UTILIZATION OF THE AMBIENT CONCENTRATION AS A CRITERION FOR STEADY-STATE AFTER EXPONENTIAL-GROWTH - SOME CULTURE EXPERIMENTS WITH OPTIMUM OR SUBOPTIMUM-N NUTRITION

Culture experiments are described in which Plantago lanceolata L. was grown from seedling till flowering under steady state conditions of op timum or suboptimum nitrate nutrition. In the optimum treatment, plant s had free access to nitrate. In two suboptimum treatments, nitrate wa s added with constant relative addition rates (RAR) of 0. 18 or 0.10 d -1 during the phase of constant relative uptake rates (RUR) of the pla nts and then with RAR's that were reduced stepwise from 0.18 to 0.07 d -1 or 0.10 to 0.04 d-1 when nutrient absorption gradually decreased. R eduction of the RAR's was aimed at maintenance of a balance between RA R and RUR. External nitrate concentrations were measured to monitor th e reductions. In the vegetative phase, the relative growth rate (RGR) and the root weight ratio (RWR) of P. lanceolata were constant. In the reproductive phase, RGR's were constant, but lower, and RWR's decreas ed. Concentrations of organic-N in leaves were stable during the exper imental period while those of the peduncles were lower and decreased w ith time. The ratio of reproductive to vegetative weight increased lin early with time. A number of plant parameters varied with N supply.