Soil Decomposer Research Articles

Phylotype diversity within soil fungal functional groups drives ecosystem stability.

Soil fungi are fundamental to plant productivity, yet their influence on the temporal stability of global terrestrial ecosystems, and their capacity to buffer plant productivity against extreme drought events, remain uncertain. Here we combined three independent global field surveys of soil fungi with a satellite-derived temporal assessment of plant productivity, and report that phylotype richness within particular fungal functional groups drives the stability of terrestrial ecosystems. The richness of fungal decomposers was consistently and positively associated with ecosystem stability worldwide, while the opposite pattern was found for the richness of fungal plant pathogens, particularly in grasslands. We further demonstrated that the richness of soil decomposers was consistently positively linked with higher resistance of plant productivity in response to extreme drought events, while that of fungal plant pathogens showed a general negative relationship with plant productivity resilience/resistance patterns. Together, our work provides evidence supporting the critical role of soil fungal diversity to secure stable plant production over time in global ecosystems, and to buffer against extreme climate events.

Rotation cropping and organic fertilizer jointly promote soil health and crop production

Identifying field management practices to promote crop production, while conserving soil health is essential to maintain long-term food production in a changing world. Also, providing experimental evidence to support the use of traditional agricultural practices is necessary to secure sustainable agriculture. Here, we conducted a long-term 12-year experiment to investigate the impact of different combinations of fertilization type (control, inorganic fertilizer, organic fertilizer) and cropping regimes (continuous cropping and rotation cropping) on the crop (tobacco) production and multiple soil attributes associated with soil health, including proportions of soil-borne pathogens and decomposers, soil microbial diversity, microbial network stability and biomass, nutrient pools and microbial resource limitations. Our long-term experiment supports that the combination of organic fertilizer with rotation cropping increased crop production by at least 40% compared to the other management combinations and improved soil nutrient pools (e.g. the content of soil organic matter), improved the relative proportion of soil decomposers, and promoted bacterial and fungal network stability and biodiversity. Furthermore, this combination treatment relieved microbial resource limitation and reduced the abundance of potential fungal plant pathogens by at least 20% compared to other management combinations. In summary, we provide experimental evidence to support that the combined use of organic fertilization and rotation cropping management can help maintain long-term soil health, crop production, and economic outputs.

Rapid transfer of C and N excreted by decomposer soil animals to plants and above-ground herbivores

The role of soil decomposer animals in nutrient cycling is commonly seen as indirect, slow and cumulative, through grazing and engineering effects on soil microbes and their mineralization activities. Here, we show that nitrogen (N) and carbon (C) movement from living soil animals to plants and herbivores can be extremely rapid. In two complementary experiments under laboratory and field conditions, we used stable isotope tracers to follow nutrient transfer from earthworms to soil, wheat seedlings, and aphids. Earthworm-derived 15N and 13C was acquired by aphids after 2 h under laboratory conditions, and 15N after 24 h in the field. Since cleansed earthworms with voided guts were introduced, the main source of this 15N and 13C likely was their highly labelled cutaneous mucus. Based on the rapid tracer appearance in a phloem-feeding herbivore (whose principal N source is free amino acids), we postulate that organic earthworm-excreted compounds, possibly amino acids and acetates, may have been involved. This would suggest a previously unknown shortcut in the terrestrial N and C cycle, however, it requires confirmation through advanced techniques such as compound-specific isotope analysis or liquid chromatography with mass spectrometry. These experimental results suggest that multitrophic linkages from living decomposers in soil to plants and aboveground consumers may happen at much shorter time scales than is generally assumed.

Ecological Implications on Insect Biodiversity

Insects are important group of organisms that are diverse forming an important component of food web. They play vital ecological functions like nutrient recyclers, soil decomposers, pollinators, biocontrol agents, soil builders and scavengers. Anthropogenic factors like habitat destruction, land fragmentation, deforestation, climate change, monocropping and urbanization threaten the native diversity of the insects with possible loss in their abundance, richness and extinction. There is a growing need to conserve the diversity of insects using tactics like maintenance of crop diversity amidst the crop areas to serve as refugia and breeding grounds for the beneficial insects, creating of breeding habitats for natural multiplication of beneficials. Adoption of minor agronomic practices leading to crop and habitat diversification benefits native insect population for their natural proliferation in agro-ecosystems.

The Selective Effects of Environmental Change on the Functional Diversity of Soil Decomposers

Whether decomposition can be affected by the biodiversity of soil organisms is an important question. Biodiversity is commonly expressed through indices that are based on species richness and abundances. Soil processes tend to saturate at low levels of species richness. A component of biodiversity is functional diversity, and we have shown that the absence of the influence of species richness on decomposition switched into a positive relationship between fauna diversity and decomposition when we expressed biodiversity in terms of interspecific functional dissimilarity. Communities with functionally dissimilar species are characterized by complementary resource use and facilitative interactions among species. It is suggested that the effects of environmental changes on ecosystem functions such as decomposition can be better understood if we have more knowledge about the selective effect of these changes on specific facets of soil biodiversity, such as functional diversity.

Plant community legacy effects on nutrient cycling, fungal decomposer communities and decomposition in a temperate grassland

Soil legacies mediated by plant species-specific microbial communities are major drivers of plant community dynamics. Most soil legacy studies focus on the role of pathogens and mutualists in driving these processes, while much less is known about plant litter-mediated changes to the soil microbial community. Here, we used an existing plant-soil feedback field experiment in which plant communities with different growth strategies (i.e., fast versus slow) and different proportions of functional groups (i.e., grasses versus forbs) were allowed to condition the soil over contrasting temporal scales (i.e., one versus two years) in a natural grassland. In the feedback phase, we removed the existent plant community, and replaced it with a standardized response plant community. We then tested the legacy effects of these different soil conditioning treatments on decomposition processes, nutrient cycling and soil decomposer community composition. Soil legacy effects on decomposition and the soil decomposer community composition were most evident right after the start of the feedback phase, but disappeared soon after the new community established. The soil conditioning time and years since disturbance affected most of the soil functions consistently, while no strong effects of plant functional group and plant growth strategy were found. We conclude that after disturbance, it is recovery time, not soil legacy effects, that is the most important factor driving soil functions.

Nitrogen, Iron and Zinc Acquisition: Key Nutrients to Aspergillus fumigatus Virulence.

Aspergillus fumigatus is a ubiquitous soil decomposer and an opportunistic pathogen that is characterized by its large metabolic machinery for acquiring nutrients from media. Lately, an ever-increasing number of genes involved in fungal nutrition has been associated with its virulence. Of these, nitrogen, iron, and zinc metabolism-related genes are particularly noteworthy, since 78% of them have a direct implication in virulence. In this review, we describe the sensing, uptake and regulation process of the acquisition of these nutrients, the connections between pathways and the virulence-implicated genes. Nevertheless, only 40% of the genes mentioned in this review have been assayed for roles in virulence, leaving a wide field of knowledge that remains uncertain and might offer new therapeutic and diagnostic targets.

Quantifying microbial control of soil organic matter dynamics at macrosystem scales

Soil organic matter (SOM) stocks, decomposition and persistence are largely the product of controls that act locally. Yet the controls are shaped and interact at multiple spatiotemporal scales, from which macrosystem patterns in SOM emerge. Theory on SOM turnover recognizes the resulting spatial and temporal conditionality in the effect sizes of controls that play out across macrosystems, and couples them through evolutionary and community assembly processes. For example, climate history shapes plant functional traits, which in turn interact with contemporary climate to influence SOM dynamics. Selection and assembly also shape the functional traits of soil decomposer communities, but it is less clear how in turn these traits influence temporal macrosystem patterns in SOM turnover. Here, we review evidence that establishes the expectation that selection and assembly should generate decomposer communities across macrosystems that have distinct functional effects on SOM dynamics. Representation of this knowledge in soil biogeochemical models affects the magnitude and direction of projected SOM responses under global change. Yet there is high uncertainty and low confidence in these projections. To address these issues, we make the case that a coordinated set of empirical practices are required which necessitate (1) greater use of statistical approaches in biogeochemistry that are suited to causative inference; (2) long-term, macrosystem-scale, observational and experimental networks to reveal conditionality in effect sizes, and embedded correlation, in controls on SOM turnover; and (3) use of multiple measurement grains to capture local- and macroscale variation in controls and outcomes, to avoid obscuring causative understanding through data aggregation. When employed together, along with process-based models to synthesize knowledge and guide further empirical work, we believe these practices will rapidly advance understanding of microbial controls on SOM and improve carbon cycle projections that guide policies on climate adaptation and mitigation.

Soil Decomposer Microarthropods Predominantly Feed on Saprotrophic Rather than Ectomycorrhizal Fungi

Soil Decomposer Microarthropods Predominantly Feed on Saprotrophic Rather than Ectomycorrhizal Fungi

Stable isotopes of amino acids indicate that soil decomposer microarthropods predominantly feed on saprotrophic fungi

AbstractSoil microarthropods are essential for nutrient cycling in forest ecosystems as they are integral components of decomposer food webs. They channel carbon and nutrients from leaf litter and roots to higher trophic levels; however, knowledge on the relative importance of different channels and on their variation with forest type is lacking. Although the importance of root‐derived inputs for sustaining soil food webs is increasingly recognized, the pathways by which they are channeled to higher trophic levels are little understood. For the channeling, ectomycorrhizal fungi may play a significant role, but until now methods allowing to separate the contribution of ectomycorrhizal and saprotrophic fungi to the nutrition of soil animal communities are lacking. Using dual analysis of 15N and 13C in amino acids (AAs), we investigated trophic positions and basal resources of two major groups of soil microarthropods, Collembola and Oribatida, in beech and spruce forests in Germany. By applying a 13C fingerprinting approach and Bayesian mixing models, we separated in a first step the relative contribution of bacteria, fungi, and plants to the nutrition of soil microarthropods. As fungi were identified as the major food source, in a second step we attempted to separate the contribution of ectomycorrhizal vs. saprotrophic fungi. For the first time, we provide direct evidence that soil microarthropods mainly rely on saprotrophic fungi, whereas ectomycorrhizal fungi are consumed by only few species. While trophic niches of Collembola and Oribatida species generally varied little between beech and spruce forests, plant detritus as basal resource of soil microarthropods was somewhat more important in beech forests, whereas in spruce forests microbial resources dominated. Overall, the dual analysis of carbon and nitrogen in AAs provided insight into food web structure of soil microarthropods in unprecedented detail, and for the first time allowed to estimate the relative importance of mycorrhizal and saprotrophic fungi for soil food web nutrition, a long‐standing riddle in soil food web ecology. The technique provides the perspective for a comprehensive understanding of the trophic structure and energy channeling in soil food webs.

The decomposition rates of leaf litter and fine root and their temperature sensitivities are influenced differently by biotic factors

Determining the temperature sensitivities of the decomposition rates of leaf litter and fine root is important for predicting the impact of climate warming on above- and belowground carbon (C) cycles in forest ecosystems. However, the responses of leaf and root decomposition rates to temperature have rarely been examined together. Here, we present the results of paired leaf litter and fine root decomposition experiments at four forest sites spanning 32° latitude in eastern China. The mean annual soil temperature explained the variances of the decomposition rates of the leaf litter (kLeaf, R2 = 0.95) and fine root (kFine root, R2 = 0.86) across the different biomes well and exerted a positive effect on the kLeaf: kFine root ratio. As a result, the sensitivity of the decomposition rate to temperature was significantly higher in the leaf litter (Q10 = 2.17 ± 0.07) than in the fine root (Q10 = 1.40 ± 0.06). The results of structural equation models indicated that the initial C:nitrogen (C:N) ratio exhibited negative effects, and phosphorus (P) cycling related enzymes activity exhibited positive effects on the kFine root when the effects of temperature were controlled. Even when the variables of these biotic factors were added, the soil temperature still exerted a dominant effect on the kLeaf. Our results suggest that temperature directly influences the kLeaf but indirectly affects the kFine root through litter quality and soil decomposers.

Mortierella Species as the Plant Growth-Promoting Fungi Present in the Agricultural Soils

In the most recent scientific reports based on the DNA or RNA-analyses a widespread presence of the filamentous fungi, Mortierella in various environments has been shown. Some strains of this genus belong to the plant growth-promoting fungi (PGPF) and are found in the bulk soil, rhizosphere and plants tissues. These microorganisms are also often found in the extremely hostile environments, responsible for improving access to the bioavailable forms of P and Fe in the soils, the synthesis of phytohormones and 1-aminocyclopropane-1-carboxylate (ACC) deaminase, and last but not least the protection of agricultural plants from pathogens. Furthermore, earlier reports classified Mortierella spp. as the saprotrophic microorganisms isolated from the forest litter, and nowadays their status as a very valuable decomposers in the agricultural soils was confirmed. The key features like the ability to survive under very unfavorable environmental conditions and the utilization of carbon sources contained in polymers like cellulose, hemicellulose, chitin make these fungi efficient as the agricultural inoculants. The growing interest in the application of Mortierella spp. is mainly due to the potential use of this genus in the increase of the nutrient uptake efficiency, positive effect in crop protection against adverse conditions, and reduction of chemical fertilizers and pesticides applied. Moreover, activities of Mortierella species selected from the wild or cultivated plants influence the soil microbiota and support the performance of the beneficial microorganisms enhancing significantly crop yield.

Direct and indirect effects of land-use intensity on plant communities across elevation in semi-natural grasslands.

Grassland biodiversity is vulnerable to land use change. How to best manage semi-natural grasslands for maintaining biodiversity is still unclear in many cases because land-use processes may depend on environmental conditions and the indirect effects of land-use on biodiversity mediated by altered abiotic and biotic factors are rarely considered. Here we evaluate the relative importance of the direct and indirect effects of grazing intensity on plant communities along an elevational gradient on a large topographic scale in the Eastern Carpathians in Ukraine. We sampled for two years 31 semi-natural grasslands exposed to cattle grazing. Within each grassland site we measured plant community properties such as the number of species, functional groups, and the proportion of species undesirable for grazing. In addition, we recorded cattle density (as a proxy for grazing intensity), soil properties (bare soil exposure, soil organic carbon, and soil pH) and densities of soil decomposers (earthworms and soil microorganisms). We used structural equation modelling to explore the direct and indirect effects of grazing intensity on plant communities along the elevation gradient. We found that cattle density decreased plant species and functional diversity but increased the proportion of undesirable species. Some of these effects were directly linked to grazing intensity (i.e., species richness), while others (i.e., functional diversity and proportion of undesirable species) were mediated via bare soil exposure. Although grazing intensity decreased with elevation, the effects of grazing on the plant community did not change along the elevation gradient. Generally, elevation had a strong positive direct effect on plant species richness as well as a negative indirect effect, mediated via altered soil acidity and decreased decomposer density. Our results indicate that plant diversity and composition are controlled by the complex interplay among grazing intensity and changing environmental conditions along an elevation gradient. Furthermore, we found lower soil pH, organic carbon and decomposer density with elevation, indicating that the effects of grazing on soil and related ecosystem functions and services in semi-natural grasslands may be more pronounced with elevation. This demonstrates that we need to account for environmental gradients when attempting to generalize effects of land-use intensity on biodiversity.

Home field advantage describes the carbon and nitrogen dynamics of Cynodon dactylon and Phoenix dactylifera leaf litters in arid sandy soil

Based on evidence from various ecosystems, it is hypothesized that interaction between leaf-litter and soil decomposer communities results in higher decomposition when leaf litter is decomposed in its home than away soil, a phenomenon called home field advantage (HFA). However, the generality of this hypothesis remains unclear due to the emergence of contrasting results across various biomes. Here, we tested if HFA also occurs in lawn grass (Cynodon dactylon; GL) and date palm (Phoenix dactylifera) leaf litter (DL) decomposition in arid sandy soil using reciprocal litter transplant mesocosms experiment. Litter decomposition was monitored by measuring CO2 emission (alkali trap), dissolved organic C (DOC), and mineral N (Nmin) over 180 days. Regression analysis was used to estimate HFA, litter quality (QI), and soil decomposer communities' ability (FA) indices. The highest HFA (69%) was observed for non-cumulative CO2 emission on day 14 that was decreased to 4% on day 180. Similarly, Nmin from leaf litter was 4 and 6% higher at home than away soil on days 90 and 180, respectively. These HFA effects were mainly attributed to higher CO2 emission and soil Nmin from grass litter at home than away-soil. In addition, microbial biomass C from GL and N immobilization from DL was lower at home than away-soil. However, we did not observe HFA for DOC on day 90 or 180. The QI indicates that CO2 emission or Nmin was lower from DL than GL irrespective of home or away soil. The QI and FA did not change over time for the aforesaid parameters despite HFA effects decreased with time for non-cumulative CO2 emission. This indicates that leaf litter and soil specific interactions did not remain constant for litter C and N cycling, and hence this interaction could be nutrient-specific during leaf litter decomposition in soil.

The consistency of home-field advantage effects with varying climate conditions

The home-field advantage (HFA) hypothesis predicts that plant litters decompose faster in the vicinity of the plant from which they are derived than away from ‘home’. Although we are aware that both litter quality and the efficiency of decomposers within soil communities (hereafter, “soil ability”) are important drivers of HFA effects, we know little on variation in HFA effects and underlying processes of these changes across years with varying climates. In order to address these questions, we repeated four years with varying climates (two mild years, 2016 & 2018 and two stressed years, 2017 & 2019) a reciprocal transplant experiment with four litter types, crossing vegetation structure and soil fertility contrasts of both litter and ecosystems (forest and grassland litters from both fertile and unfertile soils). We used the Decomposer Ability Regression Test for both types of years to search for evidence of HFA effects and conducted ANOVAs on the cross effects of vegetation structure and soil fertility contrasts to further identifying the underlying processes of changes in HFA across climates. HFA effects were only significant for the most recalcitrant litter of Pinus pinaster, and much more significant during the mild years. Litter quality was stable across species and years, whereas differences in soil ability among ecosystems of the four species were strongly affected by climate, with highly significant differences among ecosystems occurring only during the mild years. Changes in soil ability across climates (decreasing HFA effects during stressed years) were explained by an overall increase in litter decomposition in forests as compared to grasslands during the stressed years, due to the facilitation of soil decomposers by forest canopies. Our study showed that HFA effects vary across climates as a result of changes in soil ability and that forest canopies may buffer the negative effects on litter decomposition of increasing stress with climate change.

Responses of rhizosphere soil bacteria to 2-year tillage rotation treatments during fallow period in semiarid southeastern Loess Plateau.

BackgroundSoil compaction can be mitigated by deep tillage and subsoiling practices following a long period of no-tillage. Fallow tillage rotation methods are frequently used to improve water availability in the soils of the southeastern Loess Plateau region of China. Rhizosphere soil bacteria are ecologically important for the transformation of matter and energy in the plant root system and can be influenced by tillage rotation treatments. However, the effect of tillage rotations on the bacterial community and structure of rhizosphere soil is not well understood.MethodsA two-year field experiment was conducted with four tillage rotation treatments, including subsoil–subsoil (SS-SS), subsoil–deep tillage (SS-DT), deep tillage–deep tillage (DT-DT), and the control treatment of no-tillage–no-tillage (NT-NT). Our study was conducted during wheat’s fallow period to investigate the abundance, diversity, and functions of rhizosphere soil bacteria using high-throughput sequencing technology.ResultsOur results showed that tillage rotation methods significantly influenced the bacterial diversity and composition of the rhizosphere soil in the plough layer (20–40 cm depth) by altering the moisture content of the soil. The metabolism, environmental information processing, and genetic information processing of the bacteria in the rhizosphere soil were affected. The most abundant phyla across all samples were Proteobacteria, Actinobacteria, Acidobacteria, Planctomycetes, Bacteroidetes, Gemmatimonadetes, Frimicutes, Chloroflexi, Nitrospirae, and Verrucomicrobia, which are classic bacterial decomposers in soil. The bacterial diversity and composition was similar for treatments causing higher soil perturbation (SS-DT and DT-DT), which disrupted the balance between aerobic and anaerobic bacteria. The less disruptive tillage methods (SS-SS and NT-NT), preserved the integrity of the soil bacteria. However, the NT-NT treatment may have led to soil compaction, particularly in the 20–40 cm layer. These results suggested that SS-SS was the most effective tillage rotation practice to accumulate soil moisture, maintain the balance between aerobic and anaerobic bacteria, and to enhance the metabolic capacity of rhizosphere soil bacteria. This method may have a significant impact on the sustainable development and farming practices of dryland agriculture.

Isolation and Characterization of Streptomycetes with Potential to Decompose Organic Compounds During Bioremediation of Arable Soil

The study has an objective of isolating and characterizing suspected Streptomycetes with the potential to decompose organic compounds in arable soil. The isolates were grown on a culture media and a total of 61 slopes were inoculated and labeled using the following characterization tests: catalase test, gram staining, oxidase test, motility test, and oxidative-fermentative test. After characterization tests, data generated in the laboratory were analyzed and the study showed that isolates A2 (c, e), B2 (c), C1 (b), C2 (a), D1 (e) and D2 (d) were suspected to be Streptomycetes species. Isolates D1 (d) and D2 (b) were suspected to be Escherichia coli while isolates A1 (a), B2 (a, b) and D1 (a) were suspected to be Bacillus species. Isolates A1 (b), C1 (a), D1 (c), D2 (e) were suspected to be Pseudomonas species. Further identification showed that isolates A2 (d) and B1 (b) could be Enterobacter species while isolates A2 (a, b) were suspected to be Klebsiella species. The study tentatively identified Streptomycetes species; Escherichia coli; Bacillus species; Enterobacter species; Pseudomonas species and Klebsiella species. The suspected Streptomycetes identified were considered as potential organic matter decomposers in arable soil.

Dichlorobiphenyls and chlorinated benzoic acids – Emergent soil pollutants in model bacterial membranes. Langmuir monolayer and Grazing Incidence X-ray Diffraction studies

Abstract The multi-decade worldwide application of polychlorinated biphenyls (PCB) leads to the problem of soil pollution. The production and application of PCB was banned, so the gradual decrease of their concentration in the soils was expected. On the contrary, novel sources of dichlorobiphenyls as PCB 11 were identified and these emergent pollutants are still emitted to the environment. Dichlorobiphenyls and some chlorobenzoic acids (CBA) are known as dead-end PCB metabolites – they accumulate in the soils and being toxic to microorganisms lead to the impoverishment of soil decomposer consortia. The toxicity of PCB and CBA is connected with their membrane activity and accumulation in the bacterial membranes. The correlation between the phospholipid composition of the bacterial membrane and the toxicity of PCB and CBA is unfortunately unknown limiting the effective selection of bacterial species for bioremediation of polluted soils. To shed light on these phenomena we applied binary phospholipid Langmuir monolayers as model bacterial membranes. With these models we studied the phenomena of dichlorobiphenyls and selected CBA molecules' incorporation and the effects exerted by these molecules on the ordering of the phospholipid molecules at the molecular scale. For the studies of the organization of the model membranes we applied Grazing Incidence X-ray Diffraction. It turned out that the model membranes rich in cardiolipin can accumulate more pollutant molecules than the models containing phosphatidylglycerols. The accumulation of the pollutants did not cause any significant changes in the 2D crystalline structure of the former models whereas the latter were profoundly modified.

Effect of ash application on the decomposer food web and N mineralization in a Norway spruce plantation.

In the face of global climate change there is an increasing demand for biofuel, which exerts pressure on production and thus management of biofuel plantations. The intensification of whole-tree harvest from biofuel plantations increases export of nutrients. Returning ash from biofuel combustion to the forest plantations can amend the soil nutrient status and thus facilitate sustainable forest management. However, ash affects the forest floor decomposer food web, potentially changing organic matter turnover, carbon sequestration and nitrogen availability. Our aim was to examine the response of decomposer organisms, food web structure and nitrogen mineralization function after ash application. In a coniferous forest plantation amended with 0, 3, 4.5 or 6t ash ha-1, we sampled in several depths of the forest floor for key organisms of the decomposer food web (fungal biomass, 0-12cm; bacteria, protozoa, nematodes and enchytraeids, 0-3cm and 3-6cm; microarthropods and earthworms, 0-5cm), 2, 14 and 26months after ash application. We used structural equation modelling (SEM) to detangle the direct and indirect effects of ash application on organisms in the decomposer food web and on nitrogen availability. We found that ash increased the abundance of bacteria and protozoa, as well as the inorganic nitrogen pool at 0-3cm depth, whereas the effect of ash was negligible at 3-6cm depth. Earthworm abundance increased, whereas enchytraeid abundance decreased 2years after ash application. The structural equation modelling showed that ash application stimulated the bacterial feeding pathway and increased nitrogen mineralization. Contrary, ash had a negative effect on fungal biomass at the first sampling, however, this effect subdued over time. Our results suggest that as the soil decomposer food web is resilient to ash application, this is a viable option for sustainable management of biofuel plantations.

Exploring the impacts of plastics in soil – The effects of polyester textile fibers on soil invertebrates

Polyester fiber is one of the most abundant types of microplastics in the environment. A major proportion of the fibers entering wastewater treatment plants end up in sewage sludge, which is used as a soil fertilizer in many countries. As their impacts in the terrestrial environment are still poorly understood, we studied the effects of polyester fibers on enchytraeids (Enchytraeus crypticus), springtails (Folsomia candida), isopods (Porcellio scaber) and oribatid mites (Oppia nitens), all playing an important role in soil decomposer food webs. We exposed these invertebrates in the laboratory to short (12 µm–2.87 mm) and long (4–24 mm) polyester fibers, spiked in soil or in food at five concentrations ranging from 0.02% to 1.5% (w/w) and using five replicates. Overall the effects of polyester fibers on the soil invertebrates were slight. Energy reserves of the isopods were slightly affected by both fiber types, and enchytraeid reproduction decreased up to 30% with increasing fiber concentration, but only for long fibers in soil. The low ingestion of long fibers by the enchytraeids suggests that this negative impact arose from a physical harm outside the organism, or from indirect effects resulting from changes in environmental conditions. The short fibers were clearly ingested by enchytraeids and isopods, with the rate of ingestion positively related to fiber concentration in the soil. This study shows that polyester fibers are not very harmful to soil invertebrates upon short-term exposure. However, longer lasting, multigeneration studies with functional endpoints are needed to reveal the possible long-term effects on soil invertebrates and their role in the decomposition process. This study also shows that polyester fibers can enter terrestrial food web via ingestion of fibers by soil invertebrates.