Nitrate Reduction and Nitrite Utilization by Nitrifiers in an Unsaturated Hanford Sandy Loam
1975
Volz, M. G. | Belser, L. W. | Ardakani, M. S. | McLaren, A. D.
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.
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