Growth and Nitrogen Distribution Patterns in Bean Plants (Phaseolus vulgaris L.) Subjected to Ammonium Nutrition: I. Effects of Carbonates and Acidity Control

Abstract

Abstract Growth of bean plants was limited when nitrogen was supplied as (NH 4 ) 2 SO 4 in sand culture in comparison to the growth of plants receiving nitrate nitrogen. Mixing relatively insoluble carbonates with the sand, using (NH 4 ) 2 CO 3 instead of (NH 4 ) 2 SO 4 or maintaining the pH of the nutrient solution near neutrality with NaOH all prolonged the life and increased the growth of plants. Experiments in which C 13 ‐labeled carbonate was used revealed no absorption or incorporation of C 13 into the plant tissues. The changes in mineral element contents of plant tissue induced by the treatments did not account for the increased growth. In the absence of pH control, ammonium, amide, and amino acid accumulation was very high in the leaves. Maintaining the pH of the nutrient solution near neutrality stimulated N assimilation in roots, especially the synthesis of amino acids and amides. Acidity control thus prevented the accumulation of ammonium in the tops and hence lessened the possibility of toxic effects from ammonium. The increased conversion of ammonium to nontoxic metabolites in roots is considered to be thedominant process by which acidity control improved the growth of plants on ammonium nutrition.