Effects of different NH ₄ ⁺ /NO ₃ ^- ratios on the photosynthetic and physiology responses of blueberry ( <i>Vaccinium</i> spp.) seedlings growth

Abstract

Nitrogen (N) is an essential nutrient for plant growth, and ammonium (NH4+) and nitrate (NO3-) are two main forms of N that plants absorb from the soil. The total N concentration suitable for blueberry (Vaccinium spp.) growth is well known, but we want to know which NH4+/NO3- ratio is best for blueberry seedlings. We used solutions contained 3 mM N with seven NH4+/NO3- ratios (6/0, 5/1, 4/2, 3/3, 2/4, 1/5, 0/6) to grow Northsky half-high blueberry seedlings. Plant photosynthesis, biomass, physiological characteristics, and N content were measured after 60 days. Blueberry seedlings fertilized with the 5/1 (NH4+/NO3-) ratio had the longest shoot and root, the highest leaf photosynthetic rate (Pn), stomatal conductance (Gs), evaporation rate (E), and the lowest intercellular carbon dioxide (CO2) concentrations (Ci) and superoxide dismutase (SOD) activity, among the various treatments. In conclusion, the 5/1 (NH4+/NO3-) ratio treatment is recommended to promote the growth and improve the quality of blueberry.