Importance of Anaerobic Ammonium OXIDATION (ANAMMOX) IN Agricultural SOIL.

Anaerobic ammonium oxidation (ANAMMOX) is a recently described process of N2 production by coupling ammonium oxidation and nitrite reduction under anoxic conditions. Initially the anammox was discovered in a wastewater treatment facility. Since then, it has been found in numerous marine environments as a key pathway of the global nitrogen cycle. In some marine environments, more than 50% of the nitrogen loss can be attributed to anammox. Until very recently, there was limited evidence for the existence of anammox bacteria in terrestrial environments based on 16S rRNA gene analysis. The diversity and activity of anammox bacteria in the soils has yet to be examined. Therefore, we investigated various soil communities to detect anammox bacteria and to measure anammox rates and its contribution to total N2 production. Soil core samples were collected from agricultural fields in North Carolina, Kansas, Indiana, and Iowa. Each core sample was divided into surface and deep or surface, mid, and deep layers based upon the depth of the water table. By targeting hydrazine oxidase genes (hzoA and hzoB) as a genetic marker, anammox bacteria were detected from 16 out of 54 samples. Anammox bacteria were mostly found above 30 cm of surface or mid layers. Based on phylogenetic analysis of the detected hzoA/hzo B genes, soil anammox bacteria were closely associated with either Candidatus Jettenia spp. or Candidatus Anammoxoglobus spp.. The highest diversity was observed in the soil communities at North Carolina compared the samples collected other states. Soil slurry incubation experiments with 15N tracer were conducted with the samples that were positive for hzoA/hzoB gene detection. The rates of anammox and denitrification were simultaneously measured using isotope ratio mass spectrometry. Preliminary data suggested that anammox contributes substantially to total N2 production in agricultural soils. More than 50% of N2 production was mediated by anammox in North Carolina soil samples. We found that anammox bacteria are not ubiquitous in soil ecosystems. However, they may play an important role in removing nitrogen fertilizers in agricultural fields if they are present. Therefore, anammox should be considered an integral pathway in the soil nitrogen cycle.