Nitrogen Fixation by the Endophyte ofLolium

Abstract

Since the publication of the classical report of Lawes, Gilbert and Pugh (15), it has been generally accepted that the Gramineae obtain all the nitrogen they require in the combined form from the soil solution. The results of recent investigations on the relation between the fungus endophyte and the host have suggested the possibility of an atmospheric origin for part of the nitrogen present in the host. Hannig(10) isolated fungus-free races ofLolium temulentum, and showed that the infected plants had a slight power of assimilating molecular nitrogen. Hiltner(11) grew plants ofLolium temulentumunder culture conditions with, and without, nitrate nitrogen, and he found that those without did as well as those with nitrate nitrogen, from which he concluded that plants grown without nitrate nitrogen must be meeting their nitrogen requirements from atmospheric sources. It appears, however, that Hiltner's cultures were not sterile, and no special precautions were taken to ensure that the sand and water were nitrogen free. McLennan(20) repeated Hiltner's work usingLolium perenne, but great care was taken to ensure that all ingredients of the cultures were nitrogen free, and that the cultures were sterile. Under these conditions the results were negative, pointing to an absence of fixation. McLennan, however, states that her results do not preclude the possibility of fixation when small quantities of combined nitrogen are available in the medium.