Two methodological approaches are commonly used to investigate heterotrophic nitrification (Nit_h) in soil: process inhibitions and ¹⁵N tracing. Although many studies have reported Nit_h based on ¹⁵N tracing approaches, estimates via specific inhibitor are less common. Therefore, we conducted a meta-analysis to illustrate the similarities and differences of the results of soil Nit_h between the two approaches. We observed that the average result of gross Nit_h rate was significantly lower with the ¹⁵N tracing approach (1.32 mg N kg⁻¹ day⁻¹) than with the inhibitor approach (3.54 mg N kg⁻¹ day⁻¹) (p < 0.01). Possible explanations include incomplete inhibition of autotrophic nitrification (Nit_a) due to the adsorption of inhibitors on soil aggregates and the fact that the estimation of Nit_h via ¹⁵N tracing quantifies only the Nit_h fraction related to organic N oxidation. The results of linear-mixed models indicated that soil C:N ratio had a significantly positive effect on the difference of Nit_h estimated via ¹⁵N tracing and inhibitor approach, which was also supported by the paired data between natural and C- and N- manipulated soil. The average contribution of Nit_h to total nitrification, estimated by the ratio of Nit_h:(Nit_h + Nit_a) or the capacity of NO₂⁻/NO₃⁻ production when Nit_a was inhibited, in the two approaches were not significantly different (34% vs. 33%). While, soil C:N ratio also caused a significantly positive effect on the contribution of Nit_h to soil total nitrification (p < 0.05). In conclusion, the result of the relative contribution of Nit_h is less affected by approach than the result of gross Nit_h rate. In addition, soil C and N substrate availability is likely to be a critical factor affecting the estimation of soil Nit_h by the two approaches.

中文翻译：

---

15N 追踪和特异性抑制剂方法中土壤异养硝化的定量

两种方法通常用于研究土壤中的异养硝化 (Nit _h ^{)：过程抑制和15} N 示踪。尽管许多研究报告了基于^{15 N 追踪方法的 Nit} _h，但通过特定抑制剂进行的估计并不常见。因此，我们进行了荟萃分析，以说明两种方法之间土壤 Nit _h结果的异同。我们观察到¹⁵ N 追踪方法（1.32 mg N kg ^-1天^{-1 ）的总 Nit} _h率的平均结果显着低于抑制剂方法（3.54 mg N kg ^-1第⁻¹天）（p  < 0.01）。_{可能的解释包括由于抑制剂在土壤团聚体上的吸附而导致的自养硝化作用 (Nit a} )的不完全抑制，以及通过¹⁵ N 示踪估算 Nit _h仅量化与有机 N 氧化相关的 Nit _h部分这一事实。线性混合模型的结果表明，土壤 C:N 比对通过¹⁵ N 示踪和抑制剂方法估算的 Nit _h的差异具有显着的正向影响，这也得到了天然与 C- 和 N- 之间的配对数据的支持被操纵的土壤。Nit _{h的平均贡献}总硝化作用，通过 Nit _h :(Nit _h  + Nit _a ) 的比率或当 Nit _{a被抑制时 NO 2} ⁻ /NO ₃ ⁻的生产能力估算，两种方法没有显着差异（34% vs. 33%）。同时，土壤 C:N 比也对 Nit _h对土壤总硝化作用的贡献产生了显着的正向影响（p  < 0.05）。总之，Nit _h相对贡献的结果受方法的影响小于总 Nit _h的结果速度。此外，土壤 C 和 N 底物有效性可能是影响这两种方法估算土壤 Nit _{h的关键因素。}