Growth ofPhaseolus vulgarison Various Nitrogen Sources: The Importance of Urease

Abstract

Hine, J. C. and Sprent, J. I. 1988. Growth of Phaseolus vulgaris on various nitrogen sources: the importance of urease.—J. exp. Bot. 39: 1505 -1512. Rhizobium-moculated plants of Phaseolus vulgaris L. were growo with different N-sources (nitrate, ammonium, urea) and different concentrations of urea. The distribution of growth between plant parts varied with N-sources. Nitrate and ammonium were more inhibitory to nodulation than urea, which at 4 0 mol m-3 N had no effect. Urease activity varied in amount and location over a range of urea concentrations. At higher concentrations, more urea was transported to and increased urease activity was found in the shoot. Lower levels of activity in plants reliant on N2-fixation were consistent with a ureide-degradation pathway not involving urea. Moderate doses of urea could be assimilated concomitantly with N2-fixation. At higher levels of applied urea, nodulation and ureide transport to the shoots were reduced, although increased growth could not be maintained at concentrations of applied urea greater than 60 mol m-3 urea N.