Root Nodules on Podocarpus Lawrencei and Their Ecological Significance

Abstract

Nodulated roots from P. lawrencei growing on a scree on Mt. Ginini, near Canberra, have been shown by the isotopic method to fix atmospheric nitrogen. The importance of this in a plant which is a pioneer of exposed, rocky situations is discussed. Although significant, the amount of nitrogen fixed by the detached nodulated roots wa·s low: this may have been due to the small proportion of nodules with active tissue, but it is also consistent with the slow growth observed for this species. The nodulated roots also evolved hydrogen u.s observed during nitrogen fixation by legume nodules. Anatomical studies of the Podocarpu8 nodules confirmed early accounts of their general structure and mode of development but the symbiont was clearly a non-septate filamentous organism: no intracellular bacteria were observed.