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In markets where differences in the environmental performance of competing firms arise due to differences in technology that cannot be altered in the short run and firms have private information about their own current technology, I show that market competition creates a strategic disincentive for adopting ecolabels (even if the cost of adoption is negligible) to directly and credibly communicate this private information to environmentally conscious consumers. Firms adopt ecolabels only if the green premium that buyers are willing to pay is large relative to the production cost advantage of dirty firms; ecolabels reduce market power, increase the market share of clean firms, and reduce expected environmental damage. I analyze firms' strategic (long‐run) incentive to invest in the development of clean technology where the outcome of such investment is uncertain. The availability of an ecolabel to directly communicate private information about the final outcome of such an investment enhances the expected net surplus whereas it reduces the ex ante strategic incentive to invest which in turn lowers industry investment in cleaner technology, relative to the case with no ecolabels. [ABSTRACT FROM AUTHOR]

The present study focuses on the numerical modeling of the co-combustion of reject coal (RC) and sal leaves (SL) in a drop tube furnace (DTF) under different conditions, including air-fuel and oxy-fuel environments. The numerical results highlight the significant influence of replacing the N2 atmosphere with CO2 on the temperature profiles of individual fuels and their blends. For instance, when exposed to a 21%O2/79%CO2 atmosphere, Blend SL3 and Blend SL5 experience a decrease in temperature from 1372 K to 1559 K to 1327 K and 1395 K, respectively. Conversely, increasing the O2 concentration to 35% leads to a temperature rise. Furthermore, the combustion analysis reveals that the addition of 10% SL to RC in a 21%O2/79%N2 environment enhances the devolatilization rate from 1.41 × 10−12 kg/s to 1.77 × 10−12 kg/s. Additionally, the char combustion process for all blends is completed closer to the DTF inlet at 0.28 m, compared to 0.32 m for RC alone. These findings indicate that blending SL with RC promotes a favorable combustion process. Moreover, increasing the O2 concentration to 35% in oxy-fuel conditions enhances the temperature profiles. The numerical analysis demonstrates good agreement with experimental data within a range of ±5%–11%. This suggests that the developed model can be effectively utilized for optimizing and designing biomass co-firing systems in industrial applications, considering both air-fuel and oxy-fuel conditions. [ABSTRACT FROM AUTHOR]

Undergraduate institutions serve as stepping stones to students' careers. Teaching and learning in science classrooms require quality and integrated teaching–research learning experiences that prepare students to advance their careers. Using publicly available data sets and open-access data analyses software can be impactful for engaging students in meaningful research experiences while keeping institutional expenses associated with implementing and supporting research opportunities low. In this article, we share two examples of student-led data research that utilized open data and software to analyze microbial sequence data. As part of this process, we also recognized the need for discipline-specific databases that can hold a record of publicly available data. Such a setup will support undergraduate educators and students in accessing data relevant to their requirements, thereby narrowing the gap between data availability and accessibility. Finally, both examples illustrate the benefits of using open resources in supporting student learning, with the possibility of using such resources to develop course-based undergraduate research experiences as part of course curricula. [ABSTRACT FROM AUTHOR]

A series of implicit large eddy simulations have been conducted to implement thermal control on the transonic shock-boundary layer interactions (SBLIs) over a natural laminar flow airfoil, operating beyond the drag divergence Mach number. The study focuses on the SHM1 airfoil, where the baseline flow exhibits shock-induced separation under specific conditions: free stream Mach number M ∞ = 0.78 , angle of attack α = 0.38 ° , and Reynolds number R e = 8 × 10 6 . A time-periodic surface heat flux is introduced, strategically located near the shock structures of the unaltered flow, and the impact of heating vs cooling is investigated through instantaneous Schlieren visualizations and vorticity dynamics, and time-averaged load distributions and boundary layer parameters. Time-averaged Mach contours are utilized to measure the shock strength and extent, revealing that thermal control effectively mitigates the detrimental impact of transonic SBLI on the airfoil's performance. Cooling control emerges as the more effective method, and a case featuring multiple cooling controls near the shock structures demonstrates superior efficacy in controlling shock waves and suppressing shock-induced separation. This optimized configuration results in an improved aerodynamic efficiency of 12.65% compared to the baseline flow. [ABSTRACT FROM AUTHOR]

The separation-induced transition on the suction surface of a T106A low pressure turbine blade is a complex phenomenon with implications for aerodynamic performance. In this numerical investigation, we explore an adverse pressure gradient-dominated flow subjected to varying levels of free stream excitation, as the underlying separation-induced transition is a critical factor in assessing blade profile loss. By comprehensively analyzing the effects of free stream turbulence (FST) on the transition process, we delve into the various mechanisms which govern the instabilities underlying bypass transition by studying the instantaneous enstrophy field. This involves solving the two-dimensional (2D) compressible Navier–Stokes equation through a series of numerical simulations, comparing a baseline flow to cases where FST with varying turbulent intensity (T u = 4 % and 7%) is imposed at the inflow. Consistent with previous studies, the introduction of FST is observed to delay flow separation and trigger early transition. We explore the different stages of bypass transition, from the initial growth of disturbances (described by linear stability theory) to the emergence of unsteady separation bubbles that merge into turbulent spots (due to nonlinear interactions), by examining the vorticity dynamics. Utilizing the compressible enstrophy transport equation for the flow in a T106A blade passage, we highlight the various routes of bypass transition resulting from different levels of FST, emphasizing the relative contributions from baroclinicity, compressibility, and viscous terms. [ABSTRACT FROM AUTHOR]

The present study performs three-dimensional (3D) numerical simulations of coal combustion of four samples with varying ash content in a drop tube furnace (DTF) to mimic the particle heating rates observed in industrial furnaces. The numerical framework adopted is validated with prior experimental and simulation results using a 3D cylindrical geometry and a very good match is obtained for the axial temperature distribution and particle burnout rate. The combustion performance of coal samples with varying ash contents of 2.3, 16.6, 24.1, and 37.2 wt%, is explored through temperature profiles, burnout rates, particle tracking, and mass fractions of various products of combustion. A user-defined function is used to specify the 14 species, 10-step solid particle combustion with a modified eddy dissipation concept model for volatile combustion. The range of ash content considered is for Indian coal which has a high degree of heterogeneity, making the evaluation of its combustion performance, a challenge. The present work aims to provide benchmark set of results showing the evolution of the evaporated, charred, and volatile mass for the three ash contents, which has not been attempted before. It is found that the high-ash content Indian coal samples have a tendency to produce less NOx . A 9:52% reduction in the NOx is obtained for the coal sample with 37:2% ash compared to that with 16:6% ash. The results suggest that the combustion performance is enhanced when the ash content falls within an optimum range of 20 35%. [ABSTRACT FROM AUTHOR]

The present numerical investigation delves into the intricate interplay between Mach number (Ms), flow characteristics, and vorticity dynamics within a T106A low-pressure turbine (LPT) blade passage. The two-dimensional (2D) compressible Navier–Stokes equations are solved using a high-accuracy, dispersion relation preserving methodology, which is validated against benchmark direct numerical simulations. Four Ms ranging from 0.15 to 0.30 are computed in order to display the intricate response of compressibility on the separation-induced transition process. The emergence and evolution of unsteady separation bubbles along the suction surface of the T106A blade are explored, revealing a growing trend with Ms. The time-averaged boundary layer parameters evaluated along the suction surface display a delayed separation with a smaller streamwise extent with increasing Ms. However, an overall increase in the blade profile loss and a decrease in turbulent mixing are observed with increasing Ms, suggesting a detrimental effect on LPT performance. Applying the compressible enstrophy transport equation (CETE) to the flow in a T106A blade passage reveals that while a linear relationship exists between Ms and certain CETE budget terms, other terms have a nuanced dependency, which paves the way for future investigations into the role of compressibility on enstrophy dynamics. [ABSTRACT FROM AUTHOR]

The present study investigates the behavior of multi-layer Rayleigh–Taylor instability (RTI) and enstrophy transport in the flow using a three-dimensional computational framework. The dynamics of RTI are explored in a monotonically unstable stratified fluid system composed of air at different constant temperatures, initially separated by insulating partitions. Our results illustrate the formation of a multi-layer RTI system and the growth of convective mixing layers from interfaces between consecutive layers. The behavior of single-layer and multi-layer RTI is compared by considering the influence of Atwood numbers on growth and characteristics of the mixing layers. We found that the presence of multiple layers affects the onset and development of RTI. The merging of top layers leads to accelerated mixing layer growth, while the bottommost layer experiences early-stage RTI. Furthermore, we utilize the compressible enstrophy transport equation to characterize dominant mechanisms controlling the spatiotemporal evolution of the multi-layer RTI. The results highlight the significance of viscous and compressibility terms, especially in the center. In contrast, the vortex stretching term dominates near side walls for later stages of the RTI. These insights enrich the understanding of multi-layer RTI and its effects on enstrophy transport and mixing in unstably stratified fluid systems, providing valuable data for validating numerical methods and informing future research in related fields. [ABSTRACT FROM AUTHOR]

The interaction between starch and lipid gives rise to complexes that have various applications in the food industry. These complexes are known to be useful in food technology, where they influence the texture and quality of the food product, along with various other characteristics. For example, they can be used as fat replacements in different food products, delay the staling of food, improve the freeze thaw stability of products, also can be used to control the glucose levels in patients with diabetes, etc. Various techniques are used to study the structural, thermal, and chemical characteristics of these starch-lipid complexes including X-ray diffraction (XRD), scanning electron microscope (SEM), differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy. This review outlines the formation of the starch-lipid complexes, their value in the food industry, the varying effects on different types of starch and lipids in food products, and characterization of these complexes. [ABSTRACT FROM AUTHOR]

Numerical investigation of a compressible fluid in a two-dimensional rectangular lid-driven cavity (LDC) with a vertical temperature gradient is performed by solving the compressible Navier–Stokes equation. Here, we explore the role of aspect ratio (AR) (width/height) on the vorticity dynamics and redistribution by considering three ARs of 1:1, 2:1, and 3:1. The onset and propagation of the instability are explored via time-resolved and instantaneous distributions of vorticity, time-series of streamwise velocity, and its associated spectra. The flow physics reveal that the precessing vortical structures in certain square sub-cells of the rectangular LDC resemble that of orbital motion with a primary core eddy surrounded by gyrating satellite vortices, typical of a supercritical flow in a square LDC. Upon increasing the AR, there is a major shift in the vorticity transfer from the top right corner (acting as the source of maximum vorticity generation) toward the left square sub-cells in the domain. This is further aided by the convective motion due to the imposed destabilizing vertical thermal gradient. The spectra demonstrate that a multi-periodic, chaotic flow is the consistent flow feature for the rectangular LDC for Re = 5500, irrespective of the AR. The compressible enstrophy budget of the rectangular LDC with varying AR is computed for the first time. This shows the dominance of the baroclinic vorticity over the viscous diffusion terms, which was conceived of as the major contributor to the creation of rotational flow structures. [ABSTRACT FROM AUTHOR]

Here, the perturbation equation for a dissipative medium is derived from the first principles for the linearized compressible Navier–Stokes equation without Stokes' hypothesis. Dispersion relations of this generic governing equation are obtained, which exhibits both the dispersive and dissipative nature of perturbations traveling in a dissipative medium, depending upon the length scale. We specifically provide a theoretical cutoff wave number above which the perturbation equation represents diffusive and dissipative nature of the quiescent flow. It is shown that perturbation equations for pressure and velocity retain the same form in one-dimension, but it is not the same for multi-dimensional perturbation fields. Such behavior has not been reported before, as per the knowledge of the authors. [ABSTRACT FROM AUTHOR]

Numerical investigation of the coupled Kelvin–Helmholtz Rayleigh–Taylor instability (KHRTI) is presented here by solving the compressible Navier–Stokes equations for two air streams differentially heated in two halves of a three-dimensional (3D) box. Here, we explore the role of a stabilizing and destabilizing thermal gradient and that of reversing the direction of the air streams considered for Atwood numbers of ±0.1567 and dimensionless tangential shear of Δ U = 0.68 and 4.1. The onset of the KHRTI and development of the turbulent mixing layer are explored via time-resolved and instantaneous distributions of temperature and vorticity. Early stages of the KHRTI with reversed air streams follows a Kelvin–Helmholtz (KH) mechanism, with Rayleigh–Taylor (RT) dynamics becoming important at later times. This leads to an earlier development of the turbulent mixing layer. The KHRTI with stabilizing or destabilizing thermal gradients shows a dominance of the buoyancy-driven mechanism, right from the onset. The transition from laminar to turbulent mixing layer involves the creation of coherent structures of spikes, bubbles, and KH whirls for the destabilizing, stabilizing thermal gradient, and reversed shear cases, respectively. The spectra of the turbulent signals reveal a −5/3 scaling when the shear-driven mechanism is prevalent in the flow and −11/5 scaling when the buoyancy-driven effects become prominent. The compressible enstrophy budget of the KHRTI shows that the onset process is dominated by vortex stretching or compressibility effects, followed by a sharp rise in baroclinic torque contribution once the buoyancy effects become relevant. [ABSTRACT FROM AUTHOR]

A super wideband (SWB) (3.1GHz – 24.58 GHz) BPF is proposed with a notch-band using stub-loaded multi-mode resonator (MMR). The MMR is created by two pairs of stepped impedance coupling strip lines with open stubs, tightly coupled with four identical high impedance transmission lines. The center of each pair of symmetric high impedance transmission lines is connected with single open-ended shunt stub. The first responses of UWB with frequency range 3.1 – 10.5 GHz and the second response of 14.86 – 24.58 GHz are reported here for some part of FSS (Fixed-satellite radio-communication service ITU band), Space Research, and Radio Navigation purposes. A notch band appears at 12 GHz which could effectively suppress the interference of the fixed and broadcasting satellite services of the radio communication equipment. The filter is realized on FR-4 epoxy substrate (εr = 4.4 and thickness = 1.6 mm) and measured to validate the predicted results. The group delay of the filter is nearly constant and varies in the range 0.26 – 0.6 ns over the desired passband. [ABSTRACT FROM AUTHOR]

A numerical investigation of Rayleigh–Taylor instability (RTI) with different unstable thermal stratifications, and coupled Kelvin–Helmholtz (KH) and RTI (referred to as KHRTI) is performed by solving the compressible Navier–Stokes equation. Two air masses having temperature differences of Δ T * = 21.75 and 46.5 K [corresponding to Gay–Lussac numbers (Ga) of 0.073 and 0.156] are considered in an isolated box, initially separated by a non-conducting interface for studying RTI. For KHRTI, dimensionless tangential shear of Δ U = 0.92 and 1.89 is additionally imposed on the two air masses with Δ T * = 21.75 K. Onset propagation and fully developed stages of the instabilities are explored via time-resolved and instantaneous temperature and vorticity. For RTI, lower Δ T * case shows retarded growth of the mixing layer and a set of interpenetrating bubbles. The higher Δ T * case shows an accelerated growth of the mixing layer with alternating rows of spikes and bubbles. For KHRTI, flow is governed by KH dynamics at early times and RT dynamics at later times. To further understand the interaction between RT and KH mechanisms, a compressible enstrophy transport equation in Suman et al. ["A novel compressible enstrophy transport equation based analysis of instability of Magnus–Robins effects for very high rotation rates," Phys. Fluids 34, 044114 (2022)] is used. Depending on Ga, either vortex stretching or compressibility contribution terms of the enstrophy transport are dominant for RTI. Depending on the shear imposed, either baroclinic torque or viscous terms are dominant for KHRTI. [ABSTRACT FROM AUTHOR]

Investigations have been performed via implicit large eddy simulations to study the overall effects of exciting a flow field by thermal (wall-heating and wall-cooling) and vortical (with high and low frequencies) actuation. The actuator is placed on the suction surface of a natural laminar flow (SHM-1) airfoil having an angle of attack of α = 0.38 ° (cruise setting). Oncoming flow has a Mach number of 0.72, and a Reynolds number based on a chord of R e = 16.2 × 10 6 , for which a complex shock system is formed on the suction surface. Vorticity dynamics of the flow is studied using time series of vorticity at different locations above the suction surface and instantaneous contour plots of vorticity in the domain. An inspection of the flow using snapshots of ∇ ρ and ∇ (ρ T) is done to characterize the numerical schlieren. The comparative effects of the various forms of excitation on the shock–boundary layer interactions (SBLI) have been analyzed using time series of the magnitudes of ∇ ρ across the identified shock structures from numerical schlieren snapshots. Also, the role of the frequency of imposed vortical actuation has been studied using vorticity and Mach contours for a comparative understanding of the control of the SBLI. [ABSTRACT FROM AUTHOR]

Rayleigh–Taylor instability (RTI) occurs when the interface between two fluids of different densities is removed, with the heavier (cold) fluid resting on top of the lighter (hot) fluid in the equilibrium state. This arrangement is unstable due to buoyancy, in the absence of any other forces. RTI is noted across a range of length scales from very small in nuclear fusion to supernova explosion at astrophysical scales. RTI is viewed as a baroclinic instability if viscous actions are ignored. An accurate non-overlapping parallel algorithm is used to solve a three-dimensional RTI problem, employing more than 4 × 109 points and a refined time step (7.69 × 10 − 8 s) for the direct numerical simulation. Air masses at two different temperatures are initially separated by a non-conducting partition inside a box (with a temperature difference of 200 K). The impermeable partition is removed impulsively at t = 0, and the ensuing instability is triggered by an acoustic mechanism involving infra to ultrasonic pulses that travel to either side of the interface. Present high precision petascale computations enable one to capture acoustic disturbances with unprecedented accuracy without any additional interfacial disturbances. The creation of the vorticity is studied by performing enstrophy budget for the compressible flow for RTI, which shows that the viscous terms are dominant compared to the baroclinic one. [ABSTRACT FROM AUTHOR]

Balanced and healthy nutrition is a vital to attain a good immune response. Numerous studies have reported that boosting up adaptive immunity through nutritional interventions can impede viral infections. With the present leading challenge of the COVID-19 pandemic globally, maintaining good nourishment is indispensable to remain immune against the novel virus. By and large, ineffectively fed people are at a higher risk of creating different kinds of contaminations. In addition, constant and extreme contagion can cause health problems and demolish a patient's nourishing status, making them susceptible to different diseases. During the COVID-19 pandemic, everyone must screen their eating routine and nourishing status. Good nutrition can subside the ongoing unprecedented health complications and deaths. Evaluating the clinical status of COVID-19 cases at the hour of clinic confirmation is strongly recommended. Specific dietary help is prescribed to be given to those in the highhazard bunch, asymptomatic transporters, and patients with moderate or extreme COVID infection. An assortment of micronutrients techniques to treat COVID-19 can prove beneficial at the preliminary stage of the clinical attendance. The prompt supplementation of specific supplements in gentle cases can forestall the movement of sicknesses. [ABSTRACT FROM AUTHOR]

Implicit large eddy simulation results are compared to investigate the effects of wall-heating and wall-cooling on shock–boundary layer interaction over an airfoil. Heat flux is provided on the suction surface of the airfoil from x / c = 0.40 to x / c = 0.50 for a Mach number of 0.72 and a Reynolds number based on chord of R e = 16.2 × 10 6 . Flow quantities are compared for the effects of heating and cooling. Numerical Schlieren snapshots reveal an oscillation of the shock wave and its interaction with upstream propagating Kutta waves generated from the trailing edge of the airfoil. Quantitative data obtained from these Schlieren snapshots and the mean aerodynamic load values indicate a reduction in frequency of oscillation of shock wave and a decrease in shock strength for the case of heating. Flow control by heating shows higher fluctuations in flow features evident from instantaneous quantities. Both imposed excitations lead to a marginal increase in aerodynamic efficiency (lift/drag). We also compare the integral aerodynamic parameters, such as lift and drag coefficients, and their ratio, C l , C d , and C l / C d . The simulations reported here follow the techniques used in Sengupta et al. ["Thermal control of transonic shock–boundary layer interaction over a natural laminar flow airfoil," Phys. Fluids 33(12), 126110 (2021)]. [ABSTRACT FROM AUTHOR]

The effects of compressibility on the instability of a two-dimensional flow past a rotating cylinder executing high rotation rates are investigated, in detail, using a novel analysis based on the compressible enstrophy transport equation (CETE). Accurate analysis of the instability necessitates the generation of high fidelity numerical solutions, and this is achieved by employing optimized numerical methods that enable high accuracy direct numerical simulation of compressible flows. To study the effects of compressibility induced by rotation alone, a low free stream Mach number and two high rotation rates are considered, as compared to that reported in the literature. Results demonstrate single-sided vortex shedding, the presence of significant compressibility in the flow field confirmed by local Mach number, and temperature and density gradient fields with transient formation of supersonic pockets noted for the higher rotation speed cases. The temporal instability is studied by analyzing the relative contributions of different terms in the CETE to the growth of enstrophy. As per the authors' knowledge, this is the first such research effort demonstrating an application of the CETE for instabilities. Analysis shows that viscous diffusion is the dominant mechanism in creating the flow instability with a secondary role played by the baroclinic mechanism. [ABSTRACT FROM AUTHOR]

Understanding the mechanisms underlying the assembly of communities has long been the goal of many ecological studies. While several studies have evaluated community wide ecological assembly, fewer have focused on investigating the impacts of individual members within a community or assemblage on ecological assembly. Here, we adapted a previous null model β-nearest taxon index (βNTI) to measure the contribution of individual features within an ecological community to overall assembly. This new metric, called feature-level βNTI (βNTIfeat), enables researchers to determine whether ecological features (e.g., individual microbial taxa) contribute to divergence, convergence, or have insignificant impacts across spatiotemporally resolved metacommunities or meta-assemblages. Using βNTIfeat, we revealed that unclassified microbial lineages often contributed to community divergence while diverse groups (e.g., Crenarchaeota, Alphaproteobacteria, and Gammaproteobacteria) contributed to convergence. We also demonstrate that βNTIfeat can be extended to other ecological assemblages such as organic molecules comprising organic matter (OM) pools. OM had more inconsistent trends compared to the microbial community though CHO-containing molecular formulas often contributed to convergence, while nitrogen and phosphorus-containing formulas contributed to both convergence and divergence. A network analysis was used to relate βNTIfeat values from the putatively active microbial community and the OM assemblage and examine potentially common contributions to ecological assembly across different communities/assemblages. This analysis revealed that P-containing formulas often contributed to convergence/divergence separately from other ecological features and N-containing formulas often contributed to assembly in coordination with microorganisms. Additionally, members of Family Geobacteraceae were often observed to contribute to convergence/divergence in conjunction with both N- and P-containing formulas, suggesting a coordinated ecological role for family members and the nitrogen/phosphorus cycle. Overall, we show that βNTIfeat offers opportunities to investigate the community or assemblage members, which shape the phylogenetic or functional landscape, and demonstrate the potential to evaluate potential points of coordination across various community types. [ABSTRACT FROM AUTHOR]

Implicit large eddy simulations are performed to show control of shock and boundary layer interaction over a natural laminar flow airfoil by harmonic heat transfer on the suction surface at a free-stream Mach number M ∞ = 0.72 and angle of attack of α = 0.38 ° , for which experimental/flight test results exist. Surface heat flux is added in a time-periodic manner with the exciter strip located at different locations in the vicinity of the shock location at x / c ≈ 0.49 for the flow without any control. Four cases of localized excitation with Gaussian distribution centered at x / c = 0.45 , 0.48, 0.50, and 0.55 on the airfoil surface are considered, with a width of 10% chord. The effects of unsteady heat flux on shock strength, location, and modification of its structure are demonstrated by instantaneous and time-averaged flow quantities. Detailed vortical and entropy contour plots and numerical Schlieren indicate flow features, such as creation and propagation of Kutta waves and their interactions with the shock wave. Time-averaged load distributions reveal a shift in the location and strength of the shock, with altered lift and drag time histories. The Fourier transforms of lift and drag coefficients help explain the alteration of the strength and structures of the shock-induced unsteadiness. The imposed excitation results in an improvement of aerodynamic efficiency (lift to drag ratio). The numerical simulations follow the algorithm developed in Sengupta et al. [Comput. Fluids 88, 19–37 (2013)]. [ABSTRACT FROM AUTHOR]

Microbial communities in incipient soil systems serve as the only biotic force shaping landscape evolution. However, the underlying ecological forces shaping microbial community structure and function are inadequately understood. We used amplicon sequencing to determine microbial taxonomic assembly and metagenome sequencing to evaluate microbial functional assembly in incipient basaltic soil subjected to precipitation. Community composition was stratified with soil depth in the pre-precipitation samples, with surficial communities maintaining their distinct structure and diversity after precipitation, while the deeper soil samples appeared to become more uniform. The structural community assembly remained deterministic in pre- and post-precipitation periods, with homogenous selection being dominant. Metagenome analysis revealed that carbon and nitrogen functional potential was assembled stochastically. Sub-populations putatively involved in the nitrogen cycle and carbon fixation experienced counteracting assembly pressures at the deepest depths, suggesting the communities may functionally assemble to respond to short-term environmental fluctuations and impact the landscape-scale response to perturbations. We propose that contrasting assembly forces impact microbial structure and potential function in an incipient landscape; in situ landscape characteristics (here homogenous parent material) drive community structure assembly, while short-term environmental fluctuations (here precipitation) shape environmental variations that are random in the soil depth profile and drive stochastic sub-population functional dynamics. [ABSTRACT FROM AUTHOR]

Conceptual frameworks linking microbial community membership, properties, and processes with the environment and emergent function have been proposed but remain untested. Here we refine and test a recent conceptual framework using hyporheic zone sediments exposed to wetting–drying transitions. Our refined framework includes relationships between cumulative properties of a microbial community (e.g., microbial membership, community assembly properties, and biogeochemical rates), environmental features (e.g., organic matter thermodynamics), and emergent ecosystem function. Our primary aim was to evaluate the hypothesized relationships that comprise the conceptual framework and contrast outcomes from the whole and putatively active bacterial and archaeal communities. Throughout the system we found threshold-like responses to the duration of desiccation. Membership of the putatively active community – but not the whole bacterial and archaeal community – responded due to enhanced deterministic selection (an emergent community property). Concurrently, the thermodynamic properties of organic matter (OM) became less favorable for oxidation (an environmental component), and respiration decreased (a microbial process). While these responses were step functions of desiccation, we found that in deterministically assembled active communities, respiration was lower and thermodynamic properties of OM were less favorable. Placing the results in context of our conceptual framework points to previously unrecognized internal feedbacks that are initiated by disturbance and mediated by thermodynamics and that cause the impacts of disturbance to be dependent on the history of disturbance. [ABSTRACT FROM AUTHOR]