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- Author or Editor: R. Hugo Lira-Saldívar x
The uptake of nitrogen (N) in nitrate or ammonium (NH4 +) form affects physiological and metabolic processes and toxicity may develop in plants receiving high concentrations of NH4 +. The objective of the present study was to delineate the response of bell pepper plants to varying proportions of NH4 + combined with increasing concentrations of potassium (K) in the nutrient solution. Bell pepper plants were tolerant to moderate proportions of NH4 + (25% or less or 50% or less); however, higher proportions resulted in growth reduction. The application of higher K concentrations in the nutrient solution did not ameliorate the growth on vegetative plant parts; however, when K was increased to 9 mm, the yield was sustained even when 50% of total N was in the NH4 + form. Decreased shoot:root ratio and harvest index indicated that biomass accumulation was affected more in the shoot than in the root and in the fruit than in the shoot, respectively. There was a lower concentration of NH4 + in the roots compared with leaves, suggesting that the higher K concentration that resulted from the increased K in the nutrient solution was associated with NH4 + translocation through the xylem. A decrease in calcium and magnesium detected in leaves suggests an antagonistic relationship with NH4 + and K in the nutrient solution, which was correlated with the acidification of the growing medium. Higher yields when K was at 9 mm may be the result of the high photosynthetic rate and stomatal conductance (g S) detected in plants fertigated with 25% of total N as NH4 + and the higher leaf water potential when the proportion of NH4 + was 50%. The biochemical composition of fruits was affected because both high NH4 + and increased K resulted in higher ethylene production, lipid peroxidation, superoxide dismutase activity, and carotenoids.