AMMONIUM AND NITRATE INFLUENCE ON ARTICHOKE GROWTH-RATE AND UPTAKE OFINORGANIC-IONS

Artichoke plants (Cynara scolymus L.) were grown in a growth chamber i n a modified Hoagland solution for seven weeks to determine the influe nce 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 a nions and cations. Typical pH changes were recorded: the nutrient solu tion became acidified with NH4 or NH4:NO3 nutrition; pH increased when NO3 was the only N source. Ammonium-fed plants (100:0 ratio) were stu nted, with signs of marginal leaf necrosis, progressive wilting of lea ves and poor root growth. After 49 days, leaf area was 77, 998, 2,415, and 1,700 cm(2) 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 thos e with mixed NH4-NO3. Increasing NO3-N percentage in the nutrient solu tion increased water use efficiency (WUE): 623, 340, and 243 mL of wat er were necessary to produce 1 g of dry matter in 100:0, 70:30, 30:70 or 0:100 NK4:NO3 ratio, respectively. Increasing NO3 from 0 to 100% of the total N supplied in the nutrient solution, the shoot content of i norganic cations increased on an equivalent basis by 30% and organic a nions (estimated by the difference between inorganic anions and inorga nic cations) increased by 2.3 times. These results suggest that leaves are the most important site of NO3 assimilation in artichoke. By incr easing 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 thi s study suggest that NO3 is the N-form preferred by artichoke.