Succession of soil bacterial communities and network patterns in response to conventional and biodegradable microplastics: A microcosmic study in Mollisol

Microplastics alter cadmium accumulation in different soil-plant systems: Revealing the crucial roles of soil bacteria and metabolism

Cadmium (Cd) and microplastics (MPs) gradually increased to be prevalent contaminants in soil, it is important to understand their combined effects on different soil-plant systems. We studied how different doses of polylactic acid (PLA) and polyethylene (PE) affected Cd accumulation, pakchoi growth, soil chemical and microbial properties, and metabolomics in two soil types. We found that high-dose MPs decreased Cd accumulation in plants in red soil, while all MPs decreased Cd bioaccumulation in fluvo-aquic soil. This difference was primarily attributed to the increase in dissolved organic carbon (DOC) and pH in red soil by high-dose MPs, which inhibited Cd uptake by plant roots. In contrast, MPs reduced soil nitrate nitrogen and available phosphorus, and weakened Cd mobilization in fluvo-aquic soil. In addition, high-dose PLA proved detrimental to plant health, manifesting in shortened shoot and root lengths. Co-exposure of Cd and MPs induced the shifts in bacterial populations and metabolites, with specific taxa and metabolites closely linked to Cd accumulation. Overall, co-exposure of Cd and MPs regulated plant growth and Cd accumulation by driving changes in soil bacterial community and metabolic pathways caused by soil chemical properties. Our findings could provide insights into the Cd migration in different soil-plant systems under MPs exposure. ENVIRONMENTAL IMPLICATION: Microplastics (MPs) and cadmium (Cd) are common pollutants in farmland soil. Co-exposure of MPs and Cd can alter Cd accumulation in plants, and pose a potential threat to human health through the food chain. Here, we investigated the effects of different types and doses of MPs on Cd accumulation, plant growth, soil microorganisms, and metabolic pathways in different soil-plant systems. Our results can contribute to our understanding of the migration and transport of Cd by MPs in different soil-plant systems and provide a reference for the control of combined pollution in the future research.

Earthworms alleviate microplastics stress on soil microbial and protist communities

Microplastic (MP) pollution can exert significant pressure on soil ecosystems, however, the interactive effects of MPs on soil bacterial, fungal and protist communities remains poorly understood. Soil macrofauna, such as earthworms, can be directly affected by MPs, potentially leading to a range of feedbacks on the soil microbial community. To address this, we conducted a microcosm experiment to examine the effects of conventional (i.e., polyethylene, polystyrene) and biodegradable MPs (i.e. PBAT, polylactic acid) on the structure of the soil bacterial, fungal, and protist communities in the presence or absence of earthworms. We found that MP contamination negatively affected the diversity and composition of soil microbial and protist communities, with smaller-sized conventional MPs having the most pronounced effects. For example, compared with the unamended control, small-sized polyethylene MPs both significantly reduced the Shannon diversity of soil bacteria, fungi, and protist by 4.3 %, 37.0 %, and 9.1 %, respectively. Biodegradable MPs increased negative correlations among bacteria, fungi, and protists. However, earthworms mitigated these effects, enhancing the diversity and altering the composition of these communities. They also increased the niche width and stability of the soil microbial food web network. Our study indicated that earthworms help attenuate the response of soil microorganisms to MPs stress by influencing the diversity and composition of soil microorganisms and soil physicochemical properties and underscores the importance of considering macrofauna in MPs research.

Spatial distribution and assembly processes of bacterial communities in riverine and coastal ecosystems of a rapidly urbanizing megacity in China

Rapid urbanization has precipitated significant anthropogenic pollution (nutrients and pathogens) in urban rivers and their receiving systems, which consequentially disrupted the compositions and assembly of bacterial community within these ecosystems. However, there remains scarce information regarding the composition and assembly of both planktonic and benthic bacterial communities as well as pathogen distribution in such environments. In this study, full-length 16S rRNA gene sequencing was conducted to investigate the bacterial community composition, interactions, and assembly processes as well as the distribution of potential pathogens along a riverine-coastal continuum in Shenzhen megacity, China. The results indicated that both riverine and coastal bacterial communities were predominantly composed of Gammaproteobacteria (24.8 ± 12.6 %), Alphaproteobacteria (16.1 ± 9.8 %), and Bacteroidota (14.3 ± 8.6 %), while sedimentary bacterial communities exhibited significantly higher diversity compared to their planktonic counterparts. Bacterial community patterns exhibited significant divergences across different habitats, and a significant distance-decay relationship of bacterial community similarity was particularly observed within the urban river ecosystem. Moreover, the urban river ecosystem displayed a more complex bacterial co-occurrence network than the coastal ecosystem, and a low ratio of negative:positive cohesion suggested the inherent instability of these networks. Homogeneous selection and dispersal limitation emerged as the predominant influences on planktonic and sedimentary bacterial communities, respectively. Pathogenic genera such as Vibrio, Bacteroides, and Acinetobacter, known for their roles in foodborne diseases or wound infection, were also identified. Collectively, these findings provided critical insights into bacterial community dynamics and their implications for ecosystem management and pathogen risk control in riverine and coastal environments impacted by rapid urbanization.

Impacts of conventional and biodegradable microplastics in maize-soil ecosystems: Above and below ground

The increasing accumulation of microplastics (MPs) in agroecosystems has raised significant environmental and public health concerns, facilitating the application of biodegradable plastics. However, the comparative effects of conventional and biodegradable MPs in agroecosystem are still far from fully understood. Here we developed microcosm experiments to reveal the ecological effects of conventional (polyethylene [PE] and polypropylene [PP]) and biodegradable (polyadipate/butylene terephthalate [PBAT] and polycaprolactone [PCL]) MPs (0, 1%, 5%; w/w) in the maize-soil ecosystem. We found that PCL MPs reduced plant production by 73.6-75.2%, while PE, PP and PBAT MPs elicited almost negligible change. The addition of PCL MPs decreased specific enzyme activities critical for soil nutrients cycling by 71.5-95.3%. Biodegradable MPs tended to reduce bacterial α-diversity. The 1% treatments of PE and PBAT, and PCL enhanced bacterial networks complexity, whereas 5% of PE and PBAT, and PP had adverse effect. Moreover, biodegradable MPs appeared to reduce the α-diversity and networks complexity of fungal community. Overall, PCL reduced the ecosystem multifunctionality, mainly by inhibiting the microbial metabolic activity. This study offers evidence that biodegradable MPs can impair agroecosystem multifunctionality, and highlights the potential risks to replace the conventional plastics by biodegradable ones in agricultural practices.

Joint effect of black carbon deriving from wheat straw burning and plastic mulch film debris on the soil biochemical properties, bacterial and fungal communities

Black carbon (BC) formed after straw burning remains in farmland soil and coexists with plastic mulch film (PMF) debris. It is unclear how BC influences soil multifunctionality in the presence of PMF debris. In this study, we determined the joint effects of BC and PMF debris on soil biochemical properties and microbial communities. We conducted a soil microcosm experiment by adding BC formed by direct burning of wheat straw and PMF debris (polyethylene (PE) and biodegradable PMF (BP)) into soil at the dosages of 1 %, and soils were sampled on the 15th, 30th, and 100th day of soil incubation for high-throughput sequencing. The results showed that the degradation of PMF debris was accompanied by the release of microplastics (MPs). BC decreased NH4+-N (PE: 68.63 %; BP: 58.97 %) and NO3--N (PE: 12.83 %; BP: 51.37 %) and increased available phosphorus (AP) (PE: 79.12 %; BP: 26.09 %) in soil containing PMF debris. There were significant differences in enzyme activity among all the treatments. High-throughput sequencing indicated that BC reduced bacterial and fungal richness and fungal diversity in PMF debris-exposed soil, whereas PMF debris and BC resulted in significant changes in the proportion of dominant phyla and genera of bacteria and fungi, which were affected by incubation time. Furthermore, BC affected microorganisms by influencing soil properties, and pH and N content were the main influencing factors. In addition, FAPRPTAX analysis indicated that BC and PMF debris affected soil C and N cycling. These findings provide new insights into the response of soil multifunctionality to BC and PMF debris.

Comments to "Degli-Innocenti, F. The pathology of hype, hyperbole and publication bias is creating an unwarranted concern towards biodegradable mulch films" [J. Hazard. Mater. 463 (2024) 132923]

Some narratives present biodegradable plastic use for soil mulching practices in agriculture as "environmentally friendly" and "sustainable" alternatives to conventional plastics. To verify these narratives, environmental research recently started focusing on their potential impact on soil health, highlighting some concerns. The paper by Degli-Innocenti criticizes this unfolding knowledge arguing that it is affected by communication hypes, alarmistic writing and a focus on exposure scenarios purposedly crafted to yield negative effects. The quest of scientists for increased impact - the paper concludes - is the driver of such behavior. As scholars devoted to the safeguarding of scientific integrity, we set to verify whether this serious claim is grounded in evidence. Through a bibliometric analysis (using number of paper reads, citations and mentions on social media to measure the impact of publications) we found that: i) the papers pointed out by Degli-Innocenti as examples of biased works do not score higher than the median of similar publications; ii) the methodology used to support the conclusion is non-scientific; and iii) the paper does not fulfil the requirements concerning disclosure of conflicts of interests. We conclude that this paper represents a non-scientific opinion, potentially biased by a conflict of interest. We ask the paper to be clearly tagged as such, after the necessary corrections on the ethic section have been made. That being said, the paper does offer some useful insights for the definition of exposure scenarios in risk assessment. We comment and elaborate on these proposed models, hoping that this can help to advance the field.

Microplastics change soil properties, plant performance, and bacterial communities in salt-affected soils

Microplastics (MPs) are emerging contaminants found globally. However, their effects on soil-plant systems in salt-affected habitats remain unknown. Here, we examined the effects of polyethylene (PE) and polylactic acid (PLA) on soil properties, maize performance, and bacterial communities in soils with different salinity levels. Overall, MPs decreased soil electrical conductivity and increased NH4+-N and NO3--N contents. Adding NaCl alone had promoting and inhibitive effects on plant growth in a concentration-dependent manner. Overall, the addition of 0.2% PLA increased shoot biomass, while 2% PLA decreased it. Salinity increased Na content and decreased K/Na ratio in plant tissues (particularly roots), which were further modified by MPs. NaCl and MPs singly and jointly regulated the expression of functional genes related to salt tolerance in leaves, including ZMSOS1, ZMHKT1, and ZMHAK1. Exposure to NaCl alone had a slight effect on soil bacterial α-diversity, but in most cases, MPs increased ACE, Chao1, and Shannon indexes. Both MPs and NaCl altered bacterial community composition, although the specific effects varied depending on the type and concentration of MPs and the salinity level. Overall, PLA had more pronounced effects on soil-plant systems compared to PE. These findings bridge knowledge gaps in the risks of MPs in salt-affected habitats.

Discrepant soil microbial community and C cycling function responses to conventional and biodegradable microplastics

Biodegradable microplastics (MPs) are promising alternatives to conventional MPs and are of high global concern. However, their discrepant effects on soil microorganisms and functions are poorly understood. In this study, polyethylene (PE) and polylactic acid (PLA) MPs were selected to investigate the different effects on soil microbiome and C-cycling genes using high-throughput sequencing and real-time quantitative PCR, as well as the morphology and functional group changes of MPs, using scanning electron microscopy and Fourier transform infrared spectroscopy, and the driving factors were identified. The results showed that distinct taxa with potential for MP degradation and nitrogen cycling were enriched in soils with PLA and PE, respectively. PLA, smaller size (150-180 µm), and 5% (w/w) of MPs enhanced the network complexity compared with PE, larger size (250-300 µm), and 1% (w/w) of MPs, respectively. PLA increased β-glucosidase by up to 2.53 times, while PE (150-180 µm) reduced by 38.26-44.01% and PE (250-300 µm) increased by 19.00-22.51% at 30 days. Amylase was increased by up to 5.83 times by PLA (150-180 µm) but reduced by 40.26-62.96% by PLA (250-300 µm) and 16.11-43.92% by PE. The genes cbbL, cbhI, abfA, and Lac were enhanced by 37.16%- 1.99 times, 46.35%- 26.46 times, 8.41%- 69.04%, and 90.81%- 5.85 times by PLA except for PLA1B/5B at 30 days. These effects were associated with soil pH, NO3--N, and MP biodegradability. These findings systematically provide an understanding of the impact of biodegradable MPs on the potential for global climate change.

Effects of microplastics on the structure and function of bacterial communities in sediments of a freshwater lake

As an emerging pollutant, microplastics (MPs) cause widespread concern around the world owing to the serious threat they pose to ecosystems. In particular, sediments are thought to be the long-term sink for the continual accumulation of MPs in freshwater ecosystems. Polyethylene (PE) and polyethylene terephthalate (PET) have been frequently detected with large concentration variations in freshwater sediments from the lower reaches of the Yangtze River, one of the most economically developed regions in China, characterized by accelerated urbanization and industrialization, high population density and high plastics consumption. However, the impact of PE and PET on the sedimental bacterial community composition and its function has not been well reported for this specific region. Herein, PE and PET particles were added to freshwater sediments to assess the effects of different MP types on the bacterial community and its function, using three concentrations (500, 1500 and 2500 items/kg) per MP and incubations of 35, 105 and 175 days, respectively. This study identified a total of 68 phyla, 211 classes, 518 orders, 853 families and 1745 genera. Specifically, Proteobacteria, Chloroflexi, Acidobacteriota, Actinobacteriota and Firmicutes were the top five phyla. A higher bacterial diversity was obtained in control sediments than in the MP-treated sediments. The presence of MPs, whether PET or PE, had significant impact on the bacterial diversity, community structure and community composition. PICRUSt2 and FAPOTAX predictions demonstrated that MPs could potentially affect the metabolic pathways and ecologically functional groups of bacteria in the sediment. Besides the MP-related factors, such as the type, concentration and incubation time, the physicochemical parameters had an effect on the structure and function of the bacterial community in the freshwater sediment. Taken together, this study provides useful information for further understanding how MPs affect bacterial communities in the freshwater sediment of the lower reaches of the Yangtze River, China.

Impacts of polypropylene microplastics on the distribution of cadmium, enzyme activities, and bacterial community in black soil at the aggregate level

Microplastics (MPs) can co-occur widely with heavy metals in soil. This study intended to investigate the influences of the co-exposure of polyethylene MPs (0.5 %, w/w) and cadmium (Cd) in black soil on the Cd distribution, enzyme activities, and bacterial communities in both bulk soil and different sized soil aggregates (> 1, 0.50-1, 0.25-0.50, and < 0.25 mm aggregates) after a 90-day incubation. Our results showed that the existence of MPs increased the distributions of Cd in >1 mm and < 0.25 mm soil aggregates and decreased its distributions in 0.50-1 mm and 0.25-0.50 mm soil aggregates. About 12.15 %-17.65 % and 9.03 %-11.13 % of Cd were distributed in the exchangeable and oxidizable forms in bulk soil and various sized soil aggregates after the addition of MPs which were higher than those in the only Cd-treated soil (11.17 %-14.72 % and 8.66 %-10.43 %, respectively), while opposite tendency was found for Cd in the reducible form. Urease and β-glucosidase activities in the Cd-treated soils were 1.14-1.18 and 1.07-1.31 times higher than those in the Cd-MPs treated soils. MPs disturbed soil bacterial community at phylum level and increased the bacteria richness in bulk soil. The levels of predicted functional genes which are linked to the biodegradation and metabolism of exogenous substances and soil C and N cycles were altered by the co-exposure of Cd and MPs. The findings of this study could help deepen our knowledge about the responses of soil properties, especially microbial community, to the co-occurrence of MPs and heavy metals in soil.

Microplastics alter soil structure and microbial community composition

Microplastics (MPs), including conventional hard-to-biodegrade petroleum-based and faster biodegradable plant-based ones, impact soil structure and microbiota in turn affecting the biodiversity and functions of terrestrial ecosystems. Herein, we investigated the effects of conventional and biodegradable MPs on aggregate distribution and microbial community composition in microhabitats at the aggregate scale. Two MP types (polyethylene (PE) and polylactic acid (PLA) with increasing size (50, 150, and 300 μm)) were mixed with a silty loam soil (0-20 cm) at a ratio of 0.5 % (w/w) in a rice-wheat rotation system in a greenhouse under 25 °C for one year. The effects on aggregation, bacterial communities and their co-occurrence networks were investigated as a function of MP aggregate size. Conventional and biodegradable MPs generally had similar effects on soil aggregation and bacterial communities. They increased the proportion of microaggregates from 17 % to 32 %, while reducing the macroaggregates from 84 % to 68 %. The aggregate stability decreased from 1.4 mm to 1.0-1.1 mm independently of MP size due to the decline in the binding agents gluing soil particles (e.g., microbial byproducts and proteinaceous substances). MP type and amount strongly affected the bacterial community structure, accounting for 54 % of the variance. Due to less bioavailable organics, bacterial community composition within microaggregates was more sensitive to MPs addition compared to macroaggregates. Co-occurrence network analysis revealed that MPs exacerbated competition among bacteria and increased the complexity of bacterial networks. Such effects were stronger for PE than PLA MPs due to the higher persistence of PE in soils. Proteobacteria, Bacteroidetes, Chloroflexi, Actinobacteria, and Gemmatimonadetes were the keystone taxa in macroaggregates, while Actinobacteria and Chloroflexi were the keystone taxa in microaggregates. Proteobacteria, Actinobacteria, and Chloroflexi were the most sensitive bacteria to MPs addition. Overall, both conventional and biodegradable MPs reduced the portion of large and stable aggregates, altering bacterial community structures and keystone taxa, and consequently, the functions.

Microplastics alter the equilibrium of plant-soil-microbial system: A meta-analysis

Microplastics (MPs) are widely identified as emerging hazards causing considerable eco-toxicity in terrestrial ecosystems, but the impacts differ in different ecosystem functions among different chemical compositions, morphology, sizes, concentrations, and experiment duration. Given the close relationships and trade-offs between plant and soil systems, probing the "whole ecosystem" instead of individual functions must yield novel insights into MPs affecting terrestrial ecosystems. Here, a comprehensive meta-analysis was employed to reveal an unambiguous response of the plant-soil-microbial system to MPs. Results showed that in view of plant, soil, and microbial functions, the general response patterns of plant and soil functions to MPs were obviously opposite. For example, polyethylene (PE) and polyvinyl chloride (PVC) MPs highly increased plant functions, while posed negative effects on soil functions. Polystyrene (PS) and biodegradable (Bio) MPs decreased plant functions, while stimulating soil functions. Additionally, low-density polyethylene (LDPE), PE, PS, PVC, Bio, and granular MPs significantly decreased soil microbial functions. These results clearly revealed that MPs alter the equilibrium of the plant-soil-microbial system. More importantly, our results further revealed that MPs tended to increase ecosystem multifunctionality, e.g., LDPE and PVC MPs posed positive effects on ecosystem multifunctionality, PE, PS, and Bio MPs showed neutral effects on ecosystem multifunctionality. Linear regression analysis showed that under low MPs size (<100 µm), ecosystem multifunctionality was gradually reduced with the increased size of MPs. The response of ecosystem multifunctionality showed a concave shape pattern along the gradient of experimental duration which was lower than 70 days. More importantly, there was a threshold (i.e., 5% w/w) for the effects of MPs concentration on ecosystem multifunctionality, i.e., under low concentration (< 5% w/w), ecosystem multifunctionality was gradually increased with the increased concentration of MPs, while ecosystem multifunctionality was gradually decreased under high concentration (i.e., > 5% w/w). These findings emphasize the importance of studying the effects of MPs on plant-soil-microbial systems and help us identify ways to reduce the eco-toxicity of MPs and maintain environmental safety in view of an ecology perspective.

Independent and combined effects of microplastics pollution and drought on soil bacterial community

Global terrestrial ecosystems are simultaneously threatened by multiple environmental pressures, with microplastics (MPs) pollution and drought possibly being the most pressing, both of which may have unanticipated effects on soil organisms. Here, we investigated the responses of diversity, composition and functions of soil bacterial community to MPs pollution (including two MPs types: polyethylene (PE) and polylactic acid (PLA); two MPs sizes: < 20 μm and <300 μm) and drought in microcosms. We found that only 20 μm PLA MPs significantly decreased soil bacterial diversity by 17.4 % and altered soil bacterial community composition, while PE MPs and 300 μm PLA MPs had no significant effects. The copiotrophic bacteria (i.e., Proteobacteria and Firmicutes) were enriched in the 20 μm PLA MPs pollution soils due to the enhanced dissolved organic carbon contents. Moreover, our results showed that the 20 μm PLA MPs also affected the potential phenotypes and functions of soil bacterial community, increasing the potentially pathogenic, stress-tolerant, containing mobile elements and forming biofilms phenotypes, and promoting membrane transport and signal transduction pathways. These results suggested that the effects of MPs on soil bacterial community varied depending on MPs types and sizes. However, drought significantly increased soil bacterial diversity by 10.3 % and affected soil bacterial community composition in the 20 μm PLA MPs pollution soils. We also found that drought inhibited the levels of potentially pathogenic, containing mobile elements and forming biofilms phenotypes in the 20 μm PLA MPs pollution soils. Taken together, these findings reveal that drought may alleviate the adverse effects of MPs pollution on soil bacterial community, which enhances our understanding of the interactive effects of multiple global change factors on agroecosystem functions.

Biodegradable PBAT microplastics adversely affect pakchoi (Brassica chinensis L.) growth and the rhizosphere ecology: Focusing on rhizosphere microbial community composition, element metabolic potential, and root exudates

Biodegradable plastics (BPs) have gained increased attention as a promising solution to plastics pollution problem. However, BPs often exhibited limited in situ biodegradation in the soil environment, so they may also release microplastics (MPs) into soils just like conventional non-degradable plastics. Therefore, it is necessary to evaluate the impacts of biodegradable MPs (BMPs) on soil ecosystem. Here, we explored the effects of biodegradable poly(butylene adipate-co-terephthalate) (PBAT) MPs and conventional polyethylene (PE) MPs on soil-plant (pakchoi) system at three doses (0.02 %, 0.2 %, and 2 %, w/w). Results showed that PBAT MPs reduced plant growth in a dose-dependent pattern, while PE MPs exhibited no significant phytotoxicity. High-dose PBAT MPs negatively affected the rhizosphere soil nutrient availability, e.g., decreased available phosphorus and available potassium. Metagenomics analysis revealed that PBAT MPs caused more serious interference with the rhizosphere microbial community composition and function than PE MPs. In particular, compared with PE MPs, PBAT MPs induced greater changes in functional potential of carbon, nitrogen, phosphorus, and sulfur cycles, which may lead to alterations in soil biogeochemical processes and ecological functions. Moreover, untargeted metabolomics showed that PBAT MPs and PE MPs differentially affect plant root exudates. Mantel tests, correlation analysis, and partial least squares path model analysis showed that changes in plant growth and root exudates were significantly correlated with soil properties and rhizosphere microbiome driven by the MPs-rhizosphere interactions. This work improves our knowledge of how biodegradable and conventional non-degradable MPs affect plant growth and the rhizosphere ecology, highlighting that BMPs might pose greater threat to soil ecosystems than non-degradable MPs.

Metagenomic exploration of microbial and enzymatic traits involved in microplastic biodegradation

Agricultural mulch films are frequently applied to achieve high yield, resulting in large quantities of microplastic (MP) pollution in agroecosystem. However, studies focusing specifically on the diversity of MP-degrading enzymes and related microbial communities have yet to be conducted. Here, we established a soil microcosmic incubation with addition of 5% (w/w) conventional (low-density polyethylene (LDPE)) and biodegradable (blend of polylactic acid (PLA) and polybutylene adipate terephthalate (PBAT)) MPs for incubation 90 days. The DNA samples extracted from soils and plastisphere of MPs were examined by metagenomics and genome binning methods, specifically targeting carbohydrate-active enzymes (CAZymes) and plastic-degrading enzymes (PDZymes). The results revealed that plastisphere of MPs exhibited significantly distinct patterns of CAZymes and PDZymes from soils, and abundances of all examined exoenzymes were higher in plastisphere than those in soils. Plastisphere of LDPE-MPs selectively enriched proteases and alkane monooxygenase (alkB), and required families of carbohydrate-binding module (CBM) to increase the binding of CAZymes with MPs. Dissimilarly, diverse CAZymes with high abundances were observed in the plastisphere of PBAT-PLA MPs and esterases were important indicative PDZymes for PBAT-PLA degradation. The enriched exoenzymes in plastisphere of LDPE-MPs were mainly assigned to Actinobacteria while Proteobacteria with higher abundance in plastisphere of PBAT-PLA MPs containing most indicative exoenzymes. Moreover, a high-quality genome classified as Amycolatopsis japonica was reconstructed and found to contain one or more gene copies of indicative exoenzymes for polyethylene. Two novel genomes classified as Sphingomonas were selectively enriched in plastisphere of PBAT-PLA MPs and contained diverse genes encoding degrading exoenzymes. Taken together, our study highlighted the CAZymes and PDZymes can be exploited as potent microbial strategies for solving MPs pollution in croplands.

Effects of polyethylene microplastics on properties, enzyme activities, and the succession of microbial community in Mollisol: At the aggregate level

Soil, as a heterogeneous body, is composed of different-sized aggregates. There is limited data available on the potential role of microplastics (MPs) in microbial properties at the soil aggregate level. In this study, changes in microbial construction and diversity in farmland bulk soil and aggregates induced by polyethylene MPs (PE-MPs) were investigated at a dose of 0.5% (w/w) through 16s rDNA sequencing and enzyme activity measurements of different particle size aggregates in incubated soil. The presence of low-dose PE-MPs increased the proportion of >1 mm soil aggregates fraction, and decreased soil available nitrogen and available phosphorus in bulk soils. Furthermore, low-dose PE-MPs increased bacterial richness and diversity in 1-0.5 and < 0.25 mm fractions and decreased operational taxonomic unit, abundance-based coverage estimator, and Chao1 indices in bulk soil and >1 mm fractions. The levels of predicted functional genes taking part in the biodegradation and metabolism of exogenous substances also increased. At the phylum level, PE-MPs changed the proportion of Proteobacteria and Actinobacteria. The variations in soil aggregate properties were significantly correlated with the bacterial communities' composition and diversity. This study deepens our perception of the soil microenvironment, microbial community composition, and diversity in response to PE-MPs.

Drought Alleviates the Negative Effects of Microplastics on Soil Micro-Food Web Complexity and Stability

Soil ecosystems are under considerable pressure due to anthropogenic factors, including microplastics (MPs) pollution and drought. However, little is known about the interactive effects of MPs and drought on soil organisms, especially soil micro-food web. We conducted a microcosm experiment with MPs pollution (including two types and two sizes of MPs) and drought to investigate their interaction effects on soil microbial, protist, and nematode communities in soil micro-food web. We found that MPs significantly decreased the complexity and stability of soil micro-food web, with greater negative effects of biodegradable and smaller-sized MPs than conventional and larger-sized MPs. Drought had negative effects on soil micro-food web in the non-MPs pollution soils while increasing the complexity and stability of soil micro-food web in the MPs pollution soils. Drought increased the proportion of negative correlations between bacteria and fungi in the biodegradable MPs soils while decreasing the proportion of negative correlations between protists and nematodes in the smaller-sized MPs soils. Our study reveals that drought may alleviate the negative effects of MPs on soil micro-food web by reducing competition among lower trophic levels in the biodegradable MPs pollution soils while reducing competition among higher trophic levels in the smaller-sized MPs pollution soils.

Response of soybean and maize roots and soil enzyme activities to biodegradable microplastics contaminated soil

Although biodegradable plastic film is a promising alternative product for reducing polyethylene plastic pollution in agricultural soils, the effects of its residues on plant growth and soil properties remain unclear. In this study, we conducted an experiment to investigate root properties and soil enzyme activities in Poly (butylene adipate-co-terephthalate) microplastics (PBAT-MPs) contaminated soil (0 % (CK), 0.1 %, 0.2 %, 0.5 % and 1 % of dry soil weight) with soybean (Glycine max (Linn.) Merr.) and maize (Zea mays L.). The results show that PBAT-MP accumulation in soil negatively affects root growth, and alter soil enzyme activities, which may then constrain C/N cycling and potential yields. For soybean, the total root length, total root surface area and root biomass decreased by 34 %- 58 %, 34 %- 54 % and 25 %- 40 % at the harvesting stage compared to CK, respectively. The negative effects of PBAT-MPs on maize roots were greater than on soybean roots. The total root length, root surface area and root biomass of maize decreased by 37 %- 71 %, 33 %- 71 % and 24 %- 64 % at the tasseling and harvesting stage, respectively (p < 0.05). Furthermore, a statistical analysis of the data indicates that the inhibition of soybean and maize root growth by PBAT-MP accumulation was mediated by the significantly different impacts of PBAT-MP addition on C-enzyme (β-xylosidase, cellobiohydrolase, β-glucosidase) and N-enzyme activities (leucine-aminopeptidase, N-acetyl-β-glucosaminidase, alanine aminotransferase) in rhizosphere and non-rhizosphere soil, possibly due to interactions with plant-specific root exudates and microbial communities. These findings show the potential risks posed by biodegradable microplastics on the plant-soil system, and suggest that biodegradable plastic film should be applied with caution.

Distinct influence of conventional and biodegradable microplastics on microbe-driving nitrogen cycling processes in soils and plastispheres as evaluated by metagenomic analysis

Plastic mulching is one of the large contributors to microplastic (MP) accumulation in agricultural landscapes. However, the effects of conventional (PE-MPs) and biodegradable MPs (BMPs) on microbial functional and genomic information encoding nitrogen (N) cycling have yet to be addressed. Here, a soil microcosmic experiment was conducted by adding PE-MPs and BMPs to a Mollisol at dosage of 5% (w/w) followed by incubation for 90 days. The soils and MPs were examined by metagenomics and genome binning methods. The results revealed that BMPs harbored rougher surfaces and induced stronger alterations in microbial functional and taxonomic profiles in the soil and plastisphere than PE-MPs. In comparison to their respective soils, the plastispheres of PE-MPs and BMPs stimulated the processes of N fixation, N degradation and assimilatory nitrate reduction (ANRA) and reduced the gene abundances encoding nitrification and denitrification, in which BMPs induced stronger influences than PE-MPs. Ramlibacter mainly drove the differences in N cycling processes between the soils containing two types of MPs and was further enriched in the BMP plastisphere. Three high-quality genomes were identified as Ramlibacter stains with higher abundances in the plastisphere of BMP than that of PE-MP. These Ramlibacter strains had the metabolic capacities of N fixation, N degradation, ANRA and ammonium transport, which were potentially attributed to their biosynthesis and the accumulation of soil NH₄⁺-N. Taken together, our results highlight the genetic mechanisms of soil N bioavailability in the presence of biodegradable MPs, which have important implications for maintaining sustainable agriculture and controlling microplastic risk.

Molecular insights into effects of PBAT microplastics on latosol microbial diversity and DOM chemodiversity

The impact of biodegradable microplastics on the microbial community and dissolved organic matter (DOM) in latosol has not been well reported. In this study, an incubation experiment at 25 ºC for 120 days using latosol amended with low (5%) and high (10%) concentrations of polybutylene adipate terephthalate (PBAT) microplastics was carried out to explore the impacts of PBAT microplastics on soil microbial communities and DOM chemodiversity, and the intrinsic interactions between their shifts. The main bacterial and fungal phyla in soil, namely Chloroflexi, Actinobacteria, Chytridiomycota, and Rozellomycota showed a nonlinear relationship with PBAT concentration and played a pivotal role in shaping DOM chemodiversity. A higher decreased levels of lignin-like compounds and increased levels of protein-like and condensed aromatic compounds in the 5% treatment were observed than that in the 10% treatment. Furthermore, a higher increase relative abundance of CHO compounds in the 5% treatment than in the 10% treatment was ascribed to its higher oxidation degree. Co-occurrence network analysis suggested that bacteria formed more complex relationships with DOM molecules than fungi did, indicating their critical roles in DOM transformation. Our study has important implications for understanding the potential influence of biodegradable microplastics on carbon biogeochemical roles in soil.

The escalated potential of the novel isolate Bacillus cereus NJD1 for effective biodegradation of LDPE films without pre-treatment

This study focused on the biodegradation of LDPE films using a novel isolate of Bacillus obtained from soil samples collected from a 20-year-old plastic waste dump. The aim was to evaluate the biodegradability of LDPE films treated with this bacterial isolate. The results indicated a 43% weight loss of LDPE films within 120 days of treatment. The biodegradability of LDPE films was confirmed through various testing methods, including BATH, FDA, CO₂ evolution tests, and changes in total cell growth count, protein content, viability, p^H of the medium, and release of microplastics. The bacterial enzymes, including laccases, lipases, and proteases, were also identified. SEM analysis revealed biofilm formation and surface changes in treated LDPE films, while EDAX analysis showed a reduction in carbon elements. AFM analysis demonstrated differences in roughness compared to the control. Furthermore, wettability increased and tensile strength decreased, confirming the biodegradation of the isolate. FTIR spectral analysis showed changes in skeletal vibrations, such as stretches and bends, in the linear structure of polyethylene. FTIR imaging and GC-MS analysis also confirmed the biodegradation of LDPE films by the novel isolate identified as Bacillus cereus strain NJD1. The study highlights the potentiality of the bacterial isolate for safe and effective microbial remediation of LDPE films.

Biodegradable mulch films significantly affected rhizosphere microbial communities and increased peanut yield

Biodegradable mulch films are widely used to replace conventional plastic films in agricultural fields. However, their ecological effects on different microbial communities that naturally inhabit agricultural fields are scarcely explored. Herein, differences in bacterial communities recovered from biofilms, bulk soil, and rhizosphere soil were comparatively assessed for polyethylene film (PE) and biodegradable mulch film (BDM) application in peanut planted fields. The results showed that the plastic film type significantly influenced the bacterial community in different ecological niches of agricultural fields (P < 0.001). Specifically, BDMs significantly increased the diversity and abundance of bacteria in the rhizosphere soil. The bacterial communities in each ecological niche were distinguishable from each other; bacterial communities in the rhizosphere soil showed the most pronounced response among different treatments. Acidobacteria and Pseudomonas were significantly enriched in the rhizosphere soil when BDMs were used. BDMs also increased the rhizosphere soil bacterial network complexity and stability. The enrichment of beneficial bacteria in the rhizosphere soil under BDMs may also have implications for the observed increase in peanut yield. Deepening analyses indicated that Pseudoxanthomonas and Glutamicibacter are biomarkers in biofilms of PE and BDMs respectively. Our study provides new insights into the consequences of the application of different types of plastic films on microbial communities in different ecological niches of agricultural fields.

Soil bacterial community and metabolism showed a more sensitive response to PBAT biodegradable mulch residues than that of LDPE mulch residues

Biodegradable mulch film (BDM) is considered as an environmentally sustainable alternative to low density polyethylene (LDPE) mulch film. However, the low degradation rate of BDM resulted in residues in soil after service period which were similar to LDPE mulch film. Distinguishing the differential responses of crop growth, soil bacteria and metabolism to residues of BDM and LDPE mulch films is favourable for comparing the environmental toxicities of the two materials. The results indicated that emergence rate and yield of Chinese cabbage (Brassica campestris L. ssp. chinensis Makino) were significantly inhibited by two types mulch residues. BDM residues significantly decreased bacterial diversity by 1.2-2.3% through the enrichment of dominant phyla and inhibition of inferior phyla, while LDPE mulch residues not. The effects of BDM residues on soil metabolite spectrum were stronger than LDPE mulch residues with significant increase (3.9% 5.8%) in the abundance of total metabolites. Besides the pathways of metabolism, organismal systems, environmental information processing influenced by LDPE mulch resides, differential pathways including human diseases and cellular processes were also determined in soil with BDM residues. According to all the results of the present study, prior to the promotion of BDM, its influences on soil safety must be carefully investigated through critical and systematic research.