A study was conducted of factors affecting nitrate (NO ‐ 3 ) accumulation and characteristics of the nitrifying microflora in the O 2 horizon of an acid forest soil (pH 3.6–4.0) from the Adirondacks region of New York. The addition of ammonium (NH + 4 did not enhance NO ‐ 3 formation in suspensions of soil, but such an enhancement occurred if the suspensions were amended with peptone or if the soil had been previously leached with distilled water. The effect of additions of NH + 4 on NO ‐ 3 production was correlated with the influence of NH + 4 on N mineralization. Although levels of 47 µg NH + 4 ‐N/mL stimulated NO ‐ 3 formation in suspensions of leached soil, additions of 94 µg NH + 4 ‐N/mL or more were toxic. The enhancement of nitrification by low concentrations of NH + 4 was not accompanied by an increase in CO 2 fixation. Nitrapyrin inhibited nitrification in NH + 4 ‐amended but not in unamended suspensions of soil, but it suppressed CO 2 fixation in suspensions with and without added NH + 4 . Nitrapyrin stimulated N and C mineralization. The results show that nitrification in this soil is not the result of classical autotrophic nitrifiers, and a possible role for methylotroph‐type organisms in nitrification is suggested.
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Kreitinger et al. (1985) studied this question.