Abstract
I. The behavior of the root nodule bacteria to nitrate was investigated in the yeast water mannitol solution which contains ammonia as well as nitrate. It may be expected that if nitrate is atlacked as nitrogen source, the reduction process of nitrate will certainly be influenced by the presence of ammonia. The root nodnle bacteria are divided into the following groups according to the results obtained : Group 1. The reduction of nitrate is not influenced by the presence of ammonia. All of the nitrate disappear from the culture solution without leaving ammonia as well as nitrite, certainly followed by the loss of nitrogen. ……Strains from alfalfa-, lupine-, soybean- and Sesbania. Group 2. Nitrate is reduced, accompanied by a remarkable accumulation of nitrite. The presence of ammonia seems to retard further reduction of nitrite. ……Strains from alfalfa-, and cowpea-group, Mimosa, and Leucoena. Group 3. Small amounts of nitrite are produced. The reduction of nitrate seems to be retarded. ……Strains from pea-, clover-, bean-, lupine-, soybean-, and cowpea-group; Sesbania, Dalea, Indigofera, Styphnolobium, Caragana, Robinia, Sophora, and Vicia (nipponia). II. In order to see the relation of rhizobial growth to the free and combined oxygen (NO_3^-), the growth-zone in the agar shake culture was examined. Most of the strains grow in the surface layer of the yeast water mannitol agar (1% agar), though not without difference in the inner limit of growth, while few strains from alfalfa-, soybean-, and cowpea-group are able to grow to a considerable depth. These results seem to indicate that the root nodule bacteria are generally aerobic. In the nitrate yeast water mannited agar, the strains belonging to group 1 and some strains of group 2 are able to grow anoerobically to certain extent, but the others do not.
