Search

Spiders are important bio-control agents of rice insect pests such as plant- and leafhoppers. To investigate temporal changes in spider prey and variations in prey due to landscape structure around rice fields, carbon and nitrogen stable isotopes of rice field arthropods were analysed over three consecutive sampling dates during the rice cropping season. Initial isotope composition of gnats and midges emerging from submersed rice fields indicates a larval algae diet, while later values suggest a switch to rice-derived carbon. Initial δ13C values of plant- and leafhoppers were higher in fields of rice-heterogeneous landscapes, indicating migration from source populations feeding on C4 grasses into rice fields; later, their δ13C values approached those of rice. Isotope values of web-building and cursorial spiders in the earliest samples indicate aquatic gnat and midge prey. The later shift toward terrestrial herbivore prey was more pronounced for small than for larger species and in rice paddies near permanent vegetation, indicating use of prey from the surrounding landscape. The results suggest that rice field spiders are supported by three different carbon pools: (1) aquatic carbon originating from algae and (2) legacy carbon from previous growing cycles, both incorporated via between-season predation on gnats and midges, and (3) carbon from the current rice season incorporated via herbivore prey. In conclusion, fostering aquatic midge and gnat larvae, e.g. via mulching, and integrating rice fields into rice-heterogeneous landscapes likely strengthens biological control of pest species in rice paddies by supporting high populations of spiders between cropping seasons. Electronic supplementary material The online version of this article (10.1007/s00442-020-04601-3) contains supplementary material, which is available to authorized users.

Do large organisms occupy higher trophic levels? Predators are often larger than their prey in food chains, but empirical evidence for positive body mass-trophic level scaling for entire food webs mostly comes from marine communities on the basis of unicellular producers. Using published data on stable isotope compositions of 1,093 consumer species, we explored how trophic level scales with body size, food web type (green vs. brown), and phylogenetic group across biomes. In contrast to widespread assumptions, the relationship between body size and trophic level of consumers-from protists to large vertebrates-was not significant per se but varied among ecosystem types and animal groups. The correlation between body size and trophic level was strong in marine consumers, weak in freshwater consumers, and absent in terrestrial consumers, which was also observed at the scale of local food webs. Vertebrates occupied higher trophic positions than invertebrates, and green trophic chains were longer than brown ones in aquatic (primarily marine) but not in terrestrial food webs. Variations in body size of top predators suggest that terrestrial and many freshwater food webs are size compartmentalized, implying different trophic dynamics and responses to perturbations than in size-structured marine food webs.

In tropical ecosystems, interactions between arbuscular mycorrhizal fungi (AMF) and other organisms have been little studied, but may be of significant importance for understanding the role of AMF in decomposition processes and nutrient cycling. In this study, we used ingrowth cores to investigate the impacts of regular rotation of the cores, defaunation and nitrogen addition on AMF, microbial biomass and microarthropods in the fermentation/humus (F/H) and litter (L) layers of an Ecuadorian montane tropical rainforest. AMF were substantially reduced in the F/H layer (to 34% of initial), while in the L layer they remained constant during the experiment. Overall, microorganisms and microarthropods were largely independent of AMF hyphae and their exudates, however, defaunation strongly affected the recovery of their communities. Nitrogen addition increased the quality of litter material and beneficially affected microbial communities thereby increasing decomposition rates, but did not impact AMF abundance and microarthropod communities. These findings suggest that the cutoff of the carbon supply from the plant to the fungal mycelium was not compensated by switching resources in the F/H layer, underlining a strong association between AMF and living roots. While in the L layer, AMF likely competed with saprotrophic microorganisms for litter-derived resources at intermediate stages of decomposition pointing to indirect contributions of AMF to decomposition processes. Overall, the results support the view that root-derived resources are important in fueling soil food webs, but also indicate that in the studied montane rainforest these resources are only available close to roots and not channeled distant to roots via AMF.

As ubiquitous ecosystem engineers, earthworms play an important role in shaping the architecture and functioning of soil systems. However, there is limited knowledge on how earthworms modify the soil microbiome in relation to soil biogenic aggregates, hot-spots formed by earthworms, especially in agricultural systems. We investigated microbial communities in physical fractions and bulk soil from an arable field with consecutive rice - wheat cropping after manipulating earthworms and organic amendments for 13 years. Earthworms significantly enhanced soil aggregation by 33.4% across two consecutive cropping seasons. The assemblage of bacterial communities varied strongly between soil aggregate fractions and with earthworm presence, while the assemblage of fungal communities varied most with organic amendments and less between aggregate fractions. Structural equation modelling (SEM) suggests that besides direct effects on bacteria and fungi, earthworms affected bacteria indirectly via increasing soil aggregation (MWD), but mediated fungi via lowering pH, indicating that the role of soil aggregates in structuring soil bacterial communities override that of resource availability. In conclusion, results of our over-decade field experiment suggest that earthworms modify soil microbial communities primarily through mediating soil habitat architecture and affecting resource supply.

Two new species of oribatid mites of the genus Protoribates (Oribatida, Haplozetidae) are described from litter and soil in Indonesia. Protoribates prolamellatus sp. nov. differs from Protoribates lemensis Ermilov & Tolstikov, 2015 by smaller body size, and the presence of monodactylous legs and short notogastral setae. Protoribates heinrichi sp. nov. differs from all species of Protoribates by the presence of thick rostral and lamellar setae directed anteromedial and porose areas A3 located close to each other in the posterior part of the notogaster. Three other known species of Protoribates, P. bisculpturatus (Mahunka, 1988), P. cattienensis Ermilov & Anichkin, 2011 and P. paracapucinus (Mahunka, 1988), are recorded in Indonesia for the first time.

Many ecosystem functions depend on the structure of food webs, which heavily relies on the body size spectrum of the community. Despite that, little is known on how the size spectrum of soil animals responds to agricultural practices in tropical land-use systems and how these responses affect ecosystem functioning. We studied land-use-induced changes in below-ground communities in tropical lowland ecosystems in Sumatra (Jambi province, Indonesia), a hot spot of tropical rainforest conversion into rubber and oil palm plantations. The study included ca. 30,000 measured individuals from 33 high-order taxa of meso- and macrofauna spanning eight orders of magnitude in body mass. Using individual body masses, we calculated the metabolism of trophic guilds and used food web models to calculate energy fluxes and infer ecosystem functions, such as decomposition, herbivory, primary and intraguild predation. Land-use change was associated with reduced abundance and taxonomic diversity of soil invertebrates, but strong increase in total biomass and moderate changes in total energy flux. These changes were due to increased biomass of large-sized decomposers in soil, in particular earthworms, with their share in community metabolism increasing from 11% in rainforest to 59%-76% in jungle rubber, and rubber and oil palm plantations. Decomposition, that is the energy flux to decomposers, stayed unchanged, but herbivory, primary and intraguild predation decreased by an order of magnitude in plantation systems. Intraguild predation was very important, being responsible for 38% of the energy flux in rainforest according to our model. Conversion of rainforest into monoculture plantations is associated by an uneven loss of size classes and trophic levels of soil invertebrates resulting in sequestration of energy in large-sized primary consumers and restricted flux of energy to higher trophic levels. Pronounced differences between rainforest and jungle rubber reflect sensitivity of rainforest soil animal communities to moderate land-use changes. Soil communities in plantation systems sustained high total energy flux despite reduced biodiversity. The high energy flux into large decomposers but low energy fluxes into other trophic guilds suggests that trophic multifunctionality of below-ground communities is compromised in plantation systems.

Ecosystem processes and the organisms involved are generally limited by the availability of one or more elements in soil, an important phenomenon to consider for our understanding of ecosystem functioning and future changes. Especially in tropical forests, typically growing on nutrient depleted soils, nitrogen (N), phosphorus (P) or other limitations are assumed. However, large‐scale nutrient manipulation experiments revealed complex site‐specific patterns and several authors raised the need for novel approaches to reveal deeper mechanistic insights on limitation patterns, especially concerning soil microbial activity. In order to gain such deeper knowledge, based on a short review of previous small‐scale studies focusing on soil micro‐organisms, we developed an experimental approach which controls for common biases, including indirect treatment effects, addition of co‐elements or nutrient pulses. Using this technique, we tested the hypotheses that fungi growing in tropical forest soils are mainly limited by P and that N versus P limitations shift along an altitudinal gradient. Mesh bags of 38 μm filled with sand were amended with weak ion exchange resins loaded with N, P or potassium (K) and buried underneath the litter layer at three altitudinal sites in southern Ecuador. After a period of four months, the in‐growth of fungal hyphae was quantified, phospholipid fatty acids were analysed for a subset of samples, and chemical properties were determined. In line with the first hypothesis, hyphal abundance was increased in P‐amended mesh bags, indicating P limitation. However, this pattern was not significantly shifted along the altitudinal gradient. By contrast, N addition increased hyphal abundance at the lowest site, compared to significant reductions at 2,000 and 3,000 m—not only in fungi but also in bacterial abundance as indicated by PLFA analyses, contradicting common soil‐age hypotheses. Decreased nutrient immobilization and fungal in‐growth at higher elevations suggest slow microbial activity, including nitrification, which may have caused toxic ammonium accumulation. The experimental design offers a promising tool to provide more mechanistic and soil‐focused analyses specifically targeting microbes, which in this system strongly supported the hypothesis of primary fungal P limitation in tropical forest soils. A plain language summary is available for this article.

Not all individuals are the same. How this applies to soil-living creatures received little attention. Within-species variability determines the niche differentiation of coexisting species.

International audience; Sex strongly impacts genome evolution via recombination and segregation. In the absence of these processes, haplotypes within lineages of diploid organisms are predicted to accumulate mutations independently of each other and diverge over time. This so-called “Meselson effect” is regarded as a strong indicator of the long-term evolution under obligate asexuality. Here, we present genomic and transcriptomic data of three populations of the asexual oribatid mite species Oppiella nova and its sexual relative Oppiella subpectinata . We document strikingly different patterns of haplotype divergence between the two species, strongly supporting Meselson effect–like evolution and long-term asexuality in O. nova : I) variation within individuals exceeds variation between populations in O. nova but vice versa in O. subpectinata ; II) two O. nova sublineages feature a high proportion of lineage-specific heterozygous single-nucleotide polymorphisms (SNPs), indicating that haplotypes continued to diverge after lineage separation; III) the deepest split in gene trees generally separates the two haplotypes in O. nova , but populations in O. subpectinata ; and IV) the topologies of the two haplotype trees match each other. Our findings provide positive evidence for the absence of canonical sex over evolutionary time in O. nova and suggest that asexual oribatid mites can escape the dead-end fate usually associated with asexual lineages.

Salt marshes exist at the interface of the marine and the terrestrial system. Shore height differences and associated variations in inundation frequency result in altered abiotic conditions, plant communities, and resource input into the belowground system. These factors result in three unique zones, the upper salt marsh (USM), the lower salt marsh (LSM), and the pioneer zone (PZ). Marine detritus, such as micro- and macroalgae, is typically flushed into the PZ daily, with storm surges moving both salt marsh detritus and marine detritus into higher salt marsh zones. Microbial assemblages are essential for the decomposition of organic matter and have been shown to sensitively respond to changes in abiotic conditions such as oxygen supply and salinity. However, temporal and spatial dynamics of microbial communities of Wadden Sea salt marshes received little attention. We investigated the dynamics of soil microbial communities across horizontal (USM, LSM, and PZ), vertical (0-5 and 5-10-cm sediment depth), and temporal (spring, summer, and autumn) scales in the Wadden Sea salt marsh of the European North Atlantic coast using phospholipid fatty acid (PLFA) analysis. Our results show strong spatial dynamics both among salt marsh zones and between sediment depths, but temporal dynamics to be only minor. Despite varying in space and time, PLFA markers indicated that bacteria generally were the dominant microbial group across salt marsh zones and seasons, however, their dominance was most pronounced in the USM, whereas fungal biomass peaked in the LSM and algal biomass in the PZ. Only algal markers and the stress marker monounsaturated to saturated fatty acid ratio responded to seasonality. Overall, therefore, the results indicate remarkable temporal stability of salt marsh microbial communities despite strong variability in abiotic factors.

Significance Putatively ancient asexual species pose a challenge to theory because they appear to escape the predicted negative long-term consequences of asexuality. Although long-term asexuality is difficult to demonstrate, specific signatures of haplotype divergence, called the “Meselson effect,” are regarded as strong support for long-term asexuality. Here, we provide evidence for the Meselson effect in an asexual oribatid mite species, Oppiella nova, and we show that the effect is not caused by hybridization or polyploidization. Our findings provide conclusive evidence for the long-term absence of sex in O. nova and suggest that asexual oribatid mites can escape the dead-end fate usually associated with asexual reproduction., Sex strongly impacts genome evolution via recombination and segregation. In the absence of these processes, haplotypes within lineages of diploid organisms are predicted to accumulate mutations independently of each other and diverge over time. This so-called “Meselson effect” is regarded as a strong indicator of the long-term evolution under obligate asexuality. Here, we present genomic and transcriptomic data of three populations of the asexual oribatid mite species Oppiella nova and its sexual relative Oppiella subpectinata. We document strikingly different patterns of haplotype divergence between the two species, strongly supporting Meselson effect–like evolution and long-term asexuality in O. nova: I) variation within individuals exceeds variation between populations in O. nova but vice versa in O. subpectinata; II) two O. nova sublineages feature a high proportion of lineage-specific heterozygous single-nucleotide polymorphisms (SNPs), indicating that haplotypes continued to diverge after lineage separation; III) the deepest split in gene trees generally separates the two haplotypes in O. nova, but populations in O. subpectinata; and IV) the topologies of the two haplotype trees match each other. Our findings provide positive evidence for the absence of canonical sex over evolutionary time in O. nova and suggest that asexual oribatid mites can escape the dead-end fate usually associated with asexual lineages.

Individuals of species may differ in resource use within and between populations. High intraspecific variation in resource use may hamper the co-existence of species in natural communities. To better understand the intraspecific variation in trophic niches of oribatid mites (Oribatida, Acari), we quantified stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) of 40 Oribatida species that co-occurred in litter and soil of five forest types (European beech, Douglas fir, Norway spruce, two beech–conifer mixed forests) covering a range of environmental conditions. We found that although stable isotopes in litter and soil varied among forest types, δ13C and δ15N values of Oribatida and their trophic niches were remarkably stable between litter and soil, and also among forest types. We considered four trophic guilds of Oribatida representing the guild composition of the regional species pool; notably, trophic niches of Oribatida guilds also did not vary with soil depth. Furthermore, δ13C of Oribatida was more enriched (detrital shift) in European beech than in coniferous forests, but δ15N of Oribatida did not vary among forest types, indicating that basal resources of Oribatida are variable, but trophic positions are highly consistent across forest ecosystems. We conclude that trophic positions of Oribatida species and guilds are consistent across different forest types, and Oribatida species occupy virtually identical trophic niches irrespective of the soil depth they are colonizing. Overall, the results suggest that low intraspecific variability facilitates Oribatida niche differentiation and species coexistence.

Summary • Vesicular–arbuscular mycorrhiza (VAM) and earthworms are known to affect plant and herbivore performance. However, surprisingly few studies have investigated their interactions. • In a glasshouse experiment we investigated the effects of earthworms (Aporrectodea caliginosa) and VAM (Glomus intraradices) on the growth and chemistry of Plantago lanceolata and the performance of aphids (Myzus persicae). • Earthworms did not affect VAM root colonization. Earthworms enhanced shoot biomass, and VAM reduced root biomass. VAM increased plant phosphorus content, but reduced the total amount of N in leaves. Earthworms led to a preferential uptake of soil N compared with 15N from the added grass residues in the absence of VAM. Earthworm presence reduced the concentration of catalpol. Earthworms and VAM combined accelerated the development of M. persicae, while the development tended to be delayed when only VAM or earthworms were present. • We suggest that earthworms promote plant growth by enhancing soil N availability and may affect herbivores by influencing concentrations of secondary metabolites. VAM enhances the P uptake of plants, but presumably competes with plant roots for N.

Late Cenozoic climate change led to the progressive aridification of Australia over the past 15 million years. This gradual biome turnover fundamentally changed Australia’s ecosystems, opening new niches and prompting diversification of plants and animals. One example is the Australian Amitermes Group (AAG), consisting of the Australian Amitermes and affiliated genera. Although it represents the most speciose and diverse higher termite group in Australia, little is known about its evolutionary history. We used ancestral range reconstruction and diversification analyses to illuminate 1) the origin and phylogenetic relationships of the AAG, 2) biogeographical processes leading to the current continent-wide distribution, and 3) timing and pattern of diversification in the context of late Cenozoic climate change. By estimating the first time-calibrated phylogeny, we show that the AAG is a monophyletic group, whose ancestor arrived ~11-10 million years ago from Southeast Asia. Ancestral range reconstruction indicates that Australia’s monsoon region was the launching point for a continental radiation that has been shaped by range expansions and within-area speciation rather than vicariance. We found that multiple arid species diversified from mesic and tropical ancestors in the Plio-Pleistocene, but also observed diversification in the opposite direction. Finally, we show that two pulses of rapid diversification coincided with past climate change during the late Miocene and early Pliocene. Consistent with rapid diversification, species accumulation slowed, likely caused by progressive niche saturation. This study provides a stepping stone for predicting the future response of Australia’s termite fauna in the face of human-mediated climate change.

Trophic regulation of microbial communities is receiving growing interest in soil ecology. Most studies investigated the effect of higher trophic levels on microbial communities at the bulk soil level. However, microbes are not equally accessible to consumers. They may be hidden in small pores and thus protected from consumers, suggesting that trophic regulation may depend on the localization of microbes within the soil matrix. As microaggregates (< 250 µm) usually are more stable than macroaggregates (> 250 µm) and embedded in the latter, we posit that they will be less affected by trophic regulations than larger aggregates. We quantified the effect of four contrasting species of collembolans (Ceratophysella denticulata, Protaphorura fimata, Folsomia candida, Sinella curviseta) on the microbial community composition in macro- (250 µm – 2mm) and microaggregates (50 – 250 µm). To do so, we re-built consumer-prey systems comprising remaining microbial background (post-autoclaving), fungal prey (Chaetomium globosum), and collembolan species (added as single species or combined). After three months, we quantified microbial community composition using phospholipid fatty acid markers (PLFAs). We found that the microbial communities in macroaggregates were more affected by the addition of collembolans than the communities in microaggregates. In particular, the fungal-to-bacterial (F:B) ratio significantly decreased in soil macroaggregates in the presence of collembolans. In the microaggregates, the F:B ratio remained lower and unaffected by collembolan inoculation. Presumably, fungal hyphae were more abundant in macroaggregates because they offered more habitat space for them, and the collembolans reduced fungal abundance because they consumed them. On the contrary, microaggregates presumably contained microbial communities protected from consumers. In addition, collembolans increased the formation of macroaggregates but did not influence their stability, despite their negative effect on fungal abundance, a well-known stabilizing agent. Overall, we show that trophic interactions between microbial communities and collembolans depend on the aggregate size class considered and, in return, soil macroaggregation is affected by these trophic interactions.

The introduction of temporary grassland into an annual crop rotation is recognized to improve soil ecosystem services, and resulting legacies can be beneficial for the following crops. In this context, the aim of the present study was to evaluate legacy effects of introducing temporary grassland into an annual crop rotation on five ecosystem services (i) soil structure maintenance (aggregate stability), (ii) water regulation (saturated hydraulic conductivity), (iii) biodiversity conservation (microbial biomass and microbial metabolic activity, as well as microorganism, enchytraeid, springtail and earthworm communities), (iv) pathogen regulation (soil suppressiveness to Verticillium dahliae), and (v) forage production and quality. Three crop rotation schemes, maintained for twelve years, were compared in four random blocks, one being an annual crop rotation without grassland (0%), another with a medium percentage of grassland (50%, corresponding to 3 years of continuous grassland in the crop rotation), and a third one with a high percentage of grassland in the crop rotation (75%, corresponding to 6 years of continuous grassland in the crop rotation). The results showed that the grassland introduction into an annual crop rotation improved, whatever the duration of the grassland, soil structure maintenance and biodiversity conservation, while it decreased pathogen regulation and did not modify water regulation. Comparing the two crop rotations that included grassland, indicated a stronger beneficial grassland legacy effect for the higher proportion of grassland concerning soil structure maintenance and biodiversity conservation. By contrast, water regulation, pathogen regulation and forage production were not affected by the legacy of the 75% grassland during the rotation. Overall, our findings demonstrated the extent to which grassland legacies are affecting the current state of soil properties and possible ecosystem services provided. To improve ecosystem services, soil management should take legacy effects into account and consider longer timeframes to apply beneficial practices., This work was supported by the EU SoilMan project (grant number 01LC1620) funded through the 2015–2016 BiodivERsA COFUND call for research proposals, with national funders the Federal Ministry of Education and Research (BMBF), the French National Research Agency (ANR), the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS), the Spanish Ministry of Economy and Competitiveness (MINECO), the Executive Agency for Higher Education, Research, Development and Innovation Funding (UEFISCDI), the European Regional Development Fund (Centre of Excellence EcolChange). We would like to thank the National Research Infrastructure “Agro-écosystèmes, Cycles Biogéochimique et Biodiversité” (ACBB) http://www.soere-acbb for providing access to an excellent field experiment and the “the AnaEE France (ANR-11-INBS-0001)”, “AllEnvi” and “CNRS-INSU” which support it. We thank Météo France for meteorological data.

Sex strongly impacts genome evolution via recombination and segregation. In the absence of these processes, haplotypes within lineages of diploid organisms are predicted to accumulate mutations independently of each other and diverge over time. This so-called ‘Meselson effect’ is regarded as a strong indicator of the long-term evolution under obligate asexuality. Here, we present genomic and transcriptomic data of three populations of the asexual oribatid mite speciesOppiella novaand its sexual relativeOppiella subpectinata. We document strikingly different patterns of haplotype divergence between the two species, strongly supporting Meselson effect like evolution and ancient asexuality inO. nova: (I) Variation within individuals exceeds variation between populations inO. novabutvice versainO. subpectinata. (II) TwoO. novasub-lineages feature a high proportion of heterozygous genotypes and lineage-specific haplotypes, indicating that haplotypes diverged independently within the two lineages after their split. (III) The deepest split in gene trees generally separates haplotypes inO. nova, but populations inO. subpectinata. (IV) Tree topologies of the two haplotypes match each other. Our findings provide positive evidence for the absence of sex over evolutionary time inO. novaand suggest that asexual oribatid mites can escape the dead-end fate usually associated with asexual lineages.

Earth is home to over 350,000 vascular plant species that differ in their traits in innumerable ways. A key challenge is to predict how natural or anthropogenically driven changes in the identity, abundance and diversity of co-occurring plant species drive important ecosystem-level properties such as biomass production or carbon storage. Here, we analyse the extent to which 42 different ecosystem properties can be predicted by 41 plant traits in 78 experimentally manipulated grassland plots over 10 years. Despite the unprecedented number of traits analysed, the average percentage of variation in ecosystem properties jointly explained was only moderate (32.6%) within individual years, and even much lower (12.7%) across years. Most other studies linking ecosystem properties to plant traits analysed no more than six traits and, when including only six traits in our analysis, the average percentage of variation explained in across-year levels of ecosystem properties dropped to 4.8%. Furthermore, we found on average only 12.2% overlap in significant predictors among ecosystem properties, indicating that a small set of key traits able to explain multiple ecosystem properties does not exist. Our results therefore suggest that there are specific limits to the extent to which traits per se can predict the long-term functional consequences of biodiversity change, so that data on additional drivers, such as interacting abiotic factors, may be required to improve predictions of ecosystem property levels.

International audience; Plant diversity is an important driver of below-ground ecosystem functions, such as root growth, soil organic matter (SOM) storage and microbial metabolism, mainly by influencing the interactions between plant roots and soil. Dissolved organic matter (DOM), as the most mobile form of SOM, plays a crucial role for a multitude of soil processes that are central for ecosystem functioning. Thus, DOM is likely to be an important mediator of plant diversity effects on soil processes. However, the relationships between plant diversity and DOM have not been studied so far.2. We investigated the mechanisms underlying plant diversity effects on concentrations of DOM using continuous soil water sampling across 6 years and 62 plant communities in a long-term grassland biodiversity experiment in Jena, Germany. Furthermore, we investigated plant diversity effects on the molecular properties of DOM in a subset of the samples.3. Although DOM concentrations were highly variable over the course of the year with highest concentrations in summer and autumn, we found that DOM concentrations consistently increased with plant diversity across seasons. The positive plant diversity effect on DOM concentrations was mainly mediated by increased microbial activity and newly sequestered carbon in topsoil. However, the effect of soil microbial activity on DOM concentrations differed between seasons, indicating DOM consumption in winter and spring, and DOM production in summer and autumn. Furthermore, we found increased contents of small and easily decomposable DOM molecules reaching deeper soil layers with high plant diversity.4. Synthesis. Our findings suggest that plant diversity enhances the continuous downward transport of DOM in multiple ways. On the one hand, higher plant diversity results in higher DOM concentrations, on the other hand, this DOM is less degraded. This study indicates, for the first time, that higher plant diversity enhances the downward transport of dissolved molecules that likely stimulate soil development in deeper layers and therefore increase soil fertility.

Panjaitan R, Drescher J, Buchori D, Peggie D, Harahap IS, Scheu S, Hidayat P. 2020. Diversity of butterflies (Lepidoptera) across rainforest transformation systems in Jambi, Sumatra, Indonesia. Biodiversitas 21: 5119-5127. The high rate of land conversion has put pressure on biodiversity, especially in the tropics. The lowlands of Sumatra, for example, are dominated by increasingly extensive areas of oil palm and rubber monoculture plantations, while rainforests are continuously vanishing. The status of many rainforest animal populations, including iconic insect groups such as butterflies, is largely unclear. With a rapid assessment approach, we studied butterflies along land-use gradients from lowland rainforest, via jungle rubber plantations (rubber agroforest system), to monocultures of rubber and oil palm in Jambi Province, Sumatra. Butterflies were caught in a nested replication design at eight research plots at each of the forest, jungle rubber, and rubber and oil palm locations. Butterfly abundance was the highest in the rainforest (204.3±82.1), slightly lower in the jungle rubber and oil palm areas (164.9±61 and 169.3±94.9, respectively), and the lowest in the rubber plantation (108.8±38.5). Similarly, butterfly species richness was the highest in the forest and jungle rubber areas (47.1±7.7 and 38.8±7.6, respectively), followed by the oil palm area (33.3±9.8), and the lowest in the rubber plantation (26.1±9.1). Likewise, Shannon-Wiener diversity was the highest in the rainforest, at an intermediate level in the jungle rubber, and lowest in the oil palm and rubber plantations. Butterfly community composition in the rainforest was very different from that in the other three land-use systems, in which it was similar. Overall, the study demonstrates that rainforest butterfly communities cannot be sustained in agricultural systems, highlighting the importance of rainforests for conserving the diversity of arthropods.

We conducted a 15N tracer experiment in laboratory microcosms with field-fresh soil samples from a biodiversity experiment to evaluate the relationship between grassland biodiversity and N cycling. To embrace the complexity of the N cycle, we determined N exchange between five soil N pools (labile and recalcitrant organic N, dissolved NH4+ and NO3− in soil solution, and exchangeable NH4+) and eight N transformations (gross N mineralization from labile and recalcitrant organic N, NH4+ immobilization into labile and recalcitrant organic N, autotrophic nitrification, heterotrophic nitrification, NO3− immobilization, adsorption of NH4+) expected in aerobic soils with the help of the N-cycle model Ntrace. We used grassland soil of the Jena Experiment, which includes plant mixtures with 1 to 60 species and 1 to 4 functional groups (legumes, grasses, tall herbs, small herbs). The 19 soil samples of one block of the Jena Experiment were labeled with either 15NH4+ or 15NO3- or both. In the presence of legumes, gross N mineralization and autotrophic nitrification increased significantly because of higher soil N concentrations in legume-containing plots and high microbial activity. Similarly, the presence of grasses significantly increased the soil NH4+ pool, gross N mineralization, and NH4+ immobilization, likely because of enhanced microbial biomass and activity by providing large amounts of rhizodeposits through their dense root systems. In our experiment, previously reported plant species richness effects on the N cycle, observed in a larger-scale field experiment within the Jena Experiment, were not seen. However, specific plant functional groups had a significant positive impact on the N cycling in the incubated soil samples.

Tree - soil interactions depend on environmental conditions. Planting trees may strongly impact microorganisms in particular at unfavorable site conditions, compromising the functioning of soil microorganisms. To understand the effects of tree species composition on soil microorganisms, we quantified structural and functional responses of soil microorganisms to forest types across environmental conditions using substrate-induced respiration and phospholipid fatty acid analyses. Five forest types were studied including pure stands of native European beech (Fagus sylvatica), range expanding Norway spruce (Picea abies), and non-native Douglas-fir (Pseudotsuga menziesii), as well as the two conifer - beech mixtures. We found that microbial functioning strongly depends on site conditions, in particular on soil nutrients. At nutrient-poor sites, soil microorganisms were more stressed in pure and mixed coniferous forests, especially in Douglas-fir, compared to beech forests. By contrast, microbial structure and functional indicators in beech forests varied little with site conditions, likely because beech provided high amounts of root-derived resources for microbial growth. Since soil microbial communities are sensitive to Douglas-fir, planting Douglas-fir may compromise ecosystem functioning in particular at nutrient-poor sites. Overall, root-derived resources are important for determining the structure and functioning of soil microbial communities, and soil microorganisms sensitively respond to plantations containing tree species that may differ in the provisioning of these resources.

Animals that have similar morphological traits are expected to share similar ecological niches. This statement applies to individual animals within a species and thus species often serve as the functional units in ecological studies. Species are further grouped into higher-ranked taxonomic units based on their morphological similarity and thus are also expected to be ecologically similar. On the other hand, theory predicts that strong competition between closely related species can lead to differentiation of ecological niches. Due to a high diversity and limited taxonomic expertise, soil food webs are often resolved using supraspecific taxa such as families, orders or even classes as functional units. Here we for the first time empirically tested the trophic consistency of supraspecific taxa across major lineages of temperate forest soil invertebrates: Annelida, Chelicerata, Myriapoda, Crustacea and Hexapoda. Published data on stable isotope compositions of carbon and nitrogen were used to infer basal resources and trophic level, and explore the relationship between taxonomic and trophic dissimilarity of local populations. Genera and families had normal and unimodal distributions of isotope niches, suggesting that supraspecific taxa are trophically consistent. The isotopic niche of populations across different localities is better predicted by species than by supraspecific taxa. However, within the same genus, the effect of species identity on stable isotope composition of populations was not significant in 92% of cases. The link to basal resources, i.e. plants or detritus, was convergent in different lineages, while trophic levels followed the Brownian motion taxonomic model. Virtually none of the studied taxa showed pronounced trophic niche conservatism within a lineage. Supraspecific taxa are meaningful as functional units in ecological studies, but the consistency varies among taxa and thus the choice of taxonomic resolution depends on the research question; generally, identification of taxa should be more detailed in more diverse taxonomic groups. We compiled a comprehensive list of mean Δ13C and Δ15N values of invertebrate taxa from temperate forest soils allowing to refine soil food-web models when identification to species level is not feasible.

This study assesses the importance of root- and mycorrhiza-derived resources for decomposition processes and as food resources for microarthropod communities along an altitudinal gradient of tropical montane rainforests in southern Ecuador. At 1000, 2000 and 3000 m microcosms with openings of different mesh sizes (4 mm, 45 μm) or closed were exposed in the field, manipulating accessibility by roots and mycorrhizal fungi. The microcosms contained undisturbed soil with a mixture of leaf litter from three abundant plant species from the site at which the microcosms were exposed. After 12 months water content, microbial biomass, remaining litter mass, C-to-N ratio and the soil microarthropod community structure were analysed. Water content and C-to-N ratio were lower and microbial biomass was highest at the lowest altitude, while litter decomposition and microarthropod abundance were at a maximum at the intermediate altitude. Exclusion of roots and mycorrhizal fungi did not affect litter decomposition, but decreased the abundance and diversity of Oribatida, while the abundance of Collembola increased in closed microcosms. The effect of root and mycorrhizal exclusion on all investigated parameters did not differ between the three altitudes. The results indicate that in nutrient limited tropical montane rainforests mycorrhizal fungi suppress the activity of other microorganisms, potentially competing for litter-derived resources, at each of the investigated altitudes. Collembola benefitted from this reduced competition while Oribatida strongly depended on root-derived resources.

Wadden Sea macrozoobenthos has access to food sources of different quality. In addition to microphytobenthos (MPB) and macroalgae (e.g. Fucus vesiculosus Linnaeus, 1753), the invasive C4 grass Spartina anglica C.E. Hubbard has become an abundant primary producer in the Wadden Sea. To elucidate the role of different primary producers for the nutrition of typical Wadden Sea consumers, we conducted a mesocosm experiment with four food treatments ( S. anglica, F. vesiculosus , MPB and all three resources together) under a simulated tidal cycle. We used consumers of different feeding types—the omnivorous polychaete Hediste diversicolor (O.F. Muller, 1776), the interface-feeding bivalve Limecola balthica (Linnaeus, 1758) and the surface deposit-feeding snail Peringia ulvae (Pennant, 1777)—and analyzed their biomass, δ13C and δ15 N stable isotope values and fatty acid (FA) profiles. After 4 weeks, the biomass of H. diversicolor increased in treatments that contained F. vesiculosus, but decreased in the treatment with MPB. δ13C values of H. diversicolor reflected those of the food sources provided and FA profiles varied strongly between the treatments, indicating feeding on copepods and bacteria as well as macrophytes. The biomass of P. ulvae significantly increased in treatments with S. anglica and all three resources. However, δ13C values of P. ulvae differed significantly between the treatments and were unrelated to the food sources except for MPB. FA profiles confirmed the assimilation of MPB in this species. δ13C values and FA composition of L. balthica were similar in each of the treatments and did not resemble the resources provided. Instead, the high proportion of respective marker FAs indicated feeding on plankton . δ 15N values of the consumer species declined significantly in the order H. diversicolor > L. balthica > P. ulvae in each of the treatments. These results indicate different strategies in food source use of the three consumer species with the performance of the generalist feeders H. diversicolor and P. ulvae exceeding that of the selective feeder L. balthica.

The complete mitogenome of Metisotoma macnamarai (Folsom 1918) (Collembola, Isotomidae), a member of obligatory predaceous genus Metisotoma Maynard, 1951, was sequenced. It has a length of 15,177 bp, comprising 13 protein-coding genes, 22 tRNAs, and 2 rRNAs. The mitogenome has the following base composition: A = 37.1%, T = 33.3%, G = 11.8%, and C = 17.4%. Phylogenetic analysis using maximum likelihood (ML) indicates that M. macnamarai clusters as sister taxon to the genus Isotomurus, with high statistical support.

Litter decomposition is a fundamental process of biogeochemical cycles and plays a critical role in regulating carbon (C) and nutrient mineralization in terrestrial ecosystems. Examining responses of litter decomposition to altered precipitation is crucial to understand terrestrial C dynamics and its feedback to climate change. To understand the effects of reduced precipitation on litter decomposition, a two-year throughfall reduction experiment was carried out in a natural evergreen broad-leaved forest in western China. Five throughfall reduction levels were investigated: control without throughfall reduction (Ctr), 5% (W1), 10% (W2), 20% (W3) and 50% throughfall reduction (W4). Throughfall reduction significantly reduced soil moisture, which was most pronounced in W3 and W4 treatments, and this was associated by significantly reduced cumulative litter mass loss and lower decomposition constants. Also, throughfall reduction significantly altered litter C, N and P dynamics. In particular in W2, W3 and W4 treatments the release of C and N was significantly reduced, whereas in W2 and W3 the immobilization of P was increased. Overall, the results suggest that future decrease in precipitation will suppress litter decomposition, whereas microbial P limitation in litter may be aggravated in broad-leaved forest ecosystems.

Neutral lipid fatty acid (NLFA) analysis is a promising tool to investigate energy fluxes and basal resources of soil animal communities. This study aimed at investigating the effect of common handling and storage procedures in soil animal ecology on the NLFA composition and marker NLFAs. First, we tested the effect of the method of killing (by freezing and by drowning in diethylene glycol mixed with water; 1:1) on NLFA composition of the woodlouse Oniscus asellus. Additionally, we inspected the effect of two reference methods (direct freezing at −20 °C and storage in methanol at −80 °C with evaporating methanol prior to lipid extraction) after 4 and 12 months on the NLFA profile of O. asellus. We investigated the effect of the collection solution used in heat extraction of soil animals (water and glycol), storage fluids (saltwater, glycerine, ethanol and methanol) and storage time (4 and 12 months) on NLFA composition and common marker NLFAs of two Isopoda species differing in body size. The NLFA composition and marker fatty acids (FAs) did not differ between the methods of killing and between the two reference treatments but the amount of saturated FAs and the saturated-to-unsaturated FA ratio generally increased after 12 months indicating oxidation processes. Generally, the collection solution was of minor importance, whereas storage fluid and storage time strongly affected NLFA patterns. The NLFA profile of the larger species O. asellus was affected by storage in methanol and ethanol and to some extent in saltwater, while the NLFA profile of the smaller Trichoniscus pusillus was affected by each of the treatments. Notably, however, marker FAs of O. asellus and T. pusillus were not significantly affected by storing in glycerine even after 12 months in O. asellus. Therefore, if animals need to be stored prior to NLFA analysis for sorting and identification, storage in glycerine is advisable.

Gut microbiota are determined by both the food ingested and physiological conditions of the host. In soil food webs, detritivore animals occupy various trophic niches, spanning from primary decomposers to predators. However, the relative contribution of food resources and species attributes of consumers to gut microbial communities in soil detritivores has not yet been explored. In this study, we investigated gut bacteria and fungi of oribatid mites (Oribatida, Acari), ubiquitous and diverse soil microarthropods feeding on a variety of food resources, to uncover the contribution of host phylogenetic relatedness and trophic niches to the assemblages of gut microbiota. Abundance and community composition of bacteria and fungi were characterized by qPCR and Illumina sequencing, respectively. Gut bacterial communities were more closely correlated with host phylogenetic affinity, whereas gut fungal communities were more closely correlated with the trophic niches of the host. Community phylogenetic analysis suggests that deterministic processes predominated in the assembly of both bacterial and fungal communities in most of the studied oribatid mite species. Integrating phylogenetic distance and trophic niche distance of hosts resulted in the highest correlation coefficients between host species and their gut microbial communities suggesting that both evolutionary history and current trophic niches shape gut microbial communities. Bacteria in the gut may comprise commensals or mutualists facilitating digestion which potentially coevolved with the host, while the fungal community in the gut reflects the trophic niches of the consumer likely suggesting that they form part of the diet and serve as food resources of soil detritivore microarthropods.

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.

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

Earthworms are among the most important soil ecosystem engineers. Their effects on soil structure have been well documented, however, there is limited knowledge on how earthworms in the long term affect the soil microbiome, especially in arable soils. We investigated the soil microbiome of rice (cultivated under aerobic condition) and wheat fields in two consecutive seasons after manipulating earthworms and organic amendments for 14 years. Composition of soil prokaryotes and eukaryotes were analyzed by Illumina sequencing. Molecular network analysis suggest that in mulched rice fields earthworms foster species interlinked with many others and shift the dominance of prokaryotes from Planctomycetes to Proteobacteria. In contrast, in fields where residues were incorporated into the soil earthworms shifted the dominance of prokaryotes from Proteobacteria to Planctomycetes. Further, earthworms significantly increased the Proteobacteria-to-Acidobacteria ratio, a putative indicator of high nutrient turnover. Further, the ratio of prokaryote-to-eukaryote abundance was increased by earthworms when straw was incorporated into the soil. In conclusion, the results suggest that in the long term earthworms mainly modify the structure and functioning of prokaryote rather than eukaryote communities in arable fields. The effects of earthworms on the structure of microbial communities and microbial interactions are closely linked to resource management practices. The more pronounced effects of earthworms in treatments with residues mulched as compared to incorporated into the soil suggest that earthworm effects in part were due to bioturbation, i.e. mixing straw with mineral soil.