Influence of Environmental Factors on Feammox Activity in Soil Environments

Abstract:

The oxidation of ammonium (NH₄⁺) under iron reducing conditions, referred to as Feammox, has been described in recent years by several investigators. The environmental characteristics in which the Feammox process occurs need to be understood in order to determine its contribution to the nitrogen cycle. In this study, a total of 66 locations were selected covering 4 different types of soils/sediments: wetland soils (W), river sediments (R), forest soils (F), and paddy soils (P) from several locations in central New Jersey, at Tims Branch at Savannah River in South Carolina, both in the Unities States, and at several locations in the Guangdong province in China. Though soil chemical analyses, serial culturing experiments, analysis of microbial communities, and using a canonical correspondence analysis, the occurrence of the Feammox reaction and the presence of Acidimicrobiaceae bacterium A6, which plays a key role in the Feammox process⁽¹⁾, were found in 17 samples. Analyses showed that the soil pH, as well as its Fe(III) and NH₄⁺ content were the most important factors controlling the distribution of these Feammox microorganisms. Based on the results, soils in the subtropical forests and soils that are near agricultural areas could be Feammox hotspot.

Under the conditions that favor the presence and activity of Feammox microorganisms and their oxidation of NH₄⁺, denitrification bacteria were also active. However, the presence of nitrous oxide (N₂O) reducers was limited under these conditions, implying that at locations where the Feammox process is active, conditions are favoring a higher ratio of N₂O: N₂ as the nitrogen (N) end products.

Incubations of soils where the presence of Acidimicrobiaceae bacterium A6 was detected, were conducted for 120 days under two different DO levels (DO < 0.02 mg/L and DO = 0.8~1.0 mg/L) showing comparable amounts of NH₄⁺ oxidation. In the incubations with DO < 0.02 mg/L, the proportion of Acidimicrobiaceae bacteria increased and other NH₄⁺ oxidation bacteria (aerobic ammonia-oxidizing bacteria and anammox bacteria) decreased, while in the incubations with DO = 0.8~1.0 mg/L the opposite trend was observed.

References

1. Huang S., and Jaffé P.R., 2015. Biogeosciences 12, 769–779