NITROGEN BUDGET AND N-15 TRANSLOCATION IN A PERENNIAL WHEATGRASS

N-15-labelled mineral nitrogen was used to monitor nitrogen translocation within Agropyron dasystachyum, a native grass from the Canadian Mixed Prairie, grown in solution culture under greenhouse conditions. Over 50% of nitrogen used for new leaf and tiller growth was derived from internal retranslocation in plants grown with a low external nitrogen supply (nitrogen stress). This value was reduced to 11% in plants with an abundant supply of external nitrogen. Nitrogen stress increased crown and root biomass, reduced tiller biomass but had only a small negative effect on leaf biomass, relative to plants given an adequate nitrogen supply. About 40% of the nitrogen stored during a pretreatment period was translocated to new leaves and tillers in both high and low nitrogen treatments. The proportion moving to new tillers was less in plants grown under nitrogen stress. In the high nitrogen treatment, 12% of the pretreatment pool of nitrogen leaked into the solution around the roots. Plants with a low nitrogen supply retained this nitrogen in the roots, either by reduced leakage or effective scavenging.