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Soil nematode communities can provide valuable information about the structure and functions of soil food webs, and are sensitive to agricultural practices, including short-term straw incorporation. However, currently, such effects under long-term straw incorporation conditions at different fertility levels are largely unknown. Thus, we conducted a 13-year ongoing experiment to evaluate the effects of long-term straw incorporation on the structure and functions of the soil food web in low and high fertility soils through analyzing its effects on nematode communities, food web indices and metabolic footprints. Four treatments were included: straw removal (–S) under non-fertilized (–NPK) or fertilized (+NPK) conditions; and straw incorporation (+S) under –NPK or +NPK conditions. Soil samples from a 0–20 cm depth layer were collected when wheat and rice were harvested. Compared with straw removal, straw incorporation increased the abundances of total nematodes, bacterivores, plant-parasites and omnivores-predators, as well the relative abundances of omnivores-predators with increases of 73.06, 89.29, 95.31, 238.98, and 114.61% in –NPK soils and 16.23, 2.23, 19.01, 141.38, and 90.23% in +NPK soils, respectively. Regardless of sampling times and fertilization effects, straw incorporation increased the diversity and community stability of nematodes, as indicated by the Shannon-Weaver diversity index and maturity index. Enrichment and structure index did not show significant responses to straw incorporation, but a slight increase was observed in the structure index. The analysis of nematode metabolic footprints showed that straw incorporation increased the plant-parasite footprint and structure footprint by 97.27 and 305.39% in –NPK soils and by 11.29 and 149.56% in +NPK soils, but did not significantly influence enrichment, bacterivore and fungivore footprints. In conclusion, long-term straw incorporation, particularly under a low fertility level, favored the soil nematodes and regulated the soil food web mainly via a top-down effect.

Mixed cultivation of fast-growing grasses and nitrogen (N)-fixing legumes for forage production is widely considered effective for obtaining sustained high forage yields without depleting soil N levels. However, the effects of monoculture and mixed culture of these species on soil food webs are poorly understood. In this study, soil nematode communities were examined as indicators of the soil food web structure of monoculture and mixed culture of grass and legume at three N levels, i.e., 338 (low), 450 (moderate), and 675 (high) kg N ha−1 year−1 across 2 years in wet and dry seasons, using the grass Paspalum wetsfeteini and the legume Medicago sativa (alfalfa), both commonly cultivated worldwide. Repeated-measures analysis of covariance showed that compared with grass monoculture, legume monoculture and grass-legume mixture increased abundances of herbivorous, bacterivorous, and fungivorous nematodes in the soil food web under the low and moderate N fertilization levels. Principal response curve results showed that the abundance of Helicotylenchus, a plant parasite, was significantly higher under legume monoculture than other planting systems at the low N fertilization level. Structural equation model analysis indicated that the legume increased bacterivore abundance, while increasing N fertilization decreased omnivore abundance. The legume might increase the quantity and quality of food resources for soil biota, resulting in the bottom-up control of soil nematode communities. Our results indicate that targeted control of a soilborne pathogen, Helicotylenchus, is required in alfalfa-based planting systems. In addition, high inorganic N application, which is detrimental to legume-rhizobia symbiosis, nullified the otherwise positive effects of legumes on soil nematodes.

It has been well documented that organic amendment affects soil nematode community structure. However, little is known about the effect of organic amendment amount on soil nematodes. To assess the effect of the amount of organic amendments on soil nematode community structure and metabolic activity, the community composition, abundance, and metabolic footprints of soil nematodes were determined in a long-term field experiment with various amounts of organic amendment in Northeast China. Fertilization treatments included an unfertilized control (CK), chemical fertilizer without manure amendment (OM0), manure applied at 7.5 Mg ha–1 plus chemical fertilizer (OM1), and manure applied at 22.5 Mg ha–1 plus chemical fertilizer (OM2). A total of 46 nematode genera were found. Treatments with the largest amount of organic amendment had the smallest number of plant parasite genera (5), but a largest number of dominant genera (7). Soil nematodes, bacterivores, and fungivores were the most abundant in OM2, followed by OM1, and the lowest in OM0 and CK. Organic amendment increased the enrichment index (EI), and the large amount of organic amendment increased the metabolic footprints of bacterivore (Baf) and fungivore (Fuf) and enrichment footprint (Ef). The relationships between Baf (or Fuf) and the increases in soil organic carbon (ΔSOC) and total nitrogen (ΔTN) were stronger than those of bacterivore (or fungivore) abundance with ΔSOC and ΔTN, except for the relationship between bacterivore abundance and ΔSOC. The EI and Ef were positively correlated with ΔSOC and ΔTN. These findings suggest that the amount of organic amendment affects soil nematode activity and function at entry levels in soil food web, and that metabolic footprints of soil nematodes may be better indicators than their abundances in assessing their relationships with soil nutrients.

International audience; Soil trophic networks are key to biogeochemical cycles, in particular decomposition. However, few studies have yet quantified how microbial decomposition activity along environmental gradients is jointly driven by bacteria, fungi, and their respective consumers. Here, we quantified these direct and indirect effects on decomposition and contrasted them between forests and open habitats using multiple elevational gradients in the French Alps.While environmental control on microbial decomposition activity was comparable in the two habitats, the pathways and strengths of biotic predictors strongly differed. The fungal channel composition played a moderate role in forests, while the bacterial channel composition was critical in open habitats. Importantly, we found trophic regulation by consumers to be a key modulator of the direct environmental effects on decomposition in open habitats. These results highlight the need to integrate trophic regulation when predicting future ecosystem functioning.

Heavy metal induced co-selection of antibiotic resistance genes (ARGs) has become an emerging environmental issue. The guts of soil fauna offer a unique habitat in the terrestrial ecosystem and harbor a variety of microorganisms. However, the effects of heavy metals on the gut-associated ARGs of soil fauna are poorly understood. In the present study, collembolans were cultivated with four types of heavy metals (Zn, Cu, Cd, and Cr) and one antibiotic (oxytetracycline), to investigate their impact on the gut-associated ARGs. High-throughput quantitative PCR and 16S rRNA gene amplicon sequencing were used to examine changes in the gut-associated ARGs and microbial composition caused by the metals and antibiotic. The results showed that heavy metals alone induced co-selection of ARGs in the collembolan gut, but the effects were weaker than selection by oxytetracycline. When Zn or Cu was present together with oxytetracycline, there was a strong synergistic effect between the compounds, which increased the selection of ARGs in the collembolan guts. Furthermore, redundancy analysis revealed that the gut microbiota and mobile genetic elements (MGEs) were significantly correlated with the ARG composition. These results extend our understanding on effects of heavy metals on the dispersal of ARGs in the soil food web.

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 δ 15N 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 δ 15N 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 δ 15N 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.

Conservation tillage is one of the major strategies for maintaining agricultural sustainability and has significant beneficial effects on soil organic carbon (C) retention and soil organism diversity. However, how changes in soil organism populations and/or community structure under different tillage practices contribute to C sequestration in soil is not well documented. In this paper, soil nematode assemblages were used as a model to quantify C allocation in production and respiration of soil organisms in a long-term tillage trial initiated in 2001 on a Black soil (Typic Hapludoll) of Northeastern China. Soils were sampled from no tillage (NT), ridge tillage (RT) and conventional tillage (CT) practices in the soybean (Glycine max Merr.) phase of the maize (Zea mays L.) -soybean rotation. In comparison with CT, RT and NT significantly increased production and respiration C of nematodes as a consequence of more basal C flowing into soil food web. The significantly increased bacterivore metabolic C in both production and respiration under RT and NT suggests that a bacterial-channel was the predominant pathway for C entering the food web. However, the efficiency of C allocation into soil nematodes, as indicated by the ratio of respiration C to production C (R/P), varied widely between RT and NT. NT significantly improved the C storage capacity of almost all nematode trophic groups while RT predominantly promoted the C storage capacity of bacterivores. Our results suggest that NT is more favorable than RT for allocating C into soil organisms under long-term application in the Black soil of Northeast China.

The effects of diversifying wheat-based cropping systems in the Northern Great Plains (NGP) on soil chemical and physical properties is well documented: better soil tilth, improved water infiltration, and higher soil organic matter with crop rotations. However, the impact of crop rotations on soil biology is not as well understood. Nematode communities reflect soil quality and are directly observable, readily quantifiable, and occupy most of the consumer trophic levels in the soil food web. Within more humid climates, the community structure is better characterized to make associations with soil health and crop management strategies, but little is known about their community structure in semiarid regions such as the NGP. For this study, soils under contrasting cropping systems were sampled in the 15th year of a long-term study to quantify and assess the nematode community. Prior to planting, wheat-chemical fallow had a higher total nematode population than that of wheat-tilled fallow (P

Earthworms (E) and arbuscular mycorrhizal fungi (AM) as the key components of belowground organisms can form highly complex interactions in soil food web. However, little is known about the direction and power of interactive effects on plant growth and soil fertility in nutrient-limited soils. The objectives aimed to explore the interaction of AM (Claroideoglomus etunicatum) and E (Amynthas divergens yunnanensis) and its effecting mechanism on the plant (Photinia fraseri Dress) growth and nutrient availability in the desertification soils in Karst area. A 2 × 2 factor block design was completely randomly arranged for the treatments in a pot experiment. The four treatments were no E and AM, E inoculation, AM inoculation and inoculations with both E and AM. We confirmed the hypotheses tested about a positive effect of combined inoculations and a more pronounced increase in the plant height (12.5–13.4%), base diameter (24–27%), root colonization (50%) and hyphal length density (312%) compared with separate inoculation. Whereas the inoculation with E or AM had an effect only on the plant height, and AM inoculation only on the hyphal length density. The combined inoculations resulted in a greater reduce in soil pH and a higher increase in soil organic matter and readily oxidizable organic carbon. The effect of combined inoculations on the growth of base diameter, root mycorrhizal colonization and hyphal length density was closely associated with the increase in soil organic matter and soil readily oxidizable organic carbon. In contrast, the effect of separate inoculation on plant height was related with the increase in pH, total nitrogen and phosphorus, plant available nitrogen and phosphorus in soils. Earthworms and AM fungi can create different nutritional niches for plants: E had greater increase in N availability, while AM fungi in P availability. Therefore, we conclude that the combined effects have a greater potential in increasing plant growth, through the complementary and interactive mechanisms of E and AM on modifying nutrient availability in the nutrient-poor soils in Karst stony desertification land.

International audience; Conventional, intensively managed coffee plantations are currently facing environmental challenges. The use of shade trees and the organic management of coffee crops are welcome alternatives, aiming to reduce synthetic inputs and restore soil biological balance. However, little is known about the impacts of the different types of shade tree species on soil functioning and fauna. In this paper, we assess soil nutrient availability and food web structure on a 17-year old experimental coffee plantation in Turrialba in Costa Rica. Three shade types (unshaded coffee, shaded with Terminalia amazonia, and shaded with Erythrina poepiggiana) combined with two management practices (organic and conventional) were evaluated. Total C and N, inorganic N and Olsen P content, soil pH, global soil fertility, and nematode and microarthropod communities were measured in the top 10 cm soil layer, with the objective of determining how shade tree species impact the soil food web and soil C, N and P cycling under different types of management. We noted a decrease in soil inorganic N content and nematode density under conventional management (respectively -47% and -91% compared to organic management), which suggested an important biological imbalance, possibly caused by the lack of organic amendment. Under conventional management, soil nutrient availability and fauna densities were higher under shade, regardless of the shade tree species. Under organic management, only soils under E. poeppigiana, a heavily pruned. N-2 -fixing species, had increased nutrient availability and fauna density, while T amazonia shade had a null or negative impact. The effects of coffee management and shade type on soil nutrient availability were mirrored by changes in soil food web structure. Higher fertility was recorded in soil with balanced food webs. These results emphasize the importance of the choice of shade tree species for soil functions in low input systems, more so than in fertilized systems

Bacteria and fungi are the primary consumers and, thus, the decomposition pathways are described accordingly as bacterial-based or fungal-based energy channels. However, the fungi to bacteria ratios (F: B), which indicated either by microbial biomass, respiration, or growth, represents only a snapshot of the whole energy channel during a given period rather than the cumulative contribution. Even the energy channel biomass only takes into account one dimension without considering the time. We believe that the F: B ratio has been misinterpreted in an ecological sense due to a lack of a clear definition. Here, we estimated the F: B biomass ratios, production ratios (microbial biomass multiplied by the turnover rate) and assimilation ratios (the sum of microbial production and respiration) using a dataset from 192 relevant studies. The F: B biomass ratios varied from 0.106 to 9.080, depending on the methods used. Based on direct microscopy method, the fungal/(fungal + bacterial) production and assimilation ratios ranged from 0.39 to 54.78% and 0.25–45.05%, respectively; while, those ratios based on phospholipids fatty acids (PLFAs) method were 0.06–5.51% and 0.04–0.66%, respectively. We conclude that bacteria contributes greater to the energy flow in terrestrial ecosystems compared with fungi based on the F: B assimilation. The relative contribution of bacteria and fungi can be better evaluated using the F: B assimilation ratio, rather than the biomass ratio or production ratio. Nevertheless, there are still uncertainties in the estimations of microbial production and assimilation due to their complicated responses to soil fauna activities. The regulation of soil fauna on microbial biomass, turnover rate and respiration, and associated changes in the energy allocations in the soil food web should be emphasised in future studies.

At the beginning of the 20th century Louis Pasteur laid the foundations of classical microbiology, based on the cultivation of microorganisms. Microbiology ceased to be an exclusive concern in matters of health or food conservation and extended to almost all fields in Nature. Microbes were recognized as the catalysts of all the cycles of the elements in our planet. In this context, agricultural microbiology works as a catalog of curiosities that offers the possibility to isolate particular microorganism and convert them into modern additives of agriculture. However, this paradigm vanished not many years ago, after a big anomaly in bacterial counts. Biochemical tools allow us to see the new unculturable microbes and a new scenario of soil microbiology is under construction at present. The new concept of microbiome expands the complexity of the soil where any macroscopic form of life develops. Analyzing the soil microbiology at a soil microaggregates scale suggests that agricultural managements are the way of shaping soil microbiomes to improve soil quality and improve crop production and soil services without harming the environment. The integration of soil microbiomes knowledge into the other levels of the soil food web is the future of soil science and could be one of the clues to mitigate the global climate change. Fil: Wall, Luis Gabriel. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Gabbarini, Luciano Andres. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Ferrari, Alejandro Eugenio. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología; Argentina Fil: Frene, Juan Pablo. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Covelli, Julieta Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología; Argentina Fil: Reyna, Dalila Luz. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología; Argentina Fil: Robledo, Natalia Belén. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología; Argentina

Understanding the changes of soil microbial and nematode communities within aggregate fractions is essential for maintaining the stability of soil biological communities and soil health in agricultural ecosystems. However, the short- and long-term influence of converting abandoned land to tea (Camellia sinensis L.) plantations on soil aggregate-associated biological communities is still poorly understood. In this study, soil microbial and nematode communities were analyzed in soil fractions of different sizes collected from 0 to 20 cm depth in four tea plantations with the same plants (cultivar was “Sichuan tea”) of various ages (16-, 23-, 31-, and 53-years) in the hilly area of western Sichuan in China. The aggregates were separated by a dry-sieving procedure into four fractions: large (>2 mm), medium (2–1 mm), small (1–0.25 mm) macro-aggregates, and micro-aggregates ( 0.05) with most nematode abundance (bacterivores, plant-parasites, fungivores, and omnivores and predators) across aggregate fractions in different tea plantation ages, not only microbial biomass and nematode abundance but also their diversity was highest in the large macro-aggregates, indicating that these fractions had a complex biological community structure with more connections in soil food web, thus providing biological buffering and prohibiting the dominance of individual organisms via competition or predation. In the process of tea cultivation, the abundance of soil nematodes was largely dependent on microbial biomass in the macro-aggregates where pore space was large enough for nematodes to prey on microbes, while there were no correlations (P > 0.05) between microbial biomass and nematode abundance in the micro-aggregates. The 23-year-old tea plantation provided a relatively stable soil environment for the development of microbial and nematode communities, and subsequently induced an increase of soil microbial biomass, nematode abundance, and their diversity. Notably, the degradation of soil biological communities after 23-years underscores the need for sustainable soil management practices that would maintain the stability of soil biological communities and soil health after 23-years of tea cultivation in the hilly area of western Sichuan in China.

Anthropogenic nitrogen (N) deposition is an important component of global change and threatens terrestrial biodiversity. Most previous studies of the consequences of N deposition have focused on plant community responses and found that N deposition decreases plant diversity. However, the effects of N deposition on soil biodiversity and belowground biotic interactions remain poorly understood. We explored the changes in main soil food web components (microbes, nematodes, springtails, and mites) in response to elevated N deposition (60 kg N ha−1yr−1, starting from 2012 to 2014), and whether these changes are altered by the presence of plants (planting of shrubs in 2008) in a two-factorial field mesocosm experiment with 16 equally-sized plots (1 × 2 m). Our results showed that elevated N deposition negatively affected soil bacteria, while fungi showed rather neutral responses. Specifically, N deposition decreased bacteria Shannon's diversity index H′, richness, observed species abundance, bacterial activity, and resulted in a non-significant decrease of the relative abundance of rare bacterial taxa. By contrast, for fungi, only a non-significant decrease of richness was observed with N deposition. Importantly, those N deposition effects mostly occurred in the absence of planted shrubs. Moreover, shrub presence and N deposition also interactively affected the diversity of soil invertebrates, i.e., N deposition had little effect on them in the absence of planted shrubs, but resulted in an increase or a non-significant increase of soil invertebrate diversity in the presence of planted shrubs. Furthermore, N deposition did not affect the biomass/density of any soil food web component and biomass/density ratios related to soil food web structure regardless of absence or presence of planted shrubs; these indices were only affected by the presence of shrubs. Overall, these dissimilar responses of the diversity of soil microorganisms and animals to elevated N deposition indicate that plants are important mediators of N deposition effects on soil biodiversity. Thus, the present results may imply that an intact plant cover may mitigate detrimental N deposition effects on soil biodiversity.

Transgenic Bacillus thuringensis (Bt) crops are widely deployed to control lepidopterous pests with minimal impact on non-target soil invertebrates. However, most of the results were obtained from field works, the great environmental variation may conceal the small spatial-temporal scaled changes in microhabitats, such as those created near the roots (rhizosphere) or around decomposing residues (detritusphere), which are expected to impact free-living soil organisms more than the bulk soils. The objective of this study was to assess the impact of root and straw residues of transgenic crops on soil, by comparing nematode communities in the rhizosphere (soil microsites only affected by living root), the detritusphere (soil microsites affected by crop aboveground residues) and the rhizosphere-detritusphere interface (soil microsites intensively co-affected by root and residues) of Bt rice and its non-Bt near isoline. Bt rice did not affect nematode abundance and community composition, however, it enhanced the network connections within nematode communities, in both the rhizosphere and detritusphere, indicating the frequency of co-occurring species increased due to the moderate stress of crystal (Cry) as a labile resource of protein or as a moderate pressure of toxic compounds. Furthermore, 60-80% of the correlation between Cry protein (Cry1Ab/Cry1Ac) and nematode genera were positive in the rhizosphere and detritusphere of Bt rice, suggesting that higher Cry protein concentration was associated with the intensive co-occurrence among nematode populations. This finding offers new insights into how the biotic interactions of non-target soil community response to both live and dead parts of transgenic crop, highlighting the moderate stress of Cry protein might affect the community structure and consequent functioning of soil ecosystem based on the elaborately developed knowledge of biotic interactions via ecological network analysis.

Climate change is predicted to cause alterations in precipitation patterns in grasslands around the globe. The implications of these changes for soil biota and multiple key ecosystem functions that they regulate in grasslands is little known. We used soil nematodes as biological indicators in grassland ecosystems experiencing large shifts in precipitation in an arid, semiarid, and mesic grasslands. By calculating the nematode plant parasite index, maturity index, and its extensions: the enrichment, basal, channel, and structure index, we assessed grassland ecosystem response to five levels of manipulated precipitation over the course of two years. Nematode community structure described by these indices was sensitive enough to reflect community changes from the altered precipitation treatments and responded uniquely at each of the three sites. With increasing precipitation, nematode communities at the arid site became more enriched in species and switched to a more fungal-dominated decomposition pathway. The semiarid site showed a decline in nematode maturity, structure, and fungally dominated decomposition, but greater levels of enrichment, basal resources, and herbivory. In the mesic site increasing precipitation led to a nematode community with greater maturity and structure and shifted toward a fungal decomposition channel that also reflected a lower level of enrichment and plant parasites. We performed an indicator analysis to identify nematode genera representative of each grassland site and precipitation level. Nematode indicator composition was found to be significantly affected by the levels of applied precipitation and across sites, highlighting specific genera that may be affected by future precipitation regimes such as Eucephalobus in the arid site or Trichodorus from the mesic site. Nematode community analysis allowed for the detection of strong influences on the soil food web caused from extreme and moderate precipitation manipulations. This finding stresses the need for more genera level studies to be done to reflect specific ecosystem responses to climate change as well as the need for more cross site studies as site-specific differences must be accounted for ecological interpretations.

The study aims to investigate the effects of different drought treatments on the distribution of soil nematode community under the background of global warming. Light drought, moderate drought, severe drought treatments and control plot were set in the experiment. Experimental results showed that a total of 32 genera of nematodes from 18 families were identified under the four drought treatments, including 13 genera of bacterivores, 10 genera of plant-parasites, 4 genera of fungivores and 5 genera of omnivores-predators. Eucephalobus and Helicotylenchus were dominant genera under drought treatments. The quantity, genera and diversity of soil nematodes in drought treatments were significantly lower than those in control plots. The structure of the nematode community degenerated and the role of nematodes in soil food web was weakened in the agro-ecosystem after long-term drought. The study provides soil zoological basis for agro-ecosystem responding to extreme drought under climate change.

Carbon use efficiency (CUE) describes the relative partitioning of carbon (C) between anabolic and catabolic processes within the soil microbial community. Further, it represents a major factor regulating the amount of C cascading through the trophic levels of the soil food web. How CUE relates to C supply, however, remains poorly understood. The primary aim of this study was to determine how CUE varies across a range of spatial scales as a function of C substrate supply. Our secondary aim was to understand how variations in substrate CUE influences the interpretation of community level physiological profiles (CLPP). Using 16 different 14C-labelled substrates (including amino acids, sugars, organic acids and amino sugars) and soils collected at the field, regional and continental scale, we measured the rate of substrate uptake and mineralization from which we calculated CUE. Across all soils (n = 114) and substrates (n = 16), the average CUE for the microbial community was 0.568 ± 0.004 (range 0.492–0.794). While the partitioning of substrate-C within the biomass (immobilization/mineralization) over 72 h was highly conserved for some substrates (e.g. glucose), others showed a wide variability in CUE across the samples (e.g. valine). In the context of the CLPP methodology, we showed that individual sites could be statistically separated from each other, irrespective of whether the statistical analysis was based on microbial substrate uptake rate or mineralization rate. However, our results do suggest that caution is needed when ascribing observed CLPP differences to the importance of individual C pathways operating in soil due to the wide variation of CUE between substrates. In conclusion, we present new mechanistic evidence to support the paradigm that variation in ecosystem CUE may in part reflect differences in the types of C supplied to the microbial biomass.

This study assessed the carbon (C) budget and the C stocks in major compartments of the soil food web (bacteria, fungi, protists, nematodes, meso- and macrofauna) in an arable field with/without litter addition. The C stocks in the food web were more than three times higher in topsoil (0–10 cm) compared to subsoil (>40 cm). Microorganisms contained over 95% of food web C, with similar contributions of bacteria and fungi in topsoil. Litter addition did not alter C pools of soil biota after one growing season, except for the increase of fungi and fungal feeding nematodes in the topsoil. However, the C budget for functional groups changed with depth, particularly in the microfauna. This suggests food web resilience to litter amendment in terms of C pool sizes after one growing season. In contrast, the distinct depth dependent pattern indicates specific metacommunities, likely shaped by dominant abiotic and biotic habitat properties.

“Lights out” turfgrass renovation approach is a pesticide-free method of weed and pest management that can reduce weed pressure when replanting turf, switching grass types, or completing a total renovation of a designated grassy area. In this study, we addressed the feasibility of using black, geo-textile weed mats made of woven polypropylene plastic in this alternative turfgrass renovation approach. The specific objectives were: 1) to determine the most effective weed mat density to suppress weeds; 2) to determine the most effective fertilizer treatment (fertilizer × rate) to stimulate weed seed germination and drain the weed seed bank; and 3) to document changes in the biotic communities in the soil including nematodes and insects. This research was conducted in 2016 at Magoon Research Facility on the island of Oahu, Hawai’i. Our results indicated that the “lights out” method was effective, with all cover types providing better weed suppression than control plots treated with glyphosate. There were no significant differences between fertilizer treatments for weed diversity or coverage percent one-month post-fertilization. However, all plots treated with fertilizer had significantly less weed diversity and coverage after the Bermudagrass was planted, indicating that fertilization plays a crucial role in draining the weed seed bank. Soil arthropod and nematode communities were generally altered after each renovation step, indicating that covering and fertilization play a role in shaping the diversity, abundance, and maturity of the soil food web.

A current challenge for ecological research in agriculture is to identify ways in which to improve the resilience of the soil food web to extreme climate events, such as severe rainfall. Plant species composition influence soil biota communities differently, which might affect the recovery of soil food web after extreme rainfall. We compared the effects of rainfall stress up on the soil microbial food web in three planting systems: a monoculture of the focal species Zanthoxylum bungeanum and mixed cultures of Z. bungeanum and Medicago sativa or Z. bungeanum and Glycine max. We tested the effect of the presence of a legume on the recovery of trophic interactions between microorganisms and nematodes after extreme rainfall. Our results indicated that all chemical properties of the soil recovered to control levels (normal rainfall) in the three planting systems 45 days after exposure to extreme rain. However, on day 45, the bulk microbial community differed from controls in the monoculture treatment, but not in the two mixed planting treatments. The nematode community did not fully recover in the monoculture or Z. bungeanum and M. sativa treatments, while nematode populations in the combined Z. bungeanum and G. max treatment were indistinguishable from controls. G. max performed better than M. sativa in terms of increasing the resilience of microbial and nematode communities to extreme rainfall. Soil microbial biomass and nematode density were positively correlated with the available carbon and nitrogen content in soil, demonstrating a link between soil health and biological properties. This study demonstrated that certain leguminous plants can stabilize the soil food web via interactions with soil biota communities after extreme rainfall.

Improving soil health and managing beneficial and harmful nematodes using cover crops such as oilseed radish and mustard integrated with maize and soybean as rotation crops are major priorities in US sugar beet production. Despite extensive research on effects of rotation- and cover-crops on soil health, variable outcomes remain a problem. Using sandy clay loam and loam fields with known SBCN infestation, we tested how two each of oilseed (‘Defender’ and ‘Tillage’), mustard (‘Pacific Gold’ and ‘Ida Gold’), sugar beet (‘B-18RR4N’ and ‘B-10RR34’) and soybean (‘92Y80’ and ‘92M91’), and a maize (‘P9910R’) variety affect nematode community and soil food web in the 2013 and 2014 growing seasons. Each treatment (crop) was replicated six times. Maize is a non-host and Defender and Pacific Gold are poor hosts for SBCN. Nematode community composition at intervals during growing seasons and soil physiochemical properties at the end of year 1 were measured. The crops had no effect on nematodes. Nematode abundance and community indices varied by sampling time, growing season and/or soil type. Principal component analysis showed that the crops distinctly separated by soil type and only a few nematode community indices and/or soil physiochemical parameters overlapped with crop. Soil food web analysis showed depleted and degraded conditions in the sandy loam soil and disturbed and approaching enrichment in the loam soil. The study suggests a roadmap to get to agrobiologically suitable soil conditions to meet industry priorities for healthy soils.

Development from bare soil to biological soil crust (BSC) after the establishment of vegetation for sand fixation is an important desertification rehabilitation process in dryland ecosystems. While subsequent changes aboveground have been well documented, few studies focused on how BSC affects soil food webs after vegetation establishment. In this study, we investigated how soil food web channels respond to BSC, and in particular how flow of carbon from microbes to higher trophic levels is affected in Horqin Sandy Land, China. The BSC layer and 0–1 cm depth soil layer without BSC (as the control of BSC) were taken. After that, soil samples of 10 cm depth were collected and then dividing into two equal 5 cm parts for comparing soil microbe and nematode community composition in 2013 and 2014. The results showed that presence of BSC increased the phospholipid fatty acid and biomass carbon of microbes in the top layer of both years. Abundance, biomass carbon, and metabolic footprint of nematode trophic groups, including fungivores and omnivores-predators in the top layer, had higher values under BSC. Positive relationships were found between total organic carbon of BSC and biomass carbon of fungi, and between biomass carbon of fungi and fungivores. BSC enhanced carbon flow from fungi to fungivores, with higher connectance values in the fungal channel than in soil without BSC. The strengthened relationships between total organic carbon of BSC and omnivore-predator, and high connectances of the fungal channel and of the omnivore-predator channel under BSC, suggest a more reticulated channel in soil food web. It can be concluded that colonization of BSC enhances the connenctances in soil microbial food web channels, and could contribute to the resilience of dryland ecosystems.

17 Pág. Departamento de Medio Ambiente y Agronomía​ (INIA), Biochar applications can have important implications for many of the soil functions upon which agroecosystems rely, particularly regarding organic carbon storage. This study evaluated the impacts of adding a highly aromatic gasification biochar at different rates (0, 12 and 50 t ha-1) to a barley crop on the provision of crucial soil functions (carbon sequestration, water content, greenhouse gas emissions, nutrient cycling, soil food web functioning, and food production). After natural ageing in the field for six years, a wide range of soil properties representative of the studied soil functions were measured and integrated into a soil quality index. Results showed that C sequestration increased with biochar rate (23 and 68% higher than in the control for the 12 and 50 t biochar ha-1 treatments, respectively). Water content was enhanced at the 50 t ha-1 treatment depending on the sampling date. Despite biochar additions neither abating nor increasing CO2 equivalent emissions (carbon dioxide plus nitrous oxide and methane), the system shifted from being a methane sink (-0.017 ± 0.01 mg CH4-C m-2 h-1 at the 12 t ha-1 treatment), to a net source (0.025 ± 0.02 mg CH4-C m-2 h-1 at the 50 t ha-1 treatment). In addition, biochar ageing provoked a loss of nitrate mitigation potential, and indeed ammonium production was stimulated at the 50 t ha-1 rate. The 50 t ha-1 treatment also adversely affected nematode and collembolan functional diversity. Lastly, biochar did not affect barley yield. The results of the soil quality index indicated that no biochar treatment provided more benefits to our agricultural soil, and, although the 50 t ha-1 treatment increased C sequestration, this was potentially offset by its harmful effects on soil faunal communities. Therefore, application of this biochar at high rates should be avoided to prevent risks to soil biological communities., We gratefully acknowledge the funding by the project FERTICHAR (AGL2015-70393-R) of the Spanish Ministry of Economy and Competitiveness. We are also grateful to Dr. van den Brink, P. J., and Dr. Šmilauer, P. for their assistance on PRC analysis interpretation and proper use of CANOCO 5, respectively.

Soil aggregation is a key contributor to soil carbon (C) accrual and stabilization. Yet, little is known regarding how soil food web structure shifts across aggregate size and how this in turn could significantly influence soil C stabilization within aggregates. In order to cohesively understand the link between nematodes and soil C, we conducted a meta-analysis consisting of 98 observations from 11 papers to quantitatively assess how nematode community composition changes by aggregate size. Due to the small sample size of this meta-analysis publication bias was assessed through the use of funnel plots. Additionally, to prevent certain studies from skewing results, studies that were outside of the 95% Confidence Interval (CI) pooled effect were excluded from the meta-analysis. The investigation of the relationship between nematode community composition and total soil organic C across aggregate size revealed no distinct difference between the summary response ratios for total nematode abundance and all trophic groups. This finding indicates that nematode composition did not differentiate by aggregates size. Soil organic carbon (SOC) values varied by aggregate size, where microaggregates ( 2 mm). Additionally, mid-sized aggregates (0.25 mm–2 mm) had 115% greater SOC relative to macro-aggregates. SOC and total nematode abundance were negatively correlated in aggregate sizes of 0.25-2 mm (Pearson's r = −0.38, p 2 mm (Pearson's r = −0.42, p

As a widely used fungicide, the toxic impacts of pyraclostrobin on soil ecosystems have attracted extensive concern. Thus, it is very important and meaningful to develop effective strategies to alleviate its toxic effects. Therefore, in this study, we used corn straw-derived biochar produced at 500 °C as a soil amendment to study its effects on soil microbial populations, aggregation, enzymatic activities, and earthworm Eisenia fetida in pyraclostrobin-contaminated soil. Our results showed that biochar application (1%, w/w) significantly (Tukey test, p 0.25 mm). Moreover, biochar application eliminated the toxic effects of pyraclostrobin on soil microorganisms and reduced oxidative stress and DNA damage in E. fetida by increasing the dissipation of pyraclostrobin in soil. We also found that biochar and earthworms synergistically improved the soil structure and degradation of pyraclostrobin, thus indicating that the combined application of biochar and earthworms is a better strategy to improve soil physical structure, biological properties, and health. Finally, we conclude that increasing the soil food web and physical complexity by adding biochar and earthworms may improve soil health stressed by xenobiotic pollutants.

Tree roots and mycorrhizal fungi form an important resource for soil microinvertebrates; however, there is little knowledge on the role of root feeders and microbial grazers on belowground carbon flux of forest trees. Using oak (Quercus robur) microcuttings (Clone DF159) inoculated with an ectomycorrhizal symbiont partner (Piloderma croceum), the present study investigated the impact of multitrophic interactions in the rhizosphere on the carbon flow to the soil food web in a pulse-chase labelling experiment. Changes in plant biomass, microbial communities (soil phospholipid fatty acids - PLFAs) and Collembola lipid pattern (total lipid fatty acids - TLFAs) as well as the 13C incorporation into fatty acids were assessed at 2, 5 and 20 days post labelling of oak microcuttings. Microcosms were inoculated with Pratylenchus penetrans (root-feeding nematode), Protaphorura armata (fungal-feeding Collembola) or their combination. The interaction of P. penetrans and P. armata synergistically reduced oak biomass. Both soil animals independently impacted growth of microorganisms in the rhizosphere, P. penetrans inhibited whilst P. armata promoted bacterial biomass. Irrespective of treatment and time, Gram-positive bacteria derived most of the recent photoassimilated oak carbon, with amounts ranging between 80 and 92% of the total 13C allocated in microbial PLFAs. Presence of either P. armata or P. penetrans enhanced the incorporation of plant carbon in bacteria, whereas collective effects of these two functional groups was scarce. Predominantly the impact of the root-feeding nematode on belowground carbon flow diminished with time. In sum, root feeders and detritivores played independent roles in carbon allocation patterns and community structure of microorganisms in the rhizosphere of oaks.

Open-cast lignite mining consumes arable land, which has to be restored and recultivated afterwards. This process strongly dilutes the organic carbon and nitrogen pool as well as soil biological parameters of the former soil due to mixing with the underlying subsoil and parent material before redeposition. Cultivation of alfalfa is commonly used to restore agricultural land and to refill diluted C and N pools and re-establish biologic functions. Based on nematode-derived indices, we here evaluate the development of the food web during the early recovery period with N-fixing alfalfa on post-mining soil substrates in the lignite mining district west of Cologne (Germany). Nematode-derived indices revealed a fast recovery of the soil food web during this initial alfalfa cultivation. We found evidence that the applied recultivation procedure lowers the stress and disturbance level in the soil-microbial food web and improves the trophic complexity. The fast maturing of the food web was indicated by Thornenematidae nematodes, which indicated a highly structured and stable food web already after three years of alfalfa cultivation. A declining δ15N signal of the soil indicated a strong impact of N-fixation by alfalfa. Microbial and mineral N content increased during the alfalfa cultivation period. We concluded that the rapid recovery of the soil food web might not be paralleled by an equal increase of its capacity to retain N in the soil food web. This might have implications for nitrate leaching, nitrous oxide emission, and a later agricultural recultivation with common field crops.

Both climate warming and litter removal alter soil nematode communities and the structure, stability, and function of soil food webs. The soil nematode metabolic carbon footprint, based on nematode biomass and respiration, can be used to indicate ecosystem function and the response of nematodes to nutrient enrichment in the ecosystem. However, it is unclear whether or how climate warming and litter removal affect the metabolic carbon footprint of soil nematodes and soil food webs. In this study, we investigated four warming and litter removal treatments in the Qinghai-Tibet Plateau, China, to determine the effects of climate warming and litter removal on soil microbial food webs. The treatments included: (1) control (CK), (2) warming, (3) litter removal, (4) warming + litter removal. We found that warming and litter removal had significant negative effects on the diversity and richness of soil nematodes. In addition, our results showed warming indirectly and directly affected vegetation diversity, thereby altering soil nematode diversity. Vegetation played an important role in the maintenance of soil nematode community diversity. The enrichment and structural footprints reflected nematodes that could respond most rapidly to resource enrichment and those with higher trophic levels in soil food webs, respectively. Overall, warming and litter removal significantly negatively affect the enrichment metabolic footprint, indicating they could significantly reduce the external resource inputs into the food web. Both warming and litter removal reduced the structural metabolic footprint of the soil food web, although the changes were not significant, indicating that the metabolic activity of nematodes of high nutrient levels decreased and the ability to regulate the food web from top-bottom effects was weakened under warming and litter removal. The nematode functional metabolic footprints indicated that litter removal could aggravate the effect of warming on the soil food web and result in more severe degradation. The combination of warming and litter removal significantly inhibited the connectance of the bacterial channel, but had no significant effect on the fungal channel. These results suggest that the soil food web enhanced resistance to the environment by increasing the proportion of the fungal channel. It is critical to understand the responses of soil food webs to climate warming and litter removal to better predict how ecosystem functions will change in the future.

Conventional agriculture has induced serious environmental problems that are severe under greenhouse conditions because of the large chemical inputs and high levels of disturbance. Organic and low input management practices with the application of organic amendments, and elimination or reduction of synthetic fertilizer inputs and pesticides, were proposed to alleviate these problems. Existing studies have assessed the effect of different management practices on the communities of one or several types of soil organisms, but the effects on the whole soil food web are unknown. Therefore, we analyzed the impact of three management practices—organic (ORG), low input (LOW) and conventional (CON)—on the structure and biomass of soil food webs under greenhouse conditions in northern China. A range of soil biota including microorganisms, protozoa, nematodes, microarthropods, and annelids, were collected to construct the soil food web. Sampling events were carried out monthly from August to December for 0–10 and 10–20 cm soil depths. The results showed that the number of functional groups, connectance, maximum and mean of food chain length, and food web diversity were highest in ORG, indicating that the soil food web was more complex under organic management practices than the other practices tested. The total food web biomass presented a decreasing sequence of ORG > LOW > CON in both soil layers. For each trophic level, the biomass was greater in ORG than in LOW and CON, and this advantage for ORG increased with increasing trophic level, indicating that organic management practices were more beneficial to biota at higher trophic levels. The principal component analysis based on functional groups showed that the soil food web composition of LOW was between that of ORG and CON, and that of LOW and CON were more similar at 0–10 cm depth. The Bray-Curtis similarity index showed lower variability in ORG than in LOW and CON, indicating a relatively stable soil food web in the organic greenhouse. In summary, organic management practices under greenhouse conditions enhanced soil food web biomass and complexity, which was likely driven by supply of manure and the elimination of chemical inputs.

Partial substitution of chemical fertilizers by organic manure is essential for improving the soil quality and crop production. However, there is limited information regarding the complex microbial-microfaunal interactions derived from different organic or inorganic fertilizer application rate in the rhizosphere of jackfruits. Therefore, the objective was to compare the effects of organic/inorganic fertilizers on the soil food web of microbes and nematodes. Filed and greenhouse studies were set up with six treatments, including CK (no fertilizer), 100CF (100% chemical fertilizer), 30OM (30% organic manure plus 70% chemical fertilizer), 50OM (50% organic manure plus 50% chemical fertilizer), 70OM (70% organic manure plus 30% chemical fertilizer) and 100OM (100% organic manure). After 4 years application of organic manure under field conditions, there was higher soil organic matter (SOM), microbial biomass carbon (MBC), nematode diversity and jackfruit yield. Moreover, the number of total nematode, microbivorous nematodes and omnivores-predators were positively correlated with organic manure, while plant-parasites did the opposite in greenhouse experiment. Organic manure increased the abundance, richness and Shannon diversity of bacteria and fungi as well as maturity indices (MI), Shannon index (H′), Pielou evenness index (J), enrichment index (EI), structural index (SI) and nematode channel ratio (NCR) of the nematode community in greenhouse experiment. Soil pH and SOM were significantly correlated with the variation of soil microbial-microfauna. Network analysis indicated that soil amended with organic manure presented more positive correlation between beneficial nematodes and microorganisms, but a negative correlation between plant-parasites Pratylenchus and dominant fungal taxon Chytridiomycota. These results indicated the feasibility of organic manure for soil quality improvement with high SOM and pH, suggesting that the correlation between microbes and nematodes constructed by organic fertilizer may play a key role in the improvement of soil quality.

Livestock grazing and atmospheric nitrogen (N) deposition have been reported as important factors affecting soil communities. However, how different large herbivore grazing and N addition may interact to affect soil biota in grassland ecosystems is unclear. Nematodes are the most abundant metazoan in soil ecosystems, play critical roles in regulating carbon and nutrient dynamics, and are valuable bioindicators. We examined the independent and interactive effects of grazing regimes (no grazing; sheep grazing; cattle grazing; mixed grazing of sheep and cattle) and N addition (ambient N; N addition) on soil nematodes in a meadow steppe. We found that grazing and N addition interacted to influence total nematode abundance, trophic group abundance, generic richness, diversity and several nematode-based indices (maturity index, channel ratio, enrichment index). In cattle grazing treatment, N addition significantly increased total nematode abundance, and the abundance of bacterial feeders, plant feeders, and omnivore-predators, and generic richness. By contrast, in the sheep and mixed grazing treatments, N addition had a negative effect on the same variables. Moreover, N addition reduced nematode maturity, enrichment and structure indices, and enhanced nematode channel ratio, in most grazing treatments, except mixed grazing where N addition had no effect on these variables. Structural equation modeling (SEM) revealed that N addition indirectly reduced nematode abundance and richness through increased soil NO3−-N content, whereas the effects of grazing were associated with increased relative biomass of grasses. Our results suggested that the response of soil nematodes to N addition strongly depended on herbivore assemblages. Nitrogen addition enhanced soil nematode diversity and maintained a relatively complex and mature soil food web in the presence of cattle rather than sheep grazing. Furthermore, our study highlighted that under N deposition, cattle grazing could benefit the soil nematode community.

Biochar application has been recognised as an effective way to improve soil functions. In this study, we investigated how adding biochar as an amendment affects soil biological and physico-chemical properties in grazed pastures in a one-year field-based mesocosm experiment conducted on two contrasting soils – a sil-andic Andosol and a dystric Cambisol. Each site had two pastures managed under different nutrient and livestock practices: with and without effluent under dairy cow grazing on the Andosol, and with either nil or high phosphorus (P) fertiliser input under sheep grazing on the Cambisol. The soil amendment treatments were: (i) willow biochar produced at 350 °C (1% w/w); (ii) lime, added at the liming equivalence of the biochar application (positive control); (iii) no amendments (negative control). With few exceptions, after 12 months and compared with initial values and controls, biochar caused (i) an increase in soil total nitrogen (N) and Olsen P content (all P

Plant invasions often act as ecosystem 'simplifiers' to simplify diversity and community structure of soil biota. However, inconsistent relationships between plant invasion and soil fauna have been found and few studies have addressed how soil fauna communities change upon plant invasions across taxa and feeding guilds. Here, we investigated the effects of moso bamboo (Phyllostachys edulis) invasion in subtropical China on soil mesofauna communities using novel high-throughput sequencing (HTS). Specifically, we analyzed the spatio-temporal dynamics of fauna diversity and feeding guilds in the litter and soil layers for three stages of moso bamboo invasion, i.e., uninvaded (secondary broadleaved forest), moderately invaded (mixed bamboo forest) and completely invaded (P. edulis forest). Overall, we found that the completely invaded bamboo forest decreased species richness and diversity of total fauna, herbivores, and microbivores consistently across different soil layers, but less so detritivores and predators. Although we did not find any interaction effects of bamboo invasion and soil layers on soil fauna diversity indices, significant interaction effects were found on the community composition, for total fauna and their feeding guilds. Specifically, the detrimental effects of bamboo invasion on the trophic structure of soil fauna communities were more profound in the litter layer than in the soil layer, suggesting that a litter layer with more diverse taxa does not mean higher resistance to plant invasion in maintaining the soil food web structure. Taken together, our findings suggest that different responses within fauna feeding guilds to plant invasion were pervasive, and a deeper soil layer may better alleviate the negative effects of pant invasion on fauna community structure. These shifts in soil biodiversity may further degrade ecosystem functioning.

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

Soil nematode communities play a significant role in soil ecosystems. Indeed, soil nematode metabolic carbon footprint, based on nematode biomass, is used to evaluate ecosystem functioning and assess nematode response to ecosystem nutrient enrichment. However, it is unclear whether vegetation restoration affects the metabolic carbon footprint of soil nematodes and soil food webs. We selected five periods for this study including: (1) farmland (0 years), (2) grassland (30 years), (3) shrubland (60 years), (4) pioneer forest (100 years), and (5) climax forest (160 years). Community composition, diversity, and metabolic footprint of soil nematodes, and carbon flow changes through the food web were investigated. The Shannon diversity (H′) index of the soil nematode community increased in the process of restoration, and the Pielou index (J′) appeared to be lower at 30 years after vegetation restoration than at 60, 100, and 160 years. The connectance of the soil nematode food web values increased continuously, from 30 years to 160 years, reaching the highest value at 100 and 160 years, which indicated that the food web had the strongest carbon flow at 100 years after vegetation restoration on the Loess Plateau, indirectly reflecting the stability of the soil food web. Bacteria were more important than fungi in the carbon flow in the food web during vegetation restoration. The study demonstrated that vegetation restoration promoted the input of the availability of external resources, enhanced the metabolic activity of omnivorous carnivores and the soil carbon flow, and stabilized the soil food web. However, the increase in vegetation restoration time not only changed the species composition but also changed the carbon input, due to the lack of interference by agriculture. Therefore, the intrinsic mechanism needs to be studied further.

Agricultural intensification that results in conversion of forests into crop fields affects soil biodiversity including nematodes which contribute to ecosystem services and play a key role in maintenance of soil health. The nematode soil food web and metabolic footprints of a tropical forest and surrounding tea fields in Embu, Kenya were investigated. Soil samples were collected from tea fields and forest and the nematodes were identified to the genus level. The plant-parasitic index in the tea fields was high and the abundance of nematodes in cp2 class and Ba2 functional guild were greater than those in the forest. Helicotylenchus, Rotylenchus, Telotylenchus and Malenchus occurred in higher densities in the forest which also had a significantly high predator footprint. The pH, Mn, sand, clay and silt content varied across the forest and tea fields. Nematode communities in the two land use systems were distinct based on non-metric multi-dimensional scaling ordinations. Heterocephalobus which was positively correlated to pH and Helicotylenchus, Telotylenchus, Iotonchus and Rotylenchus which had a negative association with silt contributed to the dissimilarity observed in the forest and tea fields. The findings provide an insight into the effects of land use change on nematode communities in the two systems. This study will provide baseline data that can be used to make informed decisions on tea production and land use strategies that enhance soil health.

Terrestrial ecosystems are driven by different global change factors, such as atmospheric nitrogen deposition and precipitation reduction. Nitrogen deposition and precipitation reduction have a great impact on the above- and underground processes. Most previous studies mainly focused on the effects of nitrogen deposition and/or precipitation reduction on aboveground processes, while the effects on underground processes were relatively scarce. As an important part of the underground soil food web, soil nematode community occupies different nutritional niches and is sensitive to external disturbances, and it is often used as indicator for studying underground processes. However, we know little about the response of soil nematode community to nitrogen deposition and/or precipitation reduction. Here, we used a 10-year of factorial manipulation by applying nitrogen solution and reducing the amount of precipitation to the soil, and to investigate the responses of soil nematode community to nitrogen deposition and/or precipitation reduction in a temperate forest. We expected that nitrogen addition could promote while precipitation inhibited the activity of soil nematode community. Furthermore, we expected nitrogen addition and precipitation could have interactive effect on soil nematode community. Our results found that nitrogen addition and/or precipitation reduction treatment caused significant changes in the composition of soil nematode community. Nitrogen addition and nitrogen addition combined with precipitation reduction induced negative effects and significantly decreased the abundance and diversity of soil nematode community, while precipitation reduction only decreased the abundance of soil nematode community. Nitrogen addition and precipitation reduction had synergistic effect on soil nematode community with higher trophic levels. Compared with precipitation reduction treatment, the negative effect of nitrogen addition on soil nematode community was more severe. According to the structural equation model (SEM), we found that nitrogen addition and precipitation reduction could affect the abundance of soil nematode community by affecting the plant richness and soil pH. Since the decrease of enrichment index (EI) and the increase of structure index (SI), our research results revealed that nitrogen addition could lead to soil food web in a lower nutrients available condition.

Elevated atmospheric CO2 concentrations (eCO2) 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 eCO2 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 CO2 enrichment (FACE) experiment in a rice paddy agroecosystem that examined the responses of soil micro-food webs to eCO2 and exogenous nitrogen fertilization (eN) in the rhizosphere of two rice cultivars with distinctly weak and strong responses to eCO2. 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 eCO2 effects on soil micro-food webs depended strongly on N fertilization, rice cultivar and growth stage. eCO2 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 eCO2. While eCO2 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 eCO2 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 eCO2 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 eCO2 may face a trade-off by negative soil feedbacks through the accumulation of root-feeding crop pest species.

Global circulation models predict shifts in precipitation patterns in arid and semiarid ecosystems worldwide. Independently of changes in total precipitation, rainfall is expected to concentrate in less frequent but larger events, and this redistribution will increase drought severity in biomes naturally controlled by precipitation pulses and water availability. This study focuses on effects of altering rainfall patterns on the soil food web of a semiarid prairie, and on impacts of grazing on soil food web resilience to climate change. We worked in a greenhouse with undisturbed soil monoliths extracted from grazed and ungrazed field plots. We planted all monoliths with Bouteloua gracilis that was the dominant grass at the experimental site, and let the grass establish before applying two different rainfall treatments over a five-month period, equivalent to the duration of the growing season in the area. We simulated the current rainfall pattern in the experimental area and also an altered rainfall pattern consisting of concentrating the total growing season precipitation in half the number of rain events. Rainfall concentration increased the amplitude of the water pulse and lengthened the dry periods between rain events thus worsening soil water stress. We analyzed the experimental monoliths for effects of rainfall pattern and grazing management C and N content, soil organic matter mineralization and soil biota abundance and functional diversity. Based on the experimental data, we simulated soil food web stability and mineralization capacity. We concluded that (a) rainfall concentration causes loss of key soil functional groups and reinforces soil food web stability, (b) organic matter mineralization by the soil food web decreases with rainfall concentration, (c) coarse-textured soils are more responsive than fine-textured soils to modifications of the rainfall regime, (d) soil food web responsiveness to changing rainfall regime is higher in grazed prairies than in prairies excluded from herbivores.

Given the relevant role played by soil organisms in fundamental ecosystem processes, current ecological research stresses the importance of understanding the trophic structure of soil communities in order to better predict the effects that global environmental change can have on the soil food web structure and dynamics. Using stable isotope analysis, we examined the trophic ecology of six soil oribatid mite species present in the leaf litter of beech forests which mainly differed in mean annual precipitation. We explored the relationship between animal and leaf litter signatures to determine which of the two approaches, conventional calibration or a novel solution we offer using statistical control (i.e., isotopic signature of the basal resource included as a covariate in the model), is more adequate to evaluate the trophic structure of soil communities across different sites, and investigated if the trophic niches of the species varied under two different precipitation regimes. The trophic position of some species varied with rainfall; the observed enrichment in 15N in dry forests reflects trophic and spatial shifts probably resulting from changes in microbial activity and community composition. In addition, we find interactive effects between precipitation and the basal resource for some species and a lack of correlation between resource and oribatid mite stable isotope values for others. We discuss the pertinence of using conventional data calibration as it appears to mask relevant trends regarding the trophic ecology of oribatid mite species, and suggest using statistical control (a covariate approach) instead.

Soil nematode communities provide important information for soil food web structure and function. Our study focused on the impacts of different fertilization regimes on sugarcane growth, while primarily considering their effects on soil nematode responses during different growth stages. The sugarcane yields were significantly increased in plots fertilized with functional biofertilizers (BIOs) compared with plots that received chemical fertilizers. Moreover, the BIO applications significantly ( P 0.01) decreased the relative abundance of plant parasite while significantly ( P 0.01) increased the relative abundance of beneficial nematodes: Cephalobus, Cervidellus, Acrobeles, Caenorhabditis in the group of bacteriores and Ditylenchus, Tylencholaimus in the group of fungivores. Nonmetric multidimensional scaling (NMDS) revealed that soil nematode communities were primarily separated by sampling time. A network analysis showed that BIO applications led to more simplified soil nematode community, which was possibly linked with the increased bacterivore abundance and improved soil fertility. The effects of fertilization regimes were significant ( P 0.05) and accounted for 3.35% of the total variation in soil nematode communities. Soil properties (e.g., pH, organic matter, total N, available K and available P) were influenced by the fertilization regimes and different sampling time, which significantly ( P 0.05) explained 14.53% of the soil nematode variation. In conclusion, BIOs applications might facilitate sugarcane yield by increasing the relative abundance of bacterivore while decreasing plant parasites. The changes in soil nematode communities may reflect the soil fertility and health and provide evidence for the benefits of BIO applications for sugarcane crops.

Agroecosystem plant diversification at the field scale has been shown to enhance ecological pest regulation. We explored the effects of plant community composition and soil properties on the soil nematode community, with a particular interest in the regulation of banana plant-parasitic nematodes (PPN). We monitored banana phytometers (Cavendish Grande Naine cultivar) in 85 plots distributed along a plant richness gradient. Plant community composition, soil properties, abundance of bacterivorous, fungivorous and proportion of predaceous soil free-living nematodes, and abundance and damage of PPN ( Radopholus similis , Pratylenchus coffeae , Helicotylenchus multicinctus , and Meloidogyne spp.) in phytometer roots were measured. We used structural equation modeling to investigate ecological processes leading to PPN regulation. Low-stratum plant species richness, but not high-stratum, was positively related to microbivore nematode abundances, supposedly because it promoted qualitative diversity of organic inputs and micro-climatic effects supporting more soil microorganisms. Musa genotype and low-stratum plant species richness induced associational susceptibility because of differential susceptibility of Musa genotypes to PPN and because of polyphagia of PPN spreading outside the Musa family, respectively. We found no regulation of PPN by predaceous nematodes, probably because food web complexity prevented trophic cascades from propagating. Ultimately, fungivorous nematode abundance was negatively related to PPN abundance, suggesting apparent competition or increased regulation by antagonistic fungi. Our results suggest that, when facing generalist pests, cropped plant communities should be diversified to promote pest regulation but must be carefully assembled to limit pest susceptibility heterogeneity among crop genotypes and to exclude alternative host plant species.

Production practices that incorporate fall-planted cover crops into no-till agronomic crop rotations have become increasingly popular across the Northeastern United States for weed suppression and enhancing environmental stewardship. Field experiments were conducted in 2011 and 2012 to investigate effects of rotating cereal (barley, Hordeum vulgare), legume (Austrian winter pea, Pisum sativum subsp. arvense), cereal/legume cover crop mixture, and a fallow (bare-ground) control on above- and belowground fauna in a succeeding soybean crop. Free-living nematodes and soybean foliar arthropods were sampled through time to determine effects of cover crops on soil food web structure and complexity and herbivorous and beneficial arthropods, respectively. Our hypotheses were that organic matter from cover crop biomass would provide energy and nutrients to the soil food web and that increased habitat complexity from cover crop residue would provide habitat for more predatory arthropods aboveground. In general, cover crops in this no-till system had a stronger influence on the below- than aboveground fauna. There was no consistent, positive effect of cover crops on beneficial foliar arthropods or on soybean yield. Cover crops increased the soil food web structure and complexity as determined by nematode community indices. Specific effects of different cover crop types on the free-living nematode community varied within the growing season and between study years. Probable causes for differences encountered among cover crop treatments and years are discussed.

The structure of soil nematode assemblages was assessed in field plots in the San Joaquin Valley of California which have 16-year management system histories. Attributes of the ecosystem functions of the assemblages were determined in laboratory studies. The four agricultural management systems were no tillage (minimum tillage) with cover crops in the intervals between economic crops, standard tillage with cover crops, minimum tillage without cover crops and standard tillage without cover crops. The economic crops were sorghum and garbanzo beans. A soil column system was used in laboratory studies to evaluate the nitrogen mineralization ecosystem service associated with nematode assemblages in soils from the four management systems compared to that in defaunated soil. In an additional comparison, defaunated soil was amended with mineral fertilizer solution for comparison with the mineralization service of the soil fauna. Management systems using cover crops, which created a continuity of both photosynthetic production and roots in the soil, strongly enhanced the nematode assemblages in the field soil. Management systems with cover crops had greater total abundance, measured as numbers, biomass and metabolic footprints, of nematodes, and also of the functional guilds of nematodes considered important in soil fertility and as prey for predators. Leachates from soil columns with intact nematode assemblages had greater total mineral nitrogen and supported greater plant growth than those from defaunated columns. Soil carbon levels in field plots were strongly affected by the management systems. The biomass and diversity-weighted footprint of bacterivore and microbivore (bacterivores plus fungivores) nematodes, in turn, were correlated with levels of soil carbon.

Soil microbes play a key role in soil health, and understanding the functional role of this living component of soil organic matter is critical to developing sustainable systems in major vegetable production regions like Salinas, California. Soil microbial community size and composition was evaluated after six years of commercial-scale production in five organic vegetable systems in a long-term systems experiment. All systems produced lettuce, and spinach or broccoli annually, and differed in yard-waste compost inputs (none or 15.2 Mg ha −1 year −1 ), winter cover crop frequency (annually or every 4th year), and cover crop type (legume-rye, mustard, or rye). The same levels of irrigation, and supplemental fertilizer were applied to all systems. Cumulative organic matter inputs from compost and cover crop shoots over the six years ranged from 7.4 to 136.8 Mg ha −1 and caused differences in microbial biomass C (MBC) and N (MBN), and soil organic C (SOC). MBC increased by 40 mg C kg −1 soil with compost and infrequent cover cropping, and to levels that were relatively high (200–250 mg C kg −1 soil) for a loamy sand soil in systems with annual cover cropping. Changes in SOC between systems were caused primarily by compost while changes in MBC and MBN were more related to cover cropping frequency. Fatty acid methyl ester (FAME) analysis revealed differences in microbial community structure that were consistent with differences between systems in MBC and MBN. Across systems, the ratio of fungal: bacterial FAME indicators decreased over time while indicators of invertebrates, and gram positive bacteria increased. High-throughput sequencing revealed relatively few differences in bacterial phyla between systems, but the increase in cropping intensity across all systems changed the relative abundance of some bacterial phyla ( Bacteroidetes, Deinococcus-Thermus ) and genera ( Flavobacterium , Nocardioidetes ). Cover crop type and frequency also influenced the abundance of two bacterial genera ( Pseudomonas, Agromyces ). These results provide evidence that carbon (C) inputs from frequent cover cropping are the primary driver of changes in the soil food web and soil health in high-input, tillage-intensive organic vegetable production systems.

The impact of fires on nematode diversity, abundance and biomass was assessed in 20 burnt forests and 20 adjacent control plots across a 3000-km-long north-south transect in European Russia. The transect covered five main forest types (Mediterranean and broadleaved forests, southern, middle, and northern taiga). In spring 2015, we assessed major abiotic parameters of soil, soil microbial PLFA markers, and nematode community characteristics (genus richness, abundance, biomass and trophic structure) in the burnt and control plots. Generic richness was the highest in the southern taiga (22 genera) declining both northwards (down to 16) and southwards (down to 13 genera). The highest abundance of nematodes was recorded in the Mediterranean forests (139.4 ± 15.1 ind. g−1 soil dwt, control site) and the lowest in the northern taiga (10.8 ± 1.2 ind. g−1 soil dwt, burnt site). Biomass followed the same pattern with slight deviations. Abundance and biomass of soil nematodes was not significantly affected by fires in any ecoregion with the exception of Mediterranean forests. We detected consistent fire effects on the abundance of particular nematode feeding groups. Trophic groups abundance of soil nematode communities were considerably modified in burnt forests due to the increase in abundance of bacterial-feeding nematodes and reduced number of hyphal-feeding, plant-associated and plant-feeding nematodes. This increase in bacterial-feeding nematode biomass coincided with the growth of the ratio between bacterial and fungal biomass in pyrogenic soils. pH of soil solution and actual denitrification rate in the burnt forests correlated with the biomass of predatory nematodes. We conclude that, five years after fire, the structure of the microbial community, pH of soil solution and denitrification activity correlate with the ratio of feeding groups of belowground nematode communities in these forests. Taking into account considerable nematode biomass in soil, shifts in the ratio of trophic groups after fires induced by these factors may potentially lead to changes in the level of ecosystem functions which they deliver in burnt forests.

Green roofs are increasingly used in the urban environment to insulate buildings, reduce stormwater runoff and remediate biodiversity lost in construction. Most common in the Northern Hemisphere are extensive green roofs, due to their low-cost and low-maintenance requirements. However, plant growth on these roofs is often limited and this could have implications for ecosystem service provision as well as reduce the economic feasibility of green roofs as an aesthetically successful product. In addition, the increasing popularity of green roofs as an eco-product means that a high number of these roofs, that do not reach their maximum potential in terms of plant growth, already exist, highlighting a need for a successful remediation tool post-build. Previous studies suggest that the soil food web on green roofs, integral for nutrient cycling in soils, is also lacking and that this may be an effective aspect to target in order to improve plant establishment and success. Microbial inoculants have already been added to green roofs, but with little scientific research informing their application. In this field experiment we aimed to determine if the addition of these foundation species in green roof soil food webs, including mycorrhizas, Trichoderma spp . and soil bacteria, could improve the abundance and biodiversity of higher trophic species, such as microarthropods, and if this had resultant effects on plant growth on a mature green roof. It was found that some microbial inoculants were more successful at remediating soil food webs than others, with Trichoderma in particular producing higher populations of some microarthropod groups. However, these changes in microarthropod community dynamics did not have a resultant positive effect on Sedum spp . growth. The authors hypothesize that mature green roofs have an established microbial community that may limit the success of commercial inoculants. This is the first study to demonstrate multi-trophic community changes as a result of the addition of soil microbial inoculants.

At present, nanoscale materials have been produced with unprecedented speed due to their widespread use and may inevitably be released into the environment. As an effective adsorbent for heavy metals, nanoscale carbon black (CB) can be used to immobilize metals in contaminated soil, but no information is available regarding its effect on soil nematodes. In the present study, laboratory bioassays were performed to investigate the impact of three rates (1%, 3%, and 5% mass ratios) of HNO 3 or H 2 SO 4 modified nanoscale carbon black (NCB or SCB) on the abundance and composition of nematode communities during 120 d of turfgrass growth. The results showed that 5% NCB and SCB treatments significantly increased plant shoot biomass of two crops. The total number of nematode genera in the control was greater than in nano-CB treatments. Plant parasites dominated across all treatments, with dominant genus Helicotylenchus . The abundance of total nematodes and each of the four trophic groups responded negatively to nano-CB addition. Three percent and 5% NCB addition significantly decreased the abundance of total nematodes, plant parasitic and bacterivorous nematodes, compared to the control. The species diversity, richness, community evenness and maturity index of soil nematodes were significantly decreased by 3% and 5% nano-CB compared to the control. This study revealed that modified nano-CB, as an amendment with a rate of 3% or higher, could cause significant disturbance to the soil food web and thus affect soil nematodes in the short-term.

Experimental manipulations of soil fauna are a powerful tool for assessing causal relationships between belowground biodiversity and key ecosystem properties. However, preparing soil microcosm treatments without soil fauna for ecological experiments can be problematic. Methods to exclude nematodes, a ubiquitous and functionally important component of terrestrial ecosystems, have been developed for a few specific ecosystems, some of them involving the application of nematicides that may have interactive effects throughout the soil food web. Our goal was to develop a method to remove nematodes from soils of three Long Term Ecological Research (LTER) grassland sites, ranging from desert to moist, without use of chemicals and with moderate disturbance. Moreover, we aimed at testing whether the nematode removal would remain effective up to several weeks later. The following treatments were applied to ∼3-kg soil microcosms in the laboratory: (1) a 72 h heating (65 °C) - freezing (−20 °C) - heating (65 °C) cycle using soil maintained at its original water content, and pre-wetting soil 24 h before heating (65 °C) for either (2A) 48 h or (2B) 24 h. We measured treatment effects on total abundance and trophic structure of the nematode community. To investigate whether nematodes would recolonize eight weeks after treatments, we conducted a greenhouse experiment where individual seedlings of the dominant grass species for each ecosystem were transplanted to treated and non-treated (control) soils. A heat-freeze-heat cycle of 72 h using soil in its original field water content killed 60, 95, and 99% of the nematodes for the desert, semi-arid, and moist tallgrass prairie soils, respectively. Pre-wetting soil before heating increased mortality to 99% for all ecosystems after only 24 h at 65 °C. Root-feeders were the most resistant nematode trophic group. Eight weeks after treatments, there was no significant nematode recolonization for the pre-wetted 48 h heated soils from the three sites, while for the semi-arid and moist sites there was a slight recovery in abundance in soil from the 24 h heating treatment. Therefore, a treatment at 65 °C for 48 h using pre-wetted soil is recommended for eight-week long manipulative experiments in order to assure the effectiveness of the nematode removal throughout the experiment.