Nitrification inhibitor (NI) is often claimed to be efficient in mitigating nitrogen (N) losses from agricultural production systems by slowing down nitrification. Increasing evidence suggests that ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) have the genetic potential to produce nitrous oxide (N2O) and perform the first step of nitrification, but their contribution to N2O and nitrification remains unclear. Furthermore, both AOA and AOB are probably targets for NIs, but a quantitative synthesis is lacking to identify the “indicator microbe” as the best predictor of NI efficiency under different environmental conditions. In this present study, a meta-analysis to assess the response characteristics of AOB and AOA to NI application was conducted and the relationship between NI efficiency and the AOA and AOB amoA genes response under different conditions was evaluated. The dataset consisted of 48 papers (214 observations). This study showed that NIs on average reduced 58.1% of N2O emissions and increased 71.4% of soil NH4+ concentrations, respectively. When 3, 4-dimethylpyrazole phosphate (DMPP) was applied with both organic and inorganic fertilizers in alkaline medium soils, it had higher efficacy of decreasing N2O emissions than in acidic soils. The abundance of AOB amoA genes was dramatically reduced by about 50% with NI application in most soil types. Decrease in N2O emissions with NI addition was significantly correlated with AOB changes (R2 = 0.135, n = 110, P < 0.01) rather than changes in AOA, and there was an obvious correlation between the changes in NH4+ concentration and AOB amoA gene abundance after NI application (R2 = 0.037, n = 136, P = 0.014). The results indicated the principal role of AOB in nitrification, furthermore, AOB would be the best predictor of NI efficiency.
<p>In China, amounts of organic manure as basal fertilizer application along with flooding irrigation usually resulted in large N<sub>2</sub>O emissions from intensively protected vegetable soils. However, little attention paid on the N<sub>2</sub>O emission bursts after application of manure, in a newly established vegetable soil with a low-nitrate content. The nitrification inhibitor, 3,4-dimethylpyrazole phosphate (DMPP), can be used to reduce N<sub>2</sub>O emissions from agricultural soils, little is known about how DMPP affect N<sub>2</sub>&#160;emissions and gaseous nitrogen (N<sub>2</sub>O+N<sub>2</sub>) losses. Here, we conducted a microcosm experiment in a robotized incubation system under an aerobic (O<sub>2</sub>/He) condition. Dried chicken manure was applied with and without DMPP to a protected vegetable soil. Two drying-rewetting events occurred during the 19 days monitoring period, and the relevant soil properties (e.g., NO<sub>2</sub><sup>-</sup>, WFPS, DOC, DON, SMBC) were analyzed. Our results showed DMPP addition strongly retarded soil nitrification process that kept a higher NH<sub>4</sub><sup>+</sup>&#160;concentration&#160;than that of only manure application. A significant decline of NO<sub>2</sub><sup>-</sup>&#160;and NO<sub>3</sub><sup>-</sup>&#160;concentration was found in a manure-treated soil with DMPP addition. Clearly, DMPP addition significantly reduced N<sub>2</sub>O emissions from the protected vegetable soil by 77.0% and remarkably decreased N<sub>2</sub>&#160;emissions and overall N<sub>2</sub>O+N<sub>2</sub>&#160;losses (compared with manure alone) by 51.9% and 54.0%, respectively. Pearson&#160;analysis showed that soil N<sub>2</sub>O fluxes were significantly related to soil WFPS, NH<sub>4</sub><sup>+</sup>, SMBC (P<0.01) and SMBN&#160;(P<0.05), whereas N<sub>2</sub>&#160;fluxes were significantly correlated with soil WFPS, SMBC (P<0.01), NO<sub>2</sub><sup>-</sup>, NH<sub>4</sub><sup>+</sup>&#160;and&#160;SMBN (P<0.05)&#160;during the whole incubation.&#160;The fluxes of N<sub>2</sub>O+N<sub>2</sub>&#160;were positively correlated with WFPS, NO<sub>2</sub><sup>-</sup>, SMBC and SMBN, whereas&#160;negatively correlated with NH<sub>4</sub><sup>+</sup>&#160;(P<0.05). Moreover, the ratio of N<sub>2</sub>O to N<sub>2</sub>O+N<sub>2</sub>&#160;(N<sub>2</sub>O/(N<sub>2</sub>O+N<sub>2</sub>))&#160;was positively correlated with NO<sub>3</sub><sup>-</sup><sup>&#160;</sup>(P<0.05), and negatively correlated with DOC, DON and SMBC (P<0.01). An aggregated boosted tree (ABT) analysis further indicated that the relative influence of WFPS, SMBC and NH<sub>4</sub><sup>+</sup>&#160;on N<sub>2</sub>O&#160;fluxes&#160;were 19.4%, 14.9%&#160;and 12.8%, respectively. Moreover, the relative influence of WFPS on N<sub>2</sub>&#160;fluxes&#160;was the largest (47.4%), followed by SMBC and SMBN (14.3% and 9.66%, respectively).&#160;In addition, the relative influence of WFPS, SMBN and SMBC on N<sub>2</sub>O+N<sub>2</sub>&#160;losses were 32.6%, 17.0% and 12.6%, respectively, and the relative influence of SMBC, DOC and NO<sub>2</sub><sup>-</sup>&#160;on N<sub>2</sub>O/(N<sub>2</sub>O+N<sub>2</sub>) were 22.5%, 20.2% and 11.1%, respectively. In conclusion, our data show that DMPP combined with manure&#160;can significantly reduce N<sub>2</sub>O and N<sub>2</sub>&#160;emissions&#160;in a low-nitrate newly established vegetable soil, and their emissions were&#160;strongly affected by WFPS.&#160;</p>
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