Nutrient solution concentration affects growth, mineral composition, phenolic acids and flavonoids in leaves of artichoke and cardoon

A greenhouse experiment was conducted in Summer and Fall 2011 at the experimental farm of Tuscia University, central Italy, to study the effect of nutrient solution concentration (4, 20, 36, 52, or 68 mequiv·LL1) on biomass production, mineral composition, and concentrations of the major polyphenols in ‘Romolo’ artichoke and ‘Bianco Avorio’ cardoon grown in a floating system. Leaf dry biomass, leaf number, and macroelement concentrations (nitrogen, potassium, calcium, and magnesium) of artichoke and cardoon increased in response to an increase in the nutrient solution concentration, whereas an opposite trend was observed for the total polyphenols, phenolic acids (chlorogenic acid, cynarin, and caffeic acid), and the flavonoid luteolin. Artichoke and cardoon gave maximum biomass production and leaf number at 45 and 54 mequiv·LL1, respectively. Cardoon showed higher biomass and leaf number (average 1.13 kg·mL2 and 14.0 n./plant, respectively) than those observed in artichoke (average 1.07 kg·mL2 and 12.7 n./plant, respectively). The chlorogenic acid, cynarin, caffeic acid, and luteolin concentrations were higher by 204%, 462%, 580%, and 445% in cardoon leaf tissue than in that of artichoke. An improvement of leaf quality (total polyphenols, phenolic acids, and flavonoids) was obtained at the expense of leaf yield through the use of lower fertilizer concentrations in the nutrient solution.