Effect of the concentration and ionic form of nitrogen (N) on photosynthesis, growth and fruit production of blueberry (Vaccinium corymbosum L.)

The aim of this work was to evaluate the main effects and the interactions of nitrogen (N) concentration and ammonium (NH4+): nitrate (NO3-) proportion in the nutrient solution, on net photosynthesis, plant growth, production and quality of fruits on blueberry (Vaccinium corimbosum L.) plants. The studied factors were N concentration (0.6 and 6.0 mM) and NH4+: NO3- proportion (100 % NH4+, 50 % NH4+ - 50 % NO3- and 100 % NO3-). 243 days after the experiment establishment net photosynthesis (PN) was measured and a day after, leaf area (LA), shoots fresh weight (SFW) and roots fresh weight (RFW) were determined. Fruit yield (FY), fruit diameter (FD) and Brix degrees (oBrix) were evaluated in four harvests along fruit production period. The results showed higher values on PN, LA, SFW, FY and FD in plants that received 6.0 mM N as NH4+; nevertheless, N concentration altered the NH4+: NO3- proportion effects and at 0.6 mM N only FY and FD maintained such a pattern. It is concluded that N concentration modifies the effect of NH4+: NO3- proportion and it is proposed that the effects of both factors on photosynthesis, growth and fruit production of blueberry were mediated by their interaction with plant carbohydrates availability.