| Grapes(Vitis vinifera L.)are one of the four major fruit trees in the world and have an important economic value.Grapes are also a "potassium-loving fruit tree" and their potassium fertilization needs increase with the development of the berry fruits.Due to the wide variety of potassium fertilizers in grape production,the suitable potassium fertilizers for grape production have not been reported.Therefore,it is important to screen out the best potassium fertilizer for grape nutrient uptake and fruit quality improvement.In view of this,this study investigated the effects of four potassium-containing fertilizers on nutrient uptake and fruit quality formation in ’Shine Muscat’ grapes by applying the complex fertilizer,potassium nitrate,potassium sulfate and potassium dihydrogen phosphate as treatments and no potassium fertilizer as control.The mechanism of potassium-containing fertilizers affecting‘Shine Muscat’ berry fruit quality formation(sugar-acid metabolism)was investigated at the physiological and molecular levels.The study could provide a practical and theoretical basis for the nutritional growth and high quality fruit formation of ‘Shine Muscat’.The main results of the study were as follows:(1)Complex fertilizer and potassium nitrate increased the biomass of different parts(rootstock roots,rootstock stems and scions)of ’Shine Muscat’ young grapevines,while potassium sulfate and potassium dihydrogen phosphate had no significant effect.Complex fertilizer and potassium nitrate increased the total nitrogen content of different parts of ’Shine Muscat’ young grapevines to some extent,while other fertilizers decreased that.Potassium-containing fertilizers increased the total phosphorus and total potassium contents in different parts of ’Shine Muscat’ young grapevines.Compared with the control,complex fertilizer,potassium nitrate,potassium sulfate and potassium dihydrogen phosphate treatments increased the total phosphorus content in scions by 20.18%,9.77%,12.52% and30.81%,respectively,and increased the total potassium content in scions by 15.37%,8.41%,20.15% and 26.48%,respectively.The correlation and gray relational analyses showed that the soil available nutrient concentration was closely related to the nutrient accumulation by scions of ’Shine Muscat’ young grapevines.(2)Complex fertilizer increased the total nitrate content in leaves,fruit skins and fruit pulps of ’Shine Muscat’ fruiting trees to some extent,while potassium nitrate had no significant effect,and potassium sulfate and potassium dihydrogen phosphate decreased the total nitrate content.Both complex fertilizer and potassium phosphate increased the total phosphorus and total potassium contents in leaves,fruit skins and fruit pulps to some extent,while potassium nitrate and potassium sulfate had no significant effect on the total phosphorus content,and only potassium sulfate increased the total potassium content.Compared with the control,complex fertilizer,potassium sulfate and potassium dihydrogen phosphate increased the total potassium content in leaves by 17.96%,25.00% and 31.75%,respectively,and the total potassium content in fruit pulps by 10.63%,10.02% and 11.96%,respectively;potassium sulfate and potassium dihydrogen phosphate increased the total potassium content in fruit skins by 5.75% and 6.63%,respectively.The correlation and gray relational analyses showed that the soil available nutrient concentration was closely related to the nutrient uptake by ‘Shine Muscat’ berry fruits.(3)Potassium nitrate increased the single fruit weight of ‘Shine Muscat’ berry fruit by12.42% compared with the control,while the effects of complex fertilizer,potassium sulfate and potassium dihydrogen phosphate treatments on the single fruit weight of ‘Shine Muscat’berry fruit were not significant.The effects of potassium-containing fertilizers on longitudinal diameter,transverse diameter and fruit shape index of ‘Shine Muscat’ berry fruits were not significant.Potassium-containing fertilizers increased the vitamin C content and the activities of enzymes related to sugar metabolism(sucrose synthase,sucrose phosphate synthase,acid convertase and neutral convertase)at all stages of ‘Shine Muscat’ berry fruit development,and increased the contents of total soluble solid and each sugar fractions(total soluble sugar,reducing sugar,fructose,sucrose and glucose)at the later stages of ‘Shine Muscat’ berry fruit development,with potassium sulfate and potassium phosphate being the most effective in increasing sugar accumulation in ‘Shine Muscat’ berry fruits.During ‘Shine Muscat’ berry fruit ripening,complex fertilizer,potassium nitrate,potassium sulfate and potassium dihydrogen phosphate treatments increased the vitamin C content by 91.37%,119.19%,32.92% and 65.49%,respectively,increased the total soluble solid content by 1.5,1.2,3.5and 3.4 percentage points,respectively,and increased the total soluble sugar content by19.39%,17.00%,26.29% and 27.81%,respectively,compared with the control.(4)Potassium-containing fertilizers increased the activities of enzymes related to acid metabolism(phosphoenolpyruvate carboxylase,malic enzyme,malate dehydrogenase,citrate synthase,isocitrate dehydrogenase and cis-aconitate enzyme)at all stages of ‘Shine Muscat’berry fruit development and reduced the content of titratable acids and individual acid fractions at later stages of fruit development,with potassium sulfate and potassium dihydrogen phosphate being the most effective in reducing acid accumulation in ‘Shine Muscat’ berry fruits.During ‘Shine Muscat’ berry fruit ripening,complex fertilizer,potassium nitrate,potassium sulfate and potassium dihydrogen phosphate treatments decreased the titratable acid content by 0.09,0.06,0.18 and 0.17 percentage points,respectively,and increased the total soluble solid/ titratable acid ratio by 20.42%,13.69%,50.13% and 45.52%,respectively,compared with the control.In terms of the cost of applying potassium-containing fertilizers,the cost of the same amount of potassium application was:potassium sulfate < potassium nitrate < complex fertilizer < potassium dihydrogen phosphate.(5)According to the results of suger and acid metabolism,the days of 14,28 and 42 after treatment were choosed for transcriptomic analysis.The results showed that the number of differential genes between potassium-containing fertilizers and the control was highest for potassium sulfate and potassium dihydrogen phosphate.At 14,28 and 42 days after treatment,937,390 and 2057 genes were differentially expressed in the treatment group versus the control,respectively,with 19 genes differentially expressed in all these three periods.The differential expressions of genes in ‘Shine Muscat’ berry fruits treated with potassium-containing fertilizers were mainly enriched in "carbon metabolism","carbon sequestration by photosynthetic organisms","glycolysis and gluconeogenesis" and "fructose and mannose",which were the pathways associated with fruit quality formation.Moreover,four genes related to sugar metabolism(PK,PFK,GOLS1 and SS)and seven ion uptake transport genes(SOR,CNGC4,AKT2,NFXL1,PT6,OCT3 and PHT14)were identified by the transcriptomic analysis.RT-qPCR validation showed that the expressions of PK,PFK,GOLS1,SS,NFXL1,PT6,OCT3 and PHT14 gens were higher than the control at all periods after treatment,with potassium sulfate and potassium dihydrogen phosphate treatments were the highest.The expressions of SOR and AKT2 genes were higher than the control at the beginning of treatment period and lower than the control at the end of treatment period;the expression of CNGC4 gene was lower than the control at the beginning of treatment period and higher than the control at the end of treatment period.Analysis of co-expressed gene network construction got 57 co-expressed gene modules,and three of which showed significant relationships with the soluble sugar and organic acid contents.In conclusion,complex fertilizer and potassium nitrate promoted the vegetative growth of ’Shine Muscat’,and potassium nitrate also promoted the growth of ‘Shine Muscat’ berry fruits.Potassium-containing fertilizers promoted the nutrient uptake by ’Shine Muscat’grapevines to some extent.Potassium-containing fertilizers promoted the sugar accumulation,reduced the acid accumulation and improved the total soluble solid/ titratable acid ratio,thus improving ‘Shine Muscat’ berry fruit quality.Therefore,from the point of view of cost saving and efficiency increase,potassium sulfate should be applied as the main fertilizer and potassium dihydrogen phosphate as a supplement for ‘Shine Muscat’ production.Complex fertilizer and potassium nitrate should be applied as a supplement before the softening of‘Shine Muscat’ berry fruits,while potassium sulfate and potassium dihydrogen phosphate should be applied from the softening to the ripening stage to increase the sugar content,reduce the acid content and improve the sugar/ titratable acid ratio of the ‘Shine Muscat’berry fruits. |
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