Niche Differentiation Among Canonical Nitrifiers and N2O Reducers Is Linked to Varying Effects of Nitrification Inhibitors DCD and DMPP in Two Arable Soils

The regulatory mechanism controlling nitrification inhibitors-induced mitigation of nitrification and NO3--N leaching in alkaline purple soil

Nitrification inhibitors (NIs) are critical to reduce nitrogen (N) leaching losses. However, the efficacy of different NIs can be highly variable across soils and crop types, and a deeper understanding of the mechanistic basis of this efficiency variation, especially in purple soil under vegetable production, is lacking. To enrich this knowledge gap, the impact of different NIs amendment (3,4-dimethylpyrazole phosphate, DMPP; dicyandiamide, DCD; nitrapyrin, NP) on nitrification and the microbial mechanistic basis of controlling nitrate (NO3--N) leaching of vegetable purple soil was explored in southwest China. The results showed that DCD and NP effect is dose-dependent, with 10% DCD, 1% DMPP and 1% NP were found to be optimal for nitrification inhibition in vegetable purple soil. When compared with the control treatment without NIs amendments, DCD, DMPP and NP reduced NO3--N leaching by 26.3%, 30.6% and 19.2%, respectively. It was noteworthy that NO3--N leaching inhibition was mediated predominantly by inhibiting ammonia-oxidizing bacteria (AOB) abundance. DCD, NP and DMPP incorporation decreased the AOB abundance by 39.8%, 73.2% and 51.4% and suppressed the ammonia monooxygenase (AMO) activity by 22.2%, 36.8% and 28.7%, respectively, in comparison with the control treatment without NIs amendments. DMPP inhibited AOB abundance and AMO activity much more than DCD and NP. DMPP also significantly decreased AOB alpha diversity and altered their community structure, whereas DCD and NP had no significant effect. The mantel test indicated that AOB abundance and AMO activity are strongly correlated with NO3--N leaching rate. These results show that soil application of 1% DMPP effectively mitigates NO3--N leaching from sub-tropical alkaline purple vegetable soil. This study also expanded our mechanistic understanding of NO3--N leaching and its regulators in an alkaline soil vegetable production system with N fertilizer and NI inputs.

Effective strategy to improve nitrification inhibitor efficiency and minimize environmental risk with microenvironments created by ecofriendly biocomposites

Over half the global population depends on food grown with synthetic nitrogen fertilizers, but much of this nitrogen is lost as nitrates, N2O and NH3, harming the environment and health and incurring substantial environmental costs. Practical technologies aimed at enhancing nitrogen efficiency to reduce these losses promised considerable societal benefits. Nitrification inhibitors (NIs) can help reduce these losses, but their effectiveness varies, often lasting only weeks or days, for the strategy to improve NIs efficiency reducing environmental pollution that are still poorly contrived. Therefore, this study developed a novel approach by ecofriendly alginate and polyphenols to create a microenvironment (SANMP), which increased NIs based on DMPP stability at temperatures between 70 and 125 °C (47%-77% increase), in compound fertilizers (1.4%-11% increase), and in soils with a wide pH range of 5.6-7.9 (21%-27% increase). Enhanced stability can significantly increase environmental benefits in agriculture. SANMP reduces N2O emissions by 89% relative to nitrogen fertilizer-only treatments and a further 26% decrease compared to traditional DMPP formulations. Analysis of the chemical structure of alginate-metal-polyphenol hybrid materials demonstrated that DMPP immobilization, achieved through pore filling, chelation, and electrostatic attraction, significantly reduced its degradation from high temperatures, pH fluctuations, environmental ions, and soil microbial activities. The novel microenvironment offers an effective solution to the problems of high cost and unstable inhibition efficiency of DMPP, thus improving its environmental and agricultural benefits. This technology promises to offer solutions for nutrient management strategies that are efficient, highly beneficial to the environment and cost-effective.

Enhancing agroecosystem nitrogen management: microbial insights for improved nitrification inhibition

Nitrification is a key microbial process in the nitrogen (N) cycle that converts ammonia to nitrate. Excessive nitrification, typically occurring in agroecosystems, has negative environmental impacts, including eutrophication and greenhouse gas emissions. Nitrification inhibitors (NIs) are widely used to manage N in agricultural systems by reducing nitrification rates and improving N use efficiency. However, the effectiveness of NIs can vary depending on the soil conditions, which, in turn, affect the microbial community and the balance between different functional groups of nitrifying microorganisms. Understanding the mechanisms underlying the effectiveness of NIs, and how this is affected by the soil microbial communities or abiotic factors, is crucial for promoting sustainable fertilizer practices. Therefore, this review examines the different types of NIs and how abiotic parameters can influence the nitrifying community, and, therefore, the efficacy of NIs. By discussing the latest research in this field, we provide insights that could facilitate the development of more targeted, efficient, or complementary NIs that improve the application of NIs for sustainable management practices in agroecosystems.

High-throughput assays to identify archaea-targeting nitrification inhibitors

Nitrification is a microbial process that converts ammonia (NH3) to nitrite (NO2 -) and then to nitrate (NO3 -). The first and rate-limiting step in nitrification is ammonia oxidation, which is conducted by both bacteria and archaea. In agriculture, it is important to control this process as high nitrification rates result in NO3 - leaching, reduced nitrogen (N) availability for the plants and environmental problems such as eutrophication and greenhouse gas emissions. Nitrification inhibitors can be used to block nitrification, and as such reduce N pollution and improve fertilizer use efficiency (FUE) in agriculture. Currently applied inhibitors target the bacteria, and do not block nitrification by ammonia-oxidizing archaea (AOA). While it was long believed that nitrification in agroecosystems was primarily driven by bacteria, recent research has unveiled potential significant contributions from ammonia-oxidizing archaea (AOA), especially when bacterial activity is inhibited. Hence, there is also a need for AOA-targeting nitrification inhibitors. However, to date, almost no AOA-targeting inhibitors are described. Furthermore, AOA are difficult to handle, hindering their use to test or identify possible AOA-targeting nitrification inhibitors. To address the need for AOA-targeting nitrification inhibitors, we developed two miniaturized nitrification inhibition assays using an AOA-enriched nitrifying community or the AOA Nitrosospaera viennensis. These assays enable high-throughput testing of candidate AOA inhibitors. We here present detailed guidelines on the protocols and illustrate their use with some examples. We believe that these assays can contribute to the discovery of future AOA-targeting nitrification inhibitors, which could complement the currently applied inhibitors to increase nitrification inhibition efficiency in the field and as such contribute to a more sustainable agriculture.

A meta-analysis to examine whether nitrification inhibitors work through selectively inhibiting ammonia-oxidizing bacteria

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.