Nitrogen Fractions Research Articles

Analysis of complex changes in salmon salting by injection using the food additive PRE-LACKS

The paper presents the results of a comprehensive assessment of the quality of delicacy fish products - salmon fillets of weak salt made using the food additive PRE-LACKS (LLC "Vash technologist", St. Petersburg, Russia) and curing by injection. For the first time, the influence of technological factors has been studied (the concentration of a food additive (in the range recommended by the manufacturer from 3 to 5 % with a step of 1 %), as well as the value of the hydromodulus (in the range from 5 to 20 % with a step of 5 %) characterizing the ratio of masses of the fillet introduced into the thickness when injecting brine and a salted fillet piece) on the formation of a complex indicator of the finished product quality. The developed scale for a comprehensive assessment of the quality (K) of lightly salted salmon fillet of injection salting is presented, including the main groups of indicators - organoleptic and rheological, nutritional value and physico-chemical. The scale includes weighting coefficients based on the results of experimental and sensory studies - both group and for each quality indicator taken into account. It has been shown that using the fuzzy logic method made it possible to obtain the values of the selected influencing factors optimized according to the criterion of achieving the maximum value of K (in the range from 0.9 to 1.0 conventional units, corresponding to the category "delicacy product") - the concentration of the food additive and the value of the hydromodulus - 4 and 15 %, respectively. The results of assessing the influence of selected technological factors on the yield of a semi-finished product immediately after salting by injection, on the yield of finished low-salted products (after ripening), on indicators characterizing the completeness of its maturation (buffering, the ratio of the mass fraction of non-protein nitrogen to the mass fraction of total nitrogen, total acidity, mass fraction of amine nitrogen) have been presented. Based on the results of the research, technological recommendations are formulated for salting salmon by injection using the PRE-LACKS food additive to increase the yield of finished products and improve its consumer properties.

Distribution Characteristics and Source Analysis of Nitrogen and Phosphorus in Different Rivers in Two Water Period: A Case Study of Pi River and Shiting River in the Upper Reaches of Tuo River in China.

In this paper, the distribution characteristics of total nitrogen (TN), total phosphorus (TP) and fractions of nitrogen and phosphorus in water and surface sediments of the Pi and Shiting rivers in the dry and wet seasons were studied by molybdenum blue/ascorbic acid spectrophotometry and Standard Measurements and Testing (SMT). Correlation analysis, cluster analysis and principal component analysis were used to identified nitrogen and phosphorus pollution sources. The results showed that: (1) nitrogen and phosphorus in water and surface sediments in the study area were at different levels. (2) In the Pi river, the decomposition of animal and plant residues, the leachate from the accumulation of aquaculture wastewater and urban domestic sewage were the main sources of nitrogen and phosphorus pollution, while in the Shiting river, the unreasonable application of pesticides and fertilizers, the degradation of animal and plant residues, agricultural wastewater from agricultural drainage channels, industrial production wastewater and the weathering of agricultural wastes had a great impact on the nitrogen and phosphorus pollution. The results in this study provide reliable experimental data and a reference to local relevant departments for the implementation of effective control measures for the reduction of the nitrogen and phosphorus pollution load in the river basin.

Cover crops and N fertilization affect soil ammonia volatilization and N2O emission by regulating the soil labile carbon and nitrogen fractions

Introducing cover crops in monocropping systems to improve soil health has been broadly adopted worldwide. However, the impacts of different cover cropping systems on soil emissions and related soil fractions and their regulatory mechanism remain elusive. In this study, four cropping systems, i.e., relay intercropping with Orychophragmus violaceus L./cotton (OvC), Vicia villosa Roth/cotton (VvC), a cover crop mixture (Ov and Vv)/cotton (MSC) and a fallow field–cotton (FFC) system, were combined with four N application rates in a two-rotation cycle (2019–2021) to evaluate the effects on soil greenhouse gases (GHGs) emission, ammonia (NH3) volatilization, and labile carbon (C) and nitrogen (N) fractions and their relationships. Compared with the FFC system, the cumulative NH3 volatilization and nitrous oxide (N2O) emissions of OvC are noticeably reduced 13% and 58%, respectively, and those of VvC are comparable, while those of MSC are markedly increased by 15% and 24%, respectively. N fertilization significantly affects soil NH3 volatilization and N2O emissions, and a higher N rate results in more gaseous N emissions. In addition, NH3 volatilization and N2O emission are positively correlated with the soil microbial biomass N (MBN), dissolved organic N (DON), NH4+-N and NO3--N but negatively correlated with microbial biomass C (MBC) and dissolved organic C (DOC). OvC system decreased gaseous N emission by high soil MBC/MBN ratio, Vv as cover crop indirectly promote soil N2O emission through increased soil MBN, DON and MBC content, while cover crop mixtures increase soil labile C and N fractions and enhance gaseous N emission ultimately. Overall, application of N fertilizer and cover crop mixture both promoted soil NH3 and N2O emissions; the relay intercropping nonlegume cover crop Ov noticeably mitigates N2O and NH3 emissions through an increase in the soil MBC and reduce in the labile N, while introduction of the legume cover crop Vv increases N2O emissions but reduces soil NH3 volatilization due to a lower soil MBC/MBN ratio.

Model analysis of multiple breath nitrogen washout data: robustness to variations in breathing pattern.

We recently developed a model-based method for analyzing multiple breath nitrogen washout data that does not require identification of Phase-III. In the present study, we assessed the effect of irregular breathing patterns on the intra-subject variabilities of the model parameters. Nitrogen fraction at the mouth was measured in 18 healthy and 20 asthmatic subjects during triplicate performances of multiple breath nitrogen washout, during controlled (target tidal volume 1 L at 8-12 breaths per minute) and free (unrestricted) breathing. The parameters Scond, Sacin and functional residual capacity (FRC) were obtained by conventional analysis of the slope of Phase-III. Fitting the model to the washout data provided functional residual capacity (FRCM), dead space volume (VD), the coefficient of variation of regional specific ventilation ([Formula: see text]), and the model equivalent of Sacin (Sacin-M). Intra-participant coefficients of variation for the model parameters for both health and asthma were FRCM < 5.2%, VD < 5.4%, [Formula: see text] < 9.0%, and Sacin-M < 45.6% for controlled breathing, and FRCM < 4.6%, VD < 5.3%, [Formula: see text] < 13.2%, and Sacin-M < 103.2% for free breathing. The coefficients of variation limits for conventional parameters were FRC < 6.1%, with Scond < 73.6% and Sacin < 49.2% for controlled breathing and Scond < 35.0% and Sacin < 74.4% for free breathing. The model-fitting approach to multiple breath nitrogen washout analysis provides a measure of regional ventilation heterogeneity in [Formula: see text] that is less affected by irregularities in the breathing pattern than its corresponding Phase-III slope analysis parameter Scond.

Experimental and numerical study of the liquid nitrogen accumulator based on two-phase thermal stratification

Accurate control and rapid regulation of the liquid nitrogen supplying pressure are the basis for the total temperature operation of the cryogenic wind tunnel. The pressure evolution during the discharging process and external pressurization in an accumulator are measured experimentally. The thermal boundary conditions of the tank during the test are mathematically obtained with the consideration of frosting and convective heat transfer. A numerical framework of two-phase flow based on the volume of fluid (VOF) and the heat and mass transfer model is carried out. The computed results with the accommodation coefficient of β = 10−6 in the Lee model are closer to the measured values than using the original value of 0.1, and the laminar model is more suitable for the numerical study of the gas-liquid transfer in the tank than the turbulent model. The growing dynamic process of gas-liquid interface and temperature distribution during the entire test is achieved. Thermal stratification is formed though the coming liquid nitrogen is highly subcooled. The liquid level has not been stable immediately but grows slowly when the pressure reaches the set value. The simulated temperature evolution, distribution, and the final volume fraction of gaseous nitrogen are satisfactorily consistent with the experiments. The results show that the numerical model can simulate the complex heat and mass transfer characteristics inside the cryogenic accumulator and provide theoretical guidance for injection pressure control.

Effects of refrigerated storage on the functional properties of processed cheese analogue with stretchability and its mechanisms

The functionality changes of processed cheese analogue with stretchability during refrigerated storage (0–60 d) at 4 °C were explored and the possible mechanisms were investigated. The results showed that stretchability, meltability, and free oil release of the cheese analogue decreased during refrigerated storage, and stretch length decreased from >270 cm to 130.63 ± 8.24 cm after refrigerated storage. Furthermore, the pH 4.6-soluble nitrogen fractions, soluble calcium and phosphorus, and the fraction of bound water of the cheese analogue significantly increased during refrigerated storage, while the β-casein and the fraction of free water decreased. The microstructure results showed that the whey channel disappeared while the proteins were swollen and squeezed and deformed the fat globules over refrigerated time. In conclusion, the functionality changes of the cheese analogue during refrigerated storage occurred under the compound effects of proteolysis and hydration of protein as well as dissolution of bound calcium.

Effects of nitric acid rain stress on soil nitrogen fractions and fungal communities in a northern subtropical forest, China

Acid rain has severely negatively impacted terrestrial ecosystems and biogeochemical cycles. However, the potential impacts of nitric acid rain (NAR) on soil nitrogen (N) fractions and fungal community diversity in northern subtropical forest soils remain largely unevaluated. In this study, treatments of NAR at pH = 4.5 (AR4.5), pH = 3.5 (AR3.5), and pH = 2.5 (AR2.5) were randomly sprayed in a typical Quercus acutissima Carruth. stand in northern subtropical China. The soil N fractions and soil fungal communities were analyzed after a 12-month experimental period. The results revealed that compared to the control, the soil total N (TN), microbial biomass N (MBN), hydrolysable ammonium N (HAN), amino-sugar N (ASN) and amino-acid N (AAN) contents decreased significantly by 19.61–13.07 %, 20.10–9.04 %, 60.41–28.87 %, 74.10–62.25 %, and 65.69–45.64 % under stronger acidity inputs (i.e., AR2.5 and AR3.5), respectively. Besides, the AR2.5 and AR3.5 treatments increased the α-diversity indices of soil fungal communities and altered the soil fungal community structure. Moreover, the NAR treatments represented an increase in the relative abundance of Ascomycota and Mortierellomycota and a decrease in that of Basidiomycota. Mortierella, Penicillium, and Tomentella can be used as indicator genera for changes in soil fungal community structures under NAR stress. Furthermore, AAN was the main environmental factor affecting soil fungal community at the phylum and genus levels. Cumulatively, findings from this research provide valuable insight into NAR's effects on N cycling and microbial communities in forest soils.

A model‐based estimate of nitrate leaching in Germany for GHG reporting

AbstractBackgroundConversion of leached and runoff nitrate (NO3–) from agricultural land into emissions of the greenhouse gas (GHG) nitrous oxide (N2O) by denitrification in water bodies has to be reported in national GHG inventories. The global IPCC default methodology for estimating these indirect N2O emissions assumes that a fixed fraction of nitrogen (N) inputs (Fracleach) is lost through leaching and runoff. However, this method does not consider all relevant country‐specific conditions that may influence NO3– leaching.AimsThe aim of this study was to apply a model‐based approach for estimating indirect N2O emissions through NO3– leaching and runoff from agricultural soils for use in Germany's national GHG inventory.MethodsHigh‐resolution spatial data and a comprehensive model system (RAUMIS‐mGROWA‐DENUZ) were used to derive regionally differentiated and temporarily dynamic Fracleach values from N surplus and hydrogeological conditions. These were then used to estimate indirect N2O emissions in accordance with the IPCC methodology.ResultsThe nationwide average of the new implied Fracleach values was 0.099 kg N (kg N input)−1 in 2019. The new estimate of indirect N2O emissions was 10.4 Gg N2O in 1990 and 5.7 Gg N2O in 2019, which are 27 and 52% less than the calculation based on the 2006 IPCC Tier 1 methodology.ConclusionsThe model‐based method for estimating Fracleach incorporates relevant factors that influence NO3– leaching and runoff and considers site‐specific, spatially varying conditions and differences in the agrarian structure. The use of N surplus as the model driver allows annual changes in cropping conditions and the effects of N‐regulating policies and mitigation measures to be represented.

Fermentation profile, aerobic stability, chemical and mineral composition of silages of mango combined with cocoa pod husk meal

The objective was to evaluate the fermentation profile, aerobic stability, chemical composition, and mineral content of silages of mango combined with cocoa pod husk meal. A completely randomized design was adopted, including four levels (65, 70, 75, and 80%) and five repetitions, totaling 20 experimental silos that were opened after 90 days of sealing. Increasing mango levels in the silages increased the dry matter recovery, total carbohydrates, and fraction B2 of carbohydrates, and reduced gas losses, dry matter, and mineral matter. The quadratic effect was found for pH, buffering capacity, potassium, boron, iron, and nitrogen fractions A and B1 + B2. Using unconventional products such as mango combined with cocoa pod husk meal for silage making can reduce the cost of food supplementation for ruminants, and the environmental contamination.

Traceability of insects as feed: stable isotope ratio analysis of Hermetia illucens larvae and pre-pupae reared on different protein sources

Insects attract the interest of the agri-food sector because of their advantages as feed for livestock. The reason for this lies in the role of insects as alternative protein source to soybean and fish meal, common but expensive materials, and in their ability to proliferate on waste substrates, thus allowing a sustainable livestock management. Insects for feed purposes can however be problematic, in particular with regard to the safety of the substrates the insects would be reared on. Therefore, effective tracking methods are needed. This study focused on the investigation, by means of isotope ratio mass spectrometry, of larvae and pre-pupae of Hermetia illucens L. (black soldier fly (BSF)) reared on diets including protein sources of vegetable origin (wheat gluten), animal origin (bovine blood meal), or a combination of the two, in order to detect differences in their isotope ratios for δ13C and δ15N. Nitrogen isotopic ratios did not follow an incremental pattern between diets, thus not allowing the discrimination of the BSF larvae and pre-pupae, presumably due to differences in the metabolism of insects that could have influenced the fractionation of nitrogen. In the case of the carbon isotopic ratio an increasing trend was observed, directly correlating the carbon isotopic signature of BSF larvae and pre-pupae to the level of replacement of the vegetable protein source with the animal one. According to our observations, it is therefore foreseeable that the study of carbon isotope ratios could be a promising method for the traceability of insects intended for animal feeding. Given the paucity of studies in this regard, further research effort is needed to fully explain some observation reported in the present study and to ascertain the reliability of the ratio analysis of insects as a tool for tracing their feeding history.

Combined livestock grazing-exclusion and global warming decreases nitrogen mineralization by changing soil microbial community in a Tibetan alpine meadow

Alpine meadows play a key role in maintaining biodiversity, soil nutrient retention, and herders’ livelihoods in mountain regions. Livestock grazing-exclusion is common in grassland management to protect and promote the sustainable use of alpine meadows. However, there are few studies evaluating the effects of traditional light grazing practices in alpine regions and grazing-exclusion impacts on soil nutrient, especially under conditions of climate warming. In this study, we conducted a five-year grazing-exclusion and warming manipulation experiment to examine the effects of grazing-exclusion on soil nitrogen fractions, microbial communities, and enzyme activities under climate warming. Treatments consisted of light-intensity grazing, grazing-exclusion, and combined grazing-exclusion and warming. Our results showed that grazing-exclusion significantly decreased potential nitrogen mineralization at a 0–5 cm depth and at altitudes of 3850 m, 4000 m, 4150 m, and 4250 m. Combined grazing-exclusion and warming also significantly decreased potential nitrogen mineralization at a 0–5 cm depth and at relatively higher altitudes of 4000 m, 4150 m, and 4250 m. Grazing-exclusion, combined grazing-exclusion and warming all shifted microbial communities from bacteria toward fungi. Grazing-exclusion significantly decreased the relative abundances of phylum Chloroflexi (bacteria) and phylum Ascomycota (fungi), while combined grazing-exclusion and warming significantly increased the relative abundances of phylum Basidiomycota (fungi). The relative abundances of phylum Ascomycota (fungi) demonstrated a positive relationship with potential nitrogen mineralization, but the relative abundances of phylum Basidiomycota (fungi) had a negative relationship with potential nitrogen mineralization. The activities of dehydrogenase and protease in grazing-exclusion and combined grazing-exclusion and warming meadows were lower than those in grazed meadows. Our results demonstrated that in the context of climate change and global warming, grazing-exclusion is unsuitable as a tool for the sustainable management of alpine meadows from soil nitrogen mineralization and fractions point of view. Of concern, climate warming could potentially amplify the adverse effects of grazing-exclusion and causes depletion of soil nutrients in the alpine meadow. This research suggests that a light-intensity grazing (0.5 yak ha−1 year−1) is beneficial to increase soil enzyme activity and N mineralization in alpine meadows. Our results provide substantial evidence and a useful baseline and guidance for the sustainable grazing management of alpine meadows as environments change due to climate warming in the future.

Phosphorus addition regulates the growth of Chinese fir by changing needle nitrogen fractions in growing and dormant seasons

Forest productivity is generally limited by nutrient scarcity. This study aims to reveal seasonal interactions among leaf carbon (C), nitrogen (N) fractions and tree growth driven by nutrient addition in a subtropical forest. Here, a field nutrient addition experiment was conducted with six treatments, namely, +N5 (5 g N m−2 yr−1), +N10 (10 g N m−2 yr−1), +P5 (5 g P m−2 yr−1), +N5 + P5, +N10 + P5, and control (N0 + P0). C fractions (structural and non-structural carbohydrates) and N fractions (soluble N, nucleic N and protein N) in needles as well as tree growth indicated by basal area increment (BAI) were measured in growing and dormant seasons. Total N and protein N in old needles were significantly increased by P addition, while no significant differences of non-structural carbohydrates in young (<1-year old) and old needles (>1-year old) were detected among the treatments in both seasons. N and P addition increased the structural carbohydrates of old needles in dormant season. P addition decreased and increased tree growth in growing and dormant seasons, respectively. The variation of BAI was explained 18.3 % by total N and 17.8 % by protein N in growing season, and was explained 33.9 % by total N and 34.2 % by protein N in dormant season. Our study suggested that the P addition effect on Chinese fir growth mostly depends on needle N fractions. This study highlights tree seasonal growth driven by nutrient alteration might be characterized by leaf N fractions rather than C fractions in subtropical forests.

Dissolved organic nitrogen derived from wastewater denitrification: Composition and nitrogenous disinfection byproduct formation

Microbially derived dissolved organic nitrogen (mDON) is a major fraction of effluent total nitrogen at wastewater treatment plants with enhanced nutrient removal, which stimulates phytoplankton blooms and formation of toxic nitrogenous disinfection by-products (N-DBPs). This study identified denitrifiers as major contributors to mDON synthesis, and further revealed the molecular composition, influential factors and synthetic microorganisms of denitrification-derived mDON compounds leading to N-DBP formation. The maximum mDON accumulated during denitrification was 8.92% of converted inorganic nitrogen, higher than that of anammox (4.24%) and nitrification (2.76%). Sodium acetate addition at relatively high C/N ratio (5−7) favored mDON formation, compared with methanol and low C/N (1−3). Different from acetate, methanol-facilitated denitrification produced 13–69% more lignin-like compounds than proteins using Orbitrap LC-MS. The most abundant N-DBPs formed from denitrification-derived mDON were N-nitrosodibutylamine and dichloroacetonitrile (13.32 μg/mg mDON and 12.21 μg/mg mDON, respectively). Major amino acids, aspartate, glycine, and alanine were positively correlated with typical N-DBPs. Biosynthesis and degradation pathways of these N-DBP precursors were enriched in denitrifiers belonging to Rhodocyclaceae, Mycobacteriaceae and Hyphomicrobiaceae. As intensive disinfection is applied at worldwide wastewater treatment plants during COVID-19, carbon source facilitated denitrification should be better managed to reduce both effluent inorganic nitrogen and DON, mitigating DON and N-DBP associated ecological risks in receiving waters.

Optimizing resource recovery from wastewater with algae-bacteria membrane reactors

Exploiting the combination of algae and bacteria in High Rate Algal/Bacterial Ponds (HRABP) is an emerging approach for wastewater remediation and resource recovery. In this study, the advantage of adding a solid/liquid separation system to uncouple Hydraulic Retention Time (HRT) and Solid Retention Time (SRT) is explored and quantified. A long-term validated model for HRABP was run to simulate and optimize a system at large scale treating digestate. It is shown that by uncoupling HRT and SRT, adapting the liquid depth and the alkalinity content, the algae productivity increases from 9.0 to 14.5 g m−2 d−1 (for HRT = SRT in the range of 5 to 10 days) to 20.3 g m−2 d−1 (for HRT = 0.2 d and SRT = 2 d). Simulations pointed out that maximizing the algal productivity or the fraction of recovered nitrogen in the algal biomass are conflicting goals that are achieved under different operating conditions. Conditions maximising the algal productivity favour algae and heterotrophic bacteria while algae and nitrifying bacteria dominate the system under those conditions optimizing the efficiency of nitrogen recycling. Finally, increasing the influent alkalinity and adapting the water depth can boost the algal productivity without meeting conditions favourable to N2O emission, opening new perspectives for resource recovery through algal biomass valorisation.

Nitrogen fractionation towards a pre-stellar core traces isotope-selective photodissociation

Context. Isotopologue abundance ratios are important to understand the evolution of astrophysical objects and ultimately the origins of a planetary system such as our own. With nitrogen being a fundamental ingredient of pre-biotic material, understanding its chemistry and inheritance is of fundamental importance to understand the formation of the building blocks of life. Aims. We aim to study the 14N/15N ratio in HCN, HNC, and CN across the prototypical pre-stellar core L1544. This study allows us to test the proposed fractionation mechanisms for nitrogen. Methods. We present here single-dish observations of the ground state rotational transitions of the 13C and 15N isotopologues of HCN, HNC, and CN with the IRAM 30 m telescope. We analyse their column densities and compute the 14N/15N ratio map across the core for HCN. The 15N fractionation of CN and HNC is computed towards different offsets across L1544. Results. The 15N-fractionation map of HCN towards a pre-stellar core is presented here for the first time. Our map shows a very clear decrease in the 14N/15N ratio towards the southern edge of L1544, where carbon chain molecules present a peak, strongly suggesting that isotope-selective photodissociation has a strong effect on the fractionation of nitrogen across pre-stellar cores. The 14N/15N ratio in CN measured towards four positions across the core also shows a decrease towards the south-east of the core, while HNC shows the opposite behaviour. We also measured the 12CN/13CN ratio towards four positions across the core. Conclusions. The uneven illumination of the pre-stellar core L1544 provides clear evidence that 15N fractionation of HCN and CN is enhanced towards the region more exposed to the interstellar radiation field. Isotope-selective photodissociation of N2 is then a crucial process to understand 15N fractionation, as already found in protoplanetary disks. Therefore, the 15N fractionation in pre-stellar material is expected to change depending on the environment within which pre-stellar cores are embedded. The 12CN/13CN ratio also varies across the core, but its variation does not affect our conclusions as to the effect of the environment on the fractionation of nitrogen. Nevertheless, the interplay between the carbon and nitrogen fractionation across the core warrants follow-up studies.

Effect of transformed sunflower husk on enzymatic processes in the rumen &lt;I&gt;in vitro&lt;/I&gt;

Fermentation processes in the rumen of ruminants when using sunflower husk subjected to ultrasound treatment in combination with phytobiotics were studied. During the experiment, the formation of terminal metabolites in the ruminal fluid as well as the formation of methane were determined. The object of the study was the rumen fluid, which was selected from bulls of Kazakh whiteheaded breed at the age of 12 months with the average weight of 230-235 kg. Chronic rumen fistula (n = 3) was identified according to the method of A.A. Aliev. The following samples were incubated by in vitro method using the ANKOM Daisy II device (modifications D200 and D200I) according to a specialized technique: control (sample N 1): Mechanically ground husk + hydromodulus (water) + ultrasound treatment at 20 °C, 15 min, 27 kHz; sample N 2: sample N 1 + gamma-octalactone (0.25 ml); sample N 3: sample N 1 + quercetin (10.0 mg); sample N 4: sample N 1 + 7-hydroxycoumarin (2.0 mg). Each experiment was conducted in five replications. The digestibility of dry matter, concentration of volatile fatty acids, formation of nitrogenous metabolites and methane concentration were determined. The data obtained were statistically analyzed using software. New data were obtained on the effect of sunflower husk together with phytobiotics on the formation of final metabolites in the rumen fluid. The addition of biologically active substances of gamma-octalactone, quercetin, 7-hydroxycoumarin was found to increase the digestibility of dry matter relative to control by 2.0 (p ≤ 0.05), 3.1 (p ≤ 0.01) and 4.3% (p ≤ 0.05), respectively. An increase in the concentration of volatile fatty acids and nitrogenous fractions was noted when using these substances. The level of methane concentration was 10% lower than that of the control with 7-hydroxycoumarin in sample N 4 (p ≤ 0.01).

Decomposition of soil organic matter by ectomycorrhizal fungi: Mechanisms and consequences for organic nitrogen uptake and soil carbon stabilization

A major fraction of nitrogen (N) in boreal forest soils is found in organic forms associated with soil organic matter (SOM) and mineral particles. The capacity of ectomycorrhizal (ECM) fungal symbionts to access this N is debated, considering that these fungi have lost many of the genes for decomposing organic matter that were present in their saprotrophic ancestors. To gain a molecular-level understanding of the N-mining processes in ECM fungi, we developed an experimental approach where the processes of decomposition were studied in parallel with the changes in the structure and properties of the organic matter. We showed that ECM fungi have significant capacities to assimilate organic N associated with SOM and mineral surfaces. The decomposition mechanisms differ between species, reflecting the lignocellulose decomposition mechanisms found in their saprotrophic ancestors. During N-mining, the ECM fungi processed the SOM to a material with increased adsorptive properties to iron oxide mineral particles. Two pathways contributed to these changes: Extracellular modifications of the SOM and secretion of mineral surface reactive metabolites. Some of these metabolites have iron(III)-reducing activities and can participate in extracellular Fenton reactions and redox reactions at iron oxide mineral surfaces. We conclude that the traditional framework for understanding organic N acquisition by ECM fungi from recalcitrant SOM must be extended to a framework that includes how those decomposition activities affect the stabilization and reactivity of mineral-associated SOM. The activity through these complex networks of reactions is decisive for the overall effect of ECM fungal decomposition on nutrients and C-cycling in forest ecosystems.

Physiological Studies and Ultrastructure of Vigna sinensis L. and Helianthus annuus L. under Varying Levels of Nitrogen Supply.

This experiment was conducted to investigate the effects of different nitrogen fertilizers (potassium nitrate and/or urea) on shoot parameters, relative growth rate, net assimilation rate, and nitrogen fractions, as well as to conduct transmission electron microscopy, of Vigna sinensis L. (cowpea) and Helianthus annuus L. (sunflower) leaves. A general improvement was recorded in the shoot parameters of the two plants, except for a decrease in the net assimilation rate by treatment of the two plants with 100% potassium nitrate plus 100% urea. The total nitrogen, insoluble protein, and total soluble nitrogen generally decreased in cowpea shoots from the treatments but increased in case of cowpea roots and sunflower shoots and roots. The examination of the ultrastructure changes in cowpea leaves confirmed the presence of two starch granules (in response to 100% potassium nitrate, 100% potassium nitrate plus 100% urea, and the control) and three granules (in response to 50% potassium nitrate plus 50% urea) and the disappearance of the starch granules (in response to 100% urea). Despite the starch granules not being detected in the leaves of the untreated sunflower, the treated plant showed the appearance of the highest number after treatment with 50% potassium nitrate plus 50% urea (2) and the most cell size with the 100% potassium nitrate treatment. Generally, our findings demonstrated that fertilization with 50% potassium nitrate plus 50% urea has the best influence on the growth parameters and nitrogen content in the two plants, but the magnitude of response was more pronounced in case of cowpea plants.

Eco-Stoichiometric Characteristics of Rhizosphere and Bulk Soils of Smilax china L. along Vertical Zone Spectrum of Fanjing Mountain.

To explore the correlations between nutrients and stoichiometric characteristics in the rhizosphere and bulk soils of understory Smilax china L. in forest ecosystems at different altitudes and to clarify the rhizosphere effect of understory vegetation in forest ecosystems and its response strategy to altitude, providing a theoretical basis for better forest ecological environment protection and high-quality development in Fanjing Mountain. Understory Smilax china L. at four different altitudes were selected, with the differences and influencing factors of carbon (C), nitrogen (N), phosphorus (P) and potassium (K) mass fractions and stoichiometric ratios in their rhizosphere and bulk soils analyzed. The average mass fractions of total C, total N and alkali-hydrolyzed N in the rhizosphere and bulk soils of Smilax china L. at different altitudes were 224.43 and 181.55 g·kg−1; 9.56 and 6.81 g·kg−1; and 648.19 and 600.70 g·kg−1, respectively. The rhizosphere effect of Smilax china L. was significant at altitudes of 500 m and 1000 m but became not so prominent with the rise of altitude. The C:N ratio in the rhizosphere and bulk soils ranged from 19.51 to 39.75 and the C:P ratio ranged from 225.29 to 543.05. C accumulation is greater than N accumulation in the rhizosphere and bulk soils of Smilax china L., and both present P limitation. Based on the comprehensive analysis of the mass fractions and eco-stoichiometric ratios of soil nutrients, the P limitation in Fanjing Mountain forest ecosystem is commonly seen and should be addressed.

Signal-enhanced Raman spectroscopy with a multi-pass cavity for quantitative measurements of formaldehyde, major species and temperature in a one-dimensional laminar DME-air flame

While Raman spectroscopy provides opportunities for simultaneous detection and quantitative analysis of multiple species, it also suffers from certain limitations, such as low signal strength, which often makes it unsuitable for the study of minor species. The present work employs a high-repetition-rate and high-power laser and re-introduces an amplification technique to improve the detection limit, providing an up to 45-time signal enhancement. The amplification is achieved by employing a multi-pass cavity, and different modes were tested and optimized for the measurements. This multi-pass setup has enabled the detection of formaldehyde (CH2O), which is present in stoichiometric dimethyl ether (DME)-air flames on a sub-percent level, and, therefore, known to be challenging to study with Raman spectroscopy. Furthermore, Raman cross-sections of CH2O and DME, which have not been reported in the literature to the authors’ knowledge, are obtained ab initio using Raman scattering activities in the literature. The cross-sections are 6.63 and 22.43, respectively, for CH2O and DME, normalized by the Raman cross-section of nitrogen. The CH2O detection limit in flame with was estimated to 40 ppm with the present experimental settings. Mole fractions of CH2O, nitrogen (N2), water (H2O), carbon dioxide (CO2), oxygen (O2), DME (CH3OCH3), carbon monoxide (CO), and hydrogen (H2) measured in the flame show good agreement when compared with modeling results obtained using two chemical kinetic mechanisms. Flame temperatures were evaluated from the N2 Raman signals, and the steep temperature gradient is successfully resolved experimentally with the multi-pass setup and well predicted by the models.