Regulation Mechanism Of Potassium On Sugar And Acid Metabolism Of 'Red Delicious' Apple In Dryland Region Of Loess Plateau

Potassium is an important mineral element affecting the growth and quality of apples,but its mechanism for regulating fruit quality remains to be further explored.Microbial fertilizer can improve the micro-ecological environment of rhizosphere soil,promote the absorption of potassium by fruit trees,and improve fruit quality.In this study,7-year-old of the fifth generation of‘Red Delicious'apple cv.‘Vallee spur Del'was used as the research object.The two-year positioning experiment was carried out continuously.The regulation mechanism of potassium on sugar and acid metabolism in fruits and the synergistic effect of microbial and potassium fertilizers were studied through different potassium fertilizer levels and combined application of potassium fertilizer and microbial bacterial fertilizer.The theoretical basis was provided for potassium regulating the formation of fruit quality,which had important guiding significance for improving potassium utilization efficiency and apple yield and quality.The main results are as follows:1.Potassium application increased the new shoot length,new shoot thickness,louver weight and leaf size of fruit trees,increased the nitrogen,phosphorus and potassium contents of new shoots and leaves,and significantly reduced Ca and Mg contents.At different growth stages,potassium accumulation in roots,leaves and fruits increased with the increase of potassium application.Potassium application increased apple yield,single fruit weight and proportion of primary fruit(fruit diameter(>80 mm),soluble solids content,p H value,VC content and sugar-acid ratio,and decreased titratable acid content.At fruit ripening stage,soluble solids content,fruit weight and p H value were positively correlated with potassium application,while titratable acid content was negatively correlated with potassium application.The optimum dosage of K₂O was 420-546 kg/ha.2.Potassium application increased the contents of ZR,IAA and GA in young and expanding fruits,as well as ABA content in mature fruits.Single fruit weight and soluble solids content were positively correlated with GA,ZR and IAA in young fruit stage and swelling stage(P<0.01),and positively correlated with ABA content in ripening and harvesting stage(P<0.01).The titratable acid content was positively correlated with GA,ZR and IAA in young fruit stage and swelling stage(P<0.01),while negatively correlated with ABA content in ripening and harvesting stage(P<0.01).3.Potassium application significantly increased fruit fructose,glucose and sucrose content,and promoted SOX,SS,SPS and alpha-AMY activity,but excessive potassium application was not conducive to the accumulation of sugar concentration.At young fruit stage,the contents of fructose,sucrose,glucose,SPS and SS activities were positively correlated with the contents of GA,ZR and IAA(P<0.05).At fruit ripening stage,fructose,sucrose and glucose content were positively correlated with ABA content(P<0.01);starch content and alpha-AMY activity were positively correlated with ABA(P<0.05);GA,ZR,IAA and ABA content were negatively correlated with SDH activity(P<0.05),and positively correlated with SOX activity(P<0.05).4.Potassium application significantly reduced the content of malic acid and citric acid,but had no significant effect on oxaloacetic acid and succinic acid.Potassium inhibited the activities of MDH and PEPC,and promoted the activities of PEPCK and NAD-cy ME.Malic acid and oxaloacetic acid were positively correlated with ZR and IAA(P<0.01)and negatively correlated with ABA(P<0.01).MDH and PEPC were positively correlated with IAA(P<0.05)and negatively correlated with ABA(P<0.05).PEPCK was positively correlated with ABA(P<0.01).NAD-cy ME was negatively correlated with IAA(P<0.05)and positively correlated with ABA(P<0.05).5.Compared with single application of potassium fertilizer,the combination of microbial bacterial fertilizer and potassium fertilizer significantly improved the agronomic efficiency,fertilizer contribution rate and fertilizer partial productivity of potassium fertilizer.The root activity of fruit trees in 0-120 cm soil layer were significantly increased,and the fruit weight,soluble solids content and Vc content were significantly increased.The order of potassium accumulation in roots,new shoots,leaves and fruits of different growth stages was:microbial fertilizer+potassium fertilizer>potassium fertilizer>microbial fertilizer>CK,and the difference between treatments was significant(P<0.05).The fruit weight,soluble solid content and Vc content were positively correlated with soil microbial quantity and soil enzyme activity(P<0.05).