Soil pH has a stronger effect than arsenic content on shaping plastisphere bacterial communities in soil

Occurrence of microplastics and distinct plastisphere in aquatic environments of metal mining areas in South China

Microplastic pollution is a growing global environmental concern, significantly impacting aquatic ecosystems. In metal mining regions, acid mine drainage (AMD) can exacerbate the issue as microplastics may carry heavy metals, heightening the risks to both human health and ecosystems. AMD can also form a distinct plastisphere further influencing the behavior and distribution of heavy metals. This study, beginning with tailing storage, examined microplastic contamination in river water and sediment in a mining region of South China. The concentration of microplastics in water ranged from 0.2 to 6.2 items/L, predominantly comprising PS, PE and PP. In contrast, the concentration of microplastics in the sediments ranged from 14.1 to 84.8 items/kg and were mainly composed of PP. Most microplastics in both water samples and sediments are smaller than 100 microns. Industrial wastewater from mining activities was identified as the predominant source of microplastics in the AMD-polluted upstream areas while agricultural and domestic waste contributed more significantly in the downstream areas. Plastisphere biodiversity was enhanced, while the colonization of pivotal species on plastic substrates was significantly facilitated in AMD-polluted aquatic environments. In these environments, the ecological niche afforded by plastics was of ecological significance. This study offers the direct evidence of microplastic pollution and highlights the critical ecological role of microplastics in aquatic ecosystems affected by AMD.

Organic matter and microplastics nexus: A comprehensive understanding of the synergistic impact on soil health

The interactional nexus of microplastics (MPs) and organic matter (OM) can subtly disrupt the delicate balance of soil ecosystems, influencing nutrient dynamics, biodiversity, and overall soil health. To explore this complex interplay between MPs and OM concerning several perspectives, a comprehensive keyword search was conducted across key scientific databases, and the retrieved data was curated according to the PRISMA guidelines to reflect the objectives. Several studies have highlighted that organic-based inputs, such as manures, composts, and sewage sludge, widely used for soil amendment, are potential sources of MPs to soil contamination. These coinciding sources of MPs and OM raise potential concerns about their impact on overall soil health. MPs and OM have parallel characteristics and play a critical role in the soil organic carbon (SOC) and dissolved organic matter (DOM), critical for biogeochemical transformations and nutrient cycling. In light of this, the present review explores the multifaceted nexus between MPs and OM, explaining their interaction mechanisms and their effects on the biological and physicochemical properties of the soil. Despite significant implications on soil ecosystem, challenges remain in accurately quantifying the effects of MPs due to the complexities introduced by DOM. The intricate interaction between MPs and DOM can obscure analytical results, complicating efforts to separate and identify these pollutants effectively. Given these challenges, this review underscores the urgent need for innovative methods to characterize and quantify MPs in complex environmental matrices. Finally, we discuss emerging research directions aimed at advancing the detection and management of MPs in soil ecosystems.

Effects of biodegradable microplastics on soil microbial communities and activities: Insight from an ecological mesocosm experiment

Microplastics (MP) are being released into the environment at an increasing rate, causing extensive pollution in soils and affecting biota and processes. Although the use of biodegradable plastic has increased, its effects on the soil microbial community are not yet well understood. A controlled mesocosm experiment was conducted to investigate the response of soil microbial communities to increasing amounts of starch-polybutylene adipate terephthalate MPs (PBAT-BD-MPs) added to the soil. The experiment included microbes, earthworms, springtails, and plants. The PBAT-BD-MPs were added to the soil column at doses ranging from 0 to 0.8 % w/w of soil dry mass, and the columns were incubated for 11 weeks under controlled climatic conditions. Bacterial and fungal amplicon sequencing was used to investigate the dose-dependent response of the soil microbial communities' alpha and beta diversity. The alpha diversity indices of the bacterial and fungal communities increased with increasing PBAT-BD-MP concentration. Bacterial richness was highest at the highest MP concentration (0.8 %). A similar trend was observed in the fungal community, with a significant increase in fungal richness as PBAT-BD-MP concentration increased. The alpha diversity of both bacterial and fungal communities significantly increased in MP treatments compared to the control treatment. At the highest MP concentration (0.8 %), the abundance of the bacterial phylum Planctomycetes showed a significant increase, while Firmicutes showed a significant decrease. The abundance of the fungal phyla Ascomycota and Mortierellomycota also significantly increased at the highest PBAT-BD-MP concentration compared to the control group. Alongside changes in the soil microbial community, we observed a rise in soil respiration as the concentration of PBAT-BD-MPs increased. Our three-month mesocosm study demonstrates that the introduction of biodegradable microplastics into the natural standard soil environment in realistic concentrations (0-0.025-0.05-0.2-0.8 %) and particle size distribution alters the soil bacterial and fungal community.

Direct evidence for selective microbial enrichment with plastic degradation potential in the plastisphere

Plastisphere, characterized by microbial colonization on plastic debris, has attracted concern with its adverse environmental effects. The microbial features have been increasingly investigated; however, there lacks direct evidence for microplastics serving as carbon sources and enriching plastic-degrading microorganisms. Here, we obtained microbial communities from soil microplastics, analyzed the dissimilarity compared with soil, and characterized the plastic-degrading potential of isolates from plastisphere. Results showed the plastisphere communities significantly differed from soil communities and exhibited a higher relative abundance of Nocardia and Rhodococcus. To verify the selective enrichment of plastic-degrading microorganisms in the plastisphere, culture-based strategies were employed to evaluate the polyethylene (PE) degradation potential of two isolates Nocardia asteroides No.11 and Rhodococcus hoagii No.17. They could grow solely on PE and led to significant weight loss. FTIR and SEM analysis revealed the formation of new functional groups and the destruction of structural integrity on PE surfaces. Genes related to PE biodegradation were identified by genome-wide sequencing thus recognizing relevant enzymes and elucidating potential pathways. Overall, this report combined culture-free and culture-based approaches to confirm the plastic degradation potential of selectively enriched microorganisms in soil plastisphere, providing a positive perspective toward promoting microplastic biodegradation in farmland soil by enhancing natural microbial processes.

Effect of biodegradable microplastics and Cd co-pollution on Cd bioavailability and plastisphere in soil-plant system

Biodegradable plastics (BPs) are regarded as ecomaterials and are emerging as a substitute for traditional non-degradable plastics. However, the information on the interaction between biodegradable microplastics (BMPs) and cadmium (Cd) in agricultural soil is still limited. Here, lettuce plants were cultured in BMPs (polylactic acid (PLA) MPs and poly(butylene-adipate-co-terephthalate) (PBAT) MPs) and Cd co-polluted soil for 35 days. The results show that diffusive gradient in thin films technique (DGT) but not diethylenetriaminepentaacetic acid (DTPA) extraction method greatly improved the prediction reliability of Cd bioavailability in non-rhizosphere soil treated with BMPs (R2 = 0.902). BMPs increased the Cd bioavailability in non-rhizosphere soil indirectly by decreasing soil pH, cation exchange capacity (CEC), and dissolved organic carbon (DOC), rather than by directly adsorbing Cd on their surface. PLA MPs incubated in rhizosphere soil showed more considerable degradation with extremely obvious cavities and the fracture of ester functional groups on their surface than PBAT MPs. BMPs could provide ecological niches to colonize and induce microorganisms associated with BMPs' degradation to occupy a more dominant position. In addition, Cd only affected the composition and function of microbial communities in soil but not on BMPs. However, co-exposure to BMPs and Cd significantly reduced the degrees of co-occurrence network of fungal communities on PLA MPs and PBAT MPs by 37.7% and 26.7%, respectively, compared to single exposure to BMPs.

Sources, interactions, influencing factors and ecological risks of microplastics and antibiotic resistance genes in soil: A review

Microplastics (MPs) and antibiotic resistance genes (ARGs) are gaining increasing attention as they pose a threat to the ecological environment and human health as emerging contaminants. MPs has been proved to be a hot spot in ARGs, and although it has been extensively studied in water environment, the results of bibliometrics statistical analysis in this paper showed that relevant studies in soil ecological environment are currently in the initial stage. In view of this, the paper provides a systematic review of the sources, interactions, influencing factors, and ecological risks associated with MPs and ARGs in soil environments. Additionally, the mechanism and influencing factors of plastisphere formation and resistance are elaborated in detail. The MPs properties, soil physicochemical properties, soil environmental factors and agricultural activities are the primarily factors affecting the interaction between MPs and ARGs in soil. Challenges and development directions of related research in the future are also prospected. It is hoped that the review could assist in a deeper comprehension and exploration of the interaction mechanism between MPs and ARGs in soil as well as the function of MPs in the transmission process of ARGs among diverse environmental media and organisms, and provide theory basis and reference for the MPs and ARGs pollution control and remediation in soil.

Microplastics in the soil-water-food nexus: Inclusive insight into global research findings

Nuisance imposed by biotic and abiotic stressors on diverse agroecosystems remains an area of focus for the scientific fraternity. However, emerging contaminants such as microplastics (MP) have imposed additional dimension (alone or in combinations with other stressors) in agroecosystems and keep escalating the challenges to achieve sustainability. MP are recognized as persistent anthropogenic contaminants, fetch global attention due to their unique chemical features that keeps themselves unresponsive to the decaying process. This review has been theorized to assess the current research trends (along with possible gap areas), widespread use of MP, enhancement of the harshness of heavy metals (HMs), complex interactions with physico-chemical constituents of arable soil, accumulation in the edible parts of field crops, dairy products, and other sources to penetrate the food web. So far, the available review articles are oriented to a certain aspect of MP and lack a totality when considered from in soil-water-food perspective. In short, a comprehensive perspective of the adverse effects of MP on human health has been assessed. Moreover, an agro-techno-socio-health prospective-oriented critical assessment of policies and remedial measures linked with MP has provided an extra edge over other similar articles in influential future courses of research.

Global perspective of ecological risk of plastic pollution on soil microbial communities

Introduction

The impacts of plastic pollution on soil ecosystems have emerged as a significant global environmental concern. The progress in understanding how plastic pollution affects soil microbial communities and ecological functions is essential for addressing this issue effectively.

Methods

A bibliometric analysis was conducted on the literature from the Web of Science Core Collection database to offer valuable insights into the dynamics and trends in this field.

Results

To date, the effects of plastic residues on soil enzymatic activities, microbial biomass, respiration rate, community diversity and functions have been examined, whereas the effects of plastic pollution on soil microbes are still controversial.

Discussion

To include a comprehensive examination of the combined effects of plastic residue properties (Type, element composition, size and age), soil properties (soil texture, pH) at environmentally relevant concentrations with various exposure durations under field conditions in future studies is crucial for a holistic understanding of the impact of plastic pollution on soil ecosystems. Risk assessment of plastic pollution, particularly for nanoplasctics, from the perspective of soil food web and ecosystem multifunctioning is also needed. By addressing critical knowledge gaps, scholars can play a pivotal role in developing strategies to mitigate the ecological risks posed by plastic pollution on soil microorganisms.

Microbiomes on microplastics versus natural microcarriers: Stability and transformation during aquatic travel from aquaculture ponds to adjacent stream

Microplastics (MPs) with different physical-chemical properties are considered as vectors for the propagation of microbes in aquatic environments. It remains unclear how plastic types impact on the plastisphere and whether different MPs spread microbes more rapidly than natural materials in microbes across distinct water bodies as proposed previously. We used in-situ incubation to investigate the microbes attached on MPs of polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC), versus that on two natural microcarriers (quartz sands and bamboo) during the travel from aquaculture ponds with impacted by fish farming to adjacent freshwater stream. The results showed that the microbial communities on the carriers were shaped not only by environmental conditions, which were primary determinants but also by carrier types. All the tested plastics did not carry more microbes than the natural carriers during the journey. The biofilm community composition on PVC is distinct from that on PE and PP MPs and natural carriers. The plastisphere of PE and PP kept microbial proportions as natural materials did but PVC retained less than nature materials. Bamboo carried more potential pathogens than plastic polymers and quartz. The results indicated that the communities of plastisphere is polymer-type dependent, and, compared with the natural materials, MPs did not show enhanced propagation of microbes, including pathogens, cross distinct environments.

A review of amendments for simultaneously reducing Cd and As availability in paddy soils and rice grain based on meta-analysis

Arsenic (As) and cadmium (Cd) accumulation in rice grains is a global food safety issue, and various methods and materials have been used to remove or reduce As and Cd in agricultural soils and rice grains. Despite the availability of synthesized materials capable of simultaneous As and Cd reduction from soil and rice grains, the contributions, efficiency, and main ingredients of the materials for As and Cd immobilization remain unclear. The present study first summarized the biogeochemistry of As and Cd in paddy soils and their transfer in the soil-food-human continuum. We also reviewed a series of reported inorganic and organic materials for simultaneous immobilization of As and Cd in paddy soils, and their reduction efficiency of As and Cd bioavailability were listed and compared. Based on the abovementioned materials, the study conducted a meta-analysis of 38 articles with 2565 observations to quantify the impacts of materials on simultaneous As and Cd reduction from soil and rice grains. Meta-analysis results showed that combining organic and inorganic amendments corresponded to effect sizes of -62.3% and -67.8% on As and Cd accumulation in rice grains, while the effect sizes on As and Cd reduction in paddy soils were -44.2% and -46.2%, respectively. Application of Fe based materials significantly (P < 0.05) reduced As (-54.2%) and Cd (-74.9%), accounting for the highest immobilization efficiency of As and Cd in rice grain among all the reviewed materials, outweighing S, Mn, P, Si, and Ca based materials. Moreover, precipitation, surface complexation, ion exchange, and electrostatic attraction mechanisms were involved in the co-immobilization tactics. The present study underlines the application of combined organic and inorganic amendments in simultaneous As and Cd immobilization. It also highlighted that employing Fe-incorporated biochar material may be a potential strategy for co-mitigating As and Cd pollution in paddy soils and accumulation in rice grains.

Short-term impacts of polyethylene and polyacrylonitrile microplastics on soil physicochemical properties and microbial activity of a marine terrace environment in maritime Antarctica

Evidence of microplastic (MP) pollution in Antarctic terrestrial environments reinforces concerns about its potential impacts on soil, which plays a major role in ecological processes at ice-free areas. We investigated the effects of two common MP types on soil physicochemical properties and microbial responses of a marine terrace from Fildes Peninsula (King George Island, Antarctica). Soils were treated with polyethylene (PE) fragments and polyacrylonitrile (PAN) fibers at environmentally relevant doses (from 0.001% to 1% w w-1), in addition to a control treatment (0% w w-1), for 22 days in a pot incubation experiment under natural field conditions. The short-term impacts of MPs on soil physical, chemical and microbial attributes seem interrelated and were affected by both MP dose and type. The highest PAN fiber dose (0.1%) increased macro and total porosity, but decreased soil bulk density compared to control, whereas PE fragments treatments did not affect soil porosity. Soil respiration increased with increasing doses of PAN fibers reflecting impacts on physical properties. Both types of MPs increased microbial activity (fluorescein diacetate hydrolysis), decreased the cation exchange capacity but, especially PE fragments, increased Na+ saturation. The highest dose of PAN fibers and PE fragments increased total nitrogen and total organic carbon, respectively, and both decreased the soil pH. We discussed potential causes for our findings in this initial assessment and addressed the need for further research considering the complexity of environmental factors to better understand the cumulative impacts of MP pollution in Antarctic soil environments.

Arbuscular mycorrhizal fungi promote arsenic accumulation in Pteris vittata L. through arsenic solubilization in rhizosphere soil and arsenic uptake by hyphae

The introduction of arbuscular mycorrhizal fungi (AMF) is considered an effective strategy for improving the arsenic phytoremediation efficiency of Pteris vittata L. (P. vittata). However, how hyphae take up arsenic and translocate it to the root cells of P. vittata in the symbiotic mycorrhizal structure is currently unclear. In this study, the role of hyphae in arsenic enrichment in P. vittata and the mechanism of arsenic species transformation in the rhizosphere were studied via a compartmented cultivation setup. After Claroidoglomus etunicatum (C. etunicatum) colonization, the arsenic content of P. vittata increased by 234%. Hyphae contributed 32% to the accumulation of arsenic in symbionts. C. etunicatum promoted the conversion of iron and aluminum oxides to crystalline states in rhizosphere soil, promoted the desorption of arsenic bound to iron and aluminum oxides, and increased the content of available arsenic in rhizosphere soil by 116%. The transfer of arsenic from arbuscular structures to root cells was confirmed by transmission electron microscopy (TEM)/scanning electron microscopy- energy dispersive X-ray spectroscopy (SEMEDS) analysis. This study demonstrated that C. etunicatum inoculation enhances the phytoremediation efficiency of P. vittata in arsenic-contaminated soils through hyphal uptake, plant growth promotion, and alteration of the rhizosphere environment.

The soil plastisphere

Understanding the effects of plastic pollution in terrestrial ecosystems is a priority in environmental research. A central aspect of this suite of pollutants is that it entails particles, in addition to chemical compounds, and this makes plastic quite different from the vast majority of chemical environmental pollutants. Particles can be habitats for microbial communities, and plastics can be a source of chemical compounds that are released into the surrounding environment. In the aquatic literature, the term 'plastisphere' has been coined to refer to the microbial community colonizing plastic debris; here, we use a definition that also includes the immediate soil environment of these particles to align the definition with other concepts in soil microbiology. First, we highlight major differences in the plastisphere between aquatic and soil ecosystems, then we review what is currently known about the soil plastisphere, including the members of the microbial community that are enriched, and the possible mechanisms underpinning this selection. Then, we focus on outlining future prospects for research on the soil plastisphere.

Effect of Phanerochaete chrysosporium induced phosphate precipitation on bacterial diversity during the soil remediation process

Biomineralization by phosphate minerals and phosphate solubilizing fungi (PSF) has attracted great interest as a novel remediation method for heavy metal(loid) co-contaminated soil. It was very essential to investigate the microenvironment response with the application of amendments. In this study, three grain sizes of hydroxyapatites (HAP) and Phanerochaete chrysosporium (P. chrysosporium) were used to investigate the change in heavy metal(loid) fractions, soil physicochemical properties, and bacterial community during the remediation of Mangchang and Dabaoshan acidic mine soils. The results showed that the residual fractions in the two soils increased significantly after 35 days of remediation, especially that of As and Zn in Dabaoshan soils were presented at over 87%. In addition, soil pH, organic matter (OM), and available phosphorous (AP) were almost improved. 16S rRNA sequencing analysis indicated that the introduction of culture medium and P. chrysosporium alone changed bacterial abundance, but the addition of HAP changed the bacterial diversity and community composition by altering environmental conditions. The amendments in the research showed good performance on immobilizing heavy metal(loid)s and reducing their bioavailability. Moreover, the research suggested that environmental factors and soil inherent properties could influence the microbial community structure and composition.

Root-knot nematode infections and soil characteristics significantly affected microbial community composition and assembly of tobacco soil microbiota: a large-scale comparison in tobacco-growing areas

Introduction

Tobacco root-knot nematode (RKN) is a highly destructive soil-borne disease worldwide. However, there is a lack of research on the relationship between RKN and tobacco root microbial community composition under large-scale geographical conditions in China.

Methods

In this study, we collected 65 samples from 28 main tobacco-growing areas across 10 provinces in China and conducted 16S rDNA sequencing to investigate the dynamic microbial changes in tobacco soil infected by RKN compared to healthy tobacco soil. Based on the analysis of rhizosphere soil bacterial communities, changes after RKN infection, and soil environmental factors.

Results

We found the 28 tobacco-growing areas could be divided into two distinct groups with different microbial compositions and varying responses to RKN infection. In group1 of the provinces of Anhui, Henan, Shanxi, and Heilongjiang, Vicinamibacteria dominated the bacterial community, while Acidobacteriae was present in low abundance. In contrast, group2 of the other six provinces (Yunnan, Guizhou, Chongqing, Guangxi, Hubei, and Shandong) exhibited an opposite pattern. After infected by RKN, the genera Chitinophaga increased significant in group 1, while the genera Rhodococcus in group 2 exhibited a substantial increase. Alpha-diversity analysis revealed that RKN-infected tobacco exhibited a richer and more diverse rhizosphere soil bacterial community compared to healthy tobacco in most growing areas. A total of 12 kinds of soil environmental factors were measured in healthy and RKN-infected tobacco soil, and based on the co-occurrence and correlation analysis between environmental factors and microbial species, the pH level, calcium (Ca), magnesium (Mg), phosphorus (P), iron (Fe), and sodium (Na) were identified as key environmental factors influencing the population composition of rhizosphere microorganisms during RKN infection. We observed that RKN infection further increased the pH in weakly alkaline group 1 soil, while weakly acidic group 2 soil experienced a further decrease in pH. Furthermore, we identified three genera as potential biocontrol or plant growth-promoting bacteria for tobacco.

Discussion

These findings provide valuable reference data for managing RKN disease in different tobacco-growing areas and contribute to the exploration of new and effective biological control methods.

Physicochemical and biological changes on naturally aged microplastic surfaces in real environments over 10 months

Microplastics (MPs) undergo aging over time, which can influence their behavior in the environment. While laboratory-simulated studies have investigated MP aging, research on natural aging in various real environments remains limited. This study aims to investigate the physical, chemical and biological changes that occur in five types of MPs after more than 10 months of natural aging in three different real environments: seawater, air and soil. Results are compared with previous laboratory experiments. The surface roughness of all types of aged MPs was found to be higher in seawater than in air and soil, which differed from previous simulated studies that showed the highest roughness in air. All aged MPs exhibited the occurrence of hydroxyl and carbonyl groups due to the oxidation processes. Interestingly, the MPs aged in soil showed the lowest level of these functional groups, while in seawater or air, some MPs demonstrated the highest. This contrasts with previous studies indicating the highest level of oxygen-containing functional groups in aged MPs in air. Bacterial analysis identified fourteen bacterial phyla on the surface of aged MPs in all three real environments, with varying abundance in specific environments. Notably, the composition of bacterial communities in the microplastisphere was determined by the surrounding environments, independent of MP types. Natural aging is more complex than laboratory simulations, and the degree of MP aging increases with the complexity of environmental factors. These findings enhance our understanding of the natural aging of MPs in different real environments.

Inhibitory effect of polyethylene microplastics on roxarsone degradation in soils

Roxarsone (3-nitro-4-hydroxyphenylarsonic acid, Rox(V)), an extensively used organoarsenical feed additive, enters soils through the application of Rox(V)-containing manure and further degrades to highly toxic arsenicals. Microplastics, as emerging contaminants, are also frequently detected in soils. However, the effects of microplastics on soil Rox(V) degradation are unknown. A microcosm experiment was conducted to investigate soil Rox(V) degradation responses to polyethylene (PE) microplastics and the underlying mechanisms. PE microplastics inhibited soil Rox(V) degradation, with the main products being 3-amino-4-hydroxyphenylarsonic acid [3-AHPAA(V)], N-acetyl-4-hydroxy-m-arsanilic acid [N-AHPAA(V)], arsenate [As(V)], and arsenite [As(III)]. This inhibition was likely driven by the decline in soil pH by PE microplastic addition, which may directly enhance Rox(V) sorption in soils. The decreased soil pH further suppressed the nfnB gene related to nitroreduction of Rox(V) to 3-AHPAA(V) and nhoA gene associated with acetylation of 3-AHPAA(V) to N-AHPAA(V), accompanied by a decrease in the relative abundance of possible Rox(V)-degrading bacteria (e.g., Pseudomonadales), although the diversity, composition, network complexity, and assembly of soil bacterial communities were largely influenced by Rox(V) rather than PE microplastics. Our study emphasizes microplastic-induced inhibition of Rox(V) degradation in soils and the need to consider the role of microplastics in better risk assessment and remediation of Rox(V)-contaminated soils.

The responses of microbial metabolic activity, bacterial community and resistance genes under the coexistence of nanoplastics and quaternary ammonium compounds in the sewage environment

Nanoplastics (NPs) and quaternary ammonium compounds (QACs) are frequently detected in sewage. However, little is known about the risks of coexistence of NPs and QACs. In this study, the responses of microbial metabolic activity, bacterial community and resistance genes (RGs) to the exposure of polyethylene (PE), polylactic acid (PLA), silicon dioxide (SiO₂) and dodecyl dimethyl benzyl ammonium chloride (DDBAC) were focused on 2nd and 30th day of incubation in sewer environment. Bacterial community contributed 25.01 % to shape RGs and mobile genetic elements (MGEs) after two days of incubation in sewage and plastisphere. After 30 days of incubation, the most important individual factor (35.82 %) was turned to microbial metabolic activity. The metabolic capacity of the microbial communities in plastisphere was stronger than that from SiO₂ samples. Moreover, DDBAC inhibited the metabolic capacity of microorganisms in sewage samples, and increased the absolute abundances of 16S rRNA in plastisphere and sewage samples which might be similar to the hormesis effect. After 30 days of incubation, Aquabacterium was the predominant genus in plastisphere. As for SiO₂ samples, Brevundimonas was the predominant genus. QACs RGs (qacEdelta1-01, qacEdelta1-02) and antibiotic RGs (ARGs) (aac(6')-Ib, tetG-1) significantly enriched in plastisphere. There was also co-selection among qacEdelta1-01, qacEdelta1-02 and ARGs. In addition, VadinBC27 which enriched in plastisphere of PLA NPs was positively correlated with the potentially disease-causing genus Pseudomonas. It showed that after 30 days of incubation, plastisphere had an important effect on distribution and transfer of pathogenic bacteria and RGs. Plastisphere of PLA NPs also carried the risk of spreading disease.

Can simultaneous immobilization of arsenic and cadmium in paddy soils be achieved by liming?

Liming acidic paddy soils to near-neutral pH is the most cost-effective strategy to minimize cadmium (Cd) accumulation by rice. However, the liming-induced effect on arsenic (As) (im)mobilization remains controversial and is called upon for further investigation, particularly for the safe utilization of paddy soils co-contaminated with As and Cd. Here, we explored As and Cd dissolution along pH gradients in flooded paddy soils and extracted key factors accounting for their release discrepancy with liming. The minimum As and Cd dissolution occurred concurrently at pH 6.5-7.0 in an acidic paddy soil (LY). In contrast, As release was minimized at pH < 6 in the other two acidic soils (CZ and XX), while the minimum Cd release still appeared at pH 6.5-7.0. Such a discrepancy was determined largely by the relative availability of Fe under overwhelming competition from dissolved organic carbon (DOC). A mole ratio of porewater Fe/DOC at pH 6.5-7.0 is suggested as a key indicator of whether co-immobilization of As and Cd can occur in flooded paddy soils with liming. In general, a high mole ratio of porewater Fe/DOC (≥ 0.23 in LY) at pH 6.5-7.0 can endow co-immobilization of As and Cd, regardless of Fe supplement, whereas such a case is not in the other two soils with lower Fe/DOC mole ratios (0.01-0.03 in CZ and XX). Taking the example of LY, the introduction of ferrihydrite promoted the transformation of metastable As and Cd fractions to more stable ones in the soil during 35 days of flooded incubation, thus meeting a class I soil for safe rice production. This study demonstrates that the porewater Fe/DOC mole ratio can indicate a liming-induced effect on co-(im)mobilization of As and Cd in typical acidic paddy soils, providing new insights into the applicability of liming practice for the paddy soils.

Distinct distribution patterns and functional potentials of rare and abundant microorganisms between plastisphere and soils

The increasing application of plastic film has caused the "white pollution" of farmlands in greenhouses. To date, most studies on the ecology of the plastisphere have focused on the whole microbial community, with few on the rare and abundant taxa, especially in the terrestrial ecosystems. To understand the plastisphere rare and abundant taxa of bacterial and fungal communities, we collected residues of plastic film from plastic-covered soils in the greenhouse. The plastisphere was significantly different from surrounding soils in terms of alpha- and beta-diversities of abundant and rare taxa. Such discrepancies were greater in rare taxa than in abundant taxa. Besides, the enrichment of soil-borne plant pathogenic fungi in the plastisphere implied that plastic film residues can act as vectors for pathogen transmission. In the plastisphere, the stochastic process governed the assemblies of rare taxa, while deterministic assemblies dominated that of abundant taxa. However, in surrounding soils, the stochastic process played a larger role in abundant taxa as compared to rare taxa. The plastisphere showed a network of less complexity, more competitive connections, and more modules compared to surrounding soils, and rare taxa played greater roles than abundant taxa. There existed obvious discrepancies in the microbial functions between surrounding soils and plastisphere, including carbon, sulfur, nitrogen, and phosphorus cycling, and rare taxa contribute large proportions to the above cycling processes. Altogether, the findings advance our understanding of ecological mechanisms of abundant and rare taxa in the plastisphere in terrestrial ecosystems.

Plastisphere microbiome: Methodology, diversity, and functionality

Broad topics of the plastisphere in various environments are reviewed, including its methodologies, diversity, functionality, and outlook.

Effects of variable-sized polyethylene microplastics on soil chemical properties and functions and microbial communities in purple soil

Microplastic contamination of soil has drawn increased attention due to the ecological harm it poses to the soil ecosystem. However, little is known about how microplastic particle sizes affect soil chemical properties and microbial communities, particularly in purple soil. In this study, a four-week incubation experiment was conducted to evaluate the effect of polyethylene microplastics (PE MPs) with different particle sizes (i.e., 300 and 600 μm) on soil properties, extracellular polymeric substances (EPS), enzyme activities, and microbial communities in purple soil. When compared to 600 μm-PE MPs, 300 μm-PE MPs reduced contents of dissolved organic matter (DOM), EPS, and β-1,4-N-acetylglucosaminidase (NAG) activity, but increased the cation exchange capacity (CEC). High-throughput 16S rRNA gene sequencing revealed that the 300 μm-PE MPs resulted in an increase in the phylum Nitrospirae, which is associated with microplastic degradation. The data implied that smaller PE MPs improved the growth of polyethylene-degrading bacteria by adsorbing more EPS and DOM, resulting in the degradation of microplastics. Co-occurrence network analysis revealed that smaller PE MPs had lower toxicity to microbial populations than larger PE MPs, increasing the stability of the network. CEC and β-1,4-glucosidase (BG) were found to be the two major factors affecting the microbial communities by redundancy analysis (RDA). The study highlighted how microplastic particle sizes affect soil bacterial communities and soil functions.

Effect of phenol formaldehyde-associated microplastics on soil microbial community, assembly, and functioning

Increasing investigations explore the effects of plastic pollutants on bacterial communities, diversity, and functioning in various ecosystems. However, the impact of microplastics (MPs) on the eukaryotic community, microbial assemblages, and interactions is still limited. Here, we investigated bacterial and micro-eukaryotic communities and functioning in soils with different concentrations of phenol formaldehyde-associated MPs (PF-MPs), and revealed the factors, such as soil properties, microbial community assembly, and interactions between microbes, influencing them. Our results showed that a high concentration (1%) of PF-MPs decreased the microbial interactions and the contribution of deterministic processes to the community assembly of microbes, and consequently changed the communities of bacteria, but not eukaryotes. A significant and negative relationship was determined between N₂O emission rate and functional genes related to nitrification, indicating that the competitive interactions between functional microbes would affect the nitrogen cycling of soil ecosystem. We further found that vegetable biomass weakly decreased in treatments with a higher concentration of PF-MPs and positively related to the diversity of micro-eukaryotic communities and functional diversity of bacterial communities. These results suggest that a high concentration of the PF-MPs would influence crop growth by changing microbial communities, interactions, and eukaryotic and functional diversity. Our findings provide important evidence for agriculture management of phenol formaldehyde and suggest that we must consider their threats to microbial community compositions, diversity, and assemblage in soils due to the accumulation of PF-MPs widely used in the field.

Changes in the composition of rhizosphere bacterial communities in response to soil types and acid rain

It is widely known how acid rain negatively impacts plant physiology. However, the magnitude of these effects may depend on soil types. Although the response of aboveground parts has received much attention, the effects of soil types and acid rain on underground processes are yet to be studied, specifically with respect to the composition and diversity of bacterial communities in the rhizosphere. Based on a high throughput sequencing approach, this study examined how different soil types, acid rain of different pH, and interactions between the two factors influenced the growth and rhizosphere bacterial communities of Jatropha curcas L. The present study pointed out that the soil pH, total nitrogen (TN), total phosphorus (TP), total potassium (TK), and total organic carbon/total nitrogen (C/N) were more related to soil type than to acid rain. The growth of J. curcas aboveground was mainly affected by acid rain, while the underground growth was mainly influenced by soil type. Changes in bacterial abundance indicated that the genera (Burkholderia-Paraburkholde, Bryobacter, Cupriavidus, Mycobacterium, and Leptospirillu) and phyla (Acidobacteria and Actinobacteria) could likely resist acid rain to some extent, with Acidobacteria, Gemmatimonadetes and Proteobacteria being well adapted to the copiotrophic environments. Results of correlational analyses between Firmicutes and soil properties (pH, TN, TK) further indicated that this phylum was also well adapted to a nutrient-deficient habitat of low pH. Finally, while Mycobacterium and Bradyrhizobium could adapt to low pH, high soil TK contents were not conducive to their enrichment. The results also showed that acid rain shifted the bacterial groups from fast-growing copiotrophic populations to slow-growing oligotrophic ones. The RDA analysis, and Pearson's rank correlation coefficients indicated that soil pH and TK were the main factors influencing bacterial richness.

Coupled effects of microplastics and heavy metals on plants: Uptake, bioaccumulation, and environmental health perspectives

Microplastic pollution has severe ecological and environmental concerns because of its enormous production and discharge in natural ecosystems worldwide. Microplastics interact with heavy metals and metalloids like arsenic, chromium, copper, cadmium, and lead in soil and can cause detrimental effects on soil structure and microbial activities and subsequently impact the plants and human health. This article focuses on microplastic translocation from soil to plants together with heavy metals. Microplastic exposure impacts biomass, photosynthetic activity, chlorophyll content, root and shoot length in the plants through apoplastic and symplastic pathways. Microplastics can also indirectly affect the plant growth by changing soil nutrient content and microbial community structure. At the same time, microplastics can absorb heavy metals and increase phytotoxicity in plants. However, the current knowledge about the coupled effect of heavy metals and microplastics bioaccumulation in plants is limited. It is postulated that heavy metals and microplastics collectively impact the chlorophyll content, photosynthetic activity, and induction of reactive oxygen species in plants. This work also outlines the environmental health perspectives based on microplastic and heavy metals toxicity and provides a guideline for future research on the coupled effects of heavy metals and microplastics on plants and humans.

Effect of biochar on the uptake, translocation and phytotoxicity of chromium in a soil-barley pot system

Remediation of Cr-contaminated soils with biochar is an effective method, but its effect on plant detoxification has not been clarified, and the translocation pathways of different chemical forms of Cr in the soil-plant system have not been quantitatively evaluated. This study investigated the effects of magnetically modified Enteromorpha prolifera biochar (FBC) on Cr uptake, translocation and phytotoxicity in the soil and barley (Hordeum vulgare L.). When the FBC dosage increased to 30 g·kg^-1, the content of bioavailable Cr in the soil decreased by 56.82%. Additionally, the contents of Cr in H. vulgare decreased by 53.22%, and growth recovered to the normal level. Partial least squares path modelling (PLS-PM) was applied to establish two influence paths to explain how FBC impacted the whole system of soil and plants upon Cr exposure. The phytotoxic effect path of Cr suggested that FBC decreased the contents of Cr in soil and H. vulgare and then recovered growth by alleviating oxidative stress (β = -0.45) and promoting chlorophyll synthesis (β = 0.53) in shoots. The translocation and conversion path of Cr further indicated that Cr in the shoots was converted into low-migration forms and mainly trapped in cell walls and vacuoles rather than in organelles, consequently decreasing the phytotoxicity of Cr (β = -0.73). These two soil-plant paths offer new insights into the application of biochar and plants in Cr-contaminated soils.

Does bacterial community succession within the polyethylene mulching film plastisphere drive biodegradation?

Agricultural fields are severely contaminated with polyethylene mulching film (PMF) and this plastic in the natural environment can be colonized by biofilm-forming microorganisms that differ from those in the surrounding environment. In this study, we investigated the succession of the soil microbial communities in the PMF plastisphere using an artificial micro-ecosystem as well as exploring the degradation of PMF by plastisphere communities. The results indicated a significant and gradual decrease in the alpha diversity of the bacterial communities in the plastisphere and surrounding liquid. The community compositions in the plastisphere and surrounding liquid differed significantly from that in agricultural soil. Phyla and genera with the capacity to degrade polyethylene and hydrocarbon were enriched in the plastisphere, and some of these microorganisms were core members of the plastisphere community. Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) analysis detected increases in metabolism pathways for PMF plastisphere Xenobiotics Biodegradation and Metabolism, thereby suggesting the possibility of polyethylene degradation in the plastisphere. Observations by scanning electron microscopy (SEM) and confocal laser scanning microscopy demonstrated the formation of biofilms on the incubated PMF. SEM, atomic force microscopy, Fourier transform infrared spectroscopy and water contact angle detected significant changes in the surface microstructure, chemical composition and hydrophobicity change of the films, thereby suggesting that the plastisphere community degraded PMF during incubation. In conclusion, this study provides insights into the changes in agricultural soil microorganisms in the PMF plastisphere and the degradation of PMF.

Microplastics shape microbial communities affecting soil organic matter decomposition in paddy soil

Microplastics (MPs) can alter microbial communities and carbon (C) cycling in agricultural soils. However, the mechanism by which MPs affect the decomposition of microbe-driven soil organic matter remains unknown. We investigated the bacterial community succession and temporal turnover during soil organic matter decomposition in MP-amended paddy soils (none, low [0.01% w/w], or high [1% w/w]). We observed that MPs reduced the CO₂ efflux rate on day 3 and subsequently promoted it on day 15 of incubation. This increased CO₂ emission in MP-amended soil may be related to (i) enhanced hydrolase enzyme activities or; (ii) shifts in the Shannon diversity, positive group interactions, and temporal turnover rates (from 0.018 to 0.040). CO₂ efflux was positively correlated (r > 0.8, p < 0.01) with Ruminiclostridium_1, Mobilitalea, Eubacterium xylanophilum, Sporomusa, Anaerobacteriu, Papillibacter, Syntrophomonadaceae, and Ruminococcaceae_UCG_013 abundance in soil with high MPs, indicating that these genera play important roles in soil organic C mineralization. These results demonstrate how microorganisms adapt to MPs and thus influence the C cycle in MP-polluted paddy ecosystems.

Soil plastisphere: Exploration methods, influencing factors, and ecological insights

Microplastic (MP), an emerging contaminant, is globally prevalent and poses potential environmental threats and ecological risks to both aquatic and terrestrial ecosystems. When MPs enter into natural environments, they may serve as artificial substrates for microbial colonization and plastisphere formation, providing new ecological niches for microorganisms. Recent studies of the plastisphere have focused on aquatic ecosystems. However, our understanding of the soil plastisphere e.g. its formation process, microbial ecology, co-transport of organic pollutants and heavy metals, and effects on biogeochemical processes is still very limited. This review summarizes latest methods used to explore the soil plastisphere, assesses the factors influencing the microbial ecology of the soil plastisphere, and sheds light on potential ecological risks caused by the soil plastisphere. The formation and succession of soil plastisphere communities can be driven by MP characteristics and soil environmental factors. The soil plastisphere may affect a series of ecological processes, especially the co-transport of environmental contaminants, biodegradation of MPs, and soil carbon cycling. We aim to narrow the knowledge gap between the soil and aquatic plastisphere, and provide valuable guidance for future research on the soil plastisphere in MP-contaminated soils.

Evolution of prokaryotic colonisation of greenhouse plastics discarded into the environment

Current knowledge on the capacity of plastics as vectors of microorganisms and their ability to transfer microorganisms between different habitats (i.e. air, soil and river) is limited. The objective of this study was to characterise the evolution of the bacterial community adhered to environmental plastics [low-density polyethylene (LDPE)] across different environments from their point of use to their receiving environment destination in the sea. The study took place in a typical Mediterranean intermittent river basin in Larnaka, Cyprus, characterised by a large greenhouse area whose plastic debris may end up in the sea due to mismanagement. Five locations were selected to represent the environmental fate of greenhouse plastics from their use, through their abandonment in soil and subsequent transport to the river and the sea, taking samples of plastics and the surrounding environments (soil and water). The bacterial community associated with each sample was studied by 16S rRNA metabarcoding; also, the main physicochemical parameters in each environmental compartment were analysed to understand these changes. The identification and chemical changes in greenhouse plastics were tracked using Attenuated Total Reflection Fourier Transform Infra-red spectroscopy (ATR-FTIR). Scanning Electron Microscope (SEM) analysis demonstrated an evolution of the biofilm at each sampling location. β-diversity studies showed that the bacterial community adhered to plastics was significantly different from that of the surrounding environment only in samples taken from aqueous environments (freshwater and sea) (p-value p-value > 0.05). The environmental parameters (pH, salinity, total nitrogen and total phosphorus) explained the differences observed at each location to a limited extent. Furthermore, bacterial community differences among samples were lower in plastics collected from the soil than in plastics taken from rivers and seawater. Six genera (Flavobacterium, Altererythrobacter, Acinetobacter, Pleurocapsa, Georgfuchsia and Rhodococcus) were detected in the plastic, irrespective of the sampling location, confirming that greenhouse plastics can act as possible vectors of microorganisms between different environments: from their point of use, through a river system to the final coastal receiving environment. In conclusion, this study confirms the ability of greenhouse plastics to transport bacteria, including pathogens, between different environments. Future studies should evaluate these risks by performing complete sequencing metagenomics to decipher the functions of the plastisphere.

Quantifying the importance of plastic pollution for the dissemination of human pathogens: The challenges of choosing an appropriate 'control' material

Discarded plastic wastes in the environment are serious challenges for sustainable waste management and for the delivery of environmental and public health. Plastics in the environment become rapidly colonised by microbial biofilm, and importantly this so-called 'plastisphere' can also support, or even enrich human pathogens. The plastisphere provides a protective environment and could facilitate the increased survival, transport and dissemination of human pathogens and thus increase the likelihood of pathogens coming into contact with humans, e.g., through direct exposure at beaches or bathing waters. However, much of our understanding about the relative risks associated with human pathogens colonising environmental plastic pollution has been inferred from taxonomic identification of pathogens in the plastisphere, or laboratory experiments on the relative behaviour of plastics colonised by human pathogens. There is, therefore, a pressing need to understand whether plastics play a greater role in promoting the survival and dispersal of human pathogens within the environment compared to other substrates (either natural materials or other pollutants). In this paper, we consider all published studies that have detected human pathogenic bacteria on the surfaces of environmental plastic pollution and critically discuss the challenges of selecting an appropriate control material for plastisphere experiments. Whilst it is clear there is no 'perfect' control material for all plastisphere studies, understanding the context-specific role plastics play compared to other substrates for transferring human pathogens through the environment is important for quantifying the potential risk that colonised plastic pollution may have for environmental and public health.

Microbial communities on biodegradable plastics under different fertilization practices in farmland soil microcosms

Plastic mulching is a common practice in agricultural systems and is often combined with fertilization. Biodegradable plastics (BPs) are becoming an alternative to non-biodegradable plastics (non-BPs) for soil mulching. However, the effects of fertilization on the microbial communities on BPs remain unclear. Here, we explored the responses of the plastisphere to different fertilization practices in soil-based microcosms containing three BPs: polylactic acid (PLA), poly (butylene succinate) (PBS), and poly (butylene-adipate-co-terephthalate) (PBAT), and one non-BP (low-density polyethylene, LDPE). The 16S and ITS rRNA gene-based Illumina sequencing method were used to identify the bacterial and fungal communities on the plastics and in the soils. Microbial community structure on BPs was significantly different from that in soils and on LDPE. The predicted functional profiles of bacteria on BPs, especially PBAT, were distinct from those in soils. The plastisphere communities on BPs were dominated by microbes adapted to access and utilize carbon sources compared with of the communities on LDPE. Application of manure increased the alpha diversity of bacterial communities on BPs but decreased it on LDPE. The structure of bacterial communities on BPs changed with the application of manure. Our research establishes the baseline dynamics of plastisphere communities on BPs in soils.

Effects of microplastics on soil properties: Current knowledge and future perspectives

Microplastics (MPs) are a type of emerging contaminants that pose a potential threat to global terrestrial ecosystems, including agroecosystems. In recent years, MPs in soil and their adverse effects on soil health and fertility have attracted increasing concern. Based on the current knowledge, this review begins with a summary of the occurrence and characteristics of MPs in various soil environments, and then highlights the impacts of MPs on soil physical, chemical, and microbiological properties. Data show that MPs occur widely in all surveyed soil types, such as agricultural soils, industrial soils, urban soils, and unused soils, but show variation in their abundance, type, shape, and size. In most cases, MPs can change soil physical, chemical, and microbiological properties, but the effects vary, and are dependent on polymer type, shape, dose, and size. MPs-induced changes in soil fertility and the availability of pollutants may pose a potential threat to plant performance and crop productivity and safety. Particularly, MPs influence the emission of greenhouse gases from soil, ultimately leading to uncertain consequences for global climate change. More comprehensive and in-depth studies are required to fill large knowledge gaps.