Applied Soil Ecology

Aims Although ammonia-oxidising archaea (AOA) dominate nitrifier communities in many agricultural soils, the contribution of the less abundant ammonia-oxidising bacteria (AOB) to nitrogen oxide emissions, particularly nitric oxide, remains poorly understood. This study investigated the roles of AOA and AOB in regulating nitric oxide (NO) and nitrous oxide (N2O) emissions from a urea-fertilised grassland soil and evaluated the nitrification inhibitors dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP). Methods A 28-day soil incubation experiment was conducted using a denitrification incubation system to continuously monitor NO and N2O emissions. In parallel, a destructive incubation experiment was performed to determine the dynamics of ammonium (NH-N) and total oxidised nitrogen (TOxN) and to assess changes in the abundance of AOA and AOB following urea application with or without DCD or DMPP. Results AOA accounted for approximately 66% of the total ammonia-oxidising community. Neither inhibitor significantly affected AOA abundance, whereas both suppressed AOB, with DMPP showing stronger and more persistent inhibition than DCD. DMPP reduced NO emissions by 16 to 75%, whereas N2O emissions decreased by only 0.2 to 27%. The greater reduction in NO, together with the preferential suppression of AOB, suggests that low-abundance AOB contributed disproportionately to NO production despite the numerical dominance of AOA. Conclusions These findings suggest that AOB can contribute disproportionately to NO emissions despite their lower abundance relative to AOA. The preferential suppression of AOB by DMPP was associated with a substantial reduction in NO emissions, highlighting AOB-associated processes as a potential target for mitigating reactive N losses from fertilised soils.

Carbon farming practices are increasingly adopted as part of regenerative agriculture to enhance soil carbon sequestration and improve agricultural sustainability. However, their effects on the phyllosphere microbiome, and how these interact with field biodiversity, remain poorly understood. We investigated how field biodiversity and carbon farming practices (cover crops, all-in mixes, adaptive grazing and ley mixture) influence leaf microbial communities across 19 Finnish farms using ITS and 16S amplicon sequencing. Foliar fungal - but not bacterial - diversity increased with plant species richness. Carbon farming altered both fungal and bacterial community composition, but only fungal community was positively associated with disease load. Network analysis identified three candidate keystone taxa: Alternaria sp. (FASV 34) and Sporobolomyces roseus (FASV 2070), which were mutually exclusive, and Methylobacterium sp. (BASV 75), which co-occurred with FASV 2070. Together, these findings demonstrate that different carbon farming practices shape distinct leaf microbiomes cover crop systems tending to favor potential fungal pathogens, whereas ley mixture and adaptive grazing strategies promote microbial taxa associated with healthier phyllosphere communities. Our study underscores the importance of understanding the complex microbial interactions within leaf ecosystems to inform sustainable agricultural practices.

Boreal forests stretch across vast swaths of the northern hemisphere, are shaped by wildfire, and play an important role in the global carbon cycle. Microorganisms play a critical role in soil nutrient cycling in these ecosystems, yet there are many open questions about the impacts of wildfire on microbially mediated soil biogeochemical cycles. In this study, we used laboratory burns and soil incubations of intact soil cores collected from two distinct soil types -- Histosols and Gleysols -- from boreal forest within Wood Buffalo National Park, Alberta, Canada, to assess burn effects on soil bacterial and fungal community composition and function. We compared resistance and resilience to burning for microbial communities vs. resistance and resilience to burning for soil pH and soil respiration to assess the relationships between burn-induced shifts in microbial community composition, the soil environment, and microbial activity. To link shifts in microbial community composition to potential community function, we measured glucose-specific carbon use efficiency (CUE) and assessed its relationship with weighted mean predicted 16S rRNA gene copy numbers for bacterial communities and FUNGuild-estimated relative abundance of putative symbiotrophic and saprotrophic fungi in burned and unburned soils. Microbial community resistance and resilience to burning varied across soil type with higher resistance of both bacterial and fungal communities from Histosols compared to the O horizons of Gleysols. This may be explained by a larger impact of burning on microbes in the thinner Gleysol O horizons. The relatively low resilience of bacterial and fungal communities to burning as well as the failure of resilience to increase with time since burning supports previous reports of post-burn microbial community recovery occurring over years rather than months. Burning caused a decrease in CUE with larger decreases following longer, hotter burns, which correlated with an increase in weighted mean predicted 16S rRNA gene copy number, raising the possibility that copy number could serve as a proxy for post-fire CUE in boreal forest soils, though more research is needed to constrain the effects of environmental conditions, substrates, and time since fire on this relationship. These findings suggest several ways in which burn-induced shifts in microbial community composition reflect altered microbial community function in meaningful ways for soil carbon cycling.

Soil microbe communities are key indicators of ecosystem recovery, yet their integration into operational restoration monitoring remains limited. We evaluated the potential for benchmarking early Atlantic Forest restoration with reference site-based comparisons using bacteria and fungi. Samples were collected from three geographic clusters and spanned a pasture-restoration-forest land-use gradient. Using metabarcoding, we assessed whether soil microbe community diversity, structure, and functional profiles respond to restoration progress considering influences from spatial arrangement and/or successional stage (determined using NDVI). We found that OTU alpha diversity was not explained by either predictor, whereas the Shannon diversity of bacterial functions declined significantly with increasing NDVI. Bacterial and fungal OTU composition (Bray-Curtis) responded significantly to both NDVI and geographic cluster, as did microbe functional profiles, although only NDVI proved both marginally and conditionally significant. We also found that soil chemical parameters were primarily structured by geographic cluster but not by NDVI, suggesting that many abiotic edaphic conditions reflect soil history rather than current vegetation status. These findings suggest that both microbe taxonomic and functional metrics track revegetation progress and validate eDNA as a scalable, sensitive restoration monitoring framework. Importantly, our results also support the use of reference site-based monitoring for Atlantic Forest restoration.

Soil nematodes play key roles in regulating organic matter decomposition, nutrient cycling and trophic interactions in the soil ecosystem, and are very useful bioindicators of soil condition and soil health. But to characterise them, we need reliable measurements of nematode biodiversity in soils. DNA-based techniques such as metabarcoding have recently explored their biodiversity, with successful results. However, there are many methodological steps that can modify the outcome considerably and require informed decisions. In this study, we tested the effect on nematode alpha and beta diversity metrics of three methodological steps, namely i) type of extraction of genetic material from the matrix, either from soil directly with different starting amount of material or extracting nematodes first via the Baermann or Oostenbrink methods, ii) the choice of taxonomically-relevant DNA segment for amplification, with a nematode specific primer (NemF/18Sr2b) and a universal eukaryotic primer (3NDf/1132rmod), both within 18S rDNA, and iii) the selection of appropriate reference library for taxonomic assignment (comparing three nematode specialised databases and three broad taxonomic databases). Observed differences in alpha diversity were more pronounced when comparing the nematode extraction vs soil extractions. In particular, direct soil extractions co-extracted many non-nematode taxa, especially if amplified with a universal primer, which can significantly reduce the number of nematode reads obtained and therefore the accuracy of nematode community indexes and other nematode-based metrics. The choice of the reference database strongly affected the taxonomic identification, which calls for extreme caution when making this selection. Notably, specialised databases tended to over assign reads to nematodes that were detected as non-nematodes by broad taxonomic databases. However, beta diversity metrics were consistent across methods, highlighting these metrics as robust against methodological choices. Our study clearly demonstrates that the choices of methods for nematode biodiversity studies using molecular tools can have a big impact on the results, and decisions should be made consciously and carefully.

The reintroduction of extinct or endangered species to restore ecosystem function is an essential aspect of rewilding. The Wilder Blean Project at West Blean and Thornden Woods in Canterbury, UK, is committed to rewilding natural processes and enhancing biodiversity in one of England's oldest and largest areas of ancient woodland. The introduction of European bison (Bison bonasus) is an important part of the project. However, how the reintroduction of large herbivores influences local biodiversity and ecosystem functions during the early stages of rewilding remains poorly understood. Soil samples were collected from the same sampling sites before and two years after bison were reintroduced and profiled by metagenomic sequencing using Oxford Nanopore Technologies sequencing platforms. The results showed that the alpha diversity of soil organisms did not change significantly before and after the introduction of European bison, while beta diversity showed modest shifts in community composition. The relative abundance of some nitrogen-fixing and photosynthetic microbial genera showed declines in the 2024 Bison Area, while the mycorrhizal fungus genus Rhizophagus was significantly less abundant than in the 2024 Control Area. Despite relatively stable taxonomic diversity, functional composition differed significantly between the 2022 and 2024 Bison areas and among the 2024 rewilding treatments, revealing a decoupling between taxonomic diversity and functional composition. Amino acid synthesis pathways and carbon metabolism pathways were significantly enriched. These findings highlight the potential of long-read Oxford Nanopore metagenomics to reveal functional shifts that may not be apparent from taxonomic diversity alone. Although these early-stage responses cannot yet predict long-term rewilding trajectories, continued longitudinal monitoring integrating microbial, soil physicochemical, and ecosystem-level measurements will be essential to determine the persistence and ecological significance of these functional shifts.

Much of the persistent soil organic carbon (SOC) pool is microbial in origin: microorganisms process plant carbon into biomass and their necromass can associate with mineral surfaces, contributing to long-term carbon persistence. This has generated interest in microbial interventions such as inoculation to restore carbon in degraded croplands, yet their efficacy remains uncertain. The uncertainty reflects a more fundamental, unresolved question: are microbially-mediated carbon transformations governed principally by the composition of the microbial community or by the soil microenvironment? To disentangle these drivers, we conducted a reciprocal microbial community transplant experiment, introducing communities of contrasting origin from locally adjacent grassland and cropland soils into sterilised grassland and cropland soils, and incubating them for eight months with regular organic inputs. This design decouples the inoculum from the microenvironment, allowing their individual and interactive contributions to be quantified. Fungal assembly was influenced more by the inoculum, consistent with dispersal limitation, whereas bacterial assembly was governed more by the microenvironment, consistent with environmental selection. Despite receiving the same organic carbon inputs, grassland and cropland recipient soils showed distinct SOC trajectories, indicating that the soil microenvironment strongly constrained net carbon retention. Within this constraint, community composition also mattered: introducing grassland rather than cropland communities increased fungal diversity and fungal necromass and led to better SOC outcomes, expressed as net gain or reduced loss. These results show that SOC accrual emerges from interactions between the soil microenvironment and microbial community composition, with fungal community assembly particularly associated with necromass accumulation and carbon retention. They highlight the need to consider both soil conditions and microbial community composition when developing strategies to enhance SOC accrual.

Nutrient limitation is an important control on heterotrophic microbial activity that helps to stabilize the massive stocks of organic carbon held in ombrotrophic peatlands. Minerals contained in atmospheric dusts are critical nutrient sources for peatlands, yet the role of dust in supporting the below-ground microbial processes that underpin primary productivity is largely unknown. We investigated how mineral dust generated from mining waste rock (<20 {micro}m) influences element bioavailability and subsurface microbial functioning using flow-through soil mesocosms. The bioavailability of base cations (Ca, Mg, K), transition metals (Fe, Al, Ni, Cu), Al, and P was tracked over two months at three soil depths (0-6, 6-12, and 12-18 cm) using an extended sequential extraction method. We also analyzed microbial community composition (16S rRNA and ITS amplicon sequencing) and mineralization capacity (exoenzyme assays and carbon substrate incubations). After two months, the concentration of metals in the peat increased substantially after dust application, but the mobility and bioavailability varied by element. Responses of microbial communities to dust application were highly dependent on depth from the surface. Carbon substrate incubations revealed enhanced mineralization capabilities in soil from the surface zone (0-6 cm), but a relatively low stimulation of exoenzymes. Soil pH and phosphorus mobility were also impacted near the site of dust application, while acid phosphatase activity was lower throughout the column. In the middle zone (6-12 cm), the activities of {beta}-glucosidase, {beta}-xylosidase, and NAGase were higher with dust exposure. Measured microbial activity mostly remained unchanged in the lowest depth (12-18 cm). We observed increases in the relative abundances of putative saprotrophic fungi throughout the mesocosm profile. Results from this experiment show that the deposition and weathering of mineral dust can induce a complex set of changes to the capacity and nature of microbial carbon mineralization within a shallow layer of peat.

Like for many other organisms, earthworms host a microbiota consisting of bacteria, fungi and other micro-organisms originating from their surrounding environment. In earthworms, these microbes, either associated with the gut, skin, kidney-like nephridia, gizzard or cocoons, aid their hosts with the digestion of organic matter, immune responses against pathogens, and/or detoxification. Unfortunately, pollution is an increasing threat to soil health and soil biodiversity, and numerous articles have characterized both the microbial communities associated with earthworms, as well as the effects of soil pollution on these microbial communities. Here, we aim to synthesize data from across 159 articles to identify consistent global patterns and gaps in the study of earthworms' microbial communities. Additionally, we combined 16S rRNA metabarcoding data from almost 30 articles in a meta-analysis to evaluate the changes in the diversity of earthworm's and surrounding soil's bacterial microbiota after pollutant exposure. Through an evidence map, we clearly showed that most of the earthworm microbiota data came from the Eisenia fetida species reared in laboratory conditions, and only a handful of studies sequenced fungi (ITS) and protists (18S rRNA) in addition to bacteria and archaea (16S rRNA). The scarcity of studies from wild populations, environmental conditions, and the low microbial diversity targets and sources, cannot support a comprehensive view on earthworm's microbial ecology. Nonetheless, results of the meta-analysis indicate that the data did not support the occurrence of significant changes in the microbiota richness and diversity as result of pollution exposure. However, the microbial communities altered their composition, becoming more dissimilar. We suspect the microbiota response to pollution to be host-species specific, but the lack of data severely limited our ability to further elucidate the effect of pollution on earthworm microbiota.

Background and aimsExcess nitrate (NO3-), from fertilizer overuse and intensive agriculture, can pollute water and contribute to greenhouse gas production (nitrous oxide - N2O). Plant metabolites from pastural herbs such as Plantago lanceolata (plantain) can inhibit microbial nitrification of ammonium to NO3- (biological nitrification inhibition - BNI) and change soil nitrogen cycle dynamics (lower potential nitrification rate - PNR). The main aim was to investigate differential plant metabolite expression associated with BNI and lowered PNR in different soil types. MethodsSix plantain cultivars were tested for BNI potential and screened for metabolites that correlated with inhibition of the ammonia oxidising bacterium (AOB) Nitrosospira multiformis. PNR and microbiome change was then investigated in four different New Zealand soils under the plantain cultivar Agritonic and ryegrass cultivar One50. ResultsPNR under plantain was 11 to 41% lower than fallow soil while PNR under ryegrass was 0 to 39% lower. In addition to verbascoside and aucubin, plantain metabolites associated with lower PNR included plantamajoside, riboflavin 3- and 5-sulfate, plantagoguanidinic acid. Chlorogenic acid was associated with lowered PNR under ryegrass. PNR reductions, microbiome structure and the ratio of ammonia oxidising archaea (AOA) relative to AOB was modulated by soil type. ConclusionPlantain and ryegrass lowered the PNR in four different soils and was correlated with metabolites beyond just aucubin and verbascoside. Based on candidate BNI-associated metabolites identified, it was hypothesised that lowered PNR is likely indirect through mechanisms such as chelation and appears to be dependent on both plant physiology and soil physicochemistry.

Globally, contaminated soils pose serious risks to agriculture, biodiversity of ecosystems, and human health. Although a variety of monitoring and remediation methods have been developed over the years, there remains a lack of theoretical modelling to better understand the impact of contamination on soil carbon in a microbially-mediated system. In this study, we develop a model which incorporates contaminated soil organic carbon, uncontaminated soil organic carbon, dissolved organic carbon, microbes, extracellular enzymes, and CO2, to explore how different amounts of contamination and modes of contamination (pulse and press) affect microbially-mediated carbon flux within both vegetated and barren environments. The model represents contamination as a pool of contaminated soil organic carbon that is more resistant to microbial degradation than uncontaminated soil organic carbon. The results show that, in barren environments, the amount and type of contamination has no notable impact on the soil system. In contrast to this, in vegetated environments, plants mitigate the impact of large contamination inputs with differences in outcome depending on the amount and type of contamination.

Excessive application of boron-based fertilizers in agriculture has led to increased boron accumulation in soil, adversely affecting microbial communities and plant species, ultimately contributing to boron-induced desertification. This study presents the first metagenome-based analysis of boron-contaminated agricultural soil in Northern West Bengal, India, providing a comprehensive profile of the soil microbiome under boron stress. Boron-amended and unamended agricultural soil samples were analyzed using metagenomics sequencing approach over 365 days under natural environmental conditions. The results revealed a significant decline in bacterial diversity in boron-amended soil, with Firmicutes emerging as the dominant phylum. Notably, all boron-tolerant bacterial strains belonged to Firmicutes, suggesting that high boron levels impose selective pressure favouring Gram-positive bacteria. The enrichment of metal-resistant and oligotrophic bacterial taxa in boron-amended soil underscores microbial adaptation to boron stress. In addition to microbial community dynamics, we investigated plant succession in boron-enriched soil, offering novel insights into the interplay between above- and below-ground ecosystems. Our findings highlight two key adaptive traits, high boron tolerance and oligotrophic survival strategies, that enable bacterial communities to persist in boron-rich environments. These results enhance our understanding of microbial resilience in chemically stressed soils and have implications for soil health and sustainable agriculture.

Urbanisation is widely recognised as a major driver of environmental change, yet its impacts on soil microbiomes remain poorly understood, particularly outside megacities and beyond bacterial taxa. Population density is frequently used as a proxy for urban intensity, but its relevance across different microbial kingdoms and urban contexts is unclear. Here, we investigated how soil microbial communities vary across population density bands in the regional, temperate city of Hobart, Australia. Using a multi-kingdom metabarcoding approach, we analysed bacterial, fungal, and protozoan communities from soils collected in urban green spaces along a population density gradient. Bacterial alpha-diversity differed significantly across population density bands, exhibiting an inverse U-shaped relationship, with the highest diversity at green spaces in intermediate population density areas. In contrast, fungal and protozoan alpha-diversity did not vary with population density. Community composition (beta-diversity) did not differ consistently across density bands for any microbial group, and variation in soil physicochemical properties explained more community variation than population density alone. These results indicate that population density is a selective, rather than universal, driver of urban soil microbiomes and that responses to urbanisation differ markedly among microbial kingdoms. Our findings highlight important limitations of using population density as a sole indicator of urban impact and challenge the generalisability of conclusions drawn from bacteria-focused studies in large cities. By demonstrating kingdom-specific and context-dependent responses in a regional city, this study underscores the need for multi-kingdom, multi-scale approaches to better understand how urbanisation shapes soil microbiomes and their potential implications for urban ecosystem functioning and human health.

The perennial grass Miscanthus x giganteus (miscanthus) offers a sustainable alternative to traditional biomass feedstocks while improving key soil health parameters, including aggregation. Aggregate stability results from dynamic soil-plant-microbe interactions, yet the relative importance of each factor remains an active research question. Building on previous observations that miscanthus alters soil structure to improve water-holding capacity and aggregate stability, we characterized the communities of soil bacteria and arbuscular mycorrhizal fungi (AMF) across three sites in Iowa, USA, comparing miscanthus to annual maize (Zea mays L.) and non-cropped perennial turfgrass (Poa spp.). We examined whether microbiomes co-varied with soil aggregation and, if so, whether plant cover identity or life history categorization better explained the observed patterns. Bacterial and AMF communities varied across sites and plant types, with signals that life history and plant cover identity both mattered. Aggregate stability aligned with a perennial-annual divergence in microbial beta diversity, while finer-scale differences in community composition and network structure were plant-specific. Soils under perennial plants were enriched in microbial groups positively correlated with aggregate stability; we identified 61 bacterial and 8 AMF "architect" taxa for future study. Within- and cross-kingdom co-occurrence network analysis revealed greater complexity under perennial plants: 1.9-fold more network links in miscanthus bacteria-bacteria networks than in maize, and 1.7-fold more in turfgrass AMF-AMF networks. Miscanthus fundamentally shapes microbial interactions, particularly among bacteria, relating to improved soil physical structure. Understanding these soil-plant-microbe feedbacks advances the development of biomass feedstocks with a portfolio of soil health benefits for next-generation biofuels and bioproducts. IMPORTANCEPerennial bioenergy crops can provide the raw material for biofuels and bioproducts while simultaneously improving soil health. Miscanthus x giganteus (miscanthus) efficiently stabilizes soil aggregates, potentially leading to higher water retention and erosion resistance. Understanding the microbial contributions to these outcomes is key to building resilient, sustainable bioenergy systems. This study highlights the connections between communities of soil microbes--bacteria and arbuscular mycorrhizal fungi--across three sites and three plant covers, including miscanthus, maize, and turfgrass. We identify a guild of potential "microbial architects" linked to soil aggregation and show more interconnected microbial networks under the perennial plant covers compared to annual maize. These insights shed light on the interactions between soil biological communities and soil physical and chemical properties. More broadly, the results may inform efforts to harness plant-associated microbiomes for sustainable biomass production.

Characterizing the enzymatic accommodation of circular agricultural fertilizers is critical for informing strategies to remediate widespread soil sulfur hunger. Here, we present an exploratory in-silico investigation evaluating the active-site cleft of sulfate thiohydrolase (SoxB) across representative soil Proteobacteria. Following the crystallographic precedent of uncomplexed thiosulfate in PDB 2WDE, site-directed molecular docking indicated that the free thiosulfate polyanion binds favorably within the catalytic pocket (predicted affinity: -3.506 kcal/mol), yielding a substantially lower empirical energy barrier than hydrophobic elemental sulfur (S8, -1.409 kcal/mol). Comparative evaluation against the alkaline-adapted Thiobacillus denitrificans homolog revealed an elevated predicted binding affinity of -4.610 kcal/mol, suggesting a potential structural accommodation in high-pH calcareous soils (pH > 8.0). Unrestrained 5.0 ns all-atom molecular dynamics in explicit TIP3P solvent demonstrated initial structural stability of the unliganded host backbone (RMSD = 1.10 +/- 0.15 Angstrom). Energetic decomposition indicated that ligand association is governed predominantly by electrostatic interactions (delta-E_elec ~ -40 kcal/mol) with basic residues (His146, His269, Trp147; RMSF < 0.60 Angstrom), with a single-trajectory unbinding event observed at 3.2 ns. These computational observations provide an exploratory baseline characterizing the active-site electrostatic landscape of SoxB, generating working hypotheses for downstream empirical soil microcosm and in-planta trials.

Abstract Background: Soil microbiomes play critical roles in plant health and resilience, yet it is still poorly understood how disruptions in local microbial communities, such as during soil management, impact these ecological functions. In this study, we investigated how compost addition, a widely used soil management practice, and microbiome origin influence microbiome-mediated plant resistance to insects. We combined surveys of working organic farms across New York with controlled laboratory experiments, amplicon sequencing, plant-insect bioassays, and mass spectrometry. Results: Compost use was associated with shifts in the relative abundance of 20 fungal and 2 bacterial genera across ten working farms. However, no consistent changes in bacterial or fungal diversity or community structure in fields with compost were observed across the farms. Under controlled conditions using a common compost source, compost increased rhizosphere microbial diversity and significantly altered rhizosphere community structure, including the relative abundance of 6 fungal and 41 bacterial genera. Despite these substantial community-level changes, compost did not affect populations of green peach aphids (Myzus persicae) on kale (Brassica oleracea). Instead, aphid populations and plant salicylic acid concentrations were more strongly associated with microbiome origin, demonstrating that compost can substantially restructure soil and rhizosphere microbial communities without corresponding changes in microbiome-mediated plant resistance to insects. Conclusions: Our findings demonstrate that microbial diversity and compositional responses to management are not necessarily reliable indicators of all microbiome functions. More broadly, this work highlights the importance of local soil microbiome variation in shaping plant-insect interactions and emphasizes the need to link community-level responses to direct functional measurements when evaluating microbiome responses to agricultural management.

The mechanisms by which coarse woody debris (CWD) affects soil microbial diversity across different spatial scales and forest disturbance regimes remain poorly understood. This study investigated the impact of CWD from multiple tree species on forest floor bacterial and fungal communities under varying landscape-scale conditions, specifically comparing old-growth forests situated on Phaozems and Retisols with mass-windthrow areas located on loamy Retisols and sandy Podzols. We analyzed both chemical compound and metagenomic profiles of 63 CWD-associated soil samples collected from the Kaluzhskie Zaseki Nature Reserve (European part of Russia). High-throughput Illumina sequencing of the 16S rRNA gene and the ITS region was used to profile both bacterial and fungal communities, respectively. Scale-dependent diversity patterns and taxonomic accumulation were assessed using GLM, NMDS, dbRDA, and iNEXT frameworks. Our findings revealed a profound spatial decoupling in forest floor microbial communities, where a localized reduction in alpha-diversity under CWD drove a sharp increase in landscape-scale gamma-diversity. While standard soil physicochemical properties rigidly dictated baseline matrix richness, CWD operated as a powerful micro-environmental hotspot overriding these constraints. Deadwood inputs filtered out dominant matrix-associated taxa, creating highly specialized micro-refugia characterized by high compositional dispersion. This niche selection was particularly pronounced beneath Quercus logs on Phaozems and Retisols. Furthermore, post-windthrow microbial responses were heavily filtered by wood traits and baseline soil textures. On loamy Retisols within the windthrow mosaic, this breakaway dynamic was highly taxon-specific: while Acer and Fraxinus CWD triggered partitioned, site-specific hotspot dynamics yielding an exceptionally large pool of unique ASVs for bacteria, the distinct enrichment for fungal communities was primarily driven by Ulmus CWD and log-free windthrow areas. Ultimately, iNEXT accumulation profiles confirmed that deadwood does not merely multiply common soil taxa, but enriches the forest landscape by injecting critical beta-level heterogeneity into the soil matrix. These insights emphasize the role of diverse CWD retention in buffering forest microbiomes against large-scale environmental disturbances across heterogeneous soil landscapes.

Smallholder farming systems in sub-Saharan Africa are constrained by declining soil fertility, erosion, and rising fertilizer costs, creating an urgent need for scalable inputs that sustain yields while maintaining soil health. While there is some evidence that microbial inoculants may offer a promising complement to conventional fertility management, field-scale evidence in tropical cereal and tuber systems remains limited. Here, we evaluated a multi-species inoculant composed of 20-22 Bacillus and Streptomyces species on potato and maize across four sites in Rwanda over two growing seasons (2025A and 2025B). Treatments included the inoculant applied at two rates (150 and 250 g ha-1), both alone and in combination with standard fertilization (inorganic fertilizer plus manure), alongside untreated and fertilized controls. Co-application of the inoculant with standard fertilization increased yield and plant biomass beyond fertilization alone, with gains of 6-51% for maize and 3-58% for potato. However, while the inoculant applied alone outperformed untreated controls, it generally did not match standard fertilization. Responses were strongest and most consistent for large-grade potato tubers, and application rate interacted with crop type, whereby the lower dose maximized marketable tuber yield, while maize showed a positive dose-response for grain and biomass. Yield increases were not accompanied by reductions in crop nutrient density, which was instead governed by site-level differences. Altogether, these results indicate that multi-species microbial inoculants are an effective complement to existing fertility practices that may offer, pending further research, a potential pathway to partial fertilizer replacement while sustaining productivity and nutritional quality in smallholder tropical agriculture.

Soil bacterial communities exhibit biogeographic patterns along environmental gradients, yet why some environmental factors contribute more strongly to community turnover than others remains poorly understood. Here, we tested whether this variation can be explained by the phylogenetic depth at which bacterial responses to each environmental factor are conserved. Across 40 forest sites in Japan spanning multiple soil and climatic gradients, environmental factors whose bacterial responses were conserved at deeper phylogenetic levels contributed more strongly to bacterial community turnover. We further asked whether phylogenetic clades that share similar environmental responses represent ecologically meaningful units for understanding bacterial community responses. Using soil pH as a focal test case, we found that response-defined clades improved prediction of taxon-level abundance shifts and community-level compositional shifts compared with models that treated taxa as independent units. Together, these findings show that the phylogenetic depth of bacterial environmental responses links trait conservation, community turnover and soil bacterial biogeographic patterns. Significance StatementSoil bacterial communities form biogeographic patterns along environmental gradients, but it remains unclear why some environmental factors drive stronger community turnover than others. This study shows that the strength of bacterial community turnover can be predicted from the phylogenetic depth at which bacterial responses to environmental factors are conserved. Across forest soils in Japan, deeply conserved bacterial responses were linked to stronger community turnover, and clades sharing conserved responses improved prediction of both taxon- and community-level shifts. These findings identify phylogenetically conserved response structure as an organizing principle for understanding and predicting soil bacterial biogeographic patterns.

Ecosystems today are facing unprecedented environmental stress, leading to large-scale losses of habitat and ecosystem services. To address this, reconstructive efforts aim to restore habitat features and their natural complexity, biodiversity, and function. However, many reconstructive efforts fail to consider microbial communities, even though they play key roles in decomposition, nutrient cycling, and plant and animal health. Here, we use shotgun metagenomic sequencing to compare the structure and functional capacity of soil microbial communities from natural Everglades tree islands and islands constructed within a landscape-scale experimental Everglades restoration effort, followed by a manipulative greenhouse experiment to link tree sapling traits with microbiome functional genetic divergence. We found that constructed and natural island microbiomes exhibited strong, robust, and persistent divergence in both taxonomic and functional composition, with natural island microbial communities having greater functional genetic diversity and redundancy. Furthermore, we identified enrichment in functional pathways in constructed island microbiomes such as those involved in pollutant degradation that may reflect continued disturbance leading to shifts in microbiome functional profiles. Despite their capacity for functions such as nitrogen cycling we found to be important for supporting sapling growth, constructed island microbiomes displayed reduced functional genetic diversity and redundancy and were enriched in pathways associated with environmental disturbance, suggesting a potentially diminished capacity for long-term resilience. Overall, our assessment of soil microbial communities in reconstructed and natural habitats emphasizes how reconstructive restoration can impact microbial functional repertoires and highlights the importance of these hidden players in management and restoration of ecosystem health.