Microbial Mineralization Research Articles

Culture-dependent and culture-independent methods reveal microbe-clay mineral interactions by dissimilatory iron-reducing bacteria in an integral oilfield

Fe(III) may be reasonably considered as one of the most important electron acceptors in petroleum reservoir ecosystems. The microbial mineralization of clay minerals, especially montmorillonite, is also of great significance to the exploration of petroleum and gas reservoirs. The bioreduction mechanisms of iron-poor minerals in petroleum reservoirs have been poorly investigated. This study investigated the bioreduction of montmorillonite by dissimilatory iron-reducing bacteria (DIRB) in petroleum reservoirs based on culture-independent and culture-dependent methods. Microbial diversity analysis revealed that Halolactibacillus, Bacillus, Alkaliphilus, Shewanella, Clostridium, and Pseudomonas were the key genera involved in the bioreduction of Fe(III). Through the traditional culture-dependent method, most of the key genera were isolated from the samples collected from petroleum reservoirs. Traditional culture-dependent methods can be used to reveal the metabolic characteristics of microorganisms (such as iron-reduction efficiency) to further elucidate the roles of different species (B. subtilis and B. alkalitelluris) in the environment. Moreover, many species with high iron-reduction efficiencies and relatively low abundances in the samples, such as Tessaracoccus and Flaviflexus, were isolated from petroleum reservoirs for the first time. The combination of culture-dependent and culture-independent methods can be used to further the understanding of the microbial communities and the metabolic characteristics of DIRB in petroleum reservoirs. Structural alterations that occurred during the interactions of microorganisms and montmorillonite were revealed through scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray powder diffraction (XRD). The physical and chemical analysis results demonstrated that microorganisms from petroleum reservoirs can dissolve iron-poor montmorillonite and promote the release of interlayer water. The secondary minerals illite and clinoptilolite were observed in bioreduced smectite. The formation of secondary minerals was closely related to the dissolution degrees of minerals based on iron reduction.

Effects of common European tree species on soil microbial resource limitation, microbial communities and soil carbon

Studies of tree species effects on soils have revealed a significant impact on soil organic carbon (SOC) stocks and the carbon (C) distribution between forest floor and mineral soil, but the underlying mechanisms including the roles of litter traits, soil properties, and microbiome remain unclear. To address this challenge, we tested the effect of six common European tree species on the quality and nutrient availability of soil organic matter (SOM) as perceived by the naturally assembled microbial communities and explored the possible links between soil enzyme activities (EAs), microbial resource limitation, and microbial community with SOC stocks. The six studied tree species (Acer pseudoplatanus L., Fraxinus excelsior L, Fagus sylvatica L., Quercus robur L., Tilia cordata L., and Picea abies L.) were planted in common garden monocultures more than 40 years ago at six sites across Denmark. In forest floor, microbial biomass C, fungal and total microbial biomass and fungi to bacteria (F/B) ratios decreased with decreasing litter quality. Ecoenzymatic stoichiometry and relative EAs indicated that microbes in spruce forest floor were more limited by phosphorus (P) than in maple, lime, and beech, while microbes in mineral soils were less P limited in spruce than in other monocultures. Mineral soil under the tree species associated with arbuscular mycorrhizal (AM) fungi had higher microbial C and P limitation, bacterial biomass and total microbial biomass than under tree species associated with ectomycorrhizal (EcM) fungi. Our results indicated that tree species with high-quality litter (i.e. AM-associated trees) had (i) higher microbial biomass and less nutrient limitation that were conducive to higher decomposition rates and lower C stocks in the forest floor, and (ii) such tree species could lead to both greater stabilization of mineral soil C by mineral-associated OM formation and greater microbial mineralization of SOM with higher microbial resource demand. The results suggest that tree species-mediated EA, microbial resource limitation and microbial community composition are important drivers of stocks and vertical distribution of SOC among tree species and between the two types of associated mycorrhiza.

Effects of Hydroxypropyl Methylcellulose (HPMC) on the Reinforcement of Sand by Microbial-Induced Calcium Carbonate Precipitation (MICP)

Microbial-induced calcium carbonate precipitation (MICP) is a new technology used for reinforcing soils through microbial mineralization. However, the existing MICP treatment technology is more suiTable for deeper soils due to its high permeability. In this study, HPMC, a cohesive material combined with Sporosarcina pasteurii-induced calcium carbonate precipitation was used to improve the surface layer of the soil. It was also tested in different contents of bacterial solutions and cementation solutions and with a different number of MICP treatments, and was analyzed and discussed by measuring the surface layer strength, calcium carbonate content generated in the crust, rainfall erosion resistance, wind erosion resistance, and ammonia retention rate of the specimens. The microstructure of the samples was investigated by XRD and SEM. It was shown that the addition of HPMC and increasing the number of MICP treatments were effective in the increase in the calcium carbonate content in the surface crust, but had no effect on the total amount of induced calcium carbonate. The combination of HPMC addition and MICP technology can effectively reduce rainwater scour loss and wind erosion loss, and increase its rainfall erosion resistance and wind erosion resistance. Rainfall losses were reduced by up to 30% in specimens treated with HPMC for MICP technology. When the wind speed was 12 m/s, the maximum mass loss rate of the specimens treated with HPMC for MICP was only 0.828%. The addition of HPMC can effectively improve the ammonia absorption rate and reduce the release of ammonia in the process of MICP technology, which is of great significance for environmental protection. The microstructure showed that the addition of HPMC and the increase in the number of treatments using MICP technology can make the surface structure of the specimens more compact, and the calcium carbonate can more effectively fill the pores and cement the soil particles, while the addition of HPMC may not change the calcium carbonate crystal type.

Effects of Microbial-Mineral Interactions on Organic Carbon Stabilization in a Ponderosa Pine Root Zone: A Micro-Scale Approach

Soil microbial communities affect the formation of micro-scale mineral-associated organic matter (MAOM) where complex processes, including adhesion, aggregate formation, microbial mineral weathering and soil organic matter stabilization occur in a narrow zone of large biogeochemical gradients. Here we designed a field study to examine carbon stabilization mechanisms by using in-growth mesh bags containing biotite that were placed in a ponderosa pine root zone for 6 months and compared to the surrounding bulk soil. We sought to determine the composition of the microbial community in the mesh bags compared to the surrounding soils, analyze the direct interactions between microbes and biotite, and finally identify the nature of the newly formed MAOM within the mesh-bags. Our results revealed that minerals in the mesh bags were colonized by a microbial community that produced organic matter in situ. The 16S rRNA gene sequencing and ITS2 region characterization showed phylogenetic similarity between the mesh bag and bulk soil archaea/bacteria and fungi microbiomes, with significant differences in alpha- and beta-diversity and species abundances. Organic matter pools in the mesh bags, analyzed by Fourier transform ion cyclotron resonance mass spectrometry, contained protein- (peptides) and lipid-like compounds while the bulk soil OM was comprised of lignin-like and carboxyl-rich alicyclic molecules. These results support that the newly formed biotite associated organic compounds have a microbial signature in the mesh bags. High-resolution electron microscopy documented strongly adhered organic compounds to biotite surfaces, formation of microaggregates, elemental uptake at the microbe (organic matter)-mineral interface, and distortion of biotite layers. Overall, this study shows the direct and indirect involvement of soil microbial communities from the root zone of ponderosa pine in the formation of MAOM, soil organic carbon stabilization, microaggregation, and mineral weathering at micro- and nano-scales.

Experimental Study on the Shear Strength of Loess Modified by Microbial Precipitation Technology

The shear strength (vertical pressure 50, 100, 200, and 300 kPa) and soil structure of the remolded loess with different proportions of the microbial cementing solution were measured and observed by the direct shear test and scanning electron microscopy (SEM).The results showed: (1) the increase in the microbial cementation solution led to the transformation of the stress-shear displacement curve from strain hardening to strain softening, with the transition interval of 26%∼34%. (2) With the increase in the microbial cementation solution, the change of cohesion showed a trend of “M,” the inflection point of the microbial cementation solution was 14%, 22%, and 34%, while the internal friction angle showed a law of “W,” where the inflection points of the internal friction angle were about 14%, 30%, 34%, and 38%, respectively. In the range of 18%∼30%, the cohesion and internal friction angle increase with an increase in the microbial cementation solution.(3) The change of cohesion is affected by the microbial mineralization saturation and the joint action of the occurrence state of Ca2+ and HCO3- in the microbial cementation solution. The change of internal friction angle is affected by the soil particle contact, the existing form of calcium carbonate formed by microbial precipitation, pore morphology, yield, and other forces. (4) By means of SEM, the distribution morphology of the soil particles and the contact microscopic images of the loess samples modified by microorganisms with different proportions were further verified to further verify the macroscopic changes of the shear strength of the modified loess samples cemented by microorganisms with different proportions. It provides a theoretical basis for the improvement of loess soil structure characteristics by microorganism calcium carbonate precipitation technology.

Methanotrophy Alleviates Nitrogen Constraint of Carbon Turnover by Rice Root-Associated Microbiomes.

The bioavailability of nitrogen constrains primary productivity, and ecosystem stoichiometry implies stimulation of N2 fixation in association with carbon sequestration in hotspots such as paddy soils. In this study, we show that N2 fixation was triggered by methane oxidation and the methanotrophs serve as microbial engines driving the turnover of carbon and nitrogen in rice roots. 15N2-stable isotope probing showed that N2-fixing activity was stimulated 160-fold by CH4 oxidation from 0.27 to 43.3 μmol N g–1 dry weight root biomass, and approximately 42.5% of the fixed N existed in the form of 15N-NH4+ through microbial mineralization. Nitrate amendment almost completely abolished N2 fixation. Ecophysiology flux measurement indicated that methane oxidation-induced N2 fixation contributed only 1.9% of total nitrogen, whereas methanotrophy-primed mineralization accounted for 21.7% of total nitrogen to facilitate root carbon turnover. DNA-based stable isotope probing further indicated that gammaproteobacterial Methylomonas-like methanotrophs dominated N2 fixation in CH4-consuming roots, whereas nitrate addition resulted in the shift of the active population to alphaproteobacterial Methylocystis-like methanotrophs. Co-occurring pattern analysis of active microbial community further suggested that a number of keystone taxa could have played a major role in nitrogen acquisition through root decomposition and N2 fixation to facilitate nutrient cycling while maintaining soil productivity. This study thus highlights the importance of root-associated methanotrophs as both biofilters of greenhouse gas methane and microbial engines of bioavailable nitrogen for rice growth.

Amorphous and Crystalline Carbonate Biomineralization in Cyanobacterial Biofilms Induced by Synechocystis sp. PCC6803 Cultured in CaCl2–MgCl2–SrCl2 Mediums

Ca2+, Mg2+, and Sr2+ are elements with similar ionic and hydrochemical characteristics, yet the microbial mineralization behavior in their coexisting environments is seldomly explored. In this study, the cyanobacterium Synechocystis sp. PCC6803 was used to induce the precipitation of minerals in mediums with various Mg/Ca and Sr/Ca ratios (Ca2+ = 0.01 M). The medium hydrochemistry, including cell density, solution pH, and alkalinity, was recorded periodically. The bio-precipitates were characterized with X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), Fourier Translation Infrared spectroscopy (FT-IR), and Thermal Gravimetric Analyzer (TGA). The results show the growth of Synechocystis sp. PCC6803 was inhibited by increasing ionic strength, although the final alkalinity and pH values of the medium were not affected. Two crystalline minerals, calcite (CaCO3) and strontianite (SrCO3) were precipitated in the mediums with low ionic strength; these were transformed from early amorphous precipitates by a dissolution and re-precipitation mechanism. The morphology of the precipitated cyanobacterial strontianite changed from columnar to dumbbell shape and finally into a spherulite shape. High concentrations of Sr2+, like Mg2+, prolonged the stabilization of amorphous carbonate precipitates. The acidic amino acids (Glu and Asp) in the EPS of Synechocystis sp. PCC6803 cultured in mediums with high Sr2+ and high Mg2+ concentrations increased significantly, compared to those cultured in a medium with no Sr2+ or Mg2+ (p < 0.005) ions. The negative binding energy calculated by Density Functional Theory (DFT) on the binding between the two acidic amino acids (Glu and Asp) and ion-H2O complexes (Ca[H2O]6 2+, Mg[H2O]6 2+, and Sr[H2O]6 2+), indicating that they are all thermodynamically-favored processes. Consequently, lower energy was needed in their subsequent precipitation and nucleation within the EPS of Synechocystis sp. PCC6803. This inferred process was also supported by the appearance of amorphous particles in the EPS of Synechocystis sp. PCC6803.

Effect of Environmental pH on Mineralization of Anaerobic Iron-Oxidizing Bacteria.

Freshwater lakes are often polluted with various heavy metals in the Anthropocene. The iron-oxidizing microorganisms and their mineralized products can coprecipitate with many heavy metals, including Al, Zn, Cu, Cd, and Cr. As such, microbial iron oxidation can exert a profound impact on environmental remediation. The environmental pH is a key determinant regulating microbial growth and mineralization and then influences the structure of the final mineralized products of anaerobic iron-oxidizing bacteria. Freshwater lakes, in general, are neutral-pH environments. Understanding the effects of varying pH on the mineralization of iron-oxidizing bacteria under neutrophilic conditions could aid in finding out the optimal pH values that promote the coprecipitation of heavy metals. Here, two typical neutrophilic Fe(II)-oxidizing bacteria, the nitrate-reducing Acidovorax sp. strain BoFeN1 and the anoxygenic phototrophic Rhodobacter ferrooxidans strain SW2, were selected for studying how their growth and mineralization response to slight changes in circumneutral pH. By employing focused ion beam/scanning electron microscopy (FIB–SEM) and transmission electron microscopy (TEM), we examined the interplay between pH changes and anaerobic iron-oxidizing bacteria and observed that pH can significantly impact the microbial mineralization process and vice versa. Further, pH-dependent changes in the structure of mineralized products of bacterial iron oxidation were observed. Our study could provide mechanical insights into how to manipulate microbial iron oxidation for facilitating remediation of heavy metals in the environment.

Advanced montmorillonite modification by using corrosive microorganisms as an alternative filler to reinforce natural rubber

Environmental pollution is produced when physical and chemical methods are used to modify montmorillonite. Herein, an advanced approach for calcium-based montmorillonite modification through microbial mineralization and microbial sulfate respiration is proposed. Microbial-induced calcium precipitates in the gaps between microbial montmorillonite layers to produce calcium carbonate particles, thereby increasing the interlayer gap. The microbial montmorillonite was used as a filler to reinforce natural rubber, and the natural rubber achieved a favorable tensile stress of 20.7 MPa because the polymer chains were interspersed in the montmorillonite interlayers. Further, the combined use of microbial montmorillonite and carbon black in the rubber compound provided an identical reinforcing effect to that of using only carbon black. The biological strategy in this study provides a facile method to modify exfoliable two-dimensional clays as reinforcing fillers for the rubber industry.

Environmental risk of multi-year polythene film mulching and its green solution in arid irrigation region

Environmental risk of multi-year polythene film mulching (PM) was evaluated and investigated. The location observation following 19-year (2000–2018) PM in irrigated region indicated that the cumulative accumulation of soil microplastics was as high as 2900 ± 19.5 n kg−1. Microplastic accumulation was tightly associated with soil plasticizer concentration (Pearson’s r = 0.728, p <0.05), and the concentration of dominant phthalic acid esters (PAEs) was up to 117.5–705 μg kg−1. As such, we conducted organic mulching substitute experiment (2019–2020) with non-mulching (CK), maize straw mulching (SM), living clover mulching (CM), PM, PM+SM and PM+CM respectively. The data showed that organic mulching (SM, CM) achieved similar productivity benefit as PM-involved treatments (p > 0.05). Critically, total concentration of PAEs decreased by 6.43% in SM relative to CK, and by 9.61% in PM+SM relative to PM respectively. High throughput sequencing indicated that the proportions of predominant bacteria and fungi were totally lower in PM than those of organic mulching, particularly Sphingomonadaceae and Stachybotryaceae. KEGG analyses indicated that organic mulching promoted the metabolisms of polycyclic aromatic hydrocarbons, benzoic acid (probability>75%) and heterologous organism metabolism (p<0.001), due to improved microbial community assembly. Therefore, organic mulching efficiently accelerated microbial mineralization of PM pollutants, and may act as a green solution to displace PM.

Microbial response to multiple-level addition of grass organic matter in lake sediments with different salinity.

Water surface expansion of saline lakes usually causes the inundation of surrounding grassland, leading to the increase of terrestrial grass organic matter (OM) input to the lakes and the decrease of lake salinity. However, the influence of terrestrial grass OM input increase and salinity decrease on organic carbon mineralization and microbial community composition remains unknown in saline lakes. Here, microbial mineralization of terrestrial grass (Achnatherum splendens) OM at different quantity levels in lake sediments with different salinity was investigated by performing microcosm experiments. The results showed that the CO2 production rates increased with the increase of grass OM supply in the studied sediments with different salinity, which may be driven by certain microbial groups (e.g. Bacteroidota, Firmicutes, and Ascomycota). The increase of grass OM supply reduced the richness of prokaryotic community, which will decrease the size and complexity of the studied microbial networks, but increase the interaction between prokaryotic and fungal taxa. Taken together, our results suggest that the increase of terrestrial grass OM input caused by lake expansion would enhance the mineralization of organic carbon and affect the community composition and interactions of related microorganisms in lake sediments with different salinity.

Microbial mineralization at the surface layer of cement-based materials and its effect on efflorescence performance

Microbial induced calcium carbonate precipitation technology was proposed as a novel and environmentally friendly approach to strengthen the surface layer of cement-based materials in this study. The effects of microbial additives on the content of Ca(OH)2 and CaCO3 and the porosity at different depths of surface layer were studied. The relative efflorescence rate of cement mortar samples mixed microbial additives were studied. Combined with observation the surface microstructure and mineralization products, the modification mechanism of microbial mineralization at the surface layer of cement-based materials was analyzed. The results showed the porosity and relative efflorescence rate reduced due to the microorganisms. And the content of Ca(OH)2 decreased and CaCO3 increased in the surface layer of cement paste samples continuously, with the increase of microbial additives (dosage <0.4%). Due to the microbial mineralization, the reaction of Ca2+ in the pore solution with CO2 from atmosphere could be accelerated to form calcium carbonate. The shape characteristics of crystals were spherical aggregate and stacked polyhedron. The relative efflorescence rate of the sample surface was reduced by microbial mineralization because of the consumption of Ca(OH)2, which was the main substance causing efflorescence. Besides, the mineralization products filled the pores in the surface layer, reduced the porosity and compacted the surface layer of the sample.

Urea uptake by spruce tree roots in permafrost-affected soils

Biomass productivity of black spruce trees is strongly limited by soil nitrogen (N) in shallow active layer on permafrost. Trees and mycorrhizal roots are known to absorb amino acids to bypass slow N mineralization in N-limited boreal forest soils. However, amino acid uptake strategy of tree roots cannot fully explain their advantages in competition for soil N with other plants and microbes. We investigated the potentials of tree roots to absorb urea as well as amino acids and inorganic N, using tracer experiments of 13C, 15N-labelled glutamic acid and urea and 15N-labelled ammonium nitrate in black spruce forests growing on permafrost-affected soils with different permafrost table depths in the eastern edge of the Mackenzie river delta (northwest Canada). We demonstrated that black spruce roots have potentials to absorb intact urea but only in soils with shallow permafrost, where urea accumulates due to limited microbial mineralization activity. This contrasts with soils with deep permafrost table, where roots absorb amino acids and inorganic N. Allocation of fine roots to colder subsoil above permafrost provides advantages for trees monopolizing urea-N. Despite lower energy efficiency of urea utilization compared to inorganic N and amino acids, urea uptake is one of N acquisition strategies for spruce growing on N-limited subarctic soil.

Microbial Community Changes in 26,500-Year-Old Thawing Permafrost.

Northern permafrost soils store more than half of the global soil carbon. Frozen for at least two consecutive years, but often for millennia, permafrost temperatures have increased drastically in the last decades. The resulting thermal erosion leads not only to gradual thaw, resulting in an increase of seasonally thawing soil thickness, but also to abrupt thaw events, such as sudden collapses of the soil surface. These could affect 20% of the permafrost zone and half of its organic carbon, increasing accessibility for deeper rooting vegetation and microbial decomposition into greenhouse gases. Knowledge gaps include the impact of permafrost thaw on the soil microfauna as well as key taxa to change the microbial mineralization of ancient permafrost carbon stocks during erosion. Here, we present the first sequencing study of an abrupt permafrost erosion microbiome in Northeast Greenland, where a thermal erosion gully collapsed in the summer of 2018, leading to the thawing of 26,500-year-old permafrost material. We investigated which soil parameters (pH, soil carbon content, age and moisture, organic and mineral horizons, and permafrost layers) most significantly drove changes of taxonomic diversity and the abundance of soil microorganisms in two consecutive years of intense erosion. Sequencing of the prokaryotic 16S rRNA and fungal ITS2 gene regions at finely scaled depth increments revealed decreasing alpha diversity with depth, soil age, and pH. The most significant drivers of variation were found in the soil age, horizons, and permafrost layer for prokaryotic and fungal beta diversity. Permafrost was mainly dominated by Proteobacteria and Firmicutes, with Polaromonas identified as the most abundant taxon. Thawed permafrost samples indicated increased abundance of several copiotrophic phyla, such as Bacteroidia, suggesting alterations of carbon utilization pathways within eroding permafrost.

Influence of ettringite on the crack self-repairing of cement-based materials in a hydraulic environment

Abstract As a green and environmental protection method, the self-repairing technology has great expectations to be met. In this study, the influence of ettringite on the crack self-repairing of cement-based materials in a hydraulic environment was systematically analyzed. First, the composition and pore characteristics of the self-repairing carrier was studied by XRD, XRF, and the mercury injection method. The composition was basically consistent with cement-based materials, and the structure of the self-repairing carrier was relatively dense. Second, the products were analyzed by SEM and EDS, and it was found that the distribution range of crystal size was from 1 to 20 µm, the cube and flocculent accumulation was calcite, while the rod and flake crystals were ettringite. Finally, the repair effect on the surface and inside of the crack was demonstrated by the crack area repair rate and water permeability resistance. Compared with single microbial mineralization, the synergistic repair effect of microbial mineralization and ettringite formation was better in water permeability resistance. With the further increase of water pressure, its advantages would be more obvious.

Effects of Air Entrainment on Bacterial Viability in Cement Paste.

This study investigated the effect of air entrainment (AE) on bacterial viability in cementitious materials. Specimens were fabricated with Portland cement, urea, calcium lactate, and ureolytic bacteria, and with varying amounts of an AE agent. Specimens with different amounts of the AE agent were fabricated, and then a compressive strength test, quantitative polymerase chain reaction, X-ray diffraction, and thermogravimetry were used to investigate the mechanical properties, viability of bacteria, and hydrates of the specimens. The highest compressive strength was achieved by the specimen with 0.3% AE agent, while the compressive strength of the specimens decreased considerably when the incorporated AE agent was over 0.6%, due to increased porosity. The quantitative polymerase chain reaction result showed that the cell number of the viable bacteria was increased by incorporation of the AE agent, which also corresponded with an increase in CaCO3 due to microbial mineral formation. The obtained result confirmed the positive effect of AE agent incorporation in cementitious materials containing bacterial admixtures, as the viability of bacteria, which play a vital role in self-healing efficiency of concrete, was increased by the space provided by the AE agent in the cement matrix. In addition, the quantity of CaCO3 and the compressive strength were highest when 0.3% AE agent was incorporated.

Development of permafrost-affected peatlands in the southern limit of the European Russian cryolithozone and their vulnerability to future warming

Permafrost degradation due to climate warming is currently observed in the northeastern part of European Russia. Peat plateaus underlain by permafrost cover only about 20% of the Russian European cryolithozone but contain almost 50% of soil organic carbon stocks (SOC), which are considered to be vulnerable to microbial mineralization after permafrost thaw. The current study was performed at three key sites of peat plateaus located along the southern permafrost limit. SOC decomposition was studied by aerobic and anaerobic incubation experiments, conducted at 4 °C over a period of 1301 days. The CO2 production was measured in peat samples at three key sites from the active layer (AL), transitional layer (TL), permafrost layer (PL), and at one site from the deep permafrost layer (DPL), which is in contact with mineral soil at 3.7 m depth. During the experiment, the initial СО2 respiration rates significantly differed in the samples AL, TL and PL in all key sites. However, at each site in the majority of samples the CO2 respiration rates were 2–5 times aerobically higher than anaerobically. In anaerobic conditions, in all sites, the СО2 respiration rate in PL was the lowest, higher in TL and the highest in AL in all 3 sites. Projections of CO2 aerobically production for 80 years represent 1.44 ± 0.11, 6.31 ± 0.47, 30.64 ± 17.98% of initial permafrost carbon from the samples of Inta 1, Inta 11 and Kolva respectively. But under anaerobical conditions estimates are close and indicate insignificant amounts 0.30…1.90% of carbon release over a period of 80 years. We suggest that even under ideal conditions of the incubation experiment, without considering ecological inertia under natural conditions, while also permafrost temperature is close to zero, greenhouse gas release from initial SOC is significantly less than estimated.

Long‐term rice cultivation promoted microbial mineralization of organic P in a black soil

AbstractInformation on the microbiological process in paddy soil is essential to understand phosphorus (P) transformation, due to the special biogeochemical change of P in flooded rice (Oryza sativa L.)‐growing environment. However, relatively few references have been focused on this process in long‐term cultivation of black paddy soil. In this study, we investigated the effect of microbial community and phoD gene on changes in soil P fractions in a black paddy soil. The results showed that, compared with 1‐yr soil, long‐term cultivation (35‐yr rice growth) significantly increased the concentration of soil P pool (P &lt; .05). In detail, the soil available‐P increased from 15.4 to 34.8 mg kg−1, and primary‐P, secondary‐P, occluded‐P and organic‐P increased from 41.4 to 73.6 mg kg−1, 7.60 to 18.9 mg kg−1, 57.6 to 106.1 mg kg−1, and 13.7 to 29.1 mg kg−1, respectively. Notably, the microbial biomass C/P ratio decreased from 190.8 (1‐yr) to 56.2 (35‐yr), indicating that the mineralization of organic P (Po) by microorganisms played a dominant role in long‐term cultivation. The results were further verified by significantly increased soil microorganism concentration, copy number of phoD gene, and strong interaction in phoD‐harboring bacteria. The change of soil P pool was significantly affected by soil properties and phoD gene community through variance partitioning analysis, and Streptomyces and Cupriavidus were the main biomarkers affecting Po mineralization through linear discriminant analysis effect size (LEfSe) analysis. The results will be helpful to understand the microbial process of P transformation (especially for Po) and to guide the management of P fertilizer in black soil area.

Positive Priming Effects Induced by Allochthonous and Autochthonous Organic Matter Input in the Lake Sediments With Different Salinity

AbstractEcological consequences of the increased input of allochthonous and autochthonous organic matter (OM) remains unknown in saline lakes. Here, we reported microbial mineralization of algal and grass OM (represented by autochthonous and allochthonous OM, respectively) in lake sediments with different salinity (1, 40, and 120 g L−1). The addition of algal and grass OM significantly increased the CO2 production rates in the studied sediments. Algal and grass OM input can induce positive priming effect (PE). PE intensity induced by grass OM input was significantly higher than that by algal OM input. PE intensity induced by algal and grass OM input decreased with increasing salinity. Bacterial taxa affiliated with Actinomycetia, Alphaproteobacteria, Bacilli, Bacteroidia, Clostridia, and Gammaproteobacteria played important roles in driving PE generation in the studied sediments. Our finding suggested that the PEs induced by allochthonous and autochthonous OM should be considered in saline lakes that are intensively influenced by climate change.

Study on preparation of supplementary cementitious material using microbial CO2 fixation of steel slag powder

Mineral CO2 sequestration, a vital way to reduce CO2 emission, has been paid extensive attention. Industrial residues are considered a promising material for CO2 sequestration because of their low cost and secondary utilization. However, there are few methods to jointly consider CO2 emission reduction and efficient waste residue utilization, which are vital for the sustainable development of industries. In this paper, we propose a collaborative technology to prepare high-quality supplementary cementitious material (SCM) that can be used to substitute cement. Specifically, the microorganism is utilized to improve CO2 fixation and modification of steel slag powder, then its characteristics and the effects of SCM in cement-based materials are further studied. The results show that microbial mineralization can improve the stability and reactivity of steel slag powder by promoting the phase conversion of free oxides and silicates. The free CaO and MgO of modified steel slag powder decrease from 1% and 1.9% to 0% and 1%. The flexural and compressive strength reactivity index of 28-day cured samples increased from 81.1% and 78.5% to 86.8% and 87.1%, respectively. Moreover, more calcium carbonate and pozzolanic-active amorphous gel phases produced in mineralized steel slag powder improve its reactivity. The results on the enhancement mechanism show that bio-CaCO3 with high crystallinity and small particle size attach the surface of steel slag powder, which act as nucleation sites to promote cement hydration; And bio-CaCO3 participates in the cement hydration to form new products, such as hydrated calcium carboaluminate, improving the compactness of samples. Microbial mineralization increases the CO2 fixation of steel slag powder to 11.25%. When the mineralized steel slag powder is used as SCM, the sustainable efficiency of the mixed binder reaches 0.0384 MPa/(kg/m3), which is 27.15% higher than that of pure cement. This technical route is conducive to carbon neutralization and sustainable development of the construction industry.