The research team, led by Rojen Singh Thounaojam of Manipur University, spent the entirety of 2018 sampling earthworms and soils at two contrasting forest sites in the Imphal region. Site I was a reserved mixed forest in Imphal West district, while Site II was a community-protected mixed forest in Imphal East. Both sit within a subtropical monsoon climate that delivers an average annual rainfall of 1325.7 millimeters, with a wet season from June to October, a hot summer from March to May, and a cool, dry winter from November to February. The soils at both sites were sandy loam, and the vegetation included familiar subtropical trees such as Lithocarpus dealbatus, Gmelina arborea, Pinus kesiya, and Schima wallichii.

The sampling protocol was deliberately rigorous. Each month, the researchers demarcated six random plots of one square meter at each site, and within each plot they excavated four soil monoliths measuring 25 by 25 by 30 centimeters. Over the year, this yielded 72 quadrats per site, with earthworms extracted by digging and hand-sorting following the standard Tropical Soil Biology and Fertility method. Specimens were preserved in formalin and identified under stereo zoom microscopes using established taxonomic keys. Alongside the biological sampling, the team recorded soil temperature in situ each month, measured pH in soil-water suspensions, and determined moisture content gravimetrically.

What emerged from this year-long effort was a community profile that surprised the researchers. Site I harbored seven earthworm species belonging to six genera and four families, while Site II supported five species in four families. The Megascolecidae family dominated the species lists at both sites. Shannon diversity indices of 1.29 at Site I and 1.17 at Site II indicated modestly higher diversity at the reserved forest. But the headline result concerned the exotic component of the community: at Site I, exotic species made up more than 74 percent of the earthworm community, with P. corethrurus alone accounting for 62.37 percent. At Site II, the single exotic species present, P. corethrurus, constituted 38.65 percent of the community, second only to the native Drawida nepalensis at 45.89 percent.

The ecology of P. corethrurus helps explain its success. First described in 1857 by the German naturalist Fritz Müller from Santa Catarina State in Brazil, and believed to have originated in the Guiana Shield region of South America, the species is now one of the most widely distributed tropical earthworms on Earth. According to the Drilobase database, as of July 2025 it had been recorded in tropical, subtropical, and Mediterranean zones across dozens of countries on four continents. In India, it was first reported from Kerala in 1910, likely introduced through human activity associated with cassava or rubber plantations. It has since spread to nine of India’s fifteen agro-climatic zones and to eight states in Northeast India alone.

Several biological traits make this worm a formidable invader. It tolerates an exceptionally broad range of soil conditions and climates, reproduces continuously with high fecundity and hatching success, develops quickly, and can even reproduce by parthenogenesis, meaning a single individual can found a population without a mate. In the Manipur forests, the species showed remarkable spatial and temporal versatility: it was found throughout the year, in every season, and at soil depths of up to 30 centimeters, whereas most other species were confined to the upper 10 centimeters of soil and many appeared only during the rainy season. Notably, the researchers recorded P. corethrurus active at soil temperatures as low as 15 degrees Celsius, below the previously reported minimum of 17 degrees for other parts of Northeast India.

The statistical analysis reinforced the importance of climate in structuring these communities. Soil moisture and soil temperature showed significant positive correlations with every recorded species at both sites, with correlation coefficients generally ranging from about 0.69 to 0.86, while soil pH was negatively correlated with earthworm abundance. Earthworm populations peaked during the rainy season, when elevated moisture and moderate temperatures create ideal conditions for activity and reproduction. Earthworms breathe through their skin, so moisture is a critical constraint on their distribution, and the optimal soil temperature for the species recorded in this study fell between 20.21 and 24.26 degrees Celsius, within the broader 20 to 30 degree range reported for tropical and subtropical earthworms.

Why does the dominance of an exotic worm in an undisturbed forest matter? Earthworms are ecosystem engineers, and established populations of P. corethrurus have been shown elsewhere to alter soil physical structure, modify biogeochemical processes, and reshape plant and microbial communities. By accelerating leaf litter decomposition and mixing soil in the upper layers, invasive earthworms can strip away the litter layer, increase soil bulk density, and reduce soil carbon content, carbon-to-nitrogen ratios, and cation exchange capacity, ultimately degrading forest soil fertility. The density of P. corethrurus is often inversely correlated with the density of other earthworm species, and previous studies have documented the displacement of native earthworms following the establishment of exotic populations. The Manipur findings suggest a real risk that native species at these sites could decline over time.

Yet the story is not one of inevitable defeat for the natives. The native Drawida nepalensis maintained high population densities even in communities dominated by exotics, and it was the most abundant species at Site II, where natives predominated. A parallel pattern has been reported in pineapple plantations in West Tripura, where the native Drawida assamensis outcompeted P. corethrurus, apparently thanks to superior survival and competitive ability. Endogeic earthworms, which live within the soil rather than on its surface, are also known to be the most resistant ecological group to disturbance. These observations hint that some native lineages may possess the competitive arsenal to coexist with, or even resist, the invader, although the researchers caution that long-term coexistence may ultimately depend on how much habitat modification the exotic species causes.

How the worm reached these protected forests remains a question of pathways rather than capability. Earthworms disperse on their own less than 10 to 15 meters per year, so human-mediated transport is almost certainly responsible. Cocoons and worms can hitchhike in soil on vehicle tires, in potted plants, in streams and surface water, or on birds and mammals. In Manipur specifically, the authors point to a worrying and largely unregulated trend: the booming use of exotic earthworms, particularly Eisenia andrei and Eisenia fetida, for vermicomposting, with little ecological oversight or public awareness of the risks of escape and establishment. The team calls for immediate policy formulation, monitoring protocols, and public education to protect native soil biodiversity. As the invasion of P. corethrurus proceeds even in undisturbed forests, the study stands as a warning that no ecosystem, however pristine, is automatically safe from a determined, parthenogenetic, climate-tolerant invader moving quietly beneath our feet.

Subject of Research: Invasion of protected subtropical forests in Northeast India by the exotic earthworm Pontoscolex corethrurus

Article Title: Assessment of Pontoscolex corethrurus, an exotic earthworm, in contrasting protected subtropical forest habitats in North-East India

Article References: Thounaojam, R. S., Singh, K. B., Singh, T. B., Keisham, S., & Singh, T. B. (2025). Assessment of Pontoscolex corethrurus, an exotic earthworm, in contrasting protected subtropical forest habitats in North-East India. Discover Ecology, 1(1), Article 10. https://doi.org/10.1007/s44396-025-00010-z

Image Credits: AI Generated

DOI: 10.1007/s44396-025-00010-z

Keywords: Pontoscolex corethrurus, invasive species, earthworms, soil biodiversity, Manipur, Northeast India, Indo-Burma biodiversity hotspot, subtropical forest, soil ecology, ecosystem engineers, vermicomposting, species invasion

The research team, led by Phishet Sungtong and Daoroong Sungthong, compared conventional composting with vermicomposting, a mesophilic process in which the African nightcrawler earthworm Eudrilus eugeniae works alongside microbes to decompose organic matter. Each reactor contained a carefully balanced feedstock of cow manure and discarded cabbage at a ratio of 89:11 on a dry-weight basis, with some reactors receiving 7 grams of cut PLA/PBAT bag pieces, equivalent to 1 percent of the initial dry mass. The bags, collected from a campus café, were cut into 5 by 5 centimeter squares following the specimen preparation procedure of ISO 20200, the international standard for laboratory-scale disintegration testing. Twenty-eight independent reactors were prepared, with destructive sampling at days 15, 30, 60, 90, and 120.

The temperature story turned out to be central. Conventional composting initially peaked at 27 to 28 degrees Celsius before stabilizing near ambient levels, while vermicomposting held a strictly mesophilic profile of 24 to 26 degrees throughout, a range chosen to keep the earthworms alive and reproducing. Neither system reached the thermophilic phase of 58 degrees Celsius that defines industrial composting, and that matters enormously for PLA. The glass transition temperature of PLA sits around 56 to 63 degrees Celsius; below it, the polymer remains glassy, with stiff chains that resist water penetration and hydrolytic chain scission. PBAT, by contrast, with a glass transition near minus 35 degrees, stays rubbery at any composting temperature, yet its aromatic terephthalate segments remain stubbornly resistant to microbial enzymes regardless.

By day 120, the recovered plastic fragments told a nuanced tale. Vermicomposting achieved a mean disintegration of 59.91 percent, compared with 55.96 percent for conventional composting, a numerically higher result of nearly four percentage points, though the ranges overlapped and the difference was not statistically distinguishable. Notably, the vermicomposting range extended to 72.97 percent, higher than any single composting reactor achieved. The researchers attribute this edge to the combined action of earthworms and microbes: worms ingest and transport plastic fragments into the drilosphere, the biologically rich zone around their burrows, and their gut passage and castings expose the polymer to dense microbial communities in oxygen-limited microsites.

Spectroscopic evidence confirmed that the mass loss was not merely physical fragmentation. Attenuated total reflectance Fourier transform infrared spectroscopy revealed a pronounced decline in the absorbance of the ester carbonyl band near 1712 wavenumbers, dropping from 0.3304 at day zero to 0.1892 in composted and 0.3083 in vermicomposted samples, alongside a sharp decrease in the carbon-oxygen-carbon stretching band. These changes signal cleavage of the ester bonds that link the polymer chains, generating terminal hydroxyl and carboxylic acid groups that microbes can then assimilate through the tricarboxylic acid cycle into carbon dioxide, water, and biomass. Scanning electron microscopy showed the once bumpy, sponge-like surface progressively cracking, pitting, and peeling into layers, with rod-shaped cell-like structures colonizing the fracture grooves.

An intriguing metabolic twist emerged when the researchers compared the two systems chemically. The vermicomposting reactors received fresh frozen cabbage every 30 days to feed the worms, providing microbes with an abundant, easily digestible carbon source. Under carbon catabolite repression, microorganisms preferentially consume such favored substrates and suppress the synthesis of the extracellular depolymerases needed to attack recalcitrant plastic. The composting reactors, starved of new food after day 30, may have been driven by metabolic stress to upregulate polymer-degrading enzymes, using PLA/PBAT as an alternative carbon source. This may explain why the vermicomposted plastic showed a less pronounced reduction in ester absorbance despite its slightly greater mass loss.

Beyond the plastic itself, the study asked whether the resulting compost and vermicompost were safe and effective fertilizers. Both systems matured convincingly: the carbon-to-nitrogen ratio fell from 27.1 to between 16 and 20, meeting Thai agricultural standards, while cation exchange capacity nearly doubled, reflecting the formation of humic substances. Vermicompost proved the richer fertilizer, accumulating roughly twice the calcium of conventional compost, reaching 12.7 percent, thanks to the calciferous glands of earthworms excreting calcium carbonate in their castings, along with elevated potassium and sodium. Germination tests with mung bean seeds showed that phytotoxicity dropped rapidly, with the germination index exceeding 100 percent by day 15 and reaching 136 percent in vermicompost at day 120, compared with 101 percent for compost.

Heavy metal analysis added a cautionary note. Cadmium and lead remained below detection limits in all systems, and chromium traced back to the cabbage feedstock rather than the plastic. However, nickel appeared exclusively in the bioplastic-amended reactors, peaking at 37.78 milligrams per kilogram in vermicompost, likely derived from nickel oxide additives used in PLA manufacturing to improve tensile strength and confer antimicrobial properties. The researchers warn that lactic acid released during PLA degradation could locally acidify the matrix and mobilize nickel into plant-available forms, a dynamic that warrants environmental monitoring even though all measured values fell below Thai regulatory limits.

Bacterial community sequencing of the day-120 samples revealed sharply different microbial worlds. Compost samples hosted greater diversity, with Shannon indices above 9 and over a thousand observed amplicon sequence variants, dominated by Pseudomonadota, Bacillota, and Chloroflexota, with genera such as Lysinibacillus and Litorilinea prominent. Vermicompost samples were less diverse but enriched in Bacillota and Bacteroidota, including anaerobe-associated taxa such as Clostridium and Romboutsia, plausibly reflecting oxygen-limited microsites in earthworm guts and moist organic particles. Both Lysinibacillus and Clostridium are recognized plastisphere colonizers capable of secreting esterases and lipases that cleave polyester bonds, making them candidates for further investigation, though the authors are careful to note that their presence at day 120 does not prove direct involvement in plastic degradation.

The study’s practical message is clear: compostable does not mean gone. Under mesophilic conditions, PLA/PBAT bags lost more than half their mass in 120 days but remained incompletely disintegrated, and the bioplastic-amended compost actually failed the Thai agricultural standard precisely because macroscopic plastic fragments persisted. The authors suggest extending treatment duration, maintaining continuous thermophilic conditions, introducing specific polymer-degrading microorganisms, or employing advanced in-vessel reactors with real-time temperature and moisture monitoring to push degradation to completion. They also acknowledge the limits of their design, including single reactors for most sampling times and endpoint-only microbial analysis, which constrain statistical inference. Until such improvements arrive, the study offers consumers and waste managers a grounded benchmark: earthworms give compostable plastics a modest but measurable boost, yet the thermophilic heat of industrial composting remains the gold standard for making these materials truly vanish.

Subject of Research: Disintegration of PLA/PBAT bioplastic blends during composting and vermicomposting and the resulting fertilizer quality and bacterial communities

Article Title: Lab-scale comparison of PLA/PBAT disintegration in composting and vermicomposting: fertilizer quality, phytotoxicity, and day-120 bacterial community profiles

Article References: Sungtong, P., & Sungthong, D. (2026). Lab-scale comparison of PLA/PBAT disintegration in composting and vermicomposting: fertilizer quality, phytotoxicity, and day-120 bacterial community profiles. Environmental Challenges, 25, Article 101664. https://doi.org/10.1016/j.envc.2026.101664

Image Credits: AI Generated

DOI: 10.1016/j.envc.2026.101664

Keywords: PLA/PBAT, biodegradable plastics, composting, vermicomposting, earthworms, Eudrilus eugeniae, disintegration, FTIR, scanning electron microscopy, bacterial community, compost quality, heavy metals

The recognition arrives at a moment when soil ecology is moving from the margins of biology toward the center of conversations about climate, food security and biodiversity loss. Soils are among the most species-rich habitats on Earth, and the organisms that inhabit them drive processes on which nearly all terrestrial life depends. Ashwood’s book takes readers on a vertical descent through the soil profile, beginning at the surface with plant litter and ending in the deep subsoil, introducing along the way what he describes as some of the world’s strangest inhabitants and the essential roles they play in nutrient cycling, agriculture and carbon storage.

Ashwood is a soil scientist with a research background in earthworm ecology who quickly broadened his interests to encompass the full diversity of soil invertebrates. He is also a passionate macrophotographer, and that visual obsession with the hidden majority of life runs through his approach to writing. In response to the award, he said he really enjoys science communication, telling anyone who will listen about the wonders of life belowground, often with the help of his macrophotography, and that this strong desire to pass on his love of soil ecology to as broad an audience as possible is what ultimately led him to write the book.

The judging panel emphasized the book’s success in making an invisible world legible. Hefin Jones, one of the judges for the prize, described it as an engaging and accessible exploration of soil biodiversity and its importance to ecosystems and human society, noting that its major strength lies in Ashwood’s ability to communicate complex ecological processes through vivid descriptions of the largely unseen organisms that sustain soils. Fellow judge Ken Thompson said there are jaw-dropping facts on every page and that Ashwood’s narrative is greatly enlivened by his personal encounters with soil life, adventures that lend the text an immediacy and excitement making it an entertaining read.

Understanding why a popular book on soil deserves ecology’s book prize requires appreciating just how much is happening beneath a single step. A handful of grassland soil can contain billions of microorganisms and hundreds of invertebrate species spanning bacteria, fungi, protists, nematodes, mites, springtails, enchytraeids, earthworms and insect larvae. These organisms form a food web that decomposes organic matter, restructures mineral particles, regulates the flow of water and gases, and determines how much carbon is locked away versus released back to the atmosphere. Decomposition alone, the sequential breakdown of dead plant material by fungi, bacteria and their invertebrate grazers, is the process that returns nutrients locked in litter to forms that plant roots can absorb, effectively powering every forest and grassland on the planet.

The structural engineers of this underworld are the ecosystem engineers, a term most famously associated with earthworms, the group in which Ashwood began his research career. Earthworms ingest mineral soil and organic debris, mix them in their guts, and excrete casts that alter soil aggregation, porosity and microbial activity. Their burrows create macropores that channel rainfall into the profile, reducing surface runoff and erosion while giving roots low-resistance pathways to depth. Different ecological groups of earthworms occupy distinct niches, from litter-dwelling surface species to deep-burrowing anecic forms that pull organic matter down into permanent vertical burrows, and their combined activity can transform the physical architecture of an entire soil profile within years.

Below the reach of most earthworm activity lies the subsoil, the zone Ashwood’s book treats as its final destination. Subsoils are typically lower in organic matter and oxygen but enormously important as reservoirs of mineral nutrients, as sites of long-term carbon stabilization, and as habitats for specialized microbial communities adapted to scarcity. Carbon that reaches depth through leaching, root death or the transport of fine particulate organic matter can persist for centuries to millennia when protected on mineral surfaces or inside stable aggregates. The organisms that govern whether carbon is respired to carbon dioxide or stabilized in place are therefore directly implicated in one of the central feedbacks of the global climate system, which is a large part of why soil biodiversity has become a priority for researchers and policymakers alike.

Agriculture sits at the sharp end of these processes. Soil fauna and microbes underpin the fertility of farmland by mineralizing nitrogen and phosphorus, suppressing pathogens, improving water-holding capacity and building the aggregate structure that resists compaction. Intensive tillage, monoculture and agrochemical pressure can simplify belowground communities, and a growing body of research links that simplification to declining soil health. Books that translate this science for a general audience perform a function that technical literature cannot, building the public understanding and political will needed to treat soil as a living resource rather than an inert growing medium. The Marsh Ecology Book of the Year has a history of rewarding exactly this kind of influential communication, and the judges’ comments suggest Ashwood’s combination of rigorous content and personal narrative continues that tradition.

The prize itself reflects an unusual and durable model of partnership between a learned society and a charitable funder. The Marsh Charitable Trust supports a wide range of recognition schemes across conservation, culture and the arts, and 2026 marks the 30th anniversary of its collaboration with the British Ecological Society. Awarded to the book judged to have exerted the greatest influence on the science of ecology in any two-year period, the Marsh Ecology Book of the Year has become one of the most visible honors for ecological writing, and The World Beneath Our Feet is its 21st winner. Ashwood will receive the award in person during a ceremony at the BES Annual Meeting, which runs from 14 to 17 December 2026 in Birmingham and will bring together more than 1,500 ecologists to discuss the latest advances across the whole discipline.

For a field whose subject matter is literally underfoot, soil ecology has long struggled for visibility against charismatic megafauna and distant ecosystems, which makes this award more than a ceremonial pat on the back. It signals that the scientific community regards the communication of belowground biology as central to ecology’s public mission at a time when soils are being lost to erosion, degradation and sealing far faster than they can form. Ashwood’s descent from litter layer to subsoil offers readers a narrative structure for a world they will never see with the naked eye, populated by organisms whose quiet work cycles nutrients, feeds crops and stores carbon. If the judges are right that jaw-dropping facts crowd every page, the book may do for the soil what earlier classics of nature writing did for oceans and rainforests: make the invisible both vivid and worth fighting for. The World Beneath Our Feet is published by Hodder Press, with cover design by Holly Ovenden.

Subject of Research: Soil ecology and the recognition of popular science writing on soil biodiversity through the British Ecological Society's Marsh Ecology Book of the Year award

Article Title: The World Beneath Our Feet wins the British Ecological Society Book of the Year 2026

Article References: The World Beneath Our Feet wins the British Ecological Society Book of the Year 2026. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: soil ecology, soil biodiversity, British Ecological Society, Marsh Ecology Book of the Year, Frank Ashwood, earthworms, nutrient cycling, carbon storage, decomposition, ecosystem engineers, science communication, subsoil

The study was designed to address a persistent gap in soil ecology. Although many investigations have examined how fertilization affects individual groups of soil organisms, comparatively few have traced the consequences across the entire food web, spanning microbes at the base to earthworms near the top, and fewer still have done so over a time frame long enough to capture the slow, cumulative changes that define soil health. To fill that gap, a team of researchers led by first and corresponding author Professor Yunfeng Chen of the Hubei Academy of Agricultural Sciences compared four long-term treatments: chemical fertilizer supplying nitrogen, phosphorus and potassium, known as NPK; organic manure alone; a combined treatment of manure plus NPK; and an unfertilized control plot that served as the experimental baseline.

The measurement strategy was deliberately broad. Rather than tracking a single indicator organism, the team quantified biomass or abundance across key taxonomic and functional groups, including microorganisms, protozoa, nematodes, mites, collembolans, enchytraeids and earthworms. They also calculated nematode ecological indices, a set of established metrics that soil ecologists use to infer the structure and maturity of soil food webs. Together, these measurements allowed the researchers to evaluate the relative strength of two competing regulatory forces: bottom-up control, in which the availability of resources such as organic carbon and nutrients determines how many organisms higher trophic levels can support, and top-down control, in which predators and higher consumers suppress or structure the populations below them.

The headline finding was unambiguous. Long-term fertilization increased the inputs of resources entering the soil, and that surge in resources enhanced most of the functional groups the team measured. Fertilized plots supported larger and more complex communities than the unfertilized control, confirming that sustained nutrient management is a powerful lever for shaping the living architecture of agricultural soils. But the differences among fertilization strategies proved just as consequential, and here the organic treatments stood out clearly.

Manure alone and the combined manure-plus-NPK treatment outperformed pure chemical fertilizer across most groups. When the researchers expressed these gains as relative increases compared with the NPK treatment, the manure plots showed improvements ranging from 20.69 to 972.52 percent, with an average of 241.62 percent, while the combined plots ranged from 26.55 to 792.30 percent, averaging 189.02 percent. Those are not marginal differences; they represent order-of-magnitude shifts in the abundance of some soil organisms. The practical implication is that organic amendments, whether applied alone or alongside mineral fertilizers, deliver substantially more nourishment to the soil food web than chemical fertilizer alone.

Interestingly, the manure-only and combined treatments did not differ significantly from each other. The researchers attribute this convergence to high soil fertility: once fertility reaches a sufficiently high level, the distinction between the two organic approaches diminishes, and both support similarly rich communities. In other words, the food web appears to saturate, and beyond a certain threshold of resource abundance, adding mineral fertilizer on top of manure yields little additional biological benefit even though it may still matter for crop nutrition.

The evidence for bottom-up regulation was strong and came from multiple independent lines. Functional groups showed positive correlations with one another, a pattern consistent with resources flowing upward through the web and lifting every level together rather than predators imposing their own structure from above. The enrichment index, a nematode-based metric that signals an abundance of opportunistic, resource-responsive organisms, rose by 51.27 percent under manure and 28.49 percent under the combined treatment relative to chemical fertilizer alone. The enrichment footprint, a complementary measure that captures the cumulative enrichment signal across the food web, increased even more dramatically, by 11.80 percent under manure and 47.17 percent under the combined treatment relative to NPK.

To synthesize these patterns into a causal framework, the team employed partial least squares path modeling, a statistical technique well suited to disentangling direct and indirect pathways among correlated variables. The modeling confirmed what the correlations and indices had suggested: bottom-up forces predominantly determined both the structure and the total biomass of the soil food web. Resource availability, shaped by decades of fertilization, was the dominant driver, while top-down influences played a comparatively minor role in this system. For a rice–wheat rotation, where flooded and aerobic phases alternate and organic matter dynamics are complex, this finding provides a clear conceptual anchor for future soil management research.

The implications extend well beyond the experimental plots. Soil food webs underpin essential ecosystem services, including decomposition, nutrient mineralization, suppression of plant pathogens and the maintenance of soil structure. A food web enriched through bottom-up channels is, in effect, a soil with greater biological capacity to sustain crop productivity over time. The study suggests that sustained organic inputs, particularly when integrated with mineral fertilizers, effectively enhance both the complexity and the size of the soil food web primarily through this bottom-up regulatory mechanism. For farmers and policymakers weighing the trade-offs between organic and conventional inputs, the results add a biological argument in favor of manure-based strategies, whether used alone or in combination with chemical fertilizer.

The research also carries a cautionary note for the long term. Because the experiment spanned thirty years, it captured changes that short-term studies inevitably miss, including the slow accumulation of soil organic matter and the gradual response of larger, slower-reproducing organisms such as earthworms and enchytraeids. The authors’ conclusion is that fertilization is not merely a plant nutrition tool but a food-web engineering instrument, and that its effects compound over decades. As agriculture worldwide faces pressure to maintain yields while restoring degraded soils, this long-term evidence from a major cereal rotation offers a template: feed the base of the soil food web, and the rest of the web, along with the services it provides, is likely to follow.

Subject of Research: Long-term effects of chemical and organic fertilization on the soil food web in a rice–wheat cropping system

Article Title: Long-term fertilization enriches soil food web mainly through bottom-up regulation in a rice–wheat cropping system

Article References: Long-term fertilization enriches soil food web mainly through bottom-up regulation in a rice–wheat cropping system. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: soil food web, long-term fertilization, rice–wheat rotation, bottom-up regulation, manure, NPK fertilizer, nematodes, earthworms, soil fertility, enrichment index, agroecology, soil biodiversity

The new study, published in the open-access journal Microplastics and Nanoplastics, focused on Eisenia fetida, the composting earthworm that has become the standard model organism for terrestrial ecotoxicology. Rather than examining gross measures of animal health such as weight change, reproduction or survival, the researchers zoomed in on the cellular level, specifically on coelomocytes, the immune cells that circulate in the coelomic fluid of earthworms and perform functions analogous to those of white blood cells in humans. These cells come in two principal flavors: amoebocytes, which patrol tissues and engulf foreign material, and eleocytes, which are derived from chloragocytes and contribute to immunity and nutrient transport.

To test how plastic ingestion reshapes this immune cell population, the team exposed earthworms outside of soil for six days to food pellets under three conditions. One group received pellets with no microplastic particles at all, serving as the mock-treated control. A second group received food containing 10 percent by weight of pure polystyrene microplastic particles ranging from 25 to 75 micrometers in size. A third group received the same polystyrene diet but supplemented with 0.5 percent by weight of Irgafos 168, a phosphite antioxidant widely used in plastic manufacturing to prevent polymer degradation during processing. This additive-design decision is what gives the study its sharpest edge, because most laboratory toxicity tests rely on pristine, additive-free plastic spheres that bear little resemblance to the weathered, chemically loaded particles found in real environments.

One of the study’s most notable methodological achievements was the use of a non-invasive technique to harvest the earthworms’ immune cells. Instead of sacrificing the animals, the researchers induced them to expel coelomic fluid containing coelomocytes, allowing repeated sampling from the same individuals and reducing experimental variability. The recovered cells were then analyzed by flow cytometry, a laser-based technique that can distinguish and count thousands of individual cells per second based on their size, internal complexity and fluorescent labeling. This allowed the team to quantify not just the total number of immune cells, but their viability and the relative proportions of amoebocytes and eleocytes within each sample.

The first key finding was deceptively reassuring: the total number of cells isolated from the worms was not significantly affected by microplastic ingestion. In other words, earthworms eating polystyrene did not simply produce fewer coelomocytes overall. But when the researchers looked at cell viability, a different picture emerged. Earthworms that had ingested pure polystyrene particles showed significantly reduced coelomocyte viability compared with the mock-treated controls. The cells were still there, but a larger fraction of them were dead or dying, a sign that something in the plastic-exposed animals was harming the immune cells themselves.

The damage grew worse when the plastic carried its industrial additive. In worms fed the Irgafos 168-containing polystyrene, the number of living cells per milligram of body fresh weight dropped even further than in the pure-polystyrene group, indicating that the additive amplified the toxicity of the particles. The researchers backed up this in-vivo result with ex vivo assays, exposing isolated coelomocytes directly to the two particle types in the laboratory. Those experiments independently confirmed that particles supplemented with Irgafos 168 were more toxic to the cells than the pure polystyrene particles, strengthening the argument that the chemical additive, not merely the plastic polymer, drives part of the harm.

Why would an antioxidant designed to protect plastics from degradation be harmful to living cells? Irgafos 168 belongs to a class of phosphite compounds that can oxidize over time into phosphate derivatives, and laboratory studies have suggested that both the parent compound and its degradation products can interact with cell membranes and intracellular signaling. Because additives are not covalently bound to the polymer matrix, they can leach out of plastic particles once the material enters the environment and encounters warmth, digestive fluids or microbial action. When an earthworm swallows a contaminated particle, its gut becomes a reaction vessel in which these compounds can be released at close range to the very tissues responsible for defense and nutrient absorption.

Beyond the viability data, the study documented that ingestion of microplastic particles and their additives caused measurable shifts in the distribution of immune cell subpopulations compared with mock-treated worms. Changes in the balance between amoebocytes and eleocytes are more than a bookkeeping detail; they point to a reprogramming of the immune system itself. Amoebocytes are the earthworm’s first line of cellular defense against pathogens, phagocytosing bacteria and encapsulating foreign bodies, while eleocytes participate in immune regulation and reflect the metabolic state of the coelomic cavity. A skewed ratio between these populations could impair an earthworm’s ability to fight off infections, respond to other pollutants, or maintain normal physiological function, even in the absence of visible illness.

The ecological implications extend well beyond a single species in a laboratory feeding trial. Eisenia fetida serves as a surrogate for the broader community of soil-dwelling organisms that face chronic exposure to plastic contamination. Microplastic particles are now documented in agricultural soils across the globe, introduced through sewage sludge, plastic mulch films, irrigation water and the atmospheric deposition of fragmenting debris. Earthworms ingest soil particles indiscriminately as they feed, which means that plastic fragments in the 25 to 75 micrometer range fall squarely within the size class these animals routinely consume. If chronic exposure erodes immune competence in wild populations, soils could become more vulnerable to pathogen outbreaks, and the decomposition processes that underpin nutrient cycling could slow.

The study also carries a broader warning for how microplastic toxicity research is conducted. A growing body of literature has argued that testing pristine, spherical, additive-free particles systematically understates the risks posed by environmental plastics, which arrive pre-loaded with stabilizers, plasticizers, pigments and flame retardants. By deliberately including Irgafos 168 in their experimental design and demonstrating enhanced toxicity, the Bayreuth team has provided concrete experimental support for that argument. The findings suggest that regulatory assessments of microplastic risk, which often focus on the polymer alone, may need to account for the full chemical package that real-world particles carry. For now, the image that emerges from this research is a sobering one: the earthworms that quietly sustain the world’s soils are swallowing our plastic waste, and the chemical hitchhikers riding on that waste appear to reach deep into their cellular defenses, killing the very immune cells that would normally keep them safe.

Subject of Research: Effects of microplastic particle ingestion and plastic additives on earthworm immune cells

Article Title: Microplastic ingestion induces changes in coelomocyte composition of Eisenia fetida

Article References: Fritsche, J. K., Döring, M. V. R., Mauel, A., Senker, J., Feldhaar, H., Freitag, R., & Jérôme, V. (2026). Microplastic ingestion induces changes in coelomocyte composition of Eisenia fetida. Microplastics and Nanoplastics. https://doi.org/10.1186/s43591-026-00224-2

Image Credits: AI Generated

DOI: 10.1186/s43591-026-00224-2

Keywords: microplastics, polystyrene, Irgafos 168, Eisenia fetida, coelomocytes, immune cells, flow cytometry, ecotoxicology, soil health, plastic additives, earthworms, environmental toxicity