Soil Organisms Research Articles

Responses of a soil-inhabiting collembolan (Entomobrya proxima Folsom) to organic fertilizer addition illustrated by functional traits and gut bacterial community

IntroductionOrganic fertilizer offers significant advantages for sustainable agricultural development compared to inorganic fertilizers and is increasingly becoming the predominant fertilizer strategy. Functional traits and gut microbiota of soil fauna are recognized as potential indicators of environmental changes. However, there is a dearth of research examining the correlation between functional traits and intestinal microorganisms in response to organic fertilizer.MethodsIn this study, we selected Entomobrya proxima Folsom, a predominant soil collembolan species found in cropland across North China, as our subject of study. We set treatments with no organic fertilizer (CK) and three different concentrations of organic fertilizer at 1% (O1), 6% (O2), and 10% (O3). Stereomicroscopy and high-throughput amplicon sequencing were employed to elucidate the response of soil fauna to organic fertilizer through host functional traits and associated gut microbial communities.ResultsThe results indicated that the impact of organic fertilizer on the functional traits of collembolans was closely linked to the input concentration. Specifically, low input concentrations positively influenced all functional traits of Entomobrya proxima Folsom; conversely, higher input concentrations exerted an overall detrimental effect. For the gut bacterial community, the addition of organic fertilizer resulted in a significant decrease in abundance, adversely affected α-diversity, and significantly altered the structure of the gut bacterial community compared to CK. However, there was no significant effect of fertilizer concentration on these three parameters. The composition of the gut bacterial community varied due to the addition of organic fertilizer, with significant changes observed in the relative abundances of six phyla and three genera. Furthermore, body length and foreleg length may serve as potential indicators for characterizing the proportions of Alcanivorax and Sphingobacterium of gut bacterial community. Additionally, the assembly process of the gut bacterial community was strongly influenced by the amount of organic fertilizer added; this led to a narrowing niche width that is believed to contribute to an increase in species richness.DiscussionIn conclusion, adding organic fertilizer exerted multiple impacts on soil fauna, with effect sizes related to its concentration. These findings provide insights for conserving soil animals while maximizing their ecological functions and offer perspectives on optimizing sustainable agricultural management practices.

Biodiversity restated: > 99.9% of global species in Soil Biota

More than a decade of research led to the conclusion in 2022 that the Soil Biome is home to ~ 2.1 × 1024 taxa and thus supports > 99.9% of global species biodiversity, mostly Bacteria or other microbes, based upon topographic field data. A subsequent 2023 report tabulated a central value of just 1.04 × 1010 taxa claiming soils had 59 ± 15%, i.e., 44–74% (or truly 10–50%?) of the global total, while incidentally confirming upper values of ~ 90% for soil Bacteria. Incompatibility of these two studies is reviewed, supporting prior biodiversity data with the vast majority of species inhabiting soils, despite excluding viruses (now with ~ 5 × 1031 virions and 1026 species most, ~ 80%, in soils). The status of Oligochaeta (earthworms) and other taxa marked “?” in the 2023 paper are clarified. Although biota totals are increased considerably, inordinate threats of topsoil erosion and poisoning yet pertain with finality of extinction. Species affected include Keystone taxa, especially earthworms and microbes, essential for a healthy Soil foundation to sustain the Tree-of-Life inhabiting the Earth.

Enhancement of alfalfa growth resistance by arbuscular mycorrhiza and earthworm in molybdenum-contaminated soils: From the perspective of soil nutrient turnover.

Molybdenum (Mo) acts as a crucial nutrient for plant development, yet excessive soil exposure can cause detrimental effects. Molybdenosis symptoms remain subtle in many plants, largely due to the safeguarding functions of soil organisms, the fundamental biological mechanisms lack clarity. In this study, we explored the potential mechanisms for amending Mo-exposed soils with soil microbe-arbuscular mycorrhizal fungi (AMF) and soil fauna, specifically earthworms, to enhance model plant-alfalfa growth resistance through soil nutrient turnover perspectives. Our findings illustrated that excessive Mo exposure disrupted soil nutrient turnover, manifesting as exacerbated microbial C and N metabolic limitations. Consequently, this interference intensified nutrient competition between alfalfa and soil microbes, thereby impeding alfalfa nutrient uptake and growth resistance. The synergistic application of AMF and earthworms alleviated microbial C (8.55% ∼ 28.23%) and N (11.14% ∼ 37.55%) metabolic limitations by modulating soil enzyme activities, particularly P-acquiring enzyme. This co-approach facilitated enhanced C and N accumulation in alfalfa, thus improving its growth resistance (24.15% ∼ 123.74%) under Mo exposure. Furthermore, in contrast to singular treatments, the combination of AMF and earthworms bolstered mutual Mo tolerance, amplifying biological benefits for alfalfa growth. Earthworms promoted AMF colonization and the secretion of glomalin-related soil proteins (GRSP), while AMF alleviated Mo accumulation and oxidative stress in earthworms. Additionally, the AMF-induced regulation of gut metabolism reduced earthworm mortality and minimized weight loss. Our study underscores the necessity of maintaining soil biodiversity when utilizing Mo fertilizers to mitigate the potential risks of Mo over-exposure affecting soil nutrient turnover and plant growth.

Small heat shock proteins as relevant biomarkers for anthropogenic stressors in earthworms

Anthropogenic stressors in terrestrial ecosystems require focused research on adaptive responses in soil organisms such as Eisenia fetida, a model earthworm species. We analyzed the gene expression of five small heat shock proteins (sHSPs) in response to various stressors: heat stress (31 and 35 °C), desiccation (10 % and 20 % humidity), and chemical exposure (bisphenol A and endosulfan) under standard and elevated temperatures. Under moderate heat (31 °C), early upregulation of sHSP transcripts upregulation suggests their involvement in initial stress responses, possibly mitigating protein aggregation. At the higher temperature (35 °C), three sHSPs served as a defense against severe protein aggregation, a significant finding as previous studies identified only one activated heat shock protein (HSP70) in E. fetida under similar conditions. Desiccation stress at 10 % humidity activated more sHSPs than at 20 % humidity, and the expression profile at 10 % humidity closely resembled that observed under heat stress, suggesting overlapping adaptation pathways. Heat combined with chemical stress, particularly endosulfan, elevated sHSP transcription and underscored the potential of these proteins as biomarkers in multi-stressor environments. Monomeric sHSPs from E. fetida, which share homology with human sHSPs, showed the highest activity across all stressors, suggesting their key role in earthworm adaptation.

Combined effects of different-sized microplastics and fluindapyr on earthworm: Bioaccumulation, oxidative stress, histopathological responses and gut microbiota.

Soil is an important sink for microplastics (MPs) and pesticides. MPs can act as carriers for pesticides, thus induce direct and indirect effects on soil organisms. Fluindapyr (FIP), a novel succinate dehydrogenase inhibitors fungicides (SDHIs), may pose a serious threat to earthworms. However, few studies have evaluated the effects of joint exposure to MPs and FIP. Here, earthworms (Eisenia fetida) were jointly exposed to PMMA (polymethylmethacrylate) and PS (polystyrene) MPs of different sizes (0.1, 1 and 10μm) along with FIP for 28-day to investigate the toxic effects of single and joint exposure of FIP and MPs on earthworms. The results showed that joint exposure to 0.1 and 1μmMP promoted the accumulation of FIP in earthworms at the beginning of the experiment compared to the sole group, but the elimination of FIP from earthworms accelerated after 14d. In addition, the joint exposure caused more serious damages to the epidermis and intestine of earthworms and increased the severity of oxidative stress. The effects of joint exposure to FIP and MPs depended on the size of the MPs, and the strongest effects were observed in the treatment with the smallest size. The 16S rRNA sequencing results showed that the joint exposure to MPs and FIP didn't cause gut microbiota dysbiosis. However, the sole 0.1μmPS significantly altered the community diversity and richness of earthworm gut bacteria, and the relative abundance of Proteobacteria, Actinobacteria and Firmicutes was significantly changed. The obtained results inferred that MPs could influence environmental and toxicological behaviors of FIP and may provide data support for the risk assessments of MPs and FIP on soil ecosystems.

Corrigendum to “Input of high-quality litter reduces soil carbon losses due to priming in a subtropical pine forest” [Soil Biology and Biochemistry 194 (2024) 109444

Corrigendum to “Input of high-quality litter reduces soil carbon losses due to priming in a subtropical pine forest” [Soil Biology and Biochemistry 194 (2024) 109444

Study on Rapid Quantitative Detection of Soil MPs Based on Terahertz Time-Domain Spectroscopy.

The presence of microplastics (MPs) in agricultural soils substantially affects the growth, reproduction, feeding, survival, and immunity levels of soil biota. Therefore, it is crucial to investigate fast, effective, and accurate techniques for the detection of soil MPs. This work explores the integration of terahertz time-domain spectroscopy (THz-TDS) techniques with machine learning algorithms to develop a method for the classification and detection of MPs. First, THz spectral image data were preprocessed using moving average (MA). Subsequently, three classification models were developed, including random forest (RF), linear discriminant analysis, and support vector machine (SVM). Notably, the SVM model had an F1 score of 0.9817, demonstrating its ability to rapidly classify MPs in soil samples. Three regression models, namely, principal component regression (PCR), RF, and least squares support vector machine (LSSVM), were developed for the detection of three MPs polymers in agricultural soils. Six feature extraction methods were used to extract the relevant parts of the data containing key information. The results of the study showed that the regression accuracies of PCR, RF, and LSSVM were greater than 83%. Among them, the RF had the highest overall regression accuracy. Notably, PE-UVE-RF had the best performance with Rc2, Rp2, root mean square error of calibration, and root mean square error of prediction values of 0.9974, 0.9916, 0.1595, and 0.2680, respectively. Furthermore, this model gets a better performance by hypothesis testing and predicting real samples.

Soil Legacy Effects of Chromolaena odorata and Biochar Remediation Depend on Invasion Intensity

The increasing threat of biological invasion poses significant challenges to global ecosystems, necessitating urgent management measures. This study investigated the potential of biochar derived from invasive plant Chromolaena odorata, produced through anaerobic digestion, as a tool for mitigating the soil legacy effects of this species and restoring the plant community. Soil samples were collected from artificially constructed plots of invasive plant communities and were subjected to treatments with different levels of fungicide and biochar addition. Potted plant communities replicating the original species composition were established, and biomass were used to evaluate the effectiveness of soil restoration. Our results demonstrated that soil sterilization enhanced plant biomass, with invasive plants showing a more pronounced increase compared to native species, indicating different responses to the soil biota. The addition of biochar influenced plant biomass, with an optimal biochar concentration of 2% of the soil mass, promoting the growth of native plants. The application of biochar in conjunction with soil sterilization facilitated the restoration of native communities in areas with low invasion intensity. Overall, these findings provide valuable insights into the potential of biochar-based strategies for managing invasive plants and restoring ecosystems, underscoring the necessity for further research to optimize field applications and evaluate ecological impacts.

Shared community history strengthens plant diversity effects on below-ground multitrophic functioning.

The relationship of plant diversity and several ecosystem functions strengthens over time. This suggests that the restructuring of biotic interactions in the process of a community's assembly and the associated changes in function differ between species-rich and species-poor communities. An important component of these changes is the feedback between plant and soil community history. In this study, we examined the interactive effects of plant richness and community history on the trophic functions of the soil fauna community. We hypothesized that experimental removal of either soil or plant community history would diminish the positive effects of plant richness on the multitrophic functions of the soil food web, compared to mature communities. We tested this hypothesis in a long-term grassland biodiversity experiment by comparing plots across three treatments (without plant history, without plant and soil history, controls with ~20 years of plot-specific community history). We found that the relationship between plant richness and below-ground multitrophic functionality is indeed stronger in communities with shared plant and soil community history. Our findings indicate that anthropogenic disturbance can impact the functioning of the soil community through the loss of plant species but also by preventing feedbacks that develop in the process of community assembly.

ОЦЕНКА УСТОЙЧИВОСТИ ПОЧВЕННОГО ПОКРОВА К ЗАГРЯЗНЕНИЮ УГЛЕВОДОРОДАМИ НА ТЕРРИТОРИИ НАЗЕМНОГО КОМПЛЕКСА МЕСТОРОЖДЕНИЯ КАШАГАН

The development and operation of the Kashagan offshore hydrocarbon deposit is accompanied by man-made impacts not only in the Caspian Sea, but also on the coast, which is associated with the creation of an onshore infrastructure for the delivery of hydrocarbons to the consumer. Man-made impacts are complex and lead to mechanical and chemical disruption of natural landscapes. The water-air regime is deteriorating, the migration ability of elements and the geochemical balance are changing. There is also a deterioration in the growth and development of vegetation, the death of soil biota. The conducted research made it possible to determine the degree of mechanical disturbance and chemical contamination of the soil cover and to assess the soil resistance of the territory of the location of the Kashagan field's surface facilities in the area of the SPZ IOaGTP Bolashak to chemical contamination. The soil cover on the territory of IOaGTP is characterized by complexity and is represented by 12 types of soils with signs of salinity and salinity. Soils are characterized by low availability of nutrients and have low agricultural production potential or are completely unsuitable for farming. The soil cover of the territory is characterized by a high degree of self-purification from hydrocarbons.

Soil fauna trophic multifunctionality mediates the release of elements from decomposing typhoon‐generated leaf litter

Abstract Tropical cyclones (i.e. hurricanes, typhoons) cause large pulse fluxes of leaves that have not undergone senescence (i.e. green litter) to forest soils, with consequences for biogeochemical cycling. Energy and mineral nutrient concentrations of green litter are higher than the naturally senesced litter, likely affecting rates of decomposition and nutrient release, as well as the structure and composition of detrital food webs, but these effects have not been well quantified. During the typhoon ‘Hagubit’, we collected green and senesced litter from three common urban greening species, and then conducted a 316‐day field experiment to evaluate substrate quality affected the trophic multifunctionality of soil faunal communities and ultimately elemental release from the decomposing litter. Nitrogen (N), phosphorus (P), potassium (K), sodium (Na), calcium (Ca) and magnesium (Mg) were released at significantly higher rates from green litter than senesced litter. Aluminium (Al), manganese (Mn) and iron (Fe) displayed a net accumulation during litter decomposition, and the immobilization of these elements was significantly higher in green than senesced litter. Litter substrate chemistry directly affected the release rates of elements, but its influence was stronger in decomposing senesced litter compared to green litter. Detritivores dominated green and senesced litter faunal communities relative to predators, omnivores and herbivores, and these distinct fauna functional groups showed significantly positive correlation during decomposition, but soil fauna trophic multifunctionality was significantly higher in green litter and stimulated the release of elements. These findings suggest that typhoons dramatically alter the dynamics of nutrient release during litter decomposition, and the influences are mediated in part by its substrate quality and changes in soil fauna trophic multifunctionality, which has significant implications for the magnitude and timing of soil nutrient availability after typhoon disturbances. Read the free Plain Language Summary for this article on the Journal blog.

Constructed wetland - microbial fuel cell (CW-MFC) mediated bio-electrodegradation of azo dyes from textile wastewater.

Azo dyes constitute 60-70% of commercially used dyes and are complex, carcinogenic, and mutagenic pollutants that negatively impact soil composition, water bodies, flora, and fauna. Conventional azo dye degradation techniques have drawbacks such as high production and maintenance costs, use of hazardous chemicals, membrane clogging, and sludge generation. Constructed Wetland-Microbial Fuel Cells (CW-MFCs) offer a promising sustainable approach for the bio-electrodegradation of azo dyes from textile wastewater. CW-MFCs harness the phytodegradation capabilities of wetland plants like Azolla, water hyacinth, and Ipomoea, along with microalgae such as Nostoc, Oscillatoria, Chlorella, and Anabaena, to break down azo dyes into aromatic amines. These intermediates are then reduced to CO2 and H2O by microalgae in the fuel cells, while simultaneously generating electricity. CW-MFCs offer advantages including low cost, sustainability, and use of renewable energy. The valorization of the resulting algal and plant biomass further enhances the sustainability of this approach, as it can be used for biofuel production, nutraceuticals, pharmaceuticals, and bio-composting. Implementing CW-MFCs as a tertiary treatment step in textile industries aligns with the circular economy concept and contributes to achieving several Sustainable Development Goals (SDGs).

Monitoring and Modeling the Soil‐Plant System Toward Understanding Soil Health

AbstractThe soil health assessment has evolved from focusing primarily on agricultural productivity to an integrated evaluation of soil biota and biotic processes that impact soil properties. Consequently, soil health assessment has shifted from a predominantly physicochemical approach to incorporating ecological, biological and molecular microbiology indicators. This shift enables a comprehensive exploration of soil microbial community properties and their responses to environmental changes arising from climate change and anthropogenic disturbances. Despite the increasing availability of soil health indicators (physical, chemical, and biological) and data, a holistic mechanistic linkage has not yet been fully established between indicators and soil functions across multiple spatiotemporal scales. This article reviews the state‐of‐the‐art of soil health monitoring, focusing on understanding how soil‐microbiome‐plant processes contribute to feedback mechanisms and causes of changes in soil properties, as well as the impact these changes have on soil functions. Furthermore, we survey the opportunities afforded by the soil‐plant digital twin approach, an integrative framework that amalgamates process‐based models, Earth Observation data, data assimilation, and physics‐informed machine learning, to achieve a nuanced comprehension of soil health. This review delineates the prospective trajectory for monitoring soil health by embracing a digital twin approach to systematically observe and model the soil‐plant system. We further identify gaps and opportunities, and provide perspectives for future research for an enhanced understanding of the intricate interplay between soil properties, soil hydrological processes, soil‐plant hydraulics, soil microbiome, and landscape genomics.

Exploring chitin metabolite profiles and sensitivity differences in Collembola species exposed to teflubenzuron.

Effective environmental risk assessments of chemical plant protection products, such as benzoylurea pesticides, are crucial for safeguarding ecosystems. These pesticides, including teflubenzuron, target chitin synthesis in arthropods but also pose risks to non-target soil fauna like Collembola, which play essential roles in decomposition and nutrient cycling. This study combines traditional toxicity tests with a metabolomic approach to examine the interspecies specific sensitivity of three Collembola species - Sinella curviseta, Ceratophysella denticulata, and Folsomia candida - to teflubenzuron. The investigation focused on reproduction, bioaccumulation, and changes in chitin-related metabolites as indicators of pesticide impacts. Results revealed significant interspecies specific variability in sensitivity, with F. candida showing higher susceptibility towards teflubenzuron, possibly due to greater bioaccumulation factors. Metabolomic analysis highlighted distinct patterns in chitin metabolite alterations among the species, correlating with their differential sensitivity. Notably, metabolites like trehalose and glucose, crucial for chitin synthesis, were significantly affected by teflubenzuron within seven days of exposure. Despite high soil concentrations of the pesticide, S. curviseta demonstrated resilience in traditional life-history endpoints, such as reproduction and survival. However, metabolomics indicated a biochemical response to even low internal concentrations of teflubenzuron, underscoring the complexity of their interactions with environmental stressors. This study emphasizes the importance of incorporating metabolomics to understand the differential responses of non-target organisms to pesticides and advocates for species-specific risk assessments in pesticide regulation. The distinct metabolic responses among Collembola species to chitin synthesis inhibitors provide critical insights into their ecological resilience or vulnerability, enhancing our understanding of ecosystem dynamics and the potential ramifications of chemical exposure.

ACCUMULATION OF TRACE ELEMENTS IN SOIL AND FAUNA WITHIN A SITE HISTORICALLY CONTAMINATED WITH COAL COMBUSTION RESIDUES.

Legacy contaminants tied to energy production are a worldwide concern. Coal combustion residues (CCRs) contain high concentrations of potentially toxic trace elements such as arsenic (As), mercury (Hg), and selenium (Se), which can persist for decades after initial contamination. CCR disposal methods, including aquatic settling basins and landfills, can facilitate environmental exposure through intentional and accidental releases. Wildlife exposed to CCRs can experience numerous deleterious effects, such as on development, reproduction, and survival. In the current study, we quantified and compared concentrations of As, Hg, Se, and strontium (Sr) within soils and target fauna (three vertebrate and three invertebrate taxa) from a CCR-contaminated site and a reference site within the U.S. Department of Energy's Savannah River Site, South Carolina, USA. Our objectives were to 1) compare current concentrations of tested elements in soil and resident fauna to levels from our reference site, 2) assess natural attenuation of elements in soils by comparing current concentrations to historic levels, and 3) evaluate the biomagnification potential of the elements measured via body burden and trophic position correlations among fauna. Element concentrations were higher in contaminated soils than reference soils; however, concentrations in 2022 were unchanged from concentrations measured in 2003, suggesting no natural attenuation of tested elements. Additionally, target fauna had elevated As, Se, and Sr levels in comparison to reference samples. A positive correlation was observed in southern toads between Sr concentrations and trophic position, as assessed by nitrogen stable isotope ratios, suggesting potential for biomagnification of Sr within our study system. Collectively, our results demonstrate that legacy contaminants are still present and bioaccumulate in a diversity of taxa in a CCR-contaminated site that has not received effluents in over 50 years, suggesting monitoring programs in CCR-contaminated sites should be maintained long term in the absence of remediation.

Aboveground-belowground linkages across vegetation degradation gradients differ among native eucalypt communities.

Native vegetation degradation impacts soil communities and their functions. However, these impacts are often studied by comparing soil biotic attributes across qualitatively defined, discrete degradation levels within a single plant community at a specific location. Direct quantification of the relationships between vegetation and soil attributes across continuous degradation gradients and at larger scales is rare but holds greater potential to reveal robust patterns in aboveground-belowground linkages that may apply across different plant communities. We investigated how native vegetation attributes relate to soil communities and their functions across a degradation gradient within three native temperate eucalypt woodland and forest communities that differed in soil nutrient availabilities. Across remnant patches of native vegetation in the Sydney Basin bioregion, we established plots representing different levels of decline in their vegetation quality (i.e., increased exotics and canopy changes) compared to relevant reference communities. In those plots, we assessed soil community groups (microbes and fauna), carbon (C) and nutrient cycling (litter decomposition, enzyme activity, and phosphate and nitrate accumulation rates), soil pH, texture and vegetation attributes (composition, structure, and function). Our unique study design revealed that the relationships between vegetation degradation and soil biota across the food web (i.e., AM fungi, Fungi:bacteria ratio, Gram-positive bacteria, total nematodes) were highly dependent on the plant community. However, the degradation impacts on soil functions (i.e., total enzyme activity, and phosphate availability) were mostly consistent, suggesting their potential as belowground indicators of ecosystem degradation, with a notable positive association observed in phosphate availability rates. Additionally, the effects of vegetation degradation on soil biota and their functions appeared stronger in the nutrient-poor plant communities, suggesting greater vulnerability of their belowground components. Our findings call for caution when generalizing belowground responses to degradation and for further research on how nutrient availability mediates the impacts of degradation on aboveground-belowground linkages.

Assessment of technogenic pollution by silver compounds on the biological properties of the soil (Model experiment)

Introduction: Silver (Ag) has increasingly become one of the priority pollutants of soils, which is accompanied by a number of consequences for humans and soil biota. To fully assess the effects of the entry of different chemical forms of Ag into soils, it is necessary to conduct experiments with different types of soils, different exposure periods, as well as a wide range of biological indicators. The purpose of the study is to assess technogenic pollution by silver compounds (silver oxide (Ag2O) and nitrate (AgNO3)) on the biological properties of the soil in model experiment of the soil in a model experiment, followed by the use of the data obtained in the normalization of the Ag content in the soil. Materials and methods: The effect of Ag2O and AgNO3 was investigatedin specific permissible concentrations of biological indicators of the state of Haplic Chernozems Calcic (HCC), Haplic Cambisols Eutric (HCE) and Haplic Arenosols Eutric (HAE). Ecotoxicity was assessed by the degree of changes in the indicators of enzymatic activity, microbiological and phytotoxic indicators of soils 10, 30 and 90 days after contamination. Activity of catalase it was determined gasometrically, dehydrogenases, peroxidase, polyphenoloxidase, ferrireductase, ascorbatoxidase, phosphatase, invertase, urease, protease was determined photocolorimetrically, the total number of bacteria by luminescent method, Azotobacter sp. abundance by the method of fouling lumps on the Ashby medium, length of shoots and roots of wheat (Triticum aestivum L.) morphometrically. Results: It was revealed that Ag ecotoxicity was determined by the content of Ag in the soil, its form, the period from the moment of contamination and soil type. In most cases, AgNO3 had a stronger ecotoxic effect on biological parameters. Phosphatase activity and number of soil bacteria are the most sensitive indicators. The activity of invertase, urease, dehydrogenases and Azotobacter sp. abundance are the most informative indicators. Conclusion: Abundance is the most informative indicator. The results obtained to assess the ecotoxicity of soils contaminated with Ag, as well as the identified sensitive and informative indicators, can be used for diagnosis and as an indicator of the ecological state of soils.

IMulch: an investigation of the influence of polymers on a terrestrial ecosystem using the example of mulch films used in agriculture

BackgroundThis article provides an overview of the iMulch joint project, which analysed the use of polyethylene (PE) and biodegradable mulch films made of a polylactide (PLA) and polybutylene adipate terephthalate (PBAT) on agricultural land as a source of microplastic. The development of a detection methodology using Raman spectroscopy and thermo-extraction desorption gas chromatography mass–spectrometry (TED-GC–MS), the adsorption behaviour, ageing in drainage water and soil, their transport behaviour in lysimeters, ecotoxicity, uptake in plants, a life cycle assessment (LCA) and upcycling were considered.ResultsThe PE film tested showed hardly any degradation or fragmentation during the ageing tests. The biodegradable films showed incipient degradation after 8 weeks in drainage water and initial degradation after 12 weeks in soil ageing experiments. Additionally no degradation could be detected in the lysimeter test within the 24 months analysed. The biodegradable films could be metabolized in laboratory tests with some microorganisms present in the soil. This indicates that these films can be degraded in the environment if the conditions for degradation are optimal. No microorganisms or fungi that could degrade the PE film within a respective period of time were detected in the soil. Adsorption of the tested substances was not observed. Incorporated in soil, mulch film microplastic showed retention of extractable pesticides. In the ecotoxicological tests, both film types showed no acute toxic effects in the earthworm Eisenia fetida and the springtail Folsomia candida. Endocrine activity was observed in eluate samples from both films. However, aged films showed fewer effects than non-aged films.ConclusionBoth types of film show no transport or degradation in the tests under real conditions, which means that they remain in the upper soil layer, where they are available to soil organisms and can lead to high concentrations in the future. As the biodegradable film could be degraded, at least under ideal conditions, we recommend its use. However, proof of degradation must first be verified under real field conditions. In addition, we recommend the use of thicker conventional mulch films to minimize the emission of plastic particles. For this purpose, a minimum lower limit for the material thickness should be defined.Graphical

Comparing field and lab quantitative stable isotope probing for nitrogen assimilation in soil microbes.

Soil microbes are responsible for critical biogeochemical processes in natural and agricultural ecosystems. Despite their importance, the functional traits of most soil organisms remain woefully under-characterized, limiting our ability to understand how microbial populations influence the transformation of elements such as nitrogen (N) in soil. Quantitative stable isotope probing (qSIP) is a powerful tool to measure the traits of individual taxa. This method has rarely been applied in the field or with 15N to measure nitrogen assimilation. In this study, we measured genus-specific microbial nitrogen assimilation in two agricultural soils and compared field and lab 15N qSIP methods. Our results identify taxa important for nitrogen assimilation in agricultural soils, shed light on the field relevance of lab qSIP studies, and provide guidance for the future application of qSIP to measure microbial traits in the field.

Influence of ecologically relevant urea fertilizer concentrations on nematodes: A microcosm experiment

Aim of study: Urea remains one of the most widely used chemical fertilisers in the world and is used extensively in the Philippines as a major source of nitrogen for crops. However, we have a very limited understanding of its impact on soil fauna such as nematodes. In this study, we demonstrated the suitability of the microcosm set-up to assess chemical effects on nematode communities under controlled conditions and determined the effects of urea on nematode communities. Area of study: The soil samples were obtained from a relatively “less disturbed” field in Bukidnon, Central Mindanao and were taken for experimentation in a greenhouse at Premier Research Institute of Science and Mathematics (PRISM), Mindanao State University - Iligan Institute of Technology (MSU-IIT), Iligan City, Philippines. Material and Methods: The soil was collected and analysed for its physiological properties. The soil was then exposed to urea concentrations (0 mg/kg, 19.67 mg/kg, 39.33 mg/kg and 78.66 mg/kg) in a microcosm for 45 days. Nematodes were then collected and processed using a modified dish method. Main results: Firstly, the natural microcosms (without urea) showed that nematode abundance and the number of genera decreased by 28% and 35%, respectively. The results suggest that the current microcosm setup may still be useful in testing the effects of certain chemicals of interest. Secondly, no significant effects on the number of genera and diversity indices were observed with urea, except on the day 15 when nematode abundance was significantly higher at 39.33 mg/kg than at 19.67 mg/kg. Research highlights: This study shows that the above ecologically relevant urea concentrations had no negative impact on nematode community structure during the 45-day exposure.