Accumulated temperature dictates the regional structural variation of prokaryotic periphyton at soil-water interface in paddy fields

As a pervasive microbial aggregate found at the water-soil interface in paddy fields, periphyton plays crucial roles in modulating nutrient biogeochemical cycling. Consequently, it effectively mitigates non-point source pollution due to its diverse composition. Despite its significance, the mechanisms governing periphyton diversity across different rice planting regions remain poorly understood. To bridge this gap, we investigated periphyton grown in 200 paddy fields spanning 25° of latitude. Initially, we analyzed local diversity and latitudinal variations in prokaryotic communities within paddy field periphyton, identifying 7 abundant taxa, 42 moderate taxa, and 39 rare taxa as the fundamental prokaryotic framework. Subsequently, to elucidate the mechanisms governing periphyton diversity across large scales, we constructed interaction models illustrating triangular relationships among local richness, assembly, and regional variation of prokaryotic subcommunities. Our findings suggest that accumulated temperature-driven environmental filtering partially influences the assembly process of prokaryotes, thereby impacting local species richness and ultimately governing regional structural variations in periphyton. Furthermore, we determined that a latitude of 39° represents the critical threshold maximizing local species richness of periphyton in paddy fields. This study advances our understanding of the factors shaping periphyton geo-imprints and provides valuable insights into predicting their responses to environmental changes, potentially influencing rice production outcomes.

Climate-driven succession in marine microbiome biodiversity and biogeochemical function

Seasonal and El Niño-Southern Oscillation (ENSO) warming result in similar ocean changes as predicted with climate change. Climate-driven environmental cycles have strong impacts on microbiome diversity, but impacts on microbiome function are poorly understood. We quantified changes in microbial genomic diversity and functioning over 11 years covering seasonal and ENSO cycles at a coastal site in the southern California Current. We observed seasonal oscillations between large genome lineages during cold, nutrient rich conditions in winter and spring versus small genome lineages, including Prochlorococcus and Pelagibacter , in summer and fall. Parallel interannual changes separated communities depending on ENSO condition. Biodiversity shifts translated into clear oscillations in microbiome functional potential. Ocean warming induced an ecosystem with less iron but more macronutrient stress genes, depressed organic carbon degradation potential and biomass, and elevated carbon-to-nutrient biomass ratios. The consistent microbial response observed across time-scales points towards large climate-driven changes in marine ecosystems and biogeochemical cycles.

Denaturing Gradient Gel Electrophoresis Approach for Microbial Shift Analysis in Thermophilic and Mesophilic Anaerobic Digestions

To determine the evolution of microbial community and microbial shift under anaerobic processes, this study investigates the use of denaturing gradient gel electrophoresis (DGGE). In the DGGE, short- and medium-sized DNA fragments are separated based on their melting characteristics, and this technique is used in this study to understand the dominant bacterial community in mesophilic and thermophilic anaerobic digestion processes. Dairy manure is known for emitting greenhouse gases (GHGs) such as methane, and GHG emissions from manure is a biological process that is largely dependent on the manure conditions, microbial community presence in manure, and their functions. Additional efforts are needed to understand the GHG emissions from manure and develop control strategies to minimize the biological GHG emissions from manure. To study the microbial shift during anaerobic processes responsible for GHG emission, we conducted a series of manure anaerobic digestion experiments, and these experiments were conducted in lab-scale reactors operated under various temperature conditions (28 °C, 36 °C, 44 °C, and 52 °C). We examined the third variable region (V3) of the 16S rRNA gene fingerprints of bacterial presence in anaerobic environment by PCR amplification and DGGE separation. Results showed that bacterial community was affected by the temperature conditions and anaerobic incubation time of manure. The microbial community structure of the original manure changed over time during anaerobic processes, and the community composition changed substantially with the temperature of the anaerobic process. At Day 0, the sequence similarity confirmed that most of the bacteria were similar (>95%) to Acinetobacter sp. (strain: ATCC 31012), a Gram-negative bacteria, regardless of temperature conditions. At day 7, the sequence similarity of DNA fragments of reactors (28 °C) was similar to Acinetobacter sp.; however, the DNA fragments of effluent of reactors at 44 °C and 52 °C were similar to Coprothermobacter proteolyticus (strain: DSM 5265) (similarity: 97%) and Tepidimicrobium ferriphilum (strain: DSM 16624) (similarity: 100%), respectively. At day 60, the analysis showed that DNA fragments of effluent of 28 °C reactor were similar to Galbibacter mesophilus (strain: NBRC 10162) (similarity: 87%), and DNA fragments of effluent of 36 °C reactors were similar to Syntrophomonas curvata (strain: GB8-1) (similarity: 91%). In reactors with a relatively higher temperature, the DNA fragments of effluent of 44 °C reactor were similar to Dielma fastidiosa (strain: JC13) (similarity: 86%), and the DNA fragments of effluent of 52 °C reactor were similar to Coprothermobacter proteolyticus (strain: DSM 5265) (similarity: 99%). To authors' knowledge, this is one of the few studies where DGGE-based approach is utilized to study and compare microbial shifts under mesophilic and thermophilic anaerobic digestions of manure simultaneously. While there were challenges in identifying the bands during gradient gel electrophoresis, the joint use of DGGE and sequencing tool can be potentially useful for illustrating and comparing the change in microbial community structure under complex anaerobic processes and functionality of microbes for understanding the consequential GHG emissions from manure.

Body size mediates the functional potential of soil organisms by diversity and community assembly across soil aggregates

Body size is an important life-history trait that affects organism niche occupancy and ecological interactions. However, it is still unclear to what extent the assembly process of organisms with different body sizes affects soil biogeochemical cycling processes at the aggregate level. Here, we examined the diversity and community assembly of soil microorganisms (bacteria, fungi, and protists) and microfauna (nematodes) with varying body sizes. The microbial functional potential associated with carbon, nitrogen, phosphorus, and sulfur metabolism within three soil aggregate sizes (large macroaggregates, > 2 mm; small macroaggregates, 0.25-2 mm; and microaggregates, < 0.25 mm) were determined by metagenomics. We found that the smallest microbes (bacteria) had higher α-diversity and lower β-diversity and were mostly structured by stochastic processes, while all larger organisms (fungi, protists, and nematodes) had lower α-diversity and were relatively more influenced by deterministic processes. Structural equation modeling indicated that the microbial functional potential associated with carbon, nitrogen, phosphorus, and sulfur metabolism was mainly influenced by the bacterial and protist diversity in microaggregates. In contrast, the microbial functional potential was primarily mediated by the assembly processes of four organism groups, especially the nematode community in macroaggregates. This study reveals the important roles of soil organisms with different body sizes in the functional potential related to nutrient cycling, and provides new insights into the ecological processes structuring the diversity and community assembly of organisms of different body sizes at the soil aggregate level, with implications for soil nutrient cycling dynamics.

An inquiline mosquito modulates microbial diversity and function in an aquatic microecosystem

Understanding microbial roles in ecosystem function requires integrating microscopic processes into food webs. The carnivorous pitcher plant, Sarracenia purpurea, offers a tractable study system where diverse food webs of macroinvertebrates and microbes facilitate digestion of captured insect prey, releasing nutrients supporting the food web and host plant. However, how interactions between these macroinvertebrate and microbial communities contribute to ecosystem functions remains unclear. We examined the role of the pitcher plant mosquito, Wyeomyia smithii, in top-down control of the composition and function of pitcher plant microbial communities. Mosquito larval abundance was enriched or depleted across a natural population of S. purpurea pitchers over a 74-day field experiment. Bacterial community composition and microbial community function were characterized by 16S rRNA amplicon sequencing and profiling of carbon substrate use, bulk metabolic rate, hydrolytic enzyme activity, and macronutrient pools. Bacterial communities changed from pitcher opening to maturation, but larvae exerted minor effects on high-level taxonomic composition. Higher larval abundance was associated with lower diversity communities with distinct functions and elevated nitrogen availability. Treatment-independent clustering also supported roles for larvae in curating pitcher microbial communities through shifts in community diversity and function. These results demonstrate top-down control of microbial functions in an aquatic microecosystem.

Microbial community composition predicts bacterial production across ocean ecosystems

Microbial ecological functions are an emergent property of community composition. For some ecological functions, this link is strong enough that community composition can be used to estimate the quantity of an ecological function. Here, we apply random forest regression models to compare the predictive performance of community composition and environmental data for bacterial production (BP). Using data from two independent long-term ecological research sites-Palmer LTER in Antarctica and Station SPOT in California-we found that community composition was a strong predictor of BP. The top performing model achieved an R2 of 0.84 and RMSE of 20.2 pmol L-1 hr-1 on independent validation data, outperforming a model based solely on environmental data (R2 = 0.32, RMSE = 51.4 pmol L-1 hr-1). We then operationalized our top performing model, estimating BP for 346 Antarctic samples from 2015 to 2020 for which only community composition data were available. Our predictions resolved spatial trends in BP with significance in the Antarctic (P value = 1 × 10-4) and highlighted important taxa for BP across ocean basins. Our results demonstrate a strong link between microbial community composition and microbial ecosystem function and begin to leverage long-term datasets to construct models of BP based on microbial community composition.

Experimental erosion of microbial diversity decreases soil CH4 consumption rates

Biodiversity-ecosystem functioning (BEF) experiments have predominantly focused on communities of higher organisms, in particular plants, with comparably little known to date about the relevance of biodiversity for microbially driven biogeochemical processes. Methanotrophic bacteria play a key role in Earth's methane (CH4 ) cycle by removing atmospheric CH4 and reducing emissions from methanogenesis in wetlands and landfills. Here, we used a dilution-to-extinction approach to simulate diversity loss in a methanotrophic landfill cover soil community. Replicate samples were diluted 101 -107 -fold, preincubated under a high CH4 atmosphere for microbial communities to recover to comparable size, and then incubated for 86 days at constant or diurnally cycling temperature. We hypothesize that (1) CH4 consumption decreases as methanotrophic diversity is lost, and (2) this effect is more pronounced under variable temperatures. Net CH4 consumption was determined by gas chromatography. Microbial community composition was determined by DNA extraction and sequencing of amplicons specific to methanotrophs and bacteria (pmoA and 16S gene fragments). The richness of operational taxonomic units (OTU) of methanotrophic and nonmethanotrophic bacteria decreased approximately linearly with log-dilution. CH4 consumption decreased with the number of OTUs lost, independent of community size. These effects were independent of temperature cycling. The diversity effects we found occured in relatively diverse communities, challenging the notion of high functional redundancy mediating high resistance to diversity erosion in natural microbial systems. The effects also resemble the ones for higher organisms, suggesting that BEF relationships are universal across taxa and spatial scales.

Distribution heterogeneity of sediment bacterial community in the river-lake system impacted by nonferrous metal mines: Diversity, composition and co-occurrence patterns

Metal(loid) pollution caused by mining activities can affect microbial communities. However, knowledge of the diversity, composition, and co-occurrence patterns of bacterial communities in aquatic systems impacted by nonferrous metal mines. Here, the metal(loid) contents and bacterial communities in sediments from the Zijiang River (tributary to mainstream) to Dongting Lake were investigated by geochemical and molecular biology methods. The results indicated that the river sediments had lower pH and higher ecological risk of metal(loid)s than the lake sediment. The diversity and composition of bacterial communities in river sediments significantly (p < 0.05) differed from those in lake sediments, showing distributional heterogeneity. The biomarkers of tributary, mainstream, and lake sediments were mainly members of Deltaproteobacteria, Firmicutes, and Nitrospirae, respectively, reflecting species sorting in different habitats. Multivariate statistical analysis demonstrated that total and bioavailable Sb, As, and Zn were positively correlated with bacterial community richness. pH, TOC, TN, and Zn were crucial factors in shaping the distribution difference of bacterial communities. Environment-bacteria network analysis indicated that pH, SO42-, and total and bioavailable As and Sb greatly influenced the bacterial composition at the genus level. Bacteria-bacteria network analysis manifested that the co-occurrence network in mainstream sediments with a higher risk of metal(loid) pollution exhibited higher modularity and connectivity, which might be the survival mechanism for bacterial communities adapted to metal(loid) pollution. This study can provide a theoretical basis for understanding the ecological status of aquatic systems.

Twenty Years of Research in Ecosystem Functions in Aquatic Microbial Ecotoxicology

One of the major threats to freshwater biodiversity is water pollution including excessive loads of nutrients, pesticides, industrial chemicals, and/or emerging contaminants. The widespread use of organic pesticides for agricultural and nonagricultural (industry, gardening, etc.) purposes has resulted in the presence of their residues in various environments, including surface waters. However, the contribution of pesticides to the deterioration of freshwater ecosystems (i.e., biodiversity decline and ecosystem functions impairment) remains uncertain. Once in the aquatic environment, pesticides and their metabolites can interact with microbial communities, causing undesirable effects. The existing legislation on ecological quality assessment of water bodies in Europe is based on water chemical quality and biological indicator species (Water Framework Directive, Pesticides Directive), while biological functions are not yet included in monitoring programs. In the present literature review, we analyze 20 years (2000-2020) of research on ecological functions provided by microorganisms in aquatic ecosystems. We describe the set of ecosystem functions investigated in these studies and the range of endpoints used to establish causal relationships between pesticide exposure and microbial responses. We focus on studies addressing the effects of pesticides at environmentally realistic concentrations and at the microbial community level to inform the ecological relevance of the ecotoxicological assessment. Our literature review highlights that most studies were performed using benthic freshwater organisms and that autotrophic and heterotrophic communities are most often studied separately, usually testing the pesticides that target the main microbial component (i.e., herbicides for autotrophs and fungicides for heterotrophs). Overall, most studies demonstrate deleterious impacts on the functions studied, but our review points to the following shortcomings: (1) the nonsystematic analysis of microbial functions supporting aquatic ecosystems functioning, (2) the study of ecosystem functions (i.e., nutrient cycling) via proxies (i.e., potential extracellular enzymatic activity measurements) which are sometimes disconnected from the current ecosystem functions, and (3) the lack of consideration of chronic exposures to assess the impact of, adaptations to, or recovery of aquatic microbial communities from pesticides. Environ Toxicol Chem 2023;42:1867-1888. © 2023 SETAC.

Investigating the eco-evolutionary response of microbiomes to environmental change

Microorganisms are the primary engines of biogeochemical processes and foundational to the provisioning of ecosystem services to human society. Free-living microbial communities (microbiomes) and their functioning are now known to be highly sensitive to environmental change. Given microorganisms' capacity for rapid evolution, evolutionary processes could play a role in this response. Currently, however, few models of biogeochemical processes explicitly consider how microbial evolution will affect biogeochemical responses to environmental change. Here, we propose a conceptual framework for explicitly integrating evolution into microbiome-functioning relationships. We consider how microbiomes respond simultaneously to environmental change via four interrelated processes that affect overall microbiome functioning (physiological acclimation, demography, dispersal and evolution). Recent evidence in both the laboratory and the field suggests that ecological and evolutionary dynamics occur simultaneously within microbiomes; however, the implications for biogeochemistry under environmental change will depend on the timescales over which these processes contribute to a microbiome's response. Over the long term, evolution may play an increasingly important role for microbially driven biogeochemical responses to environmental change, particularly to conditions without recent historical precedent.

Combined impacts of algae-induced variations in water soluble organic matter and heavy metals on bacterial community structure in sediment from Chaohu Lake, a eutrophic shallow lake

Many lakes are suffering from eutrophication and heavy metals-contamination. However, the combined impacts of algae bloom and its induced variations in heavy metals on microbial community in sediment from eutrophic lakes remain unclear. In this study, we performed field experiments to investigate how algae bloom impacted water soluble organic matter (WSOM) and heavy metals in sediment from Chaohu Lake, a eutrophic shallow lake, and probed their combined impacts on sediment bacterial community structure. The results showed that algae bloom increased WSOM quantity, in particular, the soluble microbial by-product-like (SMP) and fulvic acid-like (Fa-L) components markedly enhanced by 203.70 % and 70.17 %, respectively. We also found that algae bloom redistributed the spatial patterns of heavy metals and altered their chemical species in sediment, then promoted contamination degree and potential ecological risk of heavy metals in sediment. Moreover, sediment bacterial community richness and diversity obviously decreased after algae bloom, and the variance partitioning analysis (VPA) results showed that combined impacts of algae-induced changes in WSOM and heavy metals explained 66.56 % of the variations in bacterial community structure. These findings depicted how algae bloom influence sediment WSOM and heavy metals, and revealed the combined impacts of algae-induced variations on microbial community structure in shallow eutrophic lake.

Aqueous Geochemical Controls on the Sestonic Microbial Community in Lakes Michigan and Superior

Despite being the largest freshwater lake system in the world, relatively little is known about the sestonic microbial community structure in the Laurentian Great Lakes. The goal of this research was to better understand this ecosystem using high-throughput sequencing of microbial communities as a function of water depth at six locations in the westernmost Great Lakes of Superior and Michigan. The water column was characterized by gradients in temperature, dissolved oxygen (DO), pH, and other physicochemical parameters with depth. Mean nitrate concentrations were 32 μmol/L, with only slight variation within and between the lakes, and with depth. Mean available phosphorus was 0.07 μmol/L, resulting in relatively large N:P ratios (97:1) indicative of P limitation. Abundances of the phyla Actinobacteria, Bacteroidetes, Cyanobacteria, Thaumarchaeota, and Verrucomicrobia differed significantly among the Lakes. Candidatus Nitrosopumilus was present in greater abundance in Lake Superior compared to Lake Michigan, suggesting the importance of ammonia-oxidating archaea in water column N cycling in Lake Superior. The Shannon diversity index was negatively correlated with pH, temperature, and salinity, and positively correlated with DO, latitude, and N₂ saturation. Results of this study suggest that DO, pH, temperature, and salinity were major drivers shaping the community composition in the Great Lakes.

Functional significance of microbial diversity in arid soils: biological soil crusts and nitrogen fixation as a model system

Microbial communities respond to changes in environmental conditions; however, how compositional shifts affect ecosystem processes is still not well-understood and it is often assumed that different microbial communities will function equally under similar environmental conditions. We evaluated this assumption of functional redundancy using biological soil crusts (BSCs) from two arid ecosystems in Mexico with contrasting climate conditions (hot and cold deserts) following an experimental approach both in the field (reciprocal transplants) and in laboratory conditions (common garden), focusing on the community's composition and potential for nitrogen fixation. Potential of nitrogen fixation was assessed through the acetylene reduction assay. Community composition and diversity was determined with T-RFLPs of nifH gene, high throughput sequencing of 16S rRNA gene amplicons and metagenomic libraries. BSCs tended to show higher potential nitrogen fixation rates when experiencing temperatures more similar to their native environment. Moreover, changes in potential nitrogen fixation, taxonomic and functional community composition, and diversity often depended on an interactive effect of origin of the communities and the environment they experienced. We interpret our results as legacy effects that result from ecological specialization of the BSC communities to their native environment. Overall, we present evidence of nonfunctional redundancy of BSCs in terms of nitrogen fixation.

Functional microbial ecology in arctic soils: the need for a year-round perspective

The microbial ecology of arctic and sub-arctic soils is an important aspect of the global carbon cycle, due to the sensitivity of the large soil carbon stocks to ongoing climate warming. These regions are characterized by strong climatic seasonality, but the emphasis of most studies on the short vegetation growing season could potentially limit our ability to predict year-round ecosystem functions. We compiled a database of studies from arctic, subarctic, and boreal environments that include sampling of microbial community and functions outside the growing season. We found that for studies comparing across seasons, in most environments, microbial biomass and community composition vary intra-annually, with the spring thaw period often identified by researchers as the most dynamic time of year. This seasonality of microbial communities will have consequences for predictions of ecosystem function under climate change if it results in: seasonality in process kinetics of microbe-mediated functions; intra-annual variation in the importance of different (a)biotic drivers; and/or potential temporal asynchrony between climate change-related perturbations and their corresponding effects. Future research should focus on (i) sampling throughout the entire year; (ii) linking these multi-season measures of microbial community composition with corresponding functional or physiological measurements to elucidate the temporal dynamics of the links between them; and (iii) identifying dominant biotic and abiotic drivers of intra-annual variation in different ecological contexts.

Elemental sulphur recovery from a sulphate-rich aqueous stream in a single hybrid linear flow channel reactor is mediated through microbial community dynamics and adaptation to reactor zones

The coupled application of biological sulphate reduction (BSR) and partial sulphide oxidation to treat sulphate-rich wastewater is an effective strategy to mitigate pollution and recover elemental sulphur for repurposing. The recent development of the hybrid linear flow channel reactor (LFCR) achieves simultaneous BSR and partial sulphide oxidation with biosulphur recovery via a floating sulphur biofilm (FSB). Here, we explore the microbial community zoning and dynamics facilitating the process. A total of three continuous LFCRs were used to evaluate the effect of reactor zones, hydraulic residence time (HRT), carbon source, namely lactate and acetate, as well as reactor geometry and scale on process performance and microbial community dynamics. Community composition of sessile and planktonic microbial consortia were resolved at a 5- and 2-day HRT through 16S rRNA amplicon sequencing. Preferential attachment and prevalence of specific phylotypes within the sessile and planktonic communities revealed clear adaptation of key microorganisms to different microenvironments. Key microbial taxa affiliated with sulphate reduction and sulphide oxidation as well as those implicated in fermentation and syntrophic metabolism, fluctuated in response to changes in HRT and process performance. Through understanding the relationship between microbial community dynamics and process performance, this research will inform better process design and optimization of the hybrid LFCR.

Deterministic mechanisms drive bacterial communities assembly in industrial wastewater treatment system

Microbial communities are responsible for biological treatment of many industrial wastewater, but our knowledge of their diversity, assembly patterns, and function is still poor. Here, we analyzed the bacterial communities of wastewater and activated sludge samples taken from 11 full-scale industrial wastewater treatment plants (IWWTPs) characterized by the same process design but different wastewater types and WWTP compartments. We found significantly different diversity and compositions of bacterial assemblages among distinct wastewater types and IWWTPs compartments. IWWTPs bacterial communities exhibited a clear species abundance distribution. The dispersal-driven process was weak in shaping IWWTP communities. Meanwhile, environmental and operating conditions were important factors in regulating the structure of the activated sludge community and pollutants removal, indicating that bacterial community was largely driven by deterministic mechanisms. The core microbial community in IWWTPs was different from that in municipal wastewater treatment plants (MWWTPs), and many taxa (e.g. the genus Citreitalea) rarely were detected before, indicating IWWTPs harbored unique core bacterial communities. Furthermore, we found that bacterial community compositions were strongly linked to activated sludge function. These findings are important to both microbial ecologists and environmental engineers, who may optimize the operation strategies jointly for maintaining biodiversity, which in turn may promote a more stable performance of the IWWTP. Overall, our study enhances the mechanistic understanding of the IWWTP microbial community diversity, assembly patterns, and function, and provides important implications for microbial ecology and wastewater treatment processes.

First Steps into Ruminal Microbiota Robustness

Despite its central role in ruminant nutrition, little is known about ruminal microbiota robustness, which is understood as the ability of the microbiota to cope with disturbances. The aim of the present review is to offer a comprehensive description of microbial robustness, as well as its potential drivers, with special focus on ruminal microbiota. First, we provide a briefing on the current knowledge about ruminal microbiota. Second, we define the concept of disturbance (any discrete event that disrupts the structure of a community and changes either the resource availability or the physical environment). Third, we discuss community resistance (the ability to remain unchanged in the face of a disturbance), resilience (the ability to return to the initial structure following a disturbance) and functional redundancy (the ability to maintain or recover initial function despite compositional changes), all of which are considered to be key properties of robust microbial communities. Then, we provide an overview of the currently available methodologies to assess community robustness, as well as its drivers (microbial diversity and network complexity) and its potential modulation through diet. Finally, we propose future lines of research on ruminal microbiota robustness.

Microbial community shifts correspond with suppression of decomposition 25 years after liming of acidic forest soils

Microbial community structure and function regularly covary with soil pH, yet effects of these interactions on soil carbon are rarely tested experimentally within natural ecosystems. We investigated the enduring (25 year) impacts of liming on microbial community structure and decomposition at an acidic northern hardwood forest, where experimental liming increased pH one unit and surprisingly doubled the organic carbon stocks of the forest floor. We show that this increase in carbon storage corresponded with restructuring of the bacterial and fungal communities that drive decomposition. In the Oe horizon, liming reduced the activities of five extracellular enzymes that mediate decomposition, while the Oa horizon showed an especially large (64%) reduction in the activity of a sixth, peroxidase, which is an oxidative enzyme central to lignocellulose degradation. Decreased enzyme activities corresponded with loss of microbial taxa important for lignocellulose decay, including large reductions in the dominant ectomycorrhizal genera Russula and Cenococcum, saprotrophic and wood decaying fungi, and Actinobacteria (Thermomonosporaceae). These results demonstrate the importance of pH as a dominant regulator of microbial community structure and illustrate how changes to this structure can produce large, otherwise unexpected increases in carbon storage in forest soils.

microTrait: A Toolset for a Trait-Based Representation of Microbial Genomes

Remote sensing approaches have revolutionized the study of macroorganisms, allowing theories of population and community ecology to be tested across increasingly larger scales without much compromise in resolution of biological complexity. In microbial ecology, our remote window into the ecology of microorganisms is through the lens of genome sequencing. For microbial organisms, recent evidence from genomes recovered from metagenomic samples corroborate a highly complex view of their metabolic diversity and other associated traits which map into high physiological complexity. Regardless, during the first decades of this omics era, microbial ecological research has primarily focused on taxa and functional genes as ecological units, favoring breadth of coverage over resolution of biological complexity manifested as physiological diversity. Recently, the rate at which provisional draft genomes are generated has increased substantially, giving new insights into ecological processes and interactions. From a genotype perspective, the wide availability of genome-centric data requires new data synthesis approaches that place organismal genomes center stage in the study of environmental roles and functional performance. Extraction of ecologically relevant traits from microbial genomes will be essential to the future of microbial ecological research. Here, we present microTrait, a computational pipeline that infers and distills ecologically relevant traits from microbial genome sequences. microTrait maps a genome sequence into a trait space, including discrete and continuous traits, as well as simple and composite. Traits are inferred from genes and pathways representing energetic, resource acquisition, and stress tolerance mechanisms, while genome-wide signatures are used to infer composite, or life history, traits of microorganisms. This approach is extensible to any microbial habitat, although we provide initial examples of this approach with reference to soil microbiomes.

Phytoplankton and Bacterial Communities’ Patterns in a Highly Dynamic Ecosystem (Central Mediterranean Sea)

The Straits of Messina (Southern Italy, Mediterranean Sea) are a very complex area: they connect two basins (Tyrrhenian and Ionian) with different hydrographic features and is characterised by upwelling and mixing phenomena. The aim of the study was to evaluate if and how the physical and chemical water conditions and hydrodynamics influenced the phytoplankton and bacterial patterns and the functioning of this ecosystem. During a late winter survey, size-fractionated phytoplankton (from 0.2 to 200 μm) biomass (chlorophyll a), cell densities and species composition as well as total picoplankton abundances, morphotype composition, and activity levels of the enzymes leucine aminopeptidase, β-glucosidase, and alkaline phosphatase were investigated. The obtained results showed a marked diversification among the water masses identified within the Straits area. The analyses of the phytoplankton diversity indices, particularly those based on phylogenetic relationships between species (indices of taxonomic diversity and distinctness), confirmed our findings. In conclusion, the patterns of phytoplankton and bacterial communities provide a suitable approach to evaluate how microbial communities respond to changing environmental scenarios. This tool could be applied to other temperate Mediterranean ecosystems.

Abundant and Rare Bacterial Taxa Structuring Differently in Sediment and Water in Thermokarst Lakes in the Yellow River Source Area, Qinghai-Tibet Plateau

Thermokarst lakes are forming from permafrost thaw and are severely affected by accelerating climate change. Sediment and water in these lakes are distinct habitats but closely connected. However, our understanding of the differences and linkages between sediment and water in thermokarst lakes remains largely unknown, especially from the perspective of community assembly mechanisms. Here, we examined bacterial communities in sediment and water in thermokarst lakes in the Yellow River Source area, Qinghai-Tibet Plateau. Bacterial taxa were divided into abundant and rare according to their relative abundance, and the Sorensen dissimilarity (β_sor) was partitioned into turnover (β_turn) and nestedness (β_nest). The whole bacterial communities and the abundant and rare subcommunities differed substantially between sediment and water in taxonomical composition, α-diversity, and β-diversity. Sediment had significantly lower α-diversity indexes but higher β-diversity than water. In general, bacterial communities are predominantly governed by strong turnover processes (β_turn/β_sor ratio of 0.925). Bacterial communities in sediment had a significantly higher β_turn/β_sor ratio than in water. Abundant subcommunities were significantly lower in the β_turn/β_sor ratio compared with rare subcommunities. The results suggest that the bacterial communities of thermokarst lakes, especially rare subcommunities or particularly in sediment, might be strongly structured by heterogeneity in the source material, environmental filtering, and geographical isolation, leading to compositionally distinct communities. This integral study increased our current knowledge of thermokarst lakes, enhancing our understanding of the community assembly rules and ecosystem structures and processes of these rapidly changing and vulnerable ecosystems.

Responses of Soil Microbial Metabolic Activity and Community Structure to Different Degraded and Restored Grassland Gradients of the Tibetan Plateau

Climate change and land-use disturbances are supposed to have severely affected the degraded alpine grasslands on the Tibetan Plateau. Artificial grassland establishment has been implemented as a restoration tool against grassland degradation. However, the impact of such degradation and restoration processes on soil microbial communities and soil quality is not clearly understood. Here, we aim to investigate how the dynamics of microbial community and soil quality of alpine grasslands respond to a gradient of degradation and that of restoration, respectively. We conducted a randomised experiment with four degradation stages (light, moderate, heavy, and extreme degradation) and three restoration stages (artificial restoration for 1, 5, and 10 years). We analysed the abundance and diversity of soil bacteria and fungi, and measured soil nutrients, enzymatic activity and microbial biomass. The concentration of soil nitrogen (TN), soil organic matter (OM) in heavy degraded grassland decreased significantly by 37.4 and 45.08% compared with that in light degraded grassland. TN and OM in 10-years restored grassland also increased significantly by 33.10 and 30.42% compared to that in 1-year restored grassland. Four soil enzymatic activity indicators related to microbial biomass decreased with degradation gradient and increased with recovery time (i.e., restoration gradient). Both bacterial and fungal community structure was significantly different among grassland degradation or restoration successional stages. The LEfSe analysis revealed that 29 fungal clades and 9 bacterial clades were susceptible to degraded succession, while16 fungal clades and 5 bacterial clades were susceptible to restoration succession. We conclude that soil quality (TN, OM, and enzymatic activity) deteriorated significantly in heavy degraded alpine grassland. Soil microbial community structure of alpine is profoundly impacted by both degradation and restoration processes, fungal communities are more sensitive to grassland succession than bacterial communities. Artificial grasslands can be used as an effective method of restoring degraded grassland, but the soil functions of artificial grassland, even after 10 years of recovery, cannot be restored to the original state of alpine grassland.

Variations and Mutual Relations of Vegetation–Soil–Microbes of Alpine Meadow in the Qinghai-Tibet Plateau under Degradation and Cultivation

Artificial cultivation had been applied to recover the meadow suffering from serious degradation in the Qinghai–Tibet Plateau. Studies focusing only on the changes in vegetation, soil and microbes along the meadow degradation were insufficient, and artificial cultivation as an important part of succession was always neglected. Here, the variables of vegetation, soil, and soil bacteria are surveyed in four types of alpine meadow in the protected lands of the Qinghai–Tibet Plateau: intact alpine meadow (IAM), moderate degradation alpine meadow (MDAM), extreme degradation alpine meadow (black soil beach (BSB)), and artificial alpine grassland (AAG). The results indicated that degradation and cultivation significantly changed the characteristics of the vegetation community, physicochemical features of the soil, and soil bacterial community diversity. Soil bacteria took a considerably longer time to adapt to degradation and cultivation than vegetation and soil. Compared to IAM and BSB, ADAM and AAG had more specific bacteria identified by ANOVA and LEfSe analysis, implying an unstable state. Combined with vegetation and soil variables, it was speculated that the unstable AAG was not significantly improved from the degraded meadow, and also lagged significantly compared to IAM. Correlation analysis revealed that aboveground biomass, species richness, vegetation coverage, SOC, C/N, BD, WC, and pH were significantly associated with bacterial diversity under community level. Aboveground biomass was an effective indicator for soil bacterial gene copies. Redundancy analysis demonstrated that the soil bacterial community is mainly regulated by the vegetation coverage, Gleason index, Simpson index, TN, TP, and pH under phylum and genus level. Partial mantel test analysis indicated that the physicochemical features of the soil were the most important factor correlating with the soil bacterial community along the degradation and cultivation, compared to other environmental factors.

Chronic Environmental Perturbation Influences Microbial Community Assembly Patterns

Acute environmental perturbations are reported to induce deterministic microbial community assembly, while it is hypothesized that chronic perturbations promote development of alternative stable states. Such acute or chronic perturbations strongly impact on the pre-adaptation capacity to the perturbation. To determine the importance of the level of microbial pre-adaptation and the community assembly processes following acute or chronic perturbations in the context of hydrocarbon contamination, a model system of pristine and polluted (hydrocarbon-contaminated) sediments was incubated in the absence or presence (discrete or repeated) of hydrocarbon amendment. The community structure of the pristine sediments changed significantly following acute perturbation, with selection of different phylotypes not initially detectable. Conversely, historically polluted sediments maintained the initial community structure, and the historical legacy effect of chronic pollution likely facilitated community stability. An alternative stable state was also reached in the pristine sediments following chronic perturbation, further demonstrating the existence of a legacy effect. Finally, ecosystem functional resilience was demonstrated through occurrence of hydrocarbon degradation by different communities in the tested sites, but the legacy effect of perturbation also strongly influenced the biotic response. This study therefore demonstrates the importance of perturbation chronicity on microbial community assembly processes and reveals ecosystem functional resilience following environmental perturbation.

Microplastics as an aquatic pollutant affect gut microbiota within aquatic animals

The adverse impact of microplastics (MPs) on gut microbiota within aquatic animals depends on the overall effect of chemicals and biofilm of MPs. Thus, it is ideal to fully understand the influences that arise from each or even all of these characteristics, which should give us a whole picture of consequences that are brought by MPs. Harmful effects of MPs on gut microbiota within aquatic organisms start from the ingestion of MPs by aquatic organisms. According to this, the present review will discuss the ingestion of MPs and its following results on gut microbial communities within aquatic animals, in which chemical components, such as plastic polymers, heavy metals and POPs, and the biofilm of MPs would be involved. This review firstly analyzed the impacts of MPs on aquatic organisms in detail about its chemical components and biofilm based on previous relevant studies. At last, the significance of field studies, functional studies and complex dynamics of gut microbial ecology in the future research of MPs affecting gut microbiota is discussed.

Meadow degradation increases spatial turnover rates of the fungal community through both niche selection and dispersal limitation

The alpine meadow ecosystem, as the main ecosystem of the Qinghai-Tibet Plateau, has been heavily degraded over the past several decades due to overgrazing and climate change. Although soil microorganisms play key roles in the stability and succession of grassland ecosystems, their response to grassland degradation has not been investigated at spatial scale. Here, we systematically analyzed the spatial turnover rates of soil prokaryotic and fungal communities in degraded and undegraded meadows through distance-decay relationship (DDR) and species area relationship (SAR), as well as the community assembly mechanisms behind them. Although the composition and structure of both fungal and prokaryotic communities showed significant changes between undegraded and degraded meadows, steeper spatial turnover rates were only observed in fungi (Degraded Alpine Meadow β = 0.0142, Undegraded Alpine Meadow β = 0.0077, P < 0.05). Mantel tests indicated that edaphic variables and vegetation factors showed significant correlations to the β diversity of fungal community only in degraded meadow, suggesting soil and vegetation heterogeneity both contributed to the variation of fungal community in that system. Correspondingly, a novel phylogenetic null model analysis demonstrated that environmental selection was enhanced in the fungal community assembly process during meadow degradation. Interestingly, dispersal limitation was also enhanced for the fungal community in the degraded meadow, and its relative contribution to other assembly process (i.e. selection and drift) showed a significant linear increase with spatial distance, suggesting that dispersal limitation played a greater role as distance increased. Our findings indicated the spatial scaling of the fungal community is altered during meadow degradation by both niche selection and dispersal limitation. This study provides a new perspective for the assessment of soil microbial responses to vegetation changes in alpine areas.

Toward a function-first framework to make soil microbial ecology predictive

Soil microbial communities perform vital ecosystem functions, such as the decomposition of organic matter to provide plant nutrition. However, despite the functional importance of soil microorganisms, attribution of ecosystem function to particular constituents of the microbial community has been impeded by a lack of information linking microbial function to community composition and structure. Here, we propose a function-first framework to predict how microbial communities influence ecosystem functions. We first view the microbial community associated with a specific function as a whole and describe the dependence of microbial functions on environmental factors (e.g., the intrinsic temperature dependence of bacterial growth rates). This step defines the aggregate functional response curve of the community. Second, the contribution of the whole community to ecosystem function can be predicted, by combining the functional response curve with current environmental conditions. Functional response curves can then be linked with taxonomic data in order to identify sets of "biomarker" taxa that signal how microbial communities regulate ecosystem functions. Ultimately, such indicator taxa may be used as a diagnostic tool, enabling predictions of ecosystem function from community composition. In this paper, we provide three examples to illustrate the proposed framework, whereby the dependence of bacterial growth on environmental factors, including temperature, pH, and salinity, is defined as the functional response curve used to interlink soil bacterial community structure and function. Applying this framework will make it possible to predict ecosystem functions directly from microbial community composition.

Distinct methane-dependent biogeochemical states in Arctic seafloor gas hydrate mounds

Archaea mediating anaerobic methane oxidation are key in preventing methane produced in marine sediments from reaching the hydrosphere; however, a complete understanding of how microbial communities in natural settings respond to changes in the flux of methane remains largely uncharacterized. We investigate microbial communities in gas hydrate-bearing seafloor mounds at Storfjordrenna, offshore Svalbard in the high Arctic, where we identify distinct methane concentration profiles that include steady-state, recently-increasing subsurface diffusive flux, and active gas seepage. Populations of anaerobic methanotrophs and sulfate-reducing bacteria were highest at the seep site, while decreased community diversity was associated with a recent increase in methane influx. Despite high methane fluxes and methanotroph doubling times estimated at 5-9 months, microbial community responses were largely synchronous with the advancement of methane into shallower sediment horizons. Together, these provide a framework for interpreting subseafloor microbial responses to methane escape in a warming Arctic Ocean.

Emergent properties of microbial communities drive accelerated biogeochemical cycling in disturbed temperate forests

Despite ever-increasing availability of detailed information about microbial community structure, relationships of microbial diversity with ecosystem functioning remain unclear. We investigated these relationships at the Coweeta Hydrologic Laboratory, where past forest disturbances (e.g., clear-cut) have altered both ecosystem processes (e.g., increased N export) and microbial communities (e.g., increased bacterial diversity). We sampled soils from disturbed and adjacent reference forests, characterized resident microbial communities, and measured several microbial C-cycle and N-cycle process rates. Microbial communities from historically disturbed soils exhibited altered ecosystem functioning, including generally higher rates of C- and N-cycle processes. Disturbed soil microbial communities also exhibited altered ecosystem multifunctionality, a composite variable consisting of all measured process rates as well as extracellular enzyme activities. Although we found few relationships between ecosystem functions and microbial alpha diversity, all functions were correlated with microbial community composition metrics, particularly r:K strategist ratios of bacterial phyla. Additionally, for both ecosystem multifunctionality and specific processes (i.e., C- and N-mineralization), microbial metrics significantly improved models seeking to explain variation in process rates. Our work sheds light on the links between microbial communities and ecosystem functioning and identifies specific microbial metrics important for modeling ecosystem responses to environmental change.

Temporal Changes in the Function of Bacterial Assemblages Associated With Decomposing Earthworms

Soil invertebrate corpse decomposition is an ecologically significant, yet poorly understood, process affecting nutrient biogeochemical cycling in terrestrial ecosystems. Here, we attempted to answer how the substrate chemistry and microbial community change during soil invertebrate (earthworm) decomposition and what roles microbes play in this process. Specifically, the dead earthworms (Amynthas corticis) were buried in two soils where the earthworms inhabited, or not, until more than 50% of the earthworm mass was lost. For both soils, earthworms decomposed faster during the early stage (between 0 and 3 days), as reflected by the higher rate of decomposition and increased accumulation of dissolved organic matter (DOM). This decomposition pattern was paralleled by bacterial community dynamics, where bacterial richness and diversity were significantly higher during early decomposition (p < 0.05) with the relative abundances of many genera decreasing as decomposition progressed. The succession of the bacterial community composition was significantly correlated with time-course changes in DOM composition (p < 0.05). Particularly, more functional groups (e.g., microbes associated with carbon, nitrogen, and sulfur cycling) were identified to be linked with the change of a specific DOM type during the early decomposition phase. By exploring the ecologically important process of soil invertebrate decomposition and its associated bacterial communities, this study provides evidence, e.g., a statistically significant positive correlation between bacterial community and DOM compositions, which supports the widely recognized yet less-tested microbial community structure–function relationship hypothesis in invertebrate decomposition.

Ectomycorrhizal fungi are associated with reduced nitrogen cycling rates in temperate forest soils without corresponding trends in bacterial functional groups

Microbial processes play a central role in controlling the availability of N in temperate forests. While bacteria, archaea, and fungi account for major inputs, transformations, and exports of N in soil, relationships between microbial community structure and N cycle fluxes have been difficult to detect and characterize. Several studies have reported differences in N cycling based on mycorrhizal type in temperate forests, but associated differences in N cycling genes underlying these fluxes are not well-understood. We explored how rates of soil N cycle fluxes vary across gradients of mycorrhizal abundance (hereafter "mycorrhizal gradients") at four temperate forest sites in Massachusetts and Indiana, USA. We paired measurements of N-fixation, net nitrification, and denitrification rates with gene abundance data for specific bacterial functional groups associated with each process. We find that the availability of NO₃ and rates of N-fixation, net nitrification, and denitrification are reduced in stands dominated by trees associated with ECM fungi. On average, rates of N-fixation and denitrification in stands dominated by trees associated with arbuscular mycorrhizal fungi were more than double the corresponding rates in stands dominated by trees associated with ectomycorrhizal fungi. Despite the structuring of flux rates across the mycorrhizal gradients, we did not find concomitant shifts in the abundances of N-cycling bacterial genes, and gene abundances were not correlated with process rates. Given that AM-associating trees are replacing ECM-associating trees throughout much of the eastern US, our results suggest that shifts in mycorrhizal dominance may accelerate N cycling independent of changes in the relative abundance of N cycling bacteria, with consequences for forest productivity and N retention.

The temperature sensitivity of soil: microbial biodiversity, growth, and carbon mineralization

Microorganisms drive soil carbon mineralization and changes in their activity with increased temperature could feedback to climate change. Variation in microbial biodiversity and the temperature sensitivities (Q₁₀) of individual taxa may explain differences in the Q₁₀ of soil respiration, a possibility not previously examined due to methodological limitations. Here, we show phylogenetic and taxonomic variation in the Q₁₀ of growth (5-35 °C) among soil bacteria from four sites, one from each of Arctic, boreal, temperate, and tropical biomes. Differences in the temperature sensitivities of taxa and the taxonomic composition of communities determined community-assembled bacterial growth Q₁₀, which was strongly predictive of soil respiration Q₁₀ within and across biomes. Our results suggest community-assembled traits of microbial taxa may enable enhanced prediction of carbon cycling feedbacks to climate change in ecosystems across the globe.

Metals Alter Membership but Not Diversity of a Headwater Stream Microbiome

Metal contamination from mining or natural weathering is a common feature of surface waters in the American west. Advances in microbial analyses have created the potential for routine sampling of aquatic microbiomes as a tool to assess the quality of stream habitat. We sought to determine if microbiome diversity and membership were affected by metal contamination and identify candidate microbial taxa to be used to indicate metal stress in stream ecosystems. We evaluated microbiome membership from sediments at multiple sites within the principal drainage of an EPA superfund site near the headwaters of the Upper Arkansas River, Leadville, CO. From each sample, we extracted DNA and sequenced the 16S rRNA gene amplicon on the Illumina MiSeq platform. We used the remaining sediments to simultaneously evaluate environmental metal concentrations. We also conducted an artificial stream mesocosm experiment using sediments collected from two of the observational study sites. The mesocosm experiment had a two-by-two factorial design: (i) location (upstream or downstream of contaminating tributary), and (ii) treatment (metal exposure or control). We found no difference in diversity between upstream and downstream sites in the field. Similarly, diversity changed very little following experimental metal exposure. However, microbiome membership differed between upstream and downstream locations and experimental metal exposure changed microbiome membership in a manner that depended on origin of the sediments used in each mesocosm.IMPORTANCE Our results suggest that microbiomes can be reliable indicators of ecosystem metal stress even when surface water chemistry and other metrics used to assess ecosystem health do not indicate ecosystem stress. Results presented in this study, in combination with previously published work on this same ecosystem, are consistent with the idea that a microbial response to metals at the base of the food web may be affecting primary consumers. If effects of metals are mediated through shifts in the microbiome, then microbial metrics, as presented here, may aid in the assessment of stream ecosystem health, which currently does not include assessments of the microbiome.

Critical Review of Polyphosphate and Polyphosphate Accumulating Organisms for Agricultural Water Quality Management

Despite ongoing management efforts, phosphorus (P) loading from agricultural landscapes continues to impair water quality. Wastewater treatment research has enhanced our knowledge of microbial mechanisms influencing P cycling, especially regarding microbes known as polyphosphate accumulating organisms (PAOs) that store P as polyphosphate (polyP) under oxic conditions and release P under anoxic conditions. However, there is limited application of PAO research to reduce agricultural P loading and improve water quality. Herein, we conducted a meta-analysis to identify articles in Web of Science on polyP and its use by PAOs across five disciplines (i.e., wastewater treatment, terrestrial, freshwater, marine, and agriculture). We also summarized research that provides preliminary support for PAO-mediated P cycling in natural habitats. Terrestrial, freshwater, marine, and agriculture disciplines had fewer polyP and PAO articles compared to wastewater treatment, with agriculture consistently having the least. Most meta-analysis articles did not overlap disciplines. We found preliminary support for PAOs in natural habitats and identified several knowledge gaps and research opportunities. There is an urgent need for interdisciplinary research linking PAOs, polyP, and oxygen availability with existing knowledge of P forms and cycling mechanisms in natural and agricultural environments to improve agricultural P management strategies and achieve water quality goals.

Patterns in Benthic Microbial Community Structure Across Environmental Gradients in the Beaufort Sea Shelf and Slope

The paradigm of tight pelagic-benthic coupling in the Arctic suggests that current and future fluctuations in sea ice, primary production, and riverine input resulting from global climate change will have major impacts on benthic ecosystems. To understand how these changes will affect benthic ecosystem function, we must characterize diversity, spatial distribution, and community composition for all faunal components. Bacteria and archaea link the biotic and abiotic realms, playing important roles in organic matter (OM) decomposition, biogeochemical cycling, and contaminant degradation, yet sediment microbial communities have rarely been examined in the North American Arctic. Shifts in microbial community structure and composition occur with shifts in OM inputs and contaminant exposure, with implications for shifts in ecological function. Furthermore, the characterization of benthic microbial communities provides a foundation from which to build focused experimental research. We assessed diversity and community structure of benthic prokaryotes in the upper 1 cm of sediments in the southern Beaufort Sea (United States and Canada), and investigated environmental correlates of prokaryotic community structure over a broad spatial scale (spanning 1,229 km) at depths ranging from 17 to 1,200 m. Based on hierarchical clustering, we identified four prokaryotic assemblages from the 85 samples analyzed. Two were largely delineated by the markedly different environmental conditions in shallow shelf vs. upper continental slope sediments. A third assemblage was mainly comprised of operational taxonomic units (OTUs) shared between the shallow shelf and upper slope assemblages. The fourth assemblage corresponded to sediments receiving heavier OM loading, likely resulting in a shallower anoxic layer. These sites may also harbor microbial mats and/or methane seeps. Substructure within these assemblages generally reflected turnover along a longitudinal gradient, which may be related to the quantity and composition of OM deposited to the seafloor; bathymetry and the Mackenzie River were the two major factors influencing prokaryote distribution on this scale. In a broader geographical context, differences in prokaryotic community structure between the Beaufort Sea and Norwegian Arctic suggest that benthic microbes may reflect regional differences in the hydrography, biogeochemistry, and bathymetry of Arctic shelf systems.

Belowground changes to community structure alter methane-cycling dynamics in Amazonia

Amazonian rainforest is undergoing increasing rates of deforestation, driven primarily by cattle pasture expansion. Forest-to-pasture conversion has been associated with increases in soil methane (CH₄) emission. To better understand the drivers of this change, we measured soil CH₄ flux, environmental conditions, and belowground microbial community structure across primary forests, cattle pastures, and secondary forests in two Amazonian regions. We show that pasture soils emit high levels of CH₄ (mean: 3454.6 ± 9482.3 μg CH₄ m^-2 d^-1), consistent with previous reports, while forest soils on average emit CH₄ at modest rates (mean: 9.8 ± 120.5 μg CH₄ m^-2 d^-1), but often act as CH₄ sinks. We report that secondary forest soils tend to consume CH₄ (mean: -10.2 ± 35.7 μg CH₄ m^-2 d^-1), demonstrating that pasture CH₄ emissions can be reversed. We apply a novel computational approach to identify microbial community attributes associated with flux independent of soil chemistry. While this revealed taxa known to produce or consume CH₄ directly (i.e. methanogens and methanotrophs, respectively), the vast majority of identified taxa are not known to cycle CH₄. Each land use type had a unique subset of taxa associated with CH₄ flux, suggesting that land use change alters CH₄ cycling through shifts in microbial community composition. Taken together, we show that microbial composition is crucial for understanding the observed CH₄ dynamics and that microorganisms provide explanatory power that cannot be captured by environmental variables.

How do soil microbial communities respond to fire in the intermediate term? Investigating direct and indirect effects associated with fire occurrence and burn severity

Fires transform soil microbial communities directly via heat-induced mortality and indirectly by altering plant and soil characteristics. Emerging evidence suggests the magnitude of changes to some plant and soil properties increases with burn severity, but the persistence of changes varies among plant and soil characteristics, ranging from months to years post-fire. Thus, which environmental attributes shape microbial communities at intermediate time points during ecosystem recovery, and how these characteristics vary with severity, remains poorly understood. We identified the network of properties that influence microbial communities three years after fire, along a burn severity gradient in Sierra Nevada mixed-conifer forest. We used phospholipid fatty acid (PLFA) analysis and bacterial 16S-rDNA amplicon sequencing to characterize the microbial community in mineral soil. Using structural equation modelling, we applied a systems approach to identifying the interconnected relationships among severity, vegetation, soil, and microbial communities. Dead tree basal area, soil pH, and extractable phosphorus increased with severity, whereas live tree basal area, forest floor mass, and the proportion of the ≥53 μm soil fraction decreased. Forest floor loss was associated with decreased soil moisture across the severity gradient, decreased live tree basal area was associated with increased shrub coverage, and increased dead tree basal area was associated with increases in total and inorganic soil nitrogen. Soil fungal abundance decreased across the severity gradient, despite a slightly positive response of fungi to lower soil moisture in high severity areas. Bacterial phylogenetic diversity was negatively related to severity and was driven by differences in nutrients and soil texture. The abundance of Bacteroidetes increased and the abundance of Acidobacteria decreased across the severity gradient due to differences in soil pH. Overall, we found that the effects of burn severity on vegetation and soil physicochemical characteristics interact to shape microbial communities at an intermediate time point in ecosystem recovery.

Warming and disturbance alter soil microbiome diversity and function in a northern forest ecotone

The response to global change by soil microbes is set to affect important ecosystem processes. These impacts could be most immediate in transitional zones, such as the temperate-boreal forest ecotone, yet previous work in these forests has primarily focused on specific subsets of microbial taxa. Here, we examined how bacterial and fungal communities respond to simulated above- and below-ground warming under realistic field conditions in closed and open canopy treatments in Minnesota, USA. Our results show that warming and canopy disturbance shifted bacterial and fungal community structure as dominant bacterial and fungal groups differed in the direction and intensity of their responses. Ectomycorrhizal and saprotrophic fungal communities with greater connectivity (higher prevalence of strongly interconnected taxa based on pairwise co-occurrence relationships) were more resistant to compositional change. Warming effects on soil enzymes involved in the hydrolytic and oxidative liberation of carbon from plant cell walls and nutrients from organic matter were most strongly linked to fungal community responses, although community structure-function relationships differed between fungal guilds. Collectively, these findings indicate that warming and disturbance will influence the composition and function of microbial communities in the temperate-boreal ecotone, and fungal responses are particularly important to understand for predicting future ecosystem functioning.

Association between Aquatic Micropollutant Dissipation and River Sediment Bacterial Communities

Assessment of micropollutant biodegradation is essential to determine the persistence of potentially hazardous chemicals in aquatic ecosystems. We studied the dissipation half-lives of 10 micropollutants in sediment-water incubations (based on the OECD 308 standard) with sediment from two European rivers sampled upstream and downstream of wastewater treatment plant (WWTP) discharge. Dissipation half-lives (DT50s) were highly variable between the tested compounds, ranging from 1.5 to 772 days. Sediment from one river sampled downstream from the WWTP showed the fastest dissipation of all micropollutants after sediment RNA normalization. By characterizing sediment bacteria using 16S rRNA sequences, bacterial community composition of a sediment was associated with its capacity for dissipating micropollutants. Bacterial amplicon sequence variants of the genera Ralstonia, Pseudomonas, Hyphomicrobium, and Novosphingobium, which are known degraders of contaminants, were significantly more abundant in the sediment incubations where fast dissipation was observed. Our study illuminates the limitations of the OECD 308 standard to account for variation of dissipation rates of micropollutants due to differences in bacterial community composition. This limitation is problematic particularly for those compounds with DT50s close to regulatory persistence criteria. Thus, it is essential to consider bacterial community composition as a source of variability in regulatory biodegradation and persistence assessments.

Niche Differentiation of Bacterial Versus Archaeal Soil Nitrifiers Induced by Ammonium Inhibition Along a Management Gradient

Soil nitrification, mediated mainly by ammonia oxidizing archaea (AOA) and bacteria (AOB), converts ammonium (NH₄⁺) to nitrite (NO₂⁻) and thence nitrate (NO₃⁻). To better understand ecological differences between AOA and AOB, we investigated the nitrification kinetics of AOA and AOB under eight replicated cropped and unmanaged ecosystems (including two fertilized natural systems) along a long-term management intensity gradient in the upper U.S. Midwest. For five of eight ecosystems, AOB but not AOA exhibited Haldane kinetics (inhibited by high NH₄⁺ additions), especially in perennial and successional systems. In contrast, AOA predominantly exhibited Michaelis-Menten kinetics, suggesting greater resistance to high nitrogen inputs than AOB. These responses suggest the potential for NH₄⁺-induced niche differentiation between AOA and AOB. Additionally, long-term fertilization significantly enhanced maximum nitrification rates (V_max) in the early successional systems for both AOA and AOB, but not in the deciduous forest systems. This was likely due to pH suppression of nitrification in the acidic forest soils, corroborated by a positive correlation of V_max with soil pH but not with amoA gene abundance. Results also demonstrated that soil nitrification potentials were relatively stable, as there were no seasonal differences. Overall, results suggest that (1) NH₄⁺ inhibition of AOB but not AOA could be another factor contributing to niche differentiation between AOA and AOB in soil, and (2) nitrification by both AOA and AOB can be significantly promoted by long-term nitrogen inputs.

Soil Bacterial and Fungal Richness Forecast Patterns of Early Pine Litter Decomposition

Discovering widespread microbial processes that drive unexpected variation in carbon cycling may improve modeling and management of soil carbon (Prescott, 2010; Wieder et al., 2015a, 2018). A first step is to identify community features linked to carbon cycle variation. We addressed this challenge using an epidemiological approach with 206 soil communities decomposing Ponderosa pine litter in 618 microcosms. Carbon flow from litter decomposition was measured over a 6-week incubation. Cumulative CO2 from microbial respiration varied two-fold among microcosms and dissolved organic carbon (DOC) from litter decomposition varied five-fold, demonstrating large functional variation despite constant environmental conditions where strong selection is expected. To investigate microbial features driving DOC concentration, two microbial community cohorts were delineated as "high" and "low" DOC. For each cohort, communities from the original soils and from the final microcosm communities after the 6-week incubation with litter were taxonomically profiled. A logistic model including total biomass, fungal richness, and bacterial richness measured in the original soils or in the final microcosm communities predicted the DOC cohort with 72 (P < 0.05) and 80 (P < 0.001) percent accuracy, respectively. The strongest predictors of the DOC cohort were biomass and either fungal richness (in the original soils) or bacterial richness (in the final microcosm communities). Successful forecasting of functional patterns after lengthy community succession in a new environment reveals strong historical contingencies. Forecasting future community function is a key advance beyond correlation of functional variance with end-state community features. The importance of taxon richness-the same feature linked to carbon fate in gut microbiome studies-underscores the need for increased understanding of biotic mechanisms that can shape richness in microbial communities independent of physicochemical conditions.

Biological invasions alter environmental microbiomes: A meta-analysis

Biological invasions impact both agricultural and natural systems. The damage can be quantified in terms of both economic loss and reduction of biodiversity. Although the literature is quite rich about the impact of invasive species on plant and animal communities, their impact on environmental microbiomes is underexplored. Here, we re-analyze publicly available data using a common framework to create a global synthesis of the effects of biological invasions on environmental microbial communities. Our findings suggest that non-native species are responsible for the loss of microbial diversity and shifts in the structure of microbial populations. Therefore, the impact of biological invasions on native ecosystems might be more pervasive than previously thought, influencing both macro- and micro-biomes. We also identified gaps in the literature which encourage research on a wider variety of environments and invaders, and the influence of invaders across seasons and geographical ranges.

Functional Associations and Resilience in Microbial Communities

Microbial communities have inherently high levels of metabolic flexibility and functional redundancy, yet the structure of microbial communities can change rapidly with environmental perturbation. To understand whether such changes observed at the taxonomic level translate into differences at the functional level, we analyzed the structure of taxonomic and functional gene distribution across Arctic and Antarctic locations. Taxonomic diversity (in terms of alpha diversity and species richness) differed significantly with location. However, we found that functional genes distributed evenly across bacterial networks and that this functional distribution was also even across different geographic locations. For example, on average 15% of the functional genes were related to carbon cycling across all bacterial networks, slightly over 21% of the genes were stress-related and only 0.5% of the genes were linked to carbon degradation functions. In such a distribution, each bacterial network includes all of the functional groups distributed following the same proportions. However, the total number of functional genes that is included in each bacterial network differs, with some clusters including many more genes than others. We found that the proportion of times a specific gene must occur to be linked to a specific cluster is 8%, meaning the relationship between the total number of genes in the cluster and the number of genes per function follows a linear pattern: smaller clusters require a gene to appear less frequently to get fixed within the cluster, while larger clusters require higher gene frequencies. We suggest that this mechanism of functional association between equally rare or equally abundant genes could have implications for ecological resilience, as non-dominant genes also associate in fully functioning ecological networks, potentially suggesting that there are always pre-existing functional networks available to exploit new ecological niches (where they can become dominant) as they emerge; for example, in the case of rapid or sudden environmental change. Furthermore, this pattern did not correlate with taxonomic distribution, suggesting that bacteria associate based on functionality and this is independent of its taxonomic position. Our analyses based on ecological networks also showed no clear evidence of recent environmental impact on polar marine microbial communities at the functional level, unless all communities analyzed have changed exactly in the same direction and intensity, which is unlikely given we are comparing areas changing at different rates.

Community structure - Ecosystem function relationships in the Congo Basin methane cycle depend on the physiological scale of function

Belowground ecosystem processes can be highly variable and difficult to predict using microbial community data. Here, we argue that this stems from at least three issues: (a) complex covariance structure of samples (with environmental conditions or spatial proximity) can make distinguishing biotic drivers a challenge; (b) communities can control ecosystem processes through multiple mechanisms, making the identification of these controls a challenge; and (c) ecosystem function assessments can be broad in physiological scale, encapsulating multiple processes with unique microbially mediated controls. We test these assertions using methane (CH₄ )-cycling processes in soil samples collected along a wetland-to-upland habitat gradient in the Congo Basin. We perform our measurements of function under controlled laboratory conditions and statistically control for environmental covariates to aid in identifying biotic drivers. We divide measurements of microbial communities into four attributes (abundance, activity, composition, and diversity) that represent different forms of community control. Lastly, our process measurements differ in physiological scale, including broader processes (gross methanogenesis and methanotrophy) that involve more mediating groups, to finer processes (hydrogenotrophic methanogenesis and high-affinity CH₄ oxidation) with fewer mediating groups. We observed that finer scale processes can be more readily predicted from microbial community structure than broader scale processes. In addition, the nature of those relationships differed, with broad processes limited by abundance while fine-scale processes were associated with diversity and composition. These findings demonstrate the importance of carefully defining the physiological scale of ecosystem function and performing community measurements that represent the range of possible controls on ecosystem processes.

Bacterial community composition and function along spatiotemporal connectivity gradients in the Danube floodplain (Vienna, Austria)

It is well recognized that river-floodplain systems contribute significantly to riverine ecosystem metabolism, and that bacteria are key players in the aquatic organic carbon cycle, but surprisingly few studies have linked bacterial community composition (BCC), function and carbon quality in these hydrologically highly dynamic habitats. We investigated aquatic BCC and extracellular enzymatic activity (EEA) related to dissolved organic carbon quality and algae composition, including the impact of a major flood event in one of the last remaining European semi-natural floodplain-systems. We found that surface connectivity of floodplain pools homogenizes BCC and EEA, whereas low connectivity led to increased BCC and EEA heterogeneity, supported by their relationship to electrical conductivity, an excellent indicator for surface connection strength. Hydrogeochemical parameters best explained variation of both BCC and EEA, while the algal community and chromophoric DOM properties explained only minor fractions of BCC variation. We conclude that intermittent surface connectivity and especially permanent isolation of floodplain pools from the main river channel may severely alter BCC and EEA, with potential consequences for nutrient cycling, ecological services and greenhouse gas emissions. Disentangling microbial structure-function coupling is therefore crucial, if we are to understand and predict the consequences of human alterations on these dynamic systems.

Consequences of microbial diversity in forest nitrogen cycling: diverse ammonifiers and specialized ammonia oxidizers

We tested the ecosystem functions of microbial diversity with a focus on ammonification (involving diverse microbial taxa) and nitrification (involving only specialized microbial taxa) in forest nitrogen cycling. This study was conducted on a forest slope, in which the soil environment and plant growth gradually changed. We measured the gross and net rates of ammonification and nitrification, the abundance of predicted ammonifiers and nitrifiers, and their community compositions in the soils. The abundance of predicted ammonifiers did not change along the soil environmental gradient, leading to no significant change in the gross ammonification rate. On the other hand,  the abundance of nitrifiers and the gross nitrification rate gradually changed. These accordingly determined the spatial distribution of net accumulation of ammonium and nitrate available to plants. The community composition of predicted ammonifiers gradually changed along the slope, implying that diverse ammonifiers were more likely to include taxa that were acclimated to the soil environment and performed ammonification at different slope locations than specialized nitrifiers. Our findings suggest that the abundance of ammonifiers and nitrifiers directly affects the corresponding nitrogen transformation rates, and that their diversity affects the stability of the rates against environmental changes. This study highlights the role of microbial diversity in biogeochemical processes under changing environments and plant growth.

Niche separation within aerobic methanotrophic bacteria across lakes and its link to methane oxidation rates

Lake methane (CH₄ ) emissions are largely controlled by aerobic methane-oxidizing bacteria (MOB) which mostly belong to the classes Alpha- and Gammaproteobacteria (Alpha- and Gamma-MOB). Despite the known metabolic and ecological differences between the two MOB groups, their main environmental drivers and their relative contribution to CH₄ oxidation rates across lakes remain unknown. Here, we quantified the two MOB groups through CARD-FISH along the water column of six temperate lakes and during incubations in which we measured ambient CH₄ oxidation rates. We found a clear niche separation of Alpha- and Gamma-MOB across lake water columns, which is mostly driven by oxygen concentration. Gamma-MOB appears to dominate methanotrophy throughout the water column, but Alpha-MOB may also be an important player particularly in well-oxygenated bottom waters. The inclusion of Gamma-MOB cell abundance improved environmental models of CH₄ oxidation rate, explaining part of the variation that could not be explained by environmental factors alone. Altogether, our results show that MOB composition is linked to CH₄ oxidation rates in lakes and that information on the MOB community can help predict CH₄ oxidation rates and thus emissions from lakes.

Predicting Microbial Species in a River Based on Physicochemical Properties by Bio-Inspired Metaheuristic Optimized Machine Learning

The main goal of the analysis of microbial ecology is to understand the relationship between Earth’s microbial community and their functions in the environment. This paper presents a proof-of-concept research to develop a bioclimatic modeling approach that leverages artificial intelligence techniques to identify the microbial species in a river as a function of physicochemical parameters. Feature reduction and selection are both utilized in the data preprocessing owing to the scarce of available data points collected and missing values of physicochemical attributes from a river in Southeast China. A bio-inspired metaheuristic optimized machine learner, which supports the adjustment to the multiple-output prediction form, is used in bioclimatic modeling. The accuracy of prediction and applicability of the model can help microbiologists and ecologists in quantifying the predicted microbial species for further experimental planning with minimal expenditure, which is become one of the most serious issues when facing dramatic changes of environmental conditions caused by global warming. This work demonstrates a neoteric approach for potential use in predicting preliminary microbial structures in the environment.