Identification of Heterotrophic Nitrification in a Sierran Forest Soil

AUTOR(ES)
RESUMO

A potential for heterotrophic nitrification was identified in soil from a mature conifer forest and from a clear-cut site. Potential rates of NO2− production were determined separately from those of NO3− by using acetylene to block autotrophic NH4+ oxidation and chlorate to block NO2− oxidation to NO3− in soil slurries. Rates of NO2− production were similar in soil from the forest and the clear-cut site and were strongly inhibited by acetylene. The rate of NO3− production was much greater than that of NO2− production, and NO3− production was not significantly affected by acetylene or chlorate. Nitrate production was partially inhibited by cycloheximide, but was not significantly reduced by streptomycin. Neither the addition of ammonium nor the addition of peptone stimulated NO3− production. 15N labeling of the NH4+ pool demonstrated that NO3− was not coming from NH4+. The potential for heterotrophic nitrification in these forest soils was greater than that for autotrophic nitrification.

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