Ammonium and Nitrate Influence on Artichoke Growth Rate and Uptake of Inorganic Ions

Artichoke plants (Cynara scolymus L.) were grown in a growth chamber in a modified Hoagland solution for seven weeks to determine the influence of ammonium:nitrate (NH4:NO3) ratio (100:0, 70:30, 30:70 and 0:100) on growth, water use, and the uptake of nitrogen (N) and inorganic anions and cations. Typical pH changes were recorded: the nutrient solution became acidified with NH4 or NH4:NO3 nutrition; pH increased when NO3 was the only N source. Ammonium-fed plants (100:0 ratio) were stunted, with signs of marginal leaf necrosis, progressive wilting of leaves and poor root growth. After 49 days, leaf area was 77, 998, 2,415, and 1,700 cm2 and dry weight was 1.0, 12.9, 38.0, and 26.0 g/plant, with NH4:NO3 100:0, 70:30, 30:70, and 0:100, respectively. Leaf area ratio (LAR) was lower in plants supplied solely with NO3 than in those with mixed NH4-NO3. Increasing NO3-N percentage in the nutrient solution increased water use efficiency (WUE): 623,340, and 243 mL of water were necessary to produce I g of dry matter in 100:0, 70:30, 30:70 or 0:100 NH4:NO3 ratio, respectively. Increasing NO3 from 0 to 100% of the total N supplied in the nutrient solution, the shoot content of inorganic cations increased on an equivalent basis by 30% and organic anions (estimated by the difference between inorganic anions and inorganic cations) increased by 2.3 times. These results suggest that leaves are the most important site of NO3 assimilation in artichoke. By increasing NH4 percentage in the nutrient solution, the tissue content of inorganic anions was generally increased, except for NO3, and the same figure was observed for the percentage of reduced N. Results from this study suggest that NO3 is the N- form preferred by artichoke.