Sequential reduction and oxidation of inorganic nitrogen, manganese, and iron in flooded soil

TLDR: In this paper, the authors studied the sequence of reduction of three electron acceptors under controlled redox potential conditions, and showed that the oxidation and reduction of these three electronacceptors were sequential, with no overlap in the oxidation or reduction of the NO3 and Mn systems and little overlap in oxidation and reducing of the Mn and Fe compounds.

Abstract: When a soil is flooded, the curtailment of O2 diffusion into the soil causes the microorganisms decomposing organic matter to switch from O2 to alternate electron acceptors. Three alternates utilized by facultative microorganisms when O2 becomes depleted are NO3 , Mn compounds, and Fe compounds. We studied the sequence of reduction of these three redox systems under controlled redox potential conditions. The redox potential of soil suspensions was changed stepwise in 50-mV increments from oxidized to reduced conditions and from reduced to oxidized conditions and maintained at each new potential for 15 d, at which time NO3, NH4, Mn, and Fe concentrations in the soil solution were analyzed. The results of this study showed that the oxidation and reduction of the three electron acceptors were sequential, with no overlap in the oxidation or reduction of the NO3 and Mn systems and little overlap in oxidation and reduction of the Mn and Fe systems. In the oxidized-to-reduced experiment, the critical redox potential at which all of the NO3was reduced and Mn first appeared in the soil solution was approximately 200 mV. The critical redox potential at which Fe appeared was 100 mV. For all three redox systems, the critical redox potentials for the oxidized-toreduced transition were approximately 50 mV lower than for the reduced-to-oxidized transition. View complete article To view this complete article, insert Disc 5 then click button8