An Isotopic Study of the Fixation of Nitrogen associated with Nodulated Plants ofAlnus,Myrica, andHippophaë

Abstract

Nodulated plants of Alnus glutinosa, Myrica gale, and Hippophaë rhamnoides, the root systems of which had been exposed to excess free ¹⁵N, showed substantial enrichment in fixed ¹⁵N content in all parts of the plant, but particularly in the root nodules. The data resemble closely those obtained by the present and previous authors with legumes under comparable conditions, and support the conclusion already drawn from experiments of traditional type that the nodules of these non-legumes are similar to those of legumes in their function and relation to the rest of the plant. Nodulated plants of Alnus and Myrica continued to fix free nitrogen concurrently with the uptake of combined nitrogen when the latter was supplied in the rooting medium in amounts unlikely to be exceeded in the field. Isotopic tests on detached nodules of one of the species (Alnus glutinosa) showed that fixation continued, and though much reduced as compared with that shown by attached nodules it considerably exceeded that experienced by the present and previous authors with detached legume nodules, on the basis of fixation per unit of total nodule nitrogen. It is probable that detached Alnus nodules present convenient material for the further study of various aspects of the fixation process.