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Soil animals and their interactions exert strong effects on ecosystem processes, such as leaf litter decomposition and nitrogen (N) cycling, thereby contributing to ecosystem functioning and stability. The understanding of how and why certain species interact is important to predict the effect of soil animal communities on ecosystem processes. Species interactions are discussed as being facilitative, antagonistic or neutral. We investigated interactions between two earthworm ( Lumbricus terrestris , Aporrectodea caliginosa ) and two Collembola species ( Heteromurus nitidus and Protaphorura armata ), representing major soil decomposer taxa. The two earthworm species are representatives of the soil macrofauna, with L. terrestris living in permanent vertical burrows and feeding on leaf litter, and A. caliginosa living in non-permanent horizontal burrows and feeding predominantly on resources in organo-mineral soil. The Collembola species are representatives of the soil mesofauna, with H. nitidus predominantly colonizing the soil litter interface and feeding on litter associated resources, whereas P. armata colonizes deeper soil layers and mainly feeds on resources in organo-mineral soil. Therefore, the species were assumed to differ in two major traits, i.e. body size (macrofauna vs. mesofauna) and food microhabitat association (“litter-associated” vs. “soil-associated”). Mesocosms with natural forest floor containing one beech ( Fagus sylvatica ) sapling were set up and incubated in the laboratory for three months. 15 N labeled beech litter was added to follow the effect of detritivore animals on N cycling and N uptake by beech saplings. We hypothesized antagonistic interactions to dominate in species with similar body size or food microhabitat association via hampering the performance (biomass, abundance) of each other thereby reducing effects on leaf litter decomposition and N cycling. On the contrary, we expected species of different body size or food microhabitat association to facilitate each other's effects on ecosystem processes. In contrast to our expectation there was no clear relationship between similarity of body size or food microhabitat association and soil fauna effects on each other. Interactions between detritivores were not consensual with L. terrestris facilitating biomass gain of A. caliginosa , while its own biomass was reduced in presence of A. caliginosa . Additionally, 15 N incorporation into A. caliginosa and the two Collembola species decreased in presence of L. terrestris, irrespective of similarity of body size or food microhabitat association. Leaf litter decomposition was increased by L. terrestris , while none of the other species affected litter decomposition. Generally, 15 N incorporation into beech saplings was significantly increased in presence of L. terrestris or H. nitidus , but reduced in two species treatments due to antagonistic interactions. Interestingly, it was increased if L. terrestris , A. caliginosa and P. armata were present together, indicating facilitative interactions between these species. The results suggest that soil fauna interactions mainly vary with the identity of species and community composition rather than with similarity of traits. This highlights the complexity of soil fauna interactions and the difficulty to predict their effects on ecosystem processes, such as litter decomposition and N cycling, in species rich communities. [ABSTRACT FROM AUTHOR]

In a litterbag study in a tropical montane rainforest in Ecuador we assessed the impact of leaf litter species identity and richness on decomposition. We incubated leaf litter of six native tree species in monocultures and all possible two and four species combinations and analysed mass loss over a period of 24 months. Mass loss in monocultures averaged 30.7% after 6 month and differed significantly between species with variations being closely related to initial concentrations of lignin, Mg and P. At later harvests mass loss in monocultures averaged 54.5% but did not vary among leaf litter species and, unexpectedly, did not increase between 12 and 24 months suggesting that litter converged towards an extremely poor common quality retarding decomposition. After 6 months mass loss of leaf litter species was significantly faster in mixtures than in monocultures, resulting in synergistic non-additive mixture effects on decomposition, whereas at later harvests mass loss of component litter species was more variable and leaf litter mixture effects differed with species richness. Mass loss in the two species mixtures did not deviate from those predicted from monocultures, while we found antagonistic non-additive mixture effects in the four species mixtures. This suggests that litter species shared a poor common quality but different chemistry resulting in negative interactions in chemically diverse litter mixtures at later stages of decomposition. Overall, the results suggest that interspecific variations in diversity and composition of structural and secondary litter compounds rather than concentrations of individual litter compounds per se, control long term leaf litter decomposition in tropical montane rainforests. Plant species diversity thus appears to act as a major driver for decomposition processes in tropical montane rainforest ecosystems, highlighting the need for increasing plant conservation efforts to protect ecosystem functioning of this threatened biodiversity hotspot. [ABSTRACT FROM AUTHOR]

Increasing infestation by insect herbivores and pathogenic fungi in response to climate change will inevitably impact the amount and quality of leaf litter inputs into the soil. However, little is known on the interactive effect of infestation severity and climate change on litter decomposition, and no such study has been published for deciduous forests in Central Europe. We assessed changes in initial chemical quality of beech ( Fagus sylvatica L.) and maple litter ( Acer platanoides L.) in response to infestation by the gall midge Mikiola fagi Hart. and the pathogenic fungus Sawadaea tulasnei Fuckel, respectively, and investigated interactive effects of infestation severity, changes in temperature and soil moisture on carbon mineralization in a short-term laboratory study. We found that infestation by the gall midge M. fagi and the pathogenic fungus S. tulasnei significantly changed the chemical quality of beech and maple litter. Changes in element concentrations were generally positive and more pronounced, and if negative less pronounced for maple than beech litter most likely due to high quality fungal tissue remaining on litter after abscission. More importantly, alterations in litter chemical quality did not translate to distinct patterns of carbon mineralization at ambient conditions, but even low amounts of infested litter accelerated carbon mineralization at moderately increased soil moisture and in particular at higher temperature. Our results indicate that insect herbivores and fungal pathogens can markedly alter initial litter chemical quality, but that afterlife effects on carbon mineralization depend on soil moisture and temperature, suggesting that increased infestation severity under projected climate change potentially increases soil carbon release in deciduous forests in Central Europe. [ABSTRACT FROM AUTHOR]

Abstract: Human activity has induced a multitude of global changes that are likely to affect the functioning of ecosystems. Although these changes act in concert, studies on interactive effects are scarce. Here, we conducted a laboratory microcosm experiment to explore the impacts of temperature (9, 12 and 15°C), changes in soil humidity (moist, dry) and plant diversity (1, 4, 16 species) on soil microbial activity and litter decomposition. We found that changes in litter decomposition did not mirror impacts on microbial measures indicating that the duration of the experiment (22 weeks) may not have been sufficient to determine the full magnitude of global change effects. However and notably, changes in temperature, humidity and plant litter diversity/composition affected in a non-additive way the microbial parameters investigated. For instance, microbial metabolic efficiency increased with plant diversity in the high moisture treatment but remained unaffected in low moisture treatment suggesting that climate changes may mask beneficial effects of biodiversity on ecosystem functioning. Moreover, litter decomposition was unaffected by plant litter diversity/composition but increased with increasing temperature in the high moisture treatment, and decreased with increasing temperature in the low moisture treatment. We conclude that it is inevitable to perform complex experiments considering multiple global change agents in order to realistically predict future changes in ecosystem functioning. Non-additive interactions highlight the context-dependency of impacts of single global change agents. [Copyright &y& Elsevier]

Abstract: Anecic earthworms have been shown to collect, concentrate and bury seeds in their burrows. Moreover, recent studies suggest that earthworms function as granivores and seedling herbivores thereby directly impacting plant community assembly. However, this has not been proven unequivocally. Further, it remains unclear if earthworms benefit from seed ingestion, i.e., if they assimilate seed carbon. We set up a series of three laboratory experiments in order to test the following hypotheses: (1) anecic earthworms (Lumbricus terrestris L.) not only ingest seeds but also seedlings, (2) ingestion of seedlings is lower than that of seeds due to a ‘size refuge’ of seedlings (i.e., they are too big to be swallowed), and (3) seeds and seedlings contribute to earthworm nutrition. L. terrestris readily consumed legume seedlings in the radicle stage, whereas legume seeds and seedlings in the cotyledon stage, and grass seeds and seedlings in the radicle and cotyledon stage were ingested in similar but lower amounts. Importantly, ingestion of seedlings, in contrast to seeds, was lethal for all plant species. Moreover, earthworm weight change varied with the functional identity and vitality of seeds and natural 15N signatures in earthworm body tissue underlined the importance of seedlings for earthworm nutrition. The results indicate that the anecic earthworm L. terrestris indeed functions as a granivore and seedling herbivore. The selectivity in seedling ingestion points at the potential of direct earthworm effects on plant community assembly. Further, seeds and seedlings most likely contribute significantly to earthworm nutrition potentially explaining the collection and concentration of seeds by L. terrestris in its middens and burrows; however, the present results call for experiments under more natural conditions. [Copyright &y& Elsevier]

Abstract: The effect of endogeic earthworms (Octolasion tyrtaeum) and the availability of clay (Montmorillonite) on the mobilization and stabilization of uniformly 14C-labelled catechol mixed into arable and forest soil was investigated in a short- and a long-term microcosm experiment. By using arable and forest soil the effect of earthworms and clay in soils differing in the saturation of the mineral matrix with organic matter was investigated. In the short-term experiment microcosms were destructively sampled when the soil had been transformed into casts. In the long-term experiment earthworm casts produced during 7days and non-processed soil were incubated for three further months. Production of CO2 and 14CO2 were measured at regular intervals. Accumulation of 14C in humic fractions (DOM, fulvic acids, humic acids and humin) of the casts and the non-processed soil and incorporation of 14C into earthworm tissue were determined. Incorporation of 14C into earthworm tissue was low, with 0.1 and 0.44% recovered in the short- and long-term experiment, respectively, suggesting that endogeic earthworms preferentially assimilate non-phenolic soil carbon. Cumulative production of CO2-C was significantly increased in casts produced from the arable soil, but lower in casts produced from the forest soil; generally, the production of CO2-C was higher in forest than in arable soil. Both soils differed in the pattern of 14CO2-C production; initially it was higher in the forest soil than in the arable soil, whereas later the opposite was true. Octolasion tyrtaeum did not affect 14CO2-C production in the forest soil, but increased it in the arable soil early in the experiment; clay counteracted this effect. Clay and O. tyrtaeum did not affect integration of 14C into humic fractions of the forest soil. In contrast, in the arable soil O. tyrtaeum increased the amount of 14C in the labile fractions, whereas clay increased it in the humin fraction. The results indicate that endogeic earthworms increase microbial activity and thus mineralization of phenolic compounds, whereas clay decreases it presumably by binding phenolic compounds to clay particles when passing through the earthworm gut. Endogeic earthworms and clay are only of minor importance for the fate of catechol in soils with high organic matter, clay and microbial biomass concentrations, but in contrast affect the fate of phenolic compounds in low clay soils. [Copyright &y& Elsevier]

Abstract: It has been hypothesized that defoliation and herbivory alter the availability of soluble carbon in the rhizosphere and thereby the biomass and activity of soil microorganisms, and presumably higher trophic levels as well. To test this hypothesis, we established a laboratory experiment investigating effects of shoot cutting of white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.) on soil microorganisms and juvenile endogeic earthworms of the species Octolasion tyrtaeum (Savigny), and Aporrectodea caliginosa (Savigny). Plants were grown in microcosms for 4 weeks, cut 5cm above the soil surface and left to regrow until microcosms were destructively sampled after another 4 weeks. Defoliation decreased total shoot biomass of T. repens but had no significant effect on shoot biomass of L. perenne. Root biomass of L. perenne significantly exceeded that of T. repens, but defoliation reduced root biomass of L. perenne and T. repens by 48.6 and 67.3%, respectively. Microbial biomass per gram of soil in treatments with L. perenne exceeded that in treatments with T. repens, but when calculated per gram of roots, microbial biomass in treatments with T. repens exceeded that in treatments with L. perenne. Defoliation of both plant species significantly increased microbial biomass. Microbial activity differed between treatments and was higher in the grass than in the clover treatment in the beginning, but the reverse was the case later. The biomass of both earthworm species decreased and was only slightly affected by the treatments. In addition, neither earthworm species affected plant growth, microbial biomass or the production of CO2. Our results suggest that defoliation of perennial ryegrass and white clover increased the availability of carbon in the rhizosphere as indicated by the increase in microbial biomass, but that quality and quantity of rhizodeposits differed over time and between plant species. Furthermore, endogeic earthworms were unable to exploit the microbial biomass pool in soil, rather, rhizosphere microorganisms appeared to have effectively competed with endogeic earthworms and exploited root exudates. [Copyright &y& Elsevier]

Abstract: The effect of endogeic earthworms (Octolasion tyrtaeum (Savigny)) on the translocation of litter-derived carbon into the upper layer of a mineral soil by fungi was investigated in a microcosm experiment. Arable soil with and without O. tyrtaeum was incubated with 13C/15N-labelled rye leaves placed on plastic rings with gaze (64μm mesh size) to avoid incorporation of leaves by earthworms. The plastic rings were positioned either on or 3cm above the soil surface, to distinguish between biotic and chemical/physical translocation of nutrients by fungi and leaching. Contact of leaves to the soil increased 13C translocation, whereas presence of O. tyrtaeum reduced the incorporation of 13C into the mineral soil in all treatments. Although biomass of O. tyrtaeum decreased during the experiment, more 13C and 15N was incorporated into earthworm tissue in treatments with contact of leaves to the soil. Contact of leaves to the soil and the presence of O. tyrtaeum increased cumulative 13CO2-C production by 18.2% and 14.1%, respectively. The concentration of the fungal bio-indicator ergosterol in the soil tended to be increased and that of the fungal-specific phospholipid fatty acid 18:2ω6 was significantly increased in treatments with contact of leaves to the soil. Earthworms reduced the concentration of ergosterol and 18:2ω6 in the soil by 14.0% and 43.2%, respectively. Total bacterial PLFAs in soil were also reduced in presence of O. tyrtaeum, but did not respond to the addition of the rye leaves. In addition, the bacterial community in treatments with O. tyrtaeum differed from that without earthworms and shifted towards an increased dominance of Gram-negative bacteria. The results indicate that litter-decomposing fungi translocate litter-derived carbon via their mycelial network in to the upper mineral soil. Endogeic earthworms decrease fungal biomass by grazing and disruption of fungal hyphae thereby counteracting the fungal-mediated translocation of carbon in soils. [Copyright &y& Elsevier]

Abstract: Soil organic matter (SOM) is the main energy resource of the great diversity of soil invertebrates but knowledge on the contribution of SOM pools of different ages to soil animal nutrition is sparse. In the present study natural stable isotope ratios were used to investigate the incorporation of decade old wheat-borne carbon into soil invertebrates of different trophic levels of a maize field 27 years after the replacement of wheat. For comparison a nearby continuous wheat field was investigated. Although the soil food web of the wheat and the maize field consisted of similar invertebrate taxa, most taxa were significantly more abundant in the wheat than in the maize field confirming that C4 plants are generally of poor food quality to soil animals due to low nutrient and high fibre contents. However, different cultivation strategies may also have contributed to differences in the abundance of invertebrates between both study sites. The mean incorporation of C3 carbon in soil animals in the maize field was 60.6±27.8%, but significantly differed between invertebrate species. Unfortunately, the field size did not entirely exclude incorporation of C3 carbon into the tissue of large and mobile invertebrates by feeding on C3 resources outside of the maize field. However, less mobile species such as endogeic earthworms incorporated high amounts of C3 carbon presumably due to the mobilisation of old carbon pools enclosed in soil aggregates and inaccessible to other soil invertebrates during gut passage. Furthermore, small and less mobile invertebrate species, such as most hemi- and epiedaphic Collembolans, also incorporated high amounts of C3 carbon likely by feeding on saprophytic fungi and microorganisms. In contrast, euedaphic Collembola incorporated only small amounts of C3 carbon suggesting preferentially feeding on maize resources. Overall, our data suggest that decade old carbon resources form an important component of the soil animal food web, but that the exploitation of old carbon resources by animal species varies with their distribution within the soil matrix, trophic position and exploitation of algae, and as an artefact to the small size of the study site, animal mobility. [Copyright &y& Elsevier]

Summary: The soil seed bank functions to escape unfavourable environmental conditions and seed predation. Anecic earthworms are increasingly recognised as important dispersers and predators of plant seeds. In contrast, the role of the usually more abundant endogeic earthworms which live and feed in the soil on plant seeds is largely unknown. We tested whether (A) endogeic earthworms (Aporrectodea rosea, Allolobophora chlorotica, Octolasion tyrtaeum, Aporrectodea caliginosa) ingest and digest grassland plant seeds (Phleum pratense, Bellis perennis, Trifolium repens, Poa trivialis, Plantago lanceolata, Medicago varia), (B) the passage of seeds through the gut of endogeic earthworms modifies seed germination, and (C) excreta (mucus and casts) of endogeic earthworms modify seed germination. As a reference effects of the well-studied anecic species Lumbricus terrestris were determined. Endogeic earthworms ingested and digested all of the studied plant seeds; however, both ingestion and digestion were earthworm and plant species specific. Moreover, passage through the gut of endogeic earthworms and their excreta modified plant seed germination (gut passage: B. perennis; excreta: Ph. pratense and Pl. lanceolata). The results indicate that endogeic earthworms may strongly impact the composition of the soil seed bank and, consequently, plant community assembly via direct and indirect effects on plant seeds. Since post-dispersal seed predation is a key factor for the structure of plant communities, with the effect on seed survival potentially exceeding that of pre-dispersal predation, seed predation and changes in germination of seeds by endogeic earthworm species is likely to drive plant community composition. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Removal of crop residues has become common practice in arable systems, however, little is known about how soil arthropod communities change in response to reduced resource availability and habitat complexity associated with residue removal. We added maize residues to wheat and maize fields and investigated soil arthropod diversity and abundance over the period of one year. Residue addition did not affect the diversity and little affected the abundance of soil arthropods in wheat and maize fields with the latter being restricted to few taxonomic groups, suggesting that at least in the short-term soil arthropods benefit little from crop residue-mediated increase in food supply and habitat structure. Contrasting the minor effects of residue addition, densities of soil arthropods were much higher in wheat than in maize fields, presumably due to more dense and more continuous coverage by plants, and higher input of root residues. Furthermore, in wheat fields density of arthropods more strongly varied with season, presumably due to more pronounced pulses of root exudates and root residues entering the soil in wheat as compared to maize fields in summer and winter, respectively. Low density and little variation in densities of soil arthropods in maize fields reflect that environmental conditions and resource supply varied little with crop coverage and season. Overall, the results point to low importance of aboveground crop residues for soil arthropod communities and highlight that belowground plant resources, i.e. root exudates and root residues are the major driver of soil arthropod communities of arable systems. Thus, at least in short term removal of crop residues for e.g., biofuel production is likely to be of minor importance for soil arthropod communities. In contrast, changing crop species from wheat to maize markedly reduces the density of soil animals threatening the ecosystem functions they provide. [ABSTRACT FROM AUTHOR]

Host-plants may rarely leave their ancestral niche and in which case they tend to be surrounded by phylogenetically distant neighbours. Phylogenetically isolated host-plants might share few mutualists with their neighbours and might suffer from a decrease in mutualist support. In addition host plants leaving their ancestral niche might face a deterioration of their abiotic and biotic environment and might hence need to invest more into mutualist partners. We tested whether phylogenetic isolation of hosts from neighbours decreases or increases abundance and activity of their mutualists and whether mutualist activity may help to compensate deterioration of the environment. We study oak-hosts and their ectomycorrhizal fungi mutualists established in the litter layer formed by the phylogenetically closely or distantly related neighbourhood. We find that oaks surrounded by phylogenetically distant neighbours show increased abundance and enzymatic activity of ectomycorrhizal fungi in the litter. Moreover, oaks surrounded by phylogenetically distant neighbours also show delayed budburst but ectomycorrhizal fungi activity partly compensates this negative effect of phylogenetic isolation. This suggests decreased nutrient availability in a phylogenetically distant litter partly compensated by increased litter-degradation by ectomycorrhizal fungi activity. Most observed effects of phylogenetic isolation cannot be explained by a change in baseline soil fertility (as reflected by nutritional status of fresh oak litter, or soil microbial biomass and activity) nor by simple reduction of percentages of oak neighbours, nor by the presence of gymnosperms. Our results show that colonizing new niche represented by the presence of distantly related neighbours may delay plant phenology but may be supported by mycorrhizal mutualists. Studies on other host-plant species are required to generalize our findings. [ABSTRACT FROM AUTHOR]

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: The origin and quantity of plant inputs to soil are primary factors controlling the size and structure of the soil microbial community. The present study aimed to elucidate and quantify the carbon (C) flow from both root and shoot litter residues into soil organic, extractable, microbial and fungal C pools. Using the shift in C stable isotope values associated with replacing C3 by C4 plants we followed root- vs. shoot litter-derived C resources into different soil C pools. We established the following treatments: Corn Maize (CM), Fodder Maize (FM), Wheat+maize Litter (WL) and Wheat (W) as reference. The Corn Maize treatment provided root- as well as shoot litter-derived C (without corn cobs) whereas Fodder Maize (FM) provided only root-derived C (aboveground shoot material was removed). Maize shoot litter was applied on the Wheat+maize Litter (WL) plots to trace the incorporation of C4 litter C into soil microorganisms. Soil samples were taken three times per year (summer, autumn, winter) over two growing seasons. Maize-derived C signal was detectable after three to six months in the following pools: soil organic C (Corg), extractable organic C (EOC), microbial biomass (Cmic) and fungal biomass (ergosterol). In spite of the lower amounts of root- than of shoot litter-derived C inputs, similar amounts were incorporated into each of the C pools in the FM and WL treatments, indicating greater importance of the root- than shoot litter-derived resources for the soil microorganisms as a basis for the belowground food web. In the CM plots twice as much maize-derived C was incorporated into the pools. After two years, maize-derived C in the CM treatment contributed 14.1, 24.7, 46.6 and 76.2% to Corg, EOC, Cmic and ergosterol pools, respectively. Fungi incorporated maize-derived C to a greater extent than did total soil microbial biomass. [Copyright &y& Elsevier]