Growth responses of Plantago to ammonium nutrition with and without pH control: Comparison of plants precultivated on nitrate or ammonium

Plantago species precultivated on either NO3 − (’nitrate plants’) or NH4 + (’ammonium plants’) were grown on 100% NH4, with and without pH adjustment. Growth, proton excretion, and changes in chemical composition were studied in detail. Under the same pH regime total net H+ effluxes were approximately equal for nitrate and ammonium plants. Nitrate plants showed higher increases in dry-matter yield and in content of organic N than ammonium plants and the adverse effects upon plant growth induced by the ammonium treatment without pH adjustment were delayed in nitrate plants. Nitrate plants appeared to benefit from ther internal nitrate pool in more than one way. In addition to the increase in organic N via nitrate reduction, NH4 +-derived organic N was also higher in nitrate plants which corresponded to an ’extra’ uptake and utilization of ammonium. This ’extra’ utilization of NH4 + in nitrate plants could be related directly to the observed changes in nitrate and organic-anion contents.