Potential Microbial Activity Research Articles

Invasion of Prosopis trees into arid ecosystem alters soil carbon and nitrogen processes and soil trace gases emissions

The invasion of drylands by leguminous mesquite (Prosopis spp.) is frequently associated with increases in the soil organic carbon (C) and nitrogen (N) pools. These increases stimulate soil microbial activity and accelerate soil C and N cycling. However, the impact of mesquite invasion on soil biogeochemistry, especially the emission of trace gases, in an ecosystem with an already established population of N-fixing plants is not well studied. To fill this knowledge gap, we quantified the in-situ soil trace gas emissions and the potential microbial activity in soils under invasive mesquite (Prosopis juliflora) trees (Prosopis), native acacia (Acacia tortilis) trees (Acacia), and in unvegetated soil between trees (Bare soil) on the western shore of the Dead Sea. To account for contributions of spatial and weather variabilities to the emission processes we conducted measurements across two geographic sites, 45 km apart, over two years, both under naturally dry soil conditions and after soil wetting. Before wetting, soil emissions of carbon dioxide (CO2) and nitric oxide (NOx) followed the order: Acacia > Prosopis ≥ Bare soil, while soil nitrous oxide (N2O) emissions were low and uniform across the three habitats. The soil inorganic N concentration, microbial biomass, and water-extractable organic C were significantly higher under the A. tortilis canopies compared with P. juliflora and Bare soil. After wetting, soil trace gases emissions increased up to 66, 1534, and 42 times, for CO2, N2O, and NOx, respectively, and remained higher under the native A. tortilis than under P. juliflora and Bare soil (Acacia > Prosopis > Bare soil). The potential soil microbial activity, however, was similar between the soils under the tree canopies. Our results show that the establishment of invasive leguminous trees increase soil CO2 and gaseous N emissions relative to the Bare soils, but not relative to native leguminous trees.

Physicochemical, Antimicrobial, Lethality and In Vitro Antioxidant Profiles of Johnu Tisane: A Coffee (Coffea Arabica) Leaf Decoction Formula

Coffee leaves-based tea has relevance in ethno-medications due to its rich phyto-constituents-related diverse pharmacologic activities. Jonhu tisane, a typical Coffea arabica leaf decoction has no supporting scientific basis amidst reported location, processing and specie-related variations. This investigated physicochemical, antimicrobial, lethality and in-vitro antioxidant profiles of Johnu tisane by acceptable methods. Results recorded moisture (92.26 %), ash (0.65 %), unsaponified matter (1.46 mg/100 g), free fatty acid (0.56 mgKOH/g), acid value (1.12 mgKOH/g), potential hydrogen (6.85), lethal concentration (1000 ppm) and concentration-dependent antimicrobial activity. Anti-oxidation results revealed total antioxidant capacity, ferric reducing antioxidant power, nitric oxide, hydrogen peroxide and 2, 2-diphynyl-1-picrylhydrazyl scavenging activities increased concentration-dependently compared to standard. Thus, Johnu tisane demonstrated low minerals and keeping quality; requisite physicochemical mix for consumption and bioactivity; high safety margin; antimicrobial potency; and requisite anti-oxidation capacity for in-vivo antioxidant role. These provided scientific support for its ethno-medicinal uses. They underscored the need to elucidate its pharmacologically active compounds; mechanistic roles in animal models; and the impact of ash to moisture mix variation on potential hydrogen, microbial and antimicrobial activities in relation to shelf life, bioactivity and in vivo anti-oxidative roles for novel insights on preserving sample quality, safety, bioactivity and in-vivo anti-oxidative outcomes.

Water and nitrogen availability define emissions of carbon dioxide and nitrogen oxides from desert soil differently

Nitrogen (N), phosphorus (P), and water, together and individually, limit soil biological processes in dryland ecosystems and therefore, the availability of each nutrient is a key determinant of ecosystem processes and functions. To assess the importance of each limiting factor for microbial activity in desert soil, we manipulated water, N, and P availability separately and combined. N, P, and NP were added at rates of 10 N or/and P g m−2 under two water regimes: one wetting event, and bi-weekly wetting–drying cycles in addition to natural rainfall. We measured soil respiration, nitrous (N2O) and nitric oxides (NOx) emissions in situ, and potential nitrification and mineralization in laboratory. Soil respiration increased by ∼30% with raised water availability but wasn't affected by nutrients availability. NOx and to a smaller extent N2O emissions, however, increased with nutrient availability but not with water. Average soil NOx flux increased up to ∼19 folds from 0.03 ± 0.01 μg N m−2 min−1 to 0.52 ± 0.10 μg N m−2 min−1 with the addition of N and N + P but only slightly with addition of P alone (p = 0.06). The removal of both water and NP limitation accelerated only NOx, but nor CO2 neither N2O emissions pointed on other than N and P limitation of soil heterotrophic processes in this alkali desert soil. The potential soil microbial activity was unaffected by the removal of neither water nor NP limitations. Our findings suggest that water primarily influences soil respiration and N availability soil NOx emissions while desert soil is a minor source of N2O. We conclude that heterotrophic and autotrophic microbial activities in desert soils are influenced differently by water and nutrients. Increasing precipitation would likely boost soil respiration and N mineralization rates, leading to decreased soil nutrient organic carbon stocks, while increased N deposition would accelerate gaseous N loss.

Effect of cover crops on soil health at different landscape positions

AbstractSoil health is crucial to reaching high yields, and growing cover crops can help improve soil conditions. The goal of this study is to determine the effects of cover crops on soil health using potential respiration, potential nitrogen mineralization, and aggregates stability as indicators of soil health. The study has been conducted since 2019 at the University of Kentucky Spindletop Farm, Lexington, KY, and involves three landscape positions receiving a treatment with cereal rye, cereal rye–crimson clover mixture, and fallow soil. This study emphasized that cover crops can enhance potential respiration and microbial activity over landscape positions, with rye being more beneficial than the mixture treatment. However, cover crops were also beneficial for aggregate stability but not for potential nitrogen mineralization.

Phosphorus mining from marine sediments adopting different carbon/nitrogen strategies driven by anaerobic reactors: The exploration of potential mechanism and microbial activities

To investigate the possibility of phosphorus (P) recovery from marine sediment and explore the role of the carbon: nitrogen ratio in affecting the internal P release under anaerobic conditions, we experimented with the external addition of carbon (acetic acid and glucose) and ammonia nitrogen (NH4-N) to expose P release mechanisms. The 24-day anaerobic incubations were conducted with four different carbon: nitrogen dosing groups including no NH4-N addition and COD/N ratios of 100, 50, and 10. The P release showed that extra NH4-N loading significantly suppressed the decomposition of P (p < 0.05) from the marine sediment, the maximum P release was 4.07 mg/L and 7.14 mg/L in acetic acid- and glucose-fed systems, respectively, without extra NH4-N addition. Additionally, the results exhibited that the imbalance of carbon: nitrogen not only failed to induce the production of organic P mineralization enzyme (alkaline phosphatase) in the sediment but also suppressed its activity under anaerobic conditions. The highest enzyme activity was observed in the group without additional NH4-N dosage, with rates of 1046.4 mg/(kg∙h) in the acetic acid- and 967.8 mg/(kg∙h) in the glucose-fed system, respectively. Microbial data analysis indicated that a decrease in the abundance of P release-regulating bacteria, including polyphosphate-accumulating organisms (Rhodobacteraceae) and sulfate-reducing bacteria (Desulfosarcinaceae), was observed in the high NH4-N addition groups. The observed reduction in enzyme activity and suppression of microbial activity mentioned above could potentially account for the inhibited P decomposition in the presence of high NH4-N addition under anaerobic conditions. The produced P-enriched solution from the bioreactors may offer a promising source for future recovery endeavors.

Early spring snowmelt and summer droughts strongly impair the resilience of bacterial community and N cycling functions in a subalpine grassland ecosystem

Subalpine grasslands support biodiversity, agriculture, and tourism but their resilience to extreme climatic events is challenged accelerating their vulnerability to tipping points. Microbial communities, central in ecosystem functioning, are usually considered more resistant and highly resilient to extreme events albeit their functional redundancy and strong selection by local harsh climatic conditions. This study explored the soil microbial responses upon recurrent spring‐summer droughts associated with early snowmelt in subalpine grasslands mesocosms set‐up at the Lautaret Pass (French Alps). Potential soil microbial respiration, nitrification and denitrification activities were monitored over a period of two growing seasons along with quantification of related gene abundances. Impacts of simulated spring‐summer drought and early snowmelt were quantified to assess their resistance and recovery. Results revealed that droughts had a low and short‐term adverse impact on bacterial total respiration supporting their hypothesized high resilience, i.e. resistance and ability to recover. Nitrification and abundances of the corresponding functional guilds showed relatively strong resistance to summer droughts but declined in response to early snowmelt. This resistance of nitrification was paralleled by the recovery of denitrification and abundances of denitrifying communities from all climatic extremes, except from the summer droughts where nitrifiers were collapsed. Denitrification and respective functional groups faced high impact of applied stresses with strong reduction in abundance and activity. Although, consequently lower denitrifiers' competition for nitrate may be positive for plant biomass production, warnings exist when considering the potential nitrate leaching as well as risks of greenhouses gases emission such as N2O from these ecosystems.

Microbial community structure characteristics among different karst aquifer systems, and its potential role in modifying hydraulic properties of karst aquifers.

Little is known about how microbial activity affects the hydraulic properties of karst aquifers. To explore the potential impacts of microbial activity on the hydraulic properties of karst aquifers, microbiological analysis, heat tracer, isotope (dissolved inorganic carbon isotope, δ13CDIC) and aqueous geochemical analyses were conducted at six monitoring wells in Northern Guangdong Province, China. Greater hydraulic conductivity corresponded to a low temperature gradient to an extent; the temperature gradient in karst groundwater aquifers can reflect the degree of dissolution. Higher HCO3 - concentrations coupled with lower d-excess and pH values at B2 and B6 reflect potential microbial activity (e.g., Sulfuricurvum kujiense) causing carbonate dissolution. Microbial activity or the input of anthropogenic acids, as evidenced by significantly more positive δ13CDIC values, potentially affect carbonate dissolution in deep karst aquifers, which eventually alters hydraulic properties of karst aquifer. However, more direct evidence is needed to quantify the effects of microbial activity on carbonate dissolution in karst aquifers.

Isolation, Characterization and Phylogenetic Analysis of Nodule-Associated Bacteria from Mimosa Pudica L.

The interaction between rhizobia and other nodule-associated bacteria assists to mitigate nutrient stress in leguminous plants by fixing atmospheric nitrogen and synthesizing plant growth regulators. The beneficial effects of microbial inoculants emphasize the need for further research and their use in modern agriculture. The present study describes the isolation, molecular identification, characterization, and phylogenetic analysis of noduleassociated bacteria from Mimosa pudica Linnaeus. Isolation and phenotypic characterization of nodule-associated bacteria were carried out according to standard procedures. Molecular characterization of the isolates was performed using 16S ribosomal RNA. Plant growth promoting the ability of selected isolates was analyzed by assessing indole acetic acid production, nitrogenfixing ability and organic acid production. Evolutionary distance and relatedness were analyzed using the neighbor-joining method. Thirteen nodule-associated bacteria were isolated and identified using 16S rRNA gene sequencing. The selected isolates such as Rhizobium sp. CU8 and three other co-resident non-rhizobial nodule-associated bacteria (Bacillus cereus MY5, Ralstonia pickettii MY1 and Lactococcus lactis MY3) exhibited plant growth promotion and other potential microbial activities. Phylogenetic analysis revealed the genetic relatedness and evolutionary significance of all the thirteen isolates reside in the root nodule of M. pudica. The present study identified four isolates with plant growth promoting properties. L. lactis MY3 is the first report as a co-resident plant growth promoter from the root nodules of M. pudica.

Summer sunlight impacts carbon turnover in a spatially heterogeneous Patagonian woodland

PurposeWe evaluated the importance of dry season (summer) sunlight on carbon (C) turnover in a Mediterranean-type climate ecosystem in the context of spatially heterogenous distribution of vegetation.MethodsWe manipulated summer sunlight exposure of litter and soil at the ecosystem scale in a natural Patagonian woodland over two years and evaluated its effect on C turnover in litter and surface soil. We measured decomposition of standing dead litter of dominant grass and shrub species, changes in labile C pools in soil microsites with and without plant litter, and potential enzyme activity of litter and both soil microsites, evaluating seasonal and legacy effects of summer sunlight exposure.ResultsSummer sunlight exposure significantly increased standing litter decomposition for both shrub and grass litter (p < 0.05). Additionally, summer sunlight significantly increased labile carbohydrate availability (saccharification) and potential microbial enzymatic activity of grass (but not shrub) litter. Interestingly, summer sunlight exposure also had effects on soil, reducing by 50% labile organic C while stimulating potential extracellular enzyme activity in both soil microsites, with and without plant litter.ConclusionSummer sunlight accelerates C loss from standing litter and soil consistently across patches of heterogeneously distributed vegetation. In addition, sunlight exposure demonstrated carryover effects on the acceleration of grass litter decay in the following rainy season, when sunlight increased decomposition five times more than in the dry season. These results suggest that summer sunlight is an important and lasting control of C turnover at the ecosystem scale even in seasonally and spatially heterogenous ecosystems.

A case study: The deployment of a novel in situ fluorimeter for monitoring biological contamination within the urban surface waters of Kolkata, India

The quality and health of many of our vital freshwater systems are poor. To tackle this with ever increasing pressures from anthropogenic and climatic changes, we must improve water quality monitoring and devise and implement more appropriate water quality parameters. Recent research has highlighted the potential for Peak T fluorescence (tryptophan-like fluorescence, TLF) to monitor microbial activity in aquatic systems. The VLux TPro (Chelsea Technologies Ltd., UK), an in situ real-time fluorimeter, was deployed in different urban freshwater bodies within Kolkata (West Bengal, India) during March 2019. This study is the first to apply this technology in surface waters within a densely populated urban area. Spot-sampling was also undertaken at 13 sampling locations enabling physicochemical analysis, bacterial enumeration and determination of nutrient (nitrate and phosphate) concentrations. This case study has demonstrated the ability of an in situ fluorimeter, VLux TPro, to successfully identify both biological contamination events and potential elevated microbial activity, related to nutrient loading, in complex surface freshwaters, without the need for expensive and time-consuming laboratory analysis.

Microbial Community Composition and Activity in Saline Soils of Coastal Agro-Ecosystems.

Soil salinity is a serious problem for agriculture in coastal regions. Nevertheless, the effects of soil salinity on microbial community composition and their metabolic activities are far from clear. To improve such understanding, we studied microbial diversity, community composition, and potential metabolic activity of agricultural soils covering non–, mild–, and severe–salinity. The results showed that salinity had no significant effect on bacterial richness; however, it was the major driver of a shift in bacterial community composition and it significantly reduced microbial activity. Abundant and diverse of microbial communities were detected in the severe–salinity soils with an enriched population of salt–tolerant species. Co–occurrence network analysis revealed stronger dependencies between species associated with severe salinity soils. Results of microcalorimetric technology indicated that, after glucose amendment, there was no significant difference in microbial potential activity among soils with the three salinity levels. Although the salt prolonged the lag time of microbial communities, the activated microorganisms had a higher growth rate. In conclusion, salinity shapes soil microbial community composition and reduces microbial activity. An addition of labile organic amendments can greatly alleviate salt restrictions on microbial activity, which provides new insight for enhancing microbial ecological functions in salt–affected soils.

Potential microbial enzyme activity in seasonal snowpack is high and reveals P limitation

AbstractMicrobes in snow and ice ecosystems in polar regions contribute substantially to C, N, and P cycling, but few studies have explored microbial activity in seasonal snow. The purpose of this study was to explore the relative importance of snow microbial processing of C, N, and P compounds in atmospheric deposition and litter and detect elemental limitations of snow microbes in Rocky Mountain conifer forests. Enzyme activity in snow was orders of magnitude greater than activity reported for lentic and lotic waters in similar environments. Proportions of C/P‐ and C/N‐acquiring enzymes suggest that snow samples were P limited, or C and P co‐limited, while lentic and lotic waters were more N limited. As such, microbes in seasonal snow may change the composition of nutrients and carbon, but these processes are vulnerable to changes in atmospheric deposition and snow extent and duration, which could affect nutrient processing across large areas.

All-In-One: Microbial Response to Natural and Anthropogenic Forcings in a Coastal Mediterranean Ecosystem, the Syracuse Bay (Ionian Sea, Italy)

Bacterial and phytoplankton communities are known to be in close relationships, but how natural and anthropogenic stressors can affect their dynamics is not fully understood. To study the response of microbial communities to environmental and human-induced perturbations, phytoplankton and bacterial communities were seasonally monitored in a Mediterranean coastal ecosystem, Syracuse Bay, where multiple conflicts co-exist. Quali-quantitative, seasonal surveys of the phytoplankton communities (diatoms, dinoflagellates and other taxa), the potential microbial enzymatic activity rates (leucine aminopeptidase, beta-glucosidase and alkaline phosphatase) and heterotrophic culturable bacterial abundance, together with the thermohaline structure and trophic status in terms of nutrient concentrations, phytoplankton biomass (as Chlorophyll-a), and total suspended and particulate organic matter, were carried out. The aim was to integrate microbial community dynamics in the context of the environmental characterization and disentangle microbial patterns related to natural changes from those driven by the anthropic impact on this ecosystem. In spite of the complex relationships between the habitat characteristics, microbial community abundance and metabolic potential, in Syracuse Bay, the availability of organic substrates differently originated by the local conditions appeared to drive the distribution and activity of microbial assemblage. A seasonal pattern of microbial abundances was observed, with the highest concentrations of phytoplankton in spring and low values in winter, whereas heterotrophic bacteria were more abundant during the autumn period. The autumn peaks of the rates of enzymatic activities suggested that not only phytoplankton-derived but also allochthonous organic polymers strongly stimulated microbial metabolism. Increased microbial response in terms of abundance and metabolic activities was detected especially at the sites directly affected by organic matter inputs related to agriculture or aquaculture activities. Nitrogen salts such as nitrate, rather than orthophosphate, were primary drivers of phytoplankton growth. This study also provides insights on the different seasonal scenarios of water quality in Syracuse Bay, which could be helpful for management plans of this Mediterranean coastal environment.

Sono-Chemical Synthesis of Silver Quantum Dots Immobilized on Exfoliated Graphitic Carbon Nitride Nanostructures Using Ginseng Extract for Photocatalytic Hydrogen Evolution, Dye Degradation, and Antimicrobial Studies.

Due to modernization and the scarcity of fossil fuel resources, energy demand is continuously increasing. In this regard, it is essential and necessary to create a renewable energy source that can meet future energy demands. Recently, the production of H2 by water splitting and removing pollutants from the water has been essential for issues of energy and environmental demands. Herein, g-C3N4 and Ag-g-C3N4 composite structures have been successfully fabricated by the ultrasonication method. The physio/photochemical properties of prepared g-C3N4 and Ag-g-C3N4 were examined with different analytical techniques such as FTIR, XRD, UV-DRS, SEM, TEM, PL, and XPS analyses. The silver quantum dots (QDS) anchored to g-C3N4 structures performed the profound photocatalytic activities of H2 production, dye degradation, and antimicrobial activity under visible-light irradiation. The Ag/g-C3N4 composite with an Ag loading of 0.02 mole has an optimum photoactivity at 335.40 μmol g−1 h−1, which is superior to other Ag loading g-C3N4 composites. The synthesized Ag/g-C3N4 nanoparticles showed potential microbial inhibition activity during the preliminary screening, and the inhibition zones were comparable to the commercial antibiotic chloramphenicol. The loading of Ag into g-C3N4 paves the suppression, recombination and transfer of photo-generated electron-hole pairs, leading to the enhancement of hydrogen production, the diminishment of pollutants in water under visible light irradiation, and antimicrobial activity against multidrug-resistant pathogens.

Integrating Decomposers, Methane-Cycling Microbes and Ecosystem Carbon Fluxes Along a Peatland Successional Gradient in a Land Uplift Region

Peatlands are carbon dioxide (CO2) sinks that, in parallel, release methane (CH4). The peatland carbon (C) balance depends on the interplay of decomposer and CH4-cycling microbes, vegetation, and environmental conditions. These interactions are susceptible to the changes that occur along a successional gradient from vascular plant-dominated systems to Sphagnum moss-dominated systems. Changes similar to this succession are predicted to occur from climate change. Here, we investigated how microbial and plant communities are interlinked with each other and with ecosystem C cycling along a successional gradient on a boreal land uplift coast. The gradient ranged from shoreline to meadows and fens, and further to bogs. Potential microbial activity (aerobic CO2 production; CH4 production and oxidation) and biomass were greatest in the early successional meadows, although their communities of aerobic decomposers (fungi, actinobacteria), methanogens, and methanotrophs did not differ from the older fens. Instead, the functional microbial communities shifted at the fen–bog transition concurrent with a sudden decrease in C fluxes. The successional patterns of decomposer versus CH4-cycling communities diverged at the bog stage, indicating strong but distinct microbial responses to Sphagnum dominance and acidity. We highlight young meadows as dynamic sites with the greatest microbial potential for C release. These hot spots of C turnover with dense sedge cover may represent a sensitive bottleneck in succession, which is necessary for eventual long-term peat accumulation. The distinctive microbes in bogs could serve as indicators of the C sink function in restoration measures that aim to stabilize the C in the peat.

Geochemical characteristics control potential microbial activity in exposed Late Quaternary alluvial deposits

Different stratigraphic sequences of Late Quaternary sediments present in a vertically exposed 29 m deep river cliff were used as a model system to understand geochemical relationships with potential microbial activity in semiarid alluvial sediments. Microbial activities involved in carbon (C) and phosphorus (P) cycling were measured by dehydrogenase, alkaline phosphatase, and microbial respiration activities. We did not observe patterns in microbial activities that could be explained by sample depth. An extensive analysis of the physical and geochemical characteristics of exposed sediments was conducted along with multivariate statistical analysis to determine the influence of geochemical variables on potential microbial activity. Principal component analysis (PCA) and canonical correlation analysis (CCA) together with Pearson correlation analysis indicated that sediment organic carbon, moisture content, palynofacies components (acid-resistant particulate organic matter) such as fungal spores, brown carbon, structured carbon, and concentrations of Al2O3, FeO, MgO, MnO, and Zr were associated significantly with microbial activities in river cliff sediment deposits. These findings highlight drivers of microbial activity with consequences for C and P biogeochemical cycles in semiarid alluvial soils/sediments of river floodplains.

Soil chemical properties rather than the abundance of active and potentially active microorganisms control soil enzyme kinetics

Soil enzymes secreted by microorganisms play a critical role in nutrient cycling, soil structure maintenance, and crop production. However, understanding of the linkage between soil enzyme kinetics and microbial metabolism and active microbial communities is remarkably limited. In this study, we measured the kinetics of three hydrolase enzymes, active microbial abundance and substrate-induced respiration (SIR) from 21 farmlands differing in their fertilities collected from the Loess Plateau, China. Results showed the high fertility soils had higher total organic carbon (TOC) and nutrient contents, potential microbial activity, the colony-forming units (CFU) of actinomycetes, and values of enzyme Vmax and Km than those of low fertility soils. We also observed that the CFU of fungi and other bacterial groups did not change with soil fertility status. Soil chemical properties explained 74.0% of the variance in Vmax and 28.3% of the variance in Km, respectively. Whereas, the abundance of main microbial groups and fungi/bacteria ratio only explained 10.2% and 7% of the variance of Vmax and Km, respectively. The interactive effect of soil properties and microbial community could explain 20.2% of the variance in Km. Our results suggest that the substrate availability would mainly drive enzyme kinetics compared to the abundance of active/potentially active microbes in the farmland soils.

Functional Soil Biological Measurements to Support Healthy Soils.

Soil microorganisms contribute significantly to terrestrial ecosystem functioning through their activities. Various methods exist to characterize soil microbial activity and functional diversity including those that focus on potential enzyme activities and the respiratory responses of microbes to different substrates. Here, we describe: (1) the fluorescein diacetate hydrolysis assay for total potential microbial enzyme activity; (2) measurement of beta-glucosidase activity using ρ-nitrophenyl (pNP); (3) multienzyme assay using 4-methylumbelliferone (MUB); and (4) MicroResp assays to measure the respiratory responses of microbes to different substrates and generate a community level physiological profile (CLPP).

Microbial Biomass Drives Seasonal Hysteresis in Litter Heterotrophic Respiration in Relation to Temperature in a Warm‐Temperate Forest

AbstractCO2 efflux from the litter layer, litter heterotrophic respiration, is an important component of the forest carbon cycle. Litter heterotrophic respiration mediated by microorganisms varies in response to seasonal environmental changes, such as temperature and moisture. Here, we aimed to quantify seasonal variation in litter heterotrophic respiration and determine how the microbial biomass influences microbial activity and hence litter heterotrophic respiration in a warm temperate forest. We performed in situ high‐frequency measurements of litter heterotrophic respiration per unit area (R_area), which are able to capture CO2 pulses during rainfall, for over 2 years. Microbial activity, which is the CO2 efflux per unit weight (R_mass) considering the change in the amount of substrate, was calculated based on R_area. In parallel, we measured substrate‐induced respiration (SIR) each month, as an index of microbial biomass. We identified seasonal hysteresis in R_area, which was higher in spring (January to July) than in fall (August to December), despite the temperature being similar in both periods. Of interest, R_mass and SIR also showed similar seasonal hysteresis in relation to temperature. Additionally, potential microbial activity without the effect of temperature and moisture was positively related to SIR. This result indicates that seasonal hysteresis with temperature in microbial activity was driven by microbial biomass seasonality, and thus, it leads to seasonal hysteresis in litter heterotrophic respiration in relation to temperature. Our findings highlight the importance of not only the environmental factors and substrate depletion but also biotic factors for estimating heterotrophic respiration.

Geochemistry and Microbiology Predict Environmental Niches With Conditions Favoring Potential Microbial Activity in the Bakken Shale.

The Bakken Shale and underlying Three Forks Formation is an important oil and gas reservoir in the United States. The hydrocarbon resources in this region are accessible using unconventional oil and gas extraction methods, including horizontal drilling and hydraulic fracturing. However, the geochemistry and microbiology of this region are not well understood, although they are known to have major implications for productivity and water management. In this study, we analyzed the produced water from 14 unconventional wells in the Bakken Shale using geochemical measurements, quantitative PCR (qPCR), and 16S rRNA gene sequencing with the overall goal of understanding the complex dynamics present in hydraulically fractured wells. Bakken Shale produced waters from this study exhibit high measurements of total dissolved solids (TDS). These conditions inhibit microbial growth, such that all samples had low microbial loads except for one sample (well 11), which had lower TDS concentrations and higher 16S rRNA gene copies. Our produced water samples had elevated chloride concentrations typical of other Bakken waters. However, they also contained a sulfate concentration trend that suggested higher occurrence of sulfate reduction, especially in wells 11 and 18. The unique geochemistry and microbial loads recorded for wells 11 and 18 suggest that the heterogeneous nature of the producing formation can provide environmental niches with conditions conducive for microbial growth. This was supported by strong correlations between the produced water microbial community and the associated geochemical parameters including sodium, chloride, and sulfate concentrations. The produced water microbial community was dominated by 19 bacterial families, all of which have previously been associated with hydrocarbon-reservoirs. These families include Halanaerobiaceae, Pseudomonadaceae, and Desulfohalobiaceae which are often associated with thiosulfate reduction, biofilm production, and sulfate reduction, respectively. Notably, well 11 was dominated by sulfate reducers. Our findings expand the current understanding of microbial life in the Bakken region and provide new insights into how the unique produced water conditions shape microbial communities. Finally, our analysis suggests that produced water chemistry is tightly linked with microbiota in the Bakken Shale and shows that additional research efforts that incorporate coupled microbial and geochemical datasets are necessary to understand this ecosystem.