Nitrogen Fertilization and Saline Solution on the Physiology, Micromorphology and Biochemical Components of Blueberry

Nitrogen formulation and saline irrigation may influence blueberry physiology, stomatal characteristics, and fruit composition. This study evaluated four NH4+–N3−–N formulations (100:0, 75:25, 0:100, and 25:75) under two salinity conditions (0 and 30 mM NaCl), plus an additional 50:50 control without NaCl, in ‘Biloxi’ blueberry grown in coconut fiber under protected cultivation. Salinity was applied through weekly irrigation with 30 mM NaCl. Leaf gas exchange was measured in three independent plants per treatment, and stomatal micromorphology was evaluated in four plants per treatment. Fruit total sugars and ascorbic acid were determined descriptively from a single composite sample per treatment. Significant formulation × salinity interactions were observed for net photosynthetic rate (A), stomatal conductance (gs), intercellular CO2 concentration (Ci), and transpiration rate (E). Salinity reduced A under the 100:0, 0:100, and 25:75 formulations, whereas the 75:25 formulation showed an increase from 2.733 to 4.500 µmol CO2 m−2 s−1. Nitrogen formulation significantly affected stomatal index and density, while salinity and its interaction with formulation were not significant for the evaluated micromorphological traits. Total sugars and ascorbic acid exhibited descriptive variation among treatments, but biological treatment effects could not be established. These findings demonstrate formulation-dependent physiological responses to intermittent saline irrigation and highlight the importance of considering the complete nutrient composition when interpreting blueberry responses.