Investigations on the root nodule bacteria of leguminous plants. XVI. Effect of air content of the medium on the function of the nodule and on the excretion of nitrogen

Abstract

THE factors which influence the functions of the root nodules of leguminous plants have been extensively investigated during the past decades. Although this research has greatly widened our knowledge of the properties and activities of the nodule bacteria, several important questions, both theoretical and practical, are still unsolved.It is a well-known fact that the effectiveness of the nodule bacteria varies greatly in different types of soil, and that in such cases it is often impossible to find a satisfactory explanation for these variations. In pursuance of our work on the leguminous plants and root-nodule bacteria we have paid particular attention to the effect of the air content of the medium on the activities of the nodule. It is quite natural that an effective fixation of nitrogen should depend upon an adequate supply of air to the nodules. Besides, it may reasonably be assumed that the strictly aerobic nodule bacteria would be incapable of action under anaerobic conditions. Nobbe and Hiltner (1893) came to the conclusion that in water cultures the function of the nodules of leguminous plants is inhibited and that they do not supply their host with nitrogenous food when all nodules are submerged. According to Thornton (1930), the lack of air supply may inhibit nitrogen fixation by bacteria in the leguminous nodule. In agar cultures he found the most efficient nodules at the surface or at the points where the agar had cracked but no nitrogen fixation where all the nodules were deeply embedded in the agar. Different results were obtained by Wilson, Hopkins and Fred, who found that even the nodules formed within the agar can fix nitrogen (see Fred, Baldwin and McCoy, 1932).These, and several other investigations cited in literature, show clearly the importance attached to the effect of air on the activities

The Effect of Charcoal on the Growth of Leguminous Plants in Sand Culture

“…Mineral nutrients were supplied in the form of a Rothamsted solution (Thornton, 1929) or of Hiltner's solution (Virtanen & von Hausen, 1935), both being free of combined nitrogen. Minor elements were supplied as the A-2 solution (Templeman, 1941)*, I ml.…”