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As extreme climate events become more frequent and intense, short-term temperature responses of ectothermic organisms can lead to decreased performance and survival. However, organisms may acclimate to these conditions through behavioural and physiological mechanisms as exposure time increases. We used a reciprocal temperature (16 °C and 24 °C) transplant experiment to determine how feeding rate and body size of an apex soil mite predator (Stratiolaelaps scimitus) (formerly Hypoaspis miles) consuming prey (Carpoglyphus lactis) (dried-fruit-mite) changed along a gradient of acclimation time (1, 3, and 7 days, with control). In the control treatments, mites reared at 24 °C fed more, but were smaller than mites reared at 16 °C. When transferred to new temperature conditions, predators that experienced cooling events had reduced feeding efficiencies driven by decreased feeding performance, despite an absence of metabolic costs, while under warming events, predators also had reduced feeding activity, but feeding increased with acclimation time. Yet predators lost more weight the longer they were exposed to warming, and continued to experience reduced feeding efficiencies (i.e., lack of weight gain after feeding); this result suggests increased metabolic costs at higher temperatures and provides a mechanism for community downsizing under warming. Overall, our results suggest that ectothermic predators can acclimate to warming events with increased exposure time, but both warming and cooling events decrease overall performance. [ABSTRACT FROM AUTHOR]

In the ecological literature, a ‘home-field advantage’ (HFA) describes the phenomenon where plant litters are broken down more quickly in their native versus a foreign environment due to a hypothesized specialised decomposer-litter relationship. Climate change is expected to spatially shift plant communities at an imbalanced rate compared to their decomposers, resulting in previously unexperienced above- and belowground pairings. Understanding decomposition dynamics has implications for global climate and carbon models, yet a clear predictive framework for the HFA has not been proposed. The ecological HFA concept is borrowed from the sports realm where extensive research has found a consistent, greater-than-random chance that teams in sports competitions win games played at their home venue because players are in better physical and psychological states. While research continues to show the sports HFA present in all types of sports independent of playing level or region, the ecological HFA has been shown inconsistently and cannot currently be generalised across scales and ecosystems. In this review, we map the ecological HFA onto a framework used to interpret the HFA in sports. First, we identify and outline the ‘game’ of decomposition, the ‘teams’ of decomposer organisms, how plants ‘coach’ this game, and also how ecological researchers are involved in their role as game ‘officials’. Second, we place parallels between the game location factors established in the sports analogy and their ecological counterparts to reveal a greater mechanistic understanding of the ecological HFA. Here we explore microbial adaptation to abiotic environments, the role of historical resource inputs, and how degree of ecosystem contrast and definitional ambiguity affect the HFA. In doing so, we discuss how microbial functional breadth, plant strategy and temporal effects play into the HFA. Using the sports HFA framework provides a novel and promising approach to understanding the ecological HFA that has been lacking, and helps identify potential factors that may not traditionally have been considered. Our framework incorporates multiple theories and views the HFA as a ‘team effort’ involving multiple components. [ABSTRACT FROM AUTHOR]

The notion that plants are tightly coupled to their belowground environment so that decomposition occurs faster in their place of origin is now a widely tested hypothesis known as the home-field advantage (HFA). Microbial adaptation to the most prevalent plant litter is the hypothesis proposed to explain decomposition results in a number of HFA studies but fails to corroborate results of many others, highlighting the need for a more comprehensive understanding of decomposition dynamics at local scales. Boreal peatlands are important ecosystems for carbon storage that are expected to be significantly affected by climate change, thus understanding decomposition dynamics in Boreal peatland systems is of global relevance. We performed a reciprocal transplant experiment using pure and mixed litters of two dominant peatland plant types ( Sphagnum moss and Carex sedge) present in differing densities at two sites differing in nutrient status in a Boreal peatland complex. Aboveground (temperature, relative humidity) and belowground (pH, moisture, available nitrogen) environmental characteristics were measured, and initial litter quality (C, N, S) was assessed with decomposition (mass loss) quantified after one year. We use linked HFA equations that help account for differences in litter quality and site conditions. While Carex lost greater overall mass than Sphagnum , both Carex and Sphagnum demonstrate a HFA, but only where they were the dominant plant of each site. This result held for both pure and mixed litters, suggesting microbial specificity to the most prevalent plant type, yet mixed litters moderated the strength of the HFA. While our results provide novel insights to plant-soil linkages and mixed litter interactions in Boreal peatlands, mechanisms underpinning microbial specificity to plant litter in these ecosystems requires further investigation. [ABSTRACT FROM AUTHOR]

Soil food webs are at the nexus of soil biodiversity, functioning, and stability. With a research history of over 35 years, soil food-web research remains a challenging and relatively specialised field. Initially receiving wide attention after the general model of William H. Hunt and colleagues in 1987, the field diversified over the last two decades across ecosystem and community ecology, empirical and theoretical approaches, network and energy flux analyses. Here we reflect on the history, status, and trends in soil food-web research and identify major perspectives and synthesis directions. After briefly reviewing modelling approaches, structure, and quantification of functioning, we distinguish modern trends in tools that can streamline food-web research, a need for proper empirical validation, collaborative approaches to push the field forward, and conclude with application perspectives. In the light of increasing data availability and public awareness about soil biodiversity, we call for synthesis across multiple dimensions of soil food-web research (e.g. different methodologies and disciplines, various spatiotemporal scales, multiple trophic levels and phyla of life), integrating the soil food-web approach to biodiversity and environmental studies, and making it more accessible to a wider community of scientists. • Soil food-web research has diversified over the last 30 years. • A synthesis across empirical studies and theoretical modelling is needed. • Major gap is scarce empirical data that can inform theoretical models. • Data collection can be facilitated by joint efforts and application of new tools. • Cross-disciplinary work is needed for applications of soil food-web modelling. [ABSTRACT FROM AUTHOR]

Hollows and hummocks of boreal peatlands differ in water table position, pH, plant community composition and biochemical properties that might affect the structure of their fungal communities. The community composition of fungi at three depths (0–5 cm, 15–20 cm, 30–35 cm) in hollows and hummocks of a nutrient-poor fen in northern Ontario, Canada were assessed by Illumina sequencing of 28S amplicons. Our metabarcoding results revealed statistically distinct fungal community composition between hollows and hummocks. Hollows contained a more diverse fungal community than hummocks. However, the middle horizon of hollows and the bottom horizon of hummocks were comparable in terms of fungal biodiversity. These layers were identified as the areas bearing the most diverse community composition of fungi, most likely driven by their similarly respective distance from the water table position. This optimum area is expected to be most affected following water table drawdown under future climate change conditions. [ABSTRACT FROM AUTHOR]

The increased prevalence of smaller-bodied species under warmer conditions (community downsizing) is hypothesized as an ecologically critical consequence of climate change, leading to changes in trophic transfer efficiency, and rates of nutrient and energy flux within ecosystems. This study used 100 intact peat-soil mescosms to measure changes in belowground biodiversity under three manipulated climate variables: elevated temperature, elevated CO 2 , and altered water table. Changes in species richness, abundance, community composition and body size spectra were used to determine whether climate change factors led to community downsizing, and elucidate any underlying mechanisms. Warming was the primary driver of compositional shifts in belowground fauna communities with the strongest effect among the smaller-bodied, non-sexually reproducing species. Increases in abundance driven by enhanced reproduction in small-bodied species rather than an increased extinction-rate among large-bodied predators was the basis of the observed downsizing. The overall consequences of warming-induced changes in belowground systems on ecosystem function are still unclear. However, as body size is intricately linked to metabolism, observed community downsizing suggests reductions in food web trophic transfer efficiency with consequences for nutrient and energy dynamics in belowground systems. [ABSTRACT FROM AUTHOR]

Current trait-based indices of soil fauna for assessing soil quality rely on extensive knowledge of life history traits for hyper-diverse groups. We look at the effects of clear-cut forest harvesting and subsequent wood ash application on the free-living nematode community using trait-based indices and body size spectra. We test the hypothesis that body size is a unifying trait and that the body size spectra can be used to demonstrate changes in soil quality while overcoming taxonomic impediments. Undisturbed boreal forest floor soils were compared with clear-cut sites amended with zero, one-half calcium equivalent wood ash, equivalent calcium reintroduction, and twice calcium reintroduction. Total abundance, trait-based metrics for the Maturity Index, and two metrics of body size spectra were calculated. Nematode abundance was not a good indicator of soil disturbance, while traditional trait-based approaches (the summed Maturity Index) demonstrated predicted changes in community structure. Analysis of two types of body size spectra elucidated how the community had changed under disturbance, and revealed that smaller bodied organisms were lost under ash amended treatments compared to both clear-cut and undisturbed forest. Using the body size spectra for nematodes is a simple addition to current trait-based approaches that can supplement soil assessments for disturbance and quality without requiring taxonomic expertise. [ABSTRACT FROM AUTHOR]

Global increases in temperature and atmospheric CO2, coupled with increasingly sporadic and intense precipitation regimes, may affect the biodiversity of boreal forest communities, potentially leading to shifts in functional process rates such as decomposition. However, the effects of these factors on microarthropod community composition have not been thoroughly studied in combination in controlled settings. We conducted a full factorial experiment exposing moss/soil mesocosms to three temperatures (11.5, 15.5, and 19.5 °C), two CO2 levels (430 ppm and 750 ppm), and three moisture levels (drought, intermediate, and saturated conditions) for 18 weeks. Following treatment, we quantified effects on species diversity of a representative group of mesofaunal microarthropods, the Collembola. We also quantified the effects of these factors on the distribution of collembolan body sizes as an indicator of functional changes in the community. We found that moisture regime was a dominant factor, with increased precipitation leading to decreased collembolan abundance and richness. The mechanisms of these detrimental effects are unclear but may be due to the saturation of air-filled soil pore space or competition with moisture-tolerant species. Severe precipitation regimes caused a general loss of abundance in species of all sizes, which may have long term effects on boreal forest soil food webs. [ABSTRACT FROM AUTHOR]

Molecular-based methods of community analysis are becoming a popular alternative to the traditional, highly specialized, and time-consuming taxonomic identifications especially for morphologically challenging groups like free-living soil nematodes. In particular, terminal restriction fragment length polymorphism (T-RFLP) analysis has become popular as a quick and efficient tool to provide researchers with broad-scale assessments of community structure. The majority of studies comparing T-RFLP with morphological-based assessments have used cultured or previously characterized communities. Here we compare morphological identification to T-RFLP analyses in a previously unexplored system for nematode diversity, the boreal forest of Ontario, Canada. Samples were collected from five silvicultural treatments over two sampling seasons with nematodes extracted using the Baermann funnel technique. We found significantly greater richness from T-RFLP analyses than morphological identifications at both sampling times, but in both cases silvicultural treatment had no effect. Despite differences in taxonomic richness, community compositional similarities were highly correlated between morphological and molecular methods for both sampling times. We suggest that both methods are reliable in studies of previously undescribed communities where the goal is community assessment under treatment. [ABSTRACT FROM AUTHOR]

Soil systems are highly biodiverse and responsible for important ecosystem processes such as decomposition, nutrient cycling, and carbon storage. Aspects of global change, including CO 2 enrichment, climate change, land use alteration, and shifts in aboveground biodiversity all have the potential to affect soil biodiversity, as well as the ecosystem-level processes that they regulate. While there is a growing body of scientific literature recognising and addressing community and ecosystem response to multiple, interacting elements of global change, soil biodiversity and soil systems are still relatively underrepresented in this literature. Yet, at the same time, soils play a major role in global carbon budgets, and therefore hold the key to understanding future climate scenarios. This special issue highlighted the current knowledge of how soil biodiversity responds to pertinent global change factors, and the ecosystem-level consequences of those changes. We received empirical and theoretical studies on land use change, nitrogen deposition, warming, elevated CO 2 atmospheric concentration as well as drought and flood. Based on the contributions included, we discuss responses of global change in different soil taxonomic groups, and identify next steps. [ABSTRACT FROM AUTHOR]

Abstract: Litter decomposition and changes in oribatid mite community composition were studied for 2 years in litterbags collected from arboreal organic matter accumulations (canopy suspended soils) and forest floors associated with western redcedar trees on Vancouver Island, British Columbia. We tested the hypotheses that lower rates of mass loss, higher nutrient levels, and different patterns of oribatid mite richness and abundance in decomposing western redcedar litter would be observed in litterbags associated with canopy suspended soils compared to forest floors. Decomposition, measured by mass loss of cedar litter in litterbags, was not significantly different in canopy and forest floor habitats, although reduced in the canopy. Abundance and richness of oribatid mites inhabiting litterbags were significantly greater on the forest floor compared to the canopy suspended soils. Canopy suspended soils had higher levels of total nitrogen, available phosphorus and potassium than the forest floor, but moisture content was significantly lower in the suspended soils. Higher nutrient levels in the canopy system are attributed to differences in coarse woody debris input (but not foliar litter), combined with reduced nutrient uptake by roots and lower mobilisation rates of nutrients by detritivorous and fungivorous microarthropods. Moisture limitation in the canopy system possibly contributed to lower mass loss in litterbags, and lower abundance and richness of oribatid mites in litterbags placed on canopy suspended soils. Patterns of oribatid mite community composition were related to mite communities associated with the underlying substrate (forest floor or canopy suspended soil) which act as source pools for individuals colonising litterbags. Successional and seasonal trends in oribatid mite communities were confounded by moisture limitation at 24 months, particularly within the canopy habitat. [Copyright &y& Elsevier]

Microbial and faunal decomposers regulate the flux of carbon and nitrogen belowground, thus controlling the storage/release of carbon and nitrogen in soil systems. Warming is anticipated to alter decomposer biomass, and accelerate organismal metabolism and soil carbon release. We parameterized six soil food webs using empirical data for 18 trophic nodes at two boreal peatland sites under three climate scenarios (control, +2 °C, +4 °C), and model carbon and nitrogen flux, loss and retention using an energetic ecostoichiometric food web model. Differences in microbial biomass between sites dictated flux under warming. The community biomass of the fungal-dominated site was more impacted by warming, but fluxes were more responsive to warming at the bacterial-dominated site. Decreased metabolic efficiency of the soil food web at both sites in response to warming led to greater per capita carbon losses, indicating the long-term carbon storage potential of both systems is diminished. • Six empirical soil food webs were created for two boreal peatland sites. • We modeled carbon flux under three climate scenarios. • Differences in microbial biomass between sites dictated flux under warming. • Fungal biomass was more impacted by warming but bacteria dictate flux response. • Decreased metabolic efficiency under warming diminishes carbon storage potential. [ABSTRACT FROM AUTHOR]

Peer-review is an integral part of the scientific process, but getting a sufficient number of busy scientists to provide constructive reviews on a manuscript can be a challenge. The majority of individuals that we polled have had experience in the last two years with having manuscripts rejected and then submitting them elsewhere and/or with receiving invitations to review the same manuscript for different journals. Many experienced these events multiple times in that period. Authors who have had manuscripts rejected from journals after review have the opportunity to improve their manuscripts in light of reviewer comments. However unless the next journal to receive the manuscript has the technical means to transfer reviews from the previous journal, most journals treat these submissions as if they had not undergone peer review. Providing authors the option to submit responses to previous reviewer comments with details about how the manuscript has been revised since rejection from the previous journal is a practical means to increase the efficiency of peer review, requiring fewer reviews and leading to more rapid publication. Pedobiologia – Journal of Soil Ecology invites authors to include previous reviewer reports and detailed responses with new submissions. [ABSTRACT FROM AUTHOR]

Soil food web models can calculate the fluxes of carbon and nitrogen between soil organisms and so estimate the impact of individual organisms on ecosystem processes. These modelling approaches go beyond standard techniques in ecology. So, an open-source tool supporting them along with an analysis of their strengths and weaknesses could help. We present the R package soilfoodwebs , which calculates carbon and nitrogen fluxes through food webs and contributes four new features that are documented in the literature but unavailable in open-source software: (1) diet and physiological rates that balance multiple chemical elements, (2) estimates of parameter and structural uncertainty, (3) estimates of direct and indirect effects of taxa on ecosystem processes, and (4) a conversion from equilibrium food web analyses to simulations that can estimate the response to change. soilfoodwebs balances carbon and nitrogen demand by adjusting each organism's diet and the efficiency with which they use carbon. We outline the theory behind the package and demonstrate its functions using soil food web models available in the literature. Our analysis shows that the calculation of fluxes and the contributions of individual taxa to mineralization or decomposition rates is the strength of the soilfoodwebs package and soil food web models. We also show that more detailed information on population regulation (i.e., density-dependence) is needed for using these models to predict trends over time. Outputs from soil food web models can be compared with ecosystem measurements (e.g., mineralization, decomposition) and guide empirical work towards functionally important and undocumented soil biodiversity. [ABSTRACT FROM AUTHOR]

Fungi play a pivotal role in the carbon sequestration potential of boreal peatlands through the process of decomposition. As such, climate-driven changes in the diversity and community composition of peatland fungal communities could have substantial impacts on carbon release from these ecosystems, especially in subsurface peat that represents an important global carbon stock. We used Illumina MiSeq sequencing of rDNA to examine fungal communities after 18 months in intact peatland mesocosms subjected to conditions associated with Canada's future climate, including: warming, elevated atmospheric CO 2 and lowered water table. Warming was the main driver of changes in fungal communities across three depths of the peat profile with both Ascomycota- and Basidiomycota-dominated groups becoming more homogenous under warming conditions. Specific changes in fungal functional groups, however, were temperature dependent with potential cellulose decomposers and mycorrhizal root-associated fungi from Basidiomycota dominant under warming of +4 °C, whereas there was a prevalence of potential lignocellulose decomposers and mycorrhizal root-associated fungi from Ascomycota under +8 °C warming. These climate change-induced shifts in the structure of fungal communities in favour of recalcitrant compound decomposers observed across a depth gradient, may reduce long-term carbon storage of boreal peatlands under future climate change scenarios. [ABSTRACT FROM AUTHOR]

Free-living soil nematodes span several trophic levels and play a key role in soil food webs. As such, the relative abundances and diversity of nematode feeding groups, along with nematode body size that is correlated with trophic transfer efficiency may provide useful information in understanding carbon and nitrogen cycling in soil systems. Yet, despite their role in soil carbon dynamics, there is a lack of knowledge regarding nematode trophic diversity in high carbon storage systems such as boreal peatlands. Here we assessed nematode communities using feeding groups (bacterivores, fungivores, herbivores, omnivores, and predators) based on mouthpart morphology, and their body sizes (length and mass) in two contrasting boreal peatlands in Northern Ontario, Canada that differ in vegetation (Sphagnum vs Carex), hydrology, nutrient availability, and microbial decomposition. We found that nematode trophic diversity was higher in the Sphagnum -dominated fen, and that the dominant nematode group corresponded to the dominant microbial group at each site. Predatory nematodes were significantly more abundant and larger in the Sphagnum -dominated fen, consistent with greater food web complexity, but the average body size of nematodes (all feeding groups included) was not significantly different between the fens. Taken together, these observed trends in nematode feeding groups and body sizes, along with higher microbial biomass in the Sphagnum -dominated fen supports the idea that the two sites may differ ecologically, and generally follow differences in microbial communities. Our study provides important baseline information for understanding peatland soil food web dynamics and their implications for carbon and nutrient dynamics. • Nematode feeding group and body size were explored at contrasting peatlands. • Predators were more abundant and larger in a Sphagnum -dominated fen. • Nematode functional diversity parallels overall soil food web trophic structure. • Nematode communities from contrasting peatlands imply different ecological function. [ABSTRACT FROM AUTHOR]

The variety and abundance of organism sizes in a community allows valuable conclusions to be drawn concerning trophic transfer efficiency, process rate dynamics, and ecological stability. Body size spectrum analyses have been applied to great effect in aquatic systems, but have only relatively recently gained interest for the description of soil communities. This approach should be added to existing sorting protocols and adopted as a standard tool of soil fauna analysis because of its ease of use, universal applicability regardless of taxonomy, and value as a predictor of both soil fauna function and response. This paper reviews the available methods for calculating soil fauna mass, constructing of body size spectra, and relating these spectra to existing fauna analysis frameworks such as the nematode maturity index. We also detail several of the functional conclusions that can be drawn from shifts in body size spectra and how this methodology can be further improved to supplement existing soil ecology methods. [ABSTRACT FROM AUTHOR]

• Both Mesostigmata adult and juvenile abundance increased under warming. • Mesostigmata assemblages shifted and average individual body mass increased. • Assemblages shifted due to the increased abundances of parthenogenetic species. • These results align with previous studies on Oribatida assemblages under warming. Increasing global mean surface temperatures from climate change will coincide with longer and more frequent short-term, extreme warming events. Because of this, habitats like boreal forests are predicted to have new temperature regimes. Boreal forest soils contain a diverse array of microarthropods and nematodes, which include the main soil predators, mesostigmatic mites (Acari: Parasitiformes: Mesostigmata). Although extensive research exists on how climate warming affects oribatid mite and collembolan communities, fewer studies have examined how warming effects Mesostigmata communities. We tested the effect of short-term (three months), intensive warming (+8 °C) on Mesostigmata communities from the boreal forest using experimental mesocosms containing forest-floor material. We collected moss mats and underlying forest floor organic material from a boreal forest and incubated them within individual mesocosms at 12 °C and 20 °C for three months, where 12 °C represented the long-term average growing season temperature and 20 °C corresponds to the potential extreme surface temperature from climate warming for the region. We enumerated all extracted microarthropods and nematodes, and identified all Mesostigmata adults to the species-level. In total, we counted 24,080 nematode individuals, and 19,582 total microarthropod individuals, of which 3349 individuals (1899 adults and 1450 juveniles) were mesostigmatic mites, consisting of 14 species. Mesostigmatic juvenile and adult abundances, along with adult community-level body mass were higher under warming, which lead to a shift in community composition. Changes to Mesostigmata communities were driven by the greater abundances of parthenogenetic species, primarily Veigaia mitis (Berlese), under warming—a response that has been shown in oribatid mite communities, but not mesostigmatic communities, before. Overall, we found that warming shifted mesostigmatic mite communities in the boreal forest, which has wide ranging implications for the soil food web. [ABSTRACT FROM AUTHOR]

Boreal peatlands play an important role in terrestrial carbon storage. Soil fauna and their trophic interactions play a key role in regulating microbial communities and the flux of carbon (C) and nitrogen (N) belowground, thus controlling the storage/release of C and N in soil systems. At northern latitudes, soil temperature and moisture conditions under climate change are predicted to become more extreme and more variable, and these factors will play an important role in regulating decomposition and ecosystem functioning, like C and N dynamics, in boreal peatlands. The objective of this research is to quantify and model the effects of experimentally imposed temperature and moisture conditions that simulate potential future climate extremes on peatland soil fauna food webs and soil C and N fluxes. Results suggest that increases in temperature and soil saturation will alter total faunal biomasses with warming increasing and soil saturation decreasing biomasses. Shifts in fauna biomass drove changes in C flux, C mineralization, and N mineralization. However, under warming, increased population turnover rate alongside decreased feeding efficiencies increased the proportion of total C flux that is lost as respiration (i.e., C mineralization). Future research is needed to better resolve the opposing changes in potential future boreal peatland C and N dynamics threatened by potential future warming and climate-mediated changes in peatland hydrology. [ABSTRACT FROM AUTHOR]

Cannibalism imperfectly recycles resources back to the same species and so decreases trophic transfer efficiency in food webs. As such, viable populations have some limit on how much of their diet can come from cannibalism. We applied a Lotka-Volterra model to derive a theoretical maximum for the proportion of the diet coming from cannibalism. This proportion is set by the food conversion efficiency for both cannibalism and alternative prey. We apply the result to sixteen published soil food web models and find that cannibalism cannot exceed 20% of the diet of most organisms, which includes eating conspecifics that were already dead. However, predators can show a strong (>80%) preference for cannibalism because encountering conspecifics is rare. Cannibalism increased carbon and nitrogen mineralization in fifteen soil food webs and had non-monotonic effects in the remaining one. Our estimates map a physiological parameter (conversion efficiency) to an ecological one (cannibalism) to help to improve model fit and to help soil ecologists identify taxa where cannibalism may be most important. - Physiological inefficiency lets us calculate a theoretical limit for cannibalism. - Maximum cannibalism rate is about 20% of the diet for most soil organisms. - Cannibalism decreases the efficiency of carbon and nitrogen flow in soil food webs. - Ignoring cannibalism biases carbon loss estimates by up to 10% and nitrogen by up to 30%. [ABSTRACT FROM AUTHOR]

• Oribatid mite community composition is driven to an extent by interactions between temperature and moisture. • Communities in the Sphagnum- and Carex -dominated fens showed contrasting responses to warming. • Warming-induced soil moisture reduction facilitated the establishment of terrestrial species and impacted semi-aquatic species. Climate warming is expected to disproportionately affect high latitude and alpine systems such as boreal peatlands. Previous studies observing changes in both plant and microbial communities suggest boreal peatlands may shift from carbon sinks to sources under warming. But few studies have investigated oribatid mites (Acari: Oribatida) under climate change scenarios in peatland systems, despite oribatid mites being well represented in terms of diversity in boreal peatlands. We performed a large-scale experimental field manipulation of warming in two contrasting peatland sites in Northern Ontario, Canada, and sampled oribatid mites over four years following three years of passive warming and one full growing season of active warming. We found that warming had contrasting effects on the oribatid mite community at both peatland sites, and depended on the peatland type. Specifically, we observed an increase in species richness at the drier, Sphagnum -dominated site and a reduction in species richness at the wetter, Carex -dominated site. That said, we suggest that these outcomes arise from the same mechanism, namely warming-induced reductions in soil moisture that impacted semi-aquatic species and facilitated the establishment of new species, likely from surrounding forests. We also observed increases in small-bodied species suggesting direct metabolic effects from warming. As such, we show that peatland oribatid mite community composition is driven to an extent by interactions between temperature and moisture but dependant on peatland type. As oribatid mite communities are responsive to multiple environmental changes, and play important mid-trophic level roles in soil food webs, changes in oribatid mite community composition may have consequences for carbon flux in peatland systems. [ABSTRACT FROM AUTHOR]

• Major soil microarthropod taxa responded differently to simulated climate change. • Oribatida and Collembola diversity increased under warming in a high rainfall year. • Mesostigmata diversity showed no response to either warming or elevated CO 2. • Annual rainfall may dictate soil faunal responses to simulated climate change. Soils systems provide essential ecosystem functions and services performed by a hyperdiverse array of fauna, but how soil communities respond to climate change remains an understudied topic. Although previous long-term studies have found variable effects of climate change manipulations on soil communities, precipitation often yields strong responses from fauna. In this study we used a field-based experiment to test how soil communities respond to active warming (+4 °C) and elevated atmospheric CO 2 concentrations (800 ppm) in the boreal forest over two consecutive years in a full factorial experimental design. We sampled and identified soil fauna across multiple taxonomic groups to determine how species abundance, richness, diversity, evenness, and community composition were affected by these simulated global climate change factors. Fauna were minimally affected by experimental treatments in the first year of sampling. However, in the second year of treatment, richness and diversity increased and soil community composition shifted as oribatid mites responded to both warming and elevated CO 2 and springtails responded to warming treatments. We propose that the enhanced response of soil communities in the second year of experimental treatment was due to greater than normal precipitation, suggesting that annual variability in weather conditions can influence soil fauna response to climate change. [ABSTRACT FROM AUTHOR]

Soils host the vast majority of life on Earth including microorganisms and animals, and supporting all terrestrial vegetation. While soil organisms are pivotal for ecosystem functioning, the assemblages of different biota from a taxonomic and functional perspective, as well as how these different organisms interact, remains poorly known. We provide a brief overview of the taxonomic and functional diversity of all major groups of soil biota across different scales and organism sizes, ranging from viruses to prokaryotes and eukaryotes. This reveals knowledge gaps in relation to all soil biodiversity groups, which are especially evident for viruses, protists, micro- and meso-fauna. We review currently-available methods to study the taxonomic and functional diversity of soil organisms by grouping all commonly-used methods into morphological, biochemical and molecular approaches. We list potentials and limitations of the methods to reveal that there is, as yet, no single method to fully characterize the biodiversity even of a single group of soil biota. Yet, we stress that we now have the methods available to enable scientists to disentangle the taxonomic and functional diversity of virtually all soil organisms. We provide a user-friendly guide to help researchers address a wider variety of soil biodiversity in their studies by discussing and critically analysing the various potentials and limitations of diverse methods to study distinct groups of soil life. We highlight that integrative methodological approaches, ideally in collaborative interactions, are key to advancing our understanding of soil biodiversity, such as the combination of morphological and molecular approaches to overcome method-specific limitations. Together, integrative efforts can provide information on the abundance, biomass, diversity and function of several groups of soil biota simultaneously. This newly-obtained integrative information on soil biodiversity will help to define the importance of soil biodiversity in ecosystem processes, functions, and services, and serve to refine food-web and earth system models. • Soil biodiversity is increasingly studied, yet knowledge remains limited. • New methods allow filling key missing knowledge gaps. • We provide an overview and guide to the main methods to study soil biodiversity. • Integrative method approaches are needed to increase our system-level understanding. • Collaborative efforts will uncover soil biodiversity and its functional importance. [ABSTRACT FROM AUTHOR]