Gas transport through porous coal contains gas laminar flow in the cleat network and gas adsorption/diffusion in the matrix block. Since permeable capacity of the cleat is greater than that of the ...matrix, change of the matrix pressure readily lags behind change in the cleat pressure. Such unsynchronized pressure changes can result in a complex compatible deformation of a cleat-matrix system, significantly affecting the coal permeability. In this paper, we investigated the cleat-matrix interaction on coal permeability by using a modified pressure pulse decay method integrated with numerical analysis. The experimental results indicate that the bulk volume of the coal sample rapidly expanded at the beginning of gas injection, and then the volume expansion rate of the coal sample slowed down as the downstream pressure of the coal sample gradually equilibrated with the upstream pressure. During this process, the coal permeability was observed to gradually decrease with time. Numerical analysis results indicate that gas transport from the cleat to the matrix can attenuate the differential pressure between the cleat and the matrix. A smaller ratio of initial matrix permeability to initial cleat permeability can prolong decay duration of the differential pressure inside the cleat-matrix system. Although the coal sample is subjected to a stress-controlled condition, the coal permeability response to gas diffusion is closer to the case using a constant volume boundary. The dynamic change of coal permeability is significantly affected by the cleat-matrix interaction, in cases where the short-term change is mainly attributable to the cleat network and the long-term change is controlled by matrix swelling/shrinkage.
Biological nitrogen (N) fixation (BNF) via diazotrophs is an important ecological process for the conversion of atmospheric N to biologically available N. Although soil diazotrophs play a dominant ...role in BNF and arbuscular mycorrhizal fungi (AMF) serve as helpers to favor BNF, the response of soil BNF and diazotrophic communities to different long‐term fertilizations and the role of AMF in diazotrophs‐driven BNF are poorly understood. Herein, a 33‐year fertilization experiment in a wheat–maize intercropping system was conducted to investigate the changes in soil BNF rates, diazotrophic and AMF communities, and their interactions after long‐term representative fertilization (chemical fertilizer, cow manure, wheat straw, and green manure). We found a remarkable increase in soil BNF rates after more than three decades of fertilization compared with nonfertilized soil, and the green manure treatment rendered the highest enhancement. The functionality strengthening was mainly associated with the increase in the absolute abundance of diazotrophs and AMF and the relative abundance of the key ecological cluster of Module #0 (gained from the co‐occurrence network of diazotrophic and AMF species) with dominant diazotrophs such as Skermanella and Azospirillum. Furthermore, although the positive correlations between diazotrophs and AMF were reduced under long‐term organic fertilization regimes, green manuring could reverse the decline within Module #0, and this had a positive relationship with the BNF rate. This study suggests that long‐term fertilization could promote N fixation and select specific groups of N fixers and their helpers in certain areas. Our work provides solid evidence that N fixation and certain groups of diazotrophic and AMF taxa and their interspecies relationship will be largely favored after the fertilized strategy of green manure.
In this study, a 33‐year fertilization experiment was conducted to investigate the changes in soil BNF rates, diazotrophic and AMF communities, and their interactions after various long‐term fertilizations. We found a remarkable increase in soil BNF rates after more than three decades of fertilization compared with nonfertilized soil, and the green manure treatment rendered the highest enhancement.
Highlights
Long‐term fertilization enhanced soil biological nitrogen fixation (BNF).
Diazotrophic and arbuscular mycorrhizal fungal (AMF) abundance is positively linked to BNF.
Key ecological cluster consisting of diazotrophs and AMF played vital roles in soil BNF.
Long‐term fertilization reduced the synergistic functions of diazotrophs and AMF.
Green manure strengthened the synergistic function within the key ecological cluster.
Shale gas is becoming an important component of the global energy supply, with permeability a critical controlling factor for long‐term gas production. Obvious deviation may exist between helium ...permeability determined using small pressure gradient (SPG) methods and methane permeability obtained under actual field production with variable pressure gradients (VPG). In order to more accurately evaluate the matrix permeability of shale, a VPG method using real gas (rather than He) is established to render permeability measurements that are more representative of reservoir conditions and hence response. Dynamic methane production experiments were performed to measure permeability using the annular space in the shale cores. For each production stage, boundary pressure is maintained at a constant and the gas production with time is measured on the basis of volume change history in the measuring pump. A mathematical model explicitly accommodating gas desorption uses pseudo‐pressure and pseudo‐time to accommodate the effects of variations in pressure‐dependent PVT parameters. Analytical and semi‐analytical solutions to the model are obtained and discussed. These provide a convenient approach to estimate radial permeability in the core by nonlinear fitting to match the semi‐analytical solution with the recorded gas production data. Results indicate that the radial permeability of the shale determined using methane is in the range of 1×10−6 – 1×10−5 mD and decreases with a decrease in average pore pressure. This is contrary to the observed change in permeability estimated using helium. Bedding geometry has a significant influence on shale permeability with permeability in parallel bedding orientation larger than that in perpendicular bedding orientation. The superiority of the VPG method is confirmed by comparing permeability test results obtained from both VPG and SPG methods. Although several assumptions are used, the results obtained from the VPG method with reservoir gas are much closer to reality and may be directly used for actual gas production evaluation and prediction, through accommodating realistic pressure dependent impacts.
Biological nitrogen fixation contributes to the pool of plant-available N in both bulk soil and the rhizosphere. Here we investigated the co-association and assemblage process of diazotrophic ...community members in both rhizosphere and bulk soil of wheat fields. The diazotrophic community structure in the rhizosphere was significantly different and comprised a less competitive and more stable network structure when compared with that of the bulk soil. Deterministic versus stochastic community assemblage processes were quantified using betaNTI scores, demonstrating that deterministic processes decreased in importance with distance from plant roots. Soil pH was correlated with diazotrophic community structure and diversity, and community structure showed greater connectivity and stability in soils with neutral pH relative to those in acidic or alkaline soils. Stochastic processes dominated the assemblage of the diazotrophic community in soils with neutral pH, while deterministic processes dominated in acidic or alkaline soils. These results suggest that soil pH may play an essential role in the interaction and assemblage processes of the diazotrophic community in the rhizosphere and bulk soils, which could enhance our understanding of biological nitrogen fixation in agricultural soils.
•Diazotrophic community differed dramatically between bulk and rhizospheric soils.•Rhizosphere diazotrophs comprised less competitive, more stable network structure.•Deterministic processes decreased in importance with distance from plant roots.•Soil pH regulates diazotrophic community co-occurrence and assemblage process.
The spatial distribution of bacteria in bulk soil has been well studied, but little is known about the bacterial biogeography in the rhizosphere of crops. Here, we investigated bacterial distribution ...in bulk soil, loosely- and tightly-bound soils, from wheat fields distributed across 800,000 km2 of the North China Plain. Bacterial community composition differed dramatically among bulk and rhizospheric soils, and bacterial diversity decreased with the root proximity. Soil pH correlated with bacterial community composition and diversity in three compartments. Bacterial community in tightly bound soil formed a hub-based network topology with higher transitivity and greater number of central nodes compared with loosely bound and bulk soils, potentially as a result of more direct ecological interactions between the members of the tightly bound soil compartment. Bulk and rhizospheric soils maintained similar compositional distance decay patterns (with equal decay rates), but distinct phylogenetic distance decay patterns (with steeper slope of tightly bound soil). Geographical distance described a relatively greater proportion of bacterial spatial distribution in tightly bound soil, compared with loosely bound soil and bulk soil. Deterministic processes dominated the assemblage of bacterial communities in all soil compartments, while phylogenetic clustering was weaker in tightly bound soil. Taken together, our results suggest distinct bacterial network structure and distribution patterns among bulk soil, loosely bound soil and tightly bound rhizospheric soil, which could possibly result in potential functional differentiation.
•Bacterial communities differed dramatically between bulk and rhizospheric soils.•Soil pH was an important factor for bacterial distribution in wheat crop fields.•Bacterial communities in rhizosphere formed hub-based network topology.•Geographic distance contributed more to bacterial distribution in rhizosphere.
Unraveling the drivers of microbial community variation in response to different environmental conditions is a major goal in ecology. Although diazotrophs play a dominant role in global biological ...nitrogen (N2) fixation, the controls on soil diazotrophic community assembly are not fully understood. In this study, we investigated soil diazotrophic communities in field plots that received long-term (30 years) fertilization treatments with Illumina MiSeq sequencing. Long-term chemical fertilization significantly changed soil diazotrophic community structure and resulted in the decrease of diazotrophic diversity, while the addition of livestock manure could maintain the diversity. Diazotrophic community structure and diversity were mostly correlated with soil pH. Deterministic processes structured diazotrophic communities in both unfertilized and fertilized soils. However, the deterministic selection on phylogenetically non-conserved traits increased phylogenetic randomness in all fertilized treatments. These trends for diazotrophs differed from those for the entire bacterial community, which was structured through deterministic processes and exhibited phylogenetic nonrandomness in unfertilized and fertilized soils. Taken together, our results indicated that long-term fertilization strongly affected the diversity, community structure and assembly processes of soil diazotrophs, which may have implications for the rate of biological N2 fixation in agricultural systems.
•Addition of livestock manure could maintain soil diazotrophic diversity.•Deterministic processes structured diazotrophic community in all treatments.•Fertilization increased phylogenetic randomness of diazotrophic communities.•Phylogenetic patterns differed between diazotrophs and bacteria.
Strong associations exist between microbial communities and soil functions in natural ecosystems at large spatial scales; however, it is unclear whether these linkages are maintained in intensively ...managed croplands and whether these associations influence plant productivity. We collected bulk and rhizosphere soils from wheat fields –one of the most functionally and economically important crops worldwide –across the North China Plain (~300,000 km2), and examined the relationship between species-level multitrophic taxa, functional genes and wheat productivity. Our work identified significant and positive correlations of wheat productivity to the relative abundance of multitrophic clusters (co-occurring groups of soil biota including bacteria, fungi, arbuscular mycorrhizal fungi, and nematodes), and absolute abundance of functional genes associated with carbon, nitrogen, phosphorus, and sulfur cycles. We observed significant, biologically meaningful correlations between plant productivity and the abundance of specific root-associated microbial taxa and functional genes. These important linkages were robust when considered in combination with spatial, climate, and edaphic variables. Our findings highlight the importance of soil multitrophic communities in regulating soil functional potential and plant productivity, and provide a list of key-stone functional genes, which could be targeted to promote food security and production.
•Relative abundance of multitrophic clusters positively relate to crop production.•Key-stone microbial groups correlate with crop production at large spatial scales.•Multitrophic microbes and functions could be bioindicators of plant production.
There is a current lack of mechanistic understanding on the relationships between a soil microbial community, crop production, and nutrient fertilization. Here, we combined ecological network theory ...with ecological resistance index to evaluate the responses of microbial community to additions of multiple inorganic and organic fertilizers, and their associations with wheat production in a 35-year field experiment. We found that microbial phylotypes were grouped into four major ecological clusters, which contained a certain proportions of fast-growers, copiotrophic groups, and potential plant pathogens. The application of combined inorganic fertilizers and cow manure led to the most resistant (less responsive) microbial community, which was associated with the highest levels of plant production, nutrient availability, and the lowest relative abundance of potential fungal plant pathogens after 35 years of nutrient fertilization. In contrast, microbial community was highly responsive (low resistance) to inorganic fertilization alone or plus wheat straw, which was associated with lower crop production, nutrient availability, and higher abundance of potential fungal plant pathogens. Our work demonstrates that the response of microbial community to long-term nutrient fertilizations largely regulates plant production in agricultural ecosystems, and suggests that manipulating these microbial phylotypes may offer a sustainable solution to the maintenance of field productivity under long-term nutrient fertilization scenarios.
•Microbial resistance to fertilization positively links to soil available nutrients.•Microbial resistance to fertilization negatively associates with plant pathogens.•Microbial resistance to fertilization positively correlates with plant production.
Methane adsorption capacity is a key factor in determining shale gas in place (GIP) – requiring that it is determined under in situ moisture conditions. Current methods may be insufficient to ...investigate these exact characteristics when applied to actual reservoirs with high or variable moisture contents. We propose a heating and cooling (HC) method to prepare shale samples to arbitrary moisture contents (Mc up to 10%). A series of CH4 adsorption experiments on two different types of shale are conducted as a function of Mc at 35 °C, 45 °C, and 55 °C, and at a CH4 pressure of up to 10 MPa. Experimental results indicate that the methane sorption capacity versus moisture content curves exhibit a linear decreasing stage, a flat stage and a convex decreasing stage, separated by two threshold moisture contents. The lower moisture content threshold (Mfc) represents coverage of the entire hydrophilic surface by a monolayer of water. The upper moisture content threshold (Msc) is the point at which no methane is adsorbed on the surface of the clay pores and adsorption capacity is further reduced as moisture content is increased. The linear stage with Mc up to the Mfc is mainly dominated by the competition between water and methane for adsorption sites on the surface of clay pores. Slope value of this stage are affected by pressure, temperature and shale compositions. The flat stage represents that the moisture content has negligible effect on shale adsorption capacity for Mc in the range Mfc to Msc. Methane adsorption capacity decreases in a convex manner above Msc, suggesting water condensation in organic pores as the surface area for methane adsorption is reduced by water blocking. A conceptual Bi-Langmuir model is presented to represent the crucial effects of moisture content on methane adsorption capacity including accurate estimations of original GIP under different reservoir conditions.
Human activity plays a crucial role in influencing PM2.5 concentration and can be assessed through nighttime light remote sensing. Therefore, it is important to investigate whether the nighttime ...light brightness can enhance the accuracy of PM2.5 simulation in different stages. Utilizing PM2.5 mobile monitoring data, this study introduces nighttime lighting brightness as an additional factor in the PM2.5 simulation model across various time periods. It compares the differences in simulation accuracy, explores the impact of nocturnal human activities on PM2.5 concentrations at different periods of the following day, and analyzes the spatial and temporal pollution pattern of PM2.5 in urban functional areas. The results show that (1) the incorporation of nighttime lighting brightness effectively enhances the model's accuracy (R2), with an improvement ranging from 0.04 to 0.12 for different periods ranges. (2) the model's accuracy improves more prominently during 8:00–12:00 on the following day, and less so during 12:00–18:00, as the PM2.5 from human activities during the night experiences a strong aggregation effect in the morning of the next day, with the effect on PM2.5 concentration declining after diffusion until the afternoon. (3) PM2.5 is primarily concentrated in urban functional areas including construction sites, roads, and industrial areas during each period. But in the period of 8:00–12:00, there is a significant level of PM2.5 pollution observed in commercial and residential areas, due to the human activities that occurred the previous night.
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•Introduce nighttime lighting brightness as an independent variable in the PM2.5 model for more accurate simulation.•To explore the influence of nocturnal human activities on PM2.5 in different periods of the next day.•Analyze the fine-scale spatial and temporal pattern of PM2.5 pollution in the city.•To explore the degree of PM2.5 pollution in different Urban functional areas.
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