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.1. 氮（N）氨化作用（ammonification）与硝化作用（nitrification）是调控土壤铵态氮（soil ammonium, NH₄⁺）有效性的两大核心微生物过程，而土壤铵态氮是植物生长所需的关键营养元素。总氨化速率（gross ammonification, GA）与总硝化速率（gross nitrification, GN）的大尺度分布格局，反映了土壤微生物对不同植被与环境条件的适应性。本研究针对中国东部3500千米南北样带（NSTEC）上的9个森林土壤，开展了GA与GN速率的调查分析。 2. 本研究采用15N标记技术（15N-labeling techniques）结合野外试验（field experiments）与实验室培养法（laboratory incubations），测定了GA与GN的原位速率（in situ rates）与潜在速率（potential rates）。结果显示，原位GA速率的平均值为4.9±0.5 mg N kg⁻¹·d⁻¹，而GA潜在速率的平均值为32.0±8.6 mg N kg⁻¹·d⁻¹；原位GN速率的平均值为1.7±0.3 mg N kg⁻¹·d⁻¹（GN潜在速率为3.2±0.6 mg N kg⁻¹·d⁻¹）。样带沿线的GA速率显著高于GN速率，且不同森林样地的GA与GN速率存在较高变异。在采样月份（2013年8月），气象因子（meteorological factors, 温度与降水量）与GA、GN速率间存在显著相关关系。不过，呼中（HZ）、东灵（DL）、太岳（TY）与鼎湖（DH）样地的原生林平均GA速率显著低于其他样地；而除凉水（LS）样地外，原生林与次生林的平均GN速率表现出一致的变化趋势。在LS与长白山（CB）样地，原生林与次生林的GA速率存在显著差异；在HZ、LS与九莲（JL）样地，则检测到GN速率的显著差异。 3. 结构方程模型（structural equation modeling）分析表明，土壤氮含量、微生物生物量氮库（microbial biomass N pool）规模与细菌丰度（bacterial abundance）是决定GA与GN原位速率的核心调控因子。土壤因子（edaphic factors）对GA与GN的强烈调控作用，说明需要优化土壤氮模型，更明确地纳入土壤因子及其对土壤氮转化（soil N transformations）过程的调控机制。