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The seed germination index (GI) serves as the principal determinant that impedes the integration of aerobic composting products into agricultural lands. The current research work predominantly focuses on exploring the correlation between physical and chemical indicators of the compost products and GI, neglecting the fundamental cause. This study systematically analyzed the composition of GI aqueous extracts from compost products derived from kitchen waste under various composting methodologies, with nitrogen, carbon, and inorganic salt as critical factors. The analytical work concluded that acetic acid, formic acid, and ammonium were the inhibitory factors influencing GI. Validation experiments introduced inhibitory factors, yielding a functional relationship formula depicting GI variations due to a single influential factor. This study conclusively identified acetic acid as the primary constraint, establishing that its inhibitory concentration corresponded to 70 % GI stands at 85 mg/L. This study will provide guidelines for the future research on enhancing aerobic composting techniques., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Atmospheric nitrogen (N) deposition could affect the structure and function of terrestrial plants. Non-N 2 -fixing lichens are used to monitor atmospheric N deposition because they rely on the deposited inorganic N ( i.e ., ammonium and nitrate) as N sources. However, the uptake capacities of lichen on ammonium and nitrate remain unclear, which hinders the application of lichen N content to accurate bioindication of atmospheric N deposition levels. We investigated ammonium and nitrate uptake capacities of Cladonia rangiferina , which was treated with ammonium alone, nitrate alone, and ammonium and nitrate mixture solutions with different mixing ratios under light and dark conditions. The results showed that N uptake rates increased with ammonium and nitrate concentrations in solutions and generally followed the Michaelis-Menten saturation kinetics. Ammonium uptake of C. rangiferina showed higher values of affinity, and was more efficient than the nitrate uptake. Both rates and amounts of nitrate uptake decreased with increasing ratios of ammonium to nitrate in solutions, while ammonium uptake showed no substantial variations, indicating an inhibition of ammonium on nitrate uptake capability. The darkness significantly decreased the maximum uptake rate and efficiency of nitrate, but had much weaker effects on lichen ammonium uptake. These findings highlight the preference of lichen on ammonium as a key N uptake strategy. It is thus necessary to consider the main types of atmospheric inorganic N deposition when using lichens to monitor atmospheric N pollution levels and evaluate N deposition based on lichen ecophysiology.

East African lakes, especially soda lakes, are home habitats for massive numbers of wildlife such as flamingos, mammals, and fishes. These lakes are known for their high primary production due to local high temperatures, light intensities, and alkalinity (inorganic carbon). However, these lakes, normally within remote areas, receive low nutrient inputs. Ammonium (NH 4 ) recycling and/or nitrogen fixation can become the major N supply mechanisms for phytoplankton. However, the driving forces on microbial N nutrition in lakes with minimal anthropogenic disturbance remain poorly understood. Using stable isotope tracer techniques, NH + ) recycling and/or nitrogen fixation can become the major N supply mechanisms for phytoplankton. However, the driving forces on microbial N nutrition in lakes with minimal anthropogenic disturbance remain poorly understood. Using stable isotope tracer techniques, NH 4 + recycling rates were measured in 18 lakes and reservoirs in East Africa (Tanzania and Kenya) during the dry season in early 2020. Three functional genes (nifH, gdh, and ureC) relating to microbial N nutrition were also measured. The regeneration of NH 4 + supported up to 71 % of the NH 4 + recycling rates at a certain range of water residence time (e.g., 5-8 years). However, CBAD showed a decreasing trend with longer water residence time, which may be influenced by changes in the algal community composition (e.g., % Cyanophyceae vs. % Bacillariophyceae). These results indicate that DOM dynamics and the water residence time have the potential to facilitate the understanding of microbial nitrogen supply status in East African lakes.4 + demands (CBAD) for all lakes and reservoirs indicate an obvious N demand from microbial community. Our study provides clear evidence that microbial NH 4 + uptake rates linked closely to the dissolved organic matter (DOM) properties (e.g., the absorption coefficient at 254 nm, percents of total fluorescence intensity contributed by microbial humic-like and protein-like components) and that water residence time drives microbial NH 4 + recycling by regulating the duration of in-lake DOM processing and influencing algal growth. Phytoplankton, especially those of Cyanophyceae, showed maximum biomass and higher NH 4 + recycling rates at a certain range of water residence time (e.g., 5-8 years). However, CBAD showed a decreasing trend with longer water residence time, which may be influenced by changes in the algal community composition (e.g., % Cyanophyceae vs. % Bacillariophyceae). These results indicate that DOM dynamics and the water residence time have the potential to facilitate the understanding of microbial nitrogen supply status in East African lakes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Landfill leachate contains ammonium and micropollutants. Ammonium can be biologically removed but bio-recalcitrant micropollutants removal requires post-treatment like ozonation. This study developed an expanded clay aggregates packed biofilm column (EBC) and demonstrated its feasibility of coupling biodegradation and ozonation (CBAO) to simultaneously remove nitrogen and bio-recalcitrant micropollutants. The first 60 days only had biodegradation process to start the bioreactor. 51 % nitrogen was biologically removed but the removal of micropollutant carbamazepine (CBZ) was only 30 %. From 61 d to 150 d, both biodegradation and ozonation were performed in the EBC. After 48 h-biodegradation, ozone gas was introduced and bubbling through EBC for 30 min to further remove residual micropollutants. At 0.4 gO 3 /gCOD, CBZ were completely removed. The average nitrogen removal efficiency (85 %) was increased by 34 % because the increased abundance of nitrifying and denitrifying bacteria in EBC. This study confirmed the promising potential of the CBAO process for treating landfill leachte., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Anammox has received increased attention due to its enhanced and cost-efficient approach to nitrogen removal. However, its practical application is complicated by strict influent NO 2 - -N ratio demands and an 11% nitrate production from the anammox process. This study was the first known research to propose and verify a system of zeolite integrated with partial denitrification and anammox (Z-PDA) in an up-flow anaerobic sludge bed (UASB) reactor. The enhanced and robust nitrogen removal resulted in an ultra-high nitrogen removal efficiency (NRE, 93.0 ± 2.0%). Zeolite adsorption and biological desorption of ammonium contributed to robust nitrogen removal with fluctuating influent NO 4 + -N ratios. Applying 16S rRNA gene sequencing found that Candidatus Brocadia and Thauera were the key bacteria responsible for anammox and partial denitrification (PD), respectively. Zeolite also acted as a biological carrier. This significantly enriched anammox bacteria with a higher relative abundance of Candidatus Brocadia, reaching 49.2%. Metagenomic analysis demonstrated that the multiple functional genes related to nitrogen removal (nrfA/H, narG/H/I) and the metabolic pathways (Biosynthesis of cofactors, the Two-component system, the Biosynthesis of nucleotide sugars, and Purine metabolism) ensured the resilience of the Z-PDA system despite influent fluctuations. Overall, this study provided novel insights into the impacts of zeolite in the PDA system. It described the fundamental mechanism of zeolite based on adsorption and biological desorption, and demonstrated a meaningful application of the anammox process in sewage treatment.2 - -N to NH 4 + -N ratios. Applying 16S rRNA gene sequencing found that Candidatus Brocadia and Thauera were the key bacteria responsible for anammox and partial denitrification (PD), respectively. Zeolite also acted as a biological carrier. This significantly enriched anammox bacteria with a higher relative abundance of Candidatus Brocadia, reaching 49.2%. Metagenomic analysis demonstrated that the multiple functional genes related to nitrogen removal (nrfA/H, narG/H/I) and the metabolic pathways (Biosynthesis of cofactors, the Two-component system, the Biosynthesis of nucleotide sugars, and Purine metabolism) ensured the resilience of the Z-PDA system despite influent fluctuations. Overall, this study provided novel insights into the impacts of zeolite in the PDA system. It described the fundamental mechanism of zeolite based on adsorption and biological desorption, and demonstrated a meaningful application of the anammox process in sewage treatment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Nitrate, the form of nitrogen often associated with kelp growth, is typically low in summer during periods of high macroalgal growth. More ephemeral, regenerated forms of nitrogen, such as ammonium and urea, are much less studied as sources of nitrogen for kelps, despite the relatively high concentrations of regenerated nitrogen found in the Southern California Bight, where kelps are common. To assess how nitrogen uptake by kelps varies by species and nitrogen form in southern California, USA, we measured uptake rates of nitrate, ammonium, and urea by Macrocystis pyrifera and Eisenia arborea individuals from four regions characterized by differences in nitrogen availability-Orange County, San Pedro, eastern Santa Catalina Island, and western Santa Catalina Island-during the summers of 2021 and 2022. Seawater samples collected at each location showed that overall nitrogen availability was low, but ammonium and urea were often more abundant than nitrate. We also quantified the internal %nitrogen of each kelp blade collected, which was positively associated with ambient environmental nitrogen concentrations at the time of collection. We observed that both kelp species readily took up nitrate, ammonium, and urea, with M. pyrifera taking up nitrate and ammonium more efficiently than E. arborea. Urea uptake efficiency for both species increased as internal percent nitrogen decreased. Our results indicate that lesser-studied, more ephemeral forms of nitrogen can readily be taken up by these kelps, with possible upregulation of urea uptake as nitrogen availability declines., (© 2024 The Authors. Journal of Phycology published by Wiley Periodicals LLC on behalf of Phycological Society of America.)

Nitrogen (N) is an essential nutrient for plants, and the sources from which it is obtained can differently affect their entire development as well as stress responses. Distinct inorganic N sources (nitrate and ammonium) can lead to fluctuations in the nitric oxide (NO) levels and thus interfere with nitric oxide (NO)-mediated responses. These could lead to changes in reactive oxygen species (ROS) homeostasis, hormone synthesis and signaling, and post-translational modifications of key proteins. As the consensus suggests that NO is primarily synthesized in the reductive pathways involving nitrate and nitrite reduction, it is expected that plants grown in a nitrate-enriched environment will produce more NO than those exposed to ammonium. Although the interplay between NO and different N sources in plants has been investigated, there are still many unanswered questions that require further elucidation. By building on previous knowledge regarding NO and N nutrition, this review expands the field by examining in more detail how NO responses are influenced by different N sources, focusing mainly on root development and abiotic stress responses., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: In case of additional authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the findings reported in this paper., (Copyright © 2024 Elsevier GmbH. All rights reserved.)

Nitrogen is an essential nutrient in the environment that exists in multiple oxidation states in nature. Numerous microbial processes are involved in its transformation. Knowledge about very complex N cycling has been growing rapidly in recent years, with new information about associated isotope effects and about the microbes involved in particular processes. Furthermore, molecular methods that are able to detect and quantify particular processes are being developed, applied and combined with other analytical approaches, which opens up new opportunities to enhance understanding of nitrogen transformation pathways. This review presents a summary of the microbial nitrogen transformation, including the respective isotope effects of nitrogen and oxygen on different nitrogen-bearing compounds (including nitrates, nitrites, ammonia and nitrous oxide), and the microbiological characteristics of these processes. It is supplemented by an overview of molecular methods applied for detecting and quantifying the activity of particular enzymes involved in N transformation pathways. This summary should help in the planning and interpretation of complex research studies applying isotope analyses of different N compounds and combining microbiological and isotopic methods in tracking complex N cycling, and in the integration of these results in modelling approaches., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Dominika Lewicka-Szczebak reports financial support was provided by Polish National Agency for Academic Exchange. Dominika Lewicka-Szczebak reports financial support was provided by National Science Centre Poland. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Catalpa bungei is a precious timber species distributed in North China where drought often occurs. To clarify adaptive responses of C. bungei to partial- and full- root-zone drought under the influence of nitrogen forms, a two-factor experiment was conducted in which well-watered (WW), partial root-zone drought in horizontal direction (H-PRD) and in vertical direction (V-PRD), and full root-zone drought (FRD) were combined with nitrate-nitrogen (NN) and ammonium-nitrogen (AN) treatments. C. bungei responded to FRD by sharply closing stomata, decreasing gas exchange rate and increasing leaf instantaneous water use efficiency (WUE i ). Under FRD condition, the growth of seedlings was severely inhibited and the effect of N forms was covered up by the drastic drought effect. In comparison, stomata conductance and gas exchanges were moderately inhibited by PRDs. WUE i in V-PRD treatment was superior to H-PRD due to the active stomata regulation resulting from a higher ABA level and active transcription of genes in abscisic acid (ABA) signaling pathway under V-PRD. Under both PRDs and FRD, nitrate benefited antioxidant defense, stomata regulation and leaf WUE i . Under V-PRD, WUE i in nitrate treatment was superior to that in ammonium treatment due to active stomata regulation by signaling network of nitric oxide (NO), Ca 2+ and ABA. Under FRD, WUE i was higher in nitrate treatment due to the favoring photosynthetic efficiency resulting from active NO signal and antioxidant defense. The interactive effect of water and N forms was significant on wood xylem development. Superoxide dismutase (SOD) and catalase (CAT) largely contributes to stress tolerance and xylem development., (© 2024. The Author(s).)

The differential soil microbial assimilation of common nitrogen (N) fertilizer compounds into the soil organic N pool is revealed using novel compound-specific amino acid (AA) 15N-stable isotope probing. The incorporation of fertilizer 15N into individual AAs reflected the known biochemistry of N assimilation-e.g. 15N-labelled ammonium (15NH4+) was assimilated most quickly and to the greatest extent into glutamate. A maximum of 12.9% of applied 15NH4+, or 11.7% of 'retained' 15NH4+ (remaining in the soil) was assimilated into the total hydrolysable AA pool in the Rowden Moor soil. Incorporation was lowest in the Rowden Moor 15N-labelled nitrate (15NO3-) treatment, at 1.7% of applied 15N or 1.6% of retained 15N. Incorporation in the 15NH4+ and 15NO3- treatments in the Winterbourne Abbas soil, and the 15N-urea treatment in both soils was between 4.4% and 6.5% of applied 15N or 5.2% and 6.4% of retained 15N. This represents a key step in greater comprehension of the microbially mediated transformations of fertilizer N to organic N and contributes to a more complete picture of soil N-cycling. The approach also mechanistically links theoretical/pure culture derived biochemical expectations and bulk level fertilizer immobilization studies, bridging these different scales of understanding., (© The Author(s) 2024. Published by Oxford University Press on behalf of FEMS.)

Labeling plant material such as detached leaves with 15 NH 4 is a very instrumental method for the characterization of metabolic pathways of mineral nitrogen assimilation and incorporation into amino acids. A procedure of labeling, followed by amino acid extraction, purification, and derivatization for gas chromatography coupled to mass spectrometry (GC/MS) analysis, is presented. The rationale of heavy isotope abundance calculations and amino acid quantification is detailed. This method is adaptable to various plant species and various kinds of investigations, such as elucidating physiological changes occurring as a result of gene mutations (overexpression or inhibition) in natural variants or genetically modified crops, or characterization of metabolic fluxes in genotypes exhibiting contrasted physiological or developmental adaptive responses to biotic and/or abiotic environmental stresses. Furthermore, the benefit of working on detached organs or pieces of organs is to investigate finely the metabolism of species that are not amenable to laboratory work, such as plants growing in natural environments or under agricultural conditions in the field.+ is a very instrumental method for the characterization of metabolic pathways of mineral nitrogen assimilation and incorporation into amino acids. A procedure of labeling, followed by amino acid extraction, purification, and derivatization for gas chromatography coupled to mass spectrometry (GC/MS) analysis, is presented. The rationale of heavy isotope abundance calculations and amino acid quantification is detailed. This method is adaptable to various plant species and various kinds of investigations, such as elucidating physiological changes occurring as a result of gene mutations (overexpression or inhibition) in natural variants or genetically modified crops, or characterization of metabolic fluxes in genotypes exhibiting contrasted physiological or developmental adaptive responses to biotic and/or abiotic environmental stresses. Furthermore, the benefit of working on detached organs or pieces of organs is to investigate finely the metabolism of species that are not amenable to laboratory work, such as plants growing in natural environments or under agricultural conditions in the field., (© 2023. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

Since the discovery of somatic embryogenesis (SE), it has been evident that nitrogen (N) metabolism is essential during morphogenesis and cell differentiation. Usually, N is supplied to cultures in vitro in three forms, ammonium (NH 4 + ), nitrate (NO 3 - ), and amino N from amino acids (AAs). Although most plants prefer NO 3 - to NH 4 + is needed for both embryo initiation and maturation is well-established in several models, such as carrot, tobacco, and rose. It is clear that N is indispensable for SE, but the mechanism that triggers the signal for embryo formation remains unknown. Here, we discuss recent studies that suggest an optimal endogenous concentration of auxin and cytokinin is closely related to N supply to plant tissue. From a molecular and biochemical perspective, we explain N's role in embryo formation, hypothesizing possible mechanisms that allow cellular differentiation by changing the nitrogen source.4 + is the primary form route to be assimilated. The balance of NO 3 - and NH 4 + determines if the morphological differentiation process will produce embryos. That the N reduction of NO 3 - is needed for both embryo initiation and maturation is well-established in several models, such as carrot, tobacco, and rose. It is clear that N is indispensable for SE, but the mechanism that triggers the signal for embryo formation remains unknown. Here, we discuss recent studies that suggest an optimal endogenous concentration of auxin and cytokinin is closely related to N supply to plant tissue. From a molecular and biochemical perspective, we explain N's role in embryo formation, hypothesizing possible mechanisms that allow cellular differentiation by changing the nitrogen source., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Understanding how plants adjust their requirements for different N forms can help elucidate plant coexistence strategies in N-limited desert ecosystems. To understand the mechanisms involved, we investigated whether two desert herbs can directly absorb dissolved organic nitrogen (N) and tested whether the patterns changed over different growth stages. Two dominant herbaceous species, Astragalus arpilobus and Arnebia decumbens, from the southern edge of the Gurbantunggut desert, China, were selected. Short-term (24 h) 15 N-labelled tracer ( 15 N-NO 3 , 15 N-NH 4 , 2- 13 C- 15 N-Glycine) treatments were conducted at two soil depths (0-5 cm and 5-15 cm) in the season of rapid growth (June) and in the peak biomass season (July). Enrichment in 13 C and 15 N was assessed in the two species receiving glycine. The ratio 13 C: 15 N was 0.21-1.39 at the 24-h harvest, suggesting that approximately 10.5-69.5% of glycine had been absorbed. The amount of absorbed 15 N was significantly affected by species, month, soil depth and N form. The two species absorbed most 15 N from the 0-5 cm soil layer, and the absorption rate in July was higher than that in June. The absorption of 15 N-NO 3 and 15 N-NH 4 was significantly higher than that of 2- 13 C- 15 N-Glycine. The results indicate that these herbs could use amino acids in the N-deficient desert ecosystem. The two co-existing species used different forms of inorganic N for their requirements and maintained a specific preference throughout various growth stages., (© 2022 German Society for Plant Sciences and The Royal Botanical Society of the Netherlands.)

Pollutants are continuously released into surface waters, which decrease the dissolved oxygen (DO) concentration and leads to the formation of black-odorous water, especially in slow-flowing urban lakes and enclosed small ponds. In situ treatment by artificial aeration or water cycling, coupled with biofilm, can address this problem without occupying large amounts of land. In this study, we designed a novel sponge-based aerobic biofilm reactor (SABR) and evaluated its performance in purifying urban surface water under different conditions. In the urban lake water treatment, the continuous inflow results revealed that the NH 4 + -N and NO 2 - -N concentrations in the effluent were stable and remained lower than 0.10 mg/L and 0.05 mg/L, respectively. Abrupt increases in the NH 4 + -N and NO 2 - -N concentrations in the influent and sudden increases in the NH 4 + -N and NO 2 - -N concentrations in the effluent were observed, and only 4 to 8 days were required for the concentrations to decline below 0.10 mg/L and 0.05 mg/L, respectively. Increases in the polyurethane sponge filling ratios in the SABRs can reduce the DO concentration but do not affect NH 4 + -N removal. When no biodegradable organic matter was present in the enclosed surface water, the degradation time of NH 4 + -N from 14.22 to 0.10 mg/L was only 9 days when SABRs were combined with water cycling, which was shorter than the time needed by water cycling alone (16 days), and most of the NH 4 + -N was converted to NO 3 - -N. When massive amounts of biodegradable organic matter were present in the enclosed surface water, 22 days were required to remove the NH 4 + -N when SABRs were combined with water cycling. Our results indicated that organic matter could be used as a carbon source to eliminate the produced NO 3 - -N in SABRs. Therefore, the newly developed bioreactor provides an effective approach for treating N-polluted urban surface waters., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Sodium tolerance and nitrogen-source preferences are two of the most fascinating and ecologically important areas in plant physiology. Spartina alterniflora is a highly salt-tolerant species and appears to prefer ammonium (NH 4 + ) as an inorganic N source, presenting a suite of aboveground physiological and biochemical mechanisms that allows growth in saline environments. Here, we tested the interactive effects of salinity (0, 200, 500 mM NaCl) and nitrogen source (NO 3 - ) as an inorganic N source, presenting a suite of aboveground physiological and biochemical mechanisms that allows growth in saline environments. Here, we tested the interactive effects of salinity (0, 200, 500 mM NaCl) and nitrogen source (NO 3 - ) on some physiological and biochemical parameters of S. alterniflora at the root level. After three months of treatments, plants were harvested to determine root growth parameters and total amino acids, proline, total soluble sugars, sucrose, and root enzyme activity. The control (0 mM NaCl) had the highest root growth rate in the medium containing only ammonium and the lowest in the medium containing only nitrate. Except for NO 4 + , NH 4 NO 3 ) on some physiological and biochemical parameters of S. alterniflora at the root level. After three months of treatments, plants were harvested to determine root growth parameters and total amino acids, proline, total soluble sugars, sucrose, and root enzyme activity. The control (0 mM NaCl) had the highest root growth rate in the medium containing only ammonium and the lowest in the medium containing only nitrate. Except for NO 3 - -fed plants. Nitrogen metabolism was characterized by higher constitutive levels of glutamate dehydrogenase (GDH) activity under ammonia nutrition, accompanied by elevated total amino acids levels in roots. The advantage of ammonium nutrition for S. alterniflora under salinity was connected to high amino acid accumulation and antioxidant enzyme activities, together with low H 4 + concentration and increased GDH activity. Ammonium improved root performance of S. alterniflora, especially under saline conditions, and may improve root antioxidant capacity and N-assimilating enzyme activities, and adjust osmotically to salinity by accumulating amino acids.3 - -fed plants. In the absence of salinity, NH 4 + -fed plants had higher superoxide dismutase, ascorbate peroxidase, glutathione reductase, and guaiacol peroxidase activities than NO 3 - -fed plants. Salinity generally promoted the activity of the principal antioxidant enzymes, more so in NH 4 + -fed plants. Nitrogen metabolism was characterized by higher constitutive levels of glutamate dehydrogenase (GDH) activity under ammonia nutrition, accompanied by elevated total amino acids levels in roots. The advantage of ammonium nutrition for S. alterniflora under salinity was connected to high amino acid accumulation and antioxidant enzyme activities, together with low H 2 O 2 concentration and increased GDH activity. Ammonium improved root performance of S. alterniflora, especially under saline conditions, and may improve root antioxidant capacity and N-assimilating enzyme activities, and adjust osmotically to salinity by accumulating amino acids., (Copyright © 2022 Elsevier Masson SAS. All rights reserved.)

Ammonia-oxidizing bacteria (AOB) attached to aquatic particles are important participants in ammonia oxidation within hypereutrophic urban river systems. To explore the effects of aquatic nitrogen pollution on particle-attached AOB in urban river, we utilized laboratory mesocosms to investigate the responses of abundances and community structure of particle-attached AOB to ammonium (NH 4 + ) and glycine (C 2 H 5 NO 2 and glycine concentrations. Treatment effects contributed significantly to the variance in particle-attached AOB communities. Although, glycine was completely transformed to ammonium within a few days and ammonium amendments would change the community structure of particle-attached AOB, the effect of glycine on the particle-attached AOB community was regulated by both the resulting ammonium concentration, as well as organic matter availability to the heterotrophic bacteria. Results suggested that high anthropogenic nitrogen loadings appeared to promote higher particle-attached AOB richness and diversity in the hypereutrophic urban river, but the effect of organic nitrogen on the particle-attached AOB community was different from the effect of inorganic nitrogen. This study informs ammonia oxidization mechanisms in the hypereutrophic urban rivers, which contributes to remediation/restoration strategies.4 + and glycine concentrations. Treatment effects contributed significantly to the variance in particle-attached AOB communities. Although, glycine was completely transformed to ammonium within a few days and ammonium amendments would change the community structure of particle-attached AOB, the effect of glycine on the particle-attached AOB community was regulated by both the resulting ammonium concentration, as well as organic matter availability to the heterotrophic bacteria. Results suggested that high anthropogenic nitrogen loadings appeared to promote higher particle-attached AOB richness and diversity in the hypereutrophic urban river, but the effect of organic nitrogen on the particle-attached AOB community was different from the effect of inorganic nitrogen. This study informs ammonia oxidization mechanisms in the hypereutrophic urban rivers, which contributes to remediation/restoration strategies., (© 2022. The Author(s), under exclusive licence to Springer Nature B.V.)

High ammonia (NH 3 ) and nitrogen oxide (NO x ) emissions are related to serious air pollution in urban areas and the negative impacts of excessive reactive nitrogen (N) deposition on many ecosystems. However, whether there is a relationship between N deposition rates and their sources with urbanization or not remains unclear in many areas. Here, we investigated the deposition rates of ammonium (NH 4 + ), nitrate (NO 3 - ), dissolved organic N, and water-insoluble particular N from July 2017 to June 2018 at two urban and two suburban sites in the Yangtze River Delta (YRD). The δ 15 N values of precipitation NH 4 + and NO 3 - were measured, and major sources were analyzed using a Bayesian isotope mixing model. Wet N deposition rates were higher in Yangzhou (developing city, 20.3-22.7 kg N ha -1  yr -1 ) than those in Nanjing (developed city, 19.4-20.5 kg N ha -1  yr -1 ), and were higher at urban sites (20.4-22.5 kg N ha -1  yr -1 ) than those at suburban sites (18.7-20.3 kg N ha -1  yr -1 ). δ 15 N values of precipitation NH 4 + increased with an increase in precipitation pH because ambient acidity affects the equilibrium isotope fractionation between NH 3 and NH 4 + and wet scavenging coefficients of NH 3 and particulate NH 4 + . For NH 4 + , combustion-related NH 3 sources (62%-65% with 5.5-6.4 kg N ha -1  yr -1 , including coal combustion, vehicle exhaust, and biomass burning) contributed more than volatilization NH 3 sources (35%-38% with 2.9-3.9 kg N ha -1  yr -1 , including fertilizer application and waste volatilization). For NO 3 - , non-fossil fuel NO x sources (50%-63% with 3.4-4.1 kg N ha -1  yr -1 , including biomass burning and microbial N cycle) were comparable to fossil fuel NO x sources (37%-50% with 2.4-3.4 kg N ha -1  yr -1 , including coal combustion and vehicle exhaust). This study evidenced high N deposition rates and the importance of combustion-related NH 3 emissions and non-fossil fuel NO x emissions in city areas of the YRD., Competing Interests: Declaration of competing interest The authors declare no competing financial interests., (Copyright © 2021. Published by Elsevier B.V.)

Through synthesizing bulk precipitation chemistry in forest sites (n = 128) from three monitoring networks, (NADP in Northern America, EMEP in Europe, and EANET in East Asia), this study quantifies the temporal changes of precipitation acidity and its dominant acidifying agents over the last two decades. Results show distinct declines of sulfate and nitrate depositions and increases of precipitation pH in northeast America and central and east Europe, but not in Asia during 1999 and 2018. The decreases of sulfate and nitrate depositions likely reflect the long-term effort of pollutant emission controls. The temporal pattern of sulfate (SO 4 2- ) and ammonium nitrogen (NH 3 -N)/nitrate nitrogen (NO - -N) equivalent ratios indicate that acid rain in the NADP and EMEP have transitioned from sulfate-dominated to nitrate-dominated, and the DIN deposition has shifted from nitrate-dominated to ammonium-dominated in recent years, owing to reductions of sulfur dioxides (SO 4 ) and nitrogen oxides (NOx) emissions. In contrast, sulfate still plays a dominant role on the acidity of precipitation than nitrate in Asia, and NH 3 -N) equivalent ratios indicate that acid rain in the NADP and EMEP have transitioned from sulfate-dominated to nitrate-dominated, and the DIN deposition has shifted from nitrate-dominated to ammonium-dominated in recent years, owing to reductions of sulfur dioxides (SO 2 ) and nitrogen oxides (NOx) emissions. In contrast, sulfate still plays a dominant role on the acidity of precipitation than nitrate in Asia, and NH 4 -N deposition also has a significant contribution in N flux due to increasing trends of ammonia emissions in Southeast Asia., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

To investigate physiological and transcriptomic regulation mechanisms underlying the distinct net fluxes of NH4+ and NO3- in different root segments of Populus species under low nitrogen (N) conditions, we used saplings of Populus × canescens supplied with either 500 (normal N) or 50 (low N) μM NH4NO3. The net fluxes of NH4+ and NO3-, the concentrations of NH4+, amino acids and organic acids and the enzymatic activities of nitrite reductase (NiR) and glutamine synthetase (GS) in root segment II (SII, 35-70 mm to the apex) were lower than those in root segment I (SI, 0-35 mm to the apex). The net NH4+ influxes and the concentrations of organic acids were elevated, whereas the concentrations of NH4+ and NO3- and the activities of NiR and GS were reduced in SI and SII in response to low N. A number of genes were significantly differentially expressed in SII vs SI and in both segments grown under low vs normal N conditions, and these genes were mainly involved in the transport of NH4+ and NO3-, N metabolism and adenosine triphosphate synthesis. Moreover, the hub gene coexpression networks were dissected and correlated with N physiological processes in SI and SII under normal and low N conditions. These results suggest that the hub gene coexpression networks play pivotal roles in regulating N uptake and assimilation, amino acid metabolism and the levels of organic acids from the tricarboxylic acid cycle in the two root segments of poplars in acclimation to low N availability., (© The Author(s) 2021. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

In the early growth stage, nutrient uptake by rice roots is weak. However, rice tillering at this stage would require high N input. Thus, it is vital to clarify the mechanism involved in tillering capacity with low N inputs. In this report, two widely-planted japonica cultivars (cvs Yangyujing 2 and Nanjing 45) were selected mainly because, unlike cv. Nanjing 45, cv. Yangyujing 2 shows low-N-induced tiller outgrowth. Responses of tillers in two rice cultivars to mixture of N forms versus sole NH 4 + supply were similar, suggesting that NH 4 + plays a pivotal role in N-modulated rice tillering. Under low NH 4 + supply, higher expression of OsAMT1.2, OsAMT1.3, OsGS1;2, and OsGS2 was recorded in the roots of cv. Yangyujing 2 in comparison with cv. Nanjing 45, ultimately resulting in higher N content and dry weight in cv. Yangyujing 2. Stronger 3 H-IAA export from tiller stems was observed in cv. Yangyujing 2, mainly due to higher expression level of auxin efflux transporters. Moreover, tillers in auxin efflux transporter mutant ospin9 did not respond to NH 4 + supply relative to wild-type plants. These findings can be used in the molecular breeding of rice varieties to simultaneously improve rice population productivity and reduce N fertilizer input., (Copyright © 2021. Published by Elsevier GmbH.)

Peatlands store one third of global soil carbon (C) and up to 15% of global soil nitrogen (N) but often have low plant nutrient availability owing to slow organic matter decomposition under acidic and waterlogged conditions. In rainwater-fed ombrotrophic peatlands, elevated atmospheric N deposition has increased N availability with potential consequences to ecosystem nutrient cycling. Here, we studied how 14 years of continuous N addition with either nitrate or ammonium had affected ericoid mycorrhizal (ERM) shrubs at Whim Bog, Scotland. We examined whether enrichment has influenced foliar nutrient stoichiometry and assessed using N stable isotopes whether potential changes in plant nutrient constraints are linked with plant N uptake through ERM fungi versus direct plant uptake. High doses of ammonium alleviated N deficiency in Calluna vulgaris and Erica tetralix, whereas low doses of ammonium and nitrate improved plant phosphorus (P) nutrition, indicated by the lowered foliar N:P ratios. Root acid phosphatase activities correlated positively with foliar N:P ratios, suggesting enhanced P uptake as a result of improved N nutrition. Elevated foliar δ 15 N of fertilized shrubs suggested that ERM fungi were less important for N supply with N fertilization. Increases in N availability in peat porewater and in direct nonmycorrhizal N uptake likely have reduced plant nitrogen uptake via mycorrhizal pathways. As the mycorrhizal N uptake correlates with the reciprocal C supply from host plants to the soil, such reduction in ERM activity may affect peat microbial communities and even accelerate C loss via decreased ERM activity and enhanced saprotrophic activity. Our results thus introduce a previously unrecognized mechanism for how anthropogenic N pollution may affect nutrient and carbon cycling within peatland ecosystems., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

Background and Aims: The utility of root hairs for nitrogen (N) acquisition is poorly understood., Methods: We explored the utility of root hairs for N acquisition in the functional-structural model SimRoot and with maize genotypes with variable root hair length (RHL) in greenhouse and field environments., Key Results: Simulation results indicate that long, dense root hairs can improve N acquisition under varying N availability. In the greenhouse, ammonium availability had no effect on RHL and low nitrate availability increased RHL, while in the field low N reduced RHL. Longer RHL was associated with 216 % increase in biomass and 237 % increase in plant N content under low-N conditions in the greenhouse and a 250 % increase in biomass and 200 % increase in plant N content in the field compared with short-RHL phenotypes. In a low-N field environment, genotypes with long RHL had 267 % greater yield than those with short RHL. We speculate that long root hairs improve N capture by increased root surface area and expanded soil exploration beyond the N depletion zone surrounding the root surface., Conclusions: We conclude that root hairs play an important role in N acquisition. We suggest that root hairs merit consideration as a breeding target for improved N acquisition in maize and other crops., (© The Author(s) 2021. Published by Oxford University Press on behalf of the Annals of Botany Company.)

Nitrogen composition on grapevines has a direct effect on the quality of wines since it contributes to develop certain volatile compounds and assists in the correct kinetics of alcoholic fermentation. Several strategies can be used to ensure nitrogen content in grapes and one of them could be the use of elicitors such as methyl jasmonate. The use of this elicitor has been proven to be efficient in the production of secondary metabolites which increases the quality of wines, but its use also has some drawbacks such as its low water solubility, high volatility, and its expensive cost. This study observes the impact on the amino acid and ammonium composition of must and wine of Monastrell grapes that have been treated with methyl jasmonate (MeJ) and methyl jasmonate n-doped calcium phosphate nanoparticles (MeJ-ACP). The first objective of this study was to compare the effect of these treatments to determine if the nitrogenous composition of the berries and wines increased. The second aim was to determine if the nanoparticle treatments showed similar effects to conventional treatments so that the ones which are more efficient and sustainable from an agricultural point of view can be selected. The results showed how both treatments increased amino acid composition in grapes and wines during two consecutive seasons and as well as the use of MeJ-ACP showed better results compared to MeJ despite using less quantity (1 mM compared to 10 mM typically). So, this application form of MeJ could be used as an alternative in order to carry out a more efficient and sustainable agriculture.

Long-term atmospheric nitrogen (N) deposition increases bioavailable N in terrestrial ecosystems, thereby influencing ecosystem productivity. However, how N deposition and its components (i.e., NO 3 - -N and NH 4 + -N) influence the spatial pattern of productivity in terrestrial ecosystems in China remains unknown. Here, we utilize published data including carbon (C) fluxes from eddy flux tower (gross ecosystem productivity, ecosystem respiration, and net ecosystem productivity) and the corresponding climate and N deposition data for 60 typical ecosystems in China. The objective was to investigate the effect of N deposition on ecosystem productivity and explore the variations of N use efficiency (NUE). Our results reveal that atmospheric total N deposition is significantly correlated with C fluxes of terrestrial ecosystems in China. Ecosystems respond variably to different components of N deposition. In detail, forest ecosystem marginally correlated with NO 3 - -N and wet deposition, while grassland ecosystem significantly correlated with NH 4 + -N and dry deposition. NUE of productivity induced by N deposition in Chinese terrestrial ecosystems was 53.95 ± 40.30 g C g -1 N, and it was influenced by precipitation and aridity index. This study quantifies the contribution of total N deposition and its associated components to productivity in terrestrial ecosystems in China, offering vital information for regional C and N management., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Historically, anthropogenic fixed nitrogen has been purposely increased to benefit food production and global development. One consequence of this increase has been to raise concentrations of nitrogen in aquatic ecosystems. To evaluate whether nitrogen pollution promotes changes in the estimates of niche space of fish communities, we examined 16 sites along a Brazilian river basin highly impacted by anthropogenic activities, especially discharge of domestic and industrial sewage from a region with more than 5 million inhabitants. We analysed the carbon (δ 13 C) and nitrogen (δ 15 N) isotope ratios of fish species and both autochthonous (periphyton) and allochthonous (course and fine particulate organic matter) basal food resources. To estimate the magnitude of nitrogen pollution, we measured the nitrate and ammonium concentrations at each site. Sampling was conducted in the dry and wet seasons to evaluate the influence of seasonality. Nitrogen pollution generally increased estimates of niche space, and seasonality influenced only the niche estimates of fish communities from polluted sites. In addition, isotopic analyses of nitrogen polluted sites yielded unrealistic estimates of trophic positioning (detritivores at the top of the food web). We conclude that changes in niche space estimates reflect both alterations in baseline isotopic values and differential trophic behaviour among fishes. Our study suggests that under conditions of high pollution, other factors appear to influence isotopic estimates of niche, such as isotopically distinct sources that have not been sampled, and/or differences in δ 15 N turnover rates between fish tissue and basal resources, creating isotopic baselines that are challenging to interpret., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Anthropogenic nitrogen (N) emissions and deposition have been increasing over past decades. However, spatiotemporal variations of N deposition levels and major sources remain unclear in many regions, which hinders making strategies of emission mitigation and evaluating effects of elevated N deposition. By investigating moss N contents and δ 15 N values in southwestern (SW) China in 1954-1964, 1970-1994, and 2005-2015, we reconstructed fluxes and source contributions of atmospheric ammonium ( NH 4 + ) and nitrate ( NO 3 - ) deposition and evaluated their historical changes. For urban and non-urban sites, averaged moss N contents did not differ between 1954-1964 and 1970-1994 (1.2%-1.3%) but increased distinctly in 2005-2015 (1.6%-2.3%), and averaged moss δ 15 N values decreased from +0.4‰ to +3.3‰ in 1954-1964 to -1.9‰ to -0.7‰ in 1974-1990, and to -4.8‰ to -3.6‰ in 2005-2015. Based on quantitative estimations, N deposition levels from the 1950s to the 2000s did not change in the earlier 20 years but were elevated substantially in the later 30 years. Moreover, the elevation of NH 4 + deposition (by 12.2 kg-N/ha/year at urban sites and 4.6 kg-N/ha/year at non-urban sties) was higher than that of NO 3 - deposition (by 6.0 and 2.9 kg-N/ha/year, respectively) in the later 30 years. This caused a shifted dominance from NO 3 - to NH 4 + in N deposition. Based on isotope source apportionments, contributions of combustion-related NH 3 sources (vehicle exhausts, coal combustion, and biomass burning) to the elevation of NH 4 + deposition were two times higher than volatilization NH 3 sources (wastes and fertilizers) in the later 30 years. Meanwhile, non-fossil fuel NO x sources (biomass burning, microbial N cycles) contributed generally more than fossil fuel NO x sources (vehicle exhausts and coal combustion) to the elevation of NO 3 - deposition. These results revealed significant contributions of combustion-related NH 3 and non-fossil fuel NO x emissions to the historical elevation of N deposition in SW China, which is useful for emission mitigation and ecological effect evaluation of atmospheric N loading., (© 2021 John Wiley & Sons Ltd.)

Nitrogen is an important factor limiting the growth and yield of rice. However, the excessive application of nitrogen will lead to water eutrophication and economic costs. To create rice varieties with high nitrogen use efficiency (NUE) has always been an arduous task in rice breeding. The processes for improving NUE include nitrogen uptake, nitrogen transport from root to shoot, nitrogen assimilation, and nitrogen redistribution, with each step being indispensable to the improvement of NUE. Here, we summarize the effects of absorption, transport, and metabolism of nitrate, ammonium, and amino acids on NUE, as well as the role of hormones in improving rice NUE. Our discussion provide insight for further research in the future.

During the past two decades, interest has developed in regard to the possibility that plant roots can take up organic N compounds directly, a concept which challenges the conventional wisdom that soil inorganic N forms ( NH 4 + and NO 3 - ) are the sole primary sources of N absorbed by plant roots. We reviewed the literature based on single or dual ( 15 N, 13 C) stable isotope labelling techniques to test the hypothesis of direct uptake. Both isotopically enriched and natural abundance approaches were reviewed. Of the methods examined, the dual enrichment technique, when combined with compound specific and position-specific stable isotope analysis, provided incontrovertible evidence for direct uptake of simple amino acids. We demonstrate that dual labelling lacks overall sensitivity due to the high C concentration in plant tissue relative to N, and the higher natural abundance of 13 C cf. 15 N, which limits the period of measurement due to isotope dilution, and hence an assessment of the long-term contribution of direct uptake to the N economy of plant communities.

Shoot branching is determined by axillary bud formation and outgrowth and remains one of the most variable determinants of yield in many crops. Plant nitrogen (N) acquired mainly in the forms of nitrate and ammonium from soil, dominates plant development, and high-yield crop production relies heavily on N fertilization. In this review, the regulation of axillary bud outgrowth by N availability and forms is summarized in plant species. The mechanisms of auxin function in this process have been well characterized and reviewed, while recent literature has highlighted that auxin export from a bud plays a critical role in N-modulating this process.

In the anaerobic ammonium oxidation (anammox) process, the anammox bacterial activity is inhibited by high chemical oxygen demand (COD) contents. In this study, the effect of the COD/total nitrogen (TN) ratio and hydraulic retention time (HRT) on the efficiency of the anammox process in a fixed-bed reactor was assessed via experiments with increasing COD/TN ratios from 0 to 7.0 and different HRTs of 6, 9, and 12 hr. Felibendy cubes were used as the biomass carrier. The presence of organic compounds affects the performance of the treatment process, and the level of influence increases with the increase in influent COD. With COD greater than 300 mg/L, the anammox process was inhibited, TN efficiency was the lowest, and effluent water quality did not yield effluent standards. The kinetic parameters U max (the maximum substrate removal rate constant) and K B (the saturation constant) of the Stover-Kincannon model corresponding to the different COD/TN ratios were determined in this study. The kinetic parameter values of the ammonium removal process decreased gradually from U max  = 0.685 g/L/day and K B  = 0.846 g/L/day, for COD/TN = 0, to U max  = 0.314 g/L/day and K B  = 0.498 g/L/day, for COD/TN = 6. The kinetic parameter of the TN removal process also decreased gradually as the COD/TN ratio in wastewater increased gradually. This means that the anammox process was inhibited as much as high organic compounds. PRACTITIONER POINTS: The higher COD/TN ratios the more anammox activity is affected, especially COD/TN = 7.0 (COD = 350 mg/L). The tolerance threshold of anammox process about organic matter concentration is 300 mg/L as COD (COD/TN ratio <6). With the COD/TN ratios from 1.0 to 6.0, the values of U max and K B constants of Stover-Kincannon model for ammonium removal by Anammox process decrease gradually from 0.685 to 0.314 and from 0.846 to 0.498, respectively., (© 2020 Water Environment Federation.)

The soil and human health issues are closely linked. Properly managed nitrogen (N) does not endanger human health and increases crop production, nevertheless when overused and uncontrolled, can contribute to side effects. This research was intended to highlight that there is a need for carrying out monitoring studies in agricultural areas in order to expand the available knowledge on the content of N forms in agricultural lands and proper management in farming practice. The impact of two types of fertilization, concerning spatially variable (VRA) and uniform (UNI) N dose, on the distribution of N forms in soils was analyzed. The analysis was performed on the basis of soil monitoring data from agricultural fields located in three different experimental sites in Poland. The analyses performed at selected sites were supported by statistical evaluation and recognition of spatial diversification of N forms in soil. It was revealed that the movement of unused N forms to deeper parts of the soil, and therefore to the groundwater system, is more limited due to VRA fertilization. Finally, it was also concluded that the management in agricultural practice should be based on the prediction of spatial variability of soil properties that allow to ensure proper application of N fertilizers, resulting in the reduction of possible N losses.

The collapse of Comamonas testosteroni R2 under chemostat conditions and the aerobic growth of strain R2 under batch conditions with phenol as the sole carbon source were investigated using physiological and transcriptomic techniques. Phenol-/catechol-degrading activities under chemostat conditions gradually decreased, suggesting that metabolites produced from strain R2 accumulated in the culture, which caused negative feedback. The competitive inhibition of phenol hydroxylase and catechol dioxygenase was observed in a crude extract of the supernatant collected from the collapsed culture. Transcriptomic analyses showed that genes related to nitrogen transport were up-regulated; the ammonium transporter amtB was up-regulated approximately 190-fold in the collapsed status, suggesting an increase in the concentration of ammonium in cells. The transcriptional levels of most of the genes related to gluconeogenesis, glycolysis, the pentose phosphate pathway, and the TCA and urea cycles decreased by ~0.7-fold in the stable status, whereas the activities of glutamate synthase and glutamine synthetase increased by ~2-fold. These results suggest that ammonium was assimilated into glutamate and glutamine via 2-oxoglutarate under the limited supply of carbon skeletons, whereas the synthesis of other amino acids and nucleotides was repressed by 0.6-fold. Furthermore, negative feedback appeared to cause an imbalance between carbon and nitrogen metabolism, resulting in collapse. The effects of amino acids on negative feedback were investigated. L-arginine allowed strain R2 to grow normally, even under growth-inhibiting conditions, suggesting that the imbalance was corrected by the stimulation of the urea cycle, resulting in the rescue of strain R2.

The mechanisms behind nitrogen removal by the submersed macrophyte-biofilm complex in wetlands remain to be fully elucidated. This study investigated the role of Myriophyllum spicatum and the biofilm on their leaves in nitrogen removal in mesocosm experiments. 15 N tracking showed that 61.9% and 30% of the 15 N, respectively, was removed from the system and assimilated by the macrophyte-biofilm complex after loading with 5.4 mg L -1 15 for 17 days. Nitrogen budget results showed that about 0.2%, 0.2% and 3.6% of the nitrogen were emitted as water-, HCl- and NaOH-soluble nitrogen-gas species, respectively. Bacteria (76.7-91.8%) were the predominant domain in all samples, followed by eukaryotes (8.0-23.0%), archaea and viruses. Network analyses showed that there were positive- and negative-correlative relationships among nitrogen-cycling genes and nitrifiers and denitrifiers. Our data highlight the important role of biofilm on submersed macrophytes for nitrogen removal.4 + for 17 days. Nitrogen budget results showed that about 0.2%, 0.2% and 3.6% of the nitrogen were emitted as water-, HCl- and NaOH-soluble nitrogen-gas species, respectively. Bacteria (76.7-91.8%) were the predominant domain in all samples, followed by eukaryotes (8.0-23.0%), archaea and viruses. Network analyses showed that there were positive- and negative-correlative relationships among nitrogen-cycling genes and nitrifiers and denitrifiers. Our data highlight the important role of biofilm on submersed macrophytes for nitrogen removal., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Water contamination is a growing environmental issue. Several harmful effects on human health and the environment are attributed to nitrogen contamination of water sources. Consequently, many countries have strict regulations on nitrogen compound concentrations in wastewater effluents. Wastewater treatment is carried out using energy- and cost-intensive biological processes, which convert nitrogen compounds into innocuous dinitrogen gas. On the other hand, nitrogen is also an essential nutrient. Artificial fertilizers are produced by fixing dinitrogen gas from the atmosphere, in an energy-intensive chemical process. Ideally, we should be able to spend less energy and chemicals to remove nitrogen from wastewater and instead recover a fraction of it for use in fertilizers and similar applications. In this review, we present an overview of various technologies of biological nitrogen removal including nitrification, denitrification, anaerobic ammonium oxidation (anammox), as well as bioelectrochemical systems and microalgal growth for nitrogen recovery. We highlighted the nitrogen removal efficiency of these systems at different temperatures and operating conditions. The advantages, practical challenges, and potential for nitrogen recovery of different treatment methods are discussed., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

Nitrogen is the main limiting nutrient after carbon, hydrogen and oxygen for photosynthetic process, phyto-hormonal, proteomic changes and growth-development of plants to complete its lifecycle. Excessive and inefficient use of N fertilizer results in enhanced crop production costs and atmospheric pollution. Atmospheric nitrogen (71%) in the molecular form is not available for the plants. For world's sustainable food production and atmospheric benefits, there is an urgent need to up-grade nitrogen use efficiency in agricultural farming system. The nitrogen use efficiency is the product of nitrogen uptake efficiency and nitrogen utilization efficiency, it varies from 30.2 to 53.2%. Nitrogen losses are too high, due to excess amount, low plant population, poor application methods etc., which can go up to 70% of total available nitrogen. These losses can be minimized up to 15-30% by adopting improved agronomic approaches such as optimal dosage of nitrogen, application of N by using canopy sensors, maintaining plant population, drip fertigation and legume based intercropping. A few transgenic studies have shown improvement in nitrogen uptake and even increase in biomass. Nitrate reductase, nitrite reductase, glutamine synthetase, glutamine oxoglutarate aminotransferase and asparagine synthetase enzyme have a great role in nitrogen metabolism. However, further studies on carbon-nitrogen metabolism and molecular changes at omic levels are required by using "whole genome sequencing technology" to improve nitrogen use efficiency. This review focus on nitrogen use efficiency that is the major concern of modern days to save economic resources without sacrificing farm yield as well as safety of global environment, i.e. greenhouse gas emissions, ammonium volatilization and nitrate leaching.

Nitrogen (N) plays an important role in agriculture crop production but the increasing application of nitrogen increases the possibilities of groundwater contamination through nitrate leaching. Nitrate leaching is the inevitable part of agriculture production which occurs during nitrogen fertilization. Hence, the quantification of nitrogen fertilizer is required to reduce nitrate leaching. In this study, nitrogen transformation and transport such as ammonium (NH 4 + ) and nitrate (NO 3 - and total nitrogen concentrations were measured using spectrophotometer at 410 nm and Kjeldahl method at varying soil depths and maize crop growth stages. Thereafter, nitrogen balance approach was used to estimate the NO 4 + , NO 3 - and total nitrogen concentrations were measured using spectrophotometer at 410 nm and Kjeldahl method at varying soil depths and maize crop growth stages. Thereafter, nitrogen balance approach was used to estimate the NO 3 - leaching. Results indicated that NO 3 - leaching in irrigated condition was higher 109% in N 75 , 179% in N 100 , and 292% in N 125 level respectively in comparison to the N 0 level in timely sowing date, while in delayed sowing date, leaching was higher 54% in N 75 , 123% in N 100 , and 184% in N 125 level respectively in comparison to N 0 level. In rainfed, the NO 3 - leaching was higher 30% in N 60 , 59% in N 80 , and 99% in N 100 level respectively in comparison to N 0 level for the timely sowing date, while in delayed sowing, leaching was higher 23% in N 60 , 44% in N 80 , and 78% in N 100 level respectively in comparison to N 0 level. The results indicate that leaching losses were less in timely sowing dates for both rainfed and irrigated maize. The study further reveals that sowing dates combination with N levels could be an effective management strategy to reduce NO 3 - leaching by minimizing the N fertilization., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The performance of a deammonification reactor fed with increasing nitrogen loading rates (NLR) was evaluated. The digestate from a continuous stirred tank reactor (CSTR) treating sludge from a swine production unit was diluted to provide different ammonia concentrations. The biomass samples from the end of each experimental phase were analyzed for microorganism community evaluation. The results proved that deammonification system supported a NLR up to 3.27 ± 0.13 g N L -1 d -1 with nitrogen removal efficiency of 83%. The specific ammonia consumption rate (µ NH3-N ) did not decrease up to this NLR proving the stability of reactor performance. Anammox bacteria genus shifted along the experiment and at the end the predominant anammox bacteria found in the reactor was candidatus Brocadia. Finally, it was proved that a deammonification reactor for nitrogen removal from CSTR digestate could be easily controlled only by monitoring pH and dissolved oxygen., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Nitrogen (N) is a crop macronutrient of major importance, which affects both plant growth and yield. In this paper we discuss the humus content (%) and various soluble N forms (NO 3 , total N, nitrate-N, ammonium-N, and organic nitrogen) available in humus sand soil samples originating from the Pallag Experimental Station of Horticulture at the University of Debrecen, Hungary. We found 45.4% nitrate-N and 13.8% nitrite-N of total N content present in the soil. Considering the percentage distribution of soluble N forms present at the Pallag Experimental Station, we recommend using this soil in further pot experiments, given that this has optimal nutrient supply capacity. In addition, we examined possible statistical correlations between humus% and N forms.- , total N, nitrate-N, ammonium-N, and organic nitrogen) available in humus sand soil samples originating from the Pallag Experimental Station of Horticulture at the University of Debrecen, Hungary. We found 45.4% nitrate-N and 13.8% nitrite-N of total N content present in the soil. Considering the percentage distribution of soluble N forms present at the Pallag Experimental Station, we recommend using this soil in further pot experiments, given that this has optimal nutrient supply capacity. In addition, we examined possible statistical correlations between humus% and N forms., Competing Interests: No competing interests were disclosed., (Copyright: © 2020 Kincses I et al.)

Plant nitrogen (N), acquired mainly in the form of nitrate and ammonium from soil, dominates growth and development, and high-yield crop production relies heavily on N fertilization. The mechanisms of root adaptation to altered supply of N forms and concentrations have been well characterized and reviewed, while reports concerning the effects of N on the architecture of vegetative and reproductive organs are limited and are widely dispersed in the literature. In this review, we summarize the nitrate and amino acid regulation of shoot branching, flowering, and panicle development, as well as the N regulation of cell division and expansion in shaping plant architecture, mainly in cereal crops. The basic regulatory steps involving the control of plant architecture by the N supply are auxin-, cytokinin-, and strigolactone-controlled cell division in shoot apical meristem and gibberellin-controlled inverse regulation of shoot height and tillering. In addition, transport of amino acids has been shown to be involved in the control of shoot branching. The N supply may alter the timing and duration of the transition from the vegetative to the reproductive growth phase, which in turn may affect cereal crop architecture, particularly the structure of panicles for grain yield. Thus, proper manipulation of N-regulated architecture can increase crop yield and N use efficiency., (© The Author(s) 2020. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

The enzymatic controlled metabolic processes in cells occur at their optimized pH ranges, therefore cellular pH homeostasis is fundamental for life. In plants, the nitrogen (N) source for uptake and assimilation, mainly in the forms of nitrate (NO3-) and ammonium (NH4+) quantitatively dominates the anion and cation equilibrium and the pH balance in cells. Here we review ionic and pH homeostasis in plant cells and regulation by N source from the rhizosphere to extra- and intracellular pH regulation for short- and long-distance N distribution and during N assimilation. In the process of N transport across membranes for uptake and compartmentation, both proton pumps and proton-coupled N transporters are essential, and their proton-binding sites may sense changes of apoplastic or intracellular pH. In addition, during N assimilation, carbon skeletons are required to synthesize amino acids, thus the combination of NO3- or NH4+ transport and assimilation results in different net charge and numbers of protons in plant cells. Efficient maintenance of N-controlled cellular pH homeostasis may improve N uptake and use efficiency, as well as enhance the resistance to abiotic stresses., (© The Author(s) 2020. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

Water and nitrogen availability limit crop productivity globally more than most other environmental factors. Plant availability of macronutrients such as nitrate is, to a large extent, regulated by the amount of water available in the soil, and, during drought episodes, crops can become simultaneously water and nitrogen limited. In this review, we explore the intricate relationship between water and nitrogen transport in plants, from transpiration-driven mass flow in the soil to uptake by roots via membrane transporters and channels and transport to aerial organs. We discuss the roles of root architecture and of suberized hydrophobic root barriers governing apoplastic water and nitrogen movement into the vascular system. We also highlight the need to identify the signalling cascades regulating water and nitrogen transport, as well as the need for targeted physiological analyses of plant traits influencing water and nitrogen uptake. We further advocate for incorporation of new phenotyping technologies, breeding strategies, and agronomic practices to improve crop yield in water- and nitrogen-limited production systems., (© The Author(s) 2020. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

Aim: Salivary urea and ammonium levels are potential biomarkers for chronic kidney disease. A fast and efficient assessment of these compounds in the saliva of healthy and diseased individuals may be a useful tool to monitor kidney function. Materials & methods: Ammonium ions were measured with an ammonia selective electrode after conversion to ammonia gas. A urease reactor was incorporated in the manifold to hydrolyze urea to ammonium, thereby providing values of ammonia from both urea and ammonium ions in the sample. The accuracy of the method was assessed by comparison with a commercially available kit for urea and ammonium determination. Conclusion: A sequential injection method for the biparametric determination of salivary urea and ammonium employing a single sequential injection manifold was successfully applied to samples collected from both healthy volunteers and chronic kidney disease patients.

Background: Although nitrogen (N) availability is a major determinant of cotton production, little is known about the importance of plants' preference for ammonium versus nitrate for better growth and nitrogen use efficiency (NUE). We aimed to assess the growth, physiology, and NUE of contrasting N-efficient cotton genotypes (Z-1017, N-efficient and GD-89, N-inefficient) supplied with low and high concentrations of ammonium- and nitrate-N., Results: The results revealed that ammonium fed plants showed poor root growth, lower dry biomass, N content, leaf chlorophyll and gas exchange than those under nitrate irrespective of the concentration. However, the highest N uptake and utilization efficiency were obtained with nitrate fed plants, which also resulted in the highest dry biomass, N content, leaf chlorophyll and gas exchange as well as root growth. The results further confirmed that N-efficient (Z-1017) genotype performed better under both N sources, showing more flexibility to contrasting N condition by increasing growth and NUE in either source of N. Moreover, multivariate analysis showed a strong relationship of root morphological traits with N utilization efficiency, suggesting the physiological importance of roots over shoots in response to low nitrate concentration., Conclusion: Thus, it was confirmed that nitrate-N is superior to ammonium-N and the use of nitrate and N-efficient genotype is the best option for optimum cotton growth and NUE. Further, field evaluation is required to confirm the hypothesis that nitrate is a preferred N source for better cotton production and NUE. © 2020 Society of Chemical Industry., (© 2020 Society of Chemical Industry.)

Nitrogen (N) is an essential macronutrient for crops. Plants have developed several responses to N fluctuations, thus optimizing the root architecture in response to N availability. Nitrate and ammonium are the main inorganic N forms taken up by plants, and act as both nutrients and signals, affecting gene expression and plant development. In this study, RNA-sequencing was applied to gain comprehensive information on the pathways underlying the response of maize root, pre-treated in an N-deprived solution, to the provision of nitrate or ammonium. The analysis of the transcriptome shows that nitrate and ammonium regulate overlapping and distinct pathways, thus leading to different responses. Ammonium activates the response to stress, while nitrate acts as a negative regulator of transmembrane transport. Both the N-source repress genes related to the cytoskeleton and reactive oxygen species detoxification. Moreover, the presence of ammonium induces the accumulation of anthocyanins, while also reducing biomass and chlorophyll and flavonoids accumulation. Furthermore, the later physiological effects of these nutrients were evaluated through the assessment of shoot and root growth, leaf pigment content and the amino acid concentrations in root and shoot, confirming the existence of common and distinct features in response to the two nitrogen forms., Competing Interests: The authors declare no conflict of interest.

Nitrogen (N) is one of the key nutrients for algal growth and is an integral part of many cellular components, for example in proteins. Being able to determine the inorganic and organic pools of N is consequently critical for algal cultivation. In this chapter we present the methods we use for determining dissolved inorganic nitrogen (DIN), dissolved organic nitrogen (DON), and particulate organic nitrogen (PON). The methods presented here for DIN rely on colorimetric methods and those of DON and PON on filtration and high temperature catalytic oxidation.

Nitrogen (N) is a macro-nutrient that is essential for growth development and resistance against biotic and abiotic stresses of plants. Nitrogen is a constituent of amino acids, proteins, nucleic acids, chlorophyll, and various primary and secondary metabolites. The atmosphere contains huge amounts of nitrogen but it cannot be taken up directly by plants. Plants can take up nitrogen in the form of nitrate, ammonium, urea, nitrite, or a combination of all these forms. In addition, in various leguminous rhizobia, bacteria can convert atmospheric nitrogen to ammonia and supply it to the plants. The form of nitrogen nutrition is also important in plant growth and resistance against pathogens. Nitrogen content has an important function in crop yield. Nitrogen deficiency can cause reduced root growth, change in root architecture, reduced plant biomass, and reduced photosynthesis. Hence, understanding the function and regulation of N metabolism is important. Several enzymes and intermediates are involved in nitrogen assimilation. Here we provide an overview of the important enzymes such as nitrate reductase, nitrite reductase, glutamine synthase, GOGAT, glutamate dehydrogenase, and alanine aminotransferase that are involved in nitrogen metabolism.

Plants benefit from the simultaneous uptake of nitrate (NO 3 ) and ammonium (NH - ), which can influence the bioaccumulation of heavy metals. Nevertheless, there are no studies on the effect of nitrogen forms on grasses used for cadmium (Cd) phytoextraction. The objective was to evaluate the response of Panicum maximum cv. Tanzania to NO 4 + ), which can influence the bioaccumulation of heavy metals. Nevertheless, there are no studies on the effect of nitrogen forms on grasses used for cadmium (Cd) phytoextraction. The objective was to evaluate the response of Panicum maximum cv. Tanzania to NO 3 - ratios (100/0, 70/30 and 50/50) and three Cd levels (0.0, 0.5 and 1.0 mM). Although it increased plant total nitrogen concentration, Cd exposure reduced shoot and root growth. Moreover, it altered nitrogen metabolism and induced the accumulation of NO 4 + ratios and Cd levels. A 3 × 3 factorial experiment was conducted under greenhouse conditions, in a randomized complete block design replicated three times, with three NO 3 mitigated toxicity symptoms, by favoring Cd accumulation in roots and maintaining normal nitrogen metabolism, plants grown with 50/50 showed increased uptake, transport and accumulation of this metal. Thus, Cd uptake and accumulation are strongly related to the form of nitrogen available, and the supply of 50/50 increases the phytoextraction of this metal.- /NH 4 + ratios (100/0, 70/30 and 50/50) and three Cd levels (0.0, 0.5 and 1.0 mM). Although it increased plant total nitrogen concentration, Cd exposure reduced shoot and root growth. Moreover, it altered nitrogen metabolism and induced the accumulation of NO 3 - and NH 4 + mainly in shoots. The supply of 50/50 disturbed glutamine synthetase activity and changed root morphology under Cd toxicity. However, while the exclusive use of NO 3 - mitigated toxicity symptoms, by favoring Cd accumulation in roots and maintaining normal nitrogen metabolism, plants grown with 50/50 showed increased uptake, transport and accumulation of this metal. Thus, Cd uptake and accumulation are strongly related to the form of nitrogen available, and the supply of 50/50 increases the phytoextraction of this metal., (Copyright © 2019. Published by Elsevier Ltd.)

Plants have evolved different strategies to utilize various forms of nitrogen (N) from the environment. While regulation of plant growth and development in response to application of inorganic N forms has been characterized, our knowledge about the effect on cell wall structure and composition is quite limited. In this study, we analysed cell walls of Brachypodium distachyon supplied with three types of inorganic N (NH4NO3, NO3-, or NH4+). Cell wall profiles showed distinct alterations in both the quantity and structures of individual polymers. Nitrate stimulated cellulose, but inhibited lignin deposition at the heading growth stage. On the other hand, ammonium supply resulted in higher concentration of mixed linkage glucans. In addition, the chemical structure of pectins and hemicelluloses was strongly influenced by the form of N. Supply of only NO3- led to alteration in xylan substitution and to lower esterification of homogalacturonan. We conclude that the physiological response to absorption of different inorganic N forms includes pleotropic remodelling of type II cell walls., (© The Author(s) 2019. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

Nitrogen pollution in aquaculture needs the efficient and cost-effective in-situ technology. This study aims to apply Marichromatium gracile YL28 to in-situ bioremediation and test its ability to maintain the nitrogen balance in aquaculture. In laboratory aquaculture system, approximately 99.96% of nitrite (1 mg/L) was removed within 7 d through denitrification coupled with assimilatory nitrate reduction. Ammonium (3.5 mg/L) of 95.6% was directly assimilated by YL28 within 7 d. Moreover, in zero exchange water from shrimp (Penaeus vannamei) aquaculture field trials (20 days), YL28 significantly reduced the ammonium accumulation (0.6 mg/L) and 99.3% of nitrite (1.25 mg/L). Toxicological studies with the Institute of Cancer Research (ICR) mice and Oryzias melastigma indicated that M. gracile YL28 can be safely applied in aquatic ecosystems. All results demonstrate that strain YL28 has high promise for future applications of removing inorganic nitrogen and maintaining the nitrogen balance from in-situ aquaculture., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Indole-3-acetaldoxime (IAOx) is a particularly relevant molecule as an intermediate in the pathway for tryptophan-dependent auxin biosynthesis. The role of IAOx in growth-signalling and root phenotype is poorly studied in cruciferous plants and mostly unknown in non-cruciferous plants. We synthesized IAOx and applied it to M. truncatula plants grown axenically with NO 3 - or urea as the sole nitrogen source. During 14 days of growth, we demonstrated that IAOx induced an increase in the number of lateral roots, especially under NH 4 nutrition, while elongation of the main root was inhibited. This phenotype is similar to the phenotype known as "superroot" previously described in SUR1- and SUR2-defective Arabidopsis mutants. The effect of IAOx, IAA or the combination of both on the root phenotype was different and dependent on the type of N-nutrition. Our results also showed the endogenous importance of IAOx in a legume plant in relation to IAA metabolism, and suggested IAOx long-distance transport depending on the nitrogen source provided. Finally, our results point out to CYP71A as the major responsible enzymes for IAA synthesis from IAOx, while they exclude indole-3-acetaldehyde oxidases.+ or urea as the sole nitrogen source. During 14 days of growth, we demonstrated that IAOx induced an increase in the number of lateral roots, especially under NH 4 + nutrition, while elongation of the main root was inhibited. This phenotype is similar to the phenotype known as "superroot" previously described in SUR1- and SUR2-defective Arabidopsis mutants. The effect of IAOx, IAA or the combination of both on the root phenotype was different and dependent on the type of N-nutrition. Our results also showed the endogenous importance of IAOx in a legume plant in relation to IAA metabolism, and suggested IAOx long-distance transport depending on the nitrogen source provided. Finally, our results point out to CYP71A as the major responsible enzymes for IAA synthesis from IAOx, while they exclude indole-3-acetaldehyde oxidases., (Copyright © 2019 Elsevier B.V. All rights reserved.)