Nitrogen nutrition is a key modulator of the sugar and organic acid content in citrus fruit

• Published in: PloS one 2019-10, Vol.14 (10), p.e0223356-e0223356
• Main Authors: Liao, Ling, Dong, Tiantian, Qiu, Xia, Rong, Yi, Wang, Zhihui, Zhu, Jin
• Format: Article
• Language: English
• Subjects: Acidity; Aconitate Hydratase - metabolism; Agriculture; Amino acids; Ascorbic acid; Biology and Life Sciences; Carboxylic Acids - metabolism; Cell division; Citric acid; Citrus; Citrus - growth & development; Citrus - metabolism; Citrus fruits; Citrus reticulata; Citrus sinensis; Cultivars; Developmental stages; Enzymes; Fertilization; Fertilizers; Food quality; Fructose; Fruits; Glucose; Glycolysis; Horticulture; Human nutrition; Irrigation; Krebs cycle; Mandarins; Metabolism; Metabolites; Monosaccharides; Nitrogen; Nitrogen - metabolism; Nitrogen fertilizers; Nutrition; Nutritional Physiological Phenomena; Organic acids; Physical Sciences; Physiology; Principal Component Analysis; Principal components analysis; Ripening; Soil; Solids; Studies; Sucrose; Sugar; Sugars - metabolism; Tricarboxylic acid cycle; Vitamin C; Vitamins
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0223356

'Huangguogan' (Citrus reticulata × C. sinensis) is a new cultivar of mandarin citrus in China, and the research on fertilization of 'Huangguogan' is very limited. In this study, the effect of N fertilization on 'Huangguogan' fruit quality was determined at ripening. Sugars (sucrose, fructose, and glucose), organic acids (pyruvic, oxalic, citric acid, etc.), and vitamin components were measured at six stages of fruit development, and eight enzymes related to the glycolytic and Krebs cycle were assessed. The 1.81 kg N y-1 treatment group showed the highest total soluble solids concentration and total soluble solids/titratable acidity ratio but the lowest titratable acidity (acid content) at ripening, while the N1 treatment (0 kg N y-1) showed the opposite trend. Sucrose and citric acid accumulated to the largest extent during fruit development. Sucrose and ascorbic acid content increased (8.46 to 50.97 mg g-1 and 8.16 to 27.39 mg g-1, respectively), while citric acid content decreased (90.81 to 0.02 mg g-1). Aconitase was the key enzyme responsible for the observed changes in citric acid. The N concentrations in ripening fruit ranged from 2.25% to 4.15%. Curve estimation and principal component analysis revealed that fruit N was positively correlated with the sugars and vitamin components and negatively correlated with the organic acids. The accumulation of these metabolites seemed closely related to the dynamic changes in fruit N concentration at the five N levels tested. In conclusion, we suggest that the 1.81 kg N y-1 treatment represents the most suitable N fertilizer treatment for 'Huangguogan' citrus fruit.