Fig 2. Chlorophylls’ and carotenoids’ response to decreased nitrogen concentration.

Chlorophylls and carotenoids were present in different concentrations in red and green lettuce, cultivated at 12, 3 or 0.75 mM nitrogen in the nutrient solution. The percentage of difference between the 3 and 12 mM treatments is represented by the white bars, difference between the 0.75 and 12 mM treatments is represented by the grey bars. Asterisks indicate that the value is significantly different from that in 12 mM treatment, asterisks in circles indicate 0.75 mM treatment values which were significantly different from those in the 12 and the 3 mM treatments (two-way ANOVA, Tukey HSD test, α = 0.05, n = 3; as calculated based on the concentrations and listed in Table 3).