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The extensive agricultural feedlot operations in the Neuse River Watershed (NRW) in North Carolina result in high nutrient loading, particularly of ammonium (NH4+). In September 2018, Hurricane Florence devastated large portions of the NRW, creating a unique opportunity to study the impact of such hydrological events on the biogeochemistry of riverine and riparian sediments. The high NH4+ concentrations, naturally acidic conditions, and elevated levels of ferric iron [Fe(III)] in Neuse River sediments and soils provide an ideal environment for Acidimicrobium sp. A6 (referred to hereon as A6), a bacterium capable of conducting the Feammox process in which NH4+ is oxidized while iron is reduced. A6 was observed in all sediment samples obtained from the Neuse River, and it is therefore predicted that this process may be an important mechanism for NH4+ removal in this river system. Incubations of NRW samples indicate that the NH4+ oxidation potential via the Feammox process in the NRW is comparable with aerobic NH4+ oxidation by heterotrophic microorganisms. Given the high demand for Fe(III) by the Feammox process, it has been unclear how such a process may occur in sedimentary environments where ferric iron [Fe(III)] might be depleted. The results presented here show that a major hydrologic storm event can result in an increase in Fe(III) and in an increase in the abundance of Fe-reducing bacteria, including Acidimicrobium sp. A6. These findings indicate that major hydrologic storm events may, via the delivery of Fe(III), be capable of enhancing Feammox activity in riverine sediments that favor the Feammox process. [ABSTRACT FROM AUTHOR]

Downy mildew (Peronospora belbahrii) is a severe disease in sweet basil. The aim of the present research was to study the effect of total nitrogen (N) concentration and NH4+ partial concentration in sweet basil fertigation on sweet basil downy mildew (SBDM). The study was conducted under controlled conditions, semi-commercial conditions, and commercial-like (field) conditions. Increasing the total N concentration in the irrigation water from 1.1 to 10.7 mM resulted in a gradual increase in N concentration in the shoots, and SBDM severity in potted sweet basil plants. Similarly, under commercial-like greenhouse conditions, higher N in the irrigation water resulted in higher SBDM severity. A high rate of 30–40% of the total N of NH4+ in the irrigation water, was associated with lower SBDM severity. Mineral concentration in the shoots of sweet basil was measured in all greenhouse plots. Shoot concentrations of N, P, K, and Ca were positively correlated with SBDM severity, while shoot concentrations of Mg and Cl negatively correlated with disease severity. In conclusion, N fertigation affected SBDM severity. We suggest that the effect of N fertigation on disease may be due to the change in N concentration in the tissue, or the change in other nutritional element (s). [ABSTRACT FROM AUTHOR]

This study examined the capacity of the giant kelp, Macrocystis pyrifera, to exhibit surge uptake as a mechanism to enhance nitrogen assimilation during seasons when nitrate is depleted. Surge uptake of nitrate, ammonium, and urea was assessed in the spring and summer with whole-blade incubation experiments using 15 N tracers. The incubation experiments showed evidence of surge uptake lasting up to 5 min for ammonium and 1 min for nitrate during the summer only. Giant kelp showed little capacity for surge uptake of urea regardless of season. The ecological importance of the patterns of surge uptake observed for ammonium and nitrate, however, is questionable, given the small scale and ephemeral nature of ammonium pulses most likely experienced by giant kelp, and the longer duration pulses of nitrate associated with internal waves and upwelling. Rather it seems more likely that uptake of ammonium and urea at ambient concentrations, combined with normal uptake of nitrate during longer duration pulses of high concentrations, sustains giant kelp growth during seasons when ambient concentrations of nitrate are low. [ABSTRACT FROM AUTHOR]

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 (δ13C) and nitrogen (δ15N) 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 δ15N turnover rates between fish tissue and basal resources, creating isotopic baselines that are challenging to interpret. [ABSTRACT FROM AUTHOR]

At the global scale, atmospheric inputs of nitrogen are an important source of the new nitrogen that supports new marine production, especially in oligotrophic open oceans and marginal seas. This study reports quantities of atmospheric deposition of dissolved inorganic nitrogen (DIN) to the largest marginal sea in the North Pacific (the oligotrophic South China Sea, SCS) based primarily on rainwater sampling in the open northwestern region (Yongxing Island) from 2013 to 2015, and aerosol sampling from the SCS basin in June 2017. Atmospheric wet and dry deposition of DIN and their potential contributions to productivity were estimated. The volume-weighted mean rainwater concentrations during the wet and dry seasons were 4.9 and 18.1 µmol L−1 for N+N(NO3−+NO2−), and 5.7 and 4.0 µmol L−1 for NH4+, respectively. Rainwater concentrations of DIN were lower in the marginal seas than in the open ocean. The aerosol NO3− concentration was 1.15±1.18 µg m−3 during the wet season, which is slightly lower than reported for the East China Sea and East Sea, but higher than in the Arabian Sea. Monthly wet and dry deposition rates ranged from 0.4–3.9 and 0.4–1.2 mmol m−2 mon−1 for NO3−, and 0.2–1.3 and 0.01–0.02 mmol m−2mon−1 for NH4+, respectively. The annual wet and dry deposition fluxes of DIN were estimated to be 16.8 and 10.1 mmol m−2yr−1, respectively. Compared to other marginal seas, the SCS receives less atmospheric NO3− inputs than the Yellow Sea, East China Sea, East Sea, and northeastern Mediterranean Sea. The total atmospheric DIN deposition may account for 1.8–11.1% of the nitrogen supporting new production and 0.7–1.8% of the nitrogen supporting primary production. [ABSTRACT FROM AUTHOR]

The increase of ammonia nitrogen, nitrite, nitrate, urea, and other dissolved nitrogen in prawn pond often causes eutrophication of water body and prawn poisoning, which brings great harm to aquaculture. Microalgae are the main biological factors in prawn pond, which can effectively utilize dissolved nitrogen. The goal of this study was to evaluate the effects of the forms and concentrations of various dissolved nitrogen on the uptake rate (ρ) by Oocystis borgei, and establish the relationship model between ammonia nitrogen uptake rate and key environmental factors using 15N isotope labeling technique. Temperature (A), light intensity (B), salinity (C), pH (D), and algal concentration (E) were the factors used to construct an empirical model. Study results showed that nitrogen concentrations had a significant effect on the uptake rates of ammonium, nitrate, nitrite, and urea (P < 0.05). Under various salinity and temperature conditions, the relative preference index (RPI) of ammonium was greater than that of nitrite, urea, and nitrate; Ammonium was the preferred nitrogen source for O. borgei. The optimal combination of environmental conditions for ρ(NH4+-N) was temperature of 20 °C, pH of 7.5, light intensity of 81 μmol m−2 s−1, salinity of 15‰, and algal concentration of 5.5 × 108 cell L−1. The model equation wasρ = 0.0017 × (A0.180B0.252C0.748D0.587E) + 0.0512, with the coefficient of determination (R2) of 0.89. No significant difference was observed between the model-predicted values and the measured values (F = 0.789, P > 0.05), which demonstrated the high fitting degree of simulation equation. This study provides valuable insight into the removal of dissolved nitrogen in a controllable prawn farming mode such as high-elevation ponds by O. borgei. [ABSTRACT FROM AUTHOR]

A shift has been predicted in future nitrogen emission scenarios from nitrous oxide to higher proportions of ammonium compounds. To investigate the interaction between increasing nitrogen load and varying nitrate:ammonium ratios (NO3−:NH4+), we performed a mesocosm experiment in an oligotrophic lake in southern Germany. We fertilized mesocosms with both roughly natural and four times the natural nitrogen wet deposition amounts in molar NO3−:NH4+ ratios of 4:1 and 1:4. We observed greater phytoplankton biomass in treatments with a relatively higher ammonium supply, but not in those with nitrate and total nitrogen load. Ammonium significantly increased the total chlorophyll a concentrations, and especially the growth of small nanophytoplankton species. The effects observed indicate that NH4+ was taken up preferentially and that spring phytoplankton in oligotrophic lakes appear to be able to respond to variations in nitrogen forms (available NO3−:NH4+ ratios) by adjusting their community composition. Such communal changes at the base of the food web may affect higher trophic levels. Therefore, the effects of varying available forms of nitrogen should also be considered in primarily phosphorus-limited aquatic systems. [ABSTRACT FROM AUTHOR]

To assess the contribution of reactive nitrogen from groundwater to surface waters, we need more knowledge on how reactive nitrogen behaves in the glacial till systems underlying many agricultural fields. Groundwater sampled from suction cups and piezometers placed in the glacial till underlying a winter wheat field shows the nitrate concentration in water leaching to deeper than 2 m below ground surface (mbg) is ~ 60 mg L−1. Within 5 mbg, all of the nitrate is removed and this appears to take place within a redox zone rather than at a sharp redox front. Ammonium released from the till is negligible. A 2D dataset reveals that the depth to the redox zone undulates between 3 and 5 mbg, perhaps a result of local variations in infiltration. It appears that the nitrate is generally reduced by the oxidation of pyrite and locally by organic matter in lenses within the till. [ABSTRACT FROM AUTHOR]

Coexistence between trees and grasses in savannas is generally assumed to be due to a combination of partial niche separation for water acquisition and disturbances impacting the demography of trees and grasses. We propose a mechanism of coexistence solely based on the partitioning of the two dominant forms of mineral nitrogen (N), ammonium (NH4+) and nitrate (NO3−). We built a mean-field model taking into account the capacity of grasses and trees to alter nitrification fluxes as well as their relative preferences for NH4+ versus NO3−. Two models were studied and parameterized for the Lamto savanna (Côte d'Ivoire): In the first model, the nitrification only depends on the quantity of available NH4+, and in the second model the nitrification rate is also controlled by tree and grass biomass. Consistent with coexistence theories, our results show that taking these two forms of mineral N into account can allow coexistence when trees and grasses have contrasting preferences for NH4+ and NO3−. Moreover, coexistence is more likely to occur for intermediate nitrification rates. Assuming that grasses are able to inhibit nitrification while trees can stimulate it, as observed in the Lamto savanna, the most likely case of coexistence would be when grasses prefer NH4+ and trees NO3−. We propose that mineral N partitioning is a stabilizing coexistence mechanism that occurs in interaction with already described mechanisms based on disturbances by fire and herbivores. This mechanism is likely relevant in many N-limited African savannas with vegetation composition similar to the one at the Lamto site, but should be thoroughly tested through empirical studies and new models taking into account spatiotemporal heterogeneity in nitrification rates. [ABSTRACT FROM AUTHOR]

Here, the fast and shorter duration synthesis route was proposed for the production of N-doped graphene by supercritical fluid method involving ammonium oxalate as a source of nitrogen. Within the different proportions of graphene oxide and nitrogen source, the nitrogen-doped graphene formed from ammonium oxalate having nitrogen content of 3.3 wt% showed an enriched specific capacitance of 274 Fg−1 at 1 A/g in 20% KOH electrolyte. The long-term stability results obtained from galvanostatic charge-discharge in ammonium oxalate-based N-doped graphene revealed that 90% specific capacitance retention was achieved up to 10,000 cycles at 10 A/g. To examine the device proficiency, a full cell was fabricated and the performance was evaluated in two different approaches. Among the different media in aqueous electrolytes, the fabricated symmetric supercapacitor has achieved a maximum specific capacitance value of 160 F/g at 1 A/g in alkaline medium (20% KOH solution). Between 20% KOH solution and 1 M NaClO4 solution in acetonitrile, the fabricated symmetric supercapacitor exhibits an energy density of 26.5 Wh/kg as well as 5.5 Wh/kg in 1 M sodium perchlorate in acetonitrile solution and 20% KOH solution, respectively. [ABSTRACT FROM AUTHOR]

Artificial soils made from waste materials offer an alternative to imported natural topsoils, notably in large-scale groundwork and reclamation projects. Benefits include diversion of waste from landfill and recycling. Nonetheless, there is limited information on the characteristics needed to support plant growth in the long term, particularly the existence of a sustainable nitrogen reservoir. Therefore, we assessed the efficacy of nitrogen cycling and retention within an artificial soil composed of 25% sand, 10% clay, 32.5% composted bark and 32.5% composted green waste over 52 weeks. Leachate was analysed for nitrogen species and nitrogen concentrations, and two of the soil columns had fertiliser added after 26 and 48 weeks. Results show that nitrate concentrations decreased from 6.73 to 0.36 mg N L−1 after 2 weeks, due to poor retention of this anion in soil, and remained low for 6 months, before increasing up to 5.87 mg N L−1 after week 26. This sharp increase in dissolved nitrate was preceded by a decrease in the ratio of dissolved organic carbon to dissolved organic nitrogen in the soil leachate. This finding indicates that the soil had become carbon-limited, leading to mineralisation of organic nitrogen by soil organisms and excretion of nitrogen. We also found that fertilisation of the soil did not alleviate carbon limitation and nitrogen loss was greater in fertilised soils, indicating nitrogen saturation. After the onset of carbon limitation, the dissolved nitrate concentrations in both the fertilised and unfertilised soils were close to exceeding the European Union threshold of concern for nitrate groundwater and river pollution. Thus, while the deployment of artificial soils is a viable option for landscaping projects, loss of nitrogen may be environmentally significant and soil management protocols must take account of both the carbon and nitrogen status of the substrate. [ABSTRACT FROM AUTHOR]

In this study, soil samples from the typical rice-wheat cropping system in Jiangsu Province, China, subjected to different fertilizer application treatments-no carbon (CK), urea (UR), straw (SR), pig manure (PM), starch (ST), and glucose (GL)-were used to determine potential anaerobic ammonium oxidation (anammox) rate and its association with bacterial abundance, diversity, and activity by using DNA stable isotope probing combined with N isotope tracing and molecular techniques. The effects of different organic carbon sources on anammox were significant, in the following order: GL > ST, SR > UR > PM; anammox activity differed significantly across treatments; however, the C active anammox bacteria were only closely related to Ca. Brocadia. The anammox hydrazine synthase β subunit functional gene sequences were highly associated with the Candidatus genus Brocadia in PM and CK treatments. The different organic carbon sources had different inhibitory effects with anammox rate, which dropped from 3.19 to 1.04 nmol dinitrogen gas g dry soil h among treatments. About 4.2-22.3% of dinitrogen gas emissions were attributed to anammox and indicated that a specific population of anammox bacteria was present and varied with the addition of exogenous organic compounds in paddy soils, although a small part of dinitrogen gas was emitted from the soil via anammox. [ABSTRACT FROM AUTHOR]

Nutrient exports from soils have important implications for long-term patterns of nutrient limitation on land and resource delivery to aquatic environments. While plant–soil systems are notably efficient at retaining limiting nutrients, spatial and temporal mismatches in resource supply and demand may create opportunities for hydrologic losses to occur. Spatial mismatches may be particularly important in peat-forming landscapes, where the development of a two-layer vertical structure can isolate plant communities on the surface from resource pools that accumulate at depth. Our objectives were to test this idea in northern Sweden, where nitrogen (N) limitation of terrestrial plants is widespread, and where peat-forming, mire ecosystems are dominant features of the landscape. We quantified vertical patterns of N chemistry in a minerogenic mire, estimated the seasonal and annual hydrologic export of organic and inorganic N from this system, and evaluated the broader influence of mire cover on N chemistry across a stream network. Relatively high concentrations of ammonium (up to 2 mg l−1) were observed in groundwater several meters below the peat surface, and N was routed to the outlet stream along deep, preferential flowpaths. Areal estimates of inorganic N export from the mire were several times greater than from an adjacent, forested catchment, with markedly higher loss rates during the growing season, when plant N demand is ostensibly greatest. At broader scales, mire cover was positively correlated with long-term concentrations of inorganic and organic N in streams across the drainage network. This study provides an example of how mire formation and peat accumulation can create broad-scale heterogeneity in nutrient supply and demand across boreal landscapes. This mismatch allows for hydrologic losses of reactive N that are independent of annual plant demand and potentially important to receiving lakes and streams. [ABSTRACT FROM AUTHOR]

Form of nitrogen present in soils is one of the factors that affect nitrogen loss. Nitrate is mobile in soils because it does not absorb on soil colloids, thus, causing it to be leached by rainfall to deeper soil layers or into the ground water. On the other hand, temporary retention and timely release of ammonium in soils regulate nitrogen availability for crops. In this study, composted paddy husk was used in studies of soil leaching, buffering capacity, and ammonium adsorption and desorption to determine the: (i) availability of exchangeable ammonium, available nitrate, and total nitrogen in an acid soil after leaching the soil for 30 days, (ii) soil buffering capacity, and (iii) ability of the composted paddy husk to adsorb and desorb ammonium from urea. Leaching of ammonium and nitrate were lower in all treatments with urea and composted paddy husk compared with urea alone. Higher retention of soil exchangeable ammonium, available nitrate, and total nitrogen of the soils with composted paddy husk were due to the high buffering capacity and cation exchange capacity of the amendment to adsorb ammonium thus, improving nitrogen availability through temporary retention on the exchange sites of the humic acids of the composted paddy husk. Nitrogen availability can be enhanced if urea is amended with composted paddy husk. [ABSTRACT FROM AUTHOR]

Diploid cells of Saccharomyces cerevisiae undergo pseudohyphal differentiation in response to nutrient depletion. Although this dimorphic transition occurs due to signals originating from carbon and nitrogen limitation, how these signals are coordinated and integrated is not understood. Results of this study indicate that the pseudohyphal defect of the mep2∆ mutant is overcome upon disruption of KRH2/ GPB1 but not KRH1/ GPB2. Further, the agar invasion defect observed in a mep2 mutant strain is suppressed only by deleting KRH2 and not KRH1. Thus, the results presented indicate that MEP2 functions by inhibiting KRH2 to trigger filamentation response when glucose becomes limiting. Biochemical data and phenotypic response to glucose replenishment reveal that KRH1 and KRH2 are differentially regulated by glucose and ammonium to induce pseudohyphae formation via the cAMP-PKA pathway. In contrast to the current view, this study clearly demonstrates that, KRH1 and KRH2 are not functionally redundant. [ABSTRACT FROM AUTHOR]

Anaerobic ammonium oxidation (anammox) as an important nitrogen removal pathway has been investigated in intertidal marshes. However, the rhizosphere-driven anammox process in these ecosystems is largely overlooked so far. In this study, the community dynamics and activities of anammox bacteria in the rhizosphere and non-rhizosphere sediments of salt-marsh grass Spartina alterniflora (a widely distributed plant in estuaries and intertidal ecosystems) were investigated using clone library analysis, quantitative PCR assay, and isotope-tracing technique. Phylogenetic analysis showed that anammox bacterial diversity was higher in the non-rhizosphere sediments ( Scalindua and Kuenenia) compared with the rhizosphere zone (only Scalindua genus). Higher abundance of anammox bacteria was detected in the rhizosphere (6.46 × 10-1.56 × 10 copies g), which was about 1.5-fold higher in comparison with that in the non-rhizosphere zone (4.22 × 10-1.12 × 10 copies g). Nitrogen isotope-tracing experiments indicated that the anammox process in the rhizosphere contributed to 12-14 % N generation with rates of 0.43-1.58 nmol N g h, while anammox activity in the non-rhizosphere zone contributed to only 4-7 % N production with significantly lower activities (0.28-0.83 nmol N g h). Overall, we propose that the rhizosphere microenvironment in intertidal marshes might provide a favorable niche for anammox bacteria and thus plays an important role in nitrogen cycling. [ABSTRACT FROM AUTHOR]

Climate change is predicted to have widespread impacts on freshwater lake and reservoir nutrient budgets by altering both hypolimnetic hypoxia and runoff, which will in turn alter the magnitude of internal and external nutrient loads. To examine the effects of these potential climate scenarios on nitrogen (N) and phosphorus (P) budgets, we conducted a whole-catchment manipulation of hypolimnetic oxygen conditions and external loads to Falling Creek Reservoir (FCR), an old, eutrophic reservoir in a reforested catchment with a history of agricultural land use. Throughout 2 years of monitoring, internal N and P loading during hypoxic conditions dominated the hypolimnetic mass of nutrients in FCR, regardless of changes in external loading. FCR commonly functioned as a net sink of N and P, except during hypoxic conditions, when the reservoir was a net source of ammonium ( $$ {\text{NH}}_{4}^{ + } $$ ) to downstream. We observed extremely high nitrate-nitrite ( $$ {\text{NO}}_{3}^{ - } {-}{\text{NO}}_{2}^{ - } $$ ), soluble reactive P (SRP), total nitrogen (TN), and total phosphorus (TP) retention rates, indicating that the reservoir served as a sink for greater than 70% of $$ {\text{NO}}_{3}^{ - } {-}{\text{NO}}_{2}^{ - } $$ inputs and greater than 30% of SRP, TN, and TP inputs, on average. Our study is notable in the length of time since reforestation (>80 years) that a reservoir is still exhibiting high N and P internal loading during hypoxia, potentially as a result of the considerable store of accumulated nutrients in its sediment from historical agricultural runoff. Our whole-catchment manipulations highlight the importance of understanding how multiple aspects of global change, waterbody and catchment characteristics, and land use history will interact to alter nutrient budgets in the future. [ABSTRACT FROM AUTHOR]

Nitrate (NO) and ammonium (NH) are the two major dissolved inorganic nitrogen (DIN) species available in streams. Human activities increase stream DIN concentrations and modify the NO:NH ratio. However, few studies have examined biofilm responses to enrichment of both DIN species. We examined biofilm responses to variation in ambient concentrations and enrichments in either NO or NH. We incubated nutrient diffusing substrata (NDS) bioassays with three treatments (DIN-free, +NO and +NH) in five streams. Biomass-specific uptake rates ( U) of NO and NH were then measured using in situ additions of N-labeled NO and NH. Biomass (estimated from changes in carbon content) and algal accrual rates, as well as U-NO of biofilms in DIN-free treatments varied among the streams in which the NDS had been incubated. Higher ambient DIN concentrations were only correlated with enhanced biofilm growth rates. U-NO was one order of magnitude greater and more variable than U-NH, however similar relative preference index (RPI) suggested that biofilms did not show a clear preference for either DIN species. Biofilm growth and DIN uptake in DIN-amended NDS (i.e., +NO and +NH) were consistently lower than in DIN-free NDS (i.e., control). Lower values in controls with respect to amended NDS were consistently more pronounced for algal accrual rates and U-NO and for the +NH than for the +NO treatments. In particular, enrichment with NH reduced biofilm U-NO uptake, which has important implications for N cycling in high NH streams. [ABSTRACT FROM AUTHOR]

Large-scale forestry operations, like clear-cutting, may impair surface water quality if not done with environmental considerations in mind. Catchment and country level estimates of nutrient loads from forestry are generally based on specific export values, i.e., changes in annual exports due to the implemented forestry operations expressed in kg ha. We introduce here a specific concentration approach as a method to estimate the impact of clear-cutting on nutrient concentrations and export in headwater streams. This new method is potentially a more dynamic and flexible tool to estimate nutrient loads caused by forestry, because variation in annual runoff can be taken into account in load assessments. We combined water quality data from eight boreal headwater catchment pairs located in Finland and Sweden, where the effect of clear-cutting on stream water quality has been studied experimentally. Statistically significant specific concentration values could be produced for total nitrogen, nitrate, ammonium, and phosphate. The significant increases in the concentrations of these nutrients occurred between 2 and 6 years after clear-cutting. Significant specific concentration values could not be produced for total phosphorus and total organic carbon with the whole dataset, although in some single studies significant increases in their concentrations after clear-cutting were observed. The presented method enables taking into account variation in runoff, temporal dynamics of effects, and the proportional size of the treated area in load calculations. The number of existing studies considering large site-specific variation in responses to clear-cutting is small, and therefore further empirical studies are needed to improve predictive capabilities of the specific concentration values. [ABSTRACT FROM AUTHOR]

Electric field was applied to enhance the activity of anaerobic ammonium oxidation (anammox) bacteria for nitrogen removal in this study. The effect of different distributive modes with the total electric field time of 6 h/24 h (R2) and 18 h/24 h (R3) at 2 V/cm was determined through long-term tests. With the continuous application time increasing from 3 to 9 h in R3 (1 to 3 h in R2), the total nitrogen removal rate (NRR) showed an acceleration trend. When the electric field was applied continuously for 9 h (R3, mode 3, application-rest time: 9 h-3 h), the NRR dramatically increased 38.7 % over that of control on day 160. Besides, it was demonstrated that the increase of crude enzyme activities and the cell quantities were the main reasons for the enhancement of nitrogen removal performance of the anammox process. Additionally, transmission electron microscope observation proved the morphological change of anammox biomass under electric field application. [ABSTRACT FROM AUTHOR]

High-affinity ammonium transporters (AMT1) are responsible for ammonium (NH) acquisition and/or perception in the micromolar range, and their expressions can be differentially regulated by nitrogen (N) availability. The present study characterised the functions of the rice ( Oryza sativa) OsAMT1.3 transporter to understand its contribution to NH acquisition and plant adaptation to environments with low N availability. Transgenic rice plants were obtained to study the activity of the OsAMT1.3 promoter (P:GFP:GUS) and the overexpression of the OsAMT1.3 gene (UBIL: OsAMT1.3:3xHA) in plants. The OsAMT1.3 promoter activity was induced strongly in the absence of N and occurred primarily in the zones of lateral root emission and root tips. Anatomical sections of the segment of root tips and the middle third showed a differential pattern of OsAMT1.3 activity. Analysis of the OsAMT1.1- 1.3 transporter expression profiles indicated that overexpression of OsAMT1.3 positively affected OsAMT1.2 expression. When subjected to a low N supply, plants overexpressing OsAMT1.3 showed lower K and C values. Additionally, these lines showed longer roots with a higher area, volume, and number of tips. The data suggested that OsAMT1.3 is involved in the ability of rice plants to adapt to low NH supplies. [ABSTRACT FROM AUTHOR]

The coastal Chukchi Sea has a particularly productive landfast ice ecosystem but is currently lacking direct measurements of nitrogen (N) cycling within the ice. Using stable isotopic tracers, we measured uptake and regeneration of ammonium and nitrate, along with primary and secondary production at three depths within landfast sea ice in the Chukchi Sea near Barrow, Alaska, during April 2011 and January 2012. These are the first data of N uptake and regeneration rates in landfast Arctic sea ice during spring and winter. Both inorganic and organic nutrient concentrations in the ice were generally higher than the water column, with the exception of phosphate, which may have limited production in certain sections of ice. Primary production at all ice depths was higher than the water column during April, but below the detection limit in January. Bacterial production in the bottom ice (0-10 cm from the ice-water interface) was consistently higher than the water column across seasons. Absolute uptake of ammonium was highest in the bottom ice and higher than absolute uptake of nitrate at all depth horizons except in the upper ice (30-40 cm from ice-water interface) during January. While N uptake rates in the ice were higher than the water column, nitrification rates were lower. Regeneration of ammonium and nitrate far exceeded uptake within the ice. The magnitude of N uptake and regeneration rates in landfast ice highlights the importance of the biological sea ice community to the region. [ABSTRACT FROM AUTHOR]

This study determined how the activity and number of nitrogen-converting microorganisms varied with changes in hydraulic retention time (HRT) and the operating regime of aerobic granular sequencing batch reactors (GSBRs) treating high-nitrogen wastewater. Continuously aerated (O-mode) GSBRs were operated at HRTs of 10-, 13- and 19-h. Then the same reactors were operated at identical HRTs but the cycles started with an anoxic phase (A/O mode). To investigate the microbial communities, DNA- and RNA-based relative real-time PCR was used. In all experimental reactors ammonium was fully removed with a removal rate up to 75 mg N-NH/(L·h), and nitrification efficiency was above 90 %. The efficiency of the removal of oxidized nitrogen forms decreased with the lengthening of HRT. The study found that variable oxic conditions (A/O mode) in the GSBR cycle stimulated the simultaneous activity of ammonium oxidizing bacteria (AOB), NO-reducers, and Anammox bacteria in aerobic granules. With both modes, the activity of nitrogen-converting bacteria was highest with a 13-h HRT. Shortening HRT, resulted in higher chemical oxygen demand and nitrogen loadings, which favored the growth of Anammox microorganisms in granules and caused a decrease in the number of AOB. With all HRTs, the number of Anammox microorganisms was about 1.5-times higher in A/O mode than in O mode. [ABSTRACT FROM AUTHOR]

Climate change is expected to cause an increased frequency of extreme events such as heavy floods and major storms. Such stochastic events have an immediate impact on surface water quality, but the long-term effects are largely unknown. In this study, we assess long-term monitoring data from two Swedish headwater catchments affected by extreme weather events. At one site, where nitrogen effects in soil water, groundwater, and stream water were studied after storm-felling and subsequent forest dieback from bark beetle attack, long-term (>5 years) but relatively modest (generally <1 mg L) increases in ammonium (NH-N) and nitrate (NO-N) concentrations were observed in the various aqueous media. At the other site, where effects on benthic fauna were studied in a stream impacted by extreme geophysical disturbances caused by rainstorm-induced flashflood, only short-term (1 year) effects were revealed both regarding diversity and composition of species. [ABSTRACT FROM AUTHOR]

Animal excretion can be a significant nutrient flux within ecosystems, where it supports primary production and facilitates microbial decomposition of organic matter. The effects of excretory products on nutrient cycling have been documented for various species and ecosystems, but temporal variation in these processes is poorly understood. We examined variation in excretion rates of a dominant grazing snail, Elimia clavaeformis, and its contribution to nutrient cycling, over the course of 14 months in a well-studied, low-nutrient stream (Walker Branch, east Tennessee, USA). Biomass-specific excretion rates of ammonium varied over twofold during the study, coinciding with seasonal changes in food availability (measured as gross primary production) and water temperature (multiple linear regression, R = 0.57, P = 0.053). The contribution of ammonium excretion to nutrient cycling varied with seasonal changes in both biological (that is, nutrient uptake rate) and physical (that is, stream flow) variables. On average, ammonium excretion accounted for 58% of stream water ammonium concentrations, 26% of whole-stream nitrogen demand, and 66% of autotrophic nitrogen uptake. Phosphorus excretion by Elimia was contrastingly low throughout the year, supplying only 1% of total dissolved phosphorus concentrations. The high average N:P ratio (89:1) of snail excretion likely exacerbated phosphorus limitation in Walker Branch. To fully characterize animal excretion rates and effects on ecosystem processes, multiple measurements through time are necessary, especially in ecosystems that experience strong seasonality. [ABSTRACT FROM AUTHOR]

OsAMT is a high-affinity ammonium transporter responsible for NH uptake by rice plants. To investigate the expression patterns of OsAMT in different genotypes in relation to nitrogen accumulation, we measured the expression of OsAMT1.1, OsAMT1.2, and OsAMT1.3 using Real-Time PCR (RT-PCR) in GD (higher N accumulation) and NG (lower N accumulation) seedlings of the Oryza sativa L. cultivar treated with 0.1 mM NHNO and 2 mM NHNO. We found that the expression level of OsAMT1.1 was significantly higher than those of OsAMT1.2 and OsAMT1.3 in the roots treated with 0.1 mM NHNO, suggesting that OsAMT1.1 contributed the most to N accumulation among the three genes. In GD root, OsAMT1.1 had significantly higher expression levels when it was up-regulated by 0.1 mM NHNO than when down-regulated by 2 mM NHNO. OsAMT1.1 was mainly found in GD roots treated with 0.1 mM NHNO. We conclude that the OsAMT1.1 in GD roots, which was significantly up-regulated by low N and down-regulated by high N, was the dominating factor in determining the higher N acquisition in GD than in NG at 0.1 mM NHNO. [ABSTRACT FROM AUTHOR]

The effects of mineral nutrient were examined on in vitro growth of Gerbera hybrida ( G. jamesonii × G. viridifolia), specifically Gerbera hybrida cv. Pasadena. Four types of experiments were conducted to quantify the effects of mineral nutrients on four in vitro growth responses (quality, shoot number, leaf number, and shoot height) of gerbera and included groups of mineral nutrients (macros/mesos, micros, and Fe), individual salts (CuSO·5HO, MnSO·4HO, ZnSO·7HO, and Fe/EDTA), and the specific ions NO, NH, and K. Experiments included mixture-amount designs that are essential for separating the effects of proportion and concentration. Highly significant effects were observed in all experiments, but the mineral nutrients with the largest effects varied among the four growth responses. For example, leaf number was strongly affected by the macronutrient group in one experiment and by NH and K, which were in the macronutrient group, in the NO/NH/K ion-specific experiment, whereas quality was strongly affected by the micronutrients ZnSO and Fe/EDTA. Because mineral nutrient effects varied significantly with the response measured, defining an appropriate formulation requires a clear definition of 'optimal' growth. [ABSTRACT FROM AUTHOR]

Phenolic wastewater was treated using anaerobic submerged membrane bioreactor (ASMBR). Effect of different solids retention times on MBR performance was studied. Various ratios of carbon to nitrogen were used in the synthetic wastewaters. During the operation, phenol concentration of feed was changed from 100 to 1000 mg L−1. Phenol concentration was increased stepwise over the first 30 days and kept constant at 1000 mg L−1, thereafter. For the first 100 days, a chemical oxygen demand (COD) to N ratio of 100:5.0 was used and this resulted in phenol and COD removal more than 99 and 95%, respectively. However, the ammonium removal decreased from 95 to 40% by increasing the phenol concentration of feed, from 100 to 1000 mg L−1. For the last 25 days, a COD to N ratio of 100:2.1 was used due to the ammonium accumulation in the ASMBR. This led to the complete ammonium removal and no ammonium was detected in the ASMBR permeate. These results suggest that in the ASMBR at high phenol loading of 1000 mg L−1, COD to N ratio of the phenolic wastewater must be 100:2.1 for ammonium removal, while at low phenol loading, COD to N ratio of 100:5.0 can be used. [ABSTRACT FROM AUTHOR]