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S. Scheu

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University of Natural Resources and Life Sciences, Vienna (BOKU)

Nico Eisenhauer

Leipzig University (Universität Leipzig)

University of Vienna

Alexandru Milcu

Centre National de la Recherche Scientifique / French National Centre for Scientific Research

Hermann Jungkunst

Cécile Villenave

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Papers by S. Scheu

Earthworms and Litter Distribution Affect Plant-Defensive Chemistry

by Susanne Wurst and S. Scheu

Journal of Chemical Ecology, 2000

Studies on plant-defensive chemistry have mainly focused on plants in direct interaction with abo... more Studies on plant-defensive chemistry have mainly focused on plants in direct interaction with aboveground and occasionally belowground herbivores and pathogens. Here we investigate whether decomposers and the spatial distribution of organic residues in soil affect plant-defensive chemistry. Litter concentrated in a patch (vs. homogeneously mixed into the soil) led to an increase in the aucubin content in shoots of Plantago lanceolata. Earthworms increased total phytosterol content of shoots, but only when the litter was mixed homogeneously into the soil. The phytosterol content increased and aphid reproduction decreased with increasing N concentration of the shoots. This study documents for the first time that earthworms and the spatial distribution of litter may change plant-defensive chemistry against herbivores.

Effects of earthworms and organic litter distribution on plant performance and aphid reproduction

by Susanne Wurst and S. Scheu

Oecologia, 2003

Mechanisms linking plant community properties to soil aggregate stability in an experimental grassland plant diversity gradient

by A. Weigelt, Nico Eisenhauer, and S. Scheu

Plant and Soil, 2013

Background and aims Soil aggregate stability depends on plant community properties, such as funct... more Background and aims Soil aggregate stability depends on plant community properties, such as functional group composition, diversity and biomass production. However, little is known about the relative importance of these drivers and the role of soil organisms in mediating plant community effects. Methods We studied soil aggregate stability in an experimental grassland plant diversity gradient and considered several explanatory variables to mechanistically Plant Soil

A comparison of the strength of biodiversity effects across multiple functions

by Anne Ebeling, A. Weigelt, and S. Scheu

Oecologia, 2013

In order to predict which ecosystem functions are most at risk from biodiversity loss, meta-analy... more In order to predict which ecosystem functions are most at risk from biodiversity loss, meta-analyses have generalised results from biodiversity experiments over different sites and ecosystem types. In contrast, comparing the strength of biodiversity effects across a large number of ecosystem processes measured in a single experiment permits more direct comparisons. Here, we present an analysis of 418 separate measures of 38 ecosystem processes. Overall, 45 % of processes were significantly affected by plant species richness, suggesting that, while diversity affects a large number of processes not all respond to biodiversity. We therefore compared the strength of plant diversity effects between different categories of ecosystem processes, grouping processes according to the year of measurement, their biogeochemical cycle, trophic level and compartment (above- or belowground) and according to whether they were measures of biodiversity or other ecosystem processes, biotic or abiotic and static or dynamic. Overall, and for several individual processes, we found that biodiversity effects became stronger over time. Measures of the carbon cycle were also affected more strongly by plant species richness than were the measures associated with the nitrogen cycle. Further, we found greater plant species richness effects on measures of biodiversity than on other processes. The differential effects of plant diversity on the various types of ecosystem processes indicate that future research and political effort should shift from a general debate about whether biodiversity loss impairs ecosystem functions to focussing on the specific functions of interest and ways to preserve them individually or in combination.

Transcriptional responses of Folsomia candida upon exposure to Aspergillus nidulans secondary metabolites in single and mixed diets

by dr. Dick Roelofs and S. Scheu

Pedobiologia, 2010

Genetic and molecular evidence to support the hypothesis that fungal secondary metabolites play a... more Genetic and molecular evidence to support the hypothesis that fungal secondary metabolites play a significant role in protecting the fungi against fungivory is scarce. We investigated the impact of fungal secondary metabolites on transcript regulation in the fungivorous springtail Folsomia candida feeding on mixed vs. single diets. Aspergillus nidulans, which is able to produce secondary metabolites including sterigmatocystin, and a knockout mutant with reduced secondary metabolism (A. nidulans LaeA) were combined with the high quality fungus Cladosporium cladosporioides as mixed diets or offered as single diets. We hypothesized that (i) A. nidulans WT triggers more genes associated with stress responses compared to the A. nidulans LaeA strain with suppressed secondary metabolism, (ii) C. cladosporioides causes significantly different transcript regulation than the A. nidulans strains LaeA and WT, and (iii) mixed diets will cause significantly different transcript expression levels than single diets. All three hypotheses are generally supported regardless of the fact that functions of many of the differentially transcribed genes are still enigmatic and that a relatively subtle response, devoid of characteristic stress response genes, was observed towards the toxic fungi in the diet. The wild type A. nidulans strain elicited 30% more differentially expressed genes than the LaeA mutant strain. Differentially expressed genes were not observed in the mixture diet of the C. cladosporoides × A. nidulans WT diet, indicating selective grazing on C. cladosporoides. The results bring molecular evidence for the existence of a link between fungal secondary metabolites and responses in springtails supporting the hypothesis that fungal secondary metabolites act as a shield against fungivory.

Soil-carbon preservation through habitat constraints and biological limitations on decomposer activity

by F. Buscot and S. Scheu

Journal of Plant Nutrition and Soil Science, 2008

We review recent experimental results on the role of soil biota in stabilizing or destabilizing s... more We review recent experimental results on the role of soil biota in stabilizing or destabilizing soil organic matter (SOM). Specifically, we analyze how the differential substrate utilization of the various decomposer organisms contributes to a decorrelation of chemical stability, residence time, and carbon (C) age of organic substrates. Along soil depth profiles, a mismatch of C allocation and abundance of decomposer organisms is consistently observed, revealing that a relevant proportion of soil C is not subjected to efficient decomposition. Results from recent field and laboratory experiments suggest that (1) bacterial utilization of labile carbon compounds is limited by short-distance transport processes and, therefore, can take place deep in the soil under conditions of effective local diffusion or convection. In contrast, (2) fungal utilization of phenolic substrates, including lignin, appears to be restricted to the upper soil layer due to the requirement for oxygen of the enzymatic reaction involved.

Impacts of earthworms and arbuscular mycorrhizal fungi (Glomus intraradices) on plant performance are not interrelated

by Nico Eisenhauer, F. Buscot, and S. Scheu

Soil Biology and Biochemistry, 2009

Lumbricus terrestris Soil organism interactions The Jena Experiment a b s t r a c t Earthworms an... more Lumbricus terrestris Soil organism interactions The Jena Experiment a b s t r a c t Earthworms and arbuscular mycorrhizal fungi (AMF) might interactively impact plant productivity; however, previous studies reported inconsistent results. We set up a three-factorial greenhouse experiment to study the effects of earthworms (Aporrectodea caliginosa Savigny and Lumbricus terrestris L.) and AMF (Glomus intraradices N.C. Schenck & G.S. Sm.) on the performance (productivity and shoot nutrient content) of plant species (Lolium perenne L., Trifolium pratense L. and Plantago lanceolata L.) belonging to the three functional groups grasses, legumes and herbs, respectively. Further, we investigated earthworm performance and plant root mycorrhization as affected by the treatments. Our results accentuate the importance of root derived resources for earthworm performance since earthworm weight (A. caliginosa and L. terrestris) and survival (L. terrestris) were significantly lower in microcosms containing P. lanceolata than in those containing T. pratense. However, earthworm performance was not affected by AMF, and plant root mycorrhization was not modified by earthworms. Although AMF effectively competed with T. pratense for soil N (as indicated by d 15 N analysis), AMF enhanced the productivity of T. pratense considerably by improving P availability. Remarkably, we found no evidence for interactive effects of earthworms and AMF on the performance of the plant species studied. This suggests that interactions between earthworms and AMF likely are of minor importance.

Functionally and phylogenetically diverse plant communities key to soil biota

by Alexandru Milcu, Bernhard Schmid, Nico Eisenhauer, and S. Scheu

Recent studies assessing the role of biological diversity for ecosystem functioning indicate that... more Recent studies assessing the role of biological diversity for ecosystem functioning indicate that the diversity of functional traits and the evolutionary history of species in a community, not the number of taxonomic units, ultimately drives the biodiversityecosystem-function relationship. Here, we simultaneously assessed the importance of plant functional trait and phylogenetic diversity as predictors of major trophic groups of soil biota (abundance and diversity), six years from the onset of a grassland biodiversity experiment. Plant functional and phylogenetic diversity were generally better predictors of soil biota than the traditionally used species or functional group richness. Functional diversity was a reliable predictor for most biota, with the exception of soil microorganisms, which were better predicted by phylogenetic diversity. These results provide empirical support for the idea that the diversity of plant functional traits and the diversity of evolutionary lineages in a community are important for maintaining higher abundances and diversity of soil communities.

Impact of above- and below-ground invertebrates on temporal and spatial stability of grassland of different diversity

by Alexandru Milcu, Nico Eisenhauer, and S. Scheu

Journal of Ecology, 2011

Recent theoretical studies suggest that the stability of ecosystem processes is not governed by d... more Recent theoretical studies suggest that the stability of ecosystem processes is not governed by diversity per se, but by multitrophic interactions in complex communities. However, experimental evidence supporting this assumption is scarce. 2. We investigated the impact of plant diversity and the presence of above-and below-ground invertebrates on the stability of plant community productivity in space and time, as well as the interrelationship between both stability measures in experimental grassland communities. 3. We sampled above-ground plant biomass on subplots with manipulated above-and belowground invertebrate densities of a grassland biodiversity experiment (Jena Experiment) 1, 4 and 6 years after the establishment of the treatments to investigate temporal stability. Moreover, we harvested spatial replicates at the last sampling date to explore spatial stability. 4. The coefficient of variation of spatial and temporal replicates served as a proxy for ecosystem stability. Both spatial and temporal stability increased to a similar extent with plant diversity. Moreover, there was a positive correlation between spatial and temporal stability, and elevated plant density might be a crucial factor governing the stability of diverse plant communities. 5. Above-ground insects generally increased temporal stability, whereas impacts of both earthworms and above-ground insects depended on plant species richness and the presence of grasses. These results suggest that inconsistent results of previous studies on the diversity-stability relationship have in part been due to neglecting higher trophic-level interactions governing ecosystem stability. 6. Changes in plant species diversity in one trophic level are thus unlikely to mirror changes in multitrophic interrelationships. Our results suggest that both above-and below-ground invertebrates decouple the relationship between spatial and temporal stability of plant community productivity by differently affecting the homogenizing mechanisms of plants in diverse plant communities. 7. Synthesis. Species extinctions and accompanying changes in multitrophic interactions are likely to result not only in alterations in the magnitude of ecosystem functions but also in its variability complicating the assessment and prediction of consequences of current biodiversity loss.

DECOMPOSERS (LUMBRICIDAE, COLLEMBOLA) AFFECT PLANT PERFORMANCE IN MODEL GRASSLANDS OF DIFFERENT DIVERSITY

by Alexandru Milcu and S. Scheu

Ecology, 2006

S. 2006. The response of decomposers (earthworms, springtails and microorganisms) to variations i... more

Plant diversity enhances the reliability of belowground processes

by Alexandru Milcu, Nico Eisenhauer, and S. Scheu

Soil Biology & Biochemistry, 2010

Theory predicts that the probability that an ecosystem will provide a consistent level of functio... more Theory predicts that the probability that an ecosystem will provide a consistent level of functioning over a given unit of time, i.e. the reliability of ecosystem processes, should increase with species richness. There is growing evidence that plant diversity increases the temporal stability of productivity, but only a few studies have investigated its impact on the reliability of ecosystem processes, and information on whether this propagates to the belowground system is virtually lacking. Using a microcosm experiment with plant communities varying in species and functional group diversity and two decomposer groups (earthworms and Collembola) we investigated the effects of plant diversity on the reliability of the belowground system and vice versa, the effect of decomposers on the reliability of plant productivity. Generally, plant diversity increased the reliability of above-and belowground processes by significantly increasing the reliability of eight out of eleven measured ecosystem parameters (six out of nine belowground responses). Plant functional group diversity had a stronger stabilising effect than species richness on above-and belowground processes including plant shoot and total biomass, microbial basal respiration and Collembola densities. By contrast, in the presence of both decomposer groups the reliability of decomposer populations was reduced. The results indicate that plant diversity effects propagate into the belowground system and increase the reliability of belowground processes via more consistent plant derived belowground inputs.

The response of decomposers (earthworms, springtails and microorganisms) to variations in species and functional group diversity of plants

by Alexandru Milcu and S. Scheu

Oikos, 2006

The responses of three decomposer groups (earthworms, springtails and microorganisms) to manipula... more The responses of three decomposer groups (earthworms, springtails and microorganisms) to manipulations in plant species diversity (1, 2, 4, 8), plant functional group diversity (1, 2, 3, 4) and functional group identity (grasses, legumes, small herbs, tall herbs) were studied in a microcosm experiment. Separate and combined treatments with earthworms and springtails were set up. Two earthworm species representing major functional groups of earthworms in grasslands were investigated, the endogeic species Aporrectodea caliginosa (Savigny) and the anecic species Lumbricus terrestris L. For springtails three species were investigated, the hemiedaphic species Heteromurus nitidus (Leleup), Folsomia candida (Willem) and the euedaphic species Protaphorura fimata (Gisin). Plant species and functional group diversity beneficially affected A. caliginosa (increase in body weight and incorporation of 15N from labelled litter) and P. fimata (density), presumably by changing the quality of belowground resources. In contrast, the biomass of L. terrestris decreased with plant species diversity but only in presence of legumes. For H. nitidus and F. candida the identity of plant functional groups was more important than plant species diversity per se. Also, the response of F. candida depended on earthworms. Microbial respiration was reduced by earthworms in more diverse plant communities, which correlated with root biomass. In contrast, microbial biomass was not affected by plant species diversity. The results suggest that belowground resource inputs from plant roots strongly modify decomposer performance and that the quality of the resources that enter the belowground subsystem is more important than their quantity. The responses of decomposers generally were not correlated with below- or aboveground plant productivity. In addition, the results document that effects of plant community composition on the performance of decomposer species depend on the presence of other decomposers.

Animal Ecosystem Engineers Modulate the Diversity-Invasibility Relationship

by Alexandru Milcu, Nico Eisenhauer, and S. Scheu

PLOS One, 2008

Background: Invasions of natural communities by non-indigenous species are currently rated as one... more Background: Invasions of natural communities by non-indigenous species are currently rated as one of the most important global-scale threats to biodiversity. Biodiversity itself is known to reduce invasions and increase stability. Disturbances by ecosystem engineers affect the distribution, establishment, and abundance of species but this has been ignored in studies on diversity-invasibility relationships.

Olfactory cues associated with fungal grazing intensity and secondary metabolite pathway modulate Collembola foraging behaviour

by Alexandru Milcu and S. Scheu

Fungal secondary compounds play an important role for springtail food choice and fitness. Little ... more Fungal secondary compounds play an important role for springtail food choice and fitness. Little is known, however, on the role of olfactory cues for Collembola foraging behaviour and whether Collembola can olfactorily perceive volatiles associated with fungal secondary metabolite pathways. We investigated the ability of three species of Collembola (Folsomia candida, Heteromurus nitidus and Supraphorura furcifera) to use olfactory cues for discriminating between fungi of different phylogenetic affiliation (Aspergillus nidulans, Cladosporium cladosporioides, Ascomycota; Laccaria bicolor, Basidiomycota) and toxicity using fungal strains of A. nidulans with reduced secondary metabolite production. Furthermore, we studied if olfactory cues from hyphae injured by grazing affect the foraging behaviour of Collembola. We hypothesized that (i) Collembola are able to olfactorily perceive and respond to fungal species/strains with different secondary metabolite pathways and that (ii) Collembola are able to sense fungal mycelia injured by grazing. Each of the Collembola species studied preferentially oriented their foraging towards fungal strains of A. nidulans with suppressed secondary metabolites, and in particular towards the mutant where the global regulator for secondary metabolites (DlaeA) has been silenced. Two of the three Collembola species (H. nitidus and S. furcifera) sensed olfactory cues of previously grazed fungi and moved towards ungrazed fungi, however, the response of S. furcifera was restricted to fungi extensively exposed to grazing (5 days) suggesting that the response varies between Collembola species.

Identification of General Patterns of Nutrient and Labile Carbon Control on Soil Carbon Dynamics Across a Successional Gradient

by Alexandru Milcu and S. Scheu

Ecosystems, 2011

Carbon (C) inputs and nutrient availability are known to affect soil organic carbon (SOC) stocks.... more Carbon (C) inputs and nutrient availability are known to affect soil organic carbon (SOC) stocks. However, general rules regarding the operation of these factors across a range of soil nutrient availabilities and substrate qualities are unidentified. “Priming” (stimulated decomposition by labile C inputs) and ‘preferential substrate utilization’ (retarded decomposition due to shifts in community composition towards microbes that do not mineralize SOC) are two hypotheses to explain effects of labile C additions on SOC dynamics. For effects of nutrient additions (nitrogen and phosphorus) on SOC dynamics, the stoichiometric (faster decomposition of materials of low carbon-to-nutrient ratios) and ‘microbial mining’ (that is, reduced breakdown of recalcitrant C forms for nutrients under fertile conditions) hypotheses have been proposed. Using the natural gradient of soil nutrient availability and substrate quality of a chronosequence, combined with labile C and nutrient amendments, we explored the support for these contrasting hypotheses. Additions of labile C, nitrogen (N), phosphorus (P), and combinations of C and N and C and P were applied to three sites: 2-year fallow grassland, mature grassland and forest, and the effects of site and nutrient additions on litter decomposition and soil C dynamics were assessed. The response to C addition supported the preferential substrate hypothesis for easily degradable litter C and the priming hypothesis for SOC, but only in nitrogen-enriched soils of the forest site. Responses to N addition supported the microbial mining hypothesis irrespective of C substrate (litter or SOC), but only in the forest site. Further, P addition effects on SOC support the stoichiometric hypothesis; P availability appeared key to soil C release (priming) in the forest site if labile C and N is available. These results clearly link previously contrasting hypotheses of the factors controlling SOC with the natural gradient in litter quality and nutrient availability that exists in ecosystems at different successional stages. A holistic theory that incorporates this variability of responses, due to different mechanisms, depending on nutrient availability and substrate quality is essential for devising management strategies to safeguard soil C stocks.

Bottom-up effects of plant diversity on multitrophic interactions in a biodiversity experiment

by Alexandru Milcu, Ernst-detlef Schulze, S. Halle, Bernhard Schmid, Nico Eisenhauer, and S. Scheu

Nature, 2010

Biodiversity is rapidly declining, and this may negatively affect ecosystem processes, including ... more Biodiversity is rapidly declining, and this may negatively affect ecosystem processes, including economically important ecosystem services. Previous studies have shown that biodiversity has positive effects on organisms and processes across trophic levels. However, only a few studies have so far incorporated an explicit food-web perspective. In an eight-year biodiversity experiment, we studied an unprecedented range of above- and below-ground organisms and multitrophic interactions. A multitrophic data set originating from a single long-term experiment allows mechanistic insights that would not be gained from meta-analysis of different experiments. Here we show that plant diversity effects dampen with increasing trophic level and degree of omnivory. This was true both for abundance and species richness of organisms. Furthermore, we present comprehensive above-ground/below-ground biodiversity food webs. Both above ground and below ground, herbivores responded more strongly to changes in plant diversity than did carnivores or omnivores. Density and richness of carnivorous taxa was independent of vegetation structure. Below-ground responses to plant diversity were consistently weaker than above-ground responses. Responses to increasing plant diversity were generally positive, but were negative for biological invasion, pathogen infestation and hyperparasitism. Our results suggest that plant diversity has strong bottom-up effects on multitrophic interaction networks, with particularly strong effects on lower trophic levels. Effects on higher trophic levels are indirectly mediated through bottom-up trophic cascades.

Diversity Promotes Temporal Stability across Levels of Ecosystem Organization in Experimental Grasslands

by Alexandru Milcu, Jussi Baade, Winfried Voigt, S. Halle, Bernhard Schmid, Nico Eisenhauer, and S. Scheu

The diversity-stability hypothesis states that current losses of biodiversity can impair the abil... more The diversity-stability hypothesis states that current losses of biodiversity can impair the ability of an ecosystem to dampen the effect of environmental perturbations on its functioning. Using data from a long-term and comprehensive biodiversity experiment, we quantified the temporal stability of 42 variables characterizing twelve ecological functions in managed grassland plots varying in plant species richness. We demonstrate that diversity increases stability i) across trophic levels (producer, consumer), ii) at both the system (community, ecosystem) and the component levels (population, functional group, phylogenetic clade), and iii) primarily for aboveground rather than belowground processes. Temporal synchronization across studied variables was mostly unaffected with increasing species richness. This study provides the strongest empirical support so far that diversity promotes stability across different ecological functions and levels of ecosystem organization in grasslands.

Earthworm and belowground competition effects on plant productivity in a plant diversity gradient

by Alexandru Milcu, Nico Eisenhauer, and S. Scheu

Oecologia, 2009

Diversity is one major factor driving plant productivity in temperate grasslands. Although decomp... more Diversity is one major factor driving plant productivity in temperate grasslands. Although decomposers like earthworms are known to affect plant productivity, interacting effects of plant diversity and earthworms on plant productivity have been neglected in field studies. We investigated in the field the effects of earthworms on plant productivity, their interaction with plant species and functional group richness, and their effects on belowground plant competition. In the framework of the Jena Experiment we determined plant community productivity (in 2004 and 2007) and performance of two phytometer plant species [Centaurea jacea (herb) and Lolium perenne (grass); in 2007 and 2008] in a plant species (from one to 16) and functional group richness gradient (from one to four). We sampled earthworm subplots and subplots with decreased earthworm density and reduced aboveground competition of phytometer plants by removing the shoot biomass of the resident plant community. Earthworms increased total plant community productivity (+11%), legume shoot biomass (+35%) and shoot biomass of the phytometer C. jacea (+21%). Further, phytometer performance decreased, i.e. belowground competition increased, with increasing plant species and functional group richness. Although single plant functional groups benefited from higher earthworm numbers, the effects did not vary with plant species and functional group richness. The present study indicates that earthworms indeed affect the productivity of semi-natural grasslands irrespective of the diversity of the plant community. Belowground competition increased with increasing plant species diversity. However, belowground competition was modified by earthworms as reflected by increased productivity of the phytometer C. jacea. Moreover, particularly legumes benefited from earthworm presence. Considering also previous studies, we suggest that earthworms and legumes form a loose mutualistic relationship affecting essential ecosystem functions in temperate grasslands, in particular decomposition and plant productivity. Further, earthworms likely alter competitive interactions among plants and the structure of plant communities by beneficially affecting certain plant functional groups.

Plant diversity drives soil microbial biomass carbon in grasslands irrespective of global environmental change factors

by Alexandru Milcu, Anja Vogel, Madhav Thakur, Nico Eisenhauer, and S. Scheu

Plant community impacts on the structure of earthworm communities depend on season and change with time

by Alexandru Milcu, Nico Eisenhauer, and S. Scheu

Soil Biology & Biochemistry, 2009

Declining plant diversity potentially threatens essential ecosystem functions driven by the decom... more Declining plant diversity potentially threatens essential ecosystem functions driven by the decomposer community, such as litter decomposition and nutrient cycling. Currently, there is no consensus on the interrelationships between plant diversity and decomposer performance and previous studies highlighted the urgent need for long-term experiments.

Earthworms and Litter Distribution Affect Plant-Defensive Chemistry

by Susanne Wurst and S. Scheu

Journal of Chemical Ecology, 2000

Studies on plant-defensive chemistry have mainly focused on plants in direct interaction with abo... more Studies on plant-defensive chemistry have mainly focused on plants in direct interaction with aboveground and occasionally belowground herbivores and pathogens. Here we investigate whether decomposers and the spatial distribution of organic residues in soil affect plant-defensive chemistry. Litter concentrated in a patch (vs. homogeneously mixed into the soil) led to an increase in the aucubin content in shoots of Plantago lanceolata. Earthworms increased total phytosterol content of shoots, but only when the litter was mixed homogeneously into the soil. The phytosterol content increased and aphid reproduction decreased with increasing N concentration of the shoots. This study documents for the first time that earthworms and the spatial distribution of litter may change plant-defensive chemistry against herbivores.

Effects of earthworms and organic litter distribution on plant performance and aphid reproduction

by Susanne Wurst and S. Scheu

Oecologia, 2003

Mechanisms linking plant community properties to soil aggregate stability in an experimental grassland plant diversity gradient

by A. Weigelt, Nico Eisenhauer, and S. Scheu

Plant and Soil, 2013

Background and aims Soil aggregate stability depends on plant community properties, such as funct... more Background and aims Soil aggregate stability depends on plant community properties, such as functional group composition, diversity and biomass production. However, little is known about the relative importance of these drivers and the role of soil organisms in mediating plant community effects. Methods We studied soil aggregate stability in an experimental grassland plant diversity gradient and considered several explanatory variables to mechanistically Plant Soil

A comparison of the strength of biodiversity effects across multiple functions

by Anne Ebeling, A. Weigelt, and S. Scheu

Oecologia, 2013

In order to predict which ecosystem functions are most at risk from biodiversity loss, meta-analy... more In order to predict which ecosystem functions are most at risk from biodiversity loss, meta-analyses have generalised results from biodiversity experiments over different sites and ecosystem types. In contrast, comparing the strength of biodiversity effects across a large number of ecosystem processes measured in a single experiment permits more direct comparisons. Here, we present an analysis of 418 separate measures of 38 ecosystem processes. Overall, 45 % of processes were significantly affected by plant species richness, suggesting that, while diversity affects a large number of processes not all respond to biodiversity. We therefore compared the strength of plant diversity effects between different categories of ecosystem processes, grouping processes according to the year of measurement, their biogeochemical cycle, trophic level and compartment (above- or belowground) and according to whether they were measures of biodiversity or other ecosystem processes, biotic or abiotic and static or dynamic. Overall, and for several individual processes, we found that biodiversity effects became stronger over time. Measures of the carbon cycle were also affected more strongly by plant species richness than were the measures associated with the nitrogen cycle. Further, we found greater plant species richness effects on measures of biodiversity than on other processes. The differential effects of plant diversity on the various types of ecosystem processes indicate that future research and political effort should shift from a general debate about whether biodiversity loss impairs ecosystem functions to focussing on the specific functions of interest and ways to preserve them individually or in combination.

Transcriptional responses of Folsomia candida upon exposure to Aspergillus nidulans secondary metabolites in single and mixed diets

by dr. Dick Roelofs and S. Scheu

Pedobiologia, 2010

Genetic and molecular evidence to support the hypothesis that fungal secondary metabolites play a... more Genetic and molecular evidence to support the hypothesis that fungal secondary metabolites play a significant role in protecting the fungi against fungivory is scarce. We investigated the impact of fungal secondary metabolites on transcript regulation in the fungivorous springtail Folsomia candida feeding on mixed vs. single diets. Aspergillus nidulans, which is able to produce secondary metabolites including sterigmatocystin, and a knockout mutant with reduced secondary metabolism (A. nidulans LaeA) were combined with the high quality fungus Cladosporium cladosporioides as mixed diets or offered as single diets. We hypothesized that (i) A. nidulans WT triggers more genes associated with stress responses compared to the A. nidulans LaeA strain with suppressed secondary metabolism, (ii) C. cladosporioides causes significantly different transcript regulation than the A. nidulans strains LaeA and WT, and (iii) mixed diets will cause significantly different transcript expression levels than single diets. All three hypotheses are generally supported regardless of the fact that functions of many of the differentially transcribed genes are still enigmatic and that a relatively subtle response, devoid of characteristic stress response genes, was observed towards the toxic fungi in the diet. The wild type A. nidulans strain elicited 30% more differentially expressed genes than the LaeA mutant strain. Differentially expressed genes were not observed in the mixture diet of the C. cladosporoides × A. nidulans WT diet, indicating selective grazing on C. cladosporoides. The results bring molecular evidence for the existence of a link between fungal secondary metabolites and responses in springtails supporting the hypothesis that fungal secondary metabolites act as a shield against fungivory.

Soil-carbon preservation through habitat constraints and biological limitations on decomposer activity

by F. Buscot and S. Scheu

Journal of Plant Nutrition and Soil Science, 2008

We review recent experimental results on the role of soil biota in stabilizing or destabilizing s... more We review recent experimental results on the role of soil biota in stabilizing or destabilizing soil organic matter (SOM). Specifically, we analyze how the differential substrate utilization of the various decomposer organisms contributes to a decorrelation of chemical stability, residence time, and carbon (C) age of organic substrates. Along soil depth profiles, a mismatch of C allocation and abundance of decomposer organisms is consistently observed, revealing that a relevant proportion of soil C is not subjected to efficient decomposition. Results from recent field and laboratory experiments suggest that (1) bacterial utilization of labile carbon compounds is limited by short-distance transport processes and, therefore, can take place deep in the soil under conditions of effective local diffusion or convection. In contrast, (2) fungal utilization of phenolic substrates, including lignin, appears to be restricted to the upper soil layer due to the requirement for oxygen of the enzymatic reaction involved.

Impacts of earthworms and arbuscular mycorrhizal fungi (Glomus intraradices) on plant performance are not interrelated

by Nico Eisenhauer, F. Buscot, and S. Scheu

Soil Biology and Biochemistry, 2009

Lumbricus terrestris Soil organism interactions The Jena Experiment a b s t r a c t Earthworms an... more Lumbricus terrestris Soil organism interactions The Jena Experiment a b s t r a c t Earthworms and arbuscular mycorrhizal fungi (AMF) might interactively impact plant productivity; however, previous studies reported inconsistent results. We set up a three-factorial greenhouse experiment to study the effects of earthworms (Aporrectodea caliginosa Savigny and Lumbricus terrestris L.) and AMF (Glomus intraradices N.C. Schenck & G.S. Sm.) on the performance (productivity and shoot nutrient content) of plant species (Lolium perenne L., Trifolium pratense L. and Plantago lanceolata L.) belonging to the three functional groups grasses, legumes and herbs, respectively. Further, we investigated earthworm performance and plant root mycorrhization as affected by the treatments. Our results accentuate the importance of root derived resources for earthworm performance since earthworm weight (A. caliginosa and L. terrestris) and survival (L. terrestris) were significantly lower in microcosms containing P. lanceolata than in those containing T. pratense. However, earthworm performance was not affected by AMF, and plant root mycorrhization was not modified by earthworms. Although AMF effectively competed with T. pratense for soil N (as indicated by d 15 N analysis), AMF enhanced the productivity of T. pratense considerably by improving P availability. Remarkably, we found no evidence for interactive effects of earthworms and AMF on the performance of the plant species studied. This suggests that interactions between earthworms and AMF likely are of minor importance.

Functionally and phylogenetically diverse plant communities key to soil biota

by Alexandru Milcu, Bernhard Schmid, Nico Eisenhauer, and S. Scheu

Recent studies assessing the role of biological diversity for ecosystem functioning indicate that... more Recent studies assessing the role of biological diversity for ecosystem functioning indicate that the diversity of functional traits and the evolutionary history of species in a community, not the number of taxonomic units, ultimately drives the biodiversityecosystem-function relationship. Here, we simultaneously assessed the importance of plant functional trait and phylogenetic diversity as predictors of major trophic groups of soil biota (abundance and diversity), six years from the onset of a grassland biodiversity experiment. Plant functional and phylogenetic diversity were generally better predictors of soil biota than the traditionally used species or functional group richness. Functional diversity was a reliable predictor for most biota, with the exception of soil microorganisms, which were better predicted by phylogenetic diversity. These results provide empirical support for the idea that the diversity of plant functional traits and the diversity of evolutionary lineages in a community are important for maintaining higher abundances and diversity of soil communities.

Impact of above- and below-ground invertebrates on temporal and spatial stability of grassland of different diversity

by Alexandru Milcu, Nico Eisenhauer, and S. Scheu

Journal of Ecology, 2011

Recent theoretical studies suggest that the stability of ecosystem processes is not governed by d... more Recent theoretical studies suggest that the stability of ecosystem processes is not governed by diversity per se, but by multitrophic interactions in complex communities. However, experimental evidence supporting this assumption is scarce. 2. We investigated the impact of plant diversity and the presence of above-and below-ground invertebrates on the stability of plant community productivity in space and time, as well as the interrelationship between both stability measures in experimental grassland communities. 3. We sampled above-ground plant biomass on subplots with manipulated above-and belowground invertebrate densities of a grassland biodiversity experiment (Jena Experiment) 1, 4 and 6 years after the establishment of the treatments to investigate temporal stability. Moreover, we harvested spatial replicates at the last sampling date to explore spatial stability. 4. The coefficient of variation of spatial and temporal replicates served as a proxy for ecosystem stability. Both spatial and temporal stability increased to a similar extent with plant diversity. Moreover, there was a positive correlation between spatial and temporal stability, and elevated plant density might be a crucial factor governing the stability of diverse plant communities. 5. Above-ground insects generally increased temporal stability, whereas impacts of both earthworms and above-ground insects depended on plant species richness and the presence of grasses. These results suggest that inconsistent results of previous studies on the diversity-stability relationship have in part been due to neglecting higher trophic-level interactions governing ecosystem stability. 6. Changes in plant species diversity in one trophic level are thus unlikely to mirror changes in multitrophic interrelationships. Our results suggest that both above-and below-ground invertebrates decouple the relationship between spatial and temporal stability of plant community productivity by differently affecting the homogenizing mechanisms of plants in diverse plant communities. 7. Synthesis. Species extinctions and accompanying changes in multitrophic interactions are likely to result not only in alterations in the magnitude of ecosystem functions but also in its variability complicating the assessment and prediction of consequences of current biodiversity loss.

DECOMPOSERS (LUMBRICIDAE, COLLEMBOLA) AFFECT PLANT PERFORMANCE IN MODEL GRASSLANDS OF DIFFERENT DIVERSITY

by Alexandru Milcu and S. Scheu

Ecology, 2006

S. 2006. The response of decomposers (earthworms, springtails and microorganisms) to variations i... more

Plant diversity enhances the reliability of belowground processes

by Alexandru Milcu, Nico Eisenhauer, and S. Scheu

Soil Biology & Biochemistry, 2010

Theory predicts that the probability that an ecosystem will provide a consistent level of functio... more Theory predicts that the probability that an ecosystem will provide a consistent level of functioning over a given unit of time, i.e. the reliability of ecosystem processes, should increase with species richness. There is growing evidence that plant diversity increases the temporal stability of productivity, but only a few studies have investigated its impact on the reliability of ecosystem processes, and information on whether this propagates to the belowground system is virtually lacking. Using a microcosm experiment with plant communities varying in species and functional group diversity and two decomposer groups (earthworms and Collembola) we investigated the effects of plant diversity on the reliability of the belowground system and vice versa, the effect of decomposers on the reliability of plant productivity. Generally, plant diversity increased the reliability of above-and belowground processes by significantly increasing the reliability of eight out of eleven measured ecosystem parameters (six out of nine belowground responses). Plant functional group diversity had a stronger stabilising effect than species richness on above-and belowground processes including plant shoot and total biomass, microbial basal respiration and Collembola densities. By contrast, in the presence of both decomposer groups the reliability of decomposer populations was reduced. The results indicate that plant diversity effects propagate into the belowground system and increase the reliability of belowground processes via more consistent plant derived belowground inputs.

The response of decomposers (earthworms, springtails and microorganisms) to variations in species and functional group diversity of plants

by Alexandru Milcu and S. Scheu

Oikos, 2006

The responses of three decomposer groups (earthworms, springtails and microorganisms) to manipula... more The responses of three decomposer groups (earthworms, springtails and microorganisms) to manipulations in plant species diversity (1, 2, 4, 8), plant functional group diversity (1, 2, 3, 4) and functional group identity (grasses, legumes, small herbs, tall herbs) were studied in a microcosm experiment. Separate and combined treatments with earthworms and springtails were set up. Two earthworm species representing major functional groups of earthworms in grasslands were investigated, the endogeic species Aporrectodea caliginosa (Savigny) and the anecic species Lumbricus terrestris L. For springtails three species were investigated, the hemiedaphic species Heteromurus nitidus (Leleup), Folsomia candida (Willem) and the euedaphic species Protaphorura fimata (Gisin). Plant species and functional group diversity beneficially affected A. caliginosa (increase in body weight and incorporation of 15N from labelled litter) and P. fimata (density), presumably by changing the quality of belowground resources. In contrast, the biomass of L. terrestris decreased with plant species diversity but only in presence of legumes. For H. nitidus and F. candida the identity of plant functional groups was more important than plant species diversity per se. Also, the response of F. candida depended on earthworms. Microbial respiration was reduced by earthworms in more diverse plant communities, which correlated with root biomass. In contrast, microbial biomass was not affected by plant species diversity. The results suggest that belowground resource inputs from plant roots strongly modify decomposer performance and that the quality of the resources that enter the belowground subsystem is more important than their quantity. The responses of decomposers generally were not correlated with below- or aboveground plant productivity. In addition, the results document that effects of plant community composition on the performance of decomposer species depend on the presence of other decomposers.

Animal Ecosystem Engineers Modulate the Diversity-Invasibility Relationship

by Alexandru Milcu, Nico Eisenhauer, and S. Scheu

PLOS One, 2008

Background: Invasions of natural communities by non-indigenous species are currently rated as one... more Background: Invasions of natural communities by non-indigenous species are currently rated as one of the most important global-scale threats to biodiversity. Biodiversity itself is known to reduce invasions and increase stability. Disturbances by ecosystem engineers affect the distribution, establishment, and abundance of species but this has been ignored in studies on diversity-invasibility relationships.

Olfactory cues associated with fungal grazing intensity and secondary metabolite pathway modulate Collembola foraging behaviour

by Alexandru Milcu and S. Scheu

Fungal secondary compounds play an important role for springtail food choice and fitness. Little ... more Fungal secondary compounds play an important role for springtail food choice and fitness. Little is known, however, on the role of olfactory cues for Collembola foraging behaviour and whether Collembola can olfactorily perceive volatiles associated with fungal secondary metabolite pathways. We investigated the ability of three species of Collembola (Folsomia candida, Heteromurus nitidus and Supraphorura furcifera) to use olfactory cues for discriminating between fungi of different phylogenetic affiliation (Aspergillus nidulans, Cladosporium cladosporioides, Ascomycota; Laccaria bicolor, Basidiomycota) and toxicity using fungal strains of A. nidulans with reduced secondary metabolite production. Furthermore, we studied if olfactory cues from hyphae injured by grazing affect the foraging behaviour of Collembola. We hypothesized that (i) Collembola are able to olfactorily perceive and respond to fungal species/strains with different secondary metabolite pathways and that (ii) Collembola are able to sense fungal mycelia injured by grazing. Each of the Collembola species studied preferentially oriented their foraging towards fungal strains of A. nidulans with suppressed secondary metabolites, and in particular towards the mutant where the global regulator for secondary metabolites (DlaeA) has been silenced. Two of the three Collembola species (H. nitidus and S. furcifera) sensed olfactory cues of previously grazed fungi and moved towards ungrazed fungi, however, the response of S. furcifera was restricted to fungi extensively exposed to grazing (5 days) suggesting that the response varies between Collembola species.

Identification of General Patterns of Nutrient and Labile Carbon Control on Soil Carbon Dynamics Across a Successional Gradient

by Alexandru Milcu and S. Scheu

Ecosystems, 2011

Carbon (C) inputs and nutrient availability are known to affect soil organic carbon (SOC) stocks.... more Carbon (C) inputs and nutrient availability are known to affect soil organic carbon (SOC) stocks. However, general rules regarding the operation of these factors across a range of soil nutrient availabilities and substrate qualities are unidentified. “Priming” (stimulated decomposition by labile C inputs) and ‘preferential substrate utilization’ (retarded decomposition due to shifts in community composition towards microbes that do not mineralize SOC) are two hypotheses to explain effects of labile C additions on SOC dynamics. For effects of nutrient additions (nitrogen and phosphorus) on SOC dynamics, the stoichiometric (faster decomposition of materials of low carbon-to-nutrient ratios) and ‘microbial mining’ (that is, reduced breakdown of recalcitrant C forms for nutrients under fertile conditions) hypotheses have been proposed. Using the natural gradient of soil nutrient availability and substrate quality of a chronosequence, combined with labile C and nutrient amendments, we explored the support for these contrasting hypotheses. Additions of labile C, nitrogen (N), phosphorus (P), and combinations of C and N and C and P were applied to three sites: 2-year fallow grassland, mature grassland and forest, and the effects of site and nutrient additions on litter decomposition and soil C dynamics were assessed. The response to C addition supported the preferential substrate hypothesis for easily degradable litter C and the priming hypothesis for SOC, but only in nitrogen-enriched soils of the forest site. Responses to N addition supported the microbial mining hypothesis irrespective of C substrate (litter or SOC), but only in the forest site. Further, P addition effects on SOC support the stoichiometric hypothesis; P availability appeared key to soil C release (priming) in the forest site if labile C and N is available. These results clearly link previously contrasting hypotheses of the factors controlling SOC with the natural gradient in litter quality and nutrient availability that exists in ecosystems at different successional stages. A holistic theory that incorporates this variability of responses, due to different mechanisms, depending on nutrient availability and substrate quality is essential for devising management strategies to safeguard soil C stocks.

Bottom-up effects of plant diversity on multitrophic interactions in a biodiversity experiment

by Alexandru Milcu, Ernst-detlef Schulze, S. Halle, Bernhard Schmid, Nico Eisenhauer, and S. Scheu

Nature, 2010

Biodiversity is rapidly declining, and this may negatively affect ecosystem processes, including ... more Biodiversity is rapidly declining, and this may negatively affect ecosystem processes, including economically important ecosystem services. Previous studies have shown that biodiversity has positive effects on organisms and processes across trophic levels. However, only a few studies have so far incorporated an explicit food-web perspective. In an eight-year biodiversity experiment, we studied an unprecedented range of above- and below-ground organisms and multitrophic interactions. A multitrophic data set originating from a single long-term experiment allows mechanistic insights that would not be gained from meta-analysis of different experiments. Here we show that plant diversity effects dampen with increasing trophic level and degree of omnivory. This was true both for abundance and species richness of organisms. Furthermore, we present comprehensive above-ground/below-ground biodiversity food webs. Both above ground and below ground, herbivores responded more strongly to changes in plant diversity than did carnivores or omnivores. Density and richness of carnivorous taxa was independent of vegetation structure. Below-ground responses to plant diversity were consistently weaker than above-ground responses. Responses to increasing plant diversity were generally positive, but were negative for biological invasion, pathogen infestation and hyperparasitism. Our results suggest that plant diversity has strong bottom-up effects on multitrophic interaction networks, with particularly strong effects on lower trophic levels. Effects on higher trophic levels are indirectly mediated through bottom-up trophic cascades.

Diversity Promotes Temporal Stability across Levels of Ecosystem Organization in Experimental Grasslands

by Alexandru Milcu, Jussi Baade, Winfried Voigt, S. Halle, Bernhard Schmid, Nico Eisenhauer, and S. Scheu

The diversity-stability hypothesis states that current losses of biodiversity can impair the abil... more The diversity-stability hypothesis states that current losses of biodiversity can impair the ability of an ecosystem to dampen the effect of environmental perturbations on its functioning. Using data from a long-term and comprehensive biodiversity experiment, we quantified the temporal stability of 42 variables characterizing twelve ecological functions in managed grassland plots varying in plant species richness. We demonstrate that diversity increases stability i) across trophic levels (producer, consumer), ii) at both the system (community, ecosystem) and the component levels (population, functional group, phylogenetic clade), and iii) primarily for aboveground rather than belowground processes. Temporal synchronization across studied variables was mostly unaffected with increasing species richness. This study provides the strongest empirical support so far that diversity promotes stability across different ecological functions and levels of ecosystem organization in grasslands.

Earthworm and belowground competition effects on plant productivity in a plant diversity gradient

by Alexandru Milcu, Nico Eisenhauer, and S. Scheu

Oecologia, 2009

Diversity is one major factor driving plant productivity in temperate grasslands. Although decomp... more Diversity is one major factor driving plant productivity in temperate grasslands. Although decomposers like earthworms are known to affect plant productivity, interacting effects of plant diversity and earthworms on plant productivity have been neglected in field studies. We investigated in the field the effects of earthworms on plant productivity, their interaction with plant species and functional group richness, and their effects on belowground plant competition. In the framework of the Jena Experiment we determined plant community productivity (in 2004 and 2007) and performance of two phytometer plant species [Centaurea jacea (herb) and Lolium perenne (grass); in 2007 and 2008] in a plant species (from one to 16) and functional group richness gradient (from one to four). We sampled earthworm subplots and subplots with decreased earthworm density and reduced aboveground competition of phytometer plants by removing the shoot biomass of the resident plant community. Earthworms increased total plant community productivity (+11%), legume shoot biomass (+35%) and shoot biomass of the phytometer C. jacea (+21%). Further, phytometer performance decreased, i.e. belowground competition increased, with increasing plant species and functional group richness. Although single plant functional groups benefited from higher earthworm numbers, the effects did not vary with plant species and functional group richness. The present study indicates that earthworms indeed affect the productivity of semi-natural grasslands irrespective of the diversity of the plant community. Belowground competition increased with increasing plant species diversity. However, belowground competition was modified by earthworms as reflected by increased productivity of the phytometer C. jacea. Moreover, particularly legumes benefited from earthworm presence. Considering also previous studies, we suggest that earthworms and legumes form a loose mutualistic relationship affecting essential ecosystem functions in temperate grasslands, in particular decomposition and plant productivity. Further, earthworms likely alter competitive interactions among plants and the structure of plant communities by beneficially affecting certain plant functional groups.

Plant diversity drives soil microbial biomass carbon in grasslands irrespective of global environmental change factors

by Alexandru Milcu, Anja Vogel, Madhav Thakur, Nico Eisenhauer, and S. Scheu

Plant community impacts on the structure of earthworm communities depend on season and change with time

by Alexandru Milcu, Nico Eisenhauer, and S. Scheu

Soil Biology & Biochemistry, 2009

Declining plant diversity potentially threatens essential ecosystem functions driven by the decom... more Declining plant diversity potentially threatens essential ecosystem functions driven by the decomposer community, such as litter decomposition and nutrient cycling. Currently, there is no consensus on the interrelationships between plant diversity and decomposer performance and previous studies highlighted the urgent need for long-term experiments.