Soil gross N ammonification and nitrification from tropical to temperate forests in eastern China

1. Nitrogen (N) ammonification and nitrification are two primary microbial processes controlling the availability of soil ammonium (NH4+), a key nutrient for vegetative growth. The large-scale patterns of gross ammonification (GA) and gross nitrification (GN) rates represent soil microbial adaptations to different vegetative and environmental conditions. In this study, we investigated GA and GN rates in nine forest soils along a 3500-km north-south transect in eastern China (NSTEC).
2. We used 15N-labeling techniques, along with field experiments and laboratory incubations, to as-sess in situ and potential rates of the GA and GN. The mean in situ GA rate was 4.9 ± 0.5 mg N kg–1 day–1, whereas the mean potential rate of GA was 32.0 ± 8.6 mg N kg–1 day–1. The mean in situ GN rate was 1.7 ± 0.3 mg N kg–1 day–1 (potential GN rate: 3.2 ± 0.6 mg N kg–1 day–1). GA was sig-nificantly higher than GN along the transect and there were high variations in GA and GN among different forests. Signific...