Nitrogen Fractions Research Articles

Harnessing Efficient ROS Generation in Carbon Dots Derived from Methyl Red for Antimicrobial Photodynamic Therapy.

The emergence of drug-resistant pathogenic microorganisms has become a public health concern, with demand for strategies to suppress their proliferation in healthcare facilities. The present study investigates the physicochemical and antimicrobial properties of carbon dots (CD-MR) derived from the methyl red azo dye. The morphological and structural analyses reveal that such carbon dots present a significant fraction of graphitic nitrogen in their structures, providing a wide emission range. Based on their low cytotoxicity against mammalian cells and tunable photoluminescence, these carbon dots are applied to bioimaging in vitro living cells. The possibility of using CD-MR to generate reactive oxygen species (ROS) is also analyzed, and a high singlet oxygen quantum efficiency is verified. Moreover, the antimicrobial activity of CD-MR is analyzed against pathogenic microorganisms Staphylococcus aureus, Candida albicans, and Cryptococcus neoformans. Kirby-Bauer susceptibility tests show that carbon dots synthesized from methyl red possess antimicrobial activity upon photoexcitation at 532 nm. The growth inhibition of C. neoformans from CD-MR photosensitization is investigated. Our results show that N-doped carbon dots synthesized from methyl red efficiently generate ROS and possess a strong antimicrobial activity against healthcare-relevant pathogens.

Combined model for 15N, 13C, and spin-state chemistry in molecular clouds

We present a new gas-grain chemical model for the combined isotopic fractionation of carbon and nitrogen in molecular clouds. To this end, we have developed gas-phase and grain-surface chemical networks where the isotope chemistry of carbon and nitrogen is coupled with a time-dependent description of spin-state chemistry, which is important for nitrogen chemistry at low temperatures. We updated the rate coefficients of some isotopic exchange reactions considered previously in the literature, and here we present a set of new exchange reactions involving molecules substituted in 13C and 15N simultaneously. We applied the model to a series of zero-dimensional simulations representing a set of physical conditions across a prototypical prestellar core, exploring the deviations of the isotopic abundance ratios in the various molecules from the elemental isotopic ratios as a function of physical conditions and time. We find that the 12C/13C ratio can deviate from the elemental ratio to a high factor depending on the molecule, and that there are highly time-dependent variations in the ratios. The HCN/H13CN ratio, for example, can obtain values of less than ten depending on the simulation time. The 14N/15N ratios tend to remain close to the assumed elemental ratio within approximately 10%, with no clearly discernible trends for the various species as a function of the physical conditions. Abundance ratios between 13C-containing molecules and 13C+15N-containing molecules however show somewhat increased levels of fractionation as a result of the newly included exchange reactions, though they still remain within a few tens of percent of the elemental 14N/15N ratio. Our results imply the existence of gradients in isotopic abundance ratios across prestellar cores, suggesting that detailed simulations are required to interpret observations of isotopically substituted molecules correctly, especially given that the various isotopic forms of a given molecule do not necessarily trace the same gas layers.

Synthesis of cellulose nitrates from Miscanthus × giganteus var. KAMIS cellulose obtained under pilot production conditions

The work is devoted to the study of a novel national raw material resource Miscanthus × Giganteus var. KAMIS, which is positioned as one of the most promising natural sources for obtaining high-quality cellulose for the purpose of its further chemical functionalisation. A batch of technical cellulose isolated from raw materials under pilot production conditions using the nitric acid method having a cellulose content of 50.2% was characterized by high α-cellulose mass fraction (92.8%) and degree of polymerisation (1200) values. On the basis of the pilot batch of technical cellulose, a sample of cellulose nitrates offering basic functional properties was obtained: mass fraction of nitrogen – 11.18%; viscosity – 48 MPa·s; solubility – 94%. The synthesised sample is characterized by extremely high solubility in acetone, confirming the production of cellulose nitric acid esters, and a high yield of 150%. IR-Fourier spectroscopy was used to identify the main functional groups in the experimental batch of technical cellulose (3384, 2902, 1639, 1428, 1370, 1319, 1161, 700–500 cm-1) and in a sample of cellulose nitrates (1659, 1278, 834, 746, 683 cm-1). Acorresponding affiliation to cellulose and cellulose nitric acid esters was established. The structural and morphological features of the fibres of the experimental batch of technical cellulose and a sample of cellulose nitrates were characterised using scanning electron microscopy. Combined methods of thermogravimetric and differential thermal analyses were used to establish high initial temperature (197 °C) and specific heat of decomposition (6.92 kJ/g) values at the beginning of intensive decomposition. The obtained results substantiate the possibility to chemically functionalise cellulose isolated from a new alternative source into cellulose nitric acid esters with satisfactory functional properties.

Contrasting effects of different organic amendments on the microbial responses to extreme temperature changes

Soil organic amendments can change microbial communities, potentially impacting their resilience to environmental stresses and, consequently, their transformation of soil carbon and nitrogen. While several studies have investigated the impact of a few organic amendments on microbial resilience to stresses in the form of absolute change in environmental conditions, the potential stress effects of different rates of change have received much less attention. The rate of change in environmental properties such as temperature may induce different microbial stress responses, given the reliance of microbial defensive mechanisms on time-dependent signalling and activation processes. In this research, we explored the relevance of the rate of temperature change as a microbial stressor and evaluated the potential use of organic amendments in steering soil ecological response. We monitored the changes in microbial properties and concentrations of different carbon and nitrogen fractions to temperature change treatments of 2.5 and 30 °C/d after the application of three commonly available rural organic amendments to a podzol soil in a laboratory incubation study. Results showed significant effects of the temperature treatments on bacterial and total microbial DNA concentrations, as well as on dissolvable and insoluble carbon and nitrogen ratios regardless of the organic amendment treatment. Temperature impacts on respiration rates, priming rates and the concentration of soil hot water extractable carbon and nitrogen differed depending on the organic amendment treatment. Results demonstrated that compost-amended soils were least sensitive to the temperature treatments, while grasses and fermented grasses treatments were generally more sensitive while showing opposite responses. Our findings indicate that organic amendments might be utilized to manipulate the impact of environmental stresses on soil carbon and nitrogen concentrations, and highlight the need for future research to investigate the relevant ecological properties and mechanisms.

Understanding the role of land use for urban stormwater management in coastal waterways

A holistic understanding of the quality and quantity of stormwater in the context of catchment land use plays a crucial role in stormwater management. This study investigated the quality and quantity of stormwater from forested, residential, industrial, and mixed land use areas. Water samples were collected from seven sites over two years at different stages of the runoff hydrograph using fixed sampling stations. Analysis of physicochemical and hydrological variables showed different patterns across the four land use types at various flow conditions highlighting the complex nature of stormwater quality influenced by catchment and rainfall characteristics. Mean concentrations of dissolved organic and oxidised nitrogen (DON and NOx-N) and dissolved organic and filterable reactive phosphorus (DOP and FRP) in stormwater from industrial, mixed-use and residential catchment types were statistically different from stormwater originating from a forested catchment. On average, residential, mixed-use and industrial catchments transported over 50 times more NOx-N to the receiving waters compared to forested catchments. Under high flow conditions, total phosphorus, FRP and total suspended solids (TSS) were mobilised, indicating that phosphorous export is directly related to sediment export regardless of the land use. The study outcomes contribute to the formulation of more effective stormwater management strategies to deal with the drivers of nutrients and TSS inputs resulting from modified land use types to minimise the urbanisation impacts on aquatic biota. In particular, the elevated dissolved nitrogen fractions from all the catchment types other than the forested catchment is a concern for receiving waters, as these can potentially impair water quality and impact the ecosystem health of downstream water bodies such as Intermittently Closed and Open Lakes or Lagoons (ICOLL). The stochastic nature of hydrology and corresponding nutrient loads should be prioritised in stormwater management action plans. However, as space limitations hinder the expansion of vegetation cover and retrofitting stormwater management devices, a paradigm shift in stormwater management is required to achieve the desired outcomes. The study outcomes further indicate that a one-size-fits-all approach to stormwater management may not deliver the desired outcomes, and a suite of tailor-made approaches targeting various flow conditions and catchment surface types is needed.

Carbon Stock, Carbon Fraction and Nitrogen Fraction of Soil Under Bamboo (Dendrocalamus asper Back.) and Non-Bamboo Vegetation

<span lang="EN-US">The type of vegetation and soil organic matter affect the carbon fraction, nitrogen fraction and soil carbon stocks that contribute to the global carbon cycle. Therefore, the calculation of the composition of the fractions in different land covers is very important as a potential indicator of the effect of land management practices on soil organic carbon dynamics and supports the reduction of carbon dioxide (CO<sub>2</sub>) and soil carbon storage. This research aimed to determine the composition of the carbon fraction, nitrogen fraction and soil carbon stock in different land cover. There were six types of land cover with vegetations of 10-year-old bamboo, 30-year-old bamboo, 50-year-old bamboo, bulrush, a mixture of brushwood and bulrush, and a mixture of <em>Albizia falcataria</em> and brushwood, each of which was sampled three times. Soil samples were used to determine microbial biomass, particulate organic, humic acid, fulvic acid and soil carbon stock. The six land cover types showed significant differences in all fractions and soil carbon stocks. Fifty-year-old bamboo vegetation has the highest carbon storage of 0.029 g g<sup>-1</sup> soil. The stable carbon fraction, in the form of humic acid and fulvic acid, in 50-year-old bamboo vegetation is more excellent than that in other vegetation. This study shows that 50-year-old bamboo vegetation has the potential to sequester carbon and store carbon in forms that decompose slowly, namely humic acid and fulvic acid, in the soil for a longer period.</span>

Erosion and deposition controlling redistribution and biodegradation of nitrogen fractions along a Mollisol agricultural landscape

Erosion and deposition controlling redistribution and biodegradation of nitrogen fractions along a Mollisol agricultural landscape

Assessment of an Oxidation Ditch's Performance via COD and Nitrogen Fractionation Analysis

The rapid population growth in the southern part of Quito, driven by the pursuit of material prosperity, has increased the production of wastewater, leading to discharges into water bodies and impacting water quality. In this context, characterizing wastewater is crucial for reliable operational decisions. This research evaluates the Quitumbe Wastewater Treatment Plant's bioreactor in relation to the fractionation of COD and nitrogen, considering the sludge age as a controlled variable. Wastewater samples were collected in March at the inlet and outlet points of the bioreactor, and a physicochemical method was used for COD fractionation. The results indicate a predominance of slowly biodegradable COD (XS) and removal rates of 95% for biodegradable COD and 93% for ammonia nitrogen, demonstrating biodegradation capacity. Incomplete nitrification was confirmed, along with a cellular retention time of 20 days. This study provides a solid foundation for improving the operational management of the Quitumbe Wastewater Treatment Plant.

Temperature, microbiological and chemical composition of broiler chickens’ excrement with litter after its composting with different doses of biodestructor

The rapid growth of production volumes of broiler chicken products both in our country and in most countries of the world is combined with an increase in industry waste. A significant percentage of this waste is poultry droppings with litter. In the absence of implemented technologies for rational disposal of broiler chicken droppings, economic and ecological problems arise locally. Considering the above, the search for effective methods of disposal of broiler chicken droppings is of scientific and practical importance. Composting poultry droppings with litter (sawdust of non-coniferous trees) can be an alternative method of rational disposal of this waste. To accelerate the fermentation of broiler litter, there is a practice of using various microbiological preparations. The effectiveness of using a biodestructor containing bacteria: Bacillus spp., Bacillus subtilis, Bacillus megatherium, Bacillus mesentericus, Bacillus mycoides during composting of broiler chicken excrement and its effect on the microbiological, chemical and physical parameters of fermented biomass remains unexplored. To conduct an experiment, 30 kg samples were formed from the excrement with the litter taken from the poultry house after broiler chickens had been reared for 42 days. In the control group, excrement samples were treated with water without a biodestructor. In the 1st, 2nd, and 3rd research groups, broiler chicken droppings were moistened with biodestructor solutions providing its doses of 143, 1430, and 2860 mg/t, respectively. Temperature and microbiological indicators were determined in the litter of broiler chickens during composting. In non-fermented litter of broiler chickens and litter composted for 150 days using a biodestructor, the crude protein content, mass fraction of Calcium, total Nitrogen and Phosphorus were determined. It has been established that the introduction of a biodestructor at a dose of 2860 mg/t of manure with a moisture content of 60.0 % leads to an increase in the activity of biochemical processes, which is confirmed by an increase in the temperature of the compost during the first hundred days of fermentation. The higher the dose of biodestructor was added to the litter of broiler chickens, the higher the KMAFAnM indicator and the numbers of Bacillus spp. bacteria in compost were higher. A regularity has been established that with the increase in the amount of biodestructor in the litter of broiler chickens, the number of Staphylococcus and Clostridium bacteria in the latter decreases. The use of a biodestructor at a dose of 2860 mg/t of broiler chicken droppings contributes to the increase of Nitrogen, crude protein, and Phosphorus in the compost and accelerates its mineralization compared to the control.

Long term conservation agriculture impact on soil nitrogen fractions and wheat (Triticum aestivum) yield in subtropical Inceptisol

The present study was carried out at ICAR-Indian Agricultural Research Institute (IARI), New Delhi over two consecutive years (2020 and 2021) to evaluate the influence of conservation agriculture (CA) and nitrogen management strategies on wheat yield in an intensified maize (Zea mays L.)-wheat (Triticum aestivum L.)-mungbean (Vigna radiata L.) cropping system. Results indicated that grain and straw yields of wheat in CA plots were higher, reaching 4829 and 7231 kg/ha, respectively. However, these yields were statistically comparable to those obtained from conventionally tilled plots (4502 and 6611 kg/ha, respectively). Significantly higher wheat grain and straw yields were observed in plots receiving nitrogen fertilizer. Interestingly, the harvest index remained unaffected by both tillage practices and nitrogen management strategies. After two seasons of wheat cultivation, CA plots had significantly higher soil nitrogen fractions, including mineral, alkali-permanganate, potentially mineralizable, microbial biomass N and total nitrogen, compared to conventionally tilled plots. Moreover, all nitrogen-receiving treatments demonstrated significantly higher nitrogen fractions at both soil depths (0–5 and 5–15 cm) compared to the control. Notably, plots treated with urea super granules exhibited superior results in enhancing plant-available nitrogen. In conclusion, this study underscores the importance of CA and various nitrogen management strategies for increasing wheat crop yield and promoting plant-available nitrogen fractions in the soil. These findings providevaluable insights for farmers and researchers looking for sustainable and efficient agricultural practices to optimize wheat production and soil health.

Changes of Soil Nitrogen Fractions and nirS-Type Denitrifier Microbial Community in Response to N Fertilizer in the Semi-Arid Area of Northeast China

The denitrification process is one of the important processes in the soil nitrogen (N) cycle, and is closely related to the loss of soil N fertilizer. Five treatments were included in this study: N0 (control, no N application); N90 (N application rate 90 kg ha−1); N150 (N application rate 150 kg ha−1); N210 (N application rate 210 kg ha−1); and N270 (N application rate 270 kg ha−1), to study the effect of different N application rates on the soil nirS-type denitrifying bacterial community structure, the influence of key enzyme activities during the denitrification process, and the main environmental factors affecting the variation of the denitrifying bacterial community in maize field soil under the mulched fertigation system in the semi-arid region of Northeast China. The results showed that increasing N fertilizer application significantly increased the contents of soil inorganic N and acid-hydrolyzable organic N, but significantly decreased pH. N fertilizer significantly increased nitrate reductase (NAR) activity and nitrite reductase (NIR) activity. Excessive application of N fertilizer significantly increased the nirS gene copy numbers, and, at the same time, significantly decreased the diversity of nirS-type soil denitrifying bacteria. Proteobacteria was the dominant denitrifying phylum in all treatments, and N application promoted the growth of Bradyrhizobium belonging to this phylum. The application of N fertilizer significantly changed the community structure of nirS denitrifying bacteria, and the NO3−-N content was the most important factor for this observation. Soil organic matter (SOM) and non-hydrolyzable N (NHN) indirectly affected the denitrifying bacterial community structure through NAR activity and NIR activity, while soil total N (TN) and nitrate N (NO3−-N) indirectly affected yield through denitrifying bacterial community structure. Although increasing N fertilizer was beneficial in increasing soil nutrients, the community structure of nirS-type denitrifying bacteria changed significantly. This is attributed to the increase in soil NO3−-N accumulation caused by a large amount of N application. The results of this research provide an important scientific basis for further research on the response mechanism of farmland soil denitrifying microorganisms to different N fertilizer managements under the mulched fertigation system in the semi-arid region of Northeast China.

Effects of endosperm type and storage length of whole-plant corn silage on nitrogen fraction, fermentation products, zein profile, and starch digestibility

Zeins are commercially important proteins found in corn endosperms. The objective of this study was to evaluate the effect of altering zein levels in corn inbred lines carrying endosperm mutations with differential allelic dosage and analyze the effects on the composition, nutritive value, and starch digestibility of whole-plant corn silage (WPCS) at 5 storage lengths. Three inbred lines carrying 3 different endosperm modifiers (opaque-2 [o2], floury-2 [fl2], and soft endosperm-1 [h1]) were pollinated with 2 pollen sources to form pairs of near-isogenic lines with either 2 or 3 doses of the mutant allele for each endosperm modifier. The experiment was designed as a split-plot design with 3 replications. Pollinated genotype was the main plot factor, and storage length was the subplot-level factor. Agronomic precautions were taken to mimic hybrid WPCS to the extent possible. Samples were collected at approximately 30% dry matter (DM) using a forage harvester and ensiled in heat-sealed plastic bags for 0, 30, 60, 120, and 240 d. Thus, the experiment consisted of 30 treatments (6 genotypes × 5 storage lengths) and 90 ensiling units (3 replications per treatment). Measurements included nutrient analysis, including crude protein, soluble crude protein, amylase-treated neutral detergent fiber, acid detergent fiber, lignin, starch, fermentation end products, zein concentration, and in vitro starch digestibility (ivSD). The nutritional profile of the inbred-based silage samples was similar to hybrid values reported in literature. Significant differences were found in fresh (unfermented) sample kernels for endosperm vitreousness and zein profiles between and within isogenic pairs. The o2 homozygous (3 doses of mutant allele) had the highest reduction in vitreousness level (74.5 to 38%) and zein concentration (6.2 to 4.7% of DM) compared with the heterozygous counterpart (2 doses of mutant allele). All genotypes showed significant reduction of total zeins and α-zeins during progressive storage length. In vitro starch digestibility increased with storage length and had significant effects of genotype and storage length but not for genotype by storage length interaction, which suggests that the storage period did not attenuate the difference in ivSD between near-isogenic pairs caused by zeins in WPCS. Both total zeins and α-zeins showed a strong negative correlation with ivSD, which agrees with the general hypothesis that the degradation of zeins increases ruminal starch degradability. Homozygous o2 was the only mutant with significantly higher ivSD compared with the heterozygous version, which suggests that, if all other conditions remain constant in a WPCS systems, substantial reductions in endosperm α-zeins are required to significantly improve ivSD in the silo.

Long‐term changes in soil carbon and nitrogen fractions in switchgrass, native grasses, and no‐till corn bioenergy production systems

AbstractCellulosic bioenergy is a primary land‐based climate mitigation strategy, with soil carbon (C) storage and nitrogen (N) conservation as important mitigation elements. Here, we present 13 years of soil C and N change under three cellulosic cropping systems: monoculture switchgrass (Panicum virgatum L.), a five native grasses polyculture, and no‐till corn (Zea mays L.). Soil C and N fractions were measured four times over 12 years. Bulk soil C in the 0–25 cm depth at the end of the study period ranged from 28.4 (± 1.4 se) Mg C ha−1 in no‐till corn, to 30.8 (± 1.4) Mg C ha−1 in switchgrass, and to 34.8 (± 1.4) Mg C ha−1 in native grasses. Mineral‐associated organic matter (MAOM) ranged from 60% to 90% and particulate organic matter (POM) from 10% to 40% of total soil C. Over 12 years, total C as well as both C fractions persisted under no‐till corn and switchgrass and increased under native grasses. In contrast, POM N stocks decreased 33% to 45% across systems, whereas MAOM N decreased only in no‐till corn and by less than 13%. Declining POM N stocks likely reflect pre‐establishment land use, which included alfalfa and manure in earlier rotations. Root production and large soil aggregate formation explained 69% (p < 0.001) and 36% (p = 0.024) of total soil C change, respectively, and 60% (p = 0.020) and 41% (p = 0.023) of soil N change, demonstrating the importance of belowground productivity and soil aggregates for producing and protecting soil C and conserving soil N. Differences between switchgrass and native grasses also indicate a dependence on plant diversity. Soil C and N benefits of bioenergy crops depend strongly on root productivity and pre‐establishment land use.

Carbon, nitrogen, and physical fractions of organic matter in recovered pastures of the Maranhense Amazon

In Maranhão State, Brazil, soils are naturally acidic, nutrient-deficient, and prone to cohesion and erosion. Removing the natural cover to establish pastures causes physical, chemical, and biological changes in the soil. Therefore, this study aimed to evaluate the contents and stocks of carbon (C), nitrogen (N), and particle-size fractions of soil organic matter (SOM) in pastures with different years of recovery, and compare them with a secondary forest in the Legal Amazon. Four treatments were evaluated: secondary forest, perennial pasture, and perennial pastures recovered for five years and eight years, both of the latter through corn + brachiaria intercropping. The contents and stocks of total organic carbon, total nitrogen, C, and N from the soil organic matter particle-size fractions, as well as the carbon management indexes (CMI) of the 0.00–0.10, 0.10–0.20, 0.20–0.30, and 0.30–0.40 m layers were evaluated. The perennial pasture environment presented the highest total soil C and N contents; however, when observing the granulometric fractions and CMI, these increases were qualitative in relation to the secondary forest. Pasture recovery over eight years contributed to an improvement of soil quality similar to secondary forest, indicating that an increase in SOM quality, quantity, and recovery time related to increased pasture capacity to accumulate C and N in the soil.

Fractions of nitrogen (including <sup>15</sup>N) and also carbon in the soil as affected by different crop residues

Fractions of nitrogen (including <sup>15</sup>N) and also carbon in the soil as affected by different crop residues

Nitrogen regime of soddy-podzolic soil with long-term use of different types and combinations of mineral fertilizers

The purpose of the work is to study the effect of various types and combinations of mineral fertilizers on the fractional composition of nitrogen in soddy-podzolic soil in a long-term stationary experiment and compare it with a virgin analogue. The studies were carried out in 2016 and 2018 on the experimental field of the Perm Research Institute of Agriculture after harvesting barley in an eight-field crop rotation deployed on soddy-podzolic heavy loamy soil. The experiment scheme: without fertilizers: N90; Р90; К90; N90P90; N90K90; P90K90; N90Р90К90. To assess the effect of nitrogen, phosphorus, potash fertilizers and their combinations on the nitrogen regime of soddy-podzolic soil, the arable soil was compared with the virgin analogue. The nitrogen fund of soddy-podzolic soil of a long-term stationary experiment is represented by 64…71 % non-hydrolyzable and 17…22 % hardly hydrolyzable forms of nitrogen. Long-term use of various types and combinations of mineral fertilizers did not significantly change the ratio of nitrogen fractions characteristic of virgin soils of this type. Nitrogen fertilizers, both with one-sided application and in combination with potassium chloride (N90К90) and superphosphate (N90P90), contributed to an increase in the total nitrogen content in the arable soil layer by 10…20 % relative to the control, mineral nitrogen compounds - by 2…3 times. Unilateral application of potash fertilizer provided an increase in the content of total nitrogen in the soil by 12 %, the introduction of superphosphate did not have a signi cant effect on the nitrogen regime of the soil. Long-term use of complete mineral fertilizer (N90P90K90) only in this way: (N90P90К90) contributed to maintaining total nitrogen at the level of virgin soil - 1490 mg/kg. Long-term unilateral application of nitrogen fertilizers increased the content of nitrate nitrogen in the soil over the entire meter layer by 1.5-2.5 times, ammonium - by 1.5-14.6 times. The reserves of mineral nitrogen in the variants N90P90, N90K90, and N90P90K90 in the 0-20 cm layer increased 2-3 times, in the 0-100 cm layer - 2 times relative to the control variant.

Carbon and nitrogen fractions control soil N2O emissions and related functional genes under land-use change in the tropics

Converting natural forests to managed ecosystems generally increases soil nitrous oxide (N2O) emission. However, the pattern and underlying mechanisms of N2O emissions after converting tropical forests to managed plantations remain elusive. Hence, a laboratory incubation study was investigated to determine soil N2O emissions of four land uses including forest, eucalyptus, rubber, and paddy field plantations in a tropical region of China. The effect of soil carbon (C) and nitrogen (N) fractions on soil N2O emissions and related functional genes was also estimated. We found that the conversion of natural forests to managed forests significantly decreased soil N2O emissions, but the conversion to paddy field had no effect. Soil N2O emissions were controlled by both nitrifying and denitrifying genes in tropical natural forest, but only by nitrifying genes in managed forests and by denitrifying genes in paddy field. Soil total N, extractable nitrate, particulate organic C (POC), and hydrolyzable ammonium N showed positive relationship with soil N2O emission. The easily oxidizable organic C (EOC), POC, and light fraction organic C (LFOC) had positive linear correlation with the abundance of AOA–amoA, AOB–amoA, nirK, and nirS genes. The ratios of dissolved organic C, EOC, POC, and LFOC to total N rather than soil C/N ratio control soil N2O emissions with a quadratic function relationship, and the local maximum values were 0.16, 0.22, 1.5, and 0.55, respectively. Our results provided a new evidence of the role of soil C and N fractions and their ratios in controlling soil N2O emissions and nitrifying and denitrifying genes in tropical soils.

Changing pattern of N2 dissociation in N2–Ar RF plasma during E–H mode transition

The behaviour of nitrogen plasma mixed with varying proportions of argon (10%–80%) is investigated under different RF discharge conditions. It is observed that at a relatively low RF power of 200 W (E-mode) the dissociation fraction (DF) of nitrogen increases with the growing concentration of argon, whereas the opposite happens for a higher RF power of 1000 W (H-mode), when the DF rapidly falls from a high value as the argon percentage starts to increase. This rising trend of DF closely follows the argon metastable fraction (MF) in the E-mode, and for the H-mode it is not followed until the argon percentage crosses the 20% mark. The electron density, temperature and electron energy probability function (EEPF) are obtained using a RF compensated Langmuir probe and to evaluate the vibrational and rotational temperatures, DF, MF etc, a separate optical emission spectroscopy technique is incorporated. At 5 × 10−3 mbar of working pressure and 10% argon content the EEPF profile reveals that the plasma changes from non-Maxwellian to Maxwellian as the RF power jumps from 200 W to 1000 W, and for a fixed RF power the high energy tail tends to move upwards with the gradual increment of argon. These observations are reverified theoretically by considering electron–electron collision frequency and electron bounce frequency as a function of electron temperature. Overall, all the major experimental phenomena in this study are explained in terms of EEPF profile, electron–electron collision effect, electron and gas temperature, electron density and argon metastable population.

Nitrogen evolution during membrane-covered aerobic composting: Interconversion between nitrogen forms and migration pathways

Aerobic composting is a promising technology for converting manure into organic fertilizer with low capital investment and easy operation. However, the large nitrogen losses in conventional aerobic composting impede its development. Interconversion of nitrogen species was studied during membrane-covered aerobic composting (MCAC) and conventional aerobic composting, and solid-, liquid-, and gas-phase nitrogen migration pathways were identified by performing nitrogen balance measurements. During the thermophilic phase, nitrogenous organic matter degradation and therefore NH3 production were faster during MCAC than uncovered composting. However, the water films inside and outside the membrane decreased NH3 release by 13.92%–22.91%. The micro-positive pressure environment during MCAC decreased N2O production and emission by 20.35%–27.01%. Less leachate was produced and therefore less nitrogen and other pollutants were released during MCAC than uncovered composting. The nitrogen succession patterns during MCAC and uncovered composting were different and NH4+ storage in organic nitrogen fractions was better facilitated during MCAC than uncovered composting. Overall, MCAC decreased total nitrogen losses by 33.24%–50.07% and effectively decreased environmental pollution and increased the nitrogen content of the produced compost.

The introduction of nitrogen from coal into the surface watershed nitrogen cycle due to coal mining activity

Human activity has doubled the turnover rate of the terrestrial nitrogen cycle, leading to a series of environmental problems. A little-studied nitrogen source in terrestrial and aquatic environments is the nitrogen release associated with rock strata. Southwest China features the largest continuous karsts in the world, featuring a fragile ecological environment but abundant coal resources. The current study selected a typical coal mining area to evaluate the migration and transformation of nitrogen related to coal mining in surface watershed. The findings reveal that the total nitrogen in coal seams was as high as 10,162.3 mg/kg, mainly in the form of organic nitrogen, followed by NH4+-N, while the content of NO3−-N was negligible. Based on the isotope fractionation and the co-evolution between Δ15NNO3-NH4 and δ15N-NO3−/δ15N-NH4+, coal mining changed the coal seams' oxidation-reduction state, resulting in the mineralization of organic nitrogen to NH4+-N. Next, NH4+-N gradually oxidized to NO3−-N. Various forms of coal-origin nitrogen may be leached out by acid mine drainage (AMD), potentially contributing >10 % of NO3−-N and 90 % of NH4+-N to the surface river. Another nitrogen source that requires serious consideration is the wide use of ammonium nitrate explosives in coal mining, as blasting residues may contribute about another 10 % to NO3−-N in surface water. Since organic nitrogen accounts for >90 % of extractable nitrogen, the release of coal-origin nitrogen may contribute much more to the total nitrogen in surface water than to NO3−-N. Based on the fractionation of nitrogen and oxygen isotopes of nitrate, low-pH AMD promotes the volatilization of nitrate in the form of nitric acid. The conversion of different forms of nitrogen in AMD will be the focus of future attention.