Nitrate Reduction and Nitrite Utilization by Nitrifiers in an Unsaturated Hanford Sandy Loam

Abstract

In order to discern any relationship between added nitrate and microbial growth in a field plot, a Hanford sandy loam was infiltrated for 5 weeks at a rate of 5 cm day−1 with a solution containing 100 ppm ‐N and 1.25 meq/liter Cl− as KNO3 and CaCl2 respectively. Nitrate‐N, NO2−‐N and Cl− concentrations in soil solution were determined and corresponding counts of nitrate reducers, denitrifiers, and NH4+‐ and NO2−‐oxidizer populations were made.Ratios of measured to applied concentrations for both NO3−‐N and Cl− were nearly identical in all solution samples taken from the unsaturated soil profile, i.e., nitrate reduction was not pronounced and NO2−‐N was less than 1 ppm.Nitrate reducer populations (6x104–6x105/g soil) were always larger than those of denitrifiers (3x103–3x104/g) and varied little with time and depth. Ammonium oxidizers (101–105/g) generally decreased with depth. In contrast, NO2− oxidizers (101–3x106/g) varied markedly with time at all depths. An increase in numbers of NO2− oxidizers, after 2 to 3 weeks, at a depth of 60 cm, is attributed to NO2− produced by reduction of NO3− at anoxic microsites within the profile. Evidently, a cyclic oxidation and reduction of nitrite and nitrate, occurring simultaneously, is responsible for growth of nitrite oxidizers in the profile.

Comparative study of enrichment methods for the isolation of autotrophic nitrifying bacteria from soil, estuarine and marine sediments

“…MacFarlane and Herbert [12] indicated that an additional source of NO 2 may be derived from the dissimilatory reduction of NO 3 to NO2, and that this supported larger populations of NO 2 oxidising bacteria within the sediments. These conclusions are in agreement with those of Voltz et al [13] and Belser [14] who reported that NO 3-dissimilation to NO 2 supported large populations of NO 2 oxidising bacteria in some soils. The reduction or absence of NO 2 oxidising bacteria in the 4-5 cm horizons of marine and estuarine sediments is probably due to their greater sensitivity to reduced concentrations of dissolved 0 2 [15].…”

Population Ecology of Nitrifying Bacteria

“…However, some evidence indicates that nitrite produced from nitrate reduction may be available for the growth of nitrite oxidizers (8,85). In this theory nitrate is reduced to nitrite in anaerobic microenvironments.…”

Biochemical Ecology of Nitrification and Denitrification

“…Volz et al (1975b) perfused a lysimeter containing a sandy loam soil low in organic matter «0.5 % carbon) with a nitrate solution and observed a peak nitrite concentration in the top 60 cm that corresponded to a low nitrate concentration. They showed that nitrate was first reduced to nitrite by nitratereducing bacteria, and the nitrite was subsequently reoxidized by nitriteoxidizing bacteria as it moved below the nitrite zone.…”