Effects Of Foliar Spraying Different Concentrations Of Nitrogen And Potassium Fertilizer On Sugar Metabolism In ‘Gala' Apple

Nitrogen is the life element of plants and potassium is an important quality element of fruit trees.Both of them play important roles in apple fruit development and quality formation.Therefore,it is important to study the effects of nitrogen and potassium on sugar metabolism in apple fruit.Choosing pure water as control treatment,the experiment involved six treatments as follows: spraying solutions of 0.1% urea(N1),0.3% urea(N2),0.5% urea(N3),0.1% K2SO4(K1),0.3% K2SO4(K2)and 0.5% K2SO4(K3)on 5-year-old potted ‘Gala' apple/M26 self-rooted apple seedling.Each treatment was carried out for 5 times and all treatments were arranged in a randomized complete block design.The contents of sorbitol,fructose,sucrose,glucose and starch and their relevant metabolic enzymes were measured during apple fruit development.The main results were as follows:1.Nitrogen supply increased fruit weight,firmness,soluble solids and titratable acid contents.The nitrogen supply was positively correlated with fruit weight and titratable acid content.That is to say,the more nitrogen supply,the heavier of fruit weight and the much of titratable acid content.By contrast,negative relationships were found between nitrogen supply and firmness as well as soluble solids.With the increase of nitrogen supply,firmness and soluble solids content decreased gradually.2.Nitrogen supply delayed the synthesis and degradation time of starch.The appropriate nitrogen fertilizer(N2)increased the activity of ADPG pyrophosphatase(AGPase)and promoted synthesis of more starch.It also could improve the ?-amylase and ?-amylase activities,catalyzing more starch into glucose.The appropriate nitrogen supply(N2)enhanced the content of fructose and glucose effectively in the whole develpoment of apple fruit.It could also increase the content of sucrose during 80-125 days after blossom,while it had less effect on sorbitol.During apple fruit development,the appropriate nitrogen fertilizer(N2)improved the activities of acid invertase(AI),sucrose synthase(SS)and sorbitol dehydrogenase(SDH),which facilicated the accumulation of fructose and glucose.In addition,appropriate nitrogen fertilizer increased sucrose phosphate synthase(SPS)activity,and thus promoted the accumulation of sucrose.Excessive nitrogen fertilizer was not conducive to the sugar accumulation in apple fruit.3.The appropriate potassium fertilizer(K2)increased the fruit weight,firmness,soluble solids content.However,excess potassium supply(K3)decreased fruit weight,firmness and soluble solid content.Potassium supply reduced the titratable acid content.The more potassium supply,the less the titratable acid content.4.The appropriate potassium fertilizer(K2)improved the activity of ADPG pyrophosphatase(AGPase),and promoted the synthesis of more starch.In addition,it increased ?-amylase and ?-amylase activity,which catalyzed more starch into glucose.The appropriate potassium fertilizer(K2)boosted the fructose and glucose content effectively in the whole apple fruit development.Moreover,it increased sucrose content during 80-125 days after blossom,while it had less effect on sorbitol.The appropriate potassium fertilizer(K2)increased sucrose synthase(SS)activity,sorbitol dehydrogenase(SDH)activity during fruit development which promoted the accumulation of fructose and glucose.What's more,it also improved acid invertase(AI)activity during 50-95 days after blossom and promoted fructose and glucose accumulation.And the appropriate potassium fertilizer(K2)increased sucrose phosphate synthase(SPS)activity,and thus promoted the accumulation of sucrose.Excess potassium was not conducive to the sugar accumulation of fruit.All these results indicated that nitrogen fertilizer and potassium fertilizer should be in appropriate content.Excess fertilizers could not only result in lower fertilizer use efficiency but also reduce fruit quality.