A ROOT BIOASSAY TEST FOR NITROGEN DEFICIENCY IN FOREST TREES

A test for nitrogen deficiency in forest trees was developed, in which the uptake of N-15 from a solution of labelled ammonium chloride by excised roots was measured. Laboratory development of the method involved the growth of Picea sitchensis (Bong.) Carr and Pinus sylvestris L. seedlings in sand culture supplied with nutrient solution containing varying concentrations of nitrogen as ammonium nitrate. When the roots of these seedlings were assayed, a negative curvilinear relationship was demonstrated between N-15 uptake and the concentration of nitrogen previously supplied in sand culture. No differences were found in the total corrected rate of nitrogen uptake from 20 or 98% N-15-enriched solutions. In field trials of the bioassay, roots were excised from a Picea abies (L.) Karst. mixture experiment and from P. sitchensis nitrogen fertilization experiments. The pattern of N-15 uptake by these roots indicated that the method is potentially useful as a rapid test for nitrogen deficiency in forest trees.