Changes In NH Research Articles

Canopy gap impacts on soil organic carbon and nutrient dynamic: a meta-analysis

Key messageThe forest canopy gaps, formed by natural or anthropogenic factors, have been found to reduce soil carbon content and increase nutrient availability. The magnitudes of these effects have been observed to increase with gap age and size, and are largely influenced by changes in temperature, precipitation, and solar radiation.ContextLocal studies have illustrated the influence of canopy gaps on the spatial heterogeneity of soil carbon and nutrients, playing a pivotal role in driving forest regeneration and succession. Nevertheless, it remains largely unknown whether the response of soil carbon and nutrient content to gap formation is consistent across forest ecosystems at global scale.AimsThe aim of this paper is to assess the homogeneity of the observed responses of soil carbon and nutrients following gap formation among a wide array of forest ecosystems and climatic regions.MethodsWe performed a meta-analysis synthesizing 2127 pairwise observations from 52 published articles to quantify the changes in in soil physical, chemical, and microbial variables resulting from gap creation in natural forests and plantations spanning tropical to boreal regions.ResultsCanopy gaps resulted in significant decrease of soil organic carbon (Corg) and microbial carbon (Cmic). The concentrations of ammonium (NH4+), nitrate (NO3−), and available phosphorus (available P) increased following gap creation. These changes mainly occurred in the growing season and in the mineral soil layer, becoming more pronounced with increasing gap age and size. The change in Corg was negatively regulated by mean annual precipitation, and was associated with the changes in Nt and Nmic. The change in NH4+ was positively regulated by mean annual temperature, and was associated with the changes in available P and oxidoreductases (Ox-EEAs). The model explaining the change in soil carbon content exhibited a higher explanatory power than the one accounting for changes in soil nutrient availability.ConclusionThe results indicated that forest canopy gaps resulted in a reduction in soil carbon content and an increase in nutrient availability. These findings contribute to a better understanding of the role of small-scale disturbances as drivers of forest ecosystem succession.

Effects of plasma treatment of digestates on pH, nitrification and nitrogen turnover during storage and after soil application

Acidification through plasma treatment technology presents a potential solution to mitigate nitrogen losses throughout the manure management chain, offering a dual benefit of atmospheric nitrogen incorporation into manures while inducing acidification. This study evaluated the use and effectiveness of plasma treatment technology as a one-time acidification strategy for digested slurry during long-term storage, its effects on slurry nitrogen (N) availability and subsequent release in the soil. A digestate from a full-scale anaerobic digester was separated using a decanter centrifuge, and the resultant liquid fraction (LF) was plasma treated to achieve three different initial pH levels (4.27, 5.03 and 5.42). After that, a storage experiment was set up for 180 days to monitor the evolution in pH and changes in NH4+, NO3- and NO2-. Concurrently, a soil incubation experiment was conducted to study the N turnover for 80 days after incorporating the organic materials (Liquid fraction, plasma-treated liquid fractions, digestate and raw slurry). Plasma treatment significantly increased total N and the proportion of inorganic N in the slurries by fixing atmospheric N as NO3- and NO2- and reduced the slurry pH depending on the treatment duration. After six months of storage, pH increased by 0.91 pH units in the plasma-treated liquid fraction with the highest initial pH (LFpH-5.42). Plasma treatment significantly increased net inorganic N release in soil by 5–14 % compared to a non-treated liquid fraction. Unexpected prolonged inhibition of NH4+ nitrification in soil for over 80 days after applying plasma-treated slurries was observed. In conclusion, plasma treatment emerges as a promising alternative to acid- and bio-acidification strategies, offering prolonged low slurry pH stabilisation, improved fertiliser value and delayed NH4+-N nitrification in soil.

Microbial adaptation to high ammonia environment in submerged anaerobic membrane bioreactor under volatile fatty acids and ammonia stresses

Anaerobic membrane bioreactor (AnMBR) is a high-rate bioreactor which is preferred over other configurations due to its potential to completely decouple solid retention time from hydraulic retention time. However, limited information is available on the bioreactor behavior under stressed environment, particularly during the startup period. The objective of this study was to investigate the effects of ammonium (NH4+) and organic loading rate (OLR) on the digestion performance and microbial population of submerged AnMBR. The findings revealed that high NH4+ was positively correlated with high methane concentration while high OLR increased methane production. The microbial analysis showed that both bacteria and archaea were influenced by the change of NH4+ and OLR. Particularly, at high OLR, Bacteroidetes were shown to be more sensitive to high NH4+ than Firmicutes, and Chloroflexi tolerated NH4+ even up to 2.5 g/L. Moreover, NH4+ was possibly the first driving factor in the change of methane production pathways from acetoclastic methanogenesis to hydrogenotrophic and methylotrophic methanogenesis. Membrane biofouling was also caused mainly by bacterial community (Firmicutes and Chloroflexi), while the contribution of archaeal community was minimal (Methanosaetaceae).

Exploration on the source of NH4+ in condensable particulate matter

Condensed particulate matter (CPM) is a type of pollutant that has attracted much attention due to its small emission size and complex composition. CPM consists of both inorganic and organic components, and exploring their sources is beneficial for understanding the emission characteristic and the control strategy of CPM. Among the inorganic components, NH4+ is one of the dominant cations contained in previous work's CPM samples, whose sources are still unclear. In this work, experiments were performed in two scales to investigate the potential sources of NH4+ contained in the CPM samples, one was based on a simulated flue gas experimental system, and the other was based on a real flue gas one. In both cases, ammonium-containing substances, gases or solutions with known concentrations, were intentionally added into the flue gas, and the changes of NH4+ and other concerned components in the CPM samples collected from the flue gas were compared to judge the source of it. The results showed that NH3 in the flue gas was the dominant source of NH4+ in the CPM samples. The presence of NH3, SO2, chlorine containing substances, ammonium sulfate and ammonium sulfite in the flue gas can affect the contents of both NH4+ and SO42− in the CPM samples.

New nitrification inhibitors based on copper(II) complex compounds

The work presents the results of research aimed at the synthesis of new nitrification inhibitors based on complex compounds of Cu2+ with 4-amino-1,2,4-triazole (ATC) and dicyandiamide (DCD). The purpose of the conducted work is the synthesis of new nitrification inhibitors based on complex copper compounds followed with subsequent studies of their structure, properties and biological activity. Four compounds of different compositions were obtained. A number of physical and chemical properties of substances were established: thermal behavior, and solubility in the KAS-28 system (a saturated solution of urea and ammonium nitrate with a nitrogen content of 28%)–water. With the help of infrared spectroscopy, the presence of functional groups and bonds inherent in ligands was proven in the synthesized compounds. Possible ways of coordination of 4-amino-1,2,4-triazole (monodentately through the atom N1 or N2) and dicyandiamide (through the group C=NH or CN with equal probability) were proposed. The content of Cu2+ ions in the synthesized compounds was determined by iodometry. The biological activity of the synthesized substances in relation to soil bacteria was investigated by the potentiometric method. The dynamics of changes in NH4+ and NO3– ions in research samples containing the obtained substances and commonly used nitrification inhibitors (ATC and DCD) was established. All results were equated relative to the control. It was established that the substance with the probable empirical formula [Cu(ATC)2(DCD)1(H2O)1]SO4 had the highest biological activity.

Optimization of Ammonia Nitrogen and Phosphorus Removal Performance and Analysis of Microbial Community Structure in Microbial Fuel Cells

In order to study the effects of operating conditions on the performance of a microbial fuel cell (MFC) for treating ammonia nitrogen (NH4+-N) and phosphate and the changes in the microbial community under optimized conditions, in this study, the response surface method (RSM) and central composite design (CCD) were used to carry out experiments and construct a model of the system to analyze the influence of the hydraulic retention time (HRT) and initial influent ammonia concentration on NH4+-N and the total phosphorus (TP) removal performance of the MFC, and the changes in the microbial community structure were analyzed. The results showed that: (1) the initial influent ammonia concentration had a greater impact than the HRT; (2) after optimizing the reaction conditions, the actual removal rates of NH4+-N and TP of the system were 94.88% and 59.39% (the predicted values were 90.18% and 56.25%), respectively; and (3) the total number of species in the optimization group decreased, and the richness of the microbial community decreased. The system conducted the orthoselection of the microbial community and optimized the structure of the microbial community. After the optimization, the dominant strains for ammonia and phosphorus removal on the cathode reactor of each system were strengthened at the phylum and genus levels. Under the coaction of the dominant strains, the efficiencies of nitrogen removal and phosphorus removal in the reactor were significantly improved. The performance optimization of and microbial community change in NH4+-N and TP removal in the MFC system were studied using RSM, which was helpful to improve the effect of nitrogen and phosphorus removal.

Effect of Filter Medium on Water Quality during Passive Biofilter Activation in a Recirculating Aquaculture System for Oncorhynchus mykiss

High-performance biofilters for water purification in recirculating aquaculture systems (RAS) ensure the safety of cultures of highly nutritious fish. As the most critical step in the functioning of biofilters is their activation, the objective of this study was to evaluate the suitability of commercial artificial media, namely RK Plast (BR-1), Mutag-BioChip30 (BR-2), and LevaPor (BR-3), for the passive activation of biofilters used in rainbow trout farming. Changes in NH4+-N, NO2−-N, NO3− -N, phosphorus, and carbon concentrations were analyzed. In the first period, an increase in NH4+-N concentration was recorded, before an increase in NO2−-N concentration (maximum concentrations ranged 0.728–1.290 and 0.982–5.198 mg N dm−3, respectively), followed by a reduction and stabilization to a level safe for the fish (both below 0.100 mg N dm−3). Concurrently, a steady increase in NO3−-N concentration was noted, with a maximum concentration between 6.521 and 7.326 mg N dm−3. Total phosphorus and total carbon ranged from 0.423 to 0.548 mg P dm−3, and from 43.8 to 45.2 mg C dm−3. The study confirmed the feasibility of using the tested artificial biofilter media for rainbow trout farming in RAS with passive biofilter activation. Biofilter activation efficiency was highest for the media with the highest specific surface area (BR-2 and BR-3). The removal of ammonium nitrogen and nitrite nitrogen was above 90%. Nitrogen biotransformation was not limited by phosphorus or carbon concentrations.

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 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 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.

How Does Crop Rotation Influence Soil Moisture, Mineral Nitrogen, and Nitrogen Use Efficiency?

Rice–wheat (RW) cropping systems are integral to global food security. Despite being practiced for decades, Chinese RW cropping systems often suffer from low productivity and poor nitrogen use efficiency (NUE), reflecting management approaches that are not well-contextualized to region and season. Here, we develop the best management guides for N fertilizer in RW systems that are designed to help raise the productivity, NUE, and environmental sustainability of winter wheat over the long term. 2-year field experiments were conducted with four N fertilizer rates (0, 135, 180, and 225 kg N ha–1), allowing contrasts of yields, soil moisture, and NUE of wheat in RW in the humid climates zones on the Jianghan Plain. We compared RW systems with soybean/maize dryland wheat (DW) systems that are similarly endemic to China: after soybean/maize is harvested, soils are often drier compared with moisture content following rice harvest. With high seasonal N application rates (180–225 kg N ha–1), wheat crop yields increased by 24% in RW which were greater than comparable yields of wheat in DW, mainly due to greater kernels per spike in the former. Across treatments and years, N accumulation in plant tissue and kernel dry matter of DW was higher than that in RW, although mean agronomic efficiency of nitrogen (AEN) and physiological efficiency of nitrogen (PEN) of RW systems were greater. As N application rates increased from 135 to 225 kg ha–1, AEN and PEN of DW decreased but changed little for RW. Soil ammonium N was much lower than that of nitrate N; changes in NH4+ and NO3– as a consequence of increasing N fertilization were similar for RW and DW. We recommend that tactical application of N fertilizer continue seasonally until midgrain filling for both the DW and RW systems. At fertilization rates above 180 kg N ha–1, yield responses disappeared but nitrate leaching increased significantly, suggesting declining environmental sustainability above this N ceiling threshold. Collectively, this study elicits many functional and agronomic trade-offs between yields, NUE, and environmental sustainability as a function of N fertilization. Our results show that yield and NUE responses measured as part of crop rotations are both more robust and more variable when derived over multiple seasons, management conditions, and sites.

Transcriptome and Proteomics Analysis of Wheat Seedling Roots Reveals That Increasing NH4 +/NO3 - Ratio Induced Root Lignification and Reduced Nitrogen Utilization.

Wheat growth and nitrogen (N) uptake gradually decrease in response to high NH4+/NO3– ratio. However, the mechanisms underlying the response of wheat seedling roots to changes in NH4+/NO3– ratio remain unclear. In this study, we investigated wheat growth, transcriptome, and proteome profiles of roots in response to increasing NH4+/NO3– ratios (Na: 100/0; Nr1: 75/25, Nr2: 50/50, Nr3: 25/75, and Nn: 0/100). High NH4+/NO3– ratio significantly reduced leaf relative chlorophyll content, Fv/Fm, and ΦII values. Both total root length and specific root length decreased with increasing NH4+/NO3– ratios. Moreover, the rise in NH4+/NO3– ratio significantly promoted O2– production. Furthermore, transcriptome sequencing and tandem mass tag-based quantitative proteome analyses identified 14,376 differentially expressed genes (DEGs) and 1,819 differentially expressed proteins (DEPs). The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis indicated that glutathione metabolism and phenylpropanoid biosynthesis were the main two shared enriched pathways across ratio comparisons. Upregulated DEGs and DEPs involving glutathione S-transferases may contribute to the prevention of oxidative stress. An increment in the NH4+/NO3– ratio induced the expression of genes and proteins involved in lignin biosynthesis, which increased root lignin content. Additionally, phylogenetic tree analysis showed that both A0A3B6NPP6 and A0A3B6LM09 belong to the cinnamyl-alcohol dehydrogenase subfamily. Fifteen downregulated DEGs were identified as high-affinity nitrate transporters or nitrate transporters. Upregulated TraesCS3D02G344800 and TraesCS3A02G350800 were involved in ammonium transport. Downregulated A0A3B6Q9B3 is involved in nitrate transport, whereas A0A3B6PQS3 is a ferredoxin-nitrite reductase. This may explain why an increase in the NH4+/NO3– ratio significantly reduced root NO3–-N content but increased NH4+-N content. Overall, these results demonstrated that increasing the NH4+/NO3– ratio at the seedling stage induced the accumulation of reactive oxygen species, which in turn enhanced root glutathione metabolism and lignification, thereby resulting in increased root oxidative tolerance at the cost of reducing nitrate transport and utilization, which reduced leaf photosynthetic capacity and, ultimately, plant biomass accumulation.

Temporal Monitoring and Assessment of Inorganic Nitrogen Content of Soil due to Nitrogen Fertilizers and their Related Cytotoxic Effects

Background: Indian economy is largely based on agriculture. Major share of agricultural investments goes into chemical fertilizers. Nitrogen (N) fertilizers are used in fields to enhance the crop yield. Most of the reports are based on growth related data, morphological and yield related data but very few reports reveal the facts about genotoxic and cytotoxic effects of these fertilizers. Therefore, the present communication is an attempt in the aforesaid direction. Methods: In a pot experiment, mineral N content of soil in the form of ammonium-N (NH4+-N) and nitrate-N (NO3--N) were analysed at regular interval of 5 days till 30 days after treatment (DAT). On the corresponding days root tip assay was done for cytotoxic analyses and also the temporal changes in NH4+-N and NO3--N contents were observed. Result: In the Ammonium nitrate treatments, higher mitotic index (MI%) percentages were obtained. While for the Urea, NH4+-N content and MI were found to have a positive correlation. Also, it was found that there is an optimum ratio of NH4+-N and NO3--N in each treatment at which the MI% was the maximum. The study gives an interesting insight for the possible cytotoxic effects of the N fertilizers.

Metabolic Remodeling during Nitrogen Fixation in Zymomonas mobilis.

ABSTRACTZymomonas mobilis is an ethanologenic bacterium currently being developed for production of advanced biofuels. Recent studies have shown that Z. mobilis can fix dinitrogen gas (N2) as a sole nitrogen source. During N2 fixation, Z. mobilis exhibits increased biomass-specific rates of ethanol production. In order to better understand the physiology of Z. mobilis during N2 fixation and during changes in ammonium (NH4+) availability, we performed liquid chromatography-mass spectrometry (LC-MS)-based targeted metabolomics and shotgun proteomics under three regimes of nitrogen availability: continuous N2 fixation, gradual NH4+ depletion, and acute NH4+ addition to N2-fixing cells. We report dynamic changes in abundance of proteins and metabolites related to nitrogen fixation, motility, ammonium assimilation, amino acid biosynthesis, nucleotide biosynthesis, isoprenoid biosynthesis, and Entner-Doudoroff (ED) glycolysis, providing insight into the regulatory mechanisms that control these processes in Z. mobilis. Our analysis identified potential physiological mechanisms that may contribute to increased specific ethanol production during N2 fixation, including decreased activity of biosynthetic pathways, increased protein abundance of alcohol dehydrogenase (ADHI), and increased thermodynamic favorability of the ED pathway. Of particular relevance to advanced biofuel production, we found that intermediates in the methylerythritol phosphate (MEP) pathway for isoprenoid biosynthesis were depleted during N2 fixation, coinciding with decreased protein abundance of deoxyxylulose 5-phosphate synthase (DXS), the first enzyme in the pathway. This implies that DXS protein abundance serves as a native control point in regulating MEP pathway activity in Z. mobilis. The results of this study will inform metabolic engineering to further develop Z. mobilis as a platform organism for biofuel production.IMPORTANCE Biofuels and bioproducts have the potential to serve as environmentally sustainable replacements for petroleum-derived fuels and commodity molecules. Advanced fuels such as higher alcohols and isoprenoids are more suitable gasoline replacements than bioethanol. Developing microbial systems to generate advanced biofuels requires metabolic engineering to reroute carbon away from ethanol and other native products and toward desired pathways, such as the MEP pathway for isoprenoid biosynthesis. However, rational engineering of microbial metabolism relies on understanding metabolic control points, in terms of both enzyme activity and thermodynamic favorability. In Z. mobilis, the factors that control glycolytic rates, ethanol production, and isoprenoid production are still not fully understood. In this study, we performed metabolomic, proteomic, and thermodynamic analysis of Z. mobilis during N2 fixation. This analysis identified key changes in metabolite levels, enzyme abundance, and glycolytic thermodynamic favorability that occurred during changes in NH4+ availability, helping to inform future efforts in metabolic engineering.

Combined Application of Flue Gas Desulfurization Gypsum and Straw Pellets to Ameliorate Sodicity, Nutrient Content, and Aggregate Stability of Sodic Soil

Flue gas desulfurization (FGD) gypsum and straw return have been recognized for their roles in reducing soil sodicity and improving soil organic matter. However, there are few studies on the effect of their combination on improving and fertilizing sodic soil. FGD gypsum at a rate of 15 t ha−1 and three types of straw (sunflower seed shell, corn stover, and corncob crushed into straw pellets) at a rate of 7.5 t ha−1 were applied to sodic soil from 2017 to 2019, and their effects on soil salinity and sodicity, nutrient content, and water-stable aggregate fractions were observed. FGD gypsum application significantly decreased soil pH, sodium adsorption ratio, and exchangeable sodium percentage, with significant changes in NH4+-N content. After FGD gypsum treatment, the 250–2000 μm aggregate fraction increased, and the <53 μm fraction decreased, resulting in an increase in the mean weight diameter of the soil aggregates. Except for corncob straw, straw application had no significant effect on soil salinity or sodicity. Straw application increased the soil organic carbon content in 2017 and increased the inorganic nitrogen content in 2017 and 2018. Moreover, FGD gypsum and straw applications interactively affected the soil NH4+-N and NO3−-N contents. Water-stable aggregates, excluding the <53 μm fraction, were not affected by straw application. The combined application of FGD gypsum and corn stover or sunflower seed shell is a feasible option for sodic soil amelioration and can control salinity and sodicity and improve soil fertility.

Clomazone improves the interactions between soil microbes and affects C and N cycling functions

Clomazone, a widely used herbicide, is mainly used in soybean fields. We previously found that clomazone alters Proteobacteria and Nitrospirae abundances and also alters urease activity, which result in changes in NH4+ and NO3− contents in soil nitrogen cycling. It remains unknown, however, how the co-occurrence patterns of species and functions of soil ecosystems change in response to clomazone applications in soil. We designed a 3-month greenhouse experiment to investigate soil microorganism dynamics in response to clomazone. Clomazone was applied at three doses (e.g., T1, T10, T100), which significantly increased bacterial abundance at days 15 and 60. Fungal abundance was stimulated at day 30 in T10-treated soils, whereas fungal abundances decreased in T100-treated soils at day 15. Clomazone altered bacterial and fungal community structures. Network analyses showed more complex and highly connected microbial communities in clomazone-treated soils. Moreover, an Acidobacteria-dominated cluster was identified within each network of clomazone-treated soils. Clomazone applied at the recommended rate decreased the functional groups that were associated with denitrification and hydrogen oxidation at days 15 and 60, and enhanced photoheterotrophy from days 30 to 60. High clomazone inputs increased trophic types (e.g., chemoheterotrophy, phototrophy, photoautotrophy and cyanobacteria) and C cycling functional groups (e.g., fermentation and cellulolysis). The half-life of clomazone ranged from 40.1 to 93.5 days in three cases. Our results provide important information for use of this herbicide.

Supplement of biochar and vermicompost amendments in coir and peat growing media improves N management and yields of leafy vegetables

A greenhouse trial assessed the effects of biochar and vermicompost as partial substitutes of conventional growing media on leafy vegetables’ yields and changes of NH4+-N and NO3−-N in growing medium and leachates. Six growing media mixtures [(a) coir, (b) coir + biochar, (c) coir + vermicompost, (d) peat, (e) peat +vermicompost, (f) peat + biochar] combined with three nitrogen (N) rates [0% (0 g N·pot−1), 50% (0.5 g N·pot−1), and 100% (1.0 g N·pot−1) commercial recommendation] were arranged in a split-plot design with three replicates. On average, the yield gap between 100% N and 50% N was improved when biochar and vermicompost were used as substitutes of coir (32% and 28% vs. 49%) and peat (14% and 18% vs. 27%). The concentrations of NH4+-N in the leachates for peat + biochar varied between 17.20 and 1.00 mg·L−1. The concentrations of NO3−-N in the leachates varied between 130.0 and 1.0 mg·L−1for coir + vermicompost, and 60 and 1.0 mg·L−1for peat + vermicompost. The residual NO3−-N in peat + biochar growing media and the leachates did not match the changes observed for NH4+-N, and the much lower residual NH4+-N indicates possible NH4+-N retention by biochar and loss through volatilization in the early growth stages. Our results show that partial substitution of peat with biochar and coir with vermicompost maintained acceptable crop yield at 50% N due probably to N supply by vermicompost and decreased residual mineral N and loss by biochar in the leachates which could be beneficial for the environment.

Nitrous oxide emissions in response to straw incorporation is regulated by historical fertilization

The incorporation of crop straw with fertilization is beneficial for soil carbon sequestration and cropland fertility improvement. Yet, relatively little is known about how fertilization regulates the emissions of the greenhouse gas nitrous oxide (N2O) in response to straw incorporation, particularly in soils subjected to long-term fertilization regimes. Herein, the arable soil subjected to a 31-year history of five inorganic or organic fertilizer regimes (unfertilized; chemical fertilizer application, NPK; 200% NPK application, 2 × NPK; manure application, M; NPK plus manure application, NPKM) was incubated with and without rice straw to evaluate how historical fertilization influences the impact of straw addition on N2O emissions. The results showed that compared to the unfertilized treatment, historical fertilization strongly increased N2O emissions by 0.48- to 34-fold, resulting from increased contents of hot water-extracted organic carbon (HWEOC), NO3−, and available phosphorus (Olsen-P). Straw addition had little impact on N2O emission from the unfertilized and NPK treatments, primarily due to Olsen-P limitation. In contrast, straw addition increased N2O emissions by 102–316% from the 2 × NPK, M, and NPKM treatments as compared to the corresponding straw-unamended treatments. These results indicated that N2O emissions in response to straw addition were largely regulated by historical fertilization. The N2O emissions were closely associated with the depletion of NO3− and decoupled from change in NH4+ content, suggesting that NO3− was the main substrate for N2O production upon straw addition. The stoichiometric ratios of HWEOC to mineral N and mineral N to Olsen-P were key factors affecting N2O emissions, underscoring the importance of resource stoichiometry in regulating N2O emissions. In conclusion, historical fertilization largely regulated the impacts of crop straw incorporation on N2O emissions via shifts in NO3− depletion and the stoichiometry of HWEOC, mineral N, and Olsen-P.

Migration and transformation of nitrogen in bioretention system during rainfall runoff

Bioretention systems have been extensively studied as a highly efficient technical measure to tackle the global threat of nitrogen pollution during global rainfall runoff. However, the migration and transformation of various forms nitrogen in bioretention system is unclear. So, in this paper, the bioretention systems with different flow regimes and planted configurations were designed to study the nitrogen removal performance and migration and transformation mechanism. The dynamic changes of NH4+-N and NO3−-N were continuously monitored within 60 h after rainfall, and the abundance of 15N isotopes in soil layer NH4+-N was simultaneously measured. The results indicated that NH4+-N was mainly intercepted in soil layer in four constructed bioretention systems with similar removal efficiencies (95.42–97.69%). However, NO3−-N was retained in submerged layer with significant different removal efficiencies (43.03–83.00%). After fitting calculation, the nitrification rate of NH4+-N (0.0626 mg kg−1 h−1) in soil was 5.31 times higher than that of the accumulation rate of NO3−-N (0.0118 mg kg−1 h−1). During the elimination process of residual NH4+-N in soil, 41.46% removed by denitrification and plant absorption assimilation, another 57.28% stored in the form of organic nitrogen or inorganic nitrogen, only 1.26% leaked out. Based on this, the content variation of TN, NH4+-N and NO3−-N could be analyzed by a system-wide and established the nitrogen balance model, which provides a new insight into the enhancement of nitrogen removal in the bioretention system.

Considering the preferences for nitrogen forms by invasive plants: a case study from a hydroponic culture experiment

SummaryAlthough preference for NH4+, NO3− or a combination of the two often differs among species, we know little about the responses of invasive plants to different inorganic N forms. Furthermore, many studies have suggested that an increase in N availability may facilitate further invasions. However, most of these studies predicted the positive feedback without considering the preference for N forms of invasive plants. Therefore, we cultivated four common invasive species (Mikania micrantha, Ipomoea cairica, Wedelia trilobata and Bidens pilosa) in South China with hydroponic media containing different forms of N (i.e. NO3−, NH4NO3 and NH4+) at equimolar concentrations. Our results showed that the N forms significantly affected the growth, biomass allocation and physiological traits of the plants. All four invasive plants supplied with NO3− alone had better performance and greater allocation to root biomass than did plants that were supplied with NH4+ alone. Moreover, the photosynthetic rate, pigment content and photosystem II activity of plants supplied with NO3− or NH4NO3 were significantly higher than those of plants supplied with NH4+alone. The results suggested that all four invasive plants preferred NO3− rather than NH4+, and changes in NO3− played an important role in furthering the invasions of these plants than did changes in NH4+. Our results implied that decreasing NO3− may be a useful tool for controlling and managing invasive plants preferring NO3−. In addition, this study highlighted the importance of considering plant N form preference to better understand plant invasions.

Fertilizer type and organic amendments affect gross N dynamics in a Chinese Chernozem

SummaryThe effects of partial substitution of synthetic fertilizer N (NPK) with equal quantities of maize (Zea mays L.) stover N (50 kg ha−1, NPKS) or cattle manure N (115 N kg ha−1, NPKM) were investigated after 23 years with respect to maize yield, biomass N uptake, residual soil N and gross soil N dynamics in a fertile Chernozem soil. Maize yields were not different among these three treatments: maize biomass N uptake followed the order NPKM≈NPK &gt; NPKS, whereas total N in soil was significantly larger under NPKM. A 15N tracing method was used to explain differences in gross N dynamics of labile and recalcitrant organic N pools and total N in soil. The results showed that NPKS and NPKM compared with NPK increased gross N mineralization by 2.8 and 1.3 times, respectively. The NPKS decreased the gross rate of N nitrification by 14%, whereas NPKM increased it by 47% compared with NPK. The NPKS stimulated microbial competition for NH4+, whereas NPKM increased NO3− immobilization compared with NPK. Our results suggested that acceleration of the soil N cycle under NPKS provided the most likely reason for the small total N stock in soil. In contrast, large organic N input and considerable immobilization of NO3− to a recalcitrant pool was probably the reason for the large total N stock under NPKM.Highlights How do fertilizer regimes affect gross N dynamics and soil N stock in a Chernozem soil? Changes in NH4+, NO3− and 15N enrichment were simulated by a two‐pool model. Mineralization of recalcitrant organic N was the main source for NH4+. Large organic N input and considerable immobilization of NO3− to a recalcitrant pool probably resulted in large total N stock under NPKM.

Dicyandiamide has more inhibitory activities on nitrification than thiosulfate.

Dicyandiamide (DCD) and thiosulfates are two type of nitrification inhibitors (NIs) that have been widely used in agriculture to improve nitrogen (N) fertilizer use efficiency and mitigate negative effect of N on environment. Little information is available concerning the comparison of the efficacy of DCD and thiosulfate on N transformations in soil. The aim of this study was to compare the effects of DCD and thiosulfate (K2S2O3) on changes of NH4+-N, nitrification inhibition and N recovery in a latosolic red soil. An incubation experiment was conducted with four treatments of control (CK), N, N+DCD, and N+K2S2O3. Soil samples were collected periodically over 50 d to determine concentrations of mineral N, and the amoA gene abundance of ammonia monooxygenase (AMO) for ammonia-oxidizing bacteria (AOB) was estimated by qPCR after 10 d incubation. In the N treatment, 67.8% of the applied N as NH4+-N disappeared from the mineral N pool and only 2.7% and 30.8% of the applied N was accumulated as NO2--N and NO3--N, respectively. Addition of DCD and thiosulfate to the soil prevented NH4+-N disappearance by 63.0% and 13.6%, respectively. DCD suppressed the production of NO2--N by 97.41%, whereas thiosulfate increased accumulation of NO2--N by 14.6%. Application of N along with DCD and thiosulfate inhibited nitrification, respectively, by 72.6% and 33.1%, resulting in the delay of the nitrification process for 30 days and 10 days, respectively. Apparent N recovery in N treatment was 66.2%, which increased by 55.2% and 4.8% by DCD and thiosulfate, respectively. Numbers of AOB amoA gene copy was significantly inhibited by both DCD and thiosulfate, and the stronger inhibition induced by DCD than thiosulfate was recorded. Results indicated that both DCD and thiosulfate were effective inhibitors for NH4+-N oxidation, NO3--N production, mineral N losses and AOB growth. DCD showed a more pronounced effect on nitrification inhibition than thiosulfate.