| China is the world's largest potato producer with the largest potato planting area and total output in the world.Hubei province is one of the important potato producing areas in China.Potassium is the most important mineral nutrient in potato,which plays an important role in the growth and quality of potato.The appropriate amount of potassium fertilizer is one of the major means to promote potato growth and improve potato yield and quality.Studying the effect of potassium fertilizer on potato growth and its regulation mechanism,and defining the appropriate potato potassium fertilizer dosage are of great significance to the rational application of potato potassium fertilizer and the development of potato industry in Hubei province.With the proposal and implementation of the"potato staple food strategy"in China in 2015,the use of potatoes to replace or partially replace other food crops into the processing of vermicella,noodles,steamed buns and other staple food is getting more and more attention.How to increase potato yield and improve potato processing quality is the important points of potato staple food strategy.Starch is the main component of potato tuber.The processing characteristics of potato starch directly affect the processing quality of potato food and the development of potato staple food.We must pay attention to the changes of potato starch processing characteristics while controlling potato yield by applying potassium fertilizer.It is of great significance to determine the effect of potash fertilizer dosage on the processing characteristics of potato starch for the production of high-quality and high-yield potato starch and the promotion of the main grain conversion process of potato.This study explored the effects of potassium application rates and the combination of potassium,nitrogen and phosphorus on growth,yield and nutrient accumulation and distribution of potatoes in different areas of Hubei province by field experiments.The regulation mechanism of potassium application on leaf growth and physiological function was explored through the changes of photosynthesis,carbon metabolism and the analysis of gene expression.The effect of potassium application rates on the processing characteristics of potato starch was deterned by studying the composition,structure,thermal properties,gelatinization properties and retrogradation properties of potato starch.The main conclusions obtained were as follows:?1?The appropriate amount of potato potassium fertilizer in Hubei Province was determinedField experiments of potato with different potassium fertilizer dosages?0,120,240,360,480 kg/ha?in plain areas of Hubei province?Yunmeng,Xiangzhou?and mountainous areas of Western Hubei province?Jianshi,Lichuan?,the potassium fertilizer effect equation was established y=-0.1983x2+114.82x+28334?Yunmeng?,y=-0.1584x2+87.158x+31149?Xiangzhou?,y=-0.1131x2+55.252x+23795?Jianshi?,y=-0.1047x2+50.688x+21138?Lichuang?.And,the optimal economic potassium fertilizer dosage in plain area and mountainous area were 258.3-276.1 kg/ha and 216.6-220.7 kg/ha,respectively.Compared to no potassium fertilizer,the average yield increased by 35.9%and 21.9%in plain area and mountainous area,with the large-size tuber rate increased and the small-size tuber rate decreased.The application of potassium fertilizer promoted the growth of every organ of potato plants,and the total dry matter of whole plants in plain and mountain areas increased by 34.5%and 21.6%respectively.With the increase of potassium fertilizer application,the potassium accumulation of potato plants ranged from209.06 kg/ha to 308.26 kg/ha,an average increase of 67.0%compared to that of no potassium fertilizer supplying.In mountainous areas,the potassium accumulation of potato plants ranged from 209.06 kg/ha and 308.26 kg/ha,an average increase of 49.3%compared to that of no potassium fertilizer treatment.More than 50%of potassium is distributed to tubers.Potato potassium fertilizer use efficiency decreases with the increase of potassium fertilizer application.The potassium fertilizer use efficiency in plain area is higher than that in western mountainous area.?2?The absorption characteristics of potato nutrients and the application ratio of NPK were determinedThe accumulation of nitrogen,phosphorus and potassium in potato plants was156.45 kg/ha,58.17 kg/ha and 266.40 kg/ha in conventional fertilization treatment,whereas in recommended condition is 153.85 kg/ha,61.74 kg/ha and 275.97 kg/ha.The accumulative distribution ratios of nitrogen,phosphorus and potassium in potato organs were tuber>leaf>stem>root.The accumulative allocation of nitrogen,phosphorus and potassium in tuber was 52.9%61.1%,70.2%76.0%and 53.9%63.5%in conventional fertilization treatment,whereas in recommended fertilization treatment was 59.8%65.9%,76.2%78.7%and 61.4%67.3%,respectively.Under optimum conditions,the average uptake of N,P2O5 and K2O per 1000kg tuber potato plant was 3.32 kg,1.33 kg and 5.95kg,respectively.When the target yield was 3750045000 kg/ha,the application rates of N,P2O5 and K2O ranged from 129219 kg/ha,70126 kg/ha,156282 kg/ha.The application rates of N,P2O5 and K2O per 1000 tubers were 3.444.86 kg/ha,1.852.81kg/ha,4.166.27 kg/ha,and the application ratio of N,P2O5 and K2O was1:0.530.58:1.171.29.The utilization efficiency of nitrogen,phosphorus and potassium fertilizers in optimized fertilization treatment was 39.2%,25.9%and 50.1%,which was7.9,14.4 and 10.3 percentage points higher than that of conventional fertilization,while the total amount of fertilizer reduced by 26.8%,the yield increased by 13.0%,the income increased by 18.5%,and the ratio of output to input increased by 49.5%.?3?The regulation mechanism of Potassium Fertilizer on leaf physiological function was revealed from physiological and molecular aspectsThe application of potassium fertilizer promoted leaf growth and tuber yield.The dry weight of single leaf and tuber yield increased by 32.7%and 45.9%respectively.On one hand,the application of potassium fertilizer promoted the synthesis of photosynthate in leaves by increasing chlorophyll content,photosynthetic rate,and the activities of rubisco,sucrose phosphate synthase and sucrose synthase,and at the maentime,reduced the content of non-structural carbohydrates and promoted the transport of assimilate.On the other hand,the application of potassium fertilizer reduced the accumulation of MDA,proline and ABA in leaves and delayed the senescence of leaves.There are differences in leaf position in the regulation of physiological function of leaves by potassium fertilizer application.The effect of potassium fertilizer application on the lower leaves was greater than that on the upper leaves.To this end,we sequenced the lower leaf transcriptome by using RNA-seq technology.The results showed that 539 genes were differentially expressed in the leaves treated with potassium fertilizer,among which 255 genes were up-regulated and 284 genes were down-regulated.GO enrichment analysis showed that the differentially expressed genes were mainly concentrated in cellular homeostasis,photosynthesis and other biological processes.KEGG enrichment analysis showed that differentially expressed genes were mainly concentrated in photosynthesis,metabolic pathways and secondary metabolic pathways.Further analysis of differentially expressed genes showed that potassium could up-regulate the expression of glutaredoxin and other genes related to cellular homeostasis,thus maintaining redox homeostasis in cells.The key genes of chlorophyll protein complex,ATPase,PS I,PS II and cytochrome b6/f complex in photosynthesis pathway were up-regulated by potassium application,which promoted leaf photosynthesis.The key enzymes in the phenylpropane pathway,such as Caffeoyl-CoA O-methyltransferase,Cinnamoyl-CoA reductase and c Cinnamyl alcohol dehydrogenase genes,were down-regulated by potassium application.Potassium deficiency stress caused a change in the direction of carbon flow to phenylpropane secondary metabolism.Meanwhile,the PYL4 gene of ABA receptor protein was down-regulated to inhibit the ABA signal.In conclusion,on the one hand,potassium promotes photosynthesis and assimilation products synthesis by up-regulating the expression of photosynthesis-related genes.On the other hand,potassium fertilizer can reduce lipid peroxidation,maintain cellular homeostasis,inhibit ABA signal and delay leaf senescence,thus promoting plant growth and increasing tuber yield.?4?The application of 270 kg/ha potassium significantly increased the content and yield of potato starch,and improved the processing quality of potato starchCompared to the application of 135 kg/ha potassium fertilizer,the potato tuber yield and starch yield were increased by increasing the amount of potassium fertilizer.Potato tuber yield and starch yield were the highest with 270 kg/ha potassium fertilizer application,which increased by 28.6%and 32.6%respectively compared with 135 kg/ha potassium fertilizer application.With increasing potassium application rates,the amylose content,phosphorus content and particle size decreased.The amount of potassium fertilizer did not alter the potato starch crystallinity type,but the crystallinity of starch increased with the increase of the amount of potassium fertilizer.Compared with the application of 135 kg/ha potassium fertilizer,increasing the amount of potassium fertilizer increased the swelling power,and the water absorption and swelling ability of starch.Thermal properties analysis showed that increasing the amount of potassium fertilizer reduced the gelatinization temperature,increased the enthalpy of gelatinization,and increased the gelatinization degree of starch.The breakdown value of starch decreased with the increase of potassium fertilizer,which indicated that the thermal stability and shear resistance of starch were improved by increasing potassium fertilizer.Meanwhile,increasing the amount of potassium fertilizer reduced the setback value,and increased the transparency of starch paste during storage,which indicated that the retrogradation of starch paste during cooling and storage was inhibited.Therefore,the processing characteristics of potato starch can be improved by properly increasing the amount of potassium fertilizer.Consideration of starch yield and starch quality,the application of270 kg/ha potassium fertilizer could obtain highest tuber and starch production with desirable starch physicochemical properties. |
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