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Collembola grazing on arbuscular mycorrhizal fungi (AMF) may affect the transfer of mycorrhizosphere C to the soil food web and the regulation of soil mycorrhizal infectivity potential. We used a plant-free mesocosm experimental system with two different mycorrhizal substrates containing either Glomus deserticola or Gigaspora gigantea and three Collembola species (Heteromurus nitidus, Folsomia candida and Protaphorura fimata) to test the hypothesis that Collembola grazing can interfere directly with AMF feeding on the mycorrhizal propagules and/or indirectly changing structure of associated microbial populations. The fatty acid (FA) composition of Collembola grazers and of their mycorrhizal food substrates was assessed. The feeding strategies of H. nitidus and P. fimata varied distinctly between mycorrhizal substrates, whereas the diet of F. candida was invariant to the presence of mycorrhizal propagules. The FA marker for G. deserticola (16:1ω5) was not detected in Collembola lipids, indicating that this AMF was not consumed. In contrast, H. nitidus and P. fimata comprised the marker for feeding G. gigantea (20:1 ω9). Both mycorrhizal substrates were no profitable diet for H. nitidus, resulting in a decline of individuals. Collembola grazed on the bacterial and fungal populations in the mycorrhizal substrate, predominantly H. nitidus that even decreased microbial biomass, resulting in significant changes in the composition of the microbial community. In sum, grazing by microarthropods can directly and indirectly modulate AMF performance as well as interactions with microorganisms, which in turn can impose on the soil infection potential from AMF propagules. [ABSTRACT FROM AUTHOR]

Abstract: Positive relationships between biodiversity and ecosystem functioning are reported in many studies. The underlying mechanisms are, however, only little understood, likely due to the focus on the aboveground system and neglecting species-specific traits. We used different clusters of tree species composition to investigate how tree species diversity and tree species identity affect belowground nematode communities. Since soil nematodes comprise different trophic groups and are strongly linked to the microbial community, results can provide insight on how soil food webs are structured. In addition, data on leaf litter and fine root biomass were included to account for different effects of aboveground and belowground resources. Clusters of three trees of one, two and three species were identified within a temperate deciduous forest. Target tree species were European beech (Fagus sylvatica), common ash (Fraxinus excelsior) and lime (Tilia cordata, T. platyphyllos) differing in physiology, leaf litter quality and type of mycorrhiza. Tree species identity strongly affected nematode trophic structure, whereas tree species diversity had no impact. Ash beneficially affected bacterial-feeding nematodes, whereas fungal feeders were suppressed, likely caused by ash litter increasing soil pH. Fostering of the bacterial food chain by ash additionally could be related to rhizodeposition gaining importance after disappearance of high quality ash litter in spring, highlighting seasonal shifts in root and leaf litter-derived resources. The negative effect of ash on fungal-feeding nematodes is suggested to be due to the lack of ectomycorrhizal fungi as ash roots only form arbuscular mycorrhiza. In contrast, beech benefited fungal feeders and detrimentally affected bacterial feeders due to more acidic soil conditions that increase the competitive strength of fungi. Lime tended to negatively impact total nematode density but positively influenced plant-feeding nematodes. Generally, beech and ash strongly but opposingly influenced the trophic structure of nematode communities suggesting that changes in tree species identity result in major shifts in the channeling of energy through decomposer food webs. The results indicate that the structure of soil food webs varies markedly with tree species and point to the importance of basal resources, i.e., leaf litter and rhizodeposits. This suggests bottom-up forces mediated by individual tree species to control major decomposition pathways rather than tree diversity. [Copyright &y& Elsevier]

Abstract: Chemical taxonomy based upon the composition of lipids is widely applied to investigate microbial communities and fatty acids have recently been employed to connect soil microbial and faunal food webs as well as to elucidate functional groups at higher trophic levels. The additional use of compound-specific isotopic analysis of 13C/12C ratios in fatty acids allows assessing specific trophic links and belowground carbon fluxes. In this review systematic patterns and processes underlying variations in the composition of fatty acids and their 13C/12C ratio are described. The emphasis is on biomarker fatty acids, their incorporation and modification, effects of pool size, and analytical methods. Further development of the application of fatty acid profiling to soil ecology should include both advances in experimental research and growth of theory. Accordingly, areas in which future experimentation can lead to progress in soil food web analysis are identified. Overall, combining fatty acid biomarker and their isotopic ratios will allow detailed insight into belowground trophic interactions. [ABSTRACT FROM AUTHOR]

Abstract: Collembola are abundant and ubiquitous soil decomposers, being particularly active in the rhizosphere of plants where they are assumed to be attracted by high microbial activity and biomass. While feeding on root associated microorganisms or organic matter they may also ingest plant roots, e.g. particularly root hairs and fine roots. Employing stable isotope analysis we investigated Collembola (Protaphorura fimata Gisin) feeding preferences and types of ingested resources. We offered Collembola two resources with distinct isotope signatures: a C4 plant (Zea mays L.) planted in soil mixed with 15N labelled litter of Lolium perenne L. (C3 plant). We hypothesised that Collembola obtain their nutrients (C and N) from different resources, with their carbon being mainly derived from resources that are closely associated to the plant root, e.g. root exudates, causing enrichment in 13C in Collembola tissue, while the incorporated nitrogen originating from litter resources. In contrast to our hypothesis, stable isotope analysis suggests that in absence of plant roots Collembola derived both the incorporated C and N predominantly from litter whereas in presence of plant roots they switched diet and obtained both C and N almost exclusively from plant roots. The results indicate that Collembola in the rhizosphere of plants, being assumed to be mainly decomposers, in fact predominately live on plant resources, presumably fine roots or root hairs, i.e. are herbivorous rather than detritivorous or fungivorous. These findings have major implications on the view how plants respond to decomposers in the rhizosphere. [Copyright &y& Elsevier]

Abstract: The lipid composition of Collembola and their potential food resources was assessed in three deciduous forest stands, in order to gain insight into food web linkages under field conditions. Fatty acids (FAs) previously assigned as trophic markers in laboratory experiments were used to investigate feeding strategies in situ. As potential food sources soil microbiota and plant debris were characterised by their phospholipid fatty acid (PLFA) composition. Both the amount and the pattern of PLFAs differed between sites and soil depth, in particular the bacterial and plant marker FAs in the upper soil layer. Thus, the availability of resources for micro-detritivores varied due to forest and soil layer. The lipid composition of vital and senescent beech leaves was predominantly influenced by metabolic status and represented a quite homogenous FA resource across forest stands. Comparing Folsomia quadrioculata, Lepidocyrtus lignorum, Neanura muscorum and Pogonognathellus longicornis between the different forests revealed FA profiles to be predominantly affected by site, suggesting a diet shift depending on resources at hand. However, species-specific differences in individual FAs occurred, likely related to feeding strategy and physiological activity. Lipids of Collembola comprised low amounts of bacterial marker FAs, and bacterial consumption may occur to some extent, particularly on Gram-positives. The marker FA for predatory feeding, , was found in several species, although in low amounts. This contradicts known feeding habits and caution is advisable in using as trophic marker. Overall, as indicated by high proportions of oleic or linoleic acid, most species were either plant litter or fungal feeders, with some transitions. The ratio ,9 is proposed as a tool to distinguish between these two major feeding strategies in Collembola. [Copyright &y& Elsevier]

Abstract: Stable isotope analysis has been used as a powerful tool in food web studies in terrestrial ecosystems. In addition the occurrence and abundance of fatty acids may serve as indicator for feeding strategies of soil animals. Here we combine both approaches and investigate the fatty acid composition, δ 13C values of bulk tissues and individual fatty acids in soil organisms. The fungi Chaetomium globosum and Cladosporium cladosporioides were isotopically labelled by fructose derived from either C3 or C4 plants, and the fungal-feeding nematode Aphelenchoides sp. was reared on C. globosum. Fungi and nematodes were used as diet for the Collembolan Protaphorura fimata. The sugar source was fractionated differently by fungal lipid metabolism in a species-specific manner that points to a sensitivity of physiological processing to the non-random distribution of 13C/12C isotopes in the molecule. As a general trend stearic acid (18:0) was depleted in 13C compared to the precursor palmitic acid (16:0), whereas its desaturation to oleic acid (18:1 ω9) favoured the 13C-rich substrate. Fatty acid profiles of P. fimata varied due to food source, indicating incorporation of dietary fatty acids into Collembolan tissue. Individuals feeding on fungi had lower amounts in C20 fatty acids, with monoenoic C20 forms not present. This pattern likely separates primary consumers (fungivores) from predators (nematode feeders). The isotopic discrimination in 13C for bulk Collembola ranged between −2.6 and 1.4‰ and was dependent on fungal species and C3/C4 system, suggesting differences at metabolic branch points and/or isotope discrimination of enzymes. Comparison of δ 13C values in individual fatty acids between consumer and diet generally showed depletion (i.e. de novo synthesis) or no changes (i.e. dietary routing), but the fractionation was not uniform and affected by the type of ingested food. Fatty acid carbon isotopes were more variable than those of bulk tissues, likely due to both the distrimination by enzymes and the different lipid origin (i.e. neutral or polar fraction). [Copyright &y& Elsevier]

The fatty acid composition of 16 different soil fungi (ascomycetes, basidiomycetes, mitosporic fungi) and a fungal-feeding nematode Aphelenchoides sp. reared on seven fungal species was investigated. Additionally, fatty acid profiles of Aphelenchoides sp. and A. saprophilus grown on the same fungal food source,Agrocybe gibberosa, were compared. Thirteen predominant fatty acids were detected in the fungi. Most of them occurred in each of the 16 species, but relative quantities of individual fatty acids differed, in particular those of unsaturated ones. Most fungal species could be differentiated from each other on this basis. Our study revealed convergence, but also, differences, in the fatty acid composition of systematically related fungi, i.e. a taxonomic or phylogenetic relationship was not necessarily accompanied by similarity in fatty acid profiles. Nematodes comprised a wider fatty acid spectrum than fungi, with 17 predominant fatty acids, and a higher amount of long-chain, polyunsaturated acids than their fungal diet. Fungal host tissue may have supplied palmitic, oleic and linoleic acid present, whereas most of the long-chain unsaturated fatty acids were synthesized by the nematodes. Unsaturated fatty acids mainly belonged to the ω6 and 9 family, indicating a carboxyl-directed desaturation as a major metabolic pathway. The fungal host significantly affected the fatty acid profile of the nematodes. However, we could not assign individual fatty acids as biomarkers reflecting the dietary source, likely due to the considerable convergence within tested fungal species. Of the basidiomycetes analyzed Laccaria laccata, was distinctly separated from the others and this difference could also be detected in the nematodes showing the influence of food type. We conclude that the lipid composition of nematodes is controlled by both the nematode and its diet and that monitoring fatty acid patterns of soil animals may therefore provide a way to detect trophic interactions in belowground food webs. [Copyright &y& Elsevier]

The effect of food resources, varying in C/N ratio, lipid and ω3 polyunsaturated fatty acid (ω3-PUFA) content, on the fitness of three Collembola species (the euedaphic Protaphorura fimata , hemiedpahic Folsomia candida and epedaphic Lepidocyrtus violaceus) was investigated. Dietary routing of fatty acids served as an indicator for resource consumption and assimilation. Laboratory feeding experiments were performed with single and mixed diets made from algae, cyanobacteria, fungi, soil bacteria or plant roots and leaves. Collembola exhibited species-specific responses in biomass and survival rate to the diets differing in quality, reflecting adaptations to their soil environment. Generally, wide dietary C/N ratios had a negative impact, with roots especially unfavorable, while the dependence on ω3-PUFAs varied. Mixing diets did mostly result in intermediate results where high-quality resources compensate for low-quality resources, with only mixes of resources favoured by Collembola in the wild showing synergistic positive effects. The results suggest that most resources of soil detritivores, irrespective of green or brown food chain, represent a non-optimal diet, with clear adaptations depending on habitat and the potential to truly exploit any resource mostly exhibited in euedaphic species. • Trophic shift of marker fatty acid can assess assimilation into consumer tissue. • Dietary ω3-fatty acid content and C/N ratio influence Collembola biomass/survival. • Effects of low-quality diet aren't compensated by mixing with high-quality diets. [ABSTRACT FROM AUTHOR]

Abstract: Recent stable isotope analyses indicate that a number of putative detritivorous soil microarthropods is not typical detritivores but rather live as predators or scavengers. Using molecular gut content analyses the present study investigates if nematodes indeed form part of the diet of oribatid mites. First, in a no-choice laboratory feeding experiment two nematode species (Phasmarhabditis hermaphrodita and Steinernema feltiae) were offered to eight species of oribatid mites and one gamasid mite. Second, after feeding for 4 and 48h on each nematode species the detection time of prey DNA in the oribatid mite species Steganacarus magnus was investigated. Third, in a field experiment nematode prey (P. hermaphrodita and S. feltiae) in the diet of microarthropods was investigated distinguishing between scavenging and predation. In the no-choice laboratory experiment not only the gamasid mite but also several of the studied oribatid mite species consumed nematodes. After feeding on nematodes for 4h prey DNA was detectable in S. magnus for only 4h, but after feeding for 48h prey DNA was detectable for 128h, indicating that the duration of feeding on prey is an important determinant for prey DNA detection. The field experiment confirmed that oribatid mite species including Liacarus subterraneus, Platynothrus peltifer and S. magnus intensively prey on nematodes. Interestingly, DNA of dead P. hermaphrodita was detectable to a similar degree as that of living individuals indicating that scavenging is of significant importance in decomposer food webs. Results of our study indicate that predation and scavenging on nematodes by “detritivorous” microarthropods in soil food webs need to be reconsidered. [Copyright &y& Elsevier]

Pest suppression is one of the desirable functions of a healthy soil. Predatory Mesostigmata soil mites, with their high degree of omnivory, are one of the most remarkable groups performing this beneficial role. Food web bottom-up effects are important for the fitness of these predators, which ultimately affects their potential as biocontrol agents. In below-ground systems, free-living nematodes (FLN) are an important diet for mites, providing essential nutrients such as omega 3 long-chain polyunsaturated fatty acids (ω3-LC PUFAs). Here we assess the food quality of nematodes for the maintenance of predator fitness, i.e. development, reproduction and lipid content. We selected two mite species, different in size and morphology, collected from vegetable crops in Israel. Additionally, five species of FLN were isolated from the same fields. Additionally, one plant-parasitic species, common across arable sites in Israel, and maintained on tomato as host, was tested. Depending on species and trophic group, nematodes varied in fatty acid profile, and both mite species generally reflected the fatty acid pattern of their diet. All nematode species were able to produce ω3-LC PUFA de novo , except the bacterial feeder Acrobeloides bodenheimeri , which had the highest proportion of ω6-PUFA. Interestingly, the latter lacking ω3-LC PUFA, was the best diet for both mites. Macrocheles aff. scutatus , a medium-sized mite with a holodorsal shield, fed and developed on all nematodes except the entomophilious Oscheius tipulae. It was able to complete its development feeding on the plant parasitic Meloidogyne incognita , yet the reproduction was almost zero. The smaller and slender Protogamasellopsis zaheri , with a split dorsal shield, developed and reproduced with all nematodes, with M. incognita as an intermediate diet. Our results demonstrate that nematode species vary in their nutritional quality as prey. However, food quality is predator species dependent, likely affecting biocontrol efficacy. Besides ω3-LC PUFA, ω6-PUFA can play an important role in the reproductive and developmental parameters of mesostigmatid mites; yet, other factors such as nematode size and behaviour have to be considered. • Lipid content and fatty acid pattern of nematodes are mainly determined by trophic group, and secondarily also by species. • The impact of nematode diet on mite life history varied, with diet quality being predator-specific. • Meloidogyna incognita allows development, not reproduction in Macrocheles aff. scutatus. • M. incognita was an intermediate diet for Protogamasellopsis zaheri. • A diet rich in ω-3 fatty acids does not necessarily benefit the fitness of mite consumers. [ABSTRACT FROM AUTHOR]

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

The synergistic and antagonistic interactions among biotic components in the rhizosphere play a crucial role in plant defence against soil-borne pathogens. We investigated if the rhizosphere helper bacterium Streptomyces sp. AcH 505 (HB) indirectly protects the plant from the parasitic nematode Pratylenchus penetrans by modifying the rhizosphere microbial community structure and whether these interactions are dependent on the growth stage of oaks. Changes in the abundance of Streptomyces sp. AcH 505 and the phospholipid fatty acid (PLFA) composition of the rhizosphere soil as well as oak shoot and root biomass were assessed. Investigated were the bud resting stage A and the bud swelling stage B with maximal root elongation of oak microcuttings at two successive harvest times. The deleterious effect of P. penetrans on oak biomass was dependent on plant development, being limited to oak microcuttings growing at the stage B. In comparison to control and HB inoculated soils, shoot biomass decreased by about 33% and 41%, and root biomass by about 33 and 48%, respectively. The antagonistic effect of Streptomyces against the nematode was linked to shifts in the rhizosphere microbial community. The Streptomyces AcH505 strain promoted growth of oak microcuttings at bud swelling stage B during maximal root elongation and enhanced the abundance of saprophytic and ectomycorrhizal fungi in the rhizosphere by 158% with respect to controls. Our results highlight the importance of Streptomyces for counteracting the damage of nematodes and promoting plant growth in natural ecosystems such as forests. [ABSTRACT FROM AUTHOR]

Trophic interactions between heterotrophic soil microbes and grazing soil invertebrates influence decomposer community composition and function. Cord-forming basidiomycete fungi are primary agents of woody litter decomposition in temperate forests. In laboratory experiments, grazing by woodlice (Isopoda) is an important factor limiting the biomass and functioning (decomposition and extracellular enzyme production) of cord-forming fungi, but its significance in the field has hitherto not been studied. Field populations of the woodlouse, Oniscus asellus, were manipulated ('reduced' [zero] or standardised at 'current' [28 m−2] or 'double' [56 m−2] density) in delimited plots inoculated with different fungi (un-inoculated, Hypholoma fasciculare or Phanerochaete velutina) and the effects on the microbial decomposer community assessed after 6 and 12 months. Oniscus asellus population density was reduced after 12 months in comparison to the standardised numbers at start. Significant differences between population densities remained, but varied between fungal inoculation treatments. Fatty acid analysis revealed O. asellus as a true generalist; markers for plants, fungi and bacteria were consistently abundant in storage lipids. Seasonal effects on microbial biomass and function were strong. Although woodlouse population density neither affected fungal biomass nor microbial community composition (ergosterol and soil phospholipid fatty acids), it influenced enzyme activities, depending on the inoculated fungus. Woodlice significantly reduced leucine aminopeptidase and lignin-degrading peroxidase activities, only in un-inoculated plots. In contrast, the highest woodlouse population density increased beech (Fagus sylvatica) wood decomposition and leucine aminopeptidase activity in P. velutina-inoculated plots. Increased enzyme activity and decomposition is likely a stress response, reflecting increased production of specific enzymes to provide the energy for mycelial repair and growth responses to grazing. Effects of grazing on fungal biomass and activity will be strongest at microsites of woodlouse aggregation and where forest floor woodlouse population densities are high. [ABSTRACT FROM AUTHOR]

Abstract: Many studies of the microbial ecology of agricultural ecosystems focus on surface soils, whereas the impacts of management practice and season on soil microbial community composition and function below the plough zone are largely neglected. Deep soils have a high potential to store carbon; therefore any management driven stimulation or repression of microorganisms in subsoil could impact biogeochemical cycling in agricultural sites. The aim of this study was to understand whether soil management affects microbial communities in the topsoil (0–10 cm), rooted zone beneath the plough layer (40–50 cm), and the unrooted zone (60–70 cm). In a field experiment with different crops [wheat (Triticum aestivum L.) and maize (Zea mays L.)] and agricultural management strategies (litter amendment) we analysed microbial biomass as phospholipid fatty acids (PLFAs) and enzyme activities involved in the C-cycle (β-glucosidase, N-acetyl-β-d-glucosaminidase, β-xylosidase, phenol- and peroxidase) across a depth transect over a period of two years. Wheat cultivation resulted in higher bacterial and fungal biomass as well as higher enzyme activities at most sampling dates in comparison to maize cultivated plots, and this effect was visible to 50 cm depth. Litter application increased bacterial and fungal biomass as well as hydrolytic enzyme activities but effects were apparent only in the topsoil. In winter high microbial biomass and enzyme activities were measured in all soil layers, possibly due to increased mobilization and translocation of organic matter into deeper soil. Hydrolytic enzyme activities decreased with depth, whereas oxidative enzyme activities showed no decrease or even an increase with depth. This could have been due to differing sorption mechanisms of hydrolytic and oxidative enzymes. Specific enzyme activities (enzyme activity per microbial biomass) were higher in the deeper layers and possible reasons are discussed. [Copyright &y& Elsevier]

Abstract: Soil food webs are important determinants for the carbon flow through terrestrial systems, with the trophic networks between microbes and microfaunal grazers forming the basis for processing plant resources. At an agricultural field site cropped with maize or wheat, plant carbon input to soil was experimentally manipulated by amendment with maize litter. The community structure of dominant micro-food web components, the bacteria, fungi, protozoa and nematodes, was investigated across a depth gradient comprising plough layer, rooted soil below plough horizon, and deeper root free soil. The community composition and diversity within micro-food webs, and the response to resource supply, were assessed in summer, the vegetation period with highest root exudation. In the plough layer amendment with plant residues increased microbial biomass as well as density of fan shaped amoeba morphotypes and of bacterial- and fungal-feeding nematodes. Diversity of food web assemblages was assessed by operational taxonomic units (OTU) for bacteria and fungi, protozoa morphotypes and nematode families. Changes in diversity were either not apparent (fungi, protozoa), negatively related to litter (bacteria) or positively linked to the presence of a specific crop plant (bacteria, nematodes). Based on nematode functional guilds and the related enrichment and structure index, general food web conditions were assigned as nutrient enriched, with a high degree of disturbance, and a dominance of the bacterial energy channel. In sum, litter amendment fostered the abundance but not the diversity of organisms as food webs remained bottom heavy with only small amounts of carbon conserved at higher trophic levels. Food web structure was more affected by the abiotic (soil profile) and biotic (crop plant) environment than by the supply with litter resources. [Copyright &y& Elsevier]

Abstract: We investigated the Collembola community at an arable field where mineral and organic fertilizers have been applied at low and high rates for 27 years. As food resources for Collembola, the soil microbial community was analyzed using phospholipid fatty acids (PLFAs). A special focus was put on AM fungi, which were estimated by the marker 16:1ω5 in PLFA (viable hyphae) and neutral lipid fatty acid (NLFA – storage fat in spores) fractions. Additionally, whole cellular lipids in crop plant tissues and manure were assessed. Greater Collembola species richness occurred in plots where mineral fertilizer was added. In contrast, soil microbial biomass including AM fungal hyphae increased with addition of organic fertilizer, while the amount of AM fungal spores and biomass of saprotrophic fungi were not affected by fertilizer type. The lipid pattern in wheat roots was altered by fertilizer type, application rate and their interaction, indicating different rhizosphere communities. In sum, the availability and composition of food resources for Collembola changed considerably due to farm management practice. The major diet of three dominant Collembola species, Isotoma viridis, Willemia anophthalma and Polyacanthella schäffer was determined by lipid profiling. Multivariate analysis demonstrated species specific lipid patterns, suggesting greater importance of species than management practice on the diet choice. Nevertheless, feeding strategy was affected by fertilizer type and availability of resources, as trophic biomarker fatty acids indicated feeding on wheat roots (and to some extent saprotrophic fungi) with mineral and a shift to soil organic matter (litter, detritus) with organic fertilization. Although AM fungi dominated the soil fungal community, the AMF marker 16:1ω5 was not detected in Collembola lipids, indicating that these were not consumed. The very low amount of saprotrophic fungi in the soil and the fact that Collembola as major fungal grazers did not feed on AM fungi indicates that the fungal energy channel in the investigated arable field is of little importance to the faunal food web. [Copyright &y& Elsevier]

Abstract: We investigated microbial biomass, fungal biomass and microbial community structure at three altitudes (1000, 2000 and 3000m) and in two soil layers [L/F layer (Layer I) and underlying H/Ah layer (Layer II)] of tropical mountain rain forests in southern Ecuador. Basal respiration, microbial biomass and concentration of ergosterol generally declined from Layer I to Layer II and peaked at 2000m. Compared to temperate forest ecosystems microbial biomass and ergosterol concentrations were generally low. Patterns in phospholipid fatty acids indicated that the composition of microbial communities markedly changed from Layer I to Layer II. These differences between layers decreased with increasing altitude. The concentration of the arbuscular mycorrhizal fungal marker PLFA 16:1ω5c decreased with altitude in Layer I but increased in Layer II. The fungal-to-bacterial ratio increased with altitude and was higher in Layer I than in Layer II. Presumably, low microbial biomass in soils of tropical forest ecosystems is due to high temperature associated with high respiration but also low litter quality, with the latter declining with altitude. These conclusions are supported by the fact that at higher altitude the microbial community changed from a bacterial-dominated to a fungal-dominated system. CCA showed that microbial biomass correlated closely with density of a number of putatively bacterial feeding testate amoeba species including Corythion dubium Taranek, 1871, Euglypha cristata Leidy, 1879, Trigonopyxis arcula Penard, 1912, Tracheleuglypha dentata Deflandre, 1928 and Trinema lineare Penard, 1890. Ergosterol concentrations, but not the PLFA 18:2ω6c, strongly correlated with the putatively fungal feeding species Phryganella acropodia (Hertwig, Lesser, 1874) Hopkinson, 1909. Generally, parallel to microbial biomass and ergosterol concentrations the density of testate amoebae peaked at 2000m. However, compared to microbial parameters changes in testate amoebae communities between two layers were less pronounced. The data suggest that density and community structure of testate amoebae are driven by the availability of food resources (bacteria and fungi) which at high altitude decrease with increasing moisture and decreasing pH. [Copyright &y& Elsevier]

Abstract: Fatty acid (FA) analysis is a promising tool to study trophic relationships in soil food webs. We determined FA biomarkers to trace bacterial food sources (Bacillus megaterium, Pseudomonas putida, Enterobacter aerogenes) of Collembola (Heteromurus nitidus, Protaphorura fimata, Folsomia candida). In addition, δ15N, δ13C, C/N ratio, body weight and NLFA/PLFA ratio (neutral lipid/phospholipid fatty acids) of Collembola were assessed. These measures indicated that P. putida ranked first, B. megaterium second and E. aerogenes third in food quality. FAs specific for bacteria were found in the NLFAs of the Collembola reflecting the respective bacterial diet. Biomarker FAs for gram-positive bacteria were methyl branched i14:0, i15:0, a15:0 and i17:0. Consumption of gram-negative bacteria was reflected by the cyclic form cy17:0 (E. aerogenes, P. putida) and by 16:1ω5 (P. putida). [Copyright &y& Elsevier]

Abstract: In soil a high number of species co-exist without extensive niche differentiation, which was assigned as ‘the enigma of soil animal species diversity’. In particular, the detritivores are regarded as food generalists. We have investigated nitrogen stable isotope ratios (15N/14N) of a major decomposer group, the Collembola, to evaluate trophic relationship and determine feeding guilds. Additionally, the δ 15N values of potential food sources such as mosses, lichens and other plant derived material (bark, nuts, leaves) were analysed. The natural variation in nitrogen isotopes was assessed in 20 Collembola taxa from three deciduous forest stands. The δ 15N signature formed a continuum from phycophages/herbivores to primary and secondary decomposers, reflecting a gradual shift from more detrital to more microbial diets. The δ 15N gradient spanned over 9 δ units, which implies a wide range in food sources used. Assuming a shift in 15N of about 3 ‰ per trophic level, the results indicate a range of three trophic levels. These variations in 15N/14N ratios suggest that trophic niches of Collembola species differ and this likely contributes to Collembola species diversity. [Copyright &y& Elsevier]

The microbiota in three distinct terrestrial habitats (biological soil crusts – BSC, crust-adhering soil beneath BSC – trans, and crust-free soil close to BSC – soil) was studied in 33 temperate forest stands differing in management intensity (ForMI). Specific lipid fractions and respective marker fatty acids were used to determine microbial biomass and community structure (phospholipid fatty acids – PLFA), energy reserves (neutral lipid fatty acids – NLFA), and community level lipid profiles (CLLP) of nematodes and enchytraeids. The density and diversity of nematode fauna were additionally determined morphologically. The highest total amounts of PLFA and NLFA occurred in the BSC, followed by soil and trans habitats, indicating stronger effects of habitats than forest management intensity. This corresponds to the distribution pattern of bacterial PLFA that dominated the soil microbiota. The highest nematode population density occurred in the BSC, followed by soil and trans. The BSC was dominated by bacterial feeders and omnivores, while plant feeding nematodes were most frequent in the crust-free soil habitat. The highest biomass of photoautotrophs also occurred in the BSC, followed by the crust-adhering and crust-free soil habitats. Redundancy analysis indicated strong effect of ForMI and total N on soil PFLAs and NFLAs across habitats. The C:N and C:S ratios were important for the separation of NLFAs while P:S accounted for the separation of PLFAs. Bacterial and fungal PLFAs largely separated the microbial community across habitats, and particularly between BSC and trans habitats. The separation of nematodes and enchytraeids by CLLP was less pronounced, and most distinct between the crust-free soil and BSC or crust-adhering soil habitats. Overall, BSC and crust-adhering soil habitats provide different suitability for microbiota, resulting in specifically adapted communities that are shaped by the management intensity and nutrient availability. • Forest management intensity shape biological soil crust with different microhabitats. • Greater effect of habitats on soil microbiota than forest management intensity. • Bacterial and fungal PLFAs separated microbial communities across habitats. • High nematode density in crust, dominated by omnivores and bacteria feeders. [ABSTRACT FROM AUTHOR]