Effects of photoaging on structure and characteristics of biofilms on microplastic in soil: Biomass and microbial community

Understanding of the environmental behaviors of microplastics is limited by a lack of knowledge about how photoaging influences biofilm formation on microplastics in soil. Here, original microplastics (OMPs) and photoaged-microplastics (AMPs) were incubated in soil to study the effect of photoaging on formation and characteristics of biofilm on the poly (butylene succinate) microplastics. Because photoaging decreased the hydrophobicity of the microplastic, the biomass of biofilm on the OMPs was nearly twice that on the AMPs in the early stage of incubation. However, the significance of the substrate on biomass in the biofilm declined as the plastisphere developed. The bacterial communities in the plastisphere were distinct from, and less diverse than, those in surrounding soil. The dominant genera in the OMPs and AMPs plastispheres were Achromobacter and Burkholderia, respectively, indicating that photoaging changed the composition of the bacterial community of biofilm at the genus level. Meantime, photoaging decreased the complexity and stability of the plastisphere bacterial community network. Results of Biolog ECO-microplate assays and functional prediction from amplicons showed that photoaging treatment enhanced the carbon metabolic capacity of the microplastic biofilm. This study provides new insights into the formation of plastispheres in soil.

Low-density polyethylene enhances the disturbance of microbiome and antibiotic resistance genes transfer in soil-earthworm system induced by pyraclostrobin

Non-antibiotic chemicals in farmlands, including microplastics (MPs) and pesticides, have the potential to influence the soil microbiome and the dissemination of antibiotic resistance genes (ARGs). Despite this, there is limited understanding of the combined effects of MPs and pesticides on microbial communities and ARGs transmission in soil ecosystems. In this study, we observed that low-density polyethylene (LDPE) microplastic enhance the accumulation of pyraclostrobin in earthworms, resulting in reduced weight and causing severe oxidative damage. Analysis of 16 S rRNA amplification revealed that exposure to pyraclostrobin and/or LDPE disrupts the microbial community structure at the phylum and genus levels, leading to reduced alpha diversity in both the soil and earthworm gut. Furthermore, co-exposure to LDPE and pyraclostrobin increased the relative abundance of ARGs in the soil and earthworm gut by 2.15 and 1.34 times, respectively, compared to exposure to pyraclostrobin alone. It correlated well with the increasing relative abundance of genera carrying ARGs. Our findings contribute novel insights into the impact of co-exposure to MPs and pesticides on soil and earthworm microbiomes, highlighting their role in promoting the transfer of ARGs. This knowledge is crucial for managing the risk associated with the dissemination of ARGs in soil ecosystems.

TRIAD method to assess ecological risks of contaminated soils in abandoned mine sites

Site-specific soil ecological risk assessment is important for protecting soil ecosystems because it reflects the environmental factors at the site to detect ecological risks and develop risk management measures. This study assessed the ecological risks from chemical pollutants in abandoned mine sites using the TRIAD approach, evaluating its overall applicability, including the tiered system of assessment. A site-specific soil ecological risk assessment was conducted for five abandoned mine sites (Sites 1-4 and R, the reference site); integrated risks (IRs) for each site were calculated. Our results of the Tier 2 assessment showed that IRs at Sites 1-4 were 0.701, 0.758, 0.840, and 0.429, respectively. The IR classification was moderate, high, high, and low risk, in that order for Sites 1-4, the same as that for Tier 1. The IR had more varied analyses, emphasizing the significance of conducting higher tiered analyses under TRIAD while maintaining a balance between soil ecosystem protection and socioeconomic costs. Multiple analyses reduced the uncertainty of IR, thus enabling efficient risk management decision-making to protect soil ecosystems. Our study provides a basis for using the TRIAD for soil assessment and establishing policies for site-specific soil ecological risk assessments.

Micro- and nanoplastics in soil: Linking sources to damage on soil ecosystem services in life cycle assessment

Soil ecosystems are crucial for providing vital ecosystem services (ES), and are increasingly pressured by the intensification and expansion of human activities, leading to potentially harmful consequences for their related ES provision. Micro- and nanoplastics (MNPs), associated with releases from various human activities, have become prevalent in various soil ecosystems and pose a global threat. Life Cycle Assessment (LCA), a tool for evaluating environmental performance of product and technology life cycles, has yet to adequately include MNPs-related damage to soil ES, owing to factors like uncertainties in MNPs environmental fate and ecotoxicological effects, and characterizing related damage on soil species loss, functional diversity, and ES. This study aims to address this gap by providing as a first step an overview of the current understanding of MNPs in soil ecosystems and proposing a conceptual approach to link MNPs impacts to soil ES damage. We find that MNPs pervade soil ecosystems worldwide, introduced through various pathways, including wastewater discharge, urban runoff, atmospheric deposition, and degradation of larger plastic debris. MNPs can inflict a range of ecotoxicity effects on soil species, including physical harm, chemical toxicity, and pollutants bioaccumulation. Methods to translate these impacts into damage on ES are under development and typically focus on discrete, yet not fully integrated aspects along the impact-to-damage pathway. We propose a conceptual framework for linking different MNPs effects on soil organisms to damage on soil species loss, functional diversity loss and loss of ES, and elaborate on each link. Proposed underlying approaches include the Threshold Indicator Taxa Analysis (TITAN) for translating ecotoxicological effects associated with MNPs into quantitative measures of soil species diversity damage; trait-based approaches for linking soil species loss to functional diversity loss; and ecological networks and Bayesian Belief Networks for linking functional diversity loss to soil ES damage. With the proposed conceptual framework, our study constitutes a starting point for including the characterization of MNPs-related damage on soil ES in LCA.

Soil microbes: a natural solution for mitigating the impact of climate change

Soil microbes are microscopic organisms that inhabit the soil and play a significant role in various ecological processes. They are essential for nutrient cycling, carbon sequestration, and maintaining soil health. Importantly, soil microbes have the potential to sequester carbon dioxide (CO2) from the atmosphere through processes like carbon fixation and storage in organic matter. Unlocking the potential of microbial-driven carbon storage holds the key to revolutionizing climate-smart agricultural practices, paving the way for sustainable productivity and environmental conservation. A fascinating tale of nature's unsung heroes is revealed by delving into the realm of soil microbes. The guardians of the Earth are these tiny creatures that live beneath our feet and discreetly work their magic to fend off the effects of climate change. These microbes are also essential for plant growth enhancement through their roles in nutrient uptake, nitrogen fixation, and synthesis of growth-promoting chemicals. By understanding and managing soil microbial communities, it is possible to improve soil health, soil water-holding capacity, and promote plant growth in agricultural and natural ecosystems. Added to it, these microbes play an important role in biodegradation, bioremediation of heavy metals, and phytoremediation, which in turn helps in treating the contaminated soils. Unfortunately, climate change events affect the diversity, composition, and metabolism of these microbes. Unlocking the microbial potential demands an interdisciplinary endeavor spanning microbiology, ecology, agronomy, and climate science. It is a call to arms for the scientific community to recognize soil microbes as invaluable partners in the fight against climate change. By implementing data-driven land management strategies and pioneering interventions, we possess the means to harness their capabilities, paving the way for climate mitigation, sustainable agriculture, and promote ecosystem resilience in the imminent future.

Current progress on fluoride occurrence in the soil environment: Sources, transformation, regulations and remediation

Fluorine is a halogen element widely distributed in nature, but due to excessive emissions from industrial manufacturing and agricultural production, etc., the soil is over-enriched with fluoride and the normal growth of plants is under stress, and it also poses a great threat to human health. In this review, we summarized the sources of fluoride in soil, and then analyzed the potential mechanisms of fluoride uptake in soil-plant systems. In addition, the main influences of soil ecosystems on plant fluoride uptake were discussed, soil management options to mitigate fluoride accumulation in plants were also summarized. The bioremediation techniques were found to be a developmental direction to improve fluoride pollution. Finally, we proposed other research directions, including fluoride uptake mechanisms in soil-plant systems at the molecular expression levels, development of visualization techniques for fluoride transport in plants, interactions mechanisms between soil microhabitats and plant metabolism affecting fluoride uptake, as well as combining abiotic additives, nanotechnology and biotechnology to remediate fluoride contamination problems.

Polyethylene and polyvinyl chloride microplastics promote soil nitrification and alter the composition of key nitrogen functional bacterial groups

Microplastics (MPs) contamination in soils seriously threatens agroecosystems globally. However, very few studies have been done on the effects of MPs on the soil nitrogen cycle and related functional microorganisms. To assess MP's impact on the soil nitrogen cycle and related functional bacteria, we carried out a one-month soil incubation experiment using typical acidic soil. The soil was amended with alfalfa meal and was spiked with 1% and 5% (mass percentage) of low-density polyethylene (LDPE) and polyvinyl chloride (PVC) MPs. Our results showed that both LDPE and PVC addition significantly increased soil nitrification rate and nitrate reductase activity, which could further promote soil denitrification. The relative abundance of diazotrophs, ammonium oxidizing, and denitrifying bacterial groups were significantly altered with MPs addition. Moreover, the MPs treatments greatly enhanced denitrifying bacteria richness. Redundancy analysis showed that nitrate reductase activity was the most significant factor affecting the soil functional bacterial community. Correlation analysis shows that Nitrosospira genus might be for the improvement of soil nitrification rate. Our results implied that MPs exposure could significantly affect the soil nitrogen cycling in farmland ecosystems by influencing essential nitrogen functional microorganisms and related enzymatic activities.

Species sensitivity distributions of micro- and nanoplastics in soil based on particle characteristics

Micro- and nanoplastics are released into the soil through various anthropogenic activities; however, research on ecological risk assessment (ERA) of soil microplastics is limited. In this study, the species sensitivity distributions (SSDs) of representative groups of soil biota were analyzed to determine their sensitivity to microplastic properties. A total of 411 datasets from apical endpoint data within 74 studies were classified and utilized in SSD estimation. The hazardous concentrations for 5% of species for microplastics was 88.18 (40.71-191.00) mg/kg soil. It has been established that small-sized microplastics are more toxic to soil organisms than larger microplastics. Most microplastics were spherical and polystyrene, exhibiting the most adverse effects among all the microplastic types assessed herein. The results suggest that physical characteristics of microplastics are important toxicity determinants in soil ecosystems. Given the potential for adverse environmental effects, further effective management strategies should urgently be employed in these areas. This study provided an integrated perspective of microplastic ecotoxicity in soil. In addition, SSDs were estimated using larger datasets and for more species than in previous studies. This is the first study to consider microplastic properties for estimating SSD.

Global meta-analysis reveals differential effects of microplastics on soil ecosystem

A large number of individual studies and meta-analyses have shown that microplastics (MPs) affect soil ecosystems. However, the effects of different concentrations and types of MPs on soil ecosystem are still unclear. Here, a comprehensive meta-analysis was performed to examine the responses of 19 variables, associated with soil properties, microbes, enzymes, and fauna, to MPs, based on 114 peer-reviewed studies. The results showed that the addition of MPs significantly reduced the soil organic carbon (SOC), total nitrogen (TN), NH₄⁺-N, pH, and diversity of bacteria, and increased the dissolved organic carbon (DOC), diversity of fungi and enzyme activities, especially enzymes related to the biogeochemical cycle. We further discussed that soil MPs exerted negative effects on soil fauna, including survival, growth, and reproduction, and that the concentration of MPs, rather than the type, was the biggest driving factor causing the toxicity of MPs affecting soil animals. More importantly, the concentrations of MPs were the main factor affecting the DOC, TN, NO₃^--N, total phosphorus (TP), available phosphorus (AP), and diversity of fungi, whereas the types of MPs were the main factors reflected in the SOC, NH₄⁺-N, pH, diversity of bacteria, and enzyme activities. This study aimed to evaluate the response of soil ecosystems to the different concentrations and types of MPs, and the largest driving factor for the toxicity of MPs.

Urbanization-land-use interactions predict antibiotic contamination in soil across urban-rural gradients

Antibiotics ubiquitously occur in soils and pose a potential threat to ecosystem health. Concurrently, urbanization and land-use intensification have transformed soil ecosystems, but how they affect antibiotic contamination remain largely unknown. Therefore, we profiled a broad-scale pattern of antibiotics in soil from agricultural lands and green spaces across urbanization gradients, and explored the hypothetical models to verify the effects of urbanization and land-use intensity on antibiotic contamination. The results showed that antibiotic concentrations and seasonality were higher in agricultural soil than in green spaces, which respectively showed linear or hump-shaped declines along with the increasing distance to urban centers. However, the response of antibiotic pollution to land-use intensity depended strongly on the urbanization level. More importantly, interactions between urbanization and land-use explained, on average, 59.6 % of the variation in antibiotic concentrations in soil across urbanization gradients. The proposed interactions can predict the non-linear changes in soil vulnerability to antibiotic contamination. Our study revealed that the urbanization can modulate the effects of land-use intensity on antibiotic concentration and seasonality in the soil environment, and that there is high stress on peri-urban soil ecosystems due to ongoing land-use changes arising from rapid urbanization processes.

Mobility indexes of Cu, Pb, and Zn in soil ecosystems with various levels of metal contamination (in Poland)

The aim of the study was to investigate and compare the soils of three groups of grassland ecosystems with varying degrees of heavy metal (Cu, Pb, and Zn) pollution as well as estimating of mobility on the basis of calculated mobility indexes (MI) expressed as a percentage of the EDTA-extracted forms of metals in their total content. A total of 55 surface soil samples were collected from various areas of Poland: urban soils, rural soils, and soils along communication routes. Heavy metal concentrations were determined in solutions after wet mineralization (using a mixture of acids) by atomic absorption spectrometry (AAS) with flame atomization. To isolate the mobile forms of metals in soils, a one-step extraction method was used with 0.05-M EDTA solution. The ranges of Cu, Pb, and Zn concentrations in soils were varied, respectively: 6.7-47.6, 61.1-563.9, and 86.4-644.5 mg·kg^-1 (A); 5.7-39.8, 13.56-45.71, and 16.3-119.6 mg·kg^-1 (B); and 1.0-195.8, 19.2-310.2, and 27.4-894.1 mg·kg^-1 (C). The average values of mobility indexes of Cu, Pb, and Zn were at the level of 40.9, 33.5, and 22.2% (A); 23.2, 27.1, and 25.9% (B); and 37.5, 34.3, and 30.7% (C). Studies have shown that metals derived from anthropogenic sources are characterized by greater mobility compared to metals of natural origin (lithological associated with the ground). The inclusion of metal mobility indices in the environmental monitoring strategy may minimize errors in assessing the actual risk associated with the potential uptake of these metals by plants and incorporation into circulation.

The transport of microplastics by ants cannot be neglected in the soil ecosystem

Microplastics (MPs) are widespread in soils and continue to migrate in response to many abiotic and biotic factors. Although some studies have explored the effects of abiotic factors (e.g., wind and water) on MP migration and distribution, there is little information on the effects of biotic factors, especially soil fauna, on this process. Ants are among the most abundant fauna on Earth and play an important role in ecosystem health. Here, we tested whether ants could transport low-density polyethylene (LDPE) MPs in the field. We also investigated the effects of ants (Pheidole sp.) on the removal rates and distribution of LDPE MPs in the laboratory compared to other potential field materials (leaf fragments and tiny stones). We found that, in the field, two ant species (Pheidole sp. and Paratrechina sp.) could actively carry LDPE MPs; the mean removal distance was 75.34 ± 4.05 cm, and the curve had a long tail extending to 140 cm. In the laboratory, the mean number of removed leaf fragments and LDPE MPs was significantly greater than that of removed tiny stones. After 14 days, the proportions of LDPE MPs, leaf fragments, and tiny stones removed into the nests by ants were 15.8%, 19.15%, and 3.3%, respectively. The proportions of LDPE MPs in the original position (not removed by ants), inside the nests, and outside the nests were 18.4%, 15.8%, and 65.8%, respectively. These results indicate that ants play an important, but neglected, role in the transport and distribution of MPs in soil ecosystems. Given the abundance and diversity of ants worldwide, the ant-mediated transport of MPs may be common in soil ecosystems. We suggest that the transport of MPs by ants may expand the distribution of MPs and influence the exposure of other soil fauna to MPs in soil ecosystems.

Long-term fertilization lowers the alkaline phosphatase activity by impacting the phoD-harboring bacterial community in rice-winter wheat rotation system

PhoD-harboring bacteria and the secreted alkaline phosphatases (ALP) are crucial in the regulation of soil phosphorus (P) cycling. However, the influential factors of these crucial indicators and their internal interactions remain controversial. Here, a long-term field experiment containing different fertilization regimes was conducted (chemical, organic, and no fertilizer applied). The results indicated that the richness and diversity of phoD-harboring bacterial community were significantly decreased after long-term fertilization. The applied fertilizer promoted the growth of competitive species, while phoD-harboring bacteria lost the advantage to outcompete other microorganisms after long-term fertilization. The decreased ALP activity was caused by the declined phoD gene abundance, which is attributed to the comprehensive effects of soil organic C (SOC), total nitrogen (TN), and various forms of P. The random forest models identified SOC, TN, and available P (AP) to be the dominant environmental factors in shaping the phoD-harboring bacterial community. In addition, some other forms of P such as organic P (Po), inorganic P (Pi) or total P (TP) also exerted significant effects. Different fertilization regimes changed the keystone genera that contributed significantly to soil ALP activities, while Pseudolabrys and Pseudomonas were predicted to be the most important genera regardless of different fertilization regimes. This study extends the understanding of the main process and mechanisms of P mobilization in response to different fertilization regimes.

Microplastics change soil properties, heavy metal availability and bacterial community in a Pb-Zn-contaminated soil

Microplastics (MPs) co-occur widely with diverse contaminants in soils. However, few data are available on their impacts on soil chemical and microbial properties of heavy metal-contaminated soils. For the first time, we investigated the changes in chemical and microbial properties of a Pb-Zn-contaminated soil as induced by six different MPs, including polyethylene (PE), polystyrene (PS), polyamide (PA), polylactic acid (PLA), polybutylene succinate (PBS), and polyhydroxybutyrate (PHB), at two doses (0.2% and 2%, w/w). After 120 days of soil incubation, significant changes were observed in soil pH, dissolved organic carbon (DOC), NH₄⁺-N, NO₃^--N, available P, the availability of Zn and Pb, and the activities of soil enzymes. Overall, MPs especially at the dose of 2% decreased the richness and diversity of bacterial communities and altered microbial community composition, causing special enrichments of specific taxa. MPs increased predicted functional genes involved in xenobiotics biodegradation and metabolism. Generally, impacts were dependent on MPs' type and dose. Changes in soil properties and heavy metal availability had significant correlations with bacterial community diversity and composition. Our findings imply that MPs co-occurring with heavy metals may change metal mobility, soil fertility, and microbial diversity and functions, thus causing a potential threat to soil ecosystem multifunctionality.

Recent advances on ecological effects of microplastics on soil environment

The mass production and wide application of plastics and their derivatives have led to the release of a large number of discarded plastic products into the natural environment, where they continue to accumulate due to their low recycling rate and long durability. These large pieces of plastic will gradually break into microplastics (<5 mm), which are highly persistent organic pollutants and attract worldwide attention due to their small particle size and potential threats to the ecosystem. Compared with the aquatic system, terrestrial systems such as soils, as sinks for microplastics, are more susceptible to plastic pollution. In this article, we comprehensively summarized the occurrence and sources of microplastics in terrestrial soil, and reviewed the eco-toxicological effects of microplastics in soil ecosystems, in terms of physical and chemical properties of soil, soil nutrient cycling, soil flora and fauna. The influence of microplastics on soil microbial community, and particularly the microbial community on the surface of microplastics, were examined in detail. The compound effects of microplastics and other pollutants, e.g., heavy metals and antibiotics, were addressed. Future challenges of research on microplastics include development of new techniques and standardization for the extraction and qualitative and quantitative analysis of microplastics in soils, toxic effects of microplastics at microbial or even molecular levels, the contribution of microplastics to antibiotic resistance genes migration, and unraveling microorganisms for the degradation of microplastics. This work provides as a better understanding of the occurrence, distribution and potential ecological risks of microplastics in terrestrial soil ecosystems.

Effect of (bio)plastics on soil environment: A review

The contribution of improperly disposed plastic wastes is globally evaluated at the level of 30% and these wastes make a particular threat to all living creatures. Thus, the evaluation of the possible impacts of plastic particles on the biotic part of ecosystems has become increasingly important in recent years. As a result, the growing number of publications concerning this subject has been observed since 2018. This paper aims to review the advances in studies on the effect of petroleum-derived plastic and bioplastic particles, taken together in the term (bio)plastics, on the terrestrial ecosystem, particularly on soil biota. It is the first review, in which both petroleum-derived plastics and bioplastics were analysed regarding their potential impacts on the soil compartment. Petroleum-derived plastics were more frequently studied than bioplastics and among analysed papers about 18% concern bioplastics. It was found that (bio)plastics did not affect the germination of seeds. However, they might contribute to the delay in germination processes. Both inhibitory and stimulating effects were observed in relation to the growth of roots and stems. (Bio)plastic microparticles did not inhibit the biochemical activity of nitrifiers and transformation of carbon compounds. Earthworms were predominantly used organisms to test the effect of petroleum-derived plastics on soil biota but there are hardly any data about bioplastics. Petroleum-derived microplastics present in soil at concentrations up to 1000 mg kg^-1 usually neither cause to the mortality of earthworms nor affect their reproduction. Micro- and nanoparticles of petroleum-derived plastics could be accumulated in the earthworm intestine and transferred in the food chain. Summarizing, a high variability of results and often appearing lack of dose-dependence relationships hamper the final evaluation of the ecotoxicity of (bio)plastics simultaneously creating a need to develop the ecotoxicological studies on (bio)plastics, especially including these on the effect of bioplastics on soil animals.

Diversity and population distribution of nematodes associated with honeybush (Cyclopia spp.) and rooibos (Aspalathus linearis) in the Western Cape province of South Africa

Nematodes are important soil organisms that constitute a key component of the soil ecosystem. A plant-parasitic survey was conducted to identify the diversity of nematodes associated with two endemic tea plants, honeybush (Cyclopia spp.) and rooibos (Aspalathus linearis) in the Western Cape province of South Africa. A total of 20 farmlands were surveyed and soil samples were collected from the rhizosphere of plants, for nematode isolation and identification based on morphological characters. Confirmation of the species of plant-parasitic nematodes was done using molecular-based tools. Nematodes were classified into various feeding groups based on their colonizer-persister (c-p) values. Plant-feeding nematodes identified from the honeybush tea plants include; Criconema mutabile, Meloidogyne hapla, M. javanica, and Xiphinema oxycaudatum, while Hoplolaimus sp., Neodolichorhynchus estherae and Pratylechus bolivianus were pathogenic on the rooibos monocultures. Bacterial and fungal feeders (Cephalobidae and Rhabditidae) were also abundant and frequently encountered in all samples. The study provides information on the diversity of nematodes associated with the indigenous herbal tea plants of South Africa.

Response of soil enzyme activities and bacterial communities to the accumulation of microplastics in an acid cropped soil

The ecological stress of microplastics (MPs) contamination in agroecosystems raise worldwide concerns. However very few studies concentrated on the effects of MPs exposure on soil microbial community. The alterations of enzymatic activities and bacterial communities were assayed by spiking 1% and 5% (w/w) of polyethylene (PE) and polyvinyl chloride (PVC) MPs in an acid soil. The results showed that both PE and PVC addition inhibited fluorescein diacetate hydrolase activity and stimulated urease and acid phosphatase activities, and declined the richness and diversity of the bacterial communities. More severe effects were observed in the PE treated soils compared to the PVC treated soils generally. The relative abundances of families Burkholderiaceae increased significantly (p < .05) after MPs addition, suggesting the bacteria associated with nitrogen fixation stimulated by the MPs input. Meanwhile, significant (p < .05) decline of Sphingomonadaceae and Xanthobacteraceae after addition of 5% PVC and 1% PE MPs, respectively implied that MPs might inhibit the biodegradation of xenobiotics in the soil. Mover, the PICRUSt analysis demonstrated that membrane transporter was a sensitive prediction functional gene of microplastics exposure in the soil. Future studies could be focused on the role of MPs on the regulation of nitrogen cycling and organic compounds degradation in soils.

Combining land preparation and vegetation restoration for optimal soil eco-hydrological services in the Loess Plateau, China

In semiarid terrestrial ecosystems, optimized eco-rehabilitation strategies, such as land preparations and planting vegetation, are keys to achieve a successful ecological restoration. Land preparations and vegetation are supposed to have the coupled and respective impacts on soil ecosystem services, which are still unclear now. In this study, eighteen experimental plots with six different combinations and repetitions of land preparations and vegetation were built in the Chinese Loess Plateau in 2014 and soil moisture storages (SMS), soil carbon stocks (SCS) and other soil nutrient stocks were calculated at 0-100 cm, also the effects of land preparations and planting vegetation on soil eco-hydrological services are analyzed by mathematical methods. The results show that leveled ditches-M. sativa had the highest SMS (125 mm) while zig terraces-P. tabulaeformis had the lowest values (88 mm). Fish-scale pits-P. tabulaeformis had the most SCS (9804 g/m²) and leveled ditches-M. sativa had the lowest values (8163 g/m²). For soil nutrient stocks, leveled benches-C. microphylla and fish-scale pits-P. tabulaeformis had the highest levels while leveled ditches-M. sativa had the lowest values. The partial redundancy analysis (pRDA) and variation partitioning (VP) analysis indicated that soil nutrient stocks were most affected by the coupling effects of land preparation and vegetation. SMS at surface (0-10 cm) were mainly affected by precipitation (58.8%). Furthermore, SMS at subsurface (10-60 cm) and deep soil layer (60-100 cm) were affected by the shared effects of vegetation and land preparation (61.3%), and vegetation (72.2%), respectively. The findings quantified the coupling and respective contributions of vegetation restoration and land preparation to soil eco-hydrological services and demonstrate that the optimal combination of eco-rehabilitation strategies can achieve a sustainable land restoration.

Biogenic transport of glyphosate in the presence of LDPE microplastics: A mesocosm experiment

The accumulation of plastic debris and herbicide residues has become a huge challenge and poses many potential risks to environmental health and soil quality. In the present study, we investigated the transport of glyphosate and its main metabolite, aminomethylphosphonic acid (AMPA) via earthworms in the presence of different concentrations of light density polyethylene microplastics in the litter layer during a 14-day mesocosm experiment. The results showed earthworm gallery weight was negatively affected by the combination of glyphosate and microplastics. Glyphosate and AMPA concentrated in the first centimetre of the top soil layer and the downward transport of glyphosate and AMPA was only detected in the earthworm burrows, ranging from 0.04 to 4.25 μg g-1 for glyphosate and from 0.01 (less than limit of detection) to 0.76 μg g-1 for AMPA. The transport rate of glyphosate (including AMPA) from the litter layer into earthworm burrows ranged from 6.6 ± 4.6% to 18.3 ± 2.4%, depending on synergetic effects of microplastics and glyphosate application. The findings imply that earthworm activities strongly influence pollutant movement into the soil, which potentially affects soil ecosystems. Further studies focused on the fate of pollutants in the microenvironment of earthworm burrows are needed.

Ecological hazard assessment of methyl ethyl ketone using the species sensitivity distribution approach in a soil ecosystem

Methyl ethyl ketone (MEK) is a common and widely used industrial solvent. However, few studies have investigated its toxicity, or its effects as a contaminant in soil ecosystems. In this study, acute and chronic toxicity data for MEK were generated, and ecological risk based on a species sensitivity distribution was assessed. Seven soil organisms from six taxonomic groups were used for acute toxicity tests and five soil organisms from four taxonomic groups were used for chronic toxicity tests. Acute and chronic soil HC₅ (hazardous concentration for 5% of species) values for MEK were estimated as 53.04 and 2.593 mg MEK/kg dry soil, respectively. This is the first study to conduct battery testing for MEK; it specifies hazardous concentrations, warns of the need for accident preparedness, and points to serious potential hazards of MEK at various levels of the soil ecosystem which can translate into greater environmental damage with implications for human health. The specific sensitivity levels determined may serve as a benchmark for establishing soil standards and strategies for ecosystem protection in the face of accidental contamination.

Trophic predator-prey relationships promote transport of microplastics compared with the single Hypoaspis aculeifer and Folsomia candida

Although the roles of earthworms and soil collembolans in the transport of microplastics have been studied previously, the effects of the soil biota at different trophic levels and interspecific relationships remain poorly understood. Here, we examine three soil microarthropod species to explore their effects on the transport of microplastics. The selected Folsomia candida and Hypoaspis aculeifer are extensively used model organisms, and Damaeus exspinosus is a common and abundant indigenous species in China. A model food chain (prey-collembolan and predator-mite) was structured to test the role of the predator-prey relationship in the transport of microplastics. Commercial Polyvinyl chloride (PVC) particles (Diameter: 80-250 μm) were selected as the test microplastics, because large amounts of PVC have persisted and accumulated in the environment. Synchronized soil microarthropods were held in plates for seven days to determine the movement of microplastics. The 5000 microplastic particles were carefully placed in the center of each plate prior to the introduction of the animals. Our results clearly show that all three microarthropod species moved and dispersed the microplastics in the plates. The 0.54%, 1.8% and 4.6% of the added microplastic particles were moved by collembolan, predatory mite and oribatid mite, respectively. Soil microarthropods (<0.2 cm) transported microplastic particles up to 9 cm. The avoidance behavior was observed in the collembolans in respect of the microplastics. The predatory -prey relationship did promote the transport of microplastics in the plates, increasing transport by 40% compared with the effects of adding single species (P < .05). Soil microarthropods commonly occur in surface soils (0-5 cm) and, due to their small body size, they can enter soil pores. Our results therefore suggest that the movement of microplastics by soil microarthropods may influence the exposure of other soil biota to microplastics and change the physical properties of soils.

Chemical speciation and enzymatic impact of silver in antimicrobial fabric buried in soil

This study investigated the impact of Ag in antibacterial fabric on soil enzymes in relation to solubility and speciation of Ag. Sections of Ag-containing sock fabric (1.0-1.5cm(2)) were incubated in soils with aerobic and anaerobic conditions and periodically determined activity of arylsulfatase, dehydrogenase and urease. Microscale distribution and speciation of Ag at the interface between socks and soil particles were investigated using micro-focused X-ray fluorescence (μ-XRF), and Ag speciation was determined using micro-focused X-ray absorption near edge structure (μ-XANES) spectroscopy. Results showed that the sock fabric consisted of elemental Ag and Ag2S. After 60-day exposure to soil, majority (50-90%) of Ag in sock did not undergo phase transformation and present as elemental Ag and Ag2S in aerobic and anaerobic conditions. A part of Ag in sock fabric was bound with soil colloids (<15%), depending on the distance from the edge of sock fabric. Soil enzyme activities were overall unaffected by Ag in sock textile after 60days of incubation, although a significant decrease in arylsulfatase activity was found only in the initial stage of soil incubation. Silver in the sock fabric is relatively stable and has little detrimental impacts on enzyme activity in ordinary soil conditions.

Can abundance of methanogen be a good indicator for CH4 flux in soil ecosystems?

Methane, which is produced by methanogenic archaea, is the second most abundant carbon compound in the atmosphere. Due to its strong radiative forcing, many studies have been conducted to determine its sources, budget, and dynamics. However, a mechanistic model of methane flux has not been developed thus far. In this study, we attempt to examine the relevance of the abundance of methanogen as a biological indicator of methane flux in three different types of soil ecosystems: permafrost, rice paddy, and mountainous wetland. We measured the annual average methane flux and abundance of methanogen in the soil ecosystems in situ. The correlation between methane flux and the abundance of methanogen exists only under a specific biogeochemical conditions such as SOM of higher than 60%, pH of 5.6-6.4, and water-saturated. Except for these conditions, significant correlations were absent. Therefore, microbial abundance information can be applied to a methane flux model selectively depending on the biogeochemical properties of the soil ecosystem.