Heterotrophic nitrification is the predominant NO3 - production pathway in acid coniferous forest soil in subtropical China

To date, occurrence and stimulation of different nitrification pathways in acidic soils remains unclear. Laboratory incubation experiments, using the acetylene inhibition and N-15 tracing methods, were conducted to study the relative importance of heterotrophic and autotrophic nitrification in two acid soils (arable (AR) and coniferous forest) in subtropical China, and to verify the reliability of the N-15 tracing model. The gross rate of autotrophic nitrification was 2.28 mg kg(-1) day(-1), while that of the heterotrophic nitrification (0.01 mg kg(-1) day(-1)) was negligible in the AR soil. On the contrary, the gross rate of autotrophic nitrification was very low (0.05 mg kg(-1) day(-1)) and the heterotrophic nitrification (0.98 mg kg(-1) day(-1)) was the predominant NO3 (-) production pathway accounting for more than 95 % of the total nitrification in the coniferous forest soil. Our results showed that the N-15 tracing model was reliable when used to study soil N transformation in acid subtropical soils.