Rate Of NO Research Articles

Comprehensive characterization of differential glycation in hepatocellular carcinoma using tissue proteomics with stable isotopic labeling.

Glycation is anon-enzymatic posttranslational modification coming from the reaction between reducing sugars and free amino groups in proteins, where early glycation products (fructosyl-lysine, FL) and advanced glycation end products (AGEs) are formed. The occurrence of glycation and accumulation of AGEs have been closely associated with hepatocellular carcinoma (HCC). Here, we reported the characterization of differential glycation in HCC using tissue proteomics with stable isotopic labeling; early glycation-modified peptides were enriched with boronate affinity chromatography (BAC), and AGEs-modified peptides were fractionated with basic reversed-phase separation. By this integrated approach, 3717 and 1137 early and advanced glycated peptides corresponding to 4007 sites on 1484 proteins were identified with afalse discovery rate (FDR) ofno more than 1%. One hundred fifty-five sites were modified with both early and advanced end glycation products. Five early and 7 advanced glycated peptides were quantified to be differentially expressed in HCC tissues relative to paired adjacent tissues. Most (8 out of 10) of the proteins corresponding to the differential glycated peptides have previously been reported with dysregulation in HCC. The results together may deepen our knowledge of glycation as well as provide insights for therapeutics.

Clinicopathological characteristics and BRCA1/BRCA2 pathogenic variants ofpatients with breast cancer.

Although BRCA genes are well-known breast cancer genes, theclinicopathological features ofbreast cancer patients carrying BRCA1/2 pathogenic variants have not been adequately defined. Thegoals ofthis study were to determine thedistribution ofBRCA1/2 variants in theTurkish population and its correlation with clinicopathological features. Clinical data of151 women who underwent BRCA1/2 gene testing at Mersin University Medical Faculty Hospital between 2016 and 2019 were retrospectively analyzed. BRCA1/2 variants were detected as pathogenic (n = 11), variants ofuncertain significance (n = 5), likely benign (n = 3), and benign (n = 81) in breast cancer cases. TheBRCA1/2 pathogenic variant carriers had ahigher histological grade, rate oftriple- negative type, Ki-67 proliferation index, and rate ofno special type carcinoma than thegroup without mutation (p = 0.03, 0.01, 0.04, and 0.02 respectively). We analyzed thedistribution ofvariants we detected in women living in our region and found that pathogenic variants in patients with breast cancer were associated with high histological grade, triple-negative type, high Ki-67 proliferation index, and histological type. Studies in diverse populations are needed to establish aclinicopathological relationship with variants more easily.

Isotope constraints on nitrogen dynamics in the upper water column of the South China Sea

The supply of nitrogen (N) from various external and internal sources into the euphotic zone, e.g., atmospheric N deposition (AND), upwelling, lateral intrusion, and remineralization, modulates the biogeochemical and climatic roles of oligotrophic oceans and complicates N dynamics in the upper water column (≤200 m). However, our ability to resolve the mechanisms controlling upper-ocean N cycling is limited by the lack of high-resolution vertical observations. Here, we analyzed concentrations and dual isotopes of nitrate (NO3–) in the upper 200 m of the oligotrophic South China Sea. By examining dual isotopic signatures of NO3– (δ15NNO3 and δ18ONO3) and multiple associated parameters vertically throughout the upper water column, we resolved the dominant N sources and processes, including AND/N2-fixation, assimilative fractionation, and nitrification, and quantitatively evaluated their contributions in the vertical distribution of NO3–, which can be separated into the Δδ18ONO3-positive (δ18ONO3−obs−δ18ONO3−200m>0) and Δδ18ONO3-negative layers (δ18ONO3−obs−δ18ONO3−200m<0) according to the deviation in δ18ONO3 at a given depth (δ18ONO3-obs) from that at 200 m (δ18ONO3-200m). In the Δδ18ONO3-positive layer, the NO3– assimilated by phytoplankton was largely sourced from nitrification (39 ± 11%) and AND/N2 fixation (17-28%), whereas these two processes accounted for 17 ± 10% and 7 ± 6% of the total NO3– pool in the Δδ18ONO3-negative layer. Considering a substantial contribution of the regenerated (nitrification-sourced) NO3– to the total NO3– pool especially in the Δδ18ONO3-positive layer, caution should be taken that the new production assessed by the rates of NO3– uptake may be significantly overestimated in the SCS. These findings not only highlight the importance of these biogeochemical processes to NO3– dynamics in the upper water column of marginal seas, but also with important implications for the estimation of biological carbon pump and/or the f-ratio.

Application of 15N tracing and bioinformatics for estimating microbial-mediated nitrogen cycle processes in oil-contaminated soils

Crude oil pollution can profoundly alter the nitrogen (N) cycle in the soil. Here, a 30-day incubation with 15N tracer approach was performed to assess the impacts of crude oil concentrations (medium: 10,000 mg kg−1; heavy: 50,000 mg kg−1) on soil N cycling based on a numerical model. Results showed that crude oil pollution significantly increased the gross N-transformation rates, but the rates of oxidation of recalcitrant organic N, the immbolization of NO3− and the adsorption of NH4+ changed differently as a function of hydrocarbon concentrations. There was no significant difference of the oxidation rate of recalcitrant organic N between the medium and heavy oil-contaminated soils (medium: 0.1149 mmol N kg−1 d−1; heavy: 0.1299 mmol N kg−1 d−1), but the rates of NO3− immobilization (0.1135 mmol N kg−1 d−1) and NH4+ adsorption were the highest (0.1148 mmol N kg−1 d−1) in the moderately oil-contaminated soils than those in the heavy polluted soil (0.0849 mmol N kg−1 d−1 and 0.0034 mmol N kg−1 d−1, respectively). The NO3− immobilization rate was 2.5-fold higher than its reduction rate, indicating that NO3− immobilization played a more important role during the process of NO3− transformation. Microbial community structure analysis indicated that phyla of Actinobacteria and Ascomycota respectively promoted the immobilization of NO3− to recalcitrant organic N and the reduction of NO3− to NH4+. The genus of Aspergillus was related to net NH4+ production, and the genera of Penicillium and Acremonium were responsible for oxidation of recalcitrant organic N to NO3−.

Effects of oxygen fertilization on damage reduction in flooded snap bean (Phaseolus vulgaris L.)

Flooding is one of the major abiotic stresses for vegetable production in Florida. Hydroponic and pot trials were conducted with snap bean to evaluate the effects of oxygen fertilization on the biochemical and physiological status of flooded snap bean plants. There were three treatments in the hydroponic trials were: (1) flooded (control), (2) bubble aeration with ambient air, and (3) hydrogen peroxide (H2O2) applied at the beginning of the trial. Plant health was evaluated by determining nitrogen (N) and phosphorus (P) uptake rates. The greenhouse pot trials were used to quantify the effects of three different application rates of solid oxygen fertilizers as calcium peroxide (CaO2) and magnesium peroxide (MgO2). The results showed that plant N and P uptake rates were significantly greater (p < 0.05) with H2O2 than without H2O2. The N uptake rates with H2O2 were like that of those with bubbling. The uptake rate of NH4+ was significantly greater than that of NO3− with the bubbling and H2O2 conditions, but the uptake rate of NO3− was significantly greater than that of NH4+ in the flooding condition. The plant height, leaf greenness, shoot biomass, and yield were all significantly greater with CaO2 or MgO2 than without either solid oxygen fertilizer. The minimum damage of flooded snap bean was found with 2 g CaO2 or 4 g MgO2 per pot. These results indicated that oxygen fertilization may potentially improve yield of flooded snap bean plants.

Plants with an ammonium preference affect soil N transformations to optimize their N acquisition

Our understanding of how plants influence the gross rates of specific soil N transformations in plant-soil systems is still rudimentary, providing the incentive for our current study. A 15N tracing study was carried out with plants known for their NH4+-preference to quantify the gross soil N transformation and gross plant N uptake rates. Significant interactions between plants and gross rates of soil N transformations were observed. The rates of NH4+ uptake by sugarcane (3.74 mg N kg−1 d−1) and tea (3.34 mg N kg−1 d−1) were much higher than microbial NH4+ immobilization rates (0.01, and 0.27 mg N kg−1 d−1, respectively), suggesting that NH4+-preferring plants outcompeted microbial NH4+ acquisition. The gross rates of NO3− immobilization increased with decreasing gross NH4+ immobilization rates, indicating a switch towards microbial NO3− uptake under high plant NH4+ demand. Moreover, the gross rates of autotrophic nitrification, the classical NO3− production pathway, was generally low in the studied acidic soil (average 0.40 mg N kg−1 d−1 in plant treatments), and was insufficient to meet the total NO3− demand (average 2.37 mg N kg−1 d−1). Gross rates of heterotrophic nitrification, ranging from 0.31 to 0.57 mg N kg−1 d−1, were stimulated by the presence of plants and were generally responsible for 49–69% of total NO3− production in the plant treatments, while this rate was negligible in the absence of plant. Heterotrophic nitrification might provide additional NO3− to meet N requirements of plants and microorganisms. This is supported by the positive correlation of gross heterotrophic nitrification coupled with gross NO3− immobilization and plant N uptake rates. Interactions between plant N acquisition and soil N transformations exist and plant-soil studies are key to identify feedbacks between plants and soil microbes.

Quantifying the nitrogen isotope effects during photochemical equilibrium between NO and NO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;: implications for &amp;lt;i&amp;gt;δ&amp;lt;/i&amp;gt;&amp;lt;sup&amp;gt;15&amp;lt;/sup&amp;gt;N in tropospheric reactive nitrogen

Abstract. Nitrogen isotope fractionations between nitrogen oxides (NO and NO2) play a significant role in determining the nitrogen isotopic compositions (δ15N) of atmospheric reactive nitrogen. Both the equilibrium isotopic exchange between NO and NO2 molecules and the isotope effects occurring during the NOx photochemical cycle are important, but both are not well constrained. The nighttime and daytime isotopic fractionations between NO and NO2 in an atmospheric simulation chamber at atmospherically relevant NOx levels were measured. Then, the impact of NOx level and NO2 photolysis rate on the combined isotopic fractionation (equilibrium isotopic exchange and photochemical cycle) between NO and NO2 was calculated. It was found that the isotope effects occurring during the NOx photochemical cycle can be described using a single fractionation factor, designated the Leighton cycle isotope effect (LCIE). The results showed that at room temperature, the fractionation factor of nitrogen isotopic exchange is 1.0289±0.0019, and the fractionation factor of LCIE (when O3 solely controls the oxidation from NO to NO2) is 0.990±0.005. The measured LCIE factor showed good agreement with previous field measurements, suggesting that it could be applied in an ambient environment, although future work is needed to assess the isotopic fractionation factors of NO+RO2/HO2→NO2. The results were used to model the NO–NO2 isotopic fractionations under several NOx conditions. The model suggested that isotopic exchange was the dominant factor when NOx&gt;20 nmol mol−1, while LCIE was more important at low NOx concentrations (&lt;1 nmol mol−1) and high rates of NO2 photolysis. These findings provided a useful tool to quantify the isotopic fractionations between tropospheric NO and NO2, which can be applied in future field observations and atmospheric chemistry models.

Nitrate reduction pathways and interactions with iron in the drainage water infiltration zone of a riparian wetland soil

Eutrophication of natural water bodies is moderated by transformation of nitrate (NO3−) in riparian wetlands, which serve as filters of infiltrating drain water from upland agricultural areas. The present study comprised field observations, laboratory experiments and metagenomic studies to describe NO3− removing transformation pathways and interactions with the cycling of iron (Fe) in a temperate riparian wetland soil profile down to 1 m depth. Water samples from piezometers showed a distinct plume of NO3− in the subsurface soil where agricultural drain water was infiltrating. However, within a distance of few meters in the water flow direction, NO3− was depleted from the percolating water. Sampling and analyses of soil from the active zone of the biogeochemical NO3− removal showed that denitrifying enzyme activity was ~ tenfold higher in the upper 0–25 cm than in the lower 25–100 cm. Yet, net transformation of NO3− was substantial also at 25–100 cm when assayed with relatively undisturbed soil samples and by 15N tracer techniques in soil slurries. Transformation pathways of dissimilatory nitrate reduction to ammonium and anaerobic ammonium oxidation were identified, but were quantitatively minor as compared to denitrification. Heterotrophic denitrification and denitrification mediated by oxidation of ferrous iron, Fe(II), were identified as important processes in the wetland soil. The latter was substantiated by geochemical observations, by rates of NO3− depletion in slurry incubations with added FeCl2, and by identification of microorganisms with known capacity of NO3− reduction coupled to Fe(II) oxidation (Acidovorax sp.). The transformation pathway of iron-mediated NO3− reduction could involve biotic and abiotic reactions, and N2O, which is a potent greenhouse gas, was a major product of the process. It remains to be seen under field conditions if N2O emission hotspots are linked to specific sites of dynamic NO3− reduction coupled to Fe(II) oxidation.

Oxidative Repair of Pyrimidine Cyclobutane Dimers by Nitrate Radicals (NO3•): A Kinetic and Computational Study

Pyrimidine cyclobutane dimers are hazardous DNA lesions formed upon exposure of DNA to UV light, which can be repaired through oxidative electron transfer (ET). Laser flash photolysis and computational studies were performed to explore the role of configuration and constitution at the cyclobutane ring on the oxidative repair process, using the nitrate radical (NO3•) as oxidant. The rate coefficients of 8–280 × 107 M−1 s−1 in acetonitrile revealed a very high reactivity of the cyclobutane dimers of N,N’-dimethylated uracil (DMU), thymine (DMT), and 6-methyluracil (DMU6-Me) towards NO3•, which likely proceeds via ET at N(1) as a major pathway. The overall rate of NO3• consumption was determined by (i) the redox potential, which was lower for the syn- than for the anti-configured dimers, and (ii) the accessibility of the reaction site for NO3•. In the trans dimers, both N(1) atoms could be approached from above and below the molecular plane, whereas in the cis dimers, only the convex side was readily accessible for NO3•. The higher reactivity of the DMT dimers compared with isomeric DMU dimers was due to the electron-donating methyl groups on the cyclobutane ring, which increased their susceptibility to oxidation. On the other hand, the approach of NO3• to the dimers of DMU6-Me was hindered by the methyl substituents adjacent to N(1), making these dimers the least reactive in this series.

Spiralling curve characterization of nitrate-nitrogen absorption in a channel at a rural-urban ecotone in Northeast China.

To determine the dynamic change characteristics of NO3-N in a rural-urban ecotone channel, five tracer tests were conducted in the Dongda Channel in the suburbs of Changchuan city, Jilin province, China, from October 2016 to April 2017. NaBr was used as conservative tracer and KNO3 served as an added nutritive salt. The kinetic features of NO3-N were simulated via the addition of tracers and by employing the spiralling curve characterization approach and the Michaelis-Menten (M-M) equation. The average absorption length of NO3--N background concentration (Sw-amb) is 199m, which is much less than the discharge channel length (2.5km), thereby suggesting that the channel has a strong NO3-N retention potential. Moreover, the M-M equation fits well the kinetic features of NO3-N adsorption. The average maximum absorption rate and subsaturation constant are 631μg(m2s)-1 and 1.46mgL-1, respectively. The correlation analysis reveals that Sw-amb and NO3--N absorption rates (NO3-Namb) are significantly negatively correlated whereas the absorption rates of NO3--N background concentration (Uamb) and NO3-Namb are significantly positively correlated. The other spiralling indices show faint correlations with the background concentration of NO3-N. Meanwhile, the hydrological factors slightly influence NO3-N retention, but the geomorphic features of the channel, including (width residual) Фw and (cross-sectional area residual) ФA, have significant correlations with most spiralling indices, thereby highlighting the relatively important roles of geomorphic features in NO3-N retention.

Effects of fumigation with 1,3-dichloropropene on soil enzyme activities and microbial communities in continuous-cropping soil

The compound 1,3-D (1,3-dichloropropene) is a potential candidate soil fumigant due to the restrictions on methyl bromide (MB). To date, little is known about the soil microbial community changes induced by 1,3-D fumigation. Therefore, soil properties, related soil enzymes, genes encoding the key enzymes of ammonia oxidation in both ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) and bacterial diversity were investigated to assess the effects of 1,3-D fumigation on the soil microbial community. The results exhibited that fumigation with 1,3-D caused accumulation of NH4+-N, but it led to decrease in the rate of NO3--N, and the concentration of NO3--N gradually recovered. At 12 weeks after transplant (WAT) of tomato seedlings, the concentration of NH4+-N and NO3--N were not statistically significant between the 1,3-D treatment groups and the untreated control group. A similar tendency was found for organic matter, soil pH, urease and protease activities. Moreover, quantitative real-time PCR (qPCR) showed that 1,3-D decreased total bacterial abundance, AOA-amoA and AOB-amoA genes. In addition, Illumina MiSeq sequencing analysis revealed that soil bacterial community diversities were significantly reduced at earlier sampling time points, and at later sampling time points, soil bacterial diversity gradually recovered, there was no significant difference compared to the control group. The present study provides useful information to evaluate the environmental safety of 1,3-D.

System-level model and experiments for irrigation water alkalinity reduction and enrichment using an atmospheric pressure dielectric barrier discharge

The treatment of distilled water with varying amounts of dissolved sodium bicarbonate (representing alkalinity) is considered using an atmospheric pressure electrical discharge. The discharge ignited between a capillary tube (used as powered electrode) and a ground electrode wrapped around the beaker holding the treated water consists of streamers propagating in ambient air and striking the water surface. The streamer interaction with water is shown to lead to a decrease in pH and an increase in nitrate concentration. The pH variation with time is shown to be similar to a titration curve for acid-base neutralization with final pH values around 3 for 22 min of treatment. The nitrate ion concentration increase with time is consistent with a two-rate system-level model that is characterized by two asymptotic rates for NO3− creation by the plasma. The two asymptotic rates are calibrated to be about 2.7 μmol/min and 22.5 μmol/min with the transition between the two rates occurring at the breakeven time that is representative of the time required for all dissolved bicarbonate to be consumed by the plasma treatment. The increase in rate of NO3− creation at the breakeven time is attributed to the increase in conductivity of the treated solution once all bicarbonate is consumed thereby modifying the plasma properties. Another system-level model that is based on the observed pH variation is also considered for comparison with measured data. While both system-level models have some discrepancies with the measurements, the two-rate model based on the nitrate ion concentration is concluded to be more useful for determining the NO3− formation rates in the context of irrigation water enrichment. The discrepancies are attributed to the simplicity of the system-level models considered here where the effect of the plasma is completely represented by the creation of just one chemical species in HNO3 thereby neglecting potentially important species such as HNO2 and H2O2. Nevertheless, the proposed system-level model could greatly assist in the design of plasma treatment systems with specified alkalinity, pH and nitrate ion levels for irrigation water.

Long-Term Effects of Tourmaline on Nitrogen Removal from Wastewater and Bacterial Community Shift in Activated Sludge at Low Temperatures

In this study, the long-term effects of ultrafine tourmaline particles (UTPs) on the removal of nitrogen in wastewater, activated sludge viability and microbial population dynamics at low temperatures were investigated. Although there was no significant effect on the effluent concentrations of nitrogen after long-term exposure to 1 g/L UTPs at low temperatures, the oxidation rate of NH4+-N and the accumulation rate of NO2−-N increased and the formation rate of NO3−-N decreased during the aerobic phase of sequencing batch reactors. However, long-term exposure to 1 g/L UTPs did not significantly affect the microbial community richness and the community diversity of activated sludge at low temperatures. The mechanism of tourmaline was studied by assessing the dominant functional species involved in biological nitrogen removal from wastewater. It was found that 1 g/L UTPs increased the removal rate of nitrogen by reducing the relative abundance of nitrite oxidizing bacteria and increasing the relative abundance of ammonia oxidizing bacteria after long-term operation at low temperatures.

Soil N transformation mechanisms can effectively conserve N in soil under saturated conditions compared to unsaturated conditions in subtropical China

The connection between moisture and nitrogen (N) transformation in soils is key to understanding N losses, particularly nitrate (NO3−) losses, and also provides a theoretical framework for appropriate water management in agricultural systems. Thus, we designed this study to provide a process-based background for management decision. We collected soil samples from the long-term field experiment in subtropical China, which was designed to examine tobacco and rice rotations under a subtropical monsoon climate. The field experiment was established in 2008 with four treatments: (1) no fertilization as control; (2) N, phosphorus (P), and potassium (K) fertilizers applied at recommended rates; (3) N fertilizers applied at rates 50% higher than the recommended amounts and P and K fertilizers applied at recommended rates; and (4) N, P, and K fertilizers applied at recommended rates with straw incorporated (NPKS). Soil samples were collected during the unsaturated tobacco-cropping season and saturated rice-cropping season and were incubated at 60% water holding capacity and under saturated conditions, respectively. Two 15N tracing treatments (15NH4NO3 and NH415NO3) and a numerical modeling method were used to quantify N transformations and gross N dynamics. Autotrophic nitrification was stimulated by N fertilizer both under unsaturated and saturated conditions. The rate of NO3− consumption (via immobilization and denitrification) increased under the NPKS treatment under saturated conditions. Secondly, the rates of processes associated with ammonium (NH4+) cycling, including mineralization of organic N, NH4+ immobilization, and dissimilatory NO3− reduction to NH4+, were all increased under saturated conditions relative to unsaturated conditions, except for autotrophic nitrification. Consequently, NO3−-N and NH4+-N concentrations were significantly lower under saturated conditions relative to unsaturated conditions, which resulted in reduced risks of N losses via runoff or leaching. Our results suggest that under saturated conditions, there is a soil N conservation mechanism which alleviates the potential risk of N losses by runoff or leaching.

The effect of peach-soybean intercropping system with straw mulching on N and P losses, surface runoff in Dianchi Lake watershed mountain area, Yunnan province, China

Field experiments were conducted with peach (local variety)-soybean intercropping system as an agro-forestry community. The results showed that the reduction rate of CODcr losses were 24.31%, 50.50% and 65.19% respectively under the precipitation strength between 25mm d-1 and 100 mm d-1 with treatments of 36 kg plot-1, 54 kg plot-1 and 72 kg plot-1 straw mulching. The reduction rate of NH4+-N losses were 12.56%, 49.38% and 58.60%, respectively; The reduction rate of NO3--N losses were 27.78%, 9.55% and 58.61%, respectively; The reduction rate of TN losses were 3.85%, 31.67% and 56.01%, respectively. The reduction rate of TP losses were 23.02%, 30.19% and 42.65%, respectively. The yields of soybean increased by 24.09%, 47.46% and 93.84%, respectively. Peach-soybean intercropping with straw mulching could decrease the runoff losses of nitrogen and phosphorus with time effect for reducing non-point sources pollution losses.

Mechanisms behind the stimulation of nitrification by N input in subtropical acid forest soil

Input of N as NH4 + is known to stimulate nitrification and to enhance the risk of N losses through NO3 − leaching in humid subtropical soils. However, the mechanisms responsible for this stimulation effect have not been fully addressed. In this study, an acid subtropical forest soil amended with urea at rates of 0, 20, 50, 100 mg N kg−1 was pre-incubated at 25 °C and 60 % water-holding capacity (WHC) for 60 days. Gross N transformation rates were then measured using a 15N tracing methodology. Gross rates of mineralization and nitrification of NH4 +-N increased (P < 0.05), while gross rate of NO3 − immobilization significantly decreased with increasing N input rates (P < 0.001). A significant relationship was established between the gross nitrification rate of NH4 + and the gross mineralization rate (R 2 = 0.991, P < 0.01), so was between net nitrification rate of NH4 + and the net mineralization rate (R 2 = 0.973, P < 0.05). Stimulation effect of N input on the gross rate of nitrification of NH4 +-N in the acid soil, partially, resulted from stimulation effect of N input on organic N mineralization, which provides pH-favorable microsites for the nitrification of NH4 + in acid soils (De Boer et al., Soil Biol Biochem 20:845–850, 1988; Prosser, Advan Microb Physiol 30:125–181, 1989). The stimulated gross nitrification rate with the decreased gross NO3 − immobilization rate under the elevated N inputs could lead to accumulation of NO3 − and to enhance the risk of NO3 − loss from humid forest soils.

Sustaining reactivity of Fe0 for nitrate reduction via electron transfer between dissolved Fe2+ and surface iron oxides

The mechanism of the effects of Fe2+aq on the reduction of NO3− by Fe0 was investigated. The effects of initial pH on the rate of NO3− reduction and the Fe0 surface characteristics revealed Fe2+aq and the characteristics of minerals on the surface of Fe0 played an important role in NO3− reduction. Both NO3− reduction and the decrease of Fe2+aq exhibited similar kinetics and were promoted by each other. This promotion was associated with the types of the surface iron oxides of Fe0. Additionally, further reduction of NO3− produced more surface iron oxides, supplying more active sites for Fe2+aq, resulting in more electron transfer between Fe2+ and surface iron oxides and a higher reaction rate. Using the isotope specificity of 57Fe Mossbauer spectroscopy, it was verified that the Fe2+aq was continuously converted into Fe3+ oxides on the surface of Fe0 and then converted into Fe3O4 via electron transfer between Fe2+ and the pre-existing surface Fe3+ oxides. Electrochemistry measurements confirmed that the spontaneous electron transfer between the Fe2+ and structural Fe3+ species accelerated the interfacial electron transfer between the Fe species and NO3−. This study provides a new insight into the interaction between Fe species and contaminants and interface electron transfer.

Short-term water stress affecting NO3− absorption by almond plants

Identifying the rates of nitrate absorption by almond plants under water stress is important for improving nitrogen use efficiency in almond orchards. This study aimed to determine the rates of nitrate absorption by almond plants subjected to short-term water stress and no water stress, and the kinetic NO3− absorption parameters in well-watered three-year-old almond plants. Two assays were performed. In the first, fourteen plants arranged in completely randomized design received nutrient solutions with water potentials (Ψw) of 0.0, −0.2, −0.4 and −0.7MPa and containing 1.2mmoll−1 KNO3. We accessed the NO3− depletion in these solutions over an 8-h interval and estimated regression curves of the quantity of nitrate in the nutrient solution (Q) as a function of time (t). Subsequently nitrate uptake rates were calculated. Water loss; nitrate reductase activity; nitrate and total N of the sap; nitrate concentration of leaf dry matter; and nitrate and nitrite concentration of root dry matter were, either, evaluated. The second assay was performed the same way of the first one, with four well-watered plants submitted to 0.3mmoll−1 KNO3 as initial concentration, and allowed estimating NO3− absorption parameters Vmax, Km and Cmin. We observed a linear decrease in the nitrate content of the containers receiving 1.2mmoll−1 of NO3− over a period of 8h. In this concentration, the rates of NO3− uptake ranged from 1.11 to 3.43μmolg−1h−1 and decreased in low water potentials at the root medium. Root nitrate reductase activity followed the same trend of nitrate absorption. In the low NO3− concentration range, the absorption showed a Michaelis–Menten pattern, being the kinetic parameters of NO3− absorption 1.15±0.27μmolg−1h−1, 28.81±4.12μmoll−1 and 17.93±1.1μmoll−1 for Vmax, Km, and Cmin, respectively. We concluded that NO3− uptake of almonds is affected by short periods of water stress, with harmful effects occurring at Ψw below −0.18MPa.

Nitrogen cycling in canopy soils of tropical montane forests responds rapidly to indirect N and P fertilization.

Although the canopy can play an important role in forest nutrient cycles, canopy-based processes are often overlooked in studies on nutrient deposition. In areas of nitrogen (N) and phosphorus (P) deposition, canopy soils may retain a significant proportion of atmospheric inputs, and also receive indirect enrichment through root uptake followed by throughfall or recycling of plant litter in the canopy. We measured net and gross rates of N cycling in canopy soils of tropical montane forests along an elevation gradient and assessed indirect effects of elevated nutrient inputs to the forest floor. Net N cycling rates were measured using the buried bag method. Gross N cycling rates were measured using (15) N pool dilution techniques. Measurements took place in the field, in the wet and dry season, using intact cores of canopy soil from three elevations (1000, 2000 and 3000m). The forest floor had been fertilized biannually with moderate amounts of N and P for 4years; treatments included control, N, P, and N+P. In control plots, gross rates of NH4 (+) transformations decreased with increasing elevation; gross rates of NO3 (-) transformations did not exhibit a clear elevation trend, but were significantly affected by season. Nutrient-addition effects were different at each elevation, but combined N+P generally increased N cycling rates at all elevations. Results showed that canopy soils could be a significant N source for epiphytes as well as contributing up to 23% of total (canopy+forest floor) mineral N production in our forests. In contrast to theories that canopy soils are decoupled from nutrient cycling in forest floor soil, N cycling in our canopy soils was sensitive to slight changes in forest floor nutrient availability. Long-term atmospheric N and P deposition may lead to increased N cycling, but also increased mineral N losses from the canopy soil system.

Denitrification, anammox and nitrate reduction in sediments of the southern Great Barrier Reef lagoon

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 478:57-70 (2013) - DOI: https://doi.org/10.3354/meps10040 Denitrification, anammox and nitrate reduction in sediments of the southern Great Barrier Reef lagoon Dirk V. Erler*,1, Lindsay A. Trott2, Daniel M. Alongi2, Bradley D. Eyre1 1Centre for Coastal Biogeochemistry, School of Environmental Science and Management, Southern Cross University, Lismore NSW 2480, Australia. 2Australian Institute of Marine Science, PMB 3, Townsville MC QLD 4810, Australia *Email: dirk.erler@scu.edu.au ABSTRACT: We provide the first reported estimates of anammox activity in tropical continental shelf sediments (southern section of the Great Barrier Reef lagoon; GBRL). The measured contribution of anammox to total N2 production was up to 70% but restricted to only 1 of the 4 (2 inshore and 2 offshore) sites assayed. Sediment characteristics (contents of total organic carbon [TOC] and manganese [Mn], C:N ratio) at this site appeared to favour anammox activity and the estimated maximum rate was 4.9 µmol m-2 h-1. Anammox bacteria may be a significant contributor to N2 production along the coastal zone of the GBRL. The availability of labile (low C:N) TOC seemed to drive denitrification to completion in the offshore sediments. However, rates of NO3- reduction to NH4+ at the offshore sites were comparable to or higher than denitrification rates. It was unclear whether dissimilatory or assimilatory processes were responsible for the observed reduction of NO3- to NH4+ at the offshore sites. At the 2 inshore sites, NO3- reduction to NH4+ was a larger sink for NO3- than denitrification. Anammox does exist in the tropical continental shelf sediments of the GBRL and should be studied further to determine its role in larger scale N cycling. The roles of assimilatory and dissimilatory nitrate reduction to ammonium also need to be assessed within the GBRL. KEY WORDS: Great Barrier Reef · Anammox · Dissimilatory/assimilatory nitrate reduction to ammonia · Denitrification Full text in pdf format PreviousNextCite this article as: Erler DV, Trott LA, Alongi DM, Eyre BD (2013) Denitrification, anammox and nitrate reduction in sediments of the southern Great Barrier Reef lagoon. Mar Ecol Prog Ser 478:57-70. https://doi.org/10.3354/meps10040 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 478. Online publication date: March 25, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.