Assimilation and partition of nitrogen in leaves of citrus species e their relationship with nutrient use efficiency

• Grant number: 16/20509-3
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: January 01, 2017
• End date: December 31, 2017
• Field of knowledge: Agronomical Sciences - Agronomy - Crop Science
• Principal Investigator: Dirceu de Mattos Junior
• Grantee: Juliana Martinatti
• Host Institution: Instituto Agronômico (IAC). Agência Paulista de Tecnologia dos Agronegócios (APTA). Secretaria de Agricultura e Abastecimento (São Paulo - Estado). Campinas , SP, Brazil

Abstract

The use of nitrogen supplied as a mineral fertilizer in Citrus production varies between 15% and 85%. Among the factors that affect the N use efficiency (NUE) are the efficiency related to the nutrient acquisition (EUNa) and biomass processing (EUNt). Among the Citrus species, lemon trees exhibited higher NUE when compared to sweet orange ones because of the lower N concentration in leaf tissue but higher yield capacity. This difference could be partially explained by the N partition into the leaves to the photosynthetic apparatus components or as structural proteins and secondary compounds. Furthermore, lemon trees recovery more N from the fertilizer than sweet orange ones, mainly in the summer, in which can be related to the activity of the nitrate reductase (NR) enzyme that catalyze the initial reaction of NO3- reduction to NO2-. On the hypothesis that lemon trees invest a smaller proportion of N to non-productive structures, such as storage organs, and have greater N assimilation capacity compared to sweet orange trees, the aim of this study is to assess in plants of both citrus species, under to different levels of N (5 and 25 g N per plant year-1), differences in N partition invested into soluble proteins (Calvin cycle and Rubisco mainly), membrane proteins (pickup pigments energy) and insoluble proteins (located in walls); as well as the efficiency in reduce the NO3- absorbed. We will analyze the N and NO3- concentrations, N partition and chlorophyll amount. In a second experiment, with the same plant growth conditions, will be assessed the activity in vivo and in vitro of the NR, and the concentrations of soluble sugar, amides, free amino acids and NO3-, in two seasons (summer and winter) and two different periods of the day (9:00 and 15:00 h). (AU)