Data from: 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. Significant
relationships were identified between meteorological factors (tempera-ture
and precipitation) and the GA and GN rates during the sampling month
(August 2013). How-ever, the mean GA rate in primary forest was
significantly lower in the Huzhong (HZ), Dongling (DL), Taiyue (TY), and
Dinghu (DH) sites compared with other sites, whereas with the exception of
the Liangshui (LS) sampling site, the mean GN rate in primary and
secondary forests showed the same trends. Significant differences in GA
rates were found between primary and secondary forests at the LS and Chang
Bai (CB) sites, and differences were detected in GN rate at the HZ, LS,
and Jiulian (JL) sites. 3. Structural equation modeling analysis suggested
that soil N contents, microbial biomass N pool sizes, and bacterial
abundance are the primary determinants of the in situ rates of GA and GN.
The strong control of edaphic factors on GA and GN indicates a need to
improve soil N models with more explicit representation of edaphic factors
and their control on soil N transformations.