Absorção e eficiência de uso de nitrogênio por cultivares de café submetidas a déficit hídrico

BOHÓRQUEZ, César Avellaneda. D.Sc.,Universidade Federal de Viçosa, September, 2019. Uptake and efficiency the use of nitrogen by coffee cultivars submitted to water stress. Advisor: Hermínia Emília Prieto Martinez. Co-advisors: Paulo Roberto Cecon and Kacilda Naomi Kuki. Climate change and the expansion of the agricultural frontier to low fertility soils have motivated research to understand the effects of abiotic stresses on the performance of coffee genotypes to identify materials with some degree of tolerance. This research has as objective to evaluate the varietal differences related to nutritional efficiency, gas exchange and chlorophyll fluorescence parameters in contrasting conditions of nitrogen and water availability (experiment 1), as well as to estimate the kinetic parameters of nitrate absorption in different phenological phases of coffee berry development (experiment 2). The experiment 1 was done in green house, under hydroponic system. Four 6-month-old arabica coffee genotypes (Mundo Novo MN, Catuaí Amarelo CA, Catuaí Vermelho CV and Acauã A) were submitted to water stress levels and high (NA) and low (NB) nitrogen doses. Was used a factorial scheme in experimental design randomized block (4x2x4) with 3 replications. The factors were: 4 cultivars, 2 nitrogen doses (NA and NB) and 4 levels of water deficits of the nutrient solution (0, -0.4, 0.8 and -1.6 MPa) established via the addition of PEG (Polyethylene glycol). Plants were harvested to estimate dry matter and total nitrogen levels in leaf, stem and roots to calculate efficiency indexes. Photosynthesis (A), carboxylation efficiency (EC), water use efficiency (EUA) and fluorescence parameter Fv / Fm were evaluated. Regressions due to the increase of water deficit showed that the absorption efficiency in NA increased to MN and CV, and decreased to CA and A. In NB the efficiencies were lower in relation to NA and increased with deficit for MN, CA and A, not varying for CV. In NB all varieties showed lower decreasing efficiencies, except for MN that did not vary. It can be concluded that MN was the variety that showed the best performance regarding absorption, translocation and utilization efficiencies in both adequate and low nitrogen availability, therefore, it is promising. Regarding gas exchange at NA dose, the CA cultivar showed the lowest reductions in A, EC and highest EUA values in response to water deficit of -0.8 MPa. The Fv / Fm parameter in the cultivars was not affected by the imposition of water deficit indicating that there was no decrease in photochemical efficiency, and that nitrogen supplementation did not interfere with this response. At NB dose the Acauã cultivar showed smaller reductions A, EC and EUA in response to water deficit of -0.4 and -1.6 MPa. Fv / Fm of the cultivars was not affected by the degree of water deficits imposed. It can be concluded that in NA dose, the CV showed better gas exchange performance and Acauã was less impacted by water deficit and low nitrogen availability. In experiment 2, 5-year-old trees were used under field conditions in the phenological phases of pin head fruit (PH), rapid expansion (RE), granation (G) and maturation (M). Trenches were dug and roots selected to induce production of new thin roots by installing a growth chamber with vermiculite, then removing and washing the roots, without detach them of the plant, to begin the nitrate exhaustion test; using 90 μmol L solution of NO3 and known volume. The exhaustion essays have began three hours after sun down and ended at about five PM. Along this time samples of the exhaustion solution were picked in an hour base. With transpiration data, the fresh weight of roots / plant, and nitrate concentration in the samples the absorption kinetic parameters Vmax, Km and NO3 absorption rate were calculated. Descriptive analysis was used to present the results. Vmax values were higher at (PH) and (M) phase. Nitrate absorption rate was higher in phase (RE) up to 20 μmol L, with higher absorption rate in phase (M) above this concentration and with lower rate in phase (G). Vmax only in the phase (RE) had a positive correlation with fruit production. Km showed lower value in (RE) phase positively affecting absorption rate, with higher values in (G) and even more in (M). It was concluded that nitrate absorption rates showed dependence on phenological phases, indicating that absorption mechanisms can modulate kinetic parameters as a function of differential demands in each phase.