Abstract
This study was carried out to determine the interaction among NH4+, NO3-, and Cl- ion uptake and to find the causes of NH4+ -related toxicity symptoms in plants fed with NH4+ as a sole nitrogen source. Seedling plants established in peat-lite and rockwool media were fed with nutrient solutions containing either NH4+ or NO3- or both NH4+ plus NO3- with or without Cl-. Plants grown with NH4+ + Cl- contained the highest levels of Cl-. Plants fed with NO3- + Cl- also showed high levels of Cl- in the tissue. The growth and tissue Cl- contents of plants fed with NH4+ were not affected by changes in Cl- concentration in the nutrient solution. Plants fed with NH4+ that was ion-balanced by high levels of SO42- plus low or no Cl- still developed the NH4+ -related toxicity symptoms. This indicates that NH4+ -related toxicity symptoms occur independently of Cl-. It was also shown that the activity of Cl-, a counterion for NH4+ uptake, was suppressed by NO3-.
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