Recurrence and Frequency of Disturbance have Cumulative Effect on Methanotrophic Activity, Abundance, and Community Structure

Extreme drought alters methane uptake but not methane sink in semi-arid steppes of Inner Mongolia

Global climate change, particularly drought, is expected to alter grassland methane (CH4) oxidation, a key natural process against atmospheric greenhouse gas accumulation, yet the extent of this effect and its interaction with future atmospheric CH4 concentrations increases remains uncertain. To address this research gap, we measured CH4 flux during an imposed three-month rain-free period corresponding to a 100-year recurrence drought in soil mesocosms collected from 16 different Eurasian steppe sites. We also investigated the abundance and composition of methanotrophs. Additionally, we conducted a laboratory experiment to explore the impact of elevated CH4 concentration on the CH4 uptake capacity of grassland soil under drought conditions. We found that regardless of the type of grassland, CH4 flux was still being absorbed at its peak, meaning that all grasslands functioned as persistent CH4 sinks even when the soil water content (SWC) was <5 %. A bell-shaped relationship between SWC and CH4 uptake was observed in the soils. The average maximum CH4 oxidation rate in the meadow steppe was higher than that in the typical and desert steppe soils during extreme drought. The experimental elevation of atmospheric CH4 concentration counteracted the anticipated reduction in CH4 uptake related to physiological water stress on methanotrophic soil microbes under the drought stress. On the contrary, we found that across the regional scale, nitrogen, phosphorous, and total soil organic content played a crucial role in moderating the duration and magnitude of CH4 uptake with respect to SWC. USC-γ (Upland Soil Cluster γ) and JR-3 (Jasper Ridge Cluster) were the dominant group of soil methanotrophic bacteria in three types of grassland. However, the methanotrophic abundance, rather than the methanotrophic community composition, was the dominant microbiological factor governing CH4 uptake during the drought.

Landfill bacteriology: Role in waste bioprocessing elevated landfill gaseselimination and heat management

This study delves into the critical role of microbial ecosystems in landfills, which are pivotal for handling municipal solid waste (MSW). Within these landfills, a complex interplay of several microorganisms (aerobic/anaerobic bacteria, archaea or methanotrophs), drives the conversion of complex substrates into simplified compounds and complete mineralization into the water, inorganic salts, and gases, including biofuel methane gas. These landfills have dominant biotic and abiotic environments where various bacterial, archaeal, and fungal groups evolve and interact to decompose substrate by enabling hydrolytic, fermentative, and methanogenic processes. Each landfill consists of diverse bio-geochemical environments with complex microbial populations, ranging from deeply underground anaerobic methanogenic systems to near-surface aerobic systems. These kinds of landfill generate leachates which in turn emerged as a significant risk to the surrounding because generated leachates are rich in toxic organic/inorganic components, heavy metals, minerals, ammonia and xenobiotics. In addition to this, microbial communities in a landfill ecosystem could not be accurately identified using lab microbial-culturing methods alone because most of the landfill's microorganisms cannot grow on a culture medium. Due to these reasons, research on landfills microbiome has flourished which has been characterized by a change from a culture-dependent approach to a more sophisticated use of molecular techniques like Sanger Sequencing and Next-Generation Sequencing (NGS). These sequencing techniques have completely revolutionized the identification and analysis of these diverse microbial communities. This review underscores the significance of microbial functions in waste decomposition, gas management, and heat control in landfills. It further explores how modern sequencing technologies have transformed our approach to studying these complex ecosystems, offering deeper insights into their taxonomic composition and functionality.

Phosphorus control and dredging decrease methane emissions from shallow lakes

Freshwater ecosystems are an important source of the greenhouse gas methane (CH₄), and their emissions are expected to increase due to eutrophication. Two commonly applied management techniques to reduce eutrophication are the addition of phosphate-binding lanthanum modified bentonite (LMB, trademark Phoslock©) and dredging, but their effect on CH₄ emissions is still poorly understood. Here, this study researched how LMB and dredging affected CH₄ emissions using a full-factorial mesocosm design monitored for 18 months. The effect was tested by measuring diffusive and ebullitive CH₄ fluxes, plant community composition, methanogen and methanotroph activity and community composition, and a range of physicochemical water and sediment variables. LMB addition decreased total CH₄ emissions, while dredging showed a trend towards decreasing CH₄ emissions. Total CH₄ emissions in all mesocosms were much higher in the summer of the second year, likely because of higher algal decomposition and organic matter availability. First, LMB addition lowered CH₄ emissions by decreasing P-availability, which reduced coverage of the floating fern Azolla filiculoides, and thereby prevented anoxia and decreased surface water NH₄⁺ concentrations, lowering CH₄ production rates. Second, dredging decreased CH₄ emissions in the first summer, possibly it removed the methanogenic community, and in the second year by preventing autumn and winter die-off of the rooted macrophyte Potamogeton cripsus. Finally, methanogen community composition was related to surface water NH₄⁺ and O₂, and porewater total phosphorus, while methanotroph community composition was related to organic matter content. To conclude, LMB addition and dredging not only improve water quality, but also decrease CH₄ emissions, mitigating climate change.

Microbial Community Resilience across Ecosystems and Multiple Disturbances

The ability of ecosystems to withstand disturbances and maintain their functions is being increasingly tested as rates of change intensify due to climate change and other human activities. Microorganisms are crucial players underpinning ecosystem functions, and the recovery of microbial communities from disturbances is therefore a key part of the complex processes determining the fate of ecosystem functioning. However, despite global environmental change consisting of numerous pressures, it is unclear and controversial how multiple disturbances affect microbial community stability and what consequences this has for ecosystem functions. This is particularly the case for those multiple or compounded disturbances that occur more frequently than the normal recovery time. The aim of this review is to provide an overview of the mechanisms that can govern the responses of microbes to multiple disturbances across aquatic and terrestrial ecosystems. We first summarize and discuss properties and mechanisms that influence resilience in aquatic and soil biomes to determine whether there are generally applicable principles. Following, we focus on interactions resulting from inherent characteristics of compounded disturbances, such as the nature of the disturbance, timing, and chronology that can lead to complex and nonadditive effects that are modulating the response of microorganisms.

A Novel Laboratory-Scale Mesocosm Setup to Study Methane Emission Mitigation by Sphagnum Mosses and Associated Methanotrophs

Degraded peatlands are often rewetted to prevent oxidation of the peat, which reduces CO₂ emission. However, the created anoxic conditions will boost methane (CH₄) production and thus emission. Here, we show that submerged Sphagnum peat mosses in rewetted-submerged peatlands can reduce CH₄ emission from peatlands with 93%. We were able to mimic the field situation in the laboratory by using a novel mesocosm set-up. By combining these with 16S rRNA gene amplicon sequencing and qPCR analysis of the pmoA and mmoX genes, we showed that submerged Sphagnum mosses act as a niche for CH₄ oxidizing bacteria. The tight association between Sphagnum peat mosses and methane oxidizing bacteria (MOB) significantly reduces CH₄ emissions by peatlands and can be studied in more detail in the mesocosm setup developed in this study.

Simultaneous enhancement of nitrate removal flux and methane utilization efficiency in MBfR for aerobic methane oxidation coupled to denitrification by using an innovative scalable double-layer membrane

Endevours on the enhancement of nitrate removal efficiency during methane oxidation coupled with denitrification (AME-D) has always overlooked the role of membrane employed. It would be highly beneficial to enrich the biomass content and to manage biofilm on the membrane, in the utilization of methane and denitrification. In this study, an innovative and scalable double-layer membrane (DLM) was designed and prepared for a membrane biofilm reactor (MBfR), to simultaneously enhance nitrate removal flux and methane utilization efficiency during aerobic methane oxidation coupled with the denitrification (AME-D) process. The DLM allowed quick bacterial attachment and biomass accumulation for biofilm growth, which would be then self-regulated for well distribution of functional microbes on/within the DLM. Upon a high biofilm density of over 70 g-VSS m^-2 achieved on the DLM, the methane utilization efficiency of the MBfR was enhanced significantly to over 1.3 times than the control MBfR with conventional polypropylene membrane. The MBfR employed DLM also demonstrated the maximum nitrate removal flux of 740 mg-NO₃^--N m^-2 d^-1 that was approximately 1.64 times of that in control MBfR at continuous-mode operation. This DLM indeed favored the enrichment of Type II aerobic methanotrophs of Methylocystaceae, and methanol-utilization denitrifiers of Rhodocyclaceae that preferentially utilize methanol as the cross-feeding intermediates to promote the methane utilization efficiency, and thus to enhance the nitrate removal flux. These results raised from new designed DLM confirmed the importance of membrane surface properties on the effectiveness of MBfR, and offered great potential to address challenging problems of MBfRs during engineering application.

Response of a methane-driven interaction network to stressor intensification

Microorganisms may reciprocally select for specific interacting partners, forming a network with interdependent relationships. The methanotrophic interaction network, comprising methanotrophs and non-methanotrophs, is thought to modulate methane oxidation and give rise to emergent properties beneficial for the methanotrophs. Therefore, microbial interaction may become relevant for community functioning under stress. However, empirical validation of the role and stressor-induced response of the interaction network remains scarce. Here, we determined the response of a complex methane-driven interaction network to a stepwise increase in NH4Cl-induced stress (0.5-4.75 g L-1, in 0.25-0.5 g L-1 increments) using enrichment of a naturally occurring complex community derived from a paddy soil in laboratory-scale incubations. Although ammonium and intermediates of ammonium oxidation are known to inhibit methane oxidation, methanotrophic activity was unexpectedly detected even in incubations with high ammonium levels, albeit rates were significantly reduced. Sequencing analysis of the 16S rRNA and pmoA genes consistently revealed divergent communities in the reference and stressed incubations. The 16S rRNA-based co-occurrence network analysis revealed that NH4Cl-induced stress intensification resulted in a less complex and modular network, likely driven by less stable interaction. Interestingly, the non-methanotrophs formed the key nodes, and appear to be relevant members of the community. Overall, stressor intensification unravels the interaction network, with adverse consequences for community functioning.

Resilience of methane cycle and microbial functional genes to drought and flood in an alkaline wetland: A metagenomic analysis

Alkaline wetlands distributed in arid or semi-arid areas are hotspots of methane (CH₄) emissions. Periods of drought and flood, although regular, are stressful events encountered by methanogenic anaerobes in alkaline wetlands. To investigate the response of the CH₄ cycle of alkaline wetlands to such stresses, we take Zhalong wetland as an example, then determined the CH₄ flux and soil microbiomes in the wetland during wet, dry, and flooded periods. The in-situ CH₄ flux in the wet period was 9.55-17.29 mg‧m^-2‧h^-1, but sharply degraded to 3.37-6.61 mg‧m^-2‧h^-1 in the dry period. It resumed to 4.51-20.80 mg‧m^-2‧h^-1 when the wetland was flooded again, which indicated that methanogenesis is quite resilient to drought. Syntrophic acetogenesis, and subsequently aceticlastic methanogenesis, were the dominant methanogenic pathways and resisted drought. Members belonging to Syntrophobacterales were the dominant syntrophic acetogens. They enter a viable but non-culturable (VBNC) state to resist drought. The dominant Methanosarcinales have the ability to repair reactive oxygen species damage during dry periods. The community of CH₄ sink was governed by anaerobic methanotrophs, which entered a VBNC state or used repair systems to survive dry periods. This study revealed the responses of the CH₄ cycle and microbial functional genes to drought and flood in alkaline wetlands.

Exploration and enrichment of methane-oxidizing bacteria derived from a rice paddy field emitting highly concentrated methane

Methane-oxidizing bacteria (MOB) possess the metabolic potential to assimilate the highly potent greenhouse gas, CH₄, and can also synthesize valuable products. Depending on their distinct and fastidious metabolic pathways, MOB are mainly divided into Type I and Type II; the latter are known as producers of polyhydroxyalkanoate (PHA). Despite the metabolic potential of MOB to synthesize PHA, the ecophysiology of MOB, especially under high CH₄ flux conditions, is yet to be understood. Therefore, in this study, a rice paddy soil receiving a high CH₄ flux from underground was used as an inoculum to enrich MOB using fed-batch operation, then the enriched Type II MOB were characterized. The transitions in the microbial community composition and CH₄ oxidation rates were monitored by 16S rRNA gene amplicon sequencing and degree of CH₄ consumption. With increasing incubation time, the initially dominant Methylomonas sp., affiliated with Type I MOB, was gradually replaced with Methylocystis sp., Type II MOB, resulting in a maximum CH₄ oxidation rate of 1.40 g-CH₄/g-biomass/day. The quantification of functional genes encoding methane monooxygenase, pmoA and PHA synthase, phaC, by quantitative PCR revealed concomitant increases in accordance with the Type II MOB enrichment. These increases in the functional genes underscore the significance of Type II MOB to mitigate greenhouse gas emission and produce PHA.

A Review of Landfill Microbiology and Ecology: A Call for Modernization With 'Next Generation' Technology

Engineered and monitored sanitary landfills have been widespread in the United States since the passage of the Clean Water Act (1972) with additional controls under RCRA Subtitle D (1991) and the Clean Air Act Amendments (1996). Concurrently, many common perceptions regarding landfill biogeochemical and microbiological processes and estimated rates of gas production also date from 2 to 4 decades ago. Herein, we summarize the recent application of modern microbiological tools as well as recent metadata analysis using California, USEPA and international data to outline an evolving view of landfill biogeochemical/microbiological processes and rates. We focus on United States landfills because these are uniformly subject to stringent national and state requirements for design, operations, monitoring, and reporting. From a microbiological perspective, because anoxic conditions and methanogenesis are rapidly established after daily burial of waste and application of cover soil, the >1000 United States landfills with thicknesses up to >100 m form a large ubiquitous group of dispersed 'dark' ecosystems dominated by anaerobic microbial decomposition pathways for food, garden waste, and paper substrates. We review past findings of landfill ecosystem processes, and reflect on the potential impact that application of modern sequencing technologies (e.g., high throughput platforms) could have on this area of research. Moreover, due to the ever evolving composition of landfilled waste reflecting transient societal practices, we also consider unusual microbial processes known or suspected to occur in landfill settings, and posit areas of research that will be needed in coming decades. With growing concerns about greenhouse gas emissions and controls, the increase of chemicals of emerging concern in the waste stream, and the potential resource that waste streams represent, application of modernized molecular and microbiological methods to landfill ecosystem research is of paramount importance.

Differentiated Mechanisms of Biochar Mitigating Straw-Induced Greenhouse Gas Emissions in Two Contrasting Paddy Soils

Straw returns to the soil is an effective way to improve soil organic carbon and reduce air pollution by straw burning, but this may increase CH₄ and N₂O emissions risks in paddy soils. Biochar has been used as a soil amendment to improve soil fertility and mitigate CH₄ and N₂O emissions. However, little is known about their interactive effect on CH₄ and N₂O emissions and the underlying microbial mechanisms. In this study, a 2-year pot experiment was conducted on two paddy soil types (an acidic Utisol, TY, and an alkaline Inceptisol, BH) to evaluate the influence of straw and biochar applications on CH₄ and N₂O emissions, and on related microbial functional genes. Results showed that straw addition markedly increased the cumulative CH₄ emissions in both soils by 4.7- to 9.1-fold and 23.8- to 72.4-fold at low (S1) and high (S2) straw input rate, respectively, and significantly increased mcrA gene abundance. Biochar amendment under the high straw input (BS2) significantly decreased CH₄ emissions by more than 50% in both soils, and increased both mcrA gene and pmoA gene abundances, with greatly enhanced pmoA gene and a decreased mcrA/pmoA gene ratio. Moreover, methanotrophs community changed distinctly in response to straw and biochar amendment in the alkaline BH soil, but showed slight change in the acidic TY soil. Straw had little effect on N₂O emissions at low input rate (S1) but significantly increased N₂O emissions at the high input rate (S2). Biochar amendment showed inconsistent effect on N₂O emissions, with a decreasing trend in the BH soil but an increasing trend in the TY soil in which high ammonia existed. Correspondingly, increased nirS and nosZ gene abundances and obvious community changes in nosZ gene containing denitrifiers in response to biochar amendment were observed in the BH soil but not in the TY soil. Overall, our results suggested that biochar amendment could markedly mitigate the CH₄ and N₂O emissions risks under a straw return practice via regulating functional microbes and soil physicochemical properties, while the performance of this practice will vary depending on soil parent material characteristics.

Ecology of Contaminant Biotransformation in the Mycosphere: Role of Transport Processes

Fungi and bacteria often share common microhabitats. Their co-occurrence and coevolution give rise to manifold ecological interactions in the mycosphere, here defined as the microhabitats surrounding and affected by hyphae and mycelia. The extensive structure of mycelia provides ideal "logistic networks" for transport of bacteria and matter in structurally and chemically heterogeneous soil ecosystems. We describe the characteristics of the mycosphere as a unique and highly dynamic bacterial habitat and a hot spot for contaminant biotransformation. In particular, we emphasize the role of the mycosphere for (i) bacterial dispersal and colonization of subsurface interfaces and new habitats, (ii) matter transport processes and contaminant bioaccessibility, and (iii) the functional stability of microbial ecosystems when exposed to environmental fluctuations such as stress or disturbances. Adopting concepts from ecological theory, the chapter disentangles bacterial-fungal impacts on contaminant biotransformation in a systemic approach that interlinks empirical data from microbial ecosystems with simulation data from computational models. This approach provides generic information on key factors, processes, and ecological principles that drive microbial contaminant biotransformation in soil. We highlight that the transport processes create favorable habitat conditions for efficient bacterial contaminant degradation in the mycosphere. In-depth observation, understanding, and prediction of the role of mycosphere transport processes will support the use of bacterial-fungal interactions in nature-based solutions for contaminant biotransformation in natural and man-made ecosystems, respectively.

Resistance and Recovery of Methane-Oxidizing Communities Depends on Stress Regime and History; A Microcosm Study

Although soil microbes are responsible for important ecosystem functions, and soils are under increasing environmental pressure, little is known about their resistance and resilience to multiple stressors. Here, we test resistance and recovery of soil methane-oxidizing communities to two different, repeated, perturbations: soil drying, ammonium addition and their combination. In replicated soil microcosms we measured methane oxidation before and after perturbations, while monitoring microbial abundance and community composition using quantitative PCR assays for the bacterial 16S rRNA and pmoA gene, and sequencing of the bacterial 16S rRNA gene. Although microbial community composition changed after soil drying, methane oxidation rates recovered, even after four desiccation events. Moreover, microcosms subjected to soil drying recovered significantly better from ammonium addition compared to microcosms not subjected to soil drying. Our results show the flexibility of microbial communities, even if abundances of dominant populations drop, ecosystem functions can recover. In addition, a history of stress may induce changes in community composition and functioning, which may in turn affect its future tolerance to different stressors.

Spatiotemporal disturbance characteristics determine functional stability and collapse risk of simulated microbial ecosystems

Terrestrial microbial ecosystems are exposed to many types of disturbances varying in their spatial and temporal characteristics. The ability to cope with these disturbances is crucial for maintaining microbial ecosystem functions, especially if disturbances recur regularly. Thus, understanding microbial ecosystem dynamics under recurrent disturbances and identifying drivers of functional stability and thresholds for functional collapse is important. Using a spatially explicit ecological model of bacterial growth, dispersal, and substrate consumption, we simulated spatially heterogeneous recurrent disturbances and investigated the dynamic response of pollutant biodegradation – exemplarily for an important ecosystem function. We found that thresholds for functional collapse are controlled by the combination of disturbance frequency and spatial configuration (spatiotemporal disturbance regime). For rare disturbances, the occurrence of functional collapse is promoted by low spatial disturbance fragmentation. For frequent disturbances, functional collapse is almost inevitable. Moreover, the relevance of bacterial growth and dispersal for functional stability also depends on the spatiotemporal disturbance regime. Under disturbance regimes with moderate severity, microbial properties can strongly affect functional stability and shift the threshold for functional collapse. Similarly, networks facilitating bacterial dispersal can delay functional collapse. Consequently, measures to enhance or sustain bacterial growth/dispersal are promising strategies to prevent functional collapses under moderate disturbance regimes.

Environmental legacy contributes to the resilience of methane consumption in a laboratory microcosm system

The increase of extreme drought and precipitation events due to climate change will alter microbial processes. Perturbation experiments demonstrated that microbes are sensitive to environmental alterations. However, only little is known on the legacy effects in microbial systems. Here, we designed a laboratory microcosm experiment using aerobic methane-consuming communities as a model system to test basic principles of microbial resilience and the role of changes in biomass and the presence of non-methanotrophic microbes in this process. We focused on enrichments from soil, sediment, and water reflecting communities with different legacy with respect to exposure to drought. Recovery rates, a recently proposed early warning indicator of a critical transition, were utilized as a measure to detect resilience loss of methane consumption during a series of dry/wet cycle perturbations. We observed a slowed recovery of enrichments originating from water samples, which suggests that the community’s legacy with a perturbation is a contributing factor for the resilience of microbial functioning.

Functional Resistance to Recurrent Spatially Heterogeneous Disturbances Is Facilitated by Increased Activity of Surviving Bacteria in a Virtual Ecosystem

Bacterial degradation of organic compounds is an important ecosystem function with relevance to, e.g., the cycling of elements or the degradation of organic contaminants. It remains an open question, however, to which extent ecosystems are able to maintain such biodegradation function under recurrent disturbances (functional resistance) and how this is related to the bacterial biomass abundance. In this paper, we use a numerical simulation approach to systematically analyze the dynamic response of a microbial population to recurrent disturbances of different spatial distribution. The spatially explicit model considers microbial degradation, growth, dispersal, and spatial networks that facilitate bacterial dispersal mimicking effects of mycelial networks in nature. We find: (i) There is a certain capacity for high resistance of biodegradation performance to recurrent disturbances. (ii) If this resistance capacity is exceeded, spatial zones of different biodegradation performance develop, ranging from no or reduced to even increased performance. (iii) Bacterial biomass and biodegradation dynamics respond inversely to the spatial fragmentation of disturbances: overall biodegradation performance improves with increasing fragmentation, but bacterial biomass declines. (iv) Bacterial dispersal networks can enhance functional resistance against recurrent disturbances, mainly by reactivating zones in the core of disturbed areas, even though this leads to an overall reduction of bacterial biomass.

Bacterial communities in soil become sensitive to drought under intensive grazing

Increasing climatic and anthropogenic pressures on soil ecosystems are expected to create a global patchwork of disturbance scenarios. Some regions will be strongly impacted by climate change, others by agricultural intensification, and others by both. Soil microbial communities are integral components of terrestrial ecosystems, but their responses to multiple perturbations are poorly understood. Here, we exposed soils from sustainably- or intensively-managed grasslands in an agro-silvo-pastoral oak woodland to month-long intensified drought and flood simulation treatments in a controlled mesocosm setting. We monitored the response of the bacterial communities at the end of one month as well as during the following month of recovery. The communities in sustainably-managed plots under all precipitation regimes were richer and more diverse than those in intensively-managed plots, and contained a lower proportion of rapidly-growing taxa. Soils from both land managements exhibited changes in bacterial community composition in response to flooding, but only intensively-managed soils were affected by drought. The ecologies of bacteria favored by both drought and flood point to both opportunism and stress tolerance as key traits shaping the community following disturbance. Finally, the response of several taxa (i.e. Chloracidobacteria RB41, Janthinobacterium sp.) to precipitation depended on land management, suggesting that the community itself affected individual disturbance responses. Our findings provide an in-depth view of the complexity of soil bacterial community responses to climatic and anthropogenic pressures in time, and highlight the potential of these stressors to have multiplicative effects on the soil biota.

Positive diversity-functioning relationships in model communities of methanotrophic bacteria

Biodiversity enhances ecosystem functions such as biomass production and nutrient cycling. Although the majority of the terrestrial biodiversity is hidden in soils, very little is known about the importance of the diversity of microbial communities for soil functioning. Here, we tested effects of biodiversity on the functioning of methanotrophs, a specialized group of soil bacteria that plays a key role in mediating greenhouse gas emissions from soils. Using pure strains of methanotrophic bacteria, we assembled artificial communities of different diversity levels, with which we inoculated sterile soil microcosms. To assess the functioning of these communities, we measured methane oxidation by gas chromatography throughout the experiment and determined changes in community composition and community size at several time points by quantitative PCR and sequencing. We demonstrate that microbial diversity had a positive overyielding effect on methane oxidation, in particular at the beginning of the experiment. This higher assimilation of CH₄ at high diversity translated into increased growth and significantly larger communities towards the end of the study. The overyielding of mixtures with respect to CH₄ consumption and community size were positively correlated. The temporal CH₄ consumption profiles of strain monocultures differed, raising the possibility that temporal complementarity of component strains drove the observed community-level strain richness effects; however, the community niche metric we derived from the temporal activity profiles did not explain the observed strain richness effect. The strain richness effect also was unrelated to both the phylogenetic and functional trait diversity of mixed communities. Overall, our results suggest that positive biodiversity-ecosystem-function relationships show similar patterns across different scales and may be widespread in nature. Additionally, biodiversity is probably also important in natural methanotrophic communities for the ecosystem function methane oxidation. Therefore, maintaining soil conditions that support a high diversity of methanotrophs may help to reduce the emission of the greenhouse gas methane.

Legacy Effects on the Recovery of Soil Bacterial Communities from Extreme Temperature Perturbation

The type and frequency of disturbances experienced by soil microbiomes is expected to increase given predicted global climate change scenarios and intensified anthropogenic pressures on ecosystems. While the direct effect of multiple disturbances to soil microbes has been explored in terms of function, their effect on the recovery of microbial community composition remains unclear. Here, we used soil microcosm experiments and multiple model disturbances to explore their short-term effect on the recovery of soil microbiota after identical or novel stresses. Soil microcosms were exposed to a heat shock to create an initial effect. Upon initial community recovery (25 days after stress), they were subjected to a second stress, either a heat or a cold shock, and they were monitored for additional 25 days. To carefully verify the bacterial response to the disturbances, we monitored changes in community composition throughout the experiment using 16S rRNA gene transcript amplicon sequencing. The application of a heat shock to soils with or without the initial heat shock resulted in similar successional dynamics, but these dynamics were faster in soils with a prior heat shock. The application of a cold shock had negligible effects on previously undisturbed soils but, in combination with an initial heat shock, caused the largest shift in the community composition. Our findings show that compounded perturbation affects bacterial community recovery by altering community structure and thus, the community's response during succession. By altering dominance patterns, disturbance legacy affects the microbiome's ability to recover from further perturbation within the 25 days studied. Our results highlight the need to consider the soil's disturbance history in the development of soil management practices in order to maintain the system's resilience.

Microbes at Surface-Air Interfaces: The Metabolic Harnessing of Relative Humidity, Surface Hygroscopicity, and Oligotrophy for Resilience

The human environment is predominantly not aqueous, and microbes are ubiquitous at the surface-air interfaces with which we interact. Yet microbial studies at surface-air interfaces are largely survival-oriented, whilst microbial metabolism has overwhelmingly been investigated from the perspective of liquid saturation. This study explored microbial survival and metabolism under desiccation, particularly the influence of relative humidity (RH), surface hygroscopicity, and nutrient availability on the interchange between these two phenomena. The combination of a hygroscopic matrix (i.e., clay or 4,000 MW polyethylene glycol) and high RH resulted in persistent measurable microbial metabolism during desiccation. In contrast, no microbial metabolism was detected at (a) hygroscopic interfaces at low RH, and (b) less hygroscopic interfaces (i.e., sand and plastic/glass) at high or low RH. Cell survival was conversely inhibited at high RH and promoted at low RH, irrespective of surface hygroscopicity. Based on this demonstration of metabolic persistence and survival inhibition at high RH, it was proposed that biofilm metabolic rates might inversely influence whole-biofilm resilience, with ‘resilience’ defined in this study as a biofilm’s capacity to recover from desiccation. The concept of whole-biofilm resilience being promoted by oligotrophy was supported in desiccation-tolerant Arthrobacter spp. biofilms, but not in desiccation-sensitive Pseudomonas aeruginosa biofilms. The ability of microbes to interact with surfaces to harness water vapor during desiccation was demonstrated, and potentially to harness oligotrophy (the most ubiquitous natural condition facing microbes) for adaptation to desiccation.