Nitrogen fixation in submerged soilsand-energy material media and the aerobic-anaerobic interface

Summary

Flooded soils usually consist of a surface aerobic phase a few millimeters thick (in contact with the atmosphere or oxygenated solution) underlain by an anaerobic phase. The objective of this research was to study nitrogen fixation in the aerobic-anaerobic interfacial area in flooded, cellulose enriched media and the utilization of the products of anaerobic decomposition of cellulose by nitrogen-fixing organisms when these products are brought under aerobic conditions by processes such as diffusion, mixing, and drying.

The medium used for these studies was basically a sand matrix supplemented with a small amount of soil and mineral nutrients. When columns of medium enriched with cellulose were sectioned after incubation in the dark under flooded conditions, the increase in content of nitrogen per gram medium in the top 2 to 3 mm of the column was as much as 10 to 15 times the increase in nitrogen content of the lower portions of the column. Periodic mixing of flooded media, alternation of shaking in nitrogen and air atmospheres, and alternate flooding and drying all enhanced fixation relative to undisturbed, continuously flooded media incubated in air. Fixation during incubation under a nitrogen atmosphere was less than fixation under air atmospheres.

The results of numerous experiments are consistent with the hypothesis that nitrogen fixation is enhanced when the products of anaerobic decomposition of cellulose are brought under aerobic conditions by any of several processes.