Root Environment Acidity as a Regulatory Factor in Ammonium Assimilation by the Bean Plant

Abstract

Previous experiments have revealed a much greater efficiency of ammonium utilization by bean plants (Phaseolus vulgaris L.) when the acidity of the ambient medium was maintained at near-neutral conditions with carbonates or hydroxides. The present investigation, in which ¹⁵N-labeled ammonium was used, permitted an assessment of the origin of nitrogen in tissue nitrogen pools with and without acidity control (CaCO₃ treated and untreated, respectively) in the root environment. Control of acidity resulted in greater ammonium uptake and greater incorporation into the amino fraction, amide, and ethanol-insoluble nitrogen by the root tissue. These differences were clearly evident by the fifth day after ammonium nitrogen had been applied.