Influence Of Different Types Research Articles

Ion Size, Electron Rate and Transfer Coefficient Effect on Hetrocharge Redox Couple (+1,0) for 2‐D Microdisk, Potential Application for Lithium Ion Battery

AbstractNumerical finite element simulations were conducted to study the electrochemical reaction in a mixture of hetrocharge redox couple in the presence of a supporting electrolyte as a potential application in lithium ion battery, occurring on both parallel and non‐parallel two dimensional (2‐D) microdisk electrodes. Ion size of supporting electrolyte and electron transfer rate by engineering of electrode types have significant effect on electrical storage. This study represents the first‐time exploration of the electrochemical behavior for hetrocharge +1,0 redox couple in presence of supporting electrolyte on a non‐parallel 2D microdisk. Impedance spectra were calculated for the electrochemical reaction on the non‐parallel 2D microdisk under varying concentrations of the redox couple and supporting electrolyte. COMSOL simulation were extended to investigate the effects of electron rate and transfer number on the Impedance spectrum, as well as the concentration of all ions and electrical potential within the electrical double layer area for the 2‐D microdisk. Analytical expressions were derived to describe the potential and concentration profiles in the double layer area, specifically for the electrochemical reaction involving hetrocharge redox couple +1, 0 on a 2‐D parallel microdisk in the presence of the supporting electrolyte. The study explored the influence of different types of supporting electrolytes, namely KF and KBr, on the impedance spectrum, concentration profile, and electrical potential profile within the electrical double layer area for the non‐parallel 2‐D microdisk. General trend of numerical impedance spectrum result with the ion size of supporting electrolyte is agreement with the available experimental data.

Influence of different types of interclass ability grouping on students’ academic achievement in mathematics: evidence from the Confucian Asian cluster

ABSTRACT Ability grouping has attracted worldwide attention in relation to various subjects among different countries and regions. However, few studies have focused on the relationship between ability grouping and students’ mathematical academic achievement in the Confucian Asian countries. Thus, in this study, we aimed to determine how different types of interclass ability grouping impact students’ academic achievement in mathematics. We analysed PISA2022 data for 34,968 students from 923 schools in six countries and regions, including Hong Kong, Macau, Taipei, Japan, South Korea, and Singapore, using a hierarchical linear model and propensity score matching. We found that overall, multi-level ability grouping reduced students’ mathematics achievement, and this negative effect was particularly significant among high-ability students, while it promoted the mathematics achievement of low-ability students to some extent.

Audiovisual Congruence and Localization Performance in Virtual Reality: 3D Loudspeaker Model vs. Human Avatar

This paper investigates audiovisual congruence in virtual reality with both horizontal and vertical offsets between audio and visual rendering. Audiovisual congruence and localization errors are assessed using loudspeaker playback and nonindividualized headphone rendering. To account for the influence of different types of visual information on congruence, presentations of a loudspeaker model and 3D human avatar were compared. Therefore, a new dataset of audiovisual speech was recorded. Results show that human avatar rendering increases perceived congruence, and experienced listeners have an increased tendency to respond with “incongruent” when a loudspeaker model is shown but not when the human avatar is presented. Moreover, a correlation is found between localization precision and audiovisual congruence for horizontally offset stimuli and avatar presentation. For vertical offsets, the angular range of congruence is generally large, and localization errors are high, so no correlation can be observed between the two. The paper contributes congruence ranges for audiovisual speech in virtual reality, which also has implications for augmented reality telepresence use.

Review of Wear and Mechanical Characteristics of Al-Si Alloy Matrix Composites Reinforced with Natural Minerals

Al-Si alloys are vital in the aerospace and automotive industries due to their high strength-to-weight ratio, excellent ductility, and superior corrosion resistance. These properties, along with good thermal conductivity, low thermal expansion, and enhanced wear resistance due to silicon, make them ideal for lightweight, high-performance components like engine parts exposed to harsh conditions and thermal cycling. In recent years, the development of aluminium metal matrix composites using Al-Si alloys as the base material has gathered significant attention. These composites are engineered by integrating various reinforcing particles into the aluminium matrix, which results in remarkable improvements in the wear resistance, hardness, and overall mechanical performance of the material. The stir casting process, a well-established and cost-effective method, is frequently employed to ensure a uniform distribution of these reinforcing particles within the matrix. This review delves into the influence of different types of reinforcing particles on the properties of Al-Si alloy-based AMCs. The incorporation of these reinforcements has been shown to significantly enhance wear resistance, reduce friction, and improve the overall strength and toughness of the composites, making them ideal candidates for high-performance applications in the automotive and aerospace sectors. Moreover, this review highlights the challenges associated with the fabrication of these composites, such as achieving a homogeneous particle distribution and minimizing porosity. It also discusses the latest advancements in processing techniques aimed at overcoming these challenges. Additionally, this review addresses the potential environmental and economic benefits of using natural reinforcements, which not only reduce material costs but also contribute to sustainable manufacturing practices.

A grey incidence-based algorithm for optimization of accelerated degradation test

PurposeThe purpose of this paper is to optimize the degradation test for products subject to multiple types of inherent stresses and external random shocks. The mechanism that shows how the variables to be optimized influence the considered multiple objectives is also aimed to be explored by using the grey incidence analysis (GIA) model.Design/methodology/approachThe Gamma process is employed to model the influences of different types of stresses and external random shocks. The GIA model is introduced to transfer multiple considered objectives as a comprehensive degree of grey incidence. The particle swarm optimization is integrated to search the globally optimal value of the characteristic variables to be optimized.FindingsThe acceleration of tested stresses and external random shocks both make the engineering systems become more vulnerable to the inherent degradation. And, the Kriging model can provide guidance of searching the optimal values of test characteristic variables and mitigate the computation burden. The grey incidence model can make the optimization focused and improve the optimality of objective values.Originality/valueThe proposed method can effectively overcome the drawbacks brought by the limitation of test data and can specify the dependence strength between the inherent degradation and external random shock. The computation cost and accuracy of optimization can be simultaneously ensured by the proposed model.

Thermodynamic and computational approaches to the stability and structural transformation of Xe + large-molecule guest substance (LMGS) hydrates

In this study, the influence of different types of large-molecule liquid substances (LMGSs) and formation conditions on the stability and structural transformation of Xe + LMGS hydrates was investigated using phase equilibria, powder X-ray diffraction (PXRD), 129Xe NMR spectroscopy, and molecular dynamics (MD) simulations. The phase equilibria of Xe hydrates in the presence of three different LMGS types (neohexane [NH], methylcyclopentane [MCP], and methylcyclohexane [MCH]) were measured in the pressure range of 0.1–1.0 MPa. The equilibrium curves of Xe + MCH and Xe + NH hydrates shifted away from that of pure Xe hydrate under low pressure, whereas they coincided with that of pure Xe hydrate under high pressure. Interestingly, the equilibrium curve of Xe + MCP hydrate aligned with that of pure Xe hydrate throughout the pressure range. PXRD and 129Xe NMR analyses demonstrated that the equilibrium curve shift under low pressure was caused by the formation of sH (Xe + LMGS) hydrates, which was attributed to the inclusion of NH or MCH. However, MCP did not participate in sH hydrate formation with Xe. MD simulations revealed that MCP in the large cages did not contribute to the thermodynamic or dynamic stability of sH hydrates. The findings of this study provide valuable insights into the development of hydrate-based noble gas capture and storage.

Biodegradable microplastics can cause more serious loss of soil organic carbon by priming effect than conventional microplastics in farmland shelterbelts

Abstract Globally, the widespread utilization of plastic products has resulted in the accumulation of microplastics (MPs) in the soil. MPs have the potential to impact the loss of soil organic carbon (SOC). Nevertheless, the influence of different types of MPs on SOC loss remains uncertain. In this study, a 38 day incubation experiment with two kinds of conventional MPs (polyethylene, polypropylene) as well as two kinds of biodegradable MPs (polyhydroxyalkanoate [PHA], polylactic acid [PLA]) were added into three types of soil (loam, sandy loam, and sandy soil) in farmland shelterbelts, and the sources of CO2 emissions was distinguished by the difference in 13C isotope abundance between the biodegradable MPs (PHA and PLA) (−10.02‰ to −9.92‰) and the soil (−24.39‰ to −22.86‰) (>10‰). In conjunction with the structural characterization of MPs, as well as soil physicochemical properties and microbial characteristics, we observed that the conventional MPs did not degrade in short term incubation, but significantly enhance soil‐derived CO2 emissions by altering the dissolved N content (‐N and dissolved total N [DTN]) and reducing microbial biomass carbon content only in sandy loam soil (p < 0.05). Biodegradable MPs degraded significantly, and enhanced soil‐derived CO2 emissions by reducing soil DTN and ‐N contents in loam, sandy loam and sandy soil (p < 0.05). Overall, the input of biodegradable MPs causes a more serious loss of SOC than conventional MPs as the soil sand content increased in short term incubation, which needs to be considered in predicting the global impact of increasing biodegradable MPs pollution. Read the free Plain Language Summary for this article on the Journal blog.

A comprehensive study on porosity modelling and its impact on fracture behavior of edge cracked FG structures using XIGA

In the present work, the fracture analysis of functionally graded (FG) porous structure containing an edge cracked is carried out in the presence of different types of porosity distributions using extended isogeometric analysis (XIGA). Firstly, the different types of porosity distribution functions are mathematically modeled in the porous FG structure across the length of the domain. The effective properties of the porous FG structure are computed using power law. Also, an additional term of porosity is incorporated in the power law to include the effect of porosity in the FG structure. The effective properties are computed across the length of the structure in the presence of different types of porosity distributions. Further, a pre-existing crack is modeled in the domain to study its influence on the fracture behaviour of porous FG structure using XIGA. To validate the accuracy, the results for the non-porous FG structure are compared with the available results in the literature (with the analytical and numerical solution), and they are found in good agreement (percentage error in the range of 0.04–––1.78%). Moreover, the comparative study is performed to investigate the influence of different types of porosity distributions on the fracture behaviour of FG structure.

Use of graphene (go and rGO) as a reinforcement filler to increase the beta phase in fluorinated copolymer nanocomposites

The present study aims to evaluate the influence of different types of graphene, graphene oxide (GO, synthesized by the Hummers method) and reduced graphene oxide (rGO, obtained by thermal reduction of GO) on the piezoelectric properties of composites based on PVDF copolymer. Hydrogen-fluorine interaction is expected to occur between GO or rGO and the fluorinated copolymer, increasing the β-conformation content in the polymer. The samples were prepared in the molten state at two concentrations of each charge inside a twin-screw extruder with interpenetrating screws. The characterizations of the nanocomposites were made according to their thermal and electrical properties. The effect of graphene incorporation into the P(VDF-TrFE) matrix was observed from thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The results obtained indicated that the incorporation of graphene contributed to the increase in the β phase content of P(VDF-TrFE), which is indicative of the increase in its piezoelectricity.

Influence of different types of dietary sugars on the intestinal mucosa and hepatic lipid metabolism in germ-free mice

The excessive consumption of dietary sugar induces changes in gut microbiota, which is associated with obesity and metabolic dysregulation. This study investigated the effects of monosaccharide and fructooligosaccharide (FOS) intake on metabolic function and intestinal environment in germ-free (GF) mice lacking gut microbiota. GF mice were provided with a chow diet and administered a water solution containing 15 % glucose, fructose, or FOS for 4 weeks. Compared with FOS, glucose, and fructose induced increased hepatic lipid accumulation, increased adipocyte size in white adipose tissue, and upregulated hepatic lipogenic gene expression. FOS exhibited notably higher activation of hepatic AMP-activated protein kinase compared with those consuming glucose or fructose. Moreover, the number of goblet cells in the intestinal mucosa increased significantly with FOS consumption. Collectively, these findings indicate that while monosaccharides caused metabolic disorders in GF mice, FOS alleviated these disorders and increased the number of goblet cells in the intestinal mucosa. These results provide evidence for the occurrence of these effects independently of the gut microbiota.

New insights into the quantiffcation of Fe(IV) using methyl phenyl sulfoxide (PMSO) as probe in the iron-based heterogeneous catalyst activated persulfate process

Ferryl ions (Fe(IV)) are often thought to play an important role in iron-based advanced oxidation processes (AOPs), and their presence is typically inferred through the unique pathway of methyl phenyl sulfoxide (PMSO) conversion to methyl phenyl sulfone (PMSO2). Here, we first employed probe method by degrading the mixed system containing PMSO, benzoic acid (BA), nitrobenzene (NB) to analyze the steady-state concentration of Fe (IV) in the iron-based heterogeneous persulfate reaction system. In addition, studies were conducted on the direct oxidation of PMSO by different oxidants under different pH conditions, and the results showed that peroxymonosulfate (PMS), sodium hypochlorite (NaClO) and sodium periodate (PI) can directly oxidize PMSO and convert it into PMSO2. Furthermore, the influence of different types of iron salts and biomass on the prepared iron-biochar (Fe-BC) for the activation of persulfate on degradation of PMSO and the formation of PMSO2 was also investigated. This study may provide new insights into the use of PMSO as a probe for the analysis of Fe(IV) in heterogeneous reaction systems.

A study on the mediating-moderate effect of the types of illicit drugs on mental health in China.

In China, over 5 million people have been identified and registered by the public security institutions for using illicit drugs. The aim of this study is to compare the influence of different types of illicit drugs on the self-reported mental health of Chinese people. In particular, we want to assess the damage of Heroin, Methamphetamine and Ketamine to mental health in a social environment where drug use is strictly regulated. The study is based on survey with 6,906 people who use drugs in Guangdong province, China. Risk of mental health issue is measured using the Brief Symptoms Inventory 18 (BSI-18) Scale, and a higher BSI-18 score indicates more severe mental health problems. The data was analyzed through multilevel regression analysis, propensity score matching analysis and mediation analysis. The three major types of illicit drugs have both moderating and mediating effects on the length of drug-use history, that Heroin use leads to longer drug-use duration, while Ketamine use causes more damage on mental health per unit time of drug-use duration. Average duration of Methamphetamine use is 0.7 year shorter than average duration of Heroin use, and average duration of Ketamine use is 1.7 year shorter than average duration of Heroin use. For each year of increase of drug-use duration, Ketamine use leads to 1.2 times more of BSI score increase than Heroin use, and 2.3 times more of BSI score increase than Methamphetamine use. These three drugs are associated with severe mental health issue in a society with strict drug regulation. Attention should be paid to the mental health of people regardless of the type of drugs they use.

Distribution of microplastics between ice and water in aquatic systems: The influence of particle properties, salinity and freshwater characteristics

Microplastics (MPs) are an anthropogenic emerging pollutant, with global contamination of both marine and freshwater systems extensively documented. The interplay of MP particle properties and environmental conditions needs to be understood in order to assess the environmental fate and evaluate mitigation measures. In cold climate, ice formation has appeared to significantly affect the distribution of MPs, but so far, limited research is available comparing different aquatic systems, especially freshwater. Experiments often rely on artificial water and specific MP model particles. This study used laboratory tests to investigate the ice-water distribution of a variety of environmentally relevant MP particle types (PP, PE, PS and PVC fragments (25–1000 μm), PET fibers (average length 821 μm, diameter 15 μm)) across different water types, including artificial water of high and low salinity, as well as natural water from a lake and a treatment wetland. Overall, ice entrapment of MPs occurred in almost all tests, but the ice-water distribution of MPs differed across the different water types tested. Among the tests with artificial water, salinity clearly increased MP concentrations in the ice, but it cannot be resolved whether this is caused by increased buoyancy, changes in ice structure, or thermohaline convection during freezing. In the natural freshwater tests, the partition of MPs was shifted towards the ice compared to what was seen in the artificial freshwater. The influence of different types of dissolved and particulate substances in the different waters on MPs fate should be considered important and further explored. In this study, the higher content of suspended solids in the lake water might have enhanced MP settling to the bottom and thereby contributed to the absence of MPs in the ice of the lake test, compared to the wetland test with low suspended solids and considerably more MPs in the ice. Furthermore, the higher negative charge in the lake water possibly stabilized the negatively charged MPs in suspension, and reduced ice entrapment. Regarding particle properties, shape had a distinct effect, with fibers being less likely incorporated into ice than fragments. No fibers were found in freshwater ice. However, it became clear that ice entrapment of MPs depends on factors other than the particles' buoyancy based on density differences and particle size and shape alone.

Characteristics of soil moisture transport in the aeration zone of subsidence areas under the disturbance of coal seam mining

High-intensity coal mining has induced a series of ecological and environmental problems issues, including surface subsidence, the development of ground cracks, and the deterioration of vegetation. The disruption of water circulation systems induced by mining, such as perched groundwater, groundwater of aeration zone, and phreatic water, is the root cause of vegetation withering. The aeration zone serves as a crucial nexus in the process of water cycling and exerts a significant influence on soil fertility. To explore the characteristics of soil moisture transport in subsidence areas under the mining disturbance, on-site monitoring of the size and morphology characteristics of subsidence areas and ground cracks was conducted in typical mining areas in Inner Mongolia, China. Subsequently, a typical soil moisture transport model was constructed in subsidence areas, the soil moisture transport patterns under the influence of different types of subsidence and cracks were analyzed, and the influence law of soil damage on soil moisture transport in the aerated zone was clarified. The results indicate that (1) Based on the occurrence and distribution characteristics of subsidence cracks, the subsidence area can be divided into tension zone, compression zone, and neutral zone; the ground cracks are divided into permanent tension cracks and dynamic cracks. (2) The drought stress effect of soil in the subsidence area is significant. Under the influence of soil structure variation, the water-holding capacity of the soil in the subsidence area decreases, and the soil moisture dissipation is strong. The soil moisture transport rate in the aeration zone of the subsidence area is ranked as follows: tension zone > neutral zone > compression zone. (3) Ground cracks can exacerbate the soil moisture transport rate in the aeration zone. After 15 d of crack appearance, the soil moisture transport reaches a relatively stable state, and the soil moisture transport rate in the surface layer of the crack is the fastest, and the loss of soil moisture is the most significant. The crack effect is not significant beyond 100 cm from the crack. This study provides a theoretical and data support for soil and vegetation remediation in mining subsidence areas.

Influence of different types of mouthwashes on force decay of elastomeric chain recommended in SARS-COV-2 pandemic.

This study aimed to compare the force decay of the power-chain elastics after exposure to anti-coronavirus 2019 (COVID-19) antiseptic mouthwashes at different intervals. A total of 300 power-chain pieces were used from American Orthodontics (AO) and Dentaurum (D) brands. Each piece composed of five loops that were selected to simulate canine retraction distally. The samples were randomly grouped according to immersion in the tested mouthwashes 0.2% povidone-iodine (PVP-I), 1% hydrogen peroxide (H2O2), and 0.2% chlorhexidine (CHX) and cetylpyridinium chloride (CPC). The maximum tensile load failure testing (MTLT) was assessed at six time points (zero, one hour, 24 hours, 1, 2 and 4 weeks). Analysis of variance (ANOVA) and Tukey's post hoc tests were used to analyse the data, where P < 0.05. Significant differences in MTLT of power-chain elastics used at different immersion intervals were observed. MTLT, in each tested group, decreased significantly as the immersion time increased with significant differences among the tested mouthwashes at each time point. H2O2 group displays a maximum force decay throughout the time intervals for both brands, in contrast to CPC group, which shows less degradation over time. Both brands are decade over time during exposure to the tested mouthwashes. CPC mouthwashes is a good option to be described for orthodontic patient during COVID-19 pandemic, whereas H2O2 mouthwashes should be avoided.

Interaction of Per- and Polyfluoroalkyl Substances with Estrogen Receptors in Rainbow Trout (Oncorhynchus mykiss): An In Silico Investigation.

Fresh water sources, including lakes, such as the Great Lakes, are some of the most important ecosystems in the world. Despite the importance of these lakes, there is increasing concern about the presence of per- and polyfluoroalkyl substances (PFAS)─among the most prevalent contaminants of our time─due to the ability of PFAS to bioaccumulate and persist in the environment, as well as to its linkages to detrimental human and animal health effects. In this study, PFAS exposure on rainbow trout (Oncorhynchus mykiss) is examined at the molecular level, focusing on the impact of PFAS binding on the alpha (α) and beta (β) estrogen receptors (ERs) using molecular dynamics simulations, binding free energy calculations, and structural analysis. ERs are involved in fundamental physiological processes, including reproductive system development, muscle regeneration, and immunity. This study shows that PFAS binds to both the estrogen α and estrogen β receptors, albeit via different binding modes, due to a modification of an amino acid in the binding site as a result of a reorientation of residues in the binding pocket. As ER overactivation can occur through environmental toxins and pollutants, this study provides insights into the influence of different types of PFAS on protein function.

Human physiological responses to different types of human-dog interactions: A randomised crossover study

Previous studies of human-dog interventions vary in terms of type of interaction, which is rarely quantified, leading to contradictory findings and limited comparability. To uncover the influence of different types of interactions, the present study investigated if it was possible to detect differences in immediate physiological measurements of healthy humans during different standardised types of interaction with a dog. Thirty-three healthy participants (women = 25, men = 8, >18 years) were exposed to four different test situations with standardised types of interaction intensity with a dog in random order: no dog present (CONTROL), looking at a dog (VISUAL), petting a dog (TACTILE) or performing tricks with a dog (ACTIVE). Each test situation lasted 10 min with a 30-min break between each. Heart rate (HR), heart rate variability (HRV) and skin conductance (tonic level (SCL) and peak counts (SCR)) were continuously recorded. Blood pressure (BP) and salivary cortisol (s-cortisol) were measured before and after each test situation. Linear Mixed Models were applied. HR, HRV, BP, SCL and SCR increased with increased interaction with the dog (for all: p < 0.001). HRV increased with decreased HR (p = 0.002), increased SCL (p = 0.027), and SCR (p < 0.001) depending on the type of interaction. Generally, s-cortisol increased with increased HR (p = 0.042), SCL increased with increased SCR (p < 0.001), and SCR increased with increased HRV (p = 0.013), depending on type of interaction. The physiological measurements HR, HRV, BP, SCL and SCR are influenced by different types of dog interaction, and thus it is important to quantify and report the type of interaction in human-dog interaction studies. (ClinicalTrials.gov ID:NCT04696419).

Consumer acceptance of different types of cultural borrowing and its internal mechanisms

In cross-regional cultural interactions, the frequent and controversial practice of cultural borrowing has attracted attention. According to the different relative statuses and comparative directions of the cultural subjects, cultural borrowing can be divided into strong-to-weak (weak-to-strong) cultural borrowing between subjects with strong (weak) status and subjects with weak (strong) status in cultural interactions, as well as equal cultural borrowing between subjects with equal status in cultural interactions. After the concept and types of cultural borrowing are defined, a multisituation experimental method is used to confirm the internal mechanisms and effect boundaries of consumers’ cultural borrowing acceptance. The results of five experiments based on over a thousand subjects indicate that different types of cultural borrowing (strong-to-weak, equal, weak-to-strong) arouse consumers’ perceived cultural threat, thereby reducing their acceptance of cultural borrowing to varying degrees. The influence of different types of cultural borrowing on perceived cultural threat is moderated by the degree of incongruent use and reality of the presentation of the borrowed culture; the influence of perceived cultural threat on cultural borrowing acceptance is moderated by the positioning of the borrowing subjects and the degree of identity in the relationship. By exploring cultural borrowing and consumer acceptance issues in the field of consumption through a series of experiments, this study effectively reveals the differentiated impacts and underlying mechanisms of different types of cultural borrowing on consumers’ acceptance responses.

Conceptual approaches to the concept of regional potential: essence, content, classification features

The article highlights the importance of the study, due to disagreements in the theoretical and methodological aspects of considering the concept of regional potential. The analysis of current scientific publications devoted to the study of various conceptual approaches to its interpretation is carried out. The paper analyzes the formulations of the concept of "regional potential" ("regional potential") by a number of authors from the point of view of content orientation to various groups of factors. The generalization was carried out according to the internal and external characteristics, the field of activity (specialization) of the region. The author’s interpretation of the concept is given. The classification of the types of regional potential is carried out, their complex structure is presented, designed taking into account rationality and complexity. Two groups of potentials have been identified – dependent and independent. The concept of aggregate potential is highlighted, which is the final indicator of regional development. As a methodological basis, the developed approach is proposed through the compilation of maps of regional potentials, which allows to unify the order of selection of fundamental factors as the criteria for the development potential of the region. The direct and indirect influence of different types of regional potential on each other is indicated. The substantial essence of the concepts is analyzed and three main approaches to the definition of regional potential are identified – factorial, resource, and effective. The basis for the development of a more detailed study of the interrelation of regional potentials is determined and emphasis is placed on the prospects for formalizing the proposed approach in order to identify mathematical dependencies to support decision-making of strategic management of the region.

Carbon type and quantity regulate soil free-living nitrogen fixation through restructuring diazotrophic community

Free-living nitrogen fixation (FLNF) is a ubiquitous and significant source of new nitrogen in ecosystems. This process requires a substantial amount of energy, and as a result, the input of labile carbon to soils may enhance FLNF. Here, we aim to explore the precise influence of different types and quantities of carbon on FLNF. We conducted experiments where sugars, carboxylic acids, and amino acids (common labile carbon inputs via root exudates) were added to cropland and forest soils. We monitored the changes in FLNF rate and diazotrophic community in response to these additions. Our findings revealed that sugars and carboxylic acids significantly stimulated FLNF rate, with an increase of up to three orders of magnitude, while amino acids either restricted FLNF or had no effect. When a mixture of sugars and carboxylic acids was added, the stimulation of FLNF was not observed until a threshold quantity of carbon was reached, indicating competition between diazotrophs and other microbes. Furthermore, the enhanced FLNF rate following carbon addition was attributable to shifts in diazotrophic community composition (e.g., increased abundance of Paenibacillus, a genus frequently used as biofertilizers), rather than to changes in the overall abundance of diazotrophs (reflected by nifH gene copy number). Our findings highlight the significant role of carbon type and quantity in regulating soil FLNF, partly through restructuring the diazotrophic community. The results have implications for predicting the response of rhizosphere FLNF to shifts in root exudation under environmental changes and can contribute to the application of diazotrophic biofertilizers in sustainable agriculture.