Non-targeted effects of nitrification inhibitors on soil free-living nitrogen fixation modified with weed management.

Biological nitrogen fixation and nitrification inhibitor applications contribute to improving soil nitrogen (N) availability, however, free-living N fixation affected by nitrification inhibitors has not been effectively evaluated in soils under different weed management methods. In this study, the effects of the nitrification inhibitors dicyandiamide (DCD) and 3, 4-dimethylpyrazole phosphate (DMPP) on the nitrogenase, nifH gene，and diazotrophic communities in soils under different weed management methods (AMB, weeds growth without mowing or glyphosate spraying; GS, glyphosate spraying; MSG, mowing and removing weeds and glyphosate spraying; and WM, mowing aboveground weeds) were investigated. Compared to the control counterparts, the DCD application decreased soil nitrogenase activity and nifH gene abundance by 4.5 % and 37.9 %, respectively, under the GS management method, and the DMPP application reduced soil nitrogenase activity by 20.4 % and reduced the nifH gene abundance by 83.4 % under the MSG management method. The application of nitrification inhibitors significantly elevated soil NH4+-N contents but decreased NO3--N contents, which had adverse impacts on soil nifH gene abundance and nitrogenase activity. The nifH gene abundances were also negatively impacted by dissolved organic N and Geobacter but were positively affected by available phosphorus and diazotrophic community structures. Nitrification inhibitors significantly inhibited Methylocella but stimulated Rhizobiales and affected soil diazotrophic communities. The nitrification inhibitors DCD and DMPP significantly altered soil diazotrophic community structures, but weed management outweighed nitrification inhibitors in reshaping soil diazotrophic community structures. The non-targeted effects of the nitrification inhibitors DMPP and DCD on soil free-living N fixation were substantially influenced by the weed management methods.

Assessing the effectiveness of 3, 4-dimethylpyrazole phosphate (DMPP) inhibitor in mitigating N2O emissions from contrasting Cd-contaminated soils.

Improving nitrogen use efficiency of chemical fertilizers is essential to mitigate the negative environmental impacts of nitrogen. Nitrification, the conversion of ammonium to nitrate via nitrite by soil microbes, is a prominent source of nitrogen loss in soil systems. The effectiveness of nitrification inhibitors in reducing nitrogen loss through inhibition of nitrification is well-documented, however, their efficacy in heavy metals-contaminated soils needs thorough investigations. The current study assessed the efficacy of nitrification inhibitor 3, 4-dimethylpyrazole phosphate (DMPP) in reducing nitrous oxide (N2O) emissions in cadmium (Cd) contaminated paddy and red soils under lab-controlled environment. Obtained results indicated the substantial reduction in N2O emissions with DMPP in paddy and red soil by 48 and 35 %, respectively. However, Cd contamination resulted in reduced efficacy of DMPP, thus decreased the N2O emissions by 36 and 25 % in paddy and red soil, respectively. It was found that addition of DMPP had a significant effect on the abundance of ammonia oxidizing bacteria (AOB) and archaea (AOA). Notably, the reduction in N2O emissions by DMPP varied with the abundance of AOB. Moreover, Cd pollution resulted in a significant (P < 0.05) reduction in the abundance of archaeal and bacterial amoA genes, as well as bacterial nirK, nirS, and nosZ genes. The combined treatment of Cd and DMPP had a detrimental impact on denitrifiers, thereby influencing the overall efficiency of DMPP. These findings provide novel insights into the application of DMPP to mitigate nitrification and its potential role in reducing N2O emissions in contaminated soils.

Digestate induces significantly higher N2O emission compared to urea under different soil properties and moisture.

Digestate is considered as an option for recycling resources and a part of the substitution for chemical fertilizers to reduce environmental impacts. However, its application may lead to significant nitrous oxide (N2O) emissions because of its high concentration of ammonium and degradable carbon. The research objectives are to evaluate how N2O emissions respond to digestate as compared to urea application and whether this depends on soil properties and moisture. Either digestate or urea (100 mg N kg-1) was applied with and without a nitrification inhibitor of 3,4-dimethylpyrazole phosphate (DMPP) to three soil types (fluvo-aquic soil, black soil, and latosol) under three different soil moisture conditions (45, 65, and 85% water-filled pore space (WFPS)) through microcosm incubations. Results showed that digestate- and urea-induced N2O emissions increased exponentially with soil moisture in the three studied soils, and the magnitude of the increase was much greater in the alkaline fluvo-aquic soil, coinciding with high net nitrification rate and transient nitrite accumulation. Compared with urea-amended soils, digestate led to significantly higher peaks in N2O and carbon dioxide (CO2) emissions, which might be due to stimulated rapid oxygen consumption and mineralized N supply. Digestate-induced N2O emissions were all more than one time higher than those induced by urea at the three moisture levels in the three studied soils, except at 85% WFPS in the fluvo-aquic soil. DMPP was more effective at mitigating N2O emissions (inhibitory efficacy: 73%-99%) in wetter digestate-fertilized soils. Overall, our study shows the contrasting effect of digestate to urea on N2O emissions under different soil properties and moisture levels. This is of particular value for determining the optimum of applying digestate under varying soil moisture conditions to minimize stimulated N2O emissions in specific soil properties.

Linking Carbendazim Accumulation with Soil and Endophytic Microbial Community Diversities, Compositions, Functions, and Assemblies: Effects of Urea-hydrogen Peroxide and Nitrification Inhibitors.

Fungicide carbendazim accumulation in soils and plants is a wide concern. Nitrogen (N) is a substantial nutrient limiting crop growth and affecting soil microbial activity and the community in degrading fungicides. We investigated the effects of urea-hydrogen peroxide (UHP) and nitrification inhibitors Dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP) on carbendazim accumulation and soil and endophytic microbial communities. The UHP application had negligible influences on soil and plant carbendazim accumulation, but the combined UHP and DCD decreased soil carbendazim accumulation by 5.31% and the combined UHP and DMPP decreased plant carbendazim accumulation by 44.36%. The combined UHP and nitrification inhibitor significantly decreased the ratios of soil Firmicutes and endophytic Ascomycota. Soil microbial community assembly was governed by the stochastic process, while the stochastic and deterministic processes governed the endophyte. Our findings could provide considerable methods to reduce fungicide accumulation in soil-plant systems with agricultural N management strategies.

Biological and chemical nitrification inhibitors exhibited different effects on soil gross N nitrification rate and N2O production: a 15N microcosm study.

Nitrification inhibitors (NIs) are considered as an effective strategy for reducing nitrification rate and related environmental nitrogen (N) loss. However, whether plant-derived biological NIs had an advantage over chemical NIs in simultaneously inhibiting nitrification rate and N2O production remains unclear. Here, we conducted an aerobic 15N microcosmic incubation experiment to compare the effects of a biological NI (methyl 3-(4-hydroxyphenyl) propionate, MHPP) with three chemical NIs, 2-chloro-6-(trichloromethyl) pyridine (nitrapyrin), dicyandiamide (DCD), and 3,4-dimethylpyrazole phosphate (DMPP) on (i) gross N mineralization and nitrification rate and (ii) the relative importance of nitrification and denitrification in N2O emission in a calcareous soil. The results showed that DMPP significantly inhibited m_gross rate (P < 0.05), whereas DCD, nitrapyrin, and MHPP only numerically inhibited it. Gross N nitrification (n_gross) rates were inhibited by 9.48% in the DCD treatment to 51.5% in the nitrapyrin treatment. Chemical NIs primarily affected the amoA gene abundance of ammonia-oxidizing bacteria (AOB), whereas biological NIs affected the amoA gene abundance of ammonia-oxidizing archaea (AOA) and AOB. AOB's community composition was more susceptible to NIs than AOA, and NIs mainly targeted Nitrosospira clusters of AOB. Chemical NIs of DCD, DMPP, and nitrapyrin proportionally reduced N2O production from nitrification and denitrification. However, the biological NI MHPP stimulated short-term N2O emission and increased the proportion of N2O from denitrification. Our findings showed that the influence of NIs on gross N mineralization rate (m_gross) was dependent on the NI type. MHPP exhibited a moderate n_gross inhibitory capacity compared with the three chemical NIs. The mechanisms of chemical and biological NIs inhibiting n_gross can be partly attributed to changes in the abundance and community of ammonia oxidizers. A more comprehensive evaluation is needed to determine whether biological NIs have advantages over chemical NIs in inhibiting greenhouse gas emissions.

DMPP attenuates lipopolysaccharide-induced lung injury by inhibiting glycocalyx degradation through activation of the cholinergic anti-inflammatory pathway.

The study aimed to investigate the therapeutic potential of 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP), an agonist of nicotinic acetylcholine receptor (nAChR), in treating acute lung injury (ALI) induced by lipopolysaccharide (LPS). A murine ALI model was developed utilizing intraperitoneal injection of LPS. We evaluated the therapeutic efficacy of DMPP treatment in LPS-induced lung injury using various approaches, including pathohistological evaluation, appraisal of pulmonary edema, and measurement of inflammatory cytokine levels and their associated pathways within lung tissues. The gene chip data of LPS-induced acute lung injury mice were retrieved from the Gene Expression Omnibus (GEO) database for gene differential expression analysis and Gene Set Enrichment Analysis (GSEA) analysis. The impact of DMPP on glycocalyx shedding was assessed by measuring the expression levels of syndecan-1 (SDC-1) and matrix metalloproteinase-9 (MMP-9). DMPP treatment significantly improved pathomorphological changes and pathological lung injury scores in the LPS-induced ALI mouse model. The genes expressed differentially in the LPS-induced ALI group in GSE2411 were found to be involved in multiple processes, including the NF-κB signaling pathway, NOD-like receptor signaling pathway, Toll-like receptor signaling pathway, as well as the JAK-STAT signaling pathway. DMPP treatment effectively downregulated pro-inflammatory cytokines, suppressed the NF-κB signaling pathway, and effectively restrained the LPS-induced upregulation of MMP-9 and shedding of syndecan-1, thereby contributing to the preservation of endothelial glycocalyx and attenuation of endothelial barrier dysfunction. The administration of DMPP has been shown to confer protection against LPS-induced acute lung injury via a cholinergic anti-inflammatory pathway, which effectively inhibits endothelial glycocalyx degradation.

Synergistic benefits of lime and 3,4-dimethylpyrazole phosphate application to mitigate the nitrous oxide emissions from acidic soils.

Acidic soils cover approximately 50 % of the arable land with high N2O emission potential. 3,4-dimethylpyrazole phosphate (DMPP) inhibits N2O emission from soils; however, its efficiency is affected by acidity. Liming is used for soil conditioning to ameliorate the effects of acidity. In the present study, we investigated the effects of liming on the efficiency of DMPP in inhibiting N2O emission in acidic soils and the mechanisms involved. We evaluated the impact of liming, DMPP, and combined application and its microbial responses in two acidic soils from Zengcheng (ZC) and Shaoguan (SG) City, Guangdong Province, China. Soils were subjected to four treatments: un-limed soil (low soil pH) + urea (LU), un-limed soil + urea + DMPP (LD), limed soil (high soil pH) + urea (HU), and limed soil + urea + DMPP (HD) for analyses of the mineral N, N2O emissions, and full-length 16S and metagenome sequencing. The results revealed that, HU significantly decreased and increased the N2O emission by 17.8 % and 235.0 % in ZC and SG, respectively, compared with LU. This was caused by a trade-off between N2O production and consumption after liming, where microbial communities and N-cycling functional genes show various compositions in different acidic soils. LD reduced N2O emission by 23.5 % in ZC, whereas decreased 1.5 % was observed in SG. Interestingly, DMPP efficiency considerably improved after liming in two acidic soils. Compared with LU, HD significantly reduced N2O emissions by 61.2 % and 48.5 % in ZC and SG, respectively. Synergy of mitigation efficiency was observed by lime and DMPP application, which was attributed to the changes in the dominant nitrifiers and the increase in N2O consumption by denitrifiers. The combined application of lime and DMPP is a high-efficiency strategy for N2O mitigation can ensure agricultural sustainability in acidic arable soils with minimal environmental damage.

Metagenomic analysis insights into the influence of 3,4-dimethylpyrazole phosphate application on nitrous oxide mitigation efficiency across different climate zones in Eastern China.

Excessive nitrogen (N) fertilization in agroecological systems increases nitrous oxide (N2O) emissions. 3,4-dimethylpyrazole phosphate (DMPP) is used to mitigate N2O losses. The influence of DMPP efficiency on N2O mitigation was clearly affected by spatiotemporal heterogeneity. Using field and incubation experiments combined with metagenomic sequencing, we aimed to investigate DMPP efficiency and the underlying microbial mechanisms in dark-brown (Siping, SP), fluvo-aquic (Cangzhou, CZ; Xinxiang, XX), and red soil (Wenzhou, WZ) from diverse climatic zones. In the field experiments, the DMPP efficiency in N2O mitigation ranged from 51.6% to 89.9%, in the order of XX, CZ, SP, and WZ. The DMPP efficiency in the incubation experiments ranged from 58.3% to 93.9%, and the order of efficiency from the highest to lowest was the same as that of the field experiments. Soil organic matter, total N, pH, texture, and taxonomic and functional α-diversity were important soil environment and microbial factors for DMPP efficiency. DMPP significantly enriched ammonia-oxidizing archaea (AOA) and nitrite-oxidizing bacteria (NOB), which promoted N-cycling with low N2O emissions. Random forest (RF) and regression analyses found that an AOA (Nitrosocosmicus) and NOB (Nitrospina) demonstrated important and positive correlation with DMPP efficiency. Moreover, genes associated with carbohydrate metabolism were important for DMPP efficiency and could influenced N-cycling and DMPP metabolism. The similar DMPP efficiency indicated that the variation in DMPP efficiency was significantly due to soil physicochemical and microbial variations. In conclusion, filling the knowledge gap regarding the response of DMPP efficiency to abiotic and biotic factors could be beneficial in DMPP applications, and in adapting more efficient strategies to improve DMPP efficiency and mitigate N2O emissions in multiple regions.

Insight into functional mechanisms of percarbamide and nitrification inhibitors in degrading fungicide residues and shaping microbial communities in soil-plant systems.

Fungicides and nitrogen (N) fertilizers are essential to maintain plant yield in current intensive agriculture. Percarbamide is a novel type of N fertilizer with strong oxidizing property, and the nitrification inhibitor is widely used in agricultural production. It may be feasible to apply percarbamide and nitrification inhibitor as N management to promote fungicide dissipations in soil-plant system. This study quantified the effects of percarbamide and nitrification inhibitor dicyandiamide (DCD) and 3, 4-dimethylpyrazole phosphate (DMPP) on carbendazim residues, and microbial communities of soil-plant systems, and relationships among carbendazim residues, soil and endophytic microbial communities and plant yields were also comprehensively quantified. Compared with the control, the percarbamide significantly reduced soil carbendazim residues by 29.4% but enhanced the lettuce yield by 28.0%. Soil carbendazim residues were significantly and negatively correlated with the soil total N and NO3--N contents. Soil microbial community structures and co-occurrence networks were more sensitive to N management than their endophytic counterparts. In comparison to the percarbamide alone, the DCD significantly increased the nodes of soil fungal community co-occurrence network which were positively correlated with the plant yield. The DCD outweighed DMPP in increasing the lettuce yield and soil fungal community stability and reshaping soil bacterial community structure. Our study suggested that soil microbial communities were more sensitive to percarbamide and nitrification inhibitor applications than their endophytic counterparts under fungicide pressure and that the DCD outweighed DMPP in reshaping microbial communities. The integrated applications of percarbamide and nitrification inhibitors were promising soil N management strategies to promote fungicide removal and stimulate microbial community in the soil-plant systems.

Mediation of gaseous emissions and improving plant productivity by DCD and DMPP nitrification inhibitors: Meta-analysis of last three decades.

Nitrification inhibitors (NIs), especially dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP), have been extensively investigated to mitigate nitrogen (N) losses from the soil and thus improve crop productivity by enhancing N use efficiency. However, to provide crop and soil-specific guidelines about using these NIs, a quantitative assessment of their efficacy in mitigating gaseous emissions, worth for nitrate leaching, and improving crop productivity under different crops and soils is yet required. Therefore, based upon 146 peer-reviewed research studies, we conducted a meta-analysis to quantify the effect of DCD and DMPP on gaseous emissions, nitrate leaching, soil inorganic N, and crop productivity under different variates. The efficacy of the NIs in reducing the emissions of CO2, CH4, NO, and N2O highly depends on the crop, soil, and experiment types. The comparative efficacy of DCD in reducing N2O emission was higher than the DMPP under maize, grasses, and fallow soils in both organic and chemical fertilizer amended soils. The use of DCD was linked to increased NH3 emission in vegetables, rice, and grasses. Depending upon the crop, soil, and fertilizer type, both the NIs decreased nitrate leaching from soils; however, DMPP was more effective. Nevertheless, the effect of DCD on crop productivity indicators, including N uptake, N use efficiency, and biomass/yield was higher than DMPP due to certain factors. Moreover, among soils, crops, and fertilizer types, the response by plant productivity indicators to the application of NIs ranged between 35 and 43%. Overall, the finding of this meta-analysis strongly suggests the use of DCD and DMPP while considering the crop, fertilizer, and soil types.

The win-win effects of nitrification inhibitors on soil-crop systems: Decreasing carbendazim residues but promoting soil bacterial community diversities and stabilities and crop yields.

Applying nitrogen (N)-cycling inhibitors is an effective measure to improve N fertilizer utilization efficiency, but the effects of N-cycling inhibitors on fungicide residues in soil-crop systems are unclear. In this study, nitrification inhibitors dicyandiamide (DCD) and 3, 4-dimethylpyrazole phosphate (DMPP) and urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) were applied into agricultural soils with fungicide carbendazim applications. The soil abiotic properties, carrot yields, carbendazim residues, bacterial communities and their comprehensive relationships were also quantified. Compared to the control treatment, the DCD and DMPP significantly decreased soil carbendazim residues by 96.2% and 96.0%, and the DMPP and NBPT significantly reduced carrot carbendazim residues by 74.3% and 60.3%, respectively. The nitrification inhibitor applications also generated significant and positive effects on carrot yields and soil bacterial community diversities. The DCD application significantly stimulated soil Bacteroidota and endophytic Myxococcota and modified soil and endophytic bacterial communities. Meanwhile, the DCD and DMPP applications also positively stimulated the co-occurrence network edges of soil bacterial communities by 32.6% and 35.2%, respectively. The linear correlation coefficients between soil carbendazim residues and pH, ETSA and NH4+-N contents were - 0.84, - 0.57 and - 0.80, respectively. The nitrification inhibitor applications generated win-win effects on the soil-crop systems by decreasing carbendazim residues but promoting soil bacterial community diversities and stabilities and crop yields.

Legume cover with optimal nitrogen management and nitrification inhibitor enhanced net ecosystem economic benefits of peach orchard.

Peach (Prunus persica L.), as a traditional kind of fruits in China, was extremely dependent on large application of nitrogen (N) fertilizer to maintain high fruit yield and commercial income, resulting in raising environmental damage risk. Therefore, a three-year field trail was conducted to clarify the environmental N loss under conventional management, investigate the positive effects of optimal N management, legume cover and 3,4-dimethylpyrazole phosphate (DMPP) on N input/output and the net ecosystem economic benefits (NEEB). There are four treatments in this study: conventional fertilizer management with 521.1 kg N ha-1 yr-1 input (CU); optimal N management including 406.4 kg N ha-1 yr-1 input and deep fertilization (OP); DMPP was added to OP at rate of 1 % (w/w) (OPD); legume (white clover) was covered to OPD (OPDG). Results showed 102.9 kg N ha-1 was removed by annual fruit and residues (including pruned branches, pruned and fallen leaves), while 70.2 kg N ha-1 was lost to the environment by ammonia (NH3), nitrous oxide (N2O) and N runoff loss under the conventional fertilizer management. While, the optimal N management mitigated NH3 volatilization about 49.3 %, further added DMPP abated N2O emission by 61.4 %, besides covered white clover lowered N runoff loss by 64.5 %. The NEEB results revealed that optimal N management combined with added DMPP and covered white clover could minimize the production cost, reduce environmental damage cost by 35.9 %, increase fruit yield by 10.3 % and achieved the maximum NEEB with improvement of 27.1 %, in comparison of the conventional fertilizer management. Generally, conventional peach cultivation constituted overwhelming N loss to raise potential environmental risk. While, extending mode of optimized N management combined with DMPP and legume cover could not only realize high fruit revenue, but also abate environmental N losses, thereby should be considered as effective strategy for sustainable fruit cropping systems.

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

The efficacy of nitrification inhibitors (NIs) dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP) varies with soil types. Understanding the microbial mechanisms for this variation may lead to better modelling of NI efficacy and therefore on-farm adoption. This study addressed the response patterns of mineral nitrogen, nitrous oxide (N2O) emission, abundances of N-cycling functional guilds and soil microbiota characteristics, in relation to urea application with or without DCD or DMPP in two arable soils (an alkaline and an acid soil). The inhibition of nitrification rate and N2O emission by NI application occurred by suppressing ammonia-oxidizing bacteria (AOB) abundances and increasing the abundances of nosZI-N2O reducers; however, abundances of ammonia-oxidizing archaea (AOA) were also stimulated with NIs-added in these two arable soils. DMPP generally had stronger inhibition efficiency than DCD, and both NIs' addition decreased Nitrobacter, while increased Nitrospira abundance only in alkaline soil. N2O emissions were positively correlated with AOB and negatively correlated with nosZI in both soils and AOA only in acid soil. Moreover, N2O emissions were also positively correlated with nirK-type denitrifiers in alkaline soil, and clade A comammox in acid soil. Amendment with DCD or DMPP altered soil microbiota community structure, but had minor effect on community composition. These results highlight a crucial role of the niche differentiation among canonical ammonia oxidizers (AOA/AOB), Nitrobacter and Nitrospira, as well as nosZI- and nosZII-N2O reducers in determining the varying efficacies of DCD and DMPP in different arable soils.

Evaluation of a crop rotation with biological inhibition potential to avoid N2O emissions in comparison with synthetic nitrification inhibition.

Agriculture has increased the release of reactive nitrogen to the environment due to crops' low nitrogen-use efficiency (NUE) after the application of nitrogen-fertilisers. Practices like the use of stabilized-fertilisers with nitrification inhibitors such as DMPP (3,4-dimethylpyrazole phosphate) have been adopted to reduce nitrogen losses. Otherwise, cover crops can be used in crop-rotation-strategies to reduce soil nitrogen pollution and benefit the following culture. Sorghum (Sorghum bicolor) could be a good candidate as it is drought tolerant and its culture can reduce nitrogen losses derived from nitrification because it exudates biological nitrification inhibitors (BNIs). This work aimed to evaluate the effect of fallow-wheat and sorghum cover crop-wheat rotations on N2O emissions and the grain yield of winter wheat crop. In addition, the suitability of DMPP addition was also analyzed. The use of sorghum as a cover crop might not be a suitable option to mitigate nitrogen losses in the subsequent crop. Although sorghum-wheat rotation was able to reduce 22% the abundance of amoA, it presented an increment of 77% in cumulative N2O emissions compared to fallow-wheat rotation, which was probably related to a greater abundance of heterotrophic-denitrification genes. On the other hand, the application of DMPP avoided the growth of ammonia-oxidizing bacteria and maintained the N2O emissions at the levels of unfertilized-soils in both rotations. As a conclusion, the use of DMPP would be recommendable regardless of the rotation since it maintains NH4+ in the soil for longer and mitigates the impact of the crop residues on nitrogen soil dynamics.

Using DMPP with cattle manure can mitigate yield-scaled global warming potential under low rainfall conditions.

Organic fertilisers can reduce the carbon (C) footprint from croplands, but adequate management strategies such as the use of nitrification inhibitors are required to minimise side-effects on nitrogen (N) losses to the atmosphere or waterbodies. This could be particularly important in a context on changing rainfall patterns due to climate change. A lysimeter experiment with maize (Zea mays L.) was set up on a coarse sandy soil to evaluate the efficacy of 3,4-dimethylpyrazole phosphate (DMPP) to mitigate nitrous oxide (N2O) emissions, nitrate (NO3-) leaching losses and net global warming potential from manure, with (R+) and without (R-) simulated rainfall events. Soil water availability was a limiting factor for plant growth and microbial processes due to low rainfall during the growing season. Nitrification was effectively inhibited by DMPP, decreasing topsoil NO3- concentrations by 28% on average and cumulative N2O losses by 82%. Most of the N2O was emitted during the growing season, with annual emission factors of 0.07% and 0.95% for manure with and without DMPP, respectively. Cumulative N2O emissions were 40% higher in R-compared to R+, possibly because of the higher topsoil NO3- concentrations. There was no effect of DMPP or rainfall amount on annual NO3- leaching losses, which corresponded to 12% of manure-N and were mainly driven by the post-harvest period. DMPP did not affect yield or N use efficiency (NUE) while R-caused severe reductions on biomass and NUE. We conclude that dry growing seasons can jeopardize crop production while concurrently increasing greenhouse gas emissions from a sandy soil. The use of nitrification inhibitors is strongly recommended under these conditions to address the climate change impacts.

[Impact of Nitrification Inhibitors on Vegetable Production Yield, Nitrogen Fertilizer Use Efficiency and Nitrous Oxide Emission Reduction in China: Meta Analysis].

Due to the long-term excessive fertilization in the vegetable system in China, nitrogen use efficiency (NUE) is low, and the environmental problem is serious. Nitrogen fertilizer combined with nitrification inhibitor is an effective strategy to alleviate the loss of active nitrogen and increase vegetable yield. However, systematic research on the above is lacking. Meta-analysis was used to systematically analyze the effects of nitrogen fertilizer combined with nitrification inhibitors[dicyandiamide (DCD), 3,4-dimethylpyrazole phosphate (DMPP), and 2-chloro-6-(trichloromethyl)pyridine (NP)] on the yield, plant nitrogen uptake, nitrogen fertilizer use efficiency, and nitrous oxide emission reduction effects in vegetable production in China. This study further revealed the impacts of different field management measures on their effects. The results showed that the combination of nitrogen fertilizer and nitrification inhibitor could significantly increase vegetable yield (9.2%), plant nitrogen uptake (10.4%), and nitrogen fertilizer use efficiency (11.2%) but reduce nitrous oxide emissions (28.4%). Among the different types of nitrification inhibitors, NP had the highest impact on the yield-increasing effect and the nitrous oxide emission reduction effect, which were 16.1% and 32.0%, respectively, followed by that of DMPP and DCD. Nitrification inhibitors could significantly increase vegetable yield (6.7%-14.7%) and reduce N2O emissions (14.6%-36.8%) in different nitrogen fertilizer rates. In neutral and alkaline vegetable soil, the yield-increasing effect and the reduction effect of nitrous oxide were higher than those in acidic soil. Nitrification inhibitors had significant effects on yield increase and nitrous oxide reduction under the conditions of greenhouse or open-field cultivation, root vegetables, and leafy vegetables. Principal component analysis (PCA) showed that soil total nitrogen content and soil pH were the main factors that promoted the increase in vegetable yields and drove nitrous oxide emissions under the application of nitrification inhibitors. In summary, nitrification inhibitors were an important measure to achieve the goal of improving quality and fertilizer use efficiency, while saving fertilizer and reducing emissions in vegetable production. Farmers should choose suitable types of nitrification inhibitors according to soil and field management measures to maximize their effectiveness.

Arbuscular Mycorrhiza and Nitrification: Disentangling Processes and Players by Using Synthetic Nitrification Inhibitors.

Both plants and their associated arbuscular mycorrhizal (AM) fungi require nitrogen (N) for their metabolism and growth. This can result in both positive and negative effects of AM symbiosis on plant N nutrition. Either way, the demand for and efficiency of uptake of mineral N from the soil by mycorrhizal plants are often higher than those of nonmycorrhizal plants. In consequence, the symbiosis of plants with AM fungi exerts important feedbacks on soil processes in general and N cycling in particular. Here, we investigated the role of the AM symbiosis in N uptake by Andropogon gerardii from an organic source (15N-labeled plant litter) that was provided beyond the direct reach of roots. In addition, we tested if pathways of 15N uptake from litter by mycorrhizal hyphae were affected by amendment with different synthetic nitrification inhibitors (dicyandiamide [DCD], nitrapyrin, or 3,4-dimethylpyrazole phosphate [DMPP]). We observed efficient acquisition of 15N by mycorrhizal plants through the mycorrhizal pathway, independent of nitrification inhibitors. These results were in stark contrast to 15N uptake by nonmycorrhizal plants, which generally took up much less 15N, and the uptake was further suppressed by nitrapyrin or DMPP amendments. Quantitative real-time PCR analyses showed that bacteria involved in the rate-limiting step of nitrification, ammonia oxidation, were suppressed similarly by the presence of AM fungi and by nitrapyrin or DMPP (but not DCD) amendments. On the other hand, abundances of ammonia-oxidizing archaea were not strongly affected by either the AM fungi or the nitrification inhibitors. IMPORTANCE Nitrogen is one of the most important elements for all life on Earth. In soil, N is present in various chemical forms and is fiercely competed for by various microorganisms as well as plants. Here, we address competition for reduced N (ammonia) between ammonia-oxidizing prokaryotes and arbuscular mycorrhizal fungi. These two functionally important groups of soil microorganisms, participating in nitrification and plant mineral nutrient acquisition, respectively, have often been studied in separation in the past. Here, we showed, using various biochemical and molecular approaches, that the fungi systematically suppress ammonia-oxidizing bacteria to an extent similar to that of some widely used synthetic nitrification inhibitors, whereas they have only a limited impact on abundance of ammonia-oxidizing archaea. Competition for free ammonium is a plausible explanation here, but it is also possible that the fungi produce some compounds acting as so-called biological nitrification inhibitors.

Effects of animal manure and nitrification inhibitor on N2O emissions and soil carbon stocks of a maize cropping system in Northeast China.

The incorporation of animal manure (AM) in soil plays an essential role in soil carbon sequestration but might induce higher soil nitrous oxide (N2O) emissions. The use of nitrification inhibitors (NI) is an effective strategy to abate N2O emission in agro-ecosystems. However, very few studies have evaluated the effectiveness of applying NI under the combined application of organic and inorganic fertilizers for increasing soil carbon sequestration and reducing N2O emissions simultaneously in Northeast China. Here, a four-year field experiment was conducted with three treatments [inorganic fertilizer (NPK), inorganic fertilizer + manure (NPKM), and inorganic fertilizer with NI + manure (NPKI + M)], in a rainfed maize cropping system in Northeast China. Plots of different treatments were kept in the same locations for 4 years. Gas samples were collected using the static closed chamber technique, and nitrous oxide (N2O) concentration in gas samples was quantified using a gas chromatograph. Soil organic carbon sequestration rate (SOCSR) was calculated based on the changes in SOC from April 2012 to October 2015. Averaged over the four years, AM incorporation significantly increased soil N2O emissions by 25.8% (p < 0.05), compared to NPK treatment. DMPP (3,4-dimethylpyrazole phosphate) significantly decreased N2O emissions by 32.5% (p < 0.05) relative to NPKM treatment. SOC content was significantly elevated by 24.1% in the NPKI + M treatment than the NPK treatment after four years of manure application (p < 0.05). The annual topsoil SOCSR for the NPKM and NPKI + M treatments was 0.57 Mg ha-1 yr-1 and 1.02 Mg ha-1 yr-1, respectively, which were significantly higher than that of NPK treatment (- 0.61 Mg ha-1 yr-1, p < 0.05). AM addition significantly increased the aboveground biomass and crop yields of maize in the fourth year. Overall, combined application of DMPP, inorganic fertilizer and AM is strongly recommended in this rainfed maize cropping system, which can increase maize yield and SOC sequestration rate, and mitigate N2O emission.

Effects of combined nitrification inhibitors on soil nitrification, maize yield and nitrogen use efficiency in three agricultural soils.

Application of nitrification inhibitors (NIs) with nitrogen (N) fertilizer is one of the most efficient ways to improve nitrogen use efficiency (NUE). To fully understand the efficiency of NIs with N fertilizer on soil nitrification, yield and NUE of maize (Zea mays L.), an outdoor pot experiment with different NIs in three soils with different pH was conducted. Five treatments were established: no fertilizer (Control); ammonium sulfate (AS); ammonium sulfate + 3, 4-dimethyl-pyrazolate phosphate (DMPP) (AD); ammonium sulfate + nitrogen protectant (N-GD) (AN); ammonium sulfate + 3, 4-dimethyl-pyrazolate phosphate + nitrogen protectant (ADN). The results showed that NIs treatments (AD, AN and ADN) significantly reduced soil nitrification in the brown and red soil, especially in AD and ADN, which decreased apparent nitrification rate by 28% - 44% (P < 0.05). All NIs treatments significantly increased yield and NUE of maize in three soils, especially ADN in the cinnamon soil and AD in the red soil were more efficiency, which significantly increased maize yield and apparent nitrogen recovery by 5.07 and 6.81 times, 4.39 and 8.16 times, respectively. No significant difference on maize yield was found in the brown soil, but AN significantly increased apparent nitrogen recovery by 70%. Given that the effect of NIs on both soil nitrification and NUE of maize, DMPP+N-GD was more efficient in the cinnamon soil, while N-GD and DMPP was the most efficiency in the brown and red soil, respectively. In addition, soil pH and soil organic matter play important role in the efficiency of NIs.

Quantitative Evaluation of Noncovalent Interactions between 3,4-Dimethyl-1H-pyrazole and Dissolved Humic Substances by NMR Spectroscopy.

Nitrification inhibitors (NI) represent a valid chemical strategy to retard nitrogen oxidation in soil and limit nitrate leaching or nitrogen oxide emission. We hypothesized that humic substances can complex NI, thus affecting their activity, mobility, and persistence in soil. Therefore, we focused on 3,4-dimethylpyrazole phosphate (DMPP) by placing it in contact with increasing concentrations of model fulvic (FA) and humic (HA) acids. The complex formation was assessed through advanced and composite NMR techniques (chemical shift drift, line-broadening effect, relaxation times, saturation transfer difference (STD), and diffusion ordered spectroscopy (DOSY)). Our results showed that both humic substances interacted with DMPP, with HA exhibiting a significantly greater affinity than FA. STD emphasized the pivotal role of the aromatic signal, for HA-DMPP association, and both alkyl methyl groups, for FA-DMPP association. The fractions of complexed DMPP were determined on the basis of self-diffusion coefficients, which were then exploited to calculate both the humo-complex affinity constants and the free Gibbs energy (Kd and ΔG for HA were 0.5169 M and -1636 kJ mol-1, respectively). We concluded that DMPP-based NI efficiency may be altered by soil organic matter, characterized by a pronounced hydrophobic nature. This is relevant to improve nitrogen management and lower its environmental impact.