Soil Food Web Functioning Research Articles

Impacts of Millipedes on Acari and Collembola Communities-A Microcosm Experiment.

Ecosystem engineers influence the structure and function of soil food webs through non-trophic interactions. The activity of large soil animals, such as earthworms, has a significant impact on the soil microarthropod community. However, the influence of millipedes on soil microarthropod communities remains largely unknown. In this microcosm experiment, we examined the effects of adding, removing, and restricting millipede activity on Acari and Collembola communities in litter and soil by conducting two destructive sampling sessions on days 10 and 30, respectively. At the time of the first sampling event (10 d), Acari and Collembola abundance was shown to increase and the alpha diversity went higher in the treatments with millipedes. At the time of the second sampling event (30 d), millipedes significantly reduced the Collembola abundance and alpha diversity. The results were even more pronounced as the millipedes moved through the soil, which caused the collembolans to be more inclined to inhabit the litter, which in turn resulted in the increase in the abundance and diversity of Acari in the soil. The rapid growth of Collembola in the absence of millipedes significantly inhibited the abundance of Acari. The presence of millipedes altered the community structure of Acari and Collembola, leading to a stronger correlation between the two communities. Changes in these communities were driven by the dominant taxa of Acari and Collembola. These findings suggest that millipedes, as key ecosystem engineers, have varying impacts on different soil microarthropods. This study enhances our understanding of biological interactions and offers a theoretical foundation for soil biodiversity conservation.

Soil nematode assemblages respond to interacting environmental changes.

Multi-factor experiments suggest that interactions among environmental changes commonly influence biodiversity and community composition. However, most field experiments manipulate only single factors. Soil food webs are critical to ecosystem health and may be particularly sensitive to interactions among environmental changes that include soil warming, eutrophication, and altered precipitation. Here, we asked how environmental changes interacted to alter soil nematode communities in a northern Chihuahuan Desert grassland. Factorial manipulations of nitrogen, winter rainfall, and nighttime warming matched predictions for regional environmental change. Warming reduced nematode diversity by 25% and genus-level richness by 32%, but declines dissipated with additional winter rain, suggesting that warming effects occurred via drying. Interactions between precipitation and nitrogen also altered nematode community composition, but only weakly affected total nematode abundance, indicating that most change involved reordering of species abundances. Specifically, under ambient precipitation, nitrogen fertilizer reduced bacterivores by 68% and herbivores by 73%, but did not affect fungivores. In contrast, under winter rain addition, nitrogen fertilization increased bacterivores by 95%, did not affect herbivores, and doubled fungivore abundance. Rain can reduce soil nitrogen availability and increase turnover in the microbial loop, potentially promoting the recovery of nematode populations overwhelmed by nitrogen eutrophication. Nematode communities were not tightly coupled to plant community composition and may instead track microbes, including biocrusts or decomposers. Our results highlight the importance of interactions among environmental change stressors for shaping the composition and function of soil food webs in drylands.

Nematode Community of a Natural Grassland Responds Sensitively to the Broad‐Spectrum Fungicide Mancozeb in Soil Microcosms

Fungicides make up the largest part of total pesticide use, with the dithiocarbamate mancozeb being widely applied as a nonsystemic contact pesticide to protect a wide range of field crops against fungal diseases. Although nematodes are key drivers of soil functioning, data on effects of fungicides, and especially mancozeb, on these nontarget organisms are scarce. Therefore, the effects of mancozeb on a soil nematode community from a natural grassland were assessed in small-scale soil microcosms. Nematodes were exposed to mancozeb-spiked soil in six nominal concentrations (7-133 mg/kg dry soil) and analyzed after 14, 56, and 84 days in terms of densities, genus composition, and functional traits. Because this fungicide is known to quickly degrade in soils (50% degradation time <1 day), mancozeb concentrations were analyzed for all sampling occasions. Chemical analysis revealed considerably lower measured concentrations compared with the aimed nominal soil concentrations at the beginning of the exposure (1-18 mg/kg dry soil), suggesting fast degradation during the spiking process. Nevertheless, the native nematode community responded sensitively to the fungicide mancozeb, revealing lower no-observed-effect concentration and 10% effect concentration (EC10) values than reported for other soil invertebrates such as springtails and earthworms. Using the EC10 for the most sensitive nematode community endpoint (percentage of predators and omnivores: 1.2 mg/kg dry soil), the risk assessment exhibited a toxicity exposure ratio of 0.66 and, thus, a high risk of mancozeb for soil nematodes. Keeping in mind their abundance and their central roles in soil food-web functioning, the demonstrated sensitivity to a widely applied fungicide underscores the relevance of the inclusion of nematodes into routine risk-assessment programs for pesticides. Environ Toxicol Chem 2022;41:2420-2430. © 2022 SETAC.

Soil food web structure and function in annual row-crop systems: How can nematode communities infer soil health?

Increased agricultural management intensity is known to degrade soil food web structure and function, however, the impact of 50+ years of contrasting agricultural management practices on soil food webs is largely unknown. The relationship between soil food web structure and sensitive soil health indicators has seldom been quantified in row crop agricultural systems in the Midwest, USA. This study aims to 1) quantify soil food web structure and function in long-term systems that range in tillage intensity and perenniality over the course of a single growing season; and 2) identify the relationship between soil health indicators and soil food web structure. Nematode feeding groups and nematode indices were used to indicate soil food web structure and soil food web function, respectively. Additionally, a suite of soil health indicators including permanganate oxidizable carbon (POXC), β-glucosidase (GLU), and N-Acetyl-β-glucosaminidase (NAG) were measured in two identical long-term experimental trials with contrasting soil types (clay versus silt loam) under two tillage intensities (chisel till (CT) vs. no-till (NT)) combined with two crop rotations (corn-soy (CS) vs. corn-forage-forage (CFF)). All samples were collected in the corn phase of the rotation. Non-metric multidimensional scaling of nematode community assemblage and vector analysis demonstrated that soil food web structure was significantly related to POXC, GLU, and NAG within CFF systems. Nematode families Thornenematidae and Rhabditidae served as indicators of improved and degraded soil food web function, respectively. Our findings indicate that including perennials within a crop rotation fosters a soil food web structure that can enhance carbon and nitrogen cycling in large scale row-crop agriculture. Moreover, this study emphasizes the potential for specific nematode families to serve as indicators of soil food web function, demonstrating that nematodes should be integrated into the soil health framework.

Investigating the role of soil mesofauna abundance and biodiversity for organic matter breakdown in arable fields.

Intact soil food webs are pivotal to maintaining essential soil functions, such as carbon recycling, sequestering, and biomass production. Although the functional role of micro‐ (e.g., bacteria and fungi) and macrofauna (e.g., earthworms) is comparatively well established, the importance of the mesofauna community (e.g., abundance and diversity of Acari and Collembola) in maintaining soil functionality is less clear. We investigated this question in a six‐month field experiment in arable soil by actively manipulating mesofauna abundance and biodiversity through the application of two legacy insecticides (lindane and methamidophos) at sufficiently high doses to reduce mesofauna abundance (well above previously registered application rates; 2.5 and 7.5 kg a.s./ha for lindane, and 0.6 and 3 kg a.s./ha for methamidophos) and measure the impact on organic matter degradation. Our results demonstrate that both insecticides had reduced Collembola and Acari abundances by up to 80% over the study's six‐month duration. In addition, we observed less pronounced and more complex changes in mesofauna biodiversity over time. These included insecticide‐dependent temporal fluctuations (both reduction and increase) for different estimates (indices) of local (alpha)‐diversity over time and no lasting impact for most estimates after six months. Even at these exceptionally high field rates, Collembola and Acari diversity was observed to generally recover by six months. In contrast, considering organic matter breakdown, we found no evidence of a treatment‐related effect. These results suggest that organic matter breakdown in arable soils is likely driven by other trophic levels (e.g., microorganisms or earthworms) with only a limited influence of the mesofauna community. We discuss these findings with regard to their implications for our current understanding of soil food web function and future European soil risk assessments. Integr Environ Assess Manag 2022;18:1423–1433. © 2021 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Long-term effects of gasification biochar application on soil functions in a Mediterranean agroecosystem: Higher addition rates sequester more carbon but pose a risk to soil faunal communities

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.

Response of the soil food web to warming and litter removal in the Tibetan Plateau, China

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.

Interactions between nitrogen availability, bacterial communities, and nematode indicators of soil food web function in response to organic amendments

As an alternative to chemical fertilizers, growers routinely apply organic amendments to provide crop nutrition, but lack information on which combinations best increase nitrogen (N) availability rates and stimulate beneficial soil micro-organisms. The objectives of this study were to characterize how organic amendments and amendment combinations influenced 1) bacterial communities, 2) nematode communities and 3) N availability and plant growth. Dry amendments (pelleted poultry manure and compost) and liquid amendments (fish hydrolysate and food hydrolysate), were tested alone and combined in laboratory incubations and a greenhouse experiment. Pelleted poultry manure caused rapid increases of bacterial taxa associated with N cycling such as Nitrosospira, Pseudomonas, Pseudoxanthomonas and Flavobacterium as well as increases in opportunistic bacterial feeding nematodes such as Panagrolaimus. The abundance of many bacterial taxa, including some N cyclers, showed strong relationships with nematode genera and nematode indices of nutrient processing. Compost increased the prevalence of bacteria such as Chryseolinea, Sporocytophaga and Phenylobacterium, which are known to degrade complex C-compounds. Both liquid amendments caused slight changes in microbial communities. While pelleted poultry manure resulted in the highest net N availability and greatest plant growth compared to controls, compost reduced plant growth unless combined with liquid amendments. Results suggest that C:N ratio and C complexity influence nematode and bacterial community compositions as well as N availability, with implications for optimizing biologically based N cycling.

Mowing did not mitigate the negative effects of nitrogen deposition on soil nematode community in a temperate steppe

Soil nematodes are the most numerous components of the soil fauna in terrestrial ecosystems. The occurrence and abundance of nematode trophic groups determine the structure and function of soil food webs. However, little is known about how nitrogen deposition and land-use practice (e.g. mowing) affect soil nematode communities. We investigated the main and interactive effects of nitrogen addition and mowing on soil nematode diversity and biomass carbon in nematode trophic groups in a temperate steppe in northern China. Nitrogen addition and mowing significantly decreased the abundance of soil nematodes and trophic diversity but had no effects on nematode richness and the Shannon-Wiener diversity. Nitrogen addition influenced soil nematode communities through decreasing soil pH. Mowing influenced soil nematode communities through decreasing soil moisture. Nitrogen addition enhanced the bacterial energy channel but mowing promoted fungal energy channel in the soil micro-food web. Our study emphasizes that ecosystem function supported by soil organisms can be greatly influenced by nitrogen deposition, and mowing cannot mitigate the negative effects of nitrogen deposition on soil food webs.

Uncovering trophic positions and food resources of soil animals using bulk natural stable isotope composition.

Despite the major importance of soil biota in nutrient and energy fluxes, interactions in soil food webs are poorly understood. Here we provide an overview of recent advances in uncovering the trophic structure of soil food webs using natural variations in stable isotope ratios. We discuss approaches of application, normalization and interpretation of stable isotope ratios along with methodological pitfalls. Analysis of published data from temperate forest ecosystems is used to outline emerging concepts and perspectives in soil food web research. In contrast to aboveground and aquatic food webs, trophic fractionation at the basal level of detrital food webs is large for carbon and small for nitrogen stable isotopes. Virtually all soil animals are enriched in 13 C as compared to plant litter. This 'detrital shift' likely reflects preferential uptake of 13 C-enriched microbial biomass and underlines the importance of microorganisms, in contrast to dead plant material, as a major food resource for the soil animal community. Soil organic matter is enriched in 15 N and 13 C relative to leaf litter. Decomposers inhabiting mineral soil layers therefore might be enriched in 15 N resulting in overlap in isotope ratios between soil-dwelling detritivores and litter-dwelling predators. By contrast, 13 C content varies little between detritivores in upper litter and in mineral soil, suggesting that they rely on similar basal resources, i.e. little decomposed organic matter. Comparing vertical isotope gradients in animals and in basal resources can be a valuable tool to assess trophic interactions and dynamics of organic matter in soil. As indicated by stable isotope composition, direct feeding on living plant material as well as on mycorrhizal fungi is likely rare among soil invertebrates. Plant carbon is taken up predominantly by saprotrophic microorganisms and channelled to higher trophic levels of the soil food web. However, feeding on photoautotrophic microorganisms and non-vascular plants may play an important role in fuelling soil food webs. The trophic niche of most high-rank animal taxa spans at least two trophic levels, implying the use of a wide range of resources. Therefore, to identify trophic species and links in food webs, low-rank taxonomic identification is required. Despite overlap in feeding strategies, stable isotope composition of the high-rank taxonomic groups reflects differences in trophic level and in the use of basal resources. Different taxonomic groups of predators and decomposers are likely linked to different pools of organic matter in soil, suggesting different functional roles and indicating that trophic niches in soil animal communities are phylogenetically structured. During last two decades studies using stable isotope analysis have elucidated the trophic structure of soil communities, clarified basal food resources of the soil food web and revealed links between above- and belowground ecosystem compartments. Extending the use of stable isotope analysis to a wider range of soil-dwelling organisms, including microfauna, and a larger array of ecosystems provides the perspective of a comprehensive understanding of the structure and functioning of soil food webs.

Microfaunal soil food webs in Mediterranean semi-arid agroecosystems. Does organic management improve soil health?

Soil food webs, which are responsible for relevant ecological functions in agroecosystems such as nutrient cycling and pest and disease suppression, represent a crucial aspect of agricultural sustainability. We studied soil properties and microfaunal food web diversity and functioning in six paired organic and conventional fields located in Central Spain to assess the effects of organic farming on soil diversity and functioning in semi-arid conditions. We hypothesized that organic farming may enhance functioning of soil food webs. Our results showed larger differences between crop types, namely olive groves and vineyards, than between farming scheme, i.e. organic and conventional fields, and few benefits of organic farming in terms of soil fertility. Soil properties (total N, C, and P, available P and K, electrical conductivity, NH4+, NO3−, soil moisture, pH) tended to present higher values in vineyards than in olive groves and in conventional than in organic fields. Some plant-parasitic nematodes were associated to organic fields, especially in vineyards, and all soils fell within a degraded soil food web condition, with low Structure and Enrichment Index values. Nematode metabolic footprints showed relevant seasonal dynamics, with the more intensive herbivore activity in spring. We conclude that the lack of conventional pesticides and mineral fertilizers is probably not enough to improve soil conservation in semi-arid Mediterranean agroecosystems, and thus active soil conservation practices, as reduced tillage or cover cropping, are required to increase agroecosystem sustainability.

Biological transfer of dietary cadmium in relation to nitrogen transfer and 15N fractionation in a soil collembolan-predatory mite food chain

Effects of cadmium (Cd) on collembolans and predatory mites have been well studied but Cd accumulation and biological transfer and the relationship between Cd trophic transfer and nitrogen (N) isotope fractionation and transfer in soil micro-arthropod food chains remain poorly understood. Here, we investigated the biological transfer and trophic toxicity of Cd and the effects of dietary Cd exposure on 15N fractionation in animal tissues and N transfer from food in a soil collembolan (Folsomia candida)-predatory mite (Hypoaspis aculeifer) food chain using experiments conducted in plate and soil systems. Synchronized F. candida were fed yeast or wheat spiked with 0 (Control), 50 (Cd50), 100 (Cd100) or 200 (Cd200) μg Cd g−1 food for two weeks and were then offered to synchronized H. aculeifer as prey for two weeks. Cadmium concentrations in tissues of both the collembolan and its predator increased as the Cd concentrations in the food yeast or wheat increased in both the plate and soil systems, and the Cd concentrations in the food and the animals were all significantly and positively correlated. Except for the controls, the Cd bioaccumulation factor (BAF) between adults of predatory mites and consumer collembolans (0.20–1.13) was 2.5–14 times higher than that from food yeast/wheat to consumer collembolans (0.02–0.08). Cadmium transfer has not altered the reproduction of the filial generation collembolans but the reproduction of the predatory mite declined by 34.3% with the Cd concentration in its juveniles reaching 5.94 μg g−1, suggesting that Cd transfer from the spiked food can present a higher toxicity to the predator H. aculeifer. Food spiked with Cd decreased the N content in the collembolan tissues assimilated from the food and enriched the 15N fraction (δ15N) in their tissues by affecting their metabolic turnover and growth rates. The Cd trophic transfer between collembolans and predatory mites from spiked food can directly increase the δ15N value of predatory mites and restrict the movement of N from collembolans to predatory mites. The δ15N of soil animals has considerable potential as a biomarker of Cd stress, 15N isotope application may be limited in Cd polluted soil ecosystems, and the N transfer function of soil food webs may be more vulnerable in polluted ecosystems.

Nematode community profiling as a soil biology monitoring tool in support of sustainable tomato production: A case study from South Africa

Management of the biological component of agricultural soils is a vital aspect of sustainable food production systems. There is a need for soil biology metrics that producers can use as a decision support tool when it comes to managing the soil biological component of agricultural soils. We evaluated the usefulness of nematode community profiling as a soil biology monitoring tool in support of a sustainable commercial-scale tomato production system in South Africa. The objectives were to: (1) study the effects of land use change on nematode communities in the tomato production region, and (2) explore the correlation between tomato crop productivity and the nematode community metrics. The enrichment index was a sensitive indicator of land use change, but the structure index was not. Although the number and proportion of free-living and plant-parasitic nematodes increased and decreased respectively, the selective amplification of specific herbivorous genera was observed. Helicotylenchus spp. was sensitive to land use change and might serve as soil health indicator in this tomato production region. Regression analysis indicated a combination of variables associated with soil pH, free-living nematodes (notably the bacterivores) and specific plant-parasitic nematode genera (Paratrichodorus spp. and Rotylenchus spp.) predicted tomato yield (R2=0.846). Despite the useful information gleaned from the nematode community metrics regarding soil food web functioning, the importance of ecologically and economically important nematode genera was re-emphasized. The results of this study highlight an important principle regarding development of soil health metrics for tomato agroecosystems: tomato crop health was not necessarily predicted solely by indicators of soil food web health and functioning.

Conservation tillage positively influences the microflora and microfauna in the black soil of Northeast China

Soil food webs are important in maintaining agricultural productivity and ecosystem health. However, our understanding is still limited with respect to the influences of tillage transitions on soil food webs. The present study aimed to quantify the response of microflora and microfauna, and their linkage to different tillage treatments: no tillage (NT), ridge tillage (RT) and conventional tillage (CT). Soil samples were collected from 0 to 20cm depth in April of 2011 after 10 years of conservation tillage. The abundance and richness of bacteria and arbuscular mycorrhizal fungi were greater in NT and RT than in CT. In case of microfauna also, similar patterns were observed with greater protozoa, bacterivores and omnivores–carnivores in NT and RT compared to CT. The connectance of the bacterial and predator–prey pathways was greater in NT and RT than in CT and that of fungal pathway was greatest in RT. The trophic relationship of the bacterial and predator–prey pathways was strengthened due to the higher water content of soil and the lower NO3–-N after the conversion of CT to NT and RT. Our study suggested that 10 years of conservation tillage can effectively enhance the structure and function of soil food webs through bottom–up effects in the black soil region of Northeast China.

Plant diversity effects on soil food webs are stronger than those of elevated CO 2 and N deposition in a long-term grassland experiment

Recent metaanalyses suggest biodiversity loss affects the functioning of ecosystems to a similar extent as other global environmental change agents. However, the abundance and functioning of soil organisms have been hypothesized to be much less responsive to such changes, particularly in plant diversity, than aboveground variables, although tests of this hypothesis are extremely rare. We examined the responses of soil food webs (soil microorganisms, nematodes, microarthropods) to 13-y manipulation of multiple environmental factors that are changing at global scales--specifically plant species richness, atmospheric CO2, and N deposition--in a grassland experiment in Minnesota. Plant diversity was a strong driver of the structure and functioning of soil food webs through several bottom-up (resource control) effects, whereas CO2 and N only had modest effects. We found few interactions between plant diversity and CO2 and N, likely because of weak interactive effects of those factors on resource availability (e.g., root biomass). Plant diversity effects likely were large because high plant diversity promoted the accumulation of soil organic matter in the site's sandy, organic matter-poor soils. Plant diversity effects were not explained by the presence of certain plant functional groups. Our results underline the prime importance of plant diversity loss cascading to soil food webs (density and diversity of soil organisms) and functions. Because the present results suggest prevailing plant diversity effects and few interactions with other global change drivers, protecting plant diversity may be of high priority to maintain the biodiversity and functioning of soils in a changing world.

Biochar in bioenergy cropping systems: impacts on soil faunal communities and linked ecosystem processes

AbstractBiochar amendment of soil and bioenergy cropping are two eco‐engineering strategies at the forefront of attempts to offset anthropogenic carbon dioxide (CO2) emissions. Both utilize the ability of plants to assimilate atmospheric CO2, and are thus intrinsically linked with soil processes. Research to date has shown that biochar and bioenergy cropping change both aboveground and belowground carbon cycling and soil fertility. Little is known, however, about the form and function of soil food webs in these altered ecosystems, or of the consequences of biodiversity changes at higher trophic levels for soil carbon sequestration. Hitherto studies on this topic have been chiefly observational, and often report contrasting results, thus adding little mechanistic understanding of biochar and bioenergy cropping impacts on soil organisms and linked ecosystem processes. This means it is difficult to predict, or control for, changes in biotic carbon cycling arising from biochar and bioenergy cropping. In this study we explore the potential mechanisms by which soil communities might be affected by biochar, particularly in soils which support bioenergy cropping. We outline the abiotic (soil quality‐mediated) and biotic (plant‐ and microbe‐mediated) shifts in the soil environment, and implications for the abundance, diversity, and composition of soil faunal communities. We offer recommendations for promoting biologically diverse, fertile soil via biochar use in bioenergy crop systems, accompanied by specific future research priorities.

Trait‐mediated diversification in nematode predator–prey systems

Nematodes are presumably the most numerous Metazoans in terrestrial habitats. They are represented at all trophic levels and are known to respond to nutrient limitation, prey availability, and microbial resources. Predatory nematodes reside at the highest trophic level, and as such their feeding habits could have a major impact on soil food web functioning. Here, we investigate the effects of gender and developmental stage on the nematode body sizes in coarse and loamy soils. Besides Neodiplogasteridae, our predators are much larger than other soil-dwelling nematodes from their early developmental stage onwards. From juvenile to adult, the predatory Aporcelaimellus (Kruskal–Wallis P < 0.001), Dorylaimoides, and Tripyla (both P < 0.01) show great length increases during their developmental growth, in contrast to their possible prey (almost all P < 0.001). Less than 4% of the prey exceeds the length of the predatory adults, but more than 30% of the prey exceeds the length of the predatory juveniles. Potential body size ratios and some physical problems experienced by small fluid feeders attacking large prey are discussed in an attempt to summarize different prey-searching mechanisms and aggregative predatory responses in the soil system.

Altered food web structure and C-flux pathways associated with mineralisation of organic amendments to agricultural soil

Application of organic materials to agricultural soils offers the potential to divert these from conventional waste streams and to reduce the use of mineral fertilisers for crop production. In addition to direct impacts of organic materials on soil physico-chemical conditions, such amendments may also affect the structure and functioning of soil food webs and the coupling of plant- and soil biological activity. In this study we investigated the impact of cattle slurry and municipal green compost applications on soil microbial and nematode communities. Specifically, we applied steady-state 13C-labelling to quantify the impacts of the amendments on transfer of plant-derived C through components of the soil food web and to determine the activity of the soil biota in mineralising amendment- and soil organic matter derived-C. Both the slurry and compost amendments significantly promoted barley N-acquisition and growth. The municipal compost amendment, but not slurry application, strongly affected soil microbial community structure and increased nematode abundance, relative to unamended soil. This was associated with increased flux of plant-derived C through bacterial (particularly Gram negative) populations in compost-amended soil and was associated with increased mineralisation of amendment- and soil organic matter-derived substrates. For slurry-amended soils, the amendment did not alter soil community structure and mineralisation of soil C was not coupled to the flux of plant-derived C through below-ground pools. The results are indicative of N-supply to barley in compost-amended soil being dependent on the functioning of the soil food web (including C-flux to it from living roots), whereas N-supply from slurry was independent of this coupling between plant and soil processes. We suggest that plant/food web interactions are important targets for development of effective management strategies for organic waste applications to agricultural soils in the context of optimising the balance between nutrient supply to crops and the susceptibility of nutrients to losses from soil.

Divergent composition but similar function of soil food webs of individual plants: plant species and community effects

Soils are extremely rich in biodiversity, and soil organisms play pivotal roles in supporting terrestrial life, but the role that individual plants and plant communities play in influencing the diversity and functioning of soil food webs remains highly debated. Plants, as primary producers and providers of resources to the soil food web, are of vital importance for the composition, structure, and functioning of soil communities. However, whether natural soil food webs that are completely open to immigration and emigration differ underneath individual plants remains unknown. In a biodiversity restoration experiment we first compared the soil nematode communities of 228 individual plants belonging to eight herbaceous species. We included grass, leguminous, and non-leguminous species. Each individual plant grew intermingled with other species, but all plant species had a different nematode community. Moreover, nematode communities were more similar when plant individuals were growing in the same as compared to different plant communities, and these effects were most apparent for the groups of bacterivorous, carnivorous, and omnivorous nematodes. Subsequently, we analyzed the composition, structure, and functioning of the complete soil food webs of 58 individual plants, belonging to two of the plant species, Lotus corniculatus (Fabaceae) and Plantago lanceolata (Plantaginaceae). We isolated and identified more than 150 taxa/groups of soil organisms. The soil community composition and structure of the entire food webs were influenced both by the species identity of the plant individual and the surrounding plant community. Unexpectedly, plant identity had the strongest effects on decomposing soil organisms, widely believed to be generalist feeders. In contrast, quantitative food web modeling showed that the composition of the plant community influenced nitrogen mineralization under individual plants, but that plant species identity did not affect nitrogen or carbon mineralization or food web stability. Hence, the composition and structure of entire soil food webs vary at the scale of individual plants and are strongly influenced by the species identity of the plant. However, the ecosystem functions these food webs provide are determined by the identity of the entire plant community.

Divergent composition but similar function of soil food webs beneath individual plants: plant species and community effects

Divergent composition but similar function of soil food webs beneath individual plants: plant species and community effects