The use of 15N pool dilution and enrichment to separate the heterotrophic and autotrophic pathways of nitrification

The techniques of 15N pool dilution and enrichment were used to separate autotrophic and heterotrophic nitrification in an acid woodland soil. Results from laboratory incubations indicated that a maximum of 8% of the observed nitrification could be the result of heterotrophic nitrifiers oxidizing organic nitrogen to nitrate without passing through the exchangeable soil ammonium pool. Autotrophic nitrification rates ranged from 0.96 to 2.64 μg N g−1 d−1, depending on the time of the year the soil was sampled. Heterotrophic nitrification rates ranged from 0.08 to 0.12 μg N g−1 d−1 and appeared unaffected by the nitrification inhibitor N-Serve.