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Gut microbiota are determined by both the food ingested and physiological conditions of the host. In soil food webs, detritivore animals occupy various trophic niches, spanning from primary decomposers to predators. However, the relative contribution of food resources and species attributes of consumers to gut microbial communities in soil detritivores has not yet been explored. In this study, we investigated gut bacteria and fungi of oribatid mites (Oribatida, Acari), ubiquitous and diverse soil microarthropods feeding on a variety of food resources, to uncover the contribution of host phylogenetic relatedness and trophic niches to the assemblages of gut microbiota. Abundance and community composition of bacteria and fungi were characterized by qPCR and Illumina sequencing, respectively. Gut bacterial communities were more closely correlated with host phylogenetic affinity, whereas gut fungal communities were more closely correlated with the trophic niches of the host. Community phylogenetic analysis suggests that deterministic processes predominated in the assembly of both bacterial and fungal communities in most of the studied oribatid mite species. Integrating phylogenetic distance and trophic niche distance of hosts resulted in the highest correlation coefficients between host species and their gut microbial communities suggesting that both evolutionary history and current trophic niches shape gut microbial communities. Bacteria in the gut may comprise commensals or mutualists facilitating digestion which potentially coevolved with the host, while the fungal community in the gut reflects the trophic niches of the consumer likely suggesting that they form part of the diet and serve as food resources of soil detritivore microarthropods. [ABSTRACT FROM AUTHOR]

Even though organic fertilization is known to promote soil nitrogen cycling ( N -cycling), it is unclear how this effect is mediated. Here we studied the potential roles of soil physiochemical properties and soil particle-size fraction (PSF) in relation to the diversity and abundance of N -cycling-related prokaryotes by sampling field sites that had been subjected to either mineral or organic fertilization for over 30 years (two independent fields subjected to both fertilization treatments). We found that organic fertilization increased the 63–200 μm sized soil fraction and the abundance of various N -cycling-related prokaryotes including diazotrophs, ammonia-oxidizers and denitrifiers. Moreover, increase in the abundance of different N -cycling-related prokaryotes varied between different size fractions: the abundance of ammonia-oxidizers and nitrate-reducers was the highest in the 63–200 μm size fraction, while the abundance of diazotrophs, ammonifiers and denitrifiers was the highest in the 200–2000 μm, 2–63 μm and 0.1–2 μm size fractions, respectively. According to structural equation modelling (SEM), soil PSF, physiochemical properties and the community structure of N -cycling-related prokaryotes within different PSFs were associated with the abundance of N -cycling-related prokaryotes in non-fractionated bulk soils. In conclusion, these results suggest that organic, but not mineral, fertilization can support the abundance of N -cycling-related prokaryotes and that the strength of the effects depends on their association with specific particle-size fractions. [ABSTRACT FROM AUTHOR]

Abstract: Plant-mediated effects of aboveground herbivory on the belowground ecosystem are well documented, but less attention has been paid to agro-ecosystems and in particular how crop cultivars with different traits (i.e. resistance to pests) shape such interactions. A fully factorial experiment was conducted using four rice cultivars with different insect-resistance, with and without the aboveground herbivore Nilaparvata lugens (brown planthopper), and to test two hypotheses (1) aboveground herbivory affects the soil microbial biomass and nematode community by altering plant performance and soil resource availability and (2) herbivory effects will depend on cultivar resistance traits. Our results suggested that cultivar resistance mediated both herbivory intensity and herbivore effects on plant performance. N. lugens decreased the availability of soil resources (soluble sugars, amino acids, organic acids, dissolved organic carbon and nitrogen), microbial biomass and percentages of bacterivores when feeding on a susceptible cultivar but increased them in a resistant cultivar. However, total nematode abundance and the percentage of plant-parasitic nematodes responded in the opposite way, increasing under a susceptible cultivar and decreasing under a resistant cultivar. The development of plant-parasites under resistant cultivars before aboveground herbivory might contribute to their resistance traits. Our findings provide evidence that N. lugens significantly reversed the pattern of soil resource availability, microbial biomass and nematode community structure (abundance and trophic composition) across cultivars with distinct resistance. In the presence of aboveground pests, the agronomic use of resistant rice cultivars could also control populations of plant-parasites and promote soil resource availability, further extended to higher trophic level of soil food web. [Copyright &y& Elsevier]

Biodiversity can enhance soil multifunctionality through strengthening biotic interactions in soil food webs, but largely unknown in agroecosystems. We therefore predicted that vermicompost, serving as an organic amendment and soil health conditioner, could enhance trophic interactions among bacteria, fungi and nematodes and mediate synergies and trade-offs among soil functions, especially when substituting synthetic fertilizer was applied to soils. Soil multifunctionality was assessed from plant growth and product quality, carbon and nutrient cycling, water and climate regulation in an intensive cropping system. Pepper, tomato and spinach were cultivated in rotation annually, with substituting vermicompost as a nutrient replacement for synthetic fertilizer for 5 years. Results showed that substituting a moderate dose of vermicompost for synthetic fertilizer offered the highest soil multifunctionality by enhancing synergies among multiple functions. The vermicompost-stimulated multifunctionality was primarily attributed to the cascading effects of the complex food web structure induced by omnivorous nematode. These effects were regulated by the physicochemical environment of the vermicompost-amended soil. Notably, the multifunctional benefits degraded when higher rates of vermicompost were applied, suggesting that over-use of vermicompost combined with an inadequate amount of synthetic fertilizer could simplify soil food web structure and decrease soil functions, mainly due to the nutrient limitation and increasing harmful substances as indicated by C:N stoichiometry, heavy metals and antibiotic resistance genes. In intensive agricultural systems, finding an optimal balance of organic amendments and synthetic fertilizer that supports complex soil food web interactions is therefore crucial for promoting multiple soil functions and particularly sustaining the production of high-quality food crops. • The highest soil multifunctionality was observed in moderate vermicompost substitution. • Moderate vermicompost addition enhanced synergies among multiple functions. • Soil food web structure coordinated by omnivores was associated with multifunctionality. • Vermicompost supported multifunctionality of ecologically intensive agriculture. [ABSTRACT FROM AUTHOR]

Global change in organismal stoichiometry and biodiversity is often correlated with energy dynamics in ecological networks that underpin the functioning of terrestrial ecosystems and services. However, we know little about which facets of biodiversity, such as taxonomic, functional, and phylogenetic diversity, account for most of the variation in the energy dynamics of ecological networks along litter stoichiometry gradients. Here, we quantified how multiple facets of biodiversity impact energy fluxes of soil food webs through time in agricultural fields incorporating litter from six plant species of varying C:N stoichiometry. We found that community biomass and energy flux in soil food webs decreased while community maintenance cost (i.e. energy flux to biomass ratio) increased with increasing litter C:N ratio. Taxonomic, functional, and phylogenetic diversity of soil nematodes declined along increasing litter C:N stoichiometry, and together explained 73 % and 51.3 % of variation in community biomass, 71.6 % and 49.2 % of variation in energy flux, and 59.8 % and 37.4 % of variation in community maintenance cost in early and later decomposition stages, respectively. Functional and taxonomic diversity were highly associated with energy dynamics in early decomposition stages, while phylogenetic diversity emerged as the central predictor in later decomposition stages. By identifying the crucial role of multi-faceted biodiversity conservation facilitated by low C:N litter in driving the energy dynamics of food webs, these findings shed new light on the applicability of energy dynamics for linking biodiversity and ecosystem functioning under global change scenarios. • Energy storage, flux and use efficiency decrease with increasing litter C:N ratio. • Multi-faceted biodiversity correlates with energy storage, flux and use efficiency. • The importance of biodiversity facets to energy dynamics differs over time. • Energy dynamics underpins biodiversity-ecosystem functional relationships. [ABSTRACT FROM AUTHOR]

Abstract: The influence of earthworms on nematodes and protozoan communities was determined during the wheat phase of a six year rice–wheat rotation agro-ecosystem. Experimental plots in the rotation had five treatments, i.e. incorporation or mulching of maize residues with or without added earthworms and a control. The addition of maize residues to soil strongly affected the abundance and community structure of nematodes and protozoa in the absence of earthworms. The presence of earthworms gave significantly lower total nematode numbers at all soil depths following maize residue incorporation than the same treatment without earthworms, and also gave lower (although not significantly) total nematode numbers in the upper soil layer following maize residue mulching than the same treatment without earthworms. This was mainly due to a significant decrease in bacterial-feeding nematode numbers. Earthworms also strongly affected the distribution of the number of total nematodes and two trophic groups (bacterial and plant feeders) with soil depth. In the presence of earthworms, total protozoan and flagellate numbers significantly increased at all soil depths following both incorporation and mulching of maize residues, while numbers of amoebae increased only when maize residues were mulched. Additionally, in earthworm casts total nematode numbers (mainly bacterial and fungal feeders) were significantly higher, whereas total protozoa numbers (mainly flagellates and amoebae) were significantly lower than that in soil from 0 to 5cm layer. These results indicated that earthworm activity could affect the abundance and community structure of microfauna, and change their distribution between soil layers and cast material, depending on the mode of application of organic residues. [Copyright &y& Elsevier]

Urbanization is threatening terrestrial biodiversity and ecosystem functions. Nematodes, as one of the most abundant animals on Earth, play diverse roles within soil food webs and contribute to vital ecosystem services. However, the effects of urbanization on soil nematode functional groups, and the ecological functions and services they provide remain poorly understood. Here, we investigated functional groups of soil nematodes across 12 cities in China and validated the results by using a global nematode dataset. Specifically, we found the proportions of omnivores (by 45∼60%) and predators (by 40∼50%) as well as temporal ecosystem stability (by 10∼20%), as indicated by the normalized difference vegetation index, were reduced in urban ecosystems, while the proportions of fungivores and bacterivores increased (30–60% and 10–20%, respectively). We identified total soil phosphorus and nitrogen as the main drivers influencing soil nematode feeding groups in urban ecosystems. Soil pH, mean annual precipitation, and mean annual temperature were predominant factors in non-urban ecosystems. We further demonstrated that nematode functional guilds contributed to ecosystem stability in urban ecosystems, but this was not true in non-urban ecosystems. Our findings evidence the homogenization effects of urbanization on key functional guilds of soil nematodes and their roles in maintaining ecosystem stability. The fact that ecosystem stability and the abundance of nematode functional guilds are closely related and driven by climatic, edaphic, and anthropogenic factors may help in setting priorities for urban soil management. • Temporal stability was reduced in urban soils. • Omnivores and predators were decreased in urban soils. • Total soil phosphorus and nitrogen were the main drivers of urban nematodes. • Soil nematodes contributed to ecosystem stability in urban ecosystems. [ABSTRACT FROM AUTHOR]

Abstract How plants cope with herbivore attack is partially modulated by the biotic and abiotic environment where the plant lives. For instance, theory predicts that soil fertility should drive patterns of plant resource allocation and defensive strategies. Earthworms, by their burrowing and casting activities, modify soil physicochemical properties and soil fertility. Therefore, earthworm-mediated changes in soil properties could alter plant physiology, plant nutritional quality, and ultimately, plant resistance against insect herbivores. We tested this hypothesis by measuring the combinatorial effects of two earthworm species, an epi-endogeic earthworm (Amynthas corticis) and an endo-anecic earthworm (Metaphire guillelmi), on soil properties, tomato plants' physiological traits and plant resistance against the western flower thrips (Frankliniella occidentalis). We found that A. corticis alone increased plant resistance more than M. guillelmi alone or the combination of two species. The increased plant resistance was associated with a significant increase in the defence-related phytohormone jasmonic acid and the production of phenolic compounds. Furthermore, we observed a strong link between earthworm-mediated changes in soil properties and plant eco-physiological traits. Our results thus build toward a better predictive model of how earthworms can simultaneously influence soil parameters, plant productivity and resistance against herbivore pests. Highlights • Earthworms positively affected soil properties and then induced changes in plant chemistry. • Earthworm single-species inoculations increased plant resistance more than dual-species inoculations. • Earthworm dual-species inoculations increased more plant nutrients instead of chemical defences. • Earthworm Amynthas corticis suppressed thrips abundance on tomato plants. [ABSTRACT FROM AUTHOR]

Nutrient amendment increases plant productivity but the effects and mechanisms on soil organic carbon (SOC) accumulation and stability remain unclear, especially in nutrient deficient alpine ecosystem. Here, based on an experiment combining nitrogen (N) and phosphorus (P) input continuously for 15 years, we found that nutrient amendment did not affect total SOC content, but increased mineral-associated C with decreasing soil aggregate stability. Despite increased total phospholipid fatty acid (PLFA) and bacteria PLFA, nutrient amendment decreased soil enzyme activities involved in C cycling. The 13C NMR analyses showed that nutrient amendment decreased the aliphaticity but enhanced aromaticity of SOC. Structural equation models indicated that P availability (Olsen-P content) was most related to shifts in microbial community composition and decreased enzyme activities. Moreover, the concomitantly reduced aggregation and increased mineral-associated C were mainly attributable to the decrease of fungal biomass and increase of bacterial biomass. Together, interconnected factors such as increased acidity, aggregate destabilization, microbial community shift towards bacteria, and loss of oxidative enzyme activities could contribute to the overall response of SOC under intensive N and P input. In particular, available P rather than N may re-shape the pattern of physical and chemical stabilization of SOC, shifting from moderately physical protection to highly chemical stability, implicating the pivotal roles of P management in C cycling of alpine ecosystem. Graphical abstract Image 1 Highlights • Nutrient (nitrogen and phosphorus) amendment decreases soil aggregate stability. • Nutrient amendment increases mineral-associated C and SOC aromaticity. • SOC chemical stability was mainly controlled by P availability via microbial composition. • Nutrient enrichment leads to bacteria-dominated microbial community. [ABSTRACT FROM AUTHOR]

Drought events are increasingly affecting the planet's biodiversity. While shrinking body size in response to drought has been observed in many vertebrate animals, whether this rule applies to microscopic animals and the mechanisms during this process remains largely unknown. To address this knowledge gap, we conducted a regional-scale investigation and a microcosm experiment to systematically evaluate the impact of drought stress on the body size of the most abundant soil animals on Earth – nematodes – across various biological scales, including community, population and individual levels. Our results showed that nematode body size declined with drought stress at all biological scales, including a community shift toward smaller-sized species, a smaller body size at the population scale, and a decrease in size-at-age of individuals. Additionally, we designed a Petri dish experiment to examine the reversible plasticity of body size under drought stress using a drought-tolerant nematode species. We found that while nematode body size could not be fully reversed when drought stress was alleviated in the offspring generation, offspring from parents that experienced severe drought conditions could acquire tolerance, leading to a relatively smaller reduction in overall body size compared to those from parents that suffered no or light drought conditions. Overall, our study suggests that the increasing frequency of drought events at the global scale will lead to a reduction in soil nematode body size, potentially causing far-reaching consequences for additional changes in the climate, as well as nutrient cycling in soils. • Nematode body size declined with drought stress at all biological scales. • Drought shifted nematodes to smaller body size across the community. • Body size cannot be fully reversed when drought stress was alleviated. • Drought-induced size-shift reduces the metabolic footprint of soil nematodes. [ABSTRACT FROM AUTHOR]

The soil microbial food web plays a vital role in soil health, nutrient cycling and agricultural productivity. Notably, there is a distinct paucity of information regarding the effects of heavy metal contamination on trophic-level interactions within the microbial food web of agricultural soils, which experience appreciably metal contamination worldwide. Herein, we investigated trophic interactions among predators (protists), their preys (bacteria and fungi) and competitors (nematodes) under four metal contamination levels using high-throughput sequencing and a laboratory verification experiment. Metal contamination decreased growth of protist-preferential prey (e.g., small-sized and gram-negative bacteria), increased the growth of protist-nonpreferential prey (e.g., pathogenic fungi and Actinobacteria), and had a limited effect on the soil protist-competitor (i.e., nematodes). This resulted in a considerable decrease in the diversity and abundance of protistan consumers and a re-arrangement of their interactions with other organisms. From a systemic view, the direct link was weaker between heavy metal contamination and the protist community than the indirect linkage, i.e., metal-induced changes in the prey community. We further validated these results with laboratory incubation trials that documented growth inhibition of protist (Colpoda) and protist-preferential prey (Spingomonas) versus growth stimulation of protist-nonpreferential prey (Arthrobacter) under metal contamination. These findings indicate that metal contamination collapses trophic-level interactions within the soil microbial food web via bottom-up regulation, providing important implications for managing trophic interactions to maintain agricultural ecosystem services under the challenge of worldwide metal contamination. [Display omitted] • Heavy metals increased bacteria/fungi diversity but decreased protist diversity. • Heavy metals impacted trophic interactions by bottom-up control. • Feeding preference of protist is the mechanism that triggered the cascade effects. [ABSTRACT FROM AUTHOR]

Soil multifunctionality is the consequence of biotic interactions that drive decomposition, nutrient cycling and net primary production. Energy flux describes the energy consumed and transferred among multitrophic groups in the soil food web, which are logically linked to multifunctionality. In a subtropical agroecosystem with an annual sweet potato-oilseed rape rotation, we explored how biochar and synthetic fertilizer jointly affected agroecosystem multifunctionality (e.g., crop production, soil carbon storage and nutrient cycling) and the energetic structure of the nematode food web during two consecutive years. Results showed that biochar increased soil multifunctionality by 37–110% mainly by promoting a uniform energy flow through the soil nematode food web, which was largely due to increased energy fluxes of fungivores and omnivores-carnivores at the expense of decreased energy flux through herbivores. Applying a lower rate of synthetic fertilizer led to non-uniform energy flow in the soil nematode food web, suggesting that nitrogen limitation could offset the stimulatory effect of biochar on soil multifunctionality. This was because biochar induced oligotrophic conditions (a stoichiometry-induced nitrogen limitation), effectively warranting that continuous biochar application would aggravate nutrient limitations to crops, especially when low rates of synthetic fertilizer are applied. Notably, soil nutrient impoverishment could lead to resource reallocation from aboveground shoot to belowground root production, thereby fueling the energy flow through the herbivore channel. Our findings highlight the importance of balancing biochar and synthetic fertilizer applications to sustain a stable energetic structure in soil nematode food webs, which are associated with greater crop production and soil health in subtropical region. • Biochar increased the energy flow uniformity and arable soil multifunctionality. • Energy flow uniformity was positivity related to multifunctionality. • Biochar stimulatory effects were weakened when reducing synthetic fertilizer input. • Sustaining multifunctionality needs complementary input of both biochar and nutrients. [ABSTRACT FROM AUTHOR]

Resource limitation hinders soil biota to sustain multiple ecosystem functions. Earthworms are known for their ecotype diversity and the ability to accelerate nutrient cycling. However, the roles of earthworm ecotype diversity in alleviating soil resource limitations have yet to be discovered. Here, we conducted a microcosm study to investigate whether the increase of earthworm ecotypes, including epigeic Eisenia foetida , endogeic Metaphire guillelmi , and epi-endogeic Amynthas corticis , could promote soil nutrient provision by stimulating soil microbial communities. Earthworm ecotype diversity resulted in greater phosphorus contents than the earthworm inoculated alone, which were associated with increased fungal richness and network complexity. The result suggests that the increase of earthworm ecotype diversity drives the fungi-based micro-food web. Further, the alternations of extracellular enzymes related to nitrogen and phosphorus hydrolysis are also coupled with the richness, community composition, and network topology of fungi rather than those of bacteria, suggesting the more predominant effects of fungi in mediating extracellular enzymes. Thus, the increase of earthworm ecotype diversity could alleviate the resource limitation by steering fungal communities to excrete more hydrolysis enzymes. Our findings shed new light on the essential roles of earthworm ecotype diversity in strengthening microbiome-mediated functions in resource limited environments. [Display omitted] • Earthworm functional diversity mitigates resource limitations in soil. • Earthworm diversity increased fungal rather than bacterial diversity. • Fungi contributed to the soil enzyme composition. • Earthworm functional diversity is needed in conserving microbiome and soil functions. [ABSTRACT FROM AUTHOR]

Earthworms could affect soil C and N cycling process to balance their energy and nutrients requirements, and they could also regulate soil microbial community structure and microbial acquisition for C and N. However, the connection between faunal and microbial stoichiometry in the coupling soil C and N cycling remains poorly understood. In a controlled laboratory experiment, we amended soil with five litters differing in litter chemistry (clover, maize stover, wheat straw, Rumex and bagasse fiber) including a no litter control and treated them without or with earthworms ( Metaphire guillelmi ). After 90 d incubation, we examined changes in earthworm tissue and microbial stoichiometry and different soil C and N fractions. Earthworm tissue C content was rather stable compared with the fluctuation in tissue N, implying that C is under stronger control and associated with higher demand than N. The presence of earthworm significantly enhanced CO 2 emissions and decreased particulate organic carbon (POC) and soil organic carbon (SOC) contents in the low lignin litter species clover, maize stover and wheat straw. Meanwhile, earthworm presence increased N 2 O cumulative emissions but exerted negligible effects on particulate organic nitrogen (PON) and soil total nitrogen (TN) contents irrespective of litter species. Correspondingly, earthworm regulated microbial C and N acquisition as C to N-degrading enzyme activity ratio were nearly doubled in the low lignin litter species clover, maize stover and wheat straw, while it was decreased in the high lignin litter species Rumex and bagasse fiber. However, the structural equation modeling indicated C loss induced by earthworms was mainly attributed to their effects on soil fungi and bacteria abundance, while much less related to C-degrading enzyme activities. In conclusion, litter species controlled earthworm effects on soil C and N loss and associated microbial acquisition for C and N, highlighting the pivotal role of resource chemistry in the regulation of soil fauna impact on soil functioning and ecosystem services. [ABSTRACT FROM AUTHOR]

Earthworms are among the most important soil ecosystem engineers. Their effects on soil structure have been well documented, however, there is limited knowledge on how earthworms in the long term affect the soil microbiome, especially in arable soils. We investigated the soil microbiome of rice (cultivated under aerobic condition) and wheat fields in two consecutive seasons after manipulating earthworms and organic amendments for 14 years. Composition of soil prokaryotes and eukaryotes were analyzed by Illumina sequencing. Molecular network analysis suggest that in mulched rice fields earthworms foster species interlinked with many others and shift the dominance of prokaryotes from Planctomycetes to Proteobacteria. In contrast, in fields where residues were incorporated into the soil earthworms shifted the dominance of prokaryotes from Proteobacteria to Planctomycetes. Further, earthworms significantly increased the Proteobacteria-to-Acidobacteria ratio, a putative indicator of high nutrient turnover. Further, the ratio of prokaryote-to-eukaryote abundance was increased by earthworms when straw was incorporated into the soil. In conclusion, the results suggest that in the long term earthworms mainly modify the structure and functioning of prokaryote rather than eukaryote communities in arable fields. The effects of earthworms on the structure of microbial communities and microbial interactions are closely linked to resource management practices. The more pronounced effects of earthworms in treatments with residues mulched as compared to incorporated into the soil suggest that earthworm effects in part were due to bioturbation, i.e. mixing straw with mineral soil. [ABSTRACT FROM AUTHOR]

Soil aggregates provide microhabitats for nematodes and microorganisms, but how nematodes and microbial community interactively drive the dynamics of soil organic carbon (SOC) pool remains unclear. Here, we examined the relationships between bacterivorous nematodes, microbial community, and the sizes and turnover rates of three SOC pools in a red soil under four fertilization regimes. The abundance and community composition of nematode and bacterial communities were examined within aggregate fractions, including large macroaggregates (LMA), small macroaggregates (SMA), and microaggregates (MA). The sizes of SOC pools in soil aggregates increased with decreasing aggregate size, while the turnover rates of SOC pools followed the opposite trend. The ratios of bacteria to fungi (B/F) and Gram-positive to Gram-negative bacteria (GP/GN) were higher in the MA fraction than in the SMA and LMA fractions. The assemblages of bacterivorous nematodes in the LMA fraction were significantly different from those in the MA and SMA fractions, primarily because of the higher abundance of the dominant genus Protorhabditis . Results of structural equation modelling indicated that the ratios of B/F and GP/GN showed stronger positive correlations with the sizes and turnover rates of SOC pools in the MA fraction compared with the LMA fraction. Conversely, bacterivores exhibited indirect relationships with the sizes and turnover rates of SOC pools through the B/F ratio in the SMA and LMA fractions. Taken together, these results highlight the functional role of nematodes and microbial community in controlling SOC pool dynamics at the aggregate scale. [ABSTRACT FROM AUTHOR]

Elevated atmospheric CO 2 concentrations (eCO 2 ) often increase plant growth but simultaneously lead to the nitrogen (N) limitation in soil. The corresponding mitigation strategy such as supplementing N fertilizer and growing high-yielding cultivars at eCO 2 would further modify soil ecosystem structure and function. Little attention has, however, been directed toward assessing the responses of soil food web. We report results from a long-term free air CO 2 enrichment (FACE) experiment in a rice paddy agroecosystem that examined the responses of soil micro-food webs to eCO 2 and exogenous nitrogen fertilization (eN) in the rhizosphere of two rice cultivars with distinctly weak and strong responses to eCO 2 . Soil micro-food web parameters, including microfauna (protists and nematodes) and soil microbes (bacteria and fungi from phospholipid fatty acid (PLFA) analysis), as well as soil C and N variables, were determined at the heading and ripening stages of rice. Results showed that eCO 2 effects on soil micro-food webs depended strongly on N fertilization, rice cultivar and growth stage. eCO 2 stimulated the fungal energy channel at the ripening stage, as evidenced by increases in fungal biomass (32%), fungi:bacteria ratio (18%) and the abundance of fungivorous nematodes (64%), mainly due to an enhanced carbon input. The eN fueled the bacterial energy channel by increasing the abundance of flagellates and bacterivorous nematodes, likely through alleviating the N-limitation of plants and rhizosphere under eCO 2 . While eCO 2 decreased the abundance of herbivorous nematodes under the weak-responsive cultivar by 59% and 47% with eN at the heading and ripening stage, respectively, the numbers of herbivorous nematodes almost tripled (×2.9; heading) and doubled (×1.6; ripening) under the strong-responsive cultivar with eCO 2 at eN due to higher root quantity and quality. Structural equation model (SEM) showed that lower trophic-level organisms were affected by bottom-up forces of altered soil resources induced by eCO 2 and eN, and effects on higher trophic level organisms were driven by bottom-up cascades with 69% of the variation being explained. Taken together, strategies to adapt climate change by growing high-yielding crop cultivars under eCO 2 may face a trade-off by negative soil feedbacks through the accumulation of root-feeding crop pest species. [ABSTRACT FROM AUTHOR]

Nutrient availability may exert major controls over soil microbial respiration, especially in carbon (C)-rich, nitrogen (N)-limited ecosystems in high elevation regions, but how soil organic matter (SOM) decomposition and its temperature sensitivity respond to long-term N & P additions in alpine ecosystems remains unclear. We examined the impact of long-term (15 yr) N & P additions on soil microbial respiration and its temperature sensitivity (Q 10 ), and assessed the relative importance of nutrient-induced alterations in substrate quality and the microbial community composition in explaining the variation in soil respiration and temperature sensitivity. We found that N & P additions significantly reduced microbial respiration rates and cumulative C efflux, but increased the Q 10 (15/5 °C). Also, N & P additions reduced the biomass of the whole microbial community, gram negative bacteria and fungi, but increased the aromaticity and aliphaticity of soil organic C substrate. Across the treatments, averaged Q 10 was positively correlated with the complexity of SOM as characterized by 13 C-NMR, supporting the prediction based on kinetic theory that SOM with recalcitrant molecular structure is with high temperature sensitivity. Together, our results showed that changes in both substrate quality and soil microbial community induced by long-term nutrient inputs may alter the response of soil microbial respiration to elevated temperature. Because the positive effects of increasing temperature sensitivity for use of lower quality substrates on C emission may be offset by lower absolute rates at any one temperature, long-term N & P additions increase the uncertainty in predicting the net soil C losses in the scenario of warming on Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Rapid urbanization profoundly affects global biodiversity. How urbanization modifies soil biodiversity and perturbs nematodes remains limited. Here, we investigated soil nematodes in four land-use types: Parks, residential areas, natural forests, and maize fields across 12 cities in China. Urban parks and surrounding forests had similar nematode richness exceeding that in urban residential areas and surrounding farmlands. Nematode communities in parks and residential areas were, however, more homogenous than in forests and farmlands. Variations in nematode assemblages in both core urban and urban surroundings were mainly due to taxa replacement, indicating that nematodes were spatially isolated in cities. Urban residential areas were colonized by the lowest number of specialists (i.e., with narrow niche width) and smaller body sizes. Urban parks, conversely, served as hotspots for soil nematodes in cities. Together, our results indicate that urbanization processes reduce nematode diversity, with e.g., 30% loss in residential areas compared to forests, and homogenize soil nematode communities. • Precipitation and temperature determined soil nematode diversity. • Urban soils have low diversity of soil nematodes. • Urbanization homogenized soil nematode community. • Urban parks are hotspots for soil nematodes. [ABSTRACT FROM AUTHOR]

Energy dynamics within ecological communities are important in delivering ecosystem services. However, it remains elusive how the energy fluxes within soil food webs respond to agricultural fertilization regimes. Here, we studied the effects of long-term organic amendments and mineral fertilizers on the energetic structure of soil nematodes from a food-web perspective. We replicated our experiment in a rice paddy and in an upland maize cropping system. Results showed that the abundance of most trophic groups was higher in organically amended soils compared with mineral fertilizer treatments in both systems. Organic amendments, but not mineral fertilizers, increased the energy flux of total nematodes and most trophic groups compared with the no-fertilizer treatment. Furthermore, organic amendments increased the relative allocation of energy flux to microbivores but decreased the relative allocation to herbivores, supporting a higher flow uniformity than mineral fertilizers. We further found that organic amendments favored a higher total energy flux by supporting a greater nematode diversity, while sustained a higher flow uniformity by altering nematode community composition. Taken together, the result provides the evidence that a complex and species-rich community could transfer more energy to support ecosystem services. A broader perspective on linkages of biodiversity and energy dynamics spanning multitrophic groups is crucial for sustainable management, particularly in the light of non-random species loss under future environmental change. [Display omitted] • Organic amendments increased total energy flux and flow uniformity. • High flow uniformity resulted from increasing relative energy flux of microbivores. • Energy fluxes and flow uniformity were positively linked with nematode diversity. • Effect of diversity decline on energy loss was stronger in paddy than upland fields. [ABSTRACT FROM AUTHOR]

Energy flux in food webs, i.e., energy consumption by different trophic groups and describing their energetic structure, has been proposed as a powerful tool to understand the relationships between biodiversity and multiple ecosystem functions (ecosystem multifunctionality). Here we examined how different fertilization regimes affected the energy flux across multitrophic levels of soil nematodes in the paddy rice and upland maize fields. We considered 13 ecosystem functions of four ecological processes related to plant productivity, nutrient cycling processes and drivers, and functional stability, which are central to energy and nutrient flow across trophic levels. To confirm whether multitrophic flux would underpin the relationships between biodiversity and multifunctionality, we compared energy flux with other approaches including taxonomic diversity, functional diversity and community composition. Results showed that organic fertilizer supported 33–340% greater multitrophic energy flux of soil nematode community and enhanced 41–264% of ecosystem multifunctionality in both fields compared with mineral fertilizer treatments. Organic fertilization enhanced ecosystem multifunctionality by favoring energy flux in multitrophic levels of soil nematodes, while fertilization-mediated changes in other facets of biodiversity were less related to multifunctionality. Our study provides empirical evidence that energy flux within food webs can be used to understand the impacts of environmental change drivers on ecosystem multifunctionality. • Organic fertilization increased ecosystem multifunctionality. • Energy flux of soil nematodes was positively related to multifunctionality. • Energy flux underpinned the link between biodiversity and multifunctionality. [ABSTRACT FROM AUTHOR]

Soil aggregates are the key functional units of soil ecosystems which are essential to biogeochemical cycling and plant growth. However, it remains unclear how fertilization regimes influence soil aggregation, associated resources, and microbial distribution among aggregates, as well as the potential subsequent impacts for other abiotic and biotic processes. For this, a long-term maize cropping field experiment was conducted in the subtropical region of China under four fertilization treatments: no fertilizer, chemical fertilization, organic fertilization, and chemical plus organic fertilization. Additionally, we classified soil aggregates into large macro-aggregates (>2 mm), small macro-aggregates (0.25–2 mm), and micro-aggregates (<0.25 mm) and compared soil nutrients, enzyme activities, and microbial communities of each aggregate fraction and bulk soil as well as crop productivity and plant carbon (C), nitrogen (N), and phosphorus (P). Results showed that long-term organic fertilization (1) increased soil C, N, and P contents within macro-aggregates, while increased bacterial and fungal biomass within all three aggregate size fractions, (2) increased N-acquiring enzyme activity, C:P, and N:P enzyme ratios but decreased phosphatase activity and C:N enzyme ratio regardless of aggregate fractions, and (3) promoted crop productivity but decreased plant C:N, C:P, and N:P ratios compared with chemical fertilization. Additionally, the fungi:bacteria ratio and phosphatase activity decreased, but the gram-positive to gram-negative bacterial ratio, C-acquiring enzyme activity, C:N and C:P enzyme ratios increased with decreasing aggregate size. The partial least squares models confirmed that macro-aggregates had strong effects on crop performance while micro-aggregates was the main determinant of microbial community. Taken together, long-term organic fertilization promotes soil functioning and crop productivity via increasing the proportion of soil macro-aggregates. • Aggregates with different sizes played distinct roles in soil functioning. • Organic fertilization increased crop productivity by promoting macro-aggregation. • Macro-aggregates is an important resource of nutrients promoted plant growth. • Resources in micro-aggregate were conducive to microbial utilization. • Microorganisms in micro-aggregates were C-limited. [ABSTRACT FROM AUTHOR]

Soil phagotrophic protists are highly abundant and play a vital role in nutrient cycling through feeding on microbes. Global change factors, individually or in combination, often affect soil bacteria and fungi, but whether and how the resulting changes may cascade to affect phagotrophic protists remain largely unknown. Combining direct microscopic counting and high-throughput sequencing of 18s rRNA gene, we examined effects of precipitation changes, warming and nitrogen (N) input on soil phagotrophic protists in a 3-yr manipulation experiment with a Tibetan alpine meadow. Precipitation addition (+30%) enhanced but precipitation reduction (−30%) and warming decreased the alpha diversity of phagotrophic protists, primarily through altering soil moisture. However, N input (12 g N m−2 y−1) increased protist abundance, and in particular, offset the negative effect of precipitation reduction on the relative abundance of phagotrophic protists through increasing the microbial biomass, implying a bottom-up trophic control. Together, these findings indicate that interactions of multiple global change drivers may affect soil protist communities directly by modifying the soil physiochemical environment and indirectly through trophic cascading, which have implications for the potential changes in their ecosystem functions in alpine meadow under future global change scenarios. [Display omitted] • Both molecular and microscopic methods were used to test phagotrophic protist communities. • Precipitation reduction and warming decreased protist diversity by reducing soil moisture. • N input offset the negative effect of precipitation reduction on phagotrophic protists. • Bottom-up trophic control explained N-stimulation of phagotrophic protist abundance. [ABSTRACT FROM AUTHOR]

Abstract: We prepared soil with greater populations of bacterial-feeding nematodes either by stimulating the native populations of the soil, adding an additional mixed community of nematodes, or by adding Caenorhabditis elegans, to investigate the effects of bacterial-feeding nematodes on root morphology, soil auxin (indolyl-3-acetic acid—IAA) concentrations and microbial community structure. In the presence of enhanced bacterial-feeding nematode populations, tomato plants had a more highly branched root system with longer and thinner roots. Root system development was greater with native nematodes than C. elegans. The changes of root morphology were accompanied by an increase of soil IAA content and an altered microbial community structure. Bacterial-feeding nematodes may have affected plant growth by stimulating hormone production through grazing-induced changes to the soil microbial community. [Copyright &y& Elsevier]

Plant roots are the primary source of soil organic carbon (C) and critically support the growth and activities of microbes in the rhizosphere. Climate change factors may, however, modify root-microbial interactions and impact C dynamics in the rhizosphere. Yet, the direction and magnitude of interactive climate change effects, as well as the underlying mechanisms, remain unclear. Here we show evidence from a field experiment demonstrating that warming and precipitation changes strengthen root controls over litter decomposition in a semi-arid grassland. While warming and precipitation reduction suppressed microbial decomposition of root litter regardless of the root presence, precipitation increase stimulated litter decomposition only in the absence of roots, suggesting that plant competition for water constraints the activities of saprophytic microbes. Root presence increased microbial biomass but reduced microbial activities such as respiration, C cycling enzymes and litter decomposition, indicating that roots exert differential effects on microbes through altering C or water availability. In addition, nitrogen (N) input significantly reduced microbial biomass and microbial activities (respiration). Together, these results showed that alterations in soil moisture induced by climate change drivers critically modulate root controls over microbial decomposition in soil. Our findings suggest that warming-enhanced plant water utilization, combined with N-induced suppression of microbes, may provide a unique mechanism through which moderate increases in precipitation, warming and N input interactively suppress microbial decomposition, thereby facilitating short-term soil C sequestration in the arid and semi-arid grasslands. • Climate change effects on root decomposition were studied in a semi-arid grassland. • Soil moisture dominated microbial responses to climate change drivers. • Root presence shifts limitation to microbes from labile C to water availability. • Roots increase microbial biomass but suppress microbial decomposing activities. [ABSTRACT FROM AUTHOR]

Litter decomposability determines litter mass loss rate, but how it affects soil carbon (C) and nitrogen (N) storage remains elusive. We compiled data from 25 litter decomposition studies tracing the fate of C and N during decomposition using stable C and N isotopes. An average of 24% of C lost from decomposing litter was recovered in the soil independent of the decomposition stage and the experimental conditions. In contrast, a higher amount of N lost from decomposing litter was recovered in the soil in laboratory (80%) than in field (58%) experiments. The proportion of the total C and N lost that was transferred to the soil was higher for slowly than for rapidly decomposing litter types. Our results demonstrate substantial soil C and especially N input from decomposing litters and suggest that slowly decomposing litters favor soil C and N storage compared to more rapidly decomposing litters. • On average a quarter of litter C loss is recovered in the soil at much lower rates than litter N. • Litter C recovery rate remained stable along the decomposition process. • Slow-decomposing litters are more efficient in incorporating litter C and N into the soil. [ABSTRACT FROM AUTHOR]

Anthropogenic activities are supposed to reduce global biodiversity and negatively influence the development of diverse groups in the tree of life. Yet how agricultural management shapes the diversity of microscopic organisms and their evolution in the soil, especially at large spatial scale, remains unknown. Here, we investigated how agricultural land-use affected the biodiversity and the underlying evolutionary events of soil nematodes by comparing their communities in natural and agricultural soils covering a latitudinal transect spanning 2500 km across China. In natural habitats, nematode phylogenetic and taxonomic diversity and species richness showed a hump-shaped relationship with latitudes and peaked at 30° N, while in agricultural habitats those community matrices did not change across the studied latitudinal spectrum. Meanwhile, agricultural management reduced both diversity and richness of nematodes with the effect being more pronounced in subtropical zones. However, evolutionary diversification rates were greater in agricultural than in natural habitats across the entire latitudinal range. This was associated with reductions of soil organic carbon and nitrogen as well as shifts of nematode community compositions towards rapidly evolving taxa (r–strategists) in agricultural habitats. Together, our results suggest that the relatively unfavorable environmental status induced by agricultural management could accelerate the community-level speciation rates of nematodes through enriching rapidly evolving taxon. These insights increase our understanding of the systematic impacts of agricultural activities on soil biodiversity that might facilitate conservation and restoration policies for the purpose of sustainable agriculture. • Phylogenetic comparative methods were applied for soil nematode diversity analysis. • Speciation rates was greater in r-strategists. • Community weighted speciation are greater in agricultural habitats. • Speciation rates were related to soil organic carbon and pH. [ABSTRACT FROM AUTHOR]

PhoD -harboring microorganisms are crucial for the regulation of soil phosphorus (P) cycling through the secretion of alkaline phosphomonoesterases and are also known to be sensitive to fertilizer inputs. However, the impacts of long-term mineral and organic fertilizer inputs on active phoD -harboring functional communities in soils remain largely unknown. In the present study, 18O-DNA-stable isotope probing coupled with high-throughput sequencing was utilized in order to characterize active phoD -harboring functional bacterial communities in soils subjected to long-term no-fertilizer (Control), mineral-only fertilizer (NPK), organic-only fertilizer (M), and the combination of mineral and organic fertilizer (NPKM) amendments. Total and active phoD gene abundance decreased in soils amended with long-term mineral fertilizer, but increased in soils under organic fertilizer amendment, compared with the non-fertilized soils. A total of 51 active phoD -harboring bacterial OTUs, mainly belonging to Actinobacteria, were identified in this study. Organically amended soils harbored a higher diversity of active bacterial community. In the active phoD -harboring functional community, Rhodococcus comprised approximately 99% of the total relative abundance in the unfertilized soil, whereas Nocardiopsis and Bacillus accounted for approximately 62% and 24%, respectively, in mineral-only fertilized soils. Active phoD -harboring communities were dominated by members of the genera Streptomyces (26–60%), Nocardia (5–9%) and Gordonia (23–41%) in all organically fertilized soils, including M and NPKM. Overall, these long-term fertilization regimes altered the abundance, richness and composition of the active phoD -harboring functional microbial community. This study provides novel insights into the responses of the active functional bacterial community that is responsible for soil P mineralization to differing long-term fertilization regimes. • The active phoD -harboring bacteria was identified by 18O-DNA-SIP technique. • Organic amendment increased the abundance and diversity of active phoD bacteria. • Different fertilization regimes shaped distinctive active phoD bacterial community. • The active phoD bacterial OTUs in fertilized soils was dominated by Actinobacteria. • In unfertilized soil, ~99% active phoD -harboring OTUs belonged to the Rhodococcus. [ABSTRACT FROM AUTHOR]

One of the greatest challenges in soil ecology is to disentangle the plant-mediated bottom-up factors regulating soil biodiversity and community composition. The soil food web, fundamentally driving nearly all ecosystem functions, is controlled by the quantity and quality of root-mediated resources. Here, a trait-based approach was adopted to explore the divergence of soil nematode functional guilds and their connections to root traits belonging to distinct plant resource-use strategies. Root traits and rhizosphere nematode functional guilds were measured on four plant species in an ex-arable field. Results showed that plant species exhibiting acquisitive strategies promoted nematode abundance in contrast to species with conservative strategies. Further, the results also supported that plant resource-use strategies could regulate nematode life strategies in a bottom-up manner. However, lower proportions of opportunist nematodes in rhizosphere were found in acquisitive plants rather than conservative plants, mainly attributed to the stronger top-down regulation as a dominant control within the former than the later ones. Structure equation modeling revealed that root length density could primarily modulate nematode abundance and functional guilds mainly through changes in nitrogen availability of rhizosphere, as indicated by mineral N and enzymatic stoichiometry. Overall, our findings extend the conceptual framework based on a trait-centred view spanning plants to the soil food web, and this knowledge is critical to understand the mechanisms of ecosystem process. • Acquisitive plants promoted nematode abundance and K-strategist nematodes. • Conservative plants supported mainly r-strategist nematodes. • Root length density was the key root trait for regulating soil nematodes. [ABSTRACT FROM AUTHOR]

Biotic interactions in the soil food web have been increasingly recognized as crucial for ecosystem functioning, however there are still knowledge gaps in terms of the associations between macrofauna and microorganisms, particularly in soil hotspot microsites. A manipulative study was performed to investigate the protist community in the drilosphere and casts of three earthworm species (epigeic Amynthas cortices , anecic Amynthas hupeiensis and endogeic Drawida gisti) and a control soil without earthworms. Results showed that earthworm presence significantly increased the relative abundance of parasitic protists (p < 0.05). The diversity of protists within drilosphere and casts depended on earthworm species, with D. gisti and A. hupeiensis increasing diversity and A. cortices decreasing protist diversity (p < 0.05). Structural equation modelling indicated that protist abundance and diversity in the drilosphere were regulated indirectly via neutralized soil pH and accelerated C and N mineralization, while in casts were affected directly through earthworm gut processing and indirectly through elevated water content. In conclusion, the marked effects on soil protist community mediated by earthworms varied from distinct earthworm species and microsites. The present study suggests the necessity to consider interactions between protist and earthworms in evaluating the effects of soil fauna on soil biota and the related ecosystem processes. • Parasitic protist in drilosphere and cast was higher than in earthworm free soil. • Protist community composition depended on earthworm species and microsite type. • Protist communities were affected by pH and nutrient availability in drilosphere. • Earthworm feeding and elevated water content determined protist community in cast. [ABSTRACT FROM AUTHOR]