Nitrification Activity Research Articles

Short-Term Effects of Abrupt Salinity Changes on Aquaculture Biofilter Performance and Microbial Communities

In recirculating aquaculture systems (RASs), ammonia excreted by fish must be converted to the less toxic nitrate before recirculation. Nitrifying microorganisms in biofilters used for this transformation can be sensitive to changes in salinity, which can present issues for systems that raise anadromous fish such as Atlantic salmon. Freshwater biofilters maintained at a low level of salinity (such as biofilters operated in coastal areas) may be better equipped to handle more drastic salinity shifts; therefore, experiments were performed on freshwater and low-salinity (3 ppt) biofilters to assess their ability to recover nitrification activity after an abrupt change in salinity (3, 20, and 33 ppt). Two-week tests showed full nitrification recovery in freshwater biofilters after a shift to 3 ppt but no ammonia oxidation in 20 or 33 ppt. Low-salinity-adapted filters (transitioned from 0 to 3 ppt) showed a small recovery (about 11%) after a shift to 20 ppt, and no activity when shifted to 33 ppt. Illumina sequencing revealed that, while nitrification was slowed or stopped with shifting salinities, the nitrifiers survived the salinity increases; conversely, the heterotrophic communities were more greatly affected and were reduced in proportion with increasing salinity. This work indicates that biofilters operated at low salinity may recover more quickly after large salinity changes, though this slight benefit may not outweigh the cost of low-level salinity maintenance. Further research into halotolerant heterotrophs in biofilms may increase the effectiveness of nitrifying biofilters under variable salinities.

Temporal enrichment of comammox Nitrospira and Ca. Nitrosocosmicus in a coastal plastisphere.

Plastic marine debris is known to harbor a unique microbiome (termed the "plastisphere") that can be important in marine biogeochemical cycles. However, the temporal dynamics in the plastisphere and their implications for marine biogeochemistry remain poorly understood. Here, we characterized the temporal dynamics of nitrifying communities in the plastisphere of plastic ropes exposed to a mangrove intertidal zone. The 39-month colonization experiment revealed that the relative abundances of Nitrospira and Candidatus Nitrosocosmicus representatives increased over time according to 16S rRNA gene amplicon sequencing analysis. The relative abundances of amoA genes in metagenomes implied that comammox Nitrospira were the dominant ammonia oxidizers in the plastisphere, and their dominance increased over time. The relative abundances of two metagenome-assembled genomes of comammox Nitrospira also increased with time and positively correlated with extracellular polymeric substances content of the plastisphere but negatively correlated with NH4+ concentration in seawater, indicating the long-term succession of these two parameters significantly influenced the ammonia-oxidizing community in the coastal plastisphere. At the end of the colonization experiment, the plastisphere exhibited high nitrification activity, leading to the release of N2O (2.52ng N2O N g-1) in a 3-day nitrification experiment. The predicted relative contribution of comammox Nitrospira to N2O production (17.9%) was higher than that of ammonia-oxidizing bacteria (4.8%) but lower than that of ammonia-oxidizing archaea (21.4%). These results provide evidence that from a long-term perspective, some coastal plastispheres will become dominated by comammox Nitrospira and thereby act as hotspots of ammonia oxidation and N2O production.

Organic fertilizer significantly mitigates N2O emissions while increase contributed of comammox Nitrospira in paddy soils

Nitrification is the dominant process for nitrous oxide (N2O) production under aerobic conditions, but the relative contribution of the autotrophic nitrifiers (the ammonia-oxidising archaea (AOA), the ammonia-oxidising bacteria (AOB) and the comammox) to this process is still unclear in some soil types. This is particularly the case in paddy soils under different fertilization regimes. We investigated active nitrifiers and their contribution to nitrification and N2O production in a range of unfertilized and fertilized paddy soils, using 13CO2-DNA based stable isotope probing (SIP) technique combined with a series of specific nitrification inhibitors, including acetylene (C2H2), 3, 4-dimethylpyrazole phosphate (DMPP) and 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO). The soils had a long-term history of fertilizer application, including chemical fertilizer only, a mixture of chemical fertilizers (70 %) and chicken manure (30 %) or a mixture of rice straw and chemical fertilizers. 13CO2-DNA-SIP and Illumina MiSeq sequencing demonstrated that comammox clades A.1 and B were active nitrifiers in all fertilized paddy soils. Inhibitor experiment showed that AOB largely contributed to nitrification activity and N2O emission in all paddy soils, while comammox contribution was more significant than AOA. Fertilization considerably altered nitrifiers' relative contribution to nitrification activity and N2O emissions. Applying organic fertilizers significantly decreased the N2O emissions but increased the contribution of comammox to the process. These findings expand the functional ecological niche of comammox, revealing their nitrification role and N2O production in other ecosystems than oligotrophic habitats.

Impact of elevated CO2 on microbial communities and functions in riparian sediments: Role of pollution levels in modulating effects

The impact of elevated CO2 levels on microorganisms is a focal point in studying the environmental effects of global climate change. A growing number of studies have demonstrated the importance of the direct effects of elevated CO2 on microorganisms, which are confounded by indirect effects that are not easily identified. Riparian zones have become key factor in identifying the environmental effects of global climate change because of their special location. However, the direct effects of elevated CO2 levels on microbial activity and function in riparian zone sediments remain unclear. In this study, three riparian sediments with different pollution risk levels of heavy metals and nutrients were selected to explore the direct response of microbial communities and functions to elevated CO2 excluding plants. The results showed that the short-term effects of elevated CO2 did not change the diversity of the bacterial and fungal communities, but altered the composition of their communities. Additionally, differences were observed in the responses of microbial functions to elevated CO2 levels among the three regions. Elevated CO2 promoted the activities of nitrification and denitrification enzymes and led to significant increases in N2O release in the three sediments, with the greatest increase of 76.09 % observed in the Yuyangshan Bay (YYS). Microbial carbon metabolism was promoted by elevated CO2 in YYS but was significantly inhibited by elevated CO2 in Gonghu Bay and Meiliang Bay. Moreover, TOC, TN, and Pb contents were identified as key factors contributing to the different microbial responses to elevated CO2 in sediments with different heavy metal and nutrient pollution. In conclusion, this study provides in-depth insights into the responses of bacteria and fungi in polluted riparian sediments to elevated CO2, which helps elucidate the complex interactions between microbial activity and environmental stressors.

Bio-refinery of organic pollutants for wastewater reclamation

With rapid development of global climate change and resource scarcity, the demand for sustainable wastewater reclamation technologies is growing rapidly. Alginate like exopolymers (ALE) are value-added biopolymers that can be recovered from excess biomass. In this study, a novel biopolymer value-driven moving bed biofilm reactor (bMBBR) was constructed to achieve high-efficiency conversion of organics to Alginate like exopolymers (ALE). The results revealed that excellent COD and low NH4+-N reduction could be achieved, with the reduction efficiencies of 87.7 ± 0.6 % and 12.6 ± 0.8 %, respectively. It is indicated that high-rate organics conversion and blockage of nitrification activity for energy saving could be simultaneous achieved in this process. Additionally, the superior settleability (SVI30 < 80 mL/g) and functional genera related to extracellular polymeric substances (EPS) secretion were observed, making it promising for ALE recovery from residual biomass. The yields of ALE extraction from biofilm and suspended biomass ranged of 232.9–381.5 mg/g VSS. The property analyses demonstrated that the biopolymer had a similarity functional group between two samples and commercial alginate. Meanwhile, the profit evaluation results suggested that the net profit could be reached of 0.54 CNY/kg SS in the present study, which was higher than that of conventional waste activated sludge (−1.92 CNY/kg SS). Moreover, the economic value of ALE (0.38 CNY/m3 wastewater treated) was also 2.93 times of that obtained from CH4 (0.13 CNY/m3 wastewater treated). In general, the present study provides a prove of concept that bio-refinery of organics into value-added biopolymers could offer a promising direction towards next generation of sustainable wastewater treatment plants.

Role of Nitrifiers Associated with Mangrove clam Polymesoda Erosa in Bioremediation.

Polymesoda erosa is a mangrove clam known for its water filtration ability. This clam was investigated for its bioremediation potential and growth in synthetic wastewater during 40 days of incubation. Variation in the nutrient composition of water, biochemical composition of the clams, and metagenomic analysis of the microorganisms associated with clam tissue were carried out. Significant differences in the concentration of ammonia (p ≤ 0.01), nitrite (p ≤ 0.001), and nitrate (p ≤ 0.05) in the wastewater were observed between day 0 and day 40. A reduction of approximately 89% in ammonia concentration at the end of the experiment was recorded indicating nitrification activity. However, biochemical parameters showed negligible differences before and after the incubation experiment. Thus suggesting that the chemosynthetic-based nutrition aids in the survival of the clam as no organic matter was added to the medium. The substantial decline in levels of ammonia in the presence of clams as compared to its absence suggests the significant role of clams in improving the water quality. Furthermore, the metagenomic analysis of the gill tissue of P. erosa revealed ~ 50% of the microbial population to consist of nitrifiers. The study highlights the contribution by the nitrifers associated with the clams not only to its growth and resilience but also to bioremediation.

Soil physicochemical and microbial properties affect nitrogen cycling in technogenically transformed coal dump soils

Mining industrial sectors deteriorate local and regional environmental quality, contributing to global ecosystem contamination. The activities of microorganisms and enzymes involved in nitrogen cycling processes were investigated in coal dump soils that had undergone technogenic transformations and reclamation. Compared to the background uncontaminated soil, the heavy metal concentrations increased to high contamination levels (the contents of mobile forms of Zn, Ni, and Cu were 66.9; 35.6; 12.9 mg/kg, respectively), salinity increased to 0.1–2.41 %. The activities of nitrification and denitrification as well as the abundance of ammonifiers reduced due to high concentrations of mobile forms, the presence of coal particles, and the salinity of soil samples. The urease activity decreased due to reduced content of soluble organic matter in disturbed soils (2.3 times lower than the background soils). Mechanical reclamation leads to a 4-fold decrease in soil toxicity levels; however, it does not enhance nitrogen cycling activity. The activity of nitrification and urease decreased by >4 times as compared to the soil of the protected area. Microbial community composition of coal mine soils was similar to that of undisturbed soil. Nitrifiers in coal mine soil were represented by the genera Nitrososphaera, Candidatus Nitrosocosmicus, Nitrosospira, Nitrosomonas, Nitrosococcus, Nitrospira, Nitrobacter. The results indicated that the disruption of nitrification process led to low nitrate content in technogenically transformed coal dump soils.

Wood Distillate Interactions with Urea in Soil: A First Step to Developing a Slow-Release Next-Generation Fertilizer.

We tested the ability of wood distillate (WD) to interact with urea in agricultural soil. WD is a sustainable material that has been addressed as a promising alternative to synthetic soil corroborants. However, there is little information about the effect of WD on the nitrogen cycle. In this study, soils with different amounts of WD and with/without urea were tested for ammonium, urease, nitrate/nitrite, and potential nitrification activity at different points in a 30 day time frame. High concentrations of WD (1-2%) inhibited the hydrolysis of urea and the oxidation of ammonium to nitrate. Thermal desorption coupled to GC-MS and high-performance liquid chromatography-tandem mass spectrometry characterization allowed us to reveal that WD-urea interactions mainly involve lignin-derived compounds in the distillate, such as catechol, resorcinol, and syringol. This study provides the first evidence of a strong interaction between WD and urea in soil that could be used to develop slow-release fertilizers.

Dairy effluent applications to a pasture enhance soil fertility and microbial activity without impacting soil bacterial and fungal community composition

Farm dairy effluents (FDE) from washing the milking parlor contain manure, urine, and chemicals and constitute a large amount of wastewater. Applying FDE as soil fertilizers to pastures can enhance forage yield and improve soil nutrient status. Since the dairy industry is increasingly attempting to maximize returns through better utilization of forage with lesser inputs, there is demand for a supply of FDE as fertilizers. Nevertheless, the impact of this practice on soil microbiota remains largely unexplored. It must be studied before large-scale soil disposal to avoid diminishing microbial diversity or enhancing pathogen abundance. This study evaluated the effects of applying lagoon-stored (Lagoon) and raw dairy effluents (Raw) at a rate of 50 kg N ha−1 in four equal doses, in comparison to urea fertilization, on soil fertility and the activity, abundance, and community structure of soil microbiota. Raw was obtained after solid separation, and Lagoon corresponds to the Raw stationed in a two-lagoon system. Microbial activity was assessed as basal respiration, potentially mineralizable N, potential nitrification activity, and enzymatic activities. The catabolic activity of the microbial community was evaluated using Biolog Ecoplates™. Bacterial and fungal community composition and diversity were analyzed through amplicon sequencing of 16S rRNA and ITS2. The application of FDE benefited soil fertility and microbial activity. Lagoon had the most potent effects on soil available P and extractable K+, Na+, Mg2+ and Ca2+. Soil treated with Raw displayed higher microbial activities, such as dehydrogenase, basal respiration, urease, and potentially mineralizable N, than the other treatments. FDE did not significantly alter the microbial composition, abundance, or functional diversity. In conclusion, in this short-term trial, despite changes in soil chemical properties and microbial activity, the composition and diversity of the bacterial and fungal communities remained unaffected by FDE irrigation.

Characteristics of Nitrogen Removal and Functional Gene Transcription of Heterotrophic Nitrification-Aerobic Denitrification Strain, Acinetobacter sp. JQ1004

In this study, the heterotrophic nitrification–aerobic denitrification strain JQ1004 was investigated in terms of its nitrogen removal mechanism and kinetic properties, laying the foundation for its application in the field of wastewater treatment. Nitrogen balance analysis revealed that the final metabolic product was N2, and approximately 54.61% of N was converted into cellular structure through assimilation. According to the fitting of the Compertz model, the maximum degradation rates of ammonia and nitrate were 7.93 mg/(L·h) and 4.08 mg/(L·h), respectively. A weakly alkaline environment was conducive to N removal, and the sensitivity of functional genes to acidic environments was amoA &gt; nirS &gt; narG. An appropriate increase in dissolved oxygen significantly enhanced heterotrophic nitrification activity, and notably, the denitrification-related functional gene narG exhibited greater tolerance to dissolved oxygen compared to nirS. The transcription level of amoA was significantly higher than that of narG or nirS, confirming that there might have been direct ammonia oxidation metabolic pathways (NH4+→NH2OH→N2) besides the complete nitrification and denitrification pathway. The annotation of nitrogen assimilation-related functional genes (including gltB, gltD, glnA, nasA, nirB, narK, nrtP, cynT, and gdhA genes) in the whole-genome sequencing analysis further confirmed the high assimilation nitrogen activity of the HN-AD strain.

Impact of Combined Electrolysis and Activated Sludge Process on Municipal Wastewater Treatment

Electrochemical methods for the treatment of municipal and industrial wastewater are used either independently or in conjunction with biological methods for pretreatment or posttreatment of biologically treated wastewater. In our work, the combination of these processes was studied, where pre-electrolysis was used to produce dissolved iron before the activation process. Electrolysis was also directly introduced into the activation using either iron or carbon electrodes. The surface of one iron electrode was 32.2 cm2, voltage at the electrodes was 21 V, and current was 270 mA. The surface of one carbon electrode was 7.54 cm2, current was 82.5 mA, and voltage at the electrodes was 21 V. Laboratory research on synthetic municipal wastewater treatment using a combination of electrolysis and activation processes showed that the use of iron electrodes increases the efficiency of phosphorus removal compared to its precipitation with iron salts. Electrolysis has shown a positive effect on the sedimentation properties of sludge and the destruction of filamentous microorganisms. Even though it negatively affected the respiration rates of activated sludge and the denitrification efficiency, it did not have a negative impact on the nitrification activity of sludge.

Testing the influence of light on nitrite cycling in the eastern tropical North Pacific

Abstract. Light is considered a strong controlling factor of nitrification rates in the surface ocean. Previous work has shown that ammonia oxidation and nitrite oxidation may be inhibited by high light levels, yet active nitrification has been measured in the sunlit surface ocean. While it is known that photosynthetically active radiation (PAR) influences microbial nitrite production and consumption, the level of inhibition of nitrification is variable across datasets. Additionally, phytoplankton have light-dependent mechanisms for nitrite production and consumption that co-occur with nitrification around the depths of the primary nitrite maximum (PNM). In this work, we experimentally determined the direct influence of light level on net nitrite production, including all major nitrite cycling processes (ammonia oxidation, nitrite oxidation, nitrate reduction and nitrite uptake) in microbial communities collected from the base of the euphotic zone. We found that although ammonia oxidation was inhibited at the depth of the PNM and was further inhibited by increasing light at all stations, it remained the dominant nitrite production process at most stations and treatments, even up to 25 % surface PAR. Nitrate addition did not enhance ammonia oxidation in our experiments but may have increased nitrate and nitrite uptake at a coastal station. In contrast to ammonia oxidation, nitrite oxidation was not clearly inhibited by light and sometimes even increased at higher light levels. Thus, accumulation of nitrite at the PNM may be modulated by changes in light, but light perturbations did not exclude nitrification from the surface ocean. Nitrite uptake and nitrate reduction were both enhanced in high-light treatments relative to low light and in some cases showed high rates in the dark. Overall, net nitrite production rates of PNM communities were highest in the dark treatments.

Restart performance of prolonged stopped down-flow hanging sponge reactor for treating of low-strength domestic sewage

The down-flow hanging sponge (DHS) reactor, a type of trickling filter used as a sponge, is a promising treatment system for low-cost sewage treatment. However, the performance of dried sponges that have been non-operational for 8 months has not been evaluated. Accordingly, herein, the re-startup process performance of a DHS reactor treating low-strength domestic sewage in Thailand that had stopped operation for over eight months was investigated. The dried sponge carrier immediately retained water in the sponge biomass-retained carrier and absorbed organic compounds. High nitrification activity of the DHS reactor was observed after 13 d, which was the same as that of the pure sponge biomass-retained carrier start-up. The tracer test results showed that the restarted DHS reactor had a high hydraulic retention time (HRT)/theoretical HRT ratio of 134.2 % at the beginning of the operation from the water retention property of the sponge carrier. Microbial community analysis showed that nitrifying microorganisms were effectively recovered in the biomass-retained sponge carrier. These results demonstrate that the sponge carriers in the DHS reactor that were left into dry condition are available for reuse and has high potential for rapid re-startup.

The dynamic features and microbial mechanism of nitrogen transformation for hydrothermal aqueous phase as fertilizer in dryland soil

Hydrothermal aqueous phase (HAP) contains abundant organics and nutrients, which have potential to partially replace chemical fertilizers for enhancing plant growth and soil quality. However, the underlying reasons for low available nitrogen (N) and high N loss in dryland soil remain unclear. A cultivation experiment was conducted using HAP or urea to supply 160 mg N kg−1 in dryland soil. The dynamic changes of soil organic matters (SOMs), pH, N forms, and N cycling genes were investigated. Results showed that SOMs from HAP stimulated urease activity and ureC, which enhanced ammonification in turn. The high-molecular-weight SOMs relatively increased during 5–30 d and then biodegraded during 30–90 d, which SUV254 changed from 0.51 to 1.47 to 0.29 L−1 m−1. This affected ureC that changed from 5.58 to 5.34 to 5.75 lg copies g−1. Relative to urea, addition HAP enhanced ON mineralization by 8.40 times during 30–90 d due to higher ureC. It decreased NO3–N by 65.35%–77.32% but increased AOB and AOA by 0.25 and 0.90 lg copies g−1 at 5 d and 90 d, respectively. It little affected nirK and increased nosZ by 0.41 lg copies g−1 at 90 d. It increased N loss by 4.59 times. The soil pH for HAP was higher than that for urea after 11 d. The comprehensive effects of high SOMs and pH, including ammonification enhancement and nitrification activity inhibition, were the primary causes of high N loss. The core idea for developing high-efficiency HAP fertilizer is to moderately inhibit ammonification and promote nitrification.

Ammonium enrichment reduces the diversity and changes the composition of ammonia-oxidizing microbial communities in agricultural soil media

Abstract. Saukoly SA, Meitiniarti VI, Nugroho RA, Krave AS. 2024. Ammonium enrichment reduces the diversity and changes the composition of ammonia-oxidizing microbial communities in agricultural soil media. Biodiversitas 25: 916-923. Nitrification is the process of ammonium oxidation to form nitrites and nitrates. Ammonium availability in the soil is one of the factors influencing the activity, abundance, and diversity of ammonia-oxidizing microorganisms (AOM). This study aimed to determine the effect of enriching a soil media with different ammonium concentrations on the abundance and diversity of AOM as well as the potential for nitrification. Soil as the media was prepared from an agricultural land receiving cow dung sewage. The media was then placed in the microcosms, and was added to a nitrification medium containing ammonium at three levels; 0 (control soil), 200 (low ammonium-enriched soil), and 500 mg L-1 (high ammonium-enriched soil). The microcosms were further incubated for 42 days at room temperature. The nitrification potential determination was based on the formation of nitrite from ammonium oxidation. The abundance of AOM and the potential nitrification were measured every 14-day interval, including day 0 as the initial condition. The AOM composition was analyzed based on the similarity level of the amoA gene sequence to the NCBI BLAST GenBank database. However, this analysis was only conducted for the control and high ammonium-enriched soil. This study indicated that ammonium enrichment increased the nitrification activity and the abundance of AOM, but it decreased the diversity of AOM communities. There were positive correlations between nitrification and nitrate potential, as well as between ammonium content and AOM abundance. Negative correlations appeared between pH and nitrification potential, nitrate concentrations, ammonium concentrations, and MPN. The diversity of ammonium-oxidizing archaea (AOA) in the control soil was higher than in the high ammonium-enriched soil. The enrichment with ammonium also changed the AOA composition. The Candidatus Nitrosocosmicus oleophilus strain of the MY3 chromosome was the most dominant archaea in the control and high ammonium-enriched soil. This implies that the high diversity of AOA in this soil may be beneficial for further use of the soil as a source for inocula in the development of nitrifiers-based biofertilizers.

Understanding vermicompost and organic manure interactions: impact on toxic elements, nitrification activity, comammox Nitrospira inopinata, and archaea/bacteria.

Vermicompost is a substantial source of nutrients, promotes soil fertility, and maintains or increases soil organic matter levels. Potentially toxic elements (PTEs) in vermicompost impact on nitrification activity. However, it is yet unknown how vermicompost affects nitrifying bacteria and archaea, comammox Nitrospira inopinata (complete ammonia oxidizers), net nitrification rates (NNRs), and PTEs. The effects of vermicompost application on NNRs, potential nitrification rates (NPs), PTEs, and the abundances of comammox N. inopinata bacteria, nitrite-oxidizing bacteria (NOB), and ammonia-oxidizing bacteria (AOB)/archaea (AOA) were studied. NNRs and NPs were significantly higher (p < 0.05) in fresh cow-dung vermicompost (stored for 40days) as compared with other organic manure. The level of PTEs (Cu2+, Fe2+, Pb2+, Cd2+, and Zn2+) was significantly lower (p < 0.05) in vermicompost as compared with compost of waste material with Trichoderma and cow dung. Comammox N. inopinata, NOB, AOB, and AOA were significantly higher (p < 0.05) in stored cow-dung vermicompost (more than 1year) as compared with other organic manure. The results of the scatterplot matrix analysis suggested that Fe2+, total nitrogen (TN), soil organic carbon (SOC), and total carbon (TC) were linearly correlated (p < 0.001) with NNRs and NPs in vermicompost and organic manure. Similarly, comammox N. inopinata bacteria, NOB, AOB, and AOA were linearly correlated (p < 0.001) with NNR and NP. These results indicated that vermicompost promoted nitrification activity by increasing microbial diversity and abundance, supplying nutrients and organic matter for microbial growth, and facilitating complex microbial interactions. It may be concluded that the influence of vermicompost, which played a great role in PTE concentration reduction, increased chemical, and biological properties, increased the growth rate of nitrifying bacteria/archaea and the nitrogen cycle.

Dietary nitrate supplementation and cognitive health: the nitric oxide-dependent neurovascular coupling hypothesis.

Diet is currently recognized as a major modifiable agent of human health. In particular, dietary nitrate has been increasingly explored as a strategy to modulate different physiological mechanisms with demonstrated benefits in multiple organs, including gastrointestinal, cardiovascular, metabolic, and endocrine systems. An intriguing exception in this scenario has been the brain, for which the evidence of the nitrate benefits remains controversial. Upon consumption, nitrate can undergo sequential reduction reactions in vivo to produce nitric oxide (•NO), a ubiquitous paracrine messenger that supports multiple physiological events such as vasodilation and neuromodulation. In the brain, •NO plays a key role in neurovascular coupling, a fine process associated with the dynamic regulation of cerebral blood flow matching the metabolic needs of neurons and crucial for sustaining brain function. Neurovascular coupling dysregulation has been associated with neurodegeneration and cognitive dysfunction during different pathological conditions and aging. We discuss the potential biological action of nitrate on brain health, concerning the molecular mechanisms underpinning this association, particularly via modulation of •NO-dependent neurovascular coupling. The impact of nitrate supplementation on cognitive performance was scrutinized through preclinical and clinical data, suggesting that intervention length and the health condition of the participants are determinants of the outcome. Also, it stresses the need for multimodal quantitative studies relating cellular and mechanistic approaches to function coupled with behavior clinical outputs to understand whether a mechanistic relationship between dietary nitrate and cognitive health is operative in the brain. If proven, it supports the exciting hypothesis of cognitive enhancement via diet.

Use of anaerobic digestate to substitute inorganic fertilisers for more sustainable nitrogen cycling

Fertiliser applications significantly contribute to agricultural greenhouse gas emissions. While crop yields and quality depend on the type and amount of chemical fertiliser supplied, there are limitations to fertiliser use, as continuous application of inorganic fertilisers can negatively affect soil fertility and result in mineral leaching. Organic fertiliser produced by Anaerobic Digestion (AD) of sewage waste (AD digestate) has been proposed as a substitute for chemical fertilisers. To investigate the potential for the use of AD digestate in pasture systems, grassland field trials were conducted on three independent farm enterprises in Ireland. AD digestate and chemical fertilisers were applied separately or in various combinations and the effects on soil mineral content, grass yield and quality compared. The analyses revealed significant improvement of soil nitrification activity along with improved fodder yield and quality. In particular, digestate application increased crude protein content of fodder by up to 22.8 % compared to fodder from plots without digestate application, that had up to 14.8% crude protein. The increase could be attributed to the white clover percentage increase from 2% (no AD digestate) to up to 31% on plots where AD digestate was applied. Strikingly, grass yields were 1.5-2-fold higher than the five-year national average (of 59.7 ± 4 kg DM/ha/day) on the plots where AD digestate was applied, either alone or in combination with chemical fertilisers. The results of this study highlight the potential of AD digestate application as a more sustainable alternative to inorganic fertilisers in grass-based pasture systems.

Exploration of the nitrification process in surface sediment of a hypereutrophic intertidal zone via hydroxylamine monitoring

Hydroxylamine is considered an indicator of nitrification, as it is both produced and consumed during the ammonium (NH4+) oxidation process. In this study, to explore the site of active nitrification and elucidate the factors controlling nitrification, hydroxylamine concentrations in the seawater and porewater of the hypereutrophic Yatsu tidal flat, eastern Japan, were measured using the iodine oxidation method with a Sep-Pak C18 cartridge. The concentrations over approximately 2 years indicated that nitrification was more active in the surface sediment than in seawater. This would support denitrification in the surface sediment via active nitrification–denitrification, which removes N. In addition, multiple linear regression analysis indicated that the concentration in porewater was positively correlated with the seawater parameters of nitrate (NO3−) concentration, NH4+ concentration, and temperature, while among porewater parameters, it was negatively correlated with the phosphate (PO43−) concentration and positively correlated with the NH4+ concentration. These relationships between hydroxylamine concentration and environmental factors suggest that porewater nitrification increases with higher temperature and NH4+ supply from seawater and porewater, as well as under oxic conditions. Our results demonstrate that hydroxylamine is a useful indicator of sediment nitrification in the hypereutrophic intertidal zone.

氮磷添加下典型温带、亚热带森林土壤氮循环功能基因丰度和微生物群落属性数据集

Nitrogen (N) and phosphorus (P) are essential nutrients for soil microbial growth and activities. There are notable differences in the concentrations of N and P and the characteristics of microbial communities observed between temperate and subtropical forests soils, and this is also true for soil vertical profiles. As a consequence of the rise in global atmospheric N deposition, soil nutrient imbalances and P limitation are increasingly aggravated in eastern China. However, there is a lack of systematic dataset showing how N deposition and P addition affect soil N cycling microbes and soil physicochemical properties in eastern China; hence a comprehensive dataset is needed to a better understanding of the impact of N deposition and P addition on soil nitrogen cycle. This dataset is constructed based on the field experimental setup in the forests of Chinese Ecosystem Research Network (CERN). To obtain a systematic dataset on N-cycling microbial communities, we conducted measurements and collected data of soil N-cycling functional genes abundance, N-cycling microbial community diversities and compositions and enzyme activities in three typical forests with N and/or P additions. We collected 0-10 cm top soils from a temperate forest (Changbai Mountain) and two subtropical forests (Qianyanzhou and Dinghu Mountain) with field N and/or P additions, and the soils along 0-80 cm vertical profiles without nutrient additions. The N-cycling functional genes involved in the datasets cover ammonia oxidizing archaea amoA, ammonia oxidizing bacteria amoA, nirK, nirS, nosZ, qnorB, narG, nir, nifH and chiA. The potential activities included in the datasets cover nitrification activity, denitrification activity, nitrogen fixation activity and organic nitrogen decomposition enzyme activity. The datasets also include soil physiochemical properties, including soil pH, moisture content, N2O emission, net nitrification rate and the concentrations of organic carbon, NH4+ , NO3− , available phosphorus, total nitrogen, total carbon, total phosphorus and dissolved organic carbon. The creation and sharing of the datasets can provide data and support for understanding the microbial mechanisms of soil N-cycling and the modelling processes under the scenario of aggravated N deposition and P addition. The datasets will also provide support for forest management efforts with regard to greenhouse gas N2O emission, N and nutrient loss in forest ecosystems.