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Despite its attractiveness for long-term carbon dioxide removal (CDR), quantifying weathering and CDR rates for enhanced weathering is a significant challenge. Moreover, the role of soil organisms, such as earthworms, in enhancing silicate weathering (both physically and chemically) has been suggested, but there is limited quantitative data on how biota, especially earthworms, contribute to inorganic carbon sequestration. To address these gaps, we conducted a mesocosm experiment with earthworms and basalt. Results indicate increases in clay and cation exchange, causing a weathering rate of over 10−12 mol total alkalinity m2 s−1, in range with other basalt experiments. Basalt amendment increased dissolved inorganic carbon export by only 4 g CO 2 m−2. During the 4.5-month experiment, we observed neither a change in organic nor in inorganic carbon content. In soils without earthworms, basalt amendment reduced soil CO₂ efflux by approximately 0.2 kg CO₂ m2, suggesting considerable CDR. This decrease was about two times larger than calculated inorganic CDR equivalents, suggesting changes in soil organic matter dynamics. Interestingly, earthworms reversed the basalt-induced reduction in soil CO₂ efflux. This reversal was partly due to reduced export of dissolved inorganic carbon but mainly driven by increased organic matter decomposition. Our study highlights the importance of including organic carbon dynamics when evaluating the CDR potential of enhanced weathering. [Display omitted] • Earthworms, when combined with basalt addition, enhanced base cation exchange. • Basalt weathered at a log minimal weathering rate of −11.65 mol TA m−2 s−1. • Base cation exchange prevented substantial DIC efflux from basalt mesocosms. • Soil water Ge/Si and δ30Si indicated that basalt formed secondary clay minerals. • Organic matter decomposition was stimulated in the presence of earthworms and basalt. [ABSTRACT FROM AUTHOR]

Generative AI (GenAI) is becoming a valuable tool for enhancing efficiency and can be used to help foster critical thinking skills among students and possibly assist in hypothesis generation. GenAI can excel at improving original content and to make it more accessible to broader audiences. While GenAI can create stunning images, inaccuracies persist, even with well-designed prompt engineering. Likewise, challenges persist in GenAI processing nuanced information accurately, highlighting the need for foundational knowledge and critical thinking when creating prompts and interpreting GenAI responses. • Generative AI can be a valuable tool, but it requires sufficient critical skills to prompt and interpret responses. • The SBB community may face a unique challenge because soil biology is not well represented in source material. • Developing prompting skills will be necessary to minimize inaccuracies. [ABSTRACT FROM AUTHOR]

The growing resistance of weeds to herbicides demands innovative strategies that harness soil biology for effective weed control. We examined the use of carbon amendments to stimulate microbial immobilization of soil nitrogen for weed control. We hypothesized that increased carbon availability will stimulate soil microbial growth, leading to greater nitrogen immobilization, which consequently decreases plant-available nitrogen and suppresses the growth of nitrogen-responsive weed species. We buried 80 19-L pots in a research farm field and added sawdust and sucrose to soils as a high carbon treatment and used unamended soils as a control. We examined eight different weed species separately, and measured plant growth, soil carbon, available nitrate, microbial carbon and nitrogen, and microbial community composition after 11 weeks of treatment. The carbon amendments altered plant-microbial competition for nitrogen, resulting in reduced biomass for most weed species. The carbon-amended soils had higher microbial biomass carbon and nitrogen, slower nitrogen cycling, and less available soil nitrogen, indicating enhanced nitrogen immobilization. The carbon treatment altered the beta diversity of soil fungi and bacteria and reduced fungal alpha diversity estimated by the Shannon index. The study results indicate that high carbon substrates can be used to modify plant-microbial competition for soil nitrogen with important implications for developing sustainable weed management practices. • High-carbon soil amendments immobilized soil available nitrogen. • Nitrogen-responsive plant growth was reduced in soils indicating nitrogen immobilization. • Soil carbon amendments enriched for distinct bacterial and fungal communities. • Fungal alpha diversity was consistently reduced in carbon-amended soils. [ABSTRACT FROM AUTHOR]

Soil micro-food webs play an important role in ecosystem functions through energy flow; they are strongly influenced by land use types. Previous studies have typically utilized the space-for-time substitution or single-time sampling method to reflect the land-use change effects by comparing differences among existing land-use types. These methods would increase random error. Research on how synchronized land-use change (starting at the same time and place) influences soil ecological processes and functions is urgently needed. Based on a controlled field experiment and seven years of observations, this study explored the effects of land-use change from natural shrubland to cropland (maize), forage land (tall-grass forage), and economic forest land (walnut plantation) on the community structure and energy dynamics of the soil micro-food webs. Cropland simplified the complexity of the soil food webs compared to the other three land-uses. Forage grassland maintained the highest biomasses of soil total microbes, fungi, and arbuscular mycorrhizal fungi. In addition, economic forest land improved the flow uniformity of the micro-food web by increasing energy transfer from resources to bacterivores, fungivores, and herbivores while decreasing herbivore energy flow to omnivores-predators. Omnivore abundance and nematode diversity were important predictors of total energy flux and flow uniformity of the soil micro-food webs, respectively. In addition, omnivores maintained the complexity of soil micro-food webs by promoting interactions among trophic groups through top-down control. Soil organisms are sensitive to the response of agricultural management and planting time, and it may take several years or more to reach a dynamic equilibrium. Different types and levels of ecosystem disturbance (e.g., tillage and no-tillage, fertilizer rates, aboveground biomass removal intensity) may be the major drivers of soil community during land use change. Our findings highlight the importance of conservation agriculture in maintaining soil food web structure and energy flow for future sustainable land uses, and that promoting omnivore abundance is essential for food web complexity and stability. • High level of disturbance in maize cropland suppressed the soil biota and food web energy flow. • Omnivores enhance the soil micro-food web complexity by strengthening the interactions between trophic groups. • Omnivore abundance is good predictor of total energy flux through soil food webs. • Nematode diversity is good indicator of flow uniformity of soil food webs. • Conservation agriculture maintains soil biota and food web energy flow and is a sustainable land use type. [ABSTRACT FROM AUTHOR]

Deadwood heterogeneity is regarded as a primary causal driver of deadwood-associated soil biodiversity, but the underlying mechanisms remain elusive. This is partly due to the technical difficulties in disentangling and quantifying different components (e.g., deadwood is both habitat and food) of heterogeneity to which soil organisms may have context-dependent responses. Furthermore, non-trophic interactions, e.g., facilitation, also add complexity to deadwood heterogeneity-biodiversity relationships, yet their influences are unaccounted for in most deadwood biodiversity studies. To address these research gaps, we sampled isopod communities from 40 logs of two isotopically distinct tree species, which had been cut and incubated reciprocally for eight years in each of two environmentally contrasting sites (e.g., differences in background isotopic signatures and litter turnover rates). We then assessed the extent to which the variation in the biodiversity of isopod communities is explained by deadwood heterogeneity induced by wood-boring beetles. Stable isotope ratios (i.e., δ13C and δ15N) were employed to examine the response of trophic diversity of isopod communities to the rarely tested food facet of deadwood heterogeneity. We hypothesized the deadwood heterogeneity is boosted by wood-boring beetles and thereby positively affects the abundance, taxonomic diversity and trophic diversity of isopod communities. Our results supported this hypothesis: the abundance and Shannon and Simpson diversity as well as trophic diversity of isopods were positively correlated to wood-boring beetle tunnel densities in both sites and across the two tree species. We observed significant tree species and reciprocal treatment effects on the δ15N values of isopods in one of the two sites. This result suggested that the use of deadwood as food sources versus habitats by isopods is environmentally dependent. This study demonstrates that there is substantial heterogeneity within deadwood that promotes the diversity and trophic diversity of macroinvertebrates. This relationship is mediated by saproxylic beetle facilitation, with implications for the roles of saproxylic beetles and within-deadwood heterogeneity in determining microbial wood decomposition in temperate forests. • Wood beetles facilitate the food and habitat facets of deadwood heterogeneity. • Stable isotopes are useful to quantify the food facet of deadwood heterogeneity. • Wood beetle facilitation increases the trophic diversity of isopods. • Isopods' dependence on deadwood may depend on soil properties. • Fine-scale deadwood heterogeneity greatly benefits soil animals with low mobility. [ABSTRACT FROM AUTHOR]

Our knowledge of the factors influencing the distribution of soil organisms is limited to specific taxonomic groups. Consequently, our understanding of the drivers shaping the entire soil multitrophic network is constrained. To address this gap, we conducted an extensive soil biodiversity monitoring program in the French Alps, using environmental DNA to obtain multi-taxon data from 418 soil samples. The spatial structure of resulting soil multitrophic networks varied significantly between and within habitats. From forests to grasslands, we observed a shift in the abundance of trophic groups from fungal to bacterial feeding channels, reflecting different ecosystem functioning. Furthermore, forest soil networks were more strongly spatially structured which could only partly be explained by abiotic conditions. Grassland soil networks were more strongly driven by plant community composition and soil characteristics. Our findings provide valuable insights into how climate and land-use changes may differentially affect soil multitrophic networks in mountains. • Soil multitrophic network composition differ between forests and grasslands. • Forest networks have more ectomycorrhiza, macro-detritivores, predators and zooparasites. • Grassland networks have more phytoparasites, decomposers, bacterivores and omnivores. • Null models show co-variation in relative abundance among interacting groups. • Space and environment shape forest networks; plants and environment shape grassland networks. [ABSTRACT FROM AUTHOR]

Earthworms are emblematic soil organisms, known to be highly beneficial to soil functioning and ecosystem sustainability. In the current context of agroecological transition, they can be inoculated in degraded soil for their beneficial effect on soil structure and plant growth. We here advocate that earthworms can be also used as conveyors of beneficial mycorrhizal fungi in soils, thus enhancing plant nutrition and promoting primary production. Through a review of the literature on earthworms and mycorrhizal fungi, this paper aims at answering the following questions: Do earthworms ingest mycorrhizal fungi? Do they convey mycorrhizal fungi in their digestive tube so they are still active when leaving earthworm intestines? Is there a spatial correlation between earthworm casts and plant roots which could enhance mycorrhizal colonization of the root system? Considering that earthworms may ingest, transport, keep active in their intestine and bring mycorrhizal fungi to the roots, they could be used as conveyors of mycorrhizal fungi in soils. Although depending on the species, their presence was found to improve the colonization of roots by mycorrhizal fungi and to increase significantly the mycorrhization percentage. This perspective paper also underlines precautions that should be taken to make available and relevant this Nature-based soil improvement method. • Earthworms can be introduced in degraded soil for improving soil fertility. • Earthworms can be also used as conveyors of beneficial mycorrhizal fungi in soils. • This nature-based solution is proposed for soil quality improvement. [ABSTRACT FROM AUTHOR]

Niche construction by biota has been frequently reported for animals and plants, but fungi have received less attention. For mycorrhizal fungi, mutualistic niche construction has been proposed where partners construct niches for each other. However, few eco-evolutionary mechanisms leading to mutualistic symbiotic feedback have been described. Here we report niche construction by two ectomycorrhiza-forming species of truffles, Tuber aestivum and T. melanosporum. The soils of 263 spots of these Tuber , which create bare patches (brûlés), have been monitored (9–10 years) in natural forests to analyze whether they meet the criteria to satisfy the mutualistic niche construction process. Soil habitat modification by these Tuber can be seen in their brûlés, where the vegetation of arbuscular mycorrhizal plants and soil organisms are largely suppressed. Tuber melanosporum brûlés were smaller more productive, and with lower vegetation cover than T. aestivum. Interactions among soil carbonates, pH, and brûlé size are associated with increased carpophore productivity, indicating positive feedback between habitat modification and fungal fitness. Both species modified the habitat differentially. Tuber aestivum brûlés had higher pH and lower total carbonate than soils outside. Tuber melanosporum brûlés had lower total carbonate and higher exchangeable Ca2+ and active carbonate than soils outside. In conclusion, brûlés show a mutualistic niche construction process because modifies their soil environment and increases the fitness of both Tuber spp. Enhanced carbonate weathering by truffles resulted in lower soil quality with a negative impact on plants, indicating that mutualistic niche construction does not equally benefit both partners. [Display omitted] • Niche construction for animals and plants has received more attention than fungi. • The monitoring of 263 truffle brûlés has confirmed the niche construction criteria. • T. aestivum brûlés had a higher pH and lower total carbonate than soils outside. • T. melanosporum brûlés had lower total carbonate & higher Ca2+ and active carbonate. • Brûlé resulted in lower soil quality with a negative impact on plants. [ABSTRACT FROM AUTHOR]

Harvesting whole-tree biomass for biofuel combustion intensifies removal of nutrients from the ecosystem. This can be partly abated by applying ash from the combustion back to the system, as the ash is rich in nutrients. Ash is very alkaline and ash application raises soil pH, which in turn can stimulate microbial activity and thus decomposition and mineralization. Our aim was to test if ash induced decomposition activity was associated with enhanced turnover of recalcitrant, i.e. relatively old, organic pools. Two experiments were conducted in the same coniferous plantation after the application of 0, 3, 4.5 and 6 t ash ha−1, and 0, 3, 9, 15 and 30 t ash ha−1, respectively. We used natural abundance of 15N in mosses, mites and ectomycorrhizal fungi 26 months after ash application, as well as temporal variation in δ15N values of ectomycorrhizal fungi, as an indicator of decomposition of recalcitrant organic matter in the first experiment. Furthermore, in the second experiment we used measurements of extracellular manganese peroxidase activity almost 4 years after ash application as an indication of potential decomposition of lignin, an important component of recalcitrant organic matter. The δ15N signature increased significantly for ectomycorrhizal fungi, dead moss, Nothroid and Gamasida mites, and manganese peroxidase activity tended to increase, with increasing ash doses. This suggests that ash application stimulates turnover of recalcitrant organic matter, which can increase the available pool of nitrogen in the system. This will potentially enhance the fertilizer value of ash. However, the δ15N in ectomycorrhizal fungi tended to peak at 18 months after ash application, before decreasing, suggesting that the turnover of recalcitrant organic matter is reduced again with time. Image 1 • We investigated if ash addition increases turnover of recalcitrant organic matter. • In a field experiment we measured δ15N in soil organisms and MnP activity in soil. • Soil organisms were δ15N enriched with increasing ash doses. • MnP activity tended to increase with increasing ash doses. • δ15N in ectomycorrhizal fungi tended to peak at 18 months after ash application. [ABSTRACT FROM AUTHOR]

Phytohormones such as cytokinins, abscisic acid (ABA) and auxins play a vital role in plant development and regulatory processes. Their role within the plant is a focus for much research, with studies using recent advances in mass spectrometry performance allowing the quantification of low levels of phytohormones extracted from plant tissues. Despite these advances, external factors influencing the production of phytohormones are less well studied. Here, a new approach is presented for the extraction of a range of phytohormones from plant growth media (soil and hydroponic solution), their identification using high mass accuracy mass spectrometry and subsequent quantification using multiple reaction monitoring (MRM). The ability to detect phytohormones in matrices other than plant tissue presents the opportunity to study further the influence of factors such as below ground organisms and soil bacteria on phytohormone production. This novel approach was therefore applied to the plant growth media from a series of experiments comparing plant growth in the presence and absence of earthworms. A small but significant increase in ABA concentration was observed in the presence of earthworms, increasing even further when plants were also present. This finding suggests that earthworms could stimulate plant ABA production. This experiment and its outcomes demonstrate the value of studying phytohormones outside plant tissue, and the potential value of further research in this area. • Mass spectrometry has been used to detect a range of phytohormones in soil and hydroponic solution. • Methods allow quantification of phytohormones at concentrations in the range of pg/g of dry soil. • Concentrations of ABA in hydroponic solution increased when both earthworms and plants were present. • These findings offer potential applications in investigating further plant – soil interaction mechanisms. [ABSTRACT FROM AUTHOR]

Soil organisms constitute multitrophic food webs, which are important determinants for nutrient and carbon flow through terrestrial systems. However, these complex interactions are not well understood, particular in the most cryptic compartment – the link between microorganisms and microfauna. The present study investigates binary trophic links between microbial prey and nematodes in a controlled semi-natural soil environment. A microcosm system with circulating airflow was filled with γ-irradiated arable soil (Luvisol), inoculated with 13C labelled microbial diet and nematode grazers, and incubated for 72 h. Signatures of 13C and CO 2 evolved from microcosms, soil phospholipid fatty acids and nematode densities were determined. Except for the model nematode Caenorhabditis elegans, all organisms joint in the 12 different investigated binary links represent dominant taxa at the arable field site. Studied were the fungal grazers Aphelenchoides saprophilus and Aphelenchus sp. in combination with the fungi Chaetomium globosum, Aspergillus terreus or Cryptococcus terreus as well as the bacterial grazers C. elegans and Acrobeloides buetschlii in combination with the bacteria Pseudomonas putida , Kitasatospora sp. or Sphingomonas trueperi. The results assigned trophic and non-trophic interactions and considerable variation between binary links. The biomass decline of S. trueperi in presence of C. elegans as well as the increased release of 13C in links of C. globosum and A. terreus with Aphelenchus sp. and S. trueperi with A. buetschlii assign nematode grazing and thus a classical predator-prey system. Such direct trophic interactions can induce distinct C fluxes within a binary link as assigned by the increased density (i.e. biomass) of C. elegans when feeding on S. trueperi. In contrast, the numbers of Aphelenchus sp. declined when feeding on A. terreus , and thus reduced C flow to the next trophic level. Grazing can also foster C allocation in microbial biomass via compensatory growth, as indicated e.g. for the link of Aphelenchus sp. with the fungi C. globosum and A. terreus. While these diverse responses to grazing were to be expected, the use of CO 2 and 13C measurements further revealed that non-trophic interactions shape C flux in a binary link, particularly in the bacterial channel. Besides the fungal link of C. terreus with Aphelenchus sp., non-trophic interactions were obvious for the bacterial links Kitasatospora sp. with C. elegans or A. buetschlii, and P. putida with A. buetschlii. The presence of nematodes caused a reduction in respiration (evolved CO 2), thus a decline in microbial activity. The formation of chemical and/or morphological defense is likely a reason for that reduced prey activity. For further studies the inclusion of such non-trophic interactions is necessary to achieve realistic models for C flow through soil food webs. • Microbial traits cause variation in palatability for nematode grazers. • Predator-prey interactions of nematodes within a functional guild differ. • Impact of non-trophic interactions on C flux depends on the specific binary link. [ABSTRACT FROM AUTHOR]

Abstract Litter decomposition is a key process determining the cycling of nutrients in ecosystems. Soil fauna plays an essential role in this process, e.g., by fragmenting and burrowing surface litter material, and thereby enhancing microbial decomposition. However, soil fauna-mediated decomposition might be influenced by interacting factors of environmental changes. Here we used a large-scale global change field experiment to test potential interacting effects between land-use type (croplands and grasslands differing in management intensity) and projected climate change on litter decomposition rates over a period of two years. For that, climate and land-use treatments were orthogonally crossed: (1) two climate scenarios: ambient vs. future; and (2) five land-use regimes: conventional farming, organic farming, intensively used meadow, extensively used meadow, and extensively used pasture. Litterbags with two mesh sizes (5 mm and 0.02 mm) were used to differentiate contributions of microbes and fauna to the mass loss of standardized crop residues. Soil fauna accounted for more than 68% of surface litter mass loss. Future climate treatment decreased decomposition rates as a result of reduced precipitation and elevated temperature during summer months. Litter decomposition and the contribution of soil fauna to it were significantly higher in croplands than in grasslands, but did not differ due to management intensity within these land-use types. In grasslands, faunal contribution to decomposition decreased under future climate. There were no interacting effects between climate change and land use on decomposition rates. These findings indicate that predicted changes in precipitation patterns and temperature will consistently decelerate litter decomposition across land-used types via both microbial and faunal effects. Graphical abstract Image 1 Highlights • Future climate decreased litter decomposition, most in summer months. • This decrease in decomposition was due to soil fauna, but not microbes. • Soil fauna-mediated decomposition was higher in croplands than grasslands. • Climate change effects on decomposition were consistent across land-use types. [ABSTRACT FROM AUTHOR]

Biodiversity and ecosystem functioning (BEF) often correlate positively with BEF studies focusing mostly on plant diversity manipulations. Plant performance is directly and indirectly impacted by soil organisms, but the role of increasing soil biodiversity on plant performance has mainly been tested in an uncontrolled way or with low biodiversity levels. An additional knowledge gap exists on the effect of (interactive) global change drivers – such as drought – on the soil BEF (sBEF) relationship. We here tested sBEF relationships by manipulating microbiome predatory protist diversity (0–30 species) in ambient controls and under abiotic (drought) and biotic stresses (nematode addition dominated by plant parasites). We then used plant (Solanum lycopersicum) biomass as a response in an 8-week greenhouse experiment. We show that the increasing biodiversity effect on plant biomass ranged from positive (up to 23% with biotic stress), to neutral (ambient conditions and with both stresses co-occurring), to negative (up to 39% with abiotic stress). Together, sBEF relationships were context-dependent and often contradicted generally reported positive (s)BEF relationships. Therefore, we propose that positive sBEF claims likely are not the norm and should be evaluated in a context-dependent manner. To better elucidate sBEF relationships, more manipulative studies should be performed under different conditions such as global change drivers and with a range of organismal groups. • SBEF relationships reported were context-dependent, challenging (s)BEF studies. • Protist diversity, though indirectly linked to plants, impacts plant performance. • We show no evidence of functional similarity effects on the sBEF relationship. [ABSTRACT FROM AUTHOR]

Abstract Entomopathogenic nematodes (EPNs) are widely distributed in soils throughout the world. Their activity as biological control agents is modulated by abiotic and biotic factors (e.g. soil type, climatic fluctuation and natural enemies). We sought to identify soil properties in a Mediterranean region, which might be managed to enhance biological control agents' services provided by EPNs. We hypothesized that responses of EPN soil food web assemblages to abiotic factors in such a Mediterranean region would be consistent with previous observations in other biomes in subtropical and temperate regions, in which pH and variables related to water content were main drivers of such association. We also expected that EPN abundance and species composition would differ between stable botanical habitats (citrus groves, palmetto areas, oaks and pines), with EPNs and associated organisms favoured in cultivated sites (citrus). In spring 2016, 50 georeferenced localities, representing four botanical habitats and two soil-ecoregions (calcareous versus non-calcareous), were surveyed. Using published and de novo real time qPCR tools, we evaluated the frequency and abundance of 10 EPN species and 13 organisms associated with EPNs: 6 nematophagous fungi (NF), 5 free-living nematodes (FLN), and 2 ectoparasitic bacteria. EPN activity was also assessed by traditional insect-baiting, allowing the evaluation of FLN-EPN mixed progeny. EPNs were detected by qPCR in 50% of localities, and strongly correlated with EPN activity. Steinernema feltiae was the dominant EPN species measured by both techniques (qPCR and insect-bait), being widespread in all Algarve, while Heterorhabditis bacteriophora was detected mainly in citrus groves. The species S. arenarium and H. indica were detected by qPCR for the first time in continental Portugal. The molecular analysis of insect cadaver progeny revealed novel FLN-EPN associations with Pristionchus maupasi and P. pacificus. EPN, FLN and NF abundance differed among botanical groups, with citrus groves supporting high numbers of all trophic guilds. Oaks also favoured EPNs. Similarly, calcareous soil-ecoregion supported higher NF, FLN and EPN abundance. Two abiotic variables (pH, and clay content) explained the community variation in multivariate analysis, consistent with key abiotic variables described for other subtropical and temperate regions. The results supported the hypothesis that cultivated perennial habitats favour EPNs and soil organisms that can limit EPN activity as biological control agents. Highlights • Entomopathogenic nematode (EPN) food webs evaluated in Mediterranean Algarve region. • Molecular tools added 2 new EPN species in Portugal to those shown as dominant. • New molecular tools revealed first mixed progeny of Pristionchus -EPN in cadavers. • EPN and associated soil organisms assemblage are driven by vegetation. • Soil pH and clay explained EPN assemblage, as in subtropical and temperate areas. [ABSTRACT FROM AUTHOR]

Fractionation of soil organic carbon (SOC) is crucial for mechanistic understanding and modeling of soil organic matter decomposition and stabilization processes. It is often aimed at separating the bulk SOC into fractions with varying turnover rates, but a comprehensive comparison of methods to achieve this is lacking. In this study, a total of 20 different SOC fractionation methods were tested by participating laboratories for their suitability to isolate fractions with varying turnover rates, using agricultural soils from three experimental sites with vegetation change from C3 to C4 22–36 years ago. Enrichment of C4-derived carbon was traced and used as a proxy for turnover rates in the fractions. Methods that apply a combination of physical (density, size) and chemical (oxidation, extraction) fractionation were identified as most effective in separating SOC into fractions with distinct turnover rates. Coarse light SOC separated by density fractionation was the most C4-carbon enriched fraction, while oxidation-resistant SOC left after extraction with NaOCl was the least C4-carbon enriched fraction. Surprisingly, even after 36 years of C4 crop cultivation in a temperate climate, no method was able to isolate a fraction with more than 76% turnover, which challenges the link to the most active plant-derived carbon pools in models. Particles with density >2.8 g cm −3 showed similar C4-carbon enrichment as oxidation-resistant SOC, highlighting the importance of sesquioxides for SOC stabilization. The importance of clay and silt-sized particles (<50 μm) for SOC stabilization was also confirmed. Particle size fractionation significantly outperformed aggregate size fractionation, due to the fact that larger aggregates contain smaller aggregates and organic matter particles of various sizes with different turnover rates. An evaluation scheme comprising different criteria was used to identify the most suitable methods for isolating fractions with distinct turnover rates, and potential benefits and trade-offs associated with a specific choice. Our findings can be of great help to select the appropriate method(s) for fractionation of agricultural soils. [ABSTRACT FROM AUTHOR]

Interactions among the species in microbial communities are important for organic matter turnover and nutrient cycling in the soil. Their responses to organic amendments have been studied recently but the co-occurrence patterns in different spatial soil habitats such as those with different sized aggregates are still unclear. Thus, we investigated networks comprising bacteria and fungi after the application of a cover crop for 9 years. The microbial community compositions and their co-occurrence networks were examined in the whole soil and different sized soil aggregates (>0.25 mm, 0.053–0.25 mm, and <0.053 mm). The microbial community compositions and their responses to the cover crop varied in the whole soil and aggregate fractions. Network analysis in the whole soil and different sized aggregates showed that the competition between fungi and bacteria in the whole soil increased due to the annual organic material input, but the fungi–bacteria relationships varied among different sized aggregates. In particular, the competition between fungi and bacteria increased in macroaggregates but decreased in silt + clay due to organic material inputs. Thus, the co-occurrence networks determined for the fungal and bacterial communities in various soil aggregates were very different from those in the whole soil, and their responses to organic inputs also varied in different spatial habitats in the soil. [ABSTRACT FROM AUTHOR]

Most of the C and N models published over past decades are based on parameters not always linked to the environment and underestimate the role of microorganisms. They are often over-parameterized, which can give multiple solutions for flow calculations between state variables. This work proposes a modelling method centred on the functioning of living organisms in order to calculate flow parameters using data on N stocks in decomposers, plant organs, symbiotic microorganisms, and the soil compartments. The model was settled via a complex N fixing and intercropping system of durum wheat/faba bean compared to the cropping of pure durum wheat and pure faba bean, all in the context of organic farming invaded by weeds and weeded by hand just before flowering. To avoid perturbation of natural exchanges of C and N, no fertilizer was added from 1997 to 2011. The equation system defined for the association of any number of plants, as well as parameters previously published for C-flow calculations were used, and only a few parameters specific to N flows were added, and are discussed. The results showed the strong link between N and C in the environment. The calculations converge toward an unique set of solutions that is consistent with literature data when available. The labile organic N of microbial origin was modelled as the main potentially available stock. Living microorganisms stored about 1% of total N, which was close to the N stock in faba bean and four times more than stock in durum wheat. Inorganic N was immobilized before flowering in competition with N requirement of durum wheat roots. Net N mineralization, mainly from decomposition of faba bean roots, started too late to improve wheat production. During the cropping period, weeds accounted for losses of 20 kg N ha −1 , while the atmospheric N 2 fixation of 90 kg N ha −1 was close to the total microbial immobilization. The model associating microbial and plant flows of C and N in complex plant covers, appears as a robust tool to quantify the exchanges of the earth organisms with the soil and atmosphere. It enables to propose essential recommendations to improve as well agro-ecology as predictions of global changes of C and N stocks. [ABSTRACT FROM AUTHOR]

Most subsoil carbon (C) turnover occurs in biopore hotspots such as root channels and earthworm burrows. Biopores allocate large C amounts into the subsoil, where a vast capacity for long-term C sequestration is predicted. We hypothesise that organic matter (OM) cycling in biopores depends on their origin. Earthworm and root biopores were induced under field conditions and were sampled from the subsoil (45–75 and 75–105 cm) after two years of biopore formation. The effects of biopore formation on OM decomposition were studied by biomarkers: neutral sugars, cutin and suberin-derived lipids, lignin-derived phenols and free lipids. The degradation stage of OM was biopore type-specific but was only governed by the soil depth in root biopores. Degradation of OM increased from earthworm biopores to root biopores and bulk soil. Hemicelluloses (GM/AX ratio) were more strongly degraded than lignin side-chains (relative change from initial values). Two years of microbial processing during biopore formation increased the GM/AX ratio in earthworm biopores from 0.65 to 1.05 and in root biopores from 0.15 to 1.35 (both relative to source biomasses). Root biopores and bulk soil had the highest GM/AX ratios (1.2–1.3), hinting to rapid processing of plant residues and accumulation of microbial residues. The regular, frequent OM inputs by earthworms stimulated microbial growth and processing of mostly bioavailable OM and, thus, relatively enriched more persistent OM (e.g. lignin). Syringyl subunits of lignin underwent low (ratio changed from 0.35 to 0.55 relative to initial input) and vanillyl subunits underwent almost no processing in earthworm biopores indicating the preferential microbial utilisation of the easily available compounds frequently replenished by earthworm activity. After two years of decomposition of the root detritus, mainly structural plant material was enriched in root biopores. Short periods (6 months) of earthworm activity effectively recharged the highly processed OM in root biopores with fresh OM. In total, deep-rooting catch crops and short-term earthworm activities promote C accumulation in the subsoil followed by biopore-specific microbial processing predominantly governed by the C input frequency. As root biopores are up to 40 times more common than earthworm biopores, they dominate the OM input into subsoils. Such C inputs create several years lasting hotspots for preferential root growth and nutrient mobilisation in the subsoil. We conclude that root- and earthworm-derived biopores are vertical pathways for plant C from the soil surface into the subsoil and for intensive processing of litter C and sequestration of microbial necromass. [ABSTRACT FROM AUTHOR]

Applications of mineral and organic fertilisers are an important agricultural practice for improving crop yields, but these applications can also affect soil properties, as well as the microbial community structure and function. The objective of this study was to compare the legacy effects of long-term applications of mineral fertiliser versus animal slurry on the composition and activity of soil microbial communities, and to investigate the significance of their application level and change in long-term management. Soils were collected from the Long-Term Nutrient Depletion Trial in Taastrup, Denmark, which consists of seven mineral and animal slurry fertilisation treatments (20 years) plus seven additional treatments that underwent a shift in their long-term management after 14 years. Microbial communities in soils receiving animal slurry had multiple substrate-induced respiration (MSIR) metabolic fingerprints that clearly differentiated them from those in mineral fertiliser-amended soils. The differences in fingerprints were mainly related to soil total C and pH. Bacterial community analysis by 16S rRNA gene amplicon sequencing showed that animal slurry applications increased bacterial community richness and diversity compared with mineral fertiliser applications, and also increased the relative abundance of several copiotrophic taxa. Even high levels of annual nutrient applications (mineral and organic) promoted copiotroph-dominated bacterial communities to the detriment of oligotrophs, with N inputs exerting a greater influence on bacterial community structure than P or K levels. Stable long-term annual fertiliser applications supported a diverse bacterial community, while a change in nutrient management decreased bacterial diversity. This study documents the differing, time-dependent effects of organic inputs and mineral fertilisation on the composition and functionality of the soil microbial community and highlights the importance of nutrient input levels for soil bacterial community structure. [ABSTRACT FROM AUTHOR]

Carbon (C) storage in forest soils can be enhanced through increasing organic C input and decreasing soil heterotrophic respiration (R H ). The inhibitory effect of biochar on R H has been extensively studied in agricultural soils, while such an effect and the mechanisms involved remain unknown in forest soils. Here, we examine the response of soil physicochemical and microbial properties to biochar application and how these factors mediate the biochar-induced change in soil R H in a subtropical bamboo plantation. Our results showed that biochar application significantly reduced R H , and markedly altered most of the studied soil properties important for R H in the bamboo plantation. Biochar application did not affect soil temperature and no relationship between soil R H and either soil moisture or labile organic C content was observed, excluding the possibility that biochar reduced the R H through changing soil temperature, moisture or labile organic C content, factors commonly considered to control R H . As compared to the control, biochar application significantly increased the aromatic C content and RubisCO enzyme activity, while decreased β-glucosidase and cellobiohydrolase (CBH) activities. In addition, the soil R H was positively ( P  < 0.01) correlated with β-glucosidase and CBH activities, while negatively ( P  < 0.05) correlated with RubisCO enzyme activity. Further, using structural equation modelling, we revealed that bicohar reduced R H through increasing the proportion of soil recalcitrant C fraction and decreasing the β-glucosidase and CBH activities in relation to the decomposition of carbohydrates and celluloses in the soil. This is the first report that increased soil organic C recalcitrancy and decreased activities of C-degrading enzymes are responsible for biochar to reduce R H in the subtropical plantation, which may be key to regulating R H in subtropical plantations through forest management. [ABSTRACT FROM AUTHOR]

Managed northern peatlands are an important source of the strong greenhouse gas nitrous oxide (N 2 O). However, N 2 O emissions from these managed peatlands display a high spatial variability, and processes governing N 2 O production and emissions from these ecosystems are still not well understood. To constrain the factors regulating N 2 O emissions from managed northern peat soils, we determined a wide set of soil physical and chemical properties of peatlands with different management histories spread across Finland, Sweden and Iceland. We included eleven peatland sites with available in situ N 2 O flux data, and complemented our analyses with detailed measurements of soil nitrogen (N) cycling processes such as N 2 O production, gross N mineralization and gross nitrification and, in addition, soil microbial biomass. This study included drained peatlands with different land-use types and management intensities, comprising forested, cultivated or only drained peatlands and afforested or abandoned agricultural peatlands. All selected peatland sites displayed a low soil carbon to nitrogen (C/N) ratio of 15–27, traditionally used to predict high N 2 O emissions. Despite the narrow C/N range, the N 2 O emissions at our sites varied greatly within and between land-use groups, ranging from 0.03 to 2.38 g N m −2 y −1 . Thus, our findings provide valuable insights into the regulatory factors underlying the variability in N 2 O emissions and show that a low C/N ratio in managed peatlands cannot be used to predict high N 2 O emissions. Instead, our results demonstrate that higher N 2 O emissions are linked to higher peat phosphorus (P) and copper (Cu) content, suggesting that low P and Cu concentrations can limit N 2 O production in peat even with sufficient N availability. While known factors such as soil moisture, oxygen content and the degree of peat humification partially explained the variability in N 2 O emissions, this study directly links soil P and Cu availability to N 2 O production processes. The availability of P and especially Cu seemed to promote nitrification activities, thereby increasing N 2 O production. Our study highlights the link between N 2 O emissions and soil P and Cu availability and the strong coupling of the soil N and P cycles in peatlands, which is to date severely understudied. [ABSTRACT FROM AUTHOR]

Soil microorganisms play critical roles in maintaining ecological functions of the northern mixed-grass prairie. While defoliation regimes and elevated precipitation affect plant community composition and primary productivity in these grasslands, their effects on soil microbiome and interactome have not been studied. We examined the response of soil microbiome and interactome to long-term (2010–2015) treatments of varying defoliation regimes (low vs. high intensity and low vs. high frequency) and two precipitation conditions (ambient vs. elevated) on two contrasting sites (a dry vs. a mesic site) in a northern mixed-grass prairie. High intensity defoliation reduced alpha-diversity and altered the beta-diversity of soil microbial communities in the mesic site but not in the dry site, while elevated precipitation reduced alpha-diversity and altered the beta-diversity of soil microbial communities in both sites. Defoliation and precipitation did not show interaction effects on overall alpha- and beta-diversity, but did combine to influence the interactome network. High intensity defoliation promoted the oligotrophic genera Spartobacteria (Verrucomicrobia), Pseudonocardia (Actinobacteria), and Conexibacter (Actinobacteria), while elevated precipitation promoted the copiotrophic genera Nitrososphaera (Thaumarchaeota), Anderseniella (Proteobacteria), Sphingomonas (Proteobacteria), and Acidobacteria Gp16 (Acidobacteria). High intensity defoliation increased the number of linkages for Alphaproteobacteria and Acidobacteria, and decreased the number of linkages for Gemmatimonadetes and Spartobacteria in the interactome networks. However, elevated precipitation increased the number of linkages for Actinobacteria and Gemmatimonadetes and decreased the number of linkages for Spartobacteria and Acidobacteria. Our results show that defoliation intensity and elevated precipitation affected the microbiome and associated interactome network within soils of the northern mixed-grass prairie by affecting different functional taxonomic groups, indicating distinct scenarios for defoliation and precipitation in affecting soil microbial communities. [ABSTRACT FROM AUTHOR]

Soil bacterivorous nematodes are key plant mutualists that increase nutrient availability for plants either by enhancing the mineralization of organic compounds (the “ mineralization pathway ”) or by increasing plant lateral root branching following shifts in internal plant metabolism, and subsequently leading to a higher volume of soil prospected by the roots (the “ hormonal pathway ”). The effects of these organisms on the nutrition of plants growing in strongly nutrient-deficient ferrallitic soils, especially in soils with limited available inorganic phosphorus (P), are poorly known, as are the pathways involved. In our study, using Oryza sativa (Poaceae) and Acrobeloides sp. (Cephalobidae), we tested the “ mineralization ” and “ hormonal ” hypotheses in an acidic P-depleted Ferralsol from the Madagascar highlands. We assessed the effect of nematode inoculation on (i) inorganic P flow from soil to plant using the 32 P labelling technique and (ii) plant root architecture using a rhizobox device. We showed that the ability of Acrobeloides sp. to enhance P uptake in plants is strongly limited in Ferralsols. However, when the soil pH was corrected with dolomite, Acrobeloides sp. increased plant P uptake probably through the “ mineralization ” pathway (higher microbial turnover). Indeed, the L-value increased by 49% in the presence of nematodes and dolomite, suggesting the production of unlabelled plant-available P, probably through a higher net P mineralization when the nematodes were inoculated. Using the rhizobox technique, we also observed increased root length in the presence of nematodes but the specific root length, the tip number and the root branching density did not increase in the presence of nematodes, suggesting that nematodes did not increase plant P uptake and growth in this soil as proposed by the “ hormonal ” hypothesis. From an ecological intensification perspective, to promote agro-ecological development in tropical regions, our results suggest that amending ferrallitic soils with P-rich organic matter and correcting soil pH with an appropriate amount of dolomite may constitute suitable agronomic actionable triggers to drive the mutualistic activity of bacterivorous nematodes. [ABSTRACT FROM AUTHOR]

Recent studies proposed a convergence in the temperature sensitivity (Q 10 ) of soil respiration (R s ) after eliminating confounding effects using novel approaches such as Singular Spectrum Analysis (SSA) or the mixed-effects model (MEM) method. However, SSA has only been applied to eddy covariance data for estimating the Q 10 with air temperature, which may result in underestimations in responses of below-ground carbon cycling processes to climate warming in coupled climate-carbon models; MEM remains untested for its suitability in single-site studies. To examine the unconfounded Q 10 of R s , these two novel methods were combined with directly measured R s for 6 years in two Tibetan alpine ecosystems. The results showed that, 1) confounded Q 10 of R s estimated from seasonal R s -temperature relationship positively correlated with the seasonality of R s , and 2) estimates of unconfounded Q 10 of R s using SSA (mean = 2.4, 95% confidence interval (CI): 2.1–2.7) and MEM (mean = 3.2, 95% CI: 2.3–4.2) were consistent with the theoretical subcellular-level Q 10 (≈2.4). These results support the convergence in the Q 10 of R s and imply a conserved R s -temperature relationship. These findings indicate that the seasonality of R s has to be eliminated from estimating the Q 10 of R s , otherwise the estimates should be questionable. They also indicate that seasonal Q 10 and its responses to warming should not be directly used in carbon-climate models as they contain confounding effects. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is a major limiting element for productivity in temperate grasslands, particularly during early spring when soil N availability is low and the vegetative demand for it is high. Therefore, knowing whether and how plant species adopt different N acquisition strategies during the winter-spring transitional period is essential for understanding ecosystem functioning in temperate grasslands. In this study, parallel experiments with 15 N tracer were conducted to examine plant N acquisition strategies during winter-spring transition in a meadow and a typical steppe in northern China. We found that soil microbes immobilized ∼20% of the 15 N tracer during the spring thawing period at both sites, and then released half of it back to the soil before late spring, confirming that soil microbes competed effectively with the plant roots for mineral N in early spring. Perennial bunch grasses adopted an active N acquisition strategy at the beginning of the spring thawing period. In contrast, perennial forbs and rhizome grasses began to take up N in the middle of the spring thawing period, and they acquired more N than the bunch grasses. However, sagebrushes and legumes accounted for little 15 N recovery, indicating their dependence on internal N accumulation or N fixation. At the ecosystem level, no significant difference in the magnitude of plant 15 N uptake was observed between the meadow steppe and typical steppe, although the plant biomass N in the meadow steppe was twice that of the typical steppe during the thawing period. This was attributed to the higher soil inorganic N and faster net N mineralization rate in the meadow steppe than in the typical steppe. Our results suggest that temporal niche differentiation in N acquisition during early spring may facilitate species coexistence in temperate grasslands despite strong plant-microbe or plant-plant competition for N. The divergent N acquisition strategies at the species level and convergent N acquisition strategies at the ecosystem level should be considered for model development to better simulate vegetation growth particularly under spring N stress. [ABSTRACT FROM AUTHOR]

Net primary productivity (NPP) influences soil food webs and ultimately the amount of carbon (C) inputs in ecosystems. Earthworms can physically protect organic matter from rapid mineralization through the formation of soil aggregates. Previous studies at the Oak Ridge National Laboratory (ORNL) Free Air CO 2 Enrichment (FACE) experiment showed that elevated [CO 2 ] (e[CO 2 ]) increased fine-root production and increased soil C through soil aggregation compared to ambient [CO 2 ] (a[CO 2 ]) conditions. Our first objective was to study the response of earthworms to increased leaf and root-litter inputs caused by increased atmospheric [CO 2 ] exposure. We also took advantage of the CO 2 shutdown at the ORNL FACE site to track the shift of the δ 13 C signal in leaf-litter, fine roots, earthworms, earthworm casts, and bulk soil. Densities of the most abundant endogeic earthworm, Diplocardia spp., were positively correlated with the previous-year production of leaf litter (r = 0.66, P = 0.02) and fine roots (r = 0.62, P = 0.03); and with the leaf-litter production (r = 0.63, P = 0.03) and fine-root production (r = 0.59, P = 0.05) two years before earthworms were sampled. Within two years after the CO 2 fumigation ceased, the 13 C/ 12 C ratio increased in leaf litter (P = 0.01) and in fine roots (P = 0.05), showing an ecosystem legacy effect on soil C inputs. However, the C isotopic composition of soil, endogeic earthworms and casts had not changed the two years after the CO 2 fumigation ended. The positive response of earthworms to increased root NPP, caused by elevated [CO 2 ], is consistent with the increased soil aggregate formation and increased soil C at the ORNL FACE in the e[CO 2 ] treatment. [ABSTRACT FROM AUTHOR]

In the polar desert ecosystem of the McMurdo Dry Valleys of Antarctica, biology is constrained by available liquid water, low temperatures, as well as the availability of organic matter and nutrient elements. These soil ecosystems are climate-sensitive, where projected future warming may have profound effects on biological communities and biogeochemical cycling. Warmer temperatures will mobilize meltwater from permafrost and glaciers, may increase precipitation and may be accompanied by pulses of nutrient availability. Enhanced water and nutrient availability have the potential to greatly influence desert soil biology and ecosystem processes. The objectives of this 5-year study were to determine which nutrient elements (C, N, P) are most limiting to dry valley soil communities and whether landscape history (i.e., in situ soil type and stoichiometry) influences soil community response to nutrient additions. After 3 years of no noticeable response, soil CO 2 flux was significantly higher under addition of C+ N than the other treatments, regardless of in situ soil stoichiometry, but microbial biomass and invertebrate abundance were variable and not influenced in the same manner. A stable isotope incubation suggests that fertilization increases C and N mineralization from organic matter via stimulating microbial activity, with loss of both the applied treatments as well in situ C and N. However, these responses are relatively short-lived, suggesting long-term impacts on C and N cycling would only occur if meltwater and nutrient pulses are sustained over time, a scenario that is increasingly likely for the dry valleys. [ABSTRACT FROM AUTHOR]

Despite a large body of studies investigating soil organic carbon (SOC) stocks and potential influencing factors, the impact of contrasting parent material, particularly in the subsoil, has received little attention. To reveal potential effects varying parent materials exert on SOC stocks, we investigated chemical ( 14 C content and overall chemical composition via 13 C NMR spectroscopy) and plant/microbial related parameters (root mass, amino sugars) of bulk soil and soil organic matter fractions from topsoil, subsoil, and rhizosphere soil at three European beech stands ( Fagus sylvatica L.) only differing in parent material (Tertiary sand, Quaternary loess, and Tertiary basalt). The results suggest that the clay fraction, its amount being largely dependent on the respective parent material, took a central role in shaping differences in SOC stocks among the investigated sites by affecting soil organic matter stabilization via organo-mineral association and aggregation. This fraction was particularly relevant in the subsoil, where it accounted for up to 80% of the bulk soil SOC stocks that decreased with decreasing amounts of the clay fraction (basalt > loess > sand site). Determining the soil's nutrient composition, parent material likely also indirectly affected SOC stocks by changing rhizosphere traits (such as fine root density or mortality) and by attracting root growth (and thus organic matter inputs) to subsoil with higher nutrient contents, where in situ root inputs in the form of rhizodeposits were likely the prime source of plant-derived SOC. However, root inputs also contributed in large part to topsoil SOC stocks and were associated with higher abundance of microbial compounds (amino sugars), whose relative importance increased with increasing soil depth. Independent of soil depth and site, amino sugars and the amount of the clay fraction, combined with parameters related to the input of organic matter (root mass and amount of the particulate organic matter fraction) explained more than 90% of the variability in SOC stocks, indicating a key role of these measures in impacting SOC stocks. Because parent material directly or indirectly influenced these parameters, we demonstrate the necessity to consider differences in parent material when estimating and predicting SOC stocks. [ABSTRACT FROM AUTHOR]

Applications of manure and chemical fertilizers can significantly modulate the bacterial communities in soil, but the effects on the soil antibiotic resistome and the underlying mechanisms remain largely unclear. In the present study, antibiotic resistance genes (ARGs) and bacterial communities were characterized using high-throughput quantitative PCR and Illumina HiSeq sequencing, respectively, in soils from a long-term (25 years) field experiment. Treatments included no fertilizers (control), chemical fertilizers (NPK), NPK with straw return (NPKS), pig manure (M), and M with chemical fertilizers (NPKM). Both NPK and NPKS decreased soil pH and induced a substantial shift in the bacterial communities, but had only moderate effect on the ARG diversity and abundance. The effect of straw return was hindered by the dominant influence of NPK. In comparison, additions of pig manure (M and NPKM) maintained the diversity of bacterial community and significantly influenced the ARG profiles by introducing extra ARGs from pig manure and boosting the soil indigenous ARG members. Manured soils harboured clusters of ARGs and transposase genes which were relatively independent of bacterial phylogenetic lineages, suggesting a strong co-occurrence of ARGs in soil bacteria which may result from horizontal gene transfers (HGT). Our results indicate the importance of HGT in the maintenance of ARG composition in agricultural soils, especially those receiving long-term manure applications. [ABSTRACT FROM AUTHOR]

Upland and paddy soils are two main agricultural land-use types. Differences in the transportation and distribution of root-derived C between these two soil types are of great significance, but given less attention. In the current study, a pot experiment with rhizobox (one root zone and four outer zones) was conducted in a continuous 13 C-CO 2 labelling chamber, cultivating rice (paddy soil) and wheat (upland soil), respectively. 13 C abundances of soil organic carbon (SOC), dissolved organic carbon (DOC), microbial biomass carbon (MBC) and bacterial community composition were measured after labelling. The 13 C atom% of SOC, DOC and MBC was lower in the root zone but higher in non-rhizosphere paddy soil, when compared with the upland soil. Similar amounts of 13 C were recovered in these two soils. In the upland soil, 83.5% of total 13 C was retained in the rhizosphere, while 71.4% in the paddy soil was transported to outer zones. Furthermore, there was a sharp decrease of root-derived C and concomitantly an abrupt succession of bacterial community between the root compartment and outer zones in the upland soil, indicating a narrow extension of wheat rhizosphere. In contrast, more gradual variations in carbon distribution and bacterial community composition were seen in the paddy soil, with a clear evidence of a transition zone. In conclusion, compared with the upland soil, more root-derived carbon is transported from rhizosphere to bulk soil in paddies, which leads to a wider range of rhizosphere and a higher rhizosphere effect. These results are helpful to understand the widely accepted distinctions in soil C stock and productivity sustainability between upland and paddy soils. It may shed light on a new perspective for improving soil fertility, especially in upland cropping systems. [ABSTRACT FROM AUTHOR]

Nematodes play significant roles in carbon and nitrogen biogeochemical cycles in soils. The contributions of individual species to these processes depend, in part, on differences in their population ecology. Formatting errors were discovered that made portions of our previously published work on this subject nearly unintelligible. Herein, we correct those errors. • Nematodes play significant roles in carbon and nitrogen biogeochemical cycles in soils. • The contributions of individual species to these processes depend, in part, on differences in their population ecology. • Formatting errors were discovered that made portions of our previously published work on this subject nearly unintelligible. • Herein, we correct those errors. [ABSTRACT FROM AUTHOR]

Neonicotinoid pesticides are widely used within agroecosystems. Due to their systemic nature and high solubility, neonicotinoids are frequently recorded in soil, water, untreated plant matter and non-target organisms. Studies have demonstrated their capacity to induce invertebrate mortality, however, very little research has been conducted beyond pollinator exposure, particularly under field conditions. Typically, many neonicotinoids are applied via seed-dressings, reducing their direct contact with pollinators, but offering an unintended soil-exposure pathway. Soil biology underpins many vital functions, from regulating water and gas flow, to maintaining physical soil structure. In this study we investigated the effect of a commercial neonicotinoid pesticide (Insyst®) on the abundance, richness, and composition of both the mesofaunal and microbial communities and associated metabolome during oilseed rape (Brassica napus L.) production. Our results showed that over a single growing season, foliar application of Insyst® (250 g ha−1, 50 g ha−1 of the active ingredient, acetamiprid) had no significant effect (P > 0.05) on the measured soil biological indexes. Seasonal variation was a significantly greater driver in regulating biological communities within the soil than Insyst® application. In addition, we showed that the active ingredient (acetamiprid) was rapidly degraded by the soil microbial community (theoretical half-life = 119 days) during the summer cropping season. These results help highlight the need for realistic field studies, as agricultural pesticides are never pure, often containing surfactants, adjuvants, or emulsifiers which alter their behaviour and ecotoxicity. Understanding the biological interactions of vital soil fauna with necessary pesticide usage will enable proper risk alleviation measures to maintain soil biological and ecological health. • Field study of the impact of neonicotinoid insecticide on soil meso- and microbiology. • Application of Insyst® (20% acetamiprid) had no significant impacts on soil biology. • Soil metabolomic function was little affected by insecticide exposure. • Active ingredient (acetamiprid) was rapidly degraded by the soil microbiome. • Seasonal variation is a greater driver of soil ecology than insecticidal compound. [ABSTRACT FROM AUTHOR]

Earthworms are important soil organisms that play critical roles in ecosystem material cycling and energy flows. Discovering and predicting the distribution of earthworm habitats is critical for managing biodiversity conservation projects and improving ecosystem health. However, earthworm data are challenging to obtain, and studies on the distribution of earthworms and factors affecting this have mainly been conducted in fields at a small scale; the spatial distribution of earthworms throughout China remains unclear. Species distribution models have been effectively used in macro-scale species suitability distribution studies; however, they have certain limitations. Thus, here, we optimized the maximum entropy model (MaxEnt) to achieve low complexity and high transferability, and the model was capable of predicting the potential distribution of earthworms in China. Modeling was based on the use of a developed database containing 286 earthworm occurrence records and 31 environmental variables (19 climatic, 9 soil, and 3 topographic variables). Results show that earthworm distribution is mainly controlled by the following environmental variables (with corresponding contribution rates): minimum temperature of the coldest month (18.47%), digital elevation model (17.65%), coarse fragments (16.72%), soil organic carbon (9.65%), soil type (7.53%), mean diurnal range (5.35%), and soil thickness (5.05%). The variables with the strongest influence on distribution are climate followed by landforms and soils. The relationship between the effect of environmental variables and earthworm distribution is not simple and linear, and each element has a certain threshold range. Only 50.67% of the total land area of China provides a suitable habitat for earthworms, and there are remarkable spatial differences. Of the various ecosystems, woodland ecosystems provide most of the suitable habitats, followed by cropland and grassland ecosystems, which together account for 45.74% of the land area. This study can be used as a reference for understanding and assessing ecosystem health, sustainability, and for enabling biodiversity conservation. • Earthworm-suitable habitats were predicted using optimized MaxEnt in China. • Factors influencing earthworm distribution were ranked and thresholds were analyzed. • Climate was more critical in changing earthworm habitats than topography and soil. • Area of suitable habitat for earthworms was 50.67% of the total land area. • Woodland and cropland ecosystems provide most of the suitable habitats for earthworms. [ABSTRACT FROM AUTHOR]

Exotic peregrine earthworms are often considered to cause environmental harm and to have a negative impact on native species, but, as ecosystem engineers, they enhance soil physical properties. Pontoscolex corethrurus is by far the most studied morphospecies and is also the most widespread in tropical areas. The term of morphospecies is used in this review because P. corethrurus may in fact constitute a complex of cryptic species. This earthworm is found in a wide range of habitats, from apparently pristine to any kind of human-disturbed environment. This review synthesizes 265 studies describing the distribution, morphology, biological and ecological traits of this morphospecies, as well as its impacts on soil conditions and communities. We then discuss the characteristics necessary for this specific morphospecies to become a successful colonizer throughout the world and the positive and negative effects it can have on the ecosystems that it has invaded. We emphasize the lack of knowledge of P. corethrurus reproductive mode and ploidy level, of its population genetics, and of the potential existence of cryptic species. To finish, we highlight the fact that data on P. corethrurus interactions with non-earthworm soil macrofauna are scarce. [ABSTRACT FROM AUTHOR]

Arid ecosystems are characterized as having stressful conditions of low energy and nutrient availability for soil microorganisms and vegetation. The rhizosphere serves as the one of most active microorganism habitats, however, the general understanding of the ecoenzymatic stoichiometry (exoenzymes) and microbial nutrient acquisition in rhizosphere soil is limited. Here, we investigated the vegetation communities and determined the soil physicochemical properties, microbial biomass, and enzymatic activities in rhizosphere under different vegetation and soil types in the arid area of the northern Loess Plateau. Type Ⅱ standard major axis (SMA) regression analysis showed that the plants played a more important role than soil properties in determining ecoenzymatic stoichiometry. Linear regression analysis displayed a microbial stoichiometric homeostasis (community-level) in rhizosphere. The Threshold Elemental Ratio (TER) revealed that the microbial nutrient metabolisms of rhizosphere were co-limited by N and P in the A. ordosica and A. cristatum communities of loess, and A. cristatum communities of feldspathic sandstone weathered soil. Binding spatial ordination analysis (RDA and CCA) demonstrated that soil physical properties (e.g., soil moisture, silt and clay contents) have more contribution to ecoenzymatic stoichiometry than the other investigated soil parameters, whereas soil nutrients (e.g., total organic carbon, nitrogen, and phosphorus) predominantly controlled microbial nutrient ratios. Therefore, the ecoenzymatic stoichiometry in rhizosphere is greatly regulated by plants and soil physical properties. The microbial N and P are co-limited under Gramineae plant in loess and feldspathic sandstone weathered soil regions. Meanwhile, the microbial nutrient limitation is mainly affected by soil nutrient supply. These findings could be crucial for illuminating rhizosphere microbial metabolism and revealing the nutrient cycling of root-soil interface under arid and oligotrophic ecosystems. [ABSTRACT FROM AUTHOR]

Input of plant material may strongly change decomposition rates of soil organic matter (SOM), i.e. causing priming effect (PE), but the underlying mechanisms are largely unknown. We found that rice straw addition in anoxic Fuyang (F) rice field soil stimulated CH 4 production from SOM at the expense of CO 2 , whereas in Uruguay (U) soil it suppressed SOM degradation to CO 2 plus CH 4 (negative PE). Reciprocal inoculation experiments with non-sterile and sterile soils showed that the soils always displayed the effect of rice straw characteristic for the live microbial community rather than for the soil physicochemical properties. Pyrosequencing of 16S rRNA genes showed that bacterial communities in these soil samples were separated into two clusters (F and U). Symbiobacterium was abundant or dominant in microbiota from U soil, but negligible in those from F soil. Network analysis indicated that the bacterial populations involved in SOM decomposition were different between soils of F and U clusters; moreover, they were more tightly connected to methanogens in U than in F clusters. Ultimately, our results suggested that the PE of rice straw is mediated by the composition and activity of soil microbial community. [ABSTRACT FROM AUTHOR]

Dispersal capacities can strongly determine an individual's ability to respond to changing environmental conditions, which would consequently influence the structure of natural communities. Nonetheless, we know little about the dispersal behaviour of soil organisms, despite some of these organisms, such as earthworms, have key roles in ecosystem functioning (e.g. organic matter decomposition). We expect that species exposed to frequent environmental changes would benefit from the capacity to escape from adverse environmental conditions and to disperse to settle in a more suitable habitat. In earthworms, we expect the epigeic group, which lives at or close to the soil surface, to have evolved higher dispersal capacities than the two other functional groups – anecic and endogeic, which live deeper in the soil. In this study, we investigated dispersal and diffusion behaviour of three species of epigeic earthworms (i.e. Eisenia fetida , Eisenia andrei and Lumbricus rubellus ) and compared these behaviours with those of anecic and endogeic earthworms, whose behaviour has been previously measured through similar experiments. In accordance with our hypothesis, our study shows that dispersal behaviour of epigeic earthworms depends on habitat quality and population density, but that those responses vary among species and that it differs only to a limited extent from behaviour of anecic and endogeic earthworms. [ABSTRACT FROM AUTHOR]

Explaining the variation in communities of soil organisms across plant communities or ecosystems remains a major challenge for ecologists. Several studies have explored how soil communities are affected along ecosystem successional gradients but most of these are based on relatively short term chronosequences. To address the impact of ecosystem age on micro-arthropod communities, we utilized a 5000 year old post-fire chronosequence, which consists of thirty lake islands differing greatly in time since fire in the boreal forested zone of northern Sweden. The Acari community did not change along this chronosequence, indicating that Acari rapidly (<60 yr) reach equilibrium after forest fire and that they are relatively unresponsive to subsequent long term changes in plant community composition and soil quality. The Collembola community composition, however, showed greater responsiveness to the chronosequence and this was best explained through their functional traits. Notably, the youngest (most recently burned) islands, which had the highest ecosystem productivity and fungal mass turnover, were dominated by soil-dwelling (eu-edaphic) Collembola species that are best positioned to take advantage of resource input to the soil. Although plant community characteristics did not emerge as powerful drivers of the Collembola community, we found that Collembola community composition was related to the quality (N and P) of the soil substrate, which reflects a long term legacy of the plant community. Collembola life history characteristics proved to be important for understanding how abundances of different taxa varied relative to one another across the gradients of plant diversity and substrate quality gradients that occur across long-term chronosequences. The causal connection between vertical stratification of Collembola and substrate quality is at present unclear but is likely to be related to their feeding preferences and microhabitat conditions. Because the soil-dwelling Collembola showed a strong decline in abundance with ecosystem retrogression while surface-dwelling Collembola did not these two life history groups may operate as functionally distinct groups within the soil food web across these long-term chronosequences. [ABSTRACT FROM AUTHOR]

Peatlands store large amounts of soil organic carbon (SOC). Drainage, required for agriculture, aerates these organic soils and triggers rapid peat decomposition. In turn, cultivation of organic soils is also accompanied by input of young organic carbon (YOC) from plant residues. The extent to which YOC inputs compensate for oxidative peat loss is unknown. Furthermore, the lability of YOC in organic soils introduced by cultivation has never been examined. Here we studied the amount and lability of YOC in two adjacent drained organic soils by a combined 13 C and 14 C approach. Soils have been under intensive arable use for several decades and were both cultivated, inter alia, with corn, a C4 plant. In 1995, one soil was converted from annual cropping to permanent cultivation with Miscanthus x giganteus , another C4 plant, while the other was converted to permanent C3 grassland in 2009. Using δ 13 C signatures, we analysed the fractions of C4 derived carbon in the soil and in CO 2 , during one month of soil incubation. This enabled us i) to estimate C4-C accumulation in both soils, and ii) to assess the lability of C4-C carbon that accumulated either at least five years prior to sampling (current grassland soil) or until sampling (current Miscanthus soil ). The fraction of C4-C derived SOC in the Miscanthus soil was 0.19 ± 0.024 in the top 30 cm, corresponding to an accumulation rate of 1.6 ± 0.2 t C4-C ha −1 yr −1 . This accumulation rate is in the range of rates found for fertile mineral soils cultivated with Miscanthus . Yet, this C4-C accumulation rate is below average C-losses of agriculturally used organic soils. The grassland soil contained a smaller fraction of 0.08 ± 0.002 C4-C in SOC. The rates of total CO 2 emitted from the two soils did not differ, but the fraction of CO 2 derived from C4-C was significantly higher in the Miscanthus soil (0.53 ± 0.05) than in the grassland (0.29 ± 0.04) soil. Hence, in both soils YOC was more labile than bulk SOC. The ratio between the fraction of decomposing C4-C and C4-C in SOC was the same for both soils indicating a similar lability of currently accumulated and aged C4-C. In both soils, the 14 C age of emitted CO 2 was younger than that of SOC, confirming an increased lability of YOC over old SOC. [ABSTRACT FROM AUTHOR]

In this study, we investigated how rhinoceros beetle larvae influence the soil bacterial community in terms of temperature. Soils with and without larvae were incubated at 17 °C, 20 °C and 23 °C for 10 weeks. At the end of the experiment, the larvae developed to adults at 23 °C, while their developmental stages were larvae and pupae at 17 °C and 20 °C, respectively. Soil C, N and P content increased in the presence of larvae. Pyrosequencing data revealed that the presence of larvae decreased the relative abundance of Proteobacteria and Acidobacteria and increased that of Actinobacteria and TM7. Principal coordinates analysis also showed a clear difference in bacterial community between plots with and without larvae while plots with larvae differed by temperature. Non-metric dimensional scaling analysis revealed that N content is the main factor that determined the effect of the treatment. In plots with larvae, the relative abundance of Dyella , Gryllotalpicola and Rhodanobacter increased greatly, thus suggesting that these genera might play a role as gut bacteria. The abundance of Telmatobacter and Gaiella increased at 23 °C compared with 17 °C in plots with larvae. Therefore, these genera might be inferred to have benefitted from frass decomposition and temperature increase. The abundance of Rhizomicrobium , Dongia and Koribacter decreased in the presence of larvae. Plots with larvae presented 41.2% less bacterial operational taxonomic units than those without larvae. Our results suggested that the presence of larvae influences the soil bacterial community's composition and diversity through frass deposits and gut bacteria. We clearly indicated that temperature exerts both positive and negative effects on some bacterial groups through changes in larval development. We show that temperature can fundamentally shift the time period of biological processes performed by soil organisms and material input. [ABSTRACT FROM AUTHOR]

Temperature is an important factor governing the community traits of N 2 O-emission related functional guilds (mainly autotrophic ammonia oxidizers and heterotrophic denitrifiers) and their activities. However, there have been few attempts to explore the broad response patterns of these guilds to temperature changes across arable soils. For this, a temperature-controlled (15, 25 and 35 °C) microcosm experiment was conducted using three arable soils (Fujian, Gansu, and Jiangsu) in China under two different fertilizations (no fertilization control (CK) and inorganic fertilization (NPK)). In conjunction with the measurement of N 2 O emission, the community structure and abundance of ammonia oxidizing archaea (AOA) and bacteria (AOB), as well as nirS - and nirK -denitrifiers were assessed using T-RFLP and quantitative PCR, respectively. The analysis of community traits indicated a consistent response pattern of AOAs to temperature in terms of guild abundance, and a consistent effect of inorganic fertilization on the abundance of AOBs, but soil-dependent response patterns to fertilization and temperature were found for nirS - and nirK -denitrifiers in terms of abundance and community structure. The correlation analysis suggested that AOAs possibly assumed a role in N 2 O emission in all the tested soils, and nirS -denitrifiers probably participated in N 2 O emission in both the Fujian and Gansu soil, while a considerable amount of N 2 O emission in the Jiangsu soil might have been derived from heterotrophic nitrification. [ABSTRACT FROM AUTHOR]

15 N 2 has played a crucial role in fundamental studies of biological N 2 fixation. However, due to operational constraints, it has more often served as a qualitative rather than a quantitative tracer of biologically-fixed N (BFN). Therefore indirect methods based either on 15 N-enrichment or 15 N-natural abundance have assumed a dominant role in quantifying N cycle processes involving BFN. However, it is only through the direct 15 N 2 approach that biological N 2 fixation can be traced through the various components of the soil-plant system. Technological advances in the automated control of the chamber environment have made the 15 N 2 technique more attractive to long-term studies. Thus the need to enclose plants in a chamber and maintain conditions conducive to plant growth should no longer be seen as a major obstacle to the use of 15 N 2 . The way is now open to evaluate the efficacy of indirect methods used to estimate the contribution of BFN to the N economies of crop and pasture systems, and the dynamics of BFN in agroecosystems. In addition, new applications of 15 N 2 such as stable isotope probing are emerging, which have the potential to characterize non-cultivated diazotrophs in a range of environments. The role of biological N 2 fixation in the formation of reactive N in the environment and its relationship with the emission of the greenhouse gas N 2 O requires further investigation. [ABSTRACT FROM AUTHOR]

Lack of dissolved organic carbon (DOC) is generally one of the key factors limiting denitrification in subsoil beneath the root zone. Despite a number of laboratory DOC amendment studies, the effects of in situ DOC infiltration on subsoil denitrification, and on subsequent end product composition, are less understood. Here, we report on the effects of in situ infiltration of a DOC-rich liquid, derived from decomposing straw, on potential denitrification rate (PDR), N 2 O/(N 2 O + N 2 ) product ratio, and nitrate stock in a 0–2 m soil profile. The results showed that in situ infiltration with a DOC-rich liquid (100 mm, 2 ton DOC ha −1 ) significantly increased the DOC concentration and PDR, and significantly decreased the N 2 O/(N 2 O + N 2 ) product ratio in the soil profile. Up to 70% of the nitrate accumulated in the 0–2 m soil profile disappeared within three weeks following the infiltration of the DOC-rich liquid. The majority of the nitrate removed could be accounted for by denitrification. The predominant end product of denitrification was N 2 . The mass ratio between the consumed DOC and nitrate-N was about 5. Our results demonstrate the significant potential for removing subsoil nitrate by in situ introduction of DOC generated from the above-ground crop biomass. [ABSTRACT FROM AUTHOR]

Ammonia oxidising archaea (AOA) are an abundant and ubiquitously distributed group of soil microorganisms and contribute significantly to nitrogen cycling processes. Soil pH has been identified as a major driver of AOA diversification, but other environmental factors may also be important. The aim of this study was to determine whether soil pH also influenced the temperature range of AOA activity in soil. This was assessed by determining rates of ammonification and net nitrification, and AOA abundance and community composition during incubation of soils with pH in the range 3.6–7.5 at 20, 30 or 40 °C for 30 days. Net nitrification was greatest at 20 or 30 °C, with variation in optimal temperature between soils, net nitrification was not detectable at 40 °C, and mineralisation was greatest at 40 °C. AOA community composition differed following incubation at 20° and 30 °C, presumably through selection and growth of populations with different temperature optima, and, at 40 °C, due to cell death. There was no significant relationship between thaumarchaeotal cell abundance and yield estimated using amoA and 16S rRNA genes, possibly due to amplification of 16S rRNA genes of non-ammonia-oxidising Thaumarchaeota. However, amoA gene abundance and yield were greater at 20 °C than 30 °C in the most acidic soils, with the opposite relationship for the most neutral soils. This is consistent with cultivated lower temperature optima for neutrophilic, rather than acidophilic soil AOA. The results indicate that pH-driven diversification may have consequences for other aspects of AOA physiology including temperature optima for growth and activity in the environment. [ABSTRACT FROM AUTHOR]

Theory and experiments suggest that rhizodeposition can accelerate N-cycling by stimulating microbial decomposition of soil organic matter (SOM). However, there are remarkably few experimental demonstrations on the degree to which variations in root exudation alter rhizosphere N dynamics in the field. We conducted a series of in situ substrate addition experiments and a modeling exercise to investigate how exudate mimics and enzyme solutions (at varying concentrations) influence rhizosphere SOM and N dynamics in a loblolly pine ( Pinus taeda ) plantation (Duke Forest). Exudates were added semi-continuously to unfertilized and fertilized soils in summer and fall; enzymes were added during the following summer. Exudate additions enhanced the microbial biomass specific activities of enzymes that degrade fast-cycling N pools (i.e., amino acids and amino sugars), and increased microbial allocation to N-degrading compounds. More, such effects occurred at low exudate concentrations in unfertilized soil and at higher concentrations in fertilized soil. Direct additions of a subset of enzymes (amino sugar- and cellulose-degrading) to soils increased net N mineralization rates, but additions of enzymes that cleave slow-cycling SOM did not. We conclude that exudates can stimulate microbes to decompose labile SOM and release N without concomitant changes in microbial biomass, yet the investment of plants to trigger this effect may be greater in N-rich soils. [ABSTRACT FROM AUTHOR]

Atmospheric carbon dioxide enrichment (eCO 2 ) often increases soil nitrous oxide (N 2 O) emissions, which has been largely attributed to increased denitrification induced by CO 2 -enhancement of soil labile C and moisture. However, the origin of the N remains unexplained. Emerging evidence suggests that eCO 2 alters plant N preference in favor of ammonium (NH 4 + -N) over nitrate (NO 3 − -N). Yet, whether and how this attributes to the enhancement of N 2 O emissions has not been investigated. We conducted a microcosm experiment with wheat ( Triticum aestivum L.) and tall fescue ( Schedonorus arundinaceus (Schreb.) Dumort.) to examine the effects of eCO 2 on soil N 2 O emissions in the presence of two N forms (NH 4 + -N or NO 3 − -N). Results obtained showed that N forms dominated eCO 2 effects on plant and microbial N utilization, and thus soil N 2 O emissions. Elevated CO 2 significantly increased the rate and the sum of N 2 O emissions by three to four folds when NO 3 − -N, but not NH 4 + -N, was supplied under both wheat and tall fescue. While enhanced N 2 O emission was more related to the reduced plant NO 3 − -N uptake under wheat, it concurred with increased labile C under tall fescue. In the presence of NO 3 − -N, significantly lower shoot biomass N and 15 N, but higher plant biomass C:N ratio, microbial biomass C and N, and/or soil extractable C indicated that eCO 2 constrained plant NO 3 − -N utilization and likely stimulated root exudation. We propose a new conceptual model in which eCO 2 -inhibition of plant NO 3 − -N uptake and/or CO 2 -enhancement of soil labile C enhances the N and/or C availability for denitrifiers and increases the intensity and/or the duration of N 2 O emissions. Together, these findings indicate that CO 2 -enhancement of soil N and labile C favors denitrification, suggesting that management of N fertilizers in intensive systems will likely become more challenging under future CO 2 scenarios. [ABSTRACT FROM AUTHOR]

The changes to soil properties due to biochar addition may affect both the direction and magnitude of priming effects. However, the mechanisms involved in biochar induced priming effects still remain largely unknown due to the limitation of methods to separate more than two carbon (C) sources (e.g. soil, biochar, substrate). We combined 14 C labeling with 13 C natural abundance to separate the total CO 2 from i) native soil organic C (SOC, C 3 signature), ii) added glucose ( 14 C labelled) and iii) biochar (C 4 signature). The primed soil CO 2 emissions following a large addition of glucose (1000 mg glucose kg −1 soil) to one Chinese and one German Luvisol soil were much larger (140% and 53% respectively) in a soil recently amended with maize derived biochar (pyrolyzed at 400 °C), compared to non amended soil. Glucose addition at a lower rate (100 mg C kg −1 soil) produced no significant differences in priming effects of native soil organic matter between the biochar amended and non-amended soils. Glucose also caused priming of biochar decomposition, with an additional C 4 biochar loss of between 270 μg CO 2 -C g −1 and 540 μg CO 2 -C g −1 depending on soils and glucose concentrations. Approaches using two stable isotopes ( 13 C and 12 C) have previously been limited to partitioning two sources (biochar C and soil organic C). Here, for the first time, 14 C labeling was combined with 13 C natural abundance to partition three C sources in a biochar amended soil. By partitioning soil CO 2 emissions derived from SOC, added biochar and glucose decomposition, this study provides a better understanding of the priming effects following addition of substrates to biochar amended soil, to approximate to the true complexity of biochar enriched soils. [ABSTRACT FROM AUTHOR]

Quantitative real-time PCR (qPCR) analysis for accurate quantification of targeted microbial genes is compromised by the presence of co-extracted inhibitors from soil samples. Dilution of DNA extracts is a commonly-used method to reduce levels of inhibition. However, the applications of dilution method are mostly empirical, and need to be further elaborated. Here, we propose a dilution model to re-evaluate dilution as a method to eliminate qPCR inhibition. We found that DNA extracts without dilution or with a minor dilution (e.g., 10-fold) resulted in qPCR inhibition for most of studied soils. However, excessive dilution (e.g., 200- or 400-fold) caused an overestimation of the quantified gene copy numbers. Only under a moderate dilution range could qPCR inhibition be efficiently eliminated, which has been well captured by our proposed dilution model. The pre-testing of qPCR inhibition for determining the appropriate dilution range for extracted DNA samples aids accurate quantification of nucleic acids in soils. [ABSTRACT FROM AUTHOR]