Nitrogen Nutrition Differentially Affects Concentrations of Photosynthetic Pigments and Antioxidant Compounds in Mexican Marigold ( Tagetes erecta L.)

Nitrogen is a major plant macronutrient and its supply affects the entire metabolism of plants. This study evaluated the effect of different nitrogen concentrations in the nutrient solution: 0, 4.2, 8.4, and 12.6 mg L −1 Mexican marigold ( Tagetes erecta L.) var. Inca plants in an open soilless culture system under greenhouse conditions on the concentration of chlorophylls, carotenoids, phenolics, and flavonoids derived from the secondary metabolism, as well as on the antioxidant activity in different tissues. With the 12.6 mg N L −1 dose, chlorophylls a, b, and total chlorophyll concentrations increased by 98.8, 11.9, and 56.6%, respectively. The highest concentrations of total carotenoids in flowers, 28–30%, were recorded in plants with doses of 8.4 mg N L −1 . With doses of 12.6 mg N L −1 , phenolic compounds and total flavonoids increased in leaves, but decreased in flowers. The low and medium N concentrations increased the antioxidant activity with respect to the control without N by 53% and 50.2%, respectively. We conclude that the applications of N in Tagetes erecta differentially affected the concentrations of photosynthetic pigments and biomolecules with antioxidant capacity, and that such effects were dependent on the doses of N tested and the plant organ evaluated.