Coffee seedlings growth under varied NO3-:NH4+ ratio: Consequences for nitrogen metabolism, amino acids profile, and regulation of plasma membrane H+-ATPase

Root plasma membrane H⁺-ATPase electrochemical equilibrium for optimum coffee plant growth can be modulated by specific ammonium:nitrate (NO₃^-:NH₄⁺) ratio supply. This study aimed to evaluate the coffee seedlings responses to varying ammonium:nitrate (NO₃^-:NH₄⁺) ratio and to depict how much NO₃^- and NH₄⁺ plants can use in terms of growth, nitrogen metabolism, amino acids profile and regulation of root plasma membrane H⁺-ATPase. Coffee plants were grown in nutrient solution with the following NO₃^-:NH₄⁺ ratios (%): 100:0; 87.5:12.5; 50:50; 0:100. Plants were grown in nutrient solution for 90 days and evaluated for growth, nitrate reductase activity as well as the modulation of H⁺-ATPase activity in the plasma membrane of the roots, amino acids profile, chlorophyll a fluorescence parameters and estimated cations and anions taken up by plants. The plants treated with the 87.5:12.5 and 50:50 NO₃^-:NH₄⁺ ratio showed higher ability to absorb nutrients maintaining balanced uptake and as a consequence, 6% and 29%, the highest dry mass yield as compared to the 0:100 NO₃^-:NH₄⁺ ratio. In addition, plants supplied with the 87.5:12.5 and 50:50 NO₃^-:NH₄⁺ ratio had respectively, 58% and 94%, greater photosynthetic capability. Those data suggest that farmers and plant nurseries could implement the 50:50 NO₃^-:NH₄⁺ ratio of nitrogen sources at coffee plantations and seedlings.