grain quality.RNA-Seq analysis showed that the differentially expressed genes were mainly enriched in'regulation of biological processes'and'metabolic processes',which indicated that foliar application of potassium fertilizer regulated grain filling by regulating metabolism of cysteine,methionine,phenylalanine and carbon sequestration of photosynthetic organisms.At the same time,foliar application of potassium fertilizer also affected the activities of related enzymes and MDA content in the upper three leaves and grains.The changes of related enzyme activities combined with the results of transcriptome analysis revealed the mechanism of potassium fertilizer affecting grain quality.(3)Under potassium deficiency conditions,the growth status and grain quality of wheat were poor.After foliar application of potassium fertilizer,the photosynthetic rate of each part of the plant in the upper three leaves,and the nitrate reductase activity were increased,thereby delaying leaf senescence and increasing grain flour quality.In this experiment,two different treatments of potassium concentration in root were set up through pot experiment to study whether spraying potassium fertilizer on leaf surface can alleviate the harm of potassium deficiency.The results showed that the photosynthetic rate and nitrate enzyme of leaves under low potassium treatment were significantly lower than those under high potassium treatment.Although Spraying Potassium Fertilizer at flowering stage could promote the increase of its content,it could not completely replace the nutrient solution with sufficient potassium concentration.The grain yield and quality indexes(protein,wet gluten,sedimentation value,microelements,dough stability time and formation time)were low under low potassium supply.The grain yield and quality were improved after spraying potassium fertilizer on leaves,but were lower than those under high potassium supply.Under different potassium treatments,the content of 7+8 subunits in HMW-GS did not change significantly,but the higher the concentration of potassium nutrient solution,the more obvious the content of 1,4+12 subunits increased.Potassium fertilizer spraying was beneficial to the improvement of subunit content under low concentration cultivation conditions.There was little difference in the molar ratio of phytic acid to trace elements under low potassium and high potassium treatment.Foliar spraying under low potassium treatment was conducive to the decrease of the molar ratio.This shows that the photosynthetic characteristics,grain yield and quality indexes of leaves under low potassium treatment are low.Spraying potassium fertilizer can make up for the damage caused by potassium deficiency,but the effect is lower than that of high potassium level.(4)The combination of potassium,nitrogen and phosphorus had a synergistic effect on the improvement of grain yield and quality.The effect of spraying potassium nitrate(K+N)was the most obvious,followed by potassium dihydrogen phosphate(K+P).The effect of spraying potassium in combination with other elements on the three flours is similar.After the milling treatment,the wet gluten content,sedimentation value,dough formation time and stability time of the three types of flour changed significantly.The effects of foliar spraying of three fertilizers on gluten content,sedimentation value,dough formation time and stability time were K+N>K+P>K>CK.In general,the wet gluten and sedimentation value of spraying potassium nitrate showed that the contents of whole flour and 85%whole flour were similar,both greater than 70%whole flour.The effects of spraying three kinds of fertilizers on the gluten content,sedimentation value,dough formation time and stability time were K+N>K+P>K>CK.In general,spraying potassium nitrate wet gluten and sedimentation value showed that the content of whole flour and 85%whole flour were similar,both greater than 70%whole flour;the formation time and stability time of the dough were 85%whole flour>whole flour>70%whole flour;The molar ratio of phytic acid to trace elements shows that the whole powder is not much different from 85%whole flour,and both are lower than70%whole powder;the HMW-GS content is all shown as 85%whole flour>whole flour>70%whole flour.In addition,foliar spraying of potassium fertilizer and potassium nitrate was conducive to the decrease of phytic acid to molar ratio,but spraying of potassium dihydrogen phosphate increased its molar ratio.Spraying potassium chloride and potassium phosphate on the leaf of potassium fertilizer did not change the distribution of quality index content in each layer,but spraying potassium nitrate made the content of relevant nutritional quality indexes in 85%whole flour and whole flour similar.Comprehensive analysis showed that among the three kinds of spraying fertilizers,potassium nitrate improved the quality indexes of flour most obviously.Therefore,foliar application of potassium fertilizer during the flowering period can be a reasonable fertilizer supplement measure in Northwest China,which is of great significance for improving grain yield and flour quality,and alleviating the negative effects of potassium deficiency.