Study On Reasonable Nitrogen Nutrition Requirement And Regulation Mechanism Of Carbon And Nitrogen Metabolism In Huangguogan

‘Huangguogan'(Citrus reticulata×C.sinensis)is a hybrid citrus cultivar.At present,the best proportion of N,P and K fertilizers of Huangguogan is known,but there are few reports about the suitable nitrogen requirement for Huangguogan cultivation.In this paper,the regulation mechanism of nitrogen fertilizer on nitrogen metabolism,sugar and acid metabolism and Photosynthesis of Huangguogan was discussed in order to provide theoretical support for rational fertilization and improvement of fruit qualityThe experimental design is divided into two parts:(1)Field experiment.Using10-year-old Huangguogan as material,5 levels of nitrogen application were set up,and the amount of nitrogen used was 0,1.36,1.81,2.26 and 2.72 kg,respectively,expressed by N₁,N₂,N₃,N₄ and N₅,respectively.The relationship between nitrogen application rate and sugar and acid metabolism and nitrogen metabolism was explored,and then the optimal amount of fertilizer of 10-year-old Huangguogan was obtained;(2)Pot experiment.Using2-year-old grafted Huangguogan seedlings as materials,7 levels of nitrogen application were set up.The amount of nitrogen used was 0,30,60,90,120,150 and 180 g,respectively,and was recorded as F₁,F₂,F₃,F₄,F₅,F₆ and F₇,respectively.The response mechanism of photosynthesis to nitrogen fertilizer was studied.On the basis of determining the suitable nitrogen application rate for seedlings,11 nitrogen ratios of nitrate and ammonium were set up.By studying the difference of photosynthetic performance of seedlings,the optimum nitrogen ratio of nitrate and ammonium was determined.The main results are as follows:1.The genes of Nitrate reductase(NR),nitrite reductase(NiR),glutamine synthetase(GS),glutamate dehydrogenase(GDH)and asparagine synthetase(AS)were cloned from Huangguogan leaves and identified as HgNR,HgNi R,HgGS,HgGDH and HgAS,respectively.Sequencing results showed that the CDs of HgNR,HgNiR,HgGS,HgGDH and HgAS ranged from 1236 BP to 2709bp in length,encoding 411-902 amino acids.Subcellular localization showed that Hg NR-GFP?HgNiR-GFP?HgGDH-GFP and HgAS-GFP were located in cytoplasm and plasma membrane;Hg GS-GFP was located in cytoplasm and mitochondria.The activity of NR,NiR,GS,GD and AS and the expression of related genes increased with the increase of nitrogen application,and the fertilization treatment of 1.81kg was the best2.The root activity,chlorophyll content,antioxidant enzyme activity,malondialdehyde content and soluble protein content of Huangguogan increased with the increase of nitrogen application.The best nitrogen treatment was 1.81 kg,followed by 1.36kg/tree.Both excessive nitrogen(2.72 kg)and nitrogen deficiency(0 kg)increased malondialdehyde content and decreased antioxidant activity.3.The treatments with 1.81 kg had the highest TSS and TSS/TA content and the lowest TA content,while the treatments with N₁ had the lowest TSS and TSS/TA content and the highest TA content.During fruit development,sucrose and citric acid changed the most,sucrose and ascorbic acid increased(8.46-50.97 mg g^-1 and 8.16-27.39 mg g^-1),while citric acid decreased(90.81-0.02 mg g^-1).The main component analysis showed that the nitrogen content of fruit was positively correlated with sugar and vitamin components,and negatively correlated with organic acid components.In conclusion,we suggest that 0.68 kg to 0.92 kg is the suitable range of nitrogen application for Huangguogan.4.The changes of photosynthetic gas parameters,chlorophyll fluorescence parameters,leaf nitrogen content,Ru Bis CO enzyme content and stomatal size were measured.The results showed that when the nitrogen application rate was 120 g the photosynthetic index was the highest.The decrease of photosynthetic rate(P_N)was related to the decrease of nitrogen content in leaves under 150 g or 180 g nitrogen supply.5.The photosynthetic performance of Huangguogan in spring,summer,autumn and winter was measured by Li-6400 portable photosynthetic system,and the difference of photosynthetic capacity of Huangguogan treated with 11 ammonium nitrate nitrogen ratios was also measured.The results showed that when NO₃^--N:NH₄⁺-N was 8:2(T₃),the P_N,Tr,WUE,Gs,Chl.a,Chl.b,Chl.a+b and Car.were higher than those of other treatments,and the treatment of pure NO₃^--N(T₁)or pure NH₄⁺-N(T₁₁)was the lowest.