• A further modification of Dioni’s mounting media to allow staining,clearing and mounting of Acari

      Chick, Andrew I. R.; University of Derby (2018-09-10)
      Modified Dioni’s media has previously been presented as an alternative to tradition Gum Chloral mounting media for microscopical specimens. This paper aims to explore a further modification of Dioni’s mounting media with the objective to provide a simple solution to clear, stain and mount Acari specimens in regions where obtaining Chloral Hydrate based media is problematic.
    • Bacterial and fungal communities in a degraded ombrotrophic peatland undergoing natural and managed re-vegetation

      Elliott, David R.; Caporn, Simon; Nwaishi, Felix; Nilsson, R. Henrik; Sen, Robin; Manchester Metropolitan University (Public Library of Science, 2015-05)
      The UK hosts 15–19% of global upland ombrotrophic (rain fed) peatlands that are estimated to store 3.2 billion tonnes of carbon and represent a critical upland habitat with regard to biodiversity and ecosystem services provision. Net production is dependent on an imbalance between growth of peat-forming Sphagnum mosses and microbial decomposition by microorganisms that are limited by cold, acidic, and anaerobic conditions. In the Southern Pennines, land-use change, drainage, and over 200 years of anthropogenic N and heavy metal deposition have contributed to severe peatland degradation manifested as a loss of vegetation leaving bare peat susceptible to erosion and deep gullying. A restoration programme designed to regain peat hydrology, stability and functionality has involved re-vegetation through nurse grass, dwarf shrub and Sphagnum re-introduction. Our aim was to characterise bacterial and fungal communities, via high-throughput rRNA gene sequencing, in the surface acrotelm/mesotelm of degraded bare peat, long-term stable vegetated peat, and natural and managed restorations. Compared to long-term vegetated areas the bare peat microbiome had significantly higher levels of oligotrophic marker phyla (Acidobacteria, Verrucomicrobia, TM6) and lower Bacteroidetes and Actinobacteria, together with much higher ligninolytic Basidiomycota. Fewer distinct microbial sequences and significantly fewer cultivable microbes were detected in bare peat compared to other areas. Microbial community structure was linked to restoration activity and correlated with soil edaphic variables (e.g. moisture and heavy metals). Although rapid community changes were evident following restoration activity, restored bare peat did not approach a similar microbial community structure to non-eroded areas even after 25 years, which may be related to the stabilisation of historic deposited heavy metals pollution in long-term stable areas. These primary findings are discussed in relation to bare peat oligotrophy, re-vegetation recalcitrance, rhizosphere-microbe-soil interactions, C, N and P cycling, trajectory of restoration, and ecosystem service implications for peatland restoration.
    • Niche partitioning of bacterial communities in biological crusts and soils under grasses, shrubs and trees in the Kalahari

      Elliott, David R.; Thomas, Andrew David; Hoon, Steve R.; Sen, Robin; Manchester Metropolitan University (Springer, 2014-06)
      The Kalahari of southern Africa is characterised by sparse vegetation interspersed with microbe-dominated biological soil crusts (BSC) which deliver a range of ecosystem services including soil stabilisation and carbon fixation. We characterised the bacterial communities of BSCs (0–1 cm depth) and the subsurface soil (1–2 cm depth) in an area typical of lightly grazed Kalahari rangelands, composed of grasses, shrubs, and trees. Our data add substantially to the limited amount of existing knowledge concerning BSC microbial community structure, by providing the first bacterial community analyses of both BSCs and subsurface soils of the Kalahari region based on a high throughput 16S ribosomal RNA gene sequencing approach. BSC bacterial communities were distinct with respect to vegetation type and soil depth, and varied in relation to soil carbon, nitrogen, and surface temperature. Cyanobacteria were predominant in the grass interspaces at the soil surface (0–1 cm) but rare in subsurface soils (1–2 cm depth) and under the shrubs and trees. Bacteroidetes were significantly more abundant in surface soils of all areas even in the absence of a consolidated crust, whilst subsurface soils yielded more sequences affiliated to Acidobacteria, Actinobacteria, Chloroflexi, and Firmicutes. The common detection of vertical stratification, even in disturbed sites, suggests a strong potential for BSC recovery after physical disruption, however severe depletion of Cyanobacteria near trees and shrubs may limit the potential for natural BSC regeneration in heavily shrub-encroached areas.
    • The influence of trees, shrubs, and grasses on microclimate, soil carbon, nitrogen, and CO2 efflux: Potential implications of shrub encroachment for Kalahari rangelands.

      Thomas, Andrew David; Elliott, David R.; Dougill, Andrew John; Stringer, Lindsay Carman; Hoon, Stephen Robert; Sen, Robin; Aberystwyth University; University of Derby; University of Leeds; Manchester Metropolitan University; Department of Geography and Earth Sciences; Aberystwyth University; Aberystwyth SY23 3DB UK; Environmental Sustainability Research Centre; University of Derby; Derby DE22 1GB UK; School of Earth and Environment; University of Leeds; Leeds LS2 9JT UK; School of Earth and Environment; University of Leeds; Leeds LS2 9JT UK; School of Science and the Environment; Manchester Metropolitan University; Manchester M1 5GD UK; School of Science and the Environment; Manchester Metropolitan University; Manchester M1 5GD UK (Wiley, 2018-03-30)
      Shrub encroachment is a well‐documented phenomenon affecting many of the world's drylands. The alteration of vegetation structure and species composition can lead to changes in local microclimate and soil properties which in turn affect carbon cycling. The objectives of this paper were to quantify differences in air temperatures, soil carbon, nitrogen, and CO2 efflux under trees (Vachellia erioloba), shrubs (Grewia flava), and annual and perennial grasses (Schmidtia kalahariensis and Eragrostis lehmanniana) collected over three seasons at a site in Kgalagadi District, Botswana, in order to determine the vegetation‐soil feedback mechanism affecting the carbon cycle. Air temperatures were logged continuously, and soil CO2 efflux was determined throughout the day and evening using closed respiration chambers and an infrared gas analyser. There were significant differences in soil carbon, total nitrogen, CO2 efflux, light, and temperatures beneath the canopies of trees, shrubs, and grasses. Daytime air temperatures beneath shrubs and trees were cooler compared with grass sites, particularly in summer months. Night‐time air temperatures under shrubs and trees were, however, warmer than at the grass sites. There was also significantly more soil carbon, nitrogen, and CO2 efflux under shrubs and trees compared with grasses. Although the differences observed in soils and microclimate may reinforce the competitive dominance of shrubs and present challenges to strategies designed to manage encroachment, they should not be viewed as entirely negative. Our findings highlight some of the dichotomies and challenges to be addressed before interventions aiming to bring about more sustainable land management can be implemented.
    • Post-feeding activity of Lucilia sericata (Diptera: Calliphoridae) on common domestic indoor surfaces and its effect on development.

      Robinson, Louise; Bryson, David; Bulling, Mark T.; Sparks, N.; Wellard, K. S.; University of Derby (Elsevier, 2018-03-13)
      Developmental data of forensically important blowflies used by entomologists to estimate minimum post mortem interval (mPMI) are established under controlled laboratory conditions for various temperature ranges throughout the stages of egg, 1st-3rd instar, puparia, and adult fly emergence. However, environmental conditions may influence the patterns of development and behaviour of blowflies, potentially impacting on these established development rates. Previous studies investigating indoor colonisation have focused on the delay to oviposition, with behaviour during the post-feeding phase in this setting often overlooked. The environment in which third instar larvae disperse when searching for a pupariation site may vary drastically at both outdoor and indoor scenarios, influencing the activity and distance travelled during this phase and possibly affecting developmental rates. This study investigated the effect of eight common domestic indoor surfaces on dispersal time, distance travelled, and behaviour of post-feeding Lucilia sericata as well as any resulting variation in development. It was found that pupariation and puparia length within a pupariation medium of sawdust (often used in laboratory settings) produced comparable results with that of carpeted environments (those deemed to be 'enclosed'). Non-carpeted environments (those which were 'exposed') produced a delay to pupariation likely due to increased activity and energy expenditure in searching for pupariation sites which enabled burial. In addition, the observed speed of travel during dispersal was seen via time lapse photography to be greater within 'exposed' conditions. Larvae which dispersed upon burnt laminate flooring were observed to travel faster than in all other conditions and showed the only significant variation (P=0.04) in the day of emergence in comparison to the control condition of sawdust. This study has demonstrated that wandering phase activity is affected by the environmental surface which has potential implications for estimating both the distance travelled by dispersing larvae in indoor conditions and with further research, may be a consideration in mPMI calculations.
    • Pseudoscorpions, an understudied and ideal microscopic study organism.

      Chick, Andrew I. R.; Andrews, Liam; University of Derby (Quekett Microscopical Club, 2017)
    • Apis mellifera (Linnaeus, 1761) (Hymenoptera: Apidae) on carrion, a note of the behaviour and a review of the literature.

      Chick, Andrew I. R.; Dye, Alex; University of Derby; Rothamsted Research (Andrew Smith Print Ltd., 2017-11-25)
      The Honeybee Apis mellifera (Linnaeus, 1761) traditionally feeds on the nectar of flowers (Núñez, 1977). A number of workers of A. mellifera were observed on whole pig carrion in woodland in Riseholme Lincoln (Grid reference SK978754) on 10 of October 2017. This paper aims to look at this odd behaviour in context of the literature.
    • Creating three dimensional, orientable, temporary invertebrate slides for photomicrography.

      Chick, Andrew I. R.; University of Derby (The Amateur Entomologists' Society, 2017-09)
    • Insect microscopy.

      Chick, Andrew I. R.; University of Derby (Crowood Press, 2016-08-26)
    • Some records of Aphodiini (Scarabaeidae) on carrion.

      Chick, Andrew I. R.; University of Derby (NERC Centre for Ecology & Hydrology, 2016)
    • Technical note: A specimen measuring device for the stereo microscope.

      Chick, Andrew I. R.; University of Derby (Quekett Microscopical Club, 2016-12)
    • Quantifying bioalbedo: a new physically based model and discussion of empirical methods for characterising biological influence on ice and snow albedo.

      Cook, Joseph M.; Hodson, Andrew J.; Flanner, Mark; Gardner, Alex; Tedstone, Andrew; Williamson, Christopher; Irvine-Fynn, Tristram D. L.; Nilsson, Johan; Bryant, Robert; Tranter, Martyn; University of Sheffield; University of Derby; University Centre in Svalbard; California Institute of Technology; University of Michigan; University of Bristol; Aberystwyth University (Copernicus Publications, 2017-11-17)
      The darkening effects of biological impurities on ice and snow have been recognised as a control on the surface energy balance of terrestrial snow, sea ice, glaciers and ice sheets. With a heightened interest in understanding the impacts of a changing climate on snow and ice processes, quantifying the impact of biological impurities on ice and snow albedo (bioalbedo) and its evolution through time is a rapidly growing field of research. However, rigorous quantification of bioalbedo has remained elusive because of difficulties in isolating the biological contribution to ice albedo from that of inorganic impurities and the variable optical properties of the ice itself. For this reason, isolation of the biological signature in reflectance data obtained from aerial/orbital platforms has not been achieved, even when ground-based biological measurements have been available. This paper provides the cell-specific optical properties that are required to model the spectral signatures and broadband darkening of ice. Applying radiative transfer theory, these properties provide the physical basis needed to link biological and glaciological ground measurements with remotely sensed reflectance data. Using these new capabilities we confirm that biological impurities can influence ice albedo, then we identify 10 challenges to the measurement of bioalbedo in the field with the aim of improving future experimental designs to better quantify bioalbedo feedbacks. These challenges are (1) ambiguity in terminology, (2) characterising snow or ice optical properties, (3) characterising solar irradiance, (4) determining optical properties of cells, (5) measuring biomass, (6) characterising vertical distribution of cells, (7) characterising abiotic impurities, (8) surface anisotropy, (9) measuring indirect albedo feedbacks, and (10) measurement and instrument configurations. This paper aims to provide a broad audience of glaciologists and biologists with an overview of radiative transfer and albedo that could support future experimental design.
    • Arthropod-microbe interactions on vertebrate remains: Potential applications in the forensic sciences.

      Tomberlin, Jeffery K.; Benbow, M. Eric; Barnes, Kate M.; Jordan, Heather R.; Texas A&M University; Michigan State University; University of Derby; Mississippi State University (John Wiley and Sons, 2017-04-08)
      Understanding the process of insect colonization of human remains is a core area of research by forensic entomologists, with several recent studies suggesting that microbial communities influence the process and timing of colonization. Such information is crucial for determining when colonization occurred as related to the postmortem interval (PMI). This chapter reviews the basic field of forensic entomology; the phases of insect behavior associated with their detection, location, and utilization of the remains as postulated by Matuszewski (Matuszewski, S. (2011) Estimating the pre-appearance interval from temperature in Necrodes littoralis L. (Coleoptera: Silphidae). Forensic Science International, 212, 180–188) and Tomberlin et al. (Tomberlin, J. K., R. Mohr, M. E. Benbow, et al. 2011. A roadmap for bridging basic and applied research in forensic entomology. Annual Review of Entomology, 56, 401–421.); and how microbes play a key role mediating this process. The chapter concludes with a discussion of potential future directions related to microbe–insect interactions in association with vertebrate remains decomposition, and this is potentially important to forensics.
    • Origin and evolution of silicic magmas at ocean islands: Perspectives from a zoned fall deposit on Ascension Island, South Atlantic.

      Chamberlain, Katy J.; Barclay, Jenni; Preece, Katie; Brown, Richard J.; Davidson, Jon P.; University of Durham; University of East Anglia (2016-11-15)
      Ascension Island, in the south Atlantic is a composite ocean island volcano with a wide variety of eruptive styles and magmatic compositions evident in its ~ 1 million year subaerial history. In this paper, new observations of a unique zoned fall deposit on the island are presented; the deposit gradationally changes from trachytic pumice at the base, through to trachy-basaltic andesite scoria at the top of the deposit. The key features of the eruptive deposits are described and are coupled with whole rock XRF data, major and trace element analyses of phenocrysts, groundmass glass and melt inclusions from samples of the compositionally-zoned fall deposit to analyse the processes leading up to and driving the explosive eruption. Closed system crystal fractionation is the dominant control on compositional zonation, with the fractionating assemblage dominated by plagioclase feldspar and olivine. This fractionation from the trachy-basaltic andesite magma occurred at pressures of ~ 250 MPa. There is no evidence for multiple stages of evolution involving changing magmatic conditions or the addition of new magmatic pulses preserved within the crystal cargo. Volatile concentrations range from 0.5 to 4.0 wt.% H2O and progressively increase in the more-evolved units, suggesting crystal fractionation concentrated volatiles into the melt phase, eventually causing internal overpressure of the system and eruption of the single compositionally-zoned magma body. Melt inclusion data combined with Fe–Ti oxide modelling suggests that the oxygen fugacity of Ascension Island magmas is not affected by degree of evolution, which concentrates H2O into the liquid phase, and thus the two systems are decoupled on Ascension, similar to that observed in Iceland. This detailed study of the zoned fall deposit on Ascension Island highlights the relatively closed-system evolution of felsic magmas at Ascension Island, in contrast to many other ocean islands, such as Tenerife and Iceland.
    • Micro-analytical perspectives on the Bishop Tuff and its magma chamber.

      Chamberlain, Katy J.; Wilson, Colin J. N.; Wallace, Paul J.; Millet, Marli Bryant; Victoria University of Wellington; Durham University; University of Oregon (Oxford Academic, 2015-04-23)
      New in situ major and trace element analytical data are presented for crystals (sanidine, plagioclase, biotite, orthopyroxene, clinopyroxene) and matrix glasses from juvenile materials representing the full Bishop Tuff sequence from the earliest fall unit (F1) to the latest ignimbrite package (Ig2Nc). These data are combined with published information to investigate the nature and zonation of the pre-eruptive Bishop magma chamber. Our data confirm that this magma chamber was a single unitary body that was thermally and compositionally zoned. The zonation was largely established prior to the growth of crystals, and also prior to mixing in the lower parts of the chamber induced by late-stage intrusion of a magma of contrasting composition and slightly higher temperature (the ‘bright-rim’ magma). Sparse mixed swirly and dacitic pumices show enrichments in Ba, Sr and Ti that identify these pumices as possible representatives of the ‘bright-rim’ magma. A model (revised from previously published work) for the pre-eruptive magma chamber comprises three main parts: (1) an upper, volumetrically dominant (∼2/3), relatively unzoned region that was the source of the earlier, eastern-erupted ignimbrite units and their coeval fall units; (2) a volumetrically minor transition zone that shows evidence for minor degrees of mixing and was the dominant source for the latest, eastern-erupted part of Ig1Eb (Sherwin subunit) and the earlier part of the northern-erupted ignimbrite (Ig 2Na); (3) a lower, volumetrically subordinate (∼1/3) region that was affected by mixing with the ‘bright-rim’ invasive magma in the lead-up to the eruption, and fed later northern-erupted units. Ingress of the ‘bright-rim’ magma introduced orthopyroxene and bright-rimmed zircon crystals, and induced partial resorption then overgrowth of rims enriched in Ti, Sr and Ba on sanidine and quartz, and development of zoning in clinopyroxene. Based on pumice proportions and associated crystal and glass chemistries through the eruptive sequence, we infer that the roof and floor of the magma chamber were stepped down to the north, such that the transition zone magma formed the floor of the southern part of the melt-dominant chamber and the roof of the northern part. Our data reinforce the previous concept of a single compositionally and thermally zoned Bishop magma chamber and additionally support a temporally constrained role for pre-eruptive magma mixing and the introduction of melts and minerals with contrasting compositions to the resident Bishop magma.
    • Timescales of mixing and mobilisation in the Bishop Tuff magma body: perspectives from diffusion chronometry.

      Chamberlain, Katy J.; Morgan, Daniel J.; Wilson, Colin J. N.; Victoria University of Wellington; University of Leeds (Springer, 2014-07-01)
      We present two-feldspar thermometry and diffusion chronometry from sanidine, orthopyroxene and quartz from multiple samples of the Bishop Tuff, California, to constrain the temperature stratification within the pre-eruptive magma body and the timescales of magma mixing prior to its evacuation. Two-feldspar thermometry yields estimates that agree well with previous Fe–Ti oxide thermometry and gives a ~80 °C temperature difference between the earlier- and later-erupted regions of the magma chamber. Using the thermometry results, we model diffusion of Ti in quartz, and Ba and Sr in sanidine as well as Fe–Mg interdiffusion in orthopyroxene to yield timescales for the formation of overgrowth rims on these crystal phases. Diffusion profiles of Ti in quartz and Fe–Mg in orthopyroxene both yield timescales of <150 years for the formation of overgrowth rims. In contrast, both Ba and Sr diffusion in sanidine yield nominal timescales 1–2 orders of magnitude longer than these two methods. The main cause for this discrepancy is inferred to be an incorrect assumption for the initial profile shape for Ba and Sr diffusion modelling (i.e. growth zoning exists). Utilising the divergent diffusion behaviour of Ba and Sr, we place constraints on the initial width of the interface and can refine our initial conditions considerably, bringing Ba and Sr data into alignment, and yielding timescales closer to 500 years, the majority of which are then within uncertainty of timescales modelled from Ti diffusion in quartz. Care must be thus taken when using Ba in sanidine geospeedometry in evolved magmatic systems where no other phases or elements are available for comparative diffusion profiling. Our diffusion modelling reveals piecemeal rejuvenation of the lower parts of the Bishop Tuff magma chamber at least 500 years prior to eruption. Timescales from our mineral profiling imply either that diffusion coefficients currently used are uncertain by 1–2 orders of magnitude, or that the minerals concerned did not experience a common history, despite being extracted from the same single pumice clasts. Introduction of the magma initiating crystallisation of the contrasting rims on sanidine, quartz, orthopyroxene and zircon was prolonged, and may be a marker of other processes that initiated the Bishop Tuff eruption rather than the trigger itself.
    • New perspectives on the Bishop Tuff from zircon textures, ages and trace elements.

      Chamberlain, Katy J.; Wilson, Colin J. N.; Wooden, Joseph L.; Charlier, Bruce L. A.; Ireland, Trevor R.; Victoria University of Wellington; Stanford University; The Open University; The Australian National University (Oxford Academic, 2013-12-19)
      We present zircon textural, trace element and U–Pb age data obtained by secondary ion mass spectrometry (SIMS) (SHRIMP-RG: sensitive high-resolution ion microprobe, reverse geometry) from 15 stratigraphically controlled Bishop Tuff samples and two Glass Mountain (GM) lava samples (domes OD and YA). Bishop zircon textures divide into four suites: (a) dominant sector-zoned grains, with (b) subordinate grains showing bright rims [lower U, Th, rare earth elements (REE)] in CL imaging, (c) sparse GM-type grains (texturally similar to zircons from GM dome YA) and (d) sparse Mesozoic xenocrysts from Sierran granitoid country rocks. All Bishop zircons from suites (a)–(c) combined have a weighted mean age of 777·9 ± 2·2 ka (95% confidence) and a tail back to ∼845 ka. Our eruption age estimate using the weighted mean of 166 rim ages of 766·6 ± 3·1 ka (95% confidence) is identical within uncertainty to published estimates from isotope-dilution thermal ionization mass spectrometry (ID-TIMS) (767·1 ± 0·9 ka, 2σ) and 40Ar/39Ar (767·4 ± 2·2 ka, 2σ) techniques, the latter using the 28·172 Ma age for the Fish Canyon sanidine standard. We estimate also an eruption age for GM dome YA of 862 ± 23 ka (95% confidence), significantly older than the currently accepted 790 ± 20 ka K–Ar age. The oldest zircon cores from late-erupted Bishop material (including those with GM-type textures) have a weighted mean age of 838·5 ± 8·8 ka (95% confidence), implying that the Bishop Tuff system was active for only ∼80 kyr, and had effectively no temporal overlap with the GM system. Trace element variations in Bishop zircons are influenced strongly for many elements by sector zoning, producing up to 3× concentration differences between sides and tips within the same growth zone. Contrasting trends in molar (Sc + Y + REE3+)/P ratios between sides and tips indicate contrasting mechanisms of substitution in different sectors of the same crystal. Concentrations of Ti in tips are double those in the sides of crystals, hindering applicability of the Ti-in-zircon thermometer, in addition to variations inherent to the 0·15–0·67 range in values proposed for aTiO2. The bright-rim portions of grains are inferred to have crystallized from the same magma as that which generated the bright rims seen under cathodoluminescence or back-scattered electron imaging on quartz and feldspar, respectively. This less evolved, slightly hotter magma invaded the deeper parts of the chamber represented in the late-erupted northern units possibly up to ∼10 kyr prior to eruption, but invaded shallower levels only very shortly before eruption, as shown by our textural information and previously proposed from the sharp delineation of quartz bright rims. By obtaining a large number of analyses from zircon separates that systematically cover the entire Bishop Tuff eruption sequence we can produce an eruption age estimate using SIMS to the same precision and accuracy as ID-TIMS and 40Ar/39Ar techniques.
    • Current issues: patient perception of clinical photography.

      Bryson, David; University of Derby; College of Life and Natural Sciences, University of Derby, Derby, UK (Taylor and Francis, 2018-01-30)
    • Detecting macroecological patterns in bacterial communities across independent studies of global soils.

      Ramirez, Kelly S.; Knight, Christopher G.; de Hollander, Mattias; Brearley, Francis Q.; Constantinides, Bede; Cotton, Anne; Creer, Si; Crowther, Thomas W.; Davison, John; Delgado-Baquerizo, Manuel; Dorrepaal, Ellen; Elliott, David R.; Fox, Graeme; Griffiths, Robert I.; Hale, Chris; Hartman, Kyle; Houlden, Ashley; Jones, David L.; Krab, Eveline J.; Maestre, Fernando T.; McGuire, Krista L.; Monteux, Sylvain; Orr, Caroline H.; van der Putten, Wim H.; Roberts, Ian S.; Robinson, David A.; Rocca, Jennifer D.; Rowntree, Jennifer; Schlaeppi, Klaus; Shepherd, Matthew; Singh, Brajesh K.; Straathof, Angela L.; Bhatnagar, Jennifer M.; Thion, Cécile; van der Heijden, Marcel G. A.; de Vries, Franciska T.; Netherlands Institute of Ecology; University of Manchester; Manchester Metropolitan University; University of Sheffield; Bangor University; University of Tartu; University of Colorado; Umeå University; University of Derby; Centre of Ecology and Hydrology; University of Warwick; Agroscope; Universidad Rey Juan Carlos; University of Oregon; Teeside University; Wageningen University; Duke University; Natural England; Western Sydney University; Boston University; University of Aberdeen (Nature, 2017-11-20)
      The emergence of high-throughput DNA sequencing methods provides unprecedented opportunities to further unravel bacterial biodiversity and its worldwide role from human health to ecosystem functioning. However, despite the abundance of sequencing studies, combining data from multiple individual studies to address macroecological questions of bacterial diversity remains methodically challenging and plagued with biases. Here, using a machine-learning approach that accounts for differences among studies and complex interactions among taxa, we merge 30 independent bacterial data sets comprising 1,998 soil samples from 21 countries. Whereas previous meta-analysis efforts have focused on bacterial diversity measures or abundances of major taxa, we show that disparate amplicon sequence data can be combined at the taxonomy-based level to assess bacterial community structure. We find that rarer taxa are more important for structuring soil communities than abundant taxa, and that these rarer taxa are better predictors of community structure than environmental factors, which are often confounded across studies. We conclude that combining data from independent studies can be used to explore bacterial community dynamics, identify potential ‘indicator’ taxa with an important role in structuring communities, and propose hypotheses on the factors that shape bacterial biogeography that have been overlooked in the past.