Discrepant responses of bacterial community and enzyme activities to conventional and biodegradable microplastics in paddy soil

Insights into soil microbial assemblages and nitrogen cycling function responses to conventional and biodegradable microplastics

Biodegradable microplastics (MPs) are proposed as sustainable alternatives to conventional MPs, yet their distinct effects on soil microbial communities and ecological functions remain insufficiently understood. This study compares the impacts of biodegradable polylactic acid (PLA) and conventional polyvinyl chloride (PVC) MPs on soil microbial assemblages and nitrogen cycling. Fluorescein diacetate hydrolase (FDAse) activity was temporarily stimulated by 2 % (w/w) PLA and PVC MPs, while 7 % (w/w) PVC MPs initially inhibited FDAse activity before promoting it. PLA MPs (2 % and 7 %, w/w) dramatically reduced bacterial diversity and altered community structure, enriching genera such as Nocardioides, Arthrobacter, Agromyces, Amycolatopsis, Saccharothrix, and Ramlibacter, known for degrading complex compounds. Conversely, PVC MPs (2 % and 7 %, w/w) showed minimal influence on bacterial diversity, with only temporary structural shifts at high concentrations (7 % w/w). Network analysis revealed greater microbial complexity with PLA MPs, where MPs-degrading taxa emerged as keystone species. PLA MPs at both concentrations notably increased the abundance of nitrogenase iron protein subunit H gene (nifH) and nitrogen-fixing bacteria, such as Bradyrhizobium, while also sustaining ammonia monooxygenase subunit A gene (AOB amoA) effects up to day 90. At higher doses (7 % w/w), PLA MPs enriched copper-containing nitrite reductase gene (nirK) and cytochrome cd1 nitrite reductase gene (nirS) abundance, boosting denitrifiers like Cupriavidus, Pseudarthrobacter, and Ensifer. In contrast, PVC MPs showed short-term effects on nitrogen cycling function. These findings have important implications for promoting sustainable agriculture and managing the environmental risks posed by MPs in soil ecosystems.

The bridging role of soil organic carbon in regulating bacterial community by microplastic pollution: Evidence from different microplastic additions

The serious threat posed by microplastics pollution to soil ecosystems and human health has attracted worldwide attention. Microplastics of different types are present in the soil environment, whereas research about the effects of different microplastics on soil ecology are limited. This study sought to determine how three common microplastics (polyethylene (PE), polystyrene (PS), and polyvinyl chloride (PVC)) affect soil physicochemical characteristics, enzyme activities, bacterial community, and their metabolic pathways at a 1 % w/w concentration. All three microplastic treatments significantly increased soil organic carbon (SOC), labile organic C fractions, and enhanced soil carbon to nitrogen ratio. PE, PS, and PVC microplastics exhibited promotion of α-glucosidase (α-GC), sucrase (SC), and alkaline phosphatase (AKP) activities. PS microplastics caused a significant increase in N-acetyl-β-D-glucosidase (NAG) and leucine aminopeptidase (LAP) activities, while PVC microplastics significantly decreased β-glucosidase (β-GC) activity. Microplastic treatments increased the bacterial community diversity while altering its composition. Proteobacteria and Chloroflexi were the dominant bacterial phyla in the soil, with microplastic treatments increasing the relative abundance of Chloroflexi and decreasing that of Proteobacteria. Functional prediction analysis indicated that microplastic treatments enriched genes involved in carbohydrate and amino acid metabolism, while reducing the abundance of genes related to signal transduction and cell motility. Correlation and pathway analyses revealed that microplastics affect bacterial community diversity and composition through direct and indirect effects (by acting on SOC or its key labile fractions), thereby influencing soil enzyme activities. In conclusion, the work emphasizes the impacts of different microplastics on soil ecosystems in terms of commonalities and dissimilarities, with the innovative finding of indirect regulation of bacterial community by SOC under microplastics contamination. This provides new perspectives for subsequent studies.

Lignosulfonate Improves Soil Fertility by Promoting Exchangeable Al3+ Immobilization and Facilitating Its Interaction with Soil Enzymes through Active Functional Group Surfaces

Soil acidification threatens soil health and sustainable agriculture, and conventional mitigation strategies have various limitations, underscoring the need for the creation of more effective and sustainable alternatives. In this study, we evaluated the effects of calcium lignosulfonate (CL) on the physicochemical properties of acidic soils (Rs, K2j, and J2s) through pot experiments. Additionally, molecular modeling calculations were employed to investigate the interaction mechanisms between CL and soil exchangeable acidity and active enzyme. The results showed that CL was superior to lime in reducing phytotoxic exchangeable Al3+, enhancing soil acidification buffering capacity, and improving soil fertility and plant biomass accumulation. These benefits were attributed to the strong competitive adsorption of exchangeable Al3+ by the CL surface active functional groups, enhanced interactions between CL and soil enzymes, and the restructuring of microbial communities. These findings provide valuable insights for developing efficient soil amendments to mitigate the effects of acidification, ultimately enhancing soil health and agricultural productivity.

Microplastics alter microbial structure and assembly processes in different soil types: Driving effects of environmental factors

Microplastics (MPs) are emerging pollutants with potential impacts on soil ecosystems. However, it is unclear how MPs-induced changes in the soil environment drive microbial structure and assembly in different soils. Here we investigated the responses of microbial structure, enzyme activities and soil properties to biodegradable polylactic acid (PLA) and conventional polythene (PE) with different doses in different soil types. Results showed that PLA generally decreased soil NH4+-N and NO3--N levels but increased dissolved organic carbon (DOC) and pH, whereas PE exhibited contrasting effects depending on soil type. MPs significantly stimulated soil urease, sucrase, catalase and phosphatase activities, with dose-dependent responses observed under PLA treatments in fluvo-aquic soil. Additionally, MPs altered microbial composition and colonized specific bacterial taxa in different soils. In microbial assemblies dominated by stochastic processes, MPs, especially PE promoted the deterministic processes. Co-occurrence patterns showed lower microbial complexity under PLA treatments compared to PE. Notably, we revealed soil-type-specific response patterns: DOC emerged as the primary driver in red soil ecosystems, while pH exerted dominant control in fluvo-aquic soil systems. Furthermore, perturbation of microbial communities by MPs affected functions related to metabolism. These findings highlight that MPs-induced shifts in microbial communities and assembly processes are soil-type-specific and mediated by soil characteristics changes, providing critical insights for assessing the ecological risks of MPs in diverse agricultural soils.

Soil C-N and microbial community were altered by polybutylene adipate terephthalate microplastics

The risks posed by biodegradable plastics to the plant-soil system have been increasingly studied due to potentially hazardous effects on soil properties and nutrient cycling. In this study, we investigated the effects of Poly (butylene adipate-co-terephthalate) microplastics (PBAT-MPs) on soil carbon, nitrogen and microbial communities under different levels of contamination (0 % (control), 0.1 %, 0.2 %, 0.5 % and 1 %), in soils planted with soybean (Glycine max (Linn.) Merr.) and maize (Zea mays L.). The results showed that PBAT-MPs significantly altered soil dissolved organic carbon, dissolved organic nitrogen and nitrate nitrogen contents, and that these effects varied by plant type and growth stage (p < 0.05). PBAT-MPs significantly increased soil microbial biomass carbon and nitrogen for both plants (p < 0.05), except for microbial biomass nitrogen at the soybean flowering stage. PBAT-MPs altered the β-diversity and composition of bacterial and fungal communities, increasing the relative abundances of Proteobacteria but decreasing the relative abundances of Acidobacteriota for both plants. FAPROTAX analysis showed that PBAT-MPs had significant effects on functional bacterial groups related to the nitrogen and carbon cycle, that varied by plant type and growth stage. These results suggest that biodegradable microplastics may have plant-specific effects on soil microbial communities and microbial metabolism, and thereby influence soil carbon and nitrogen cycling.

Effects of polyethylene microplastics on soil microbial assembly and ecosystem multifunctionality in the remote mountain: Altitude matters

Microplastics (MPs) are ubiquitously present in almost every ecosystem globally, including the remote mountains. To date, the effects of MPs on the properties and functioning of soils in remote mountainous ecosystems have been less explored. This study aimed to investigate the ecological impacts of polyethylene (PE) MPs at ∼0.2 % (w/w) on soils in three typical altitude zones of Changbai Mountain, China, including the mixed coniferous and broad-leaved forest (MF) zone, birch forest (BF) zone, and alpine tundra (AT) zone. The results showed that PE MPs exerted diverse effects on soil carbon and nitrogen nutrients across altitude zones but consistently increased soil pH. PE MPs enhanced the humification of soil dissolved organic matter (DOM) and the α-diversity of the bacterial community in the lower-altitude MF zone but exerted negligible effects in the higher-altitude BF and AT zones. Phyla Proteobacteria and Actinobacteria dominated bacterial communities under all treatments but exhibited opposite variation patterns on exposure to MPs. PE MPs contributed to the enrichment of a larger number of carbohydrate-active enzymes (CAZy) gene families in the BF and particularly MF zones. Soil ecosystem multifunctionality was significantly improved by PE MPs in the AT and MF zones but was less affected in the BF zone. The soil bacterial diversity, pH, organic carbon, DOM chemodiversity, and climatic factors (i.e., mean annual temperature) were the pivotal predictors of soil ecosystem multifunctionality. This study provides new insights for evaluating the ecological impacts of MPs on soils in remote mountains.

Effects of Aging Biodegradable Agricultural Films on Soil Physicochemical Properties and Heavy Metal Speciation

Through soil incubation experiments, the effects of aged PBAT + PLA (polybutylene adipate terephthalate + polylactic acid) film fragments were analyzed. Surface characteristics and chemical structures of the films changed significantly after one (T2) and two years (T1) of aging compared to new films (T3). Both new and aged fragments reduced soil pH, altered enzyme activities, and influenced dissolved organic matter (DOM) fluorescence. Alkaline phosphatase activity declined by 33.2%, 23.8%, and 11.6% for T1, T2, and T3, respectively, while urease and sucrase activities increased in a time-dependent manner. The degree of soil humification rose by 66.4%, 60.4%, 49.3%, and 88.6% for T1, T2, T3, and T4, respectively, compared to the control (CK). Aged films exhibited stronger DOM fluorescence intensity than new films. Tessier extraction analysis revealed a decrease in exchangeable Cd by 22.9%, 13.1%, and 10.2% for T1, T2, and T3, respectively, while organically bound Cu increased. Correlation analysis indicated a significant positive relationship between soil humification and heavy metal bioavailability. These findings provide insight into the ecological effects of biodegradable agricultural films, offering a theoretical foundation for assessing their environmental risks and safety.

Assessment of the Effects of Garlic (Allium sativum L.) Stalk Incorporation on Soil Fertility and Bacterial Biodiversity

The lone application of ammonium fertilizer is one of the most commonly used measures to supplement soil nutrients. At the same time, it also causes soil acidification and leads to many environmental problems, such as soil degradation and eutrophication. Garlic (Allium sativum L.) stalk (RGS) returning has been widely researched for its benefits related to soil organic carbon (SOC) and crop yields. However, few have researched the effects of the incorporation of RGS mixed with ammonium fertilizer on soil physicochemical properties and the bacterial community composition. We incubated soil with the control (N0); ammonium sulfate (AS); and ammonium sulfate combined with 1%, 2%, 3%, and 5% (rate of the dry soil weight) garlic stalk at 25 °C and 60% water-filled pore spaces (WFPS) for 67 days. We measured the soil properties before and on the last day of the experiment. The results showed that adding RGS increased the contents of soil potassium (K), magnesium (Mg), and total nitrogen (TN), but it significantly decreased soil nitrate (NO3-). In addition, adding RGS increased the relative abundance of r-strategists and the soil r/K ratio. The α diversity of soil bacteria reached the highest value with 3% treatment. Compared to AS, RGS increased the relative abundance of Firmicutes and Actinobacteria but decreased that of Proteobacteria and Acidobacteria. The function genes of Replication_and_Repair and Cell_Motility were enhanced after adding AS, while the function genes of Metabolism_of_Other_Amino_Acids, Enzyme_Families, and Metabolism were enhanced with increased RGS rates. Although SOC increased, NO3- significantly decreased with the increase in the returning levels, which could be due to the strong decreases in nitrifying bacteria with increases in RGS rates from 3% to 5%. Therefore, adding RGS at 3% is suitable for soil bacterial biodiversity and nutrient balance.

Microplastic effects on soil nitrogen cycling enzymes: A global meta-analysis of environmental and edaphic factors

Microplastic accumulation in soil ecosystems poses significant environmental concerns, potentially impacting nitrogen cycling processes and ecosystem health. This meta-analysis of 147 studies (1138 data points) assessed the impact of microplastics (MPs) on soil nitrogen-acquisition enzymes. We found that MPs exposure significantly increased soil urease (UE) and leucine aminopeptidase activities by 7.6 % and 8.0 %, respectively, while N-acetyl-β-D-glucosaminidase activity was not significantly affected. Biodegradable MPs showed more pronounced effects compared to conventional MPs. Enzyme activities were influenced by MPs properties (e.g., polymer type, size, concentration), experimental conditions (e.g., field or laboratory setting, temperature, nitrogen fertilization), and soil properties (e.g., clay content, pH, organic carbon, total nitrogen). For instance, acidic soils enhanced UE activity, while neutral soils reduced it. These findings emphasize the complex interactions between MPs and soil ecosystems, highlighting the need for context-specific environmental management strategies and policy-making approaches to mitigate the impacts of MPs pollution on soil health.

NO3--N pulse supply caused by biodegradable plastics exacerbates Trifolium repens L. invasion

The exacerbation of plant invasion by microplastics attracted widespread attention. Pulse resource hypothesis is popular theory to elucidate plant invasion. Our previous work demonstrated biodegradable microplastics (BMPs) could increase the arbuscular mycorrhizal fungi (AMF) colonization rate. Reportedly, AMF can enhance rhizobia colonization. Therefore, we infer the coexistence of BMPs with legumes may lead to an increased colonization of rhizobia with negative feedback regulation of N fixation. This could result in NO3--N pulse supply, thereby exacerbating plant invasion. Subsequently, a 60-day pot experiment was conducted using Trifolium repens L. as invasive plant and Oxalis corniculata L. as native plant, with 1% or 5% wt BMPs. AMF colonization, BMPs degradation, NO3--N content and pulse supply, rhizobia colonization, relative competitive intensity, replacement diagrams and NO3--N utilization were determined. The mechanism was clarified through heat map and structural equation model. The results reveal the greater the NO3--N consumption by BMPs, the more AMF promoted rhizobia colonization in T. repens, thereby the larger the pulse amplitude of NO3--N supply, then, the higher the NO3--N utilization rate of T. repens. It exacerbates T. repens invasion. This study clarifies effects of BMPs on rhizobia's N fixation, and enriches the evidence on mechanism of BMPs exacerbating plant invasion.

Influence of biodegradable microplastics on soil carbon cycling: Insights from soil respiration, enzyme activity, carbon use efficiency and microbial community

The rising prevalence of biodegradable microplastics (BMPs) in soils has raised concerns about their impacts on soil ecosystems and carbon cycling. This study investigates the effects of different BMPs on soil carbon cycling, focusing on soil respiration, enzyme activities, and carbon use efficiency (CUE) from 13C-labeled dissolved organic carbon (DOC) in an upland soil. The BMPs tested were polybutylene adipate terephthalate (PBAT), polyhydroxyalkanoates (PHA), and polylactic acid (PLA), at high (H, 1% w/w) and low (L, 0.1% w/w) concentrations. Over a 64-day incubation, cumulative CO2 emissions increased in the PHA_L, PHA_H, and PLA_H treatments, with the highest rise of 665% PHA_H treatment. Microbial biomass carbon (MBC) ranged from 97.73 ± 3.03 mg C kg⁻1 in the control to 223.09 ± 7.91 mg C kg⁻1 in PHA_H, with microbial CUE peaking at 0.26 in PHA_H. Enzymatic activities were notably affected: β-glucosidase (BG) increased by 50% in PLA_H, while cellobiohydrolase (CBH) activity decreased by up to 62% in PBAT_H and PLA_L. N-acetylglucosaminidase (NAG) and phosphatase (AP) activities were highest in PHA_H, indicating enhanced nutrient cycling. Microbial community structure based on PLFAs was significantly altered, with total PLFA content increasing by 191% in PHA_H. Correlation analysis and partial least squares path modeling (PLS-PM) revealed that BMP concentration, DOC content, and microbial diversity were positively correlated with microbial CUE. This study highlights the significant role of BMPs in influencing soil carbon cycling, primarily through their effects on microbial diversity and soil enzyme activities.

Simultaneous removal of ammonia, copper ions and sulfamethoxazole from aquaculture wastewater with low carbon to nitrogen ratio enhanced by manganese redox driven by a two-stage synergistic bioreactor: Optimization and potential mechanism

The problem of low carbon-nitrogen ratio (C/N) in wastewater is a major challenge for biological treatment, especially the complex pollution of ammonia nitrogen (NH4+-N), sulfamethoxazole (SMX), and copper ions (Cu(II)). Herein, a strain of Pseudoxanthomonas sp. MA23 with manganese (Mn) reduction-coupled ammonia oxidation properties was isolated. Subsequently, kaolin and bentonite were used as the main raw materials, and a mixture of coconut shell biochar (CSBC) and different Mn ores were added to make ceramsite carriers to load the target strain MA23. To achieve complete N removal and Mn redox process, Dechloromonas sp. YZ8 with Mn redox and denitrification performance was introduced, and a second-stage bioreactor was constructed with volcanic rock as the biocarrier. The results showed that the bioreactor was most effective when the hydraulic retention time (HRT) was 20.0 and 2.0 h, C/N was 1.5, and pH was 6.5. The response of the bioreactors was investigated by inflowing different concentrations of Cu(II) and SMX. Appropriate Cu(II) concentrations promoted the electron transfer in the system, and Cu(II) and SMX were together removed by biological action and chemisorption. Furthermore, genes involved in N metabolism were enriched in the bioreactors and the microorganisms responded to environmental changes by up or down-regulating relevant metabolic genes. The synergistic system proposed in this study provided a promising attempt to simultaneously address NH4+-N-Cu(II)-SMX pollution in low C/N wastewater.

Unveiling the impact of biodegradable polylactic acid microplastics on meadow soil health

Soil microplastics (MPs) pollution has garnered considerable attention in recent years. The use of biodegradable plastics for mulching has led to significant quantities of plastic entering agro-ecosystems. However, the effects of biodegradable polylactic acid (PLA) plastics on meadow soils remain underexplored. This study investigates the impacts of PLA-MPs of varying particle sizes and concentrations on soil physicochemical properties, enzyme activities, and microbial communities through a 60-day incubation experiment. PLA-MPs increased the pH, soil organic matter, total nitrogen (TN) and available potassium (AK) content, as well as enhanced the activities of superoxide dismutase (S-SOD), peroxidase (S-POD), soil catalase (S-CAT), β-glucosidase (S-β-GC) and urease (S-UE) activities. Conversely, a decrease in alkaline phosphatase (S-ALP) activity was observed. The influence of PLA-MPs on soil physicochemical properties was more pronounced with larger particle sizes, whereas smaller particles had a greater effect on enzyme activities. Additionally, PLA-MPs led to an increase in the abundance of Acidobacteriota, Chloroflexi, and Gemmatimonadota, while the abundance of Proteobacteria, Actinobacteriota, and Patescibacteria declined. Mantel test analysis showed that changes in microbial community composition affected soil properties such as pH, AK, S-UE and S-β-GC. Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt2) analysis demonstrated that PLA-MPs modify bacterial metabolic pathways. Our results suggest that particle size and concentration of PLA-MPs differentially affect soil nutrients and microbial community structure and function, with more significant effects observed at larger particle sizes and higher concentrations.

Microplastics regulate soil microbial activities: Evidence from catalase, dehydrogenase, and fluorescein diacetate hydrolase

Soil microbiomes drive many soil processes and maintain the ecological functions of terrestrial ecosystems. Microplastics (MPs, size <5 mm) are pervasive emerging contaminants worldwide. However, how MPs affect soil microbial activity has not been well elucidated. This review article first highlights the effects of MPs on overall soil microbial activities represented by three soil enzymes, i.e., catalase, dehydrogenase, and fluorescein diacetate hydrolase (FDAse), and explores the underlying mechanisms and influencing factors. Abundant evidence confirms that MPs can change soil microbial activities. However, existing results vary greatly from inhibition to promotion and non-significance, depending on polymer type, degradability, dose, size, shape, additive, and aging degree of the target MPs, soil physicochemical and biological properties, and exposure conditions, such as exposure time, temperature, and agricultural practices (e.g., planting, fertilization, soil amendment, and pesticide application). MPs can directly affect microbial activities by acting as carbon sources, releasing additives and pollutants, and shaping microbial communities via plastisphere effects. Smaller MPs (e.g., nanoplastics, 1 to <1000 nm) can also damage microbial cells through penetration. Indirectly, MPs can change soil attributes, fertility, the toxicity of co-existing pollutants, and the performance of soil fauna and plants, thus regulating soil microbiomes and their activities. In conclusion, MPs can regulate soil microbial activities and consequently pose cascading consequences for ecosystem functioning.

Aggravation of Cd availability in the plastisphere of paddy soil

Soil plastisphere has attracted many concerns, however, its influence on cadmium (Cd) availability in paddy soil was still unclear. This study carried out batch microcosmic and bagging experiments to explore the influence of microplastic (MPs) on Cd availability in paddy soil under flooding conditions in the view of plastisphere. Results showed that the presence of MPs could act as plastisphere micro-environment. The bacterial community composition changed dramatically around the plastisphere compared with MPs-contaminated bulk soil and control soil. The relative abundance of Symbiobacteraceae, Rhodocyclaceae and Bryobacteraceae was improved in the plastisphere which contributed to the enhanced the reduction of Fe(III) and sulfate in flooding paddy soil. The higher content of Fe(II) and S content contributed to the enrichment of Cd in the plastisphere which aggravated Cd availability in paddy soil under flooding conditions. The partial least squares structure equation modeling results confirmed the presence of MPs in paddy soil could act as plastisphere which could change the bacterial community composition and improve the content Fe and S that was conductive to gather Cd in plastisphere. This study shed lights on the understanding of the role of plastisphere on Cd availability in paddy field ecosystem under flooding conditions.

Comparative evaluation of the impacts of different microplastics on greenhouse gas emissions, microbial community structure, and ecosystem multifunctionality in paddy soil

Although the increasing accumulation of microplastics (MPs) in terrestrial soil ecosystems has aroused worldwide concern, research remains limited on their potential impacts on soil processes and ecosystem functionality. Here, through a 41-day microcosm experiment, we found that polylactic acid (PLA), low-density polyethylene (LDPE), and polypropylene (PP) MPs consistently increased soil carbon nutrients and pH but had varying effects on soil nitrogen nutrients and the chemodiversity of dissolved organic matter (DOM). Different treatments led to notable shifts in the α-diversity and composition of soil microbial community, with phyla Proteobacteria and Ascomycota consistently enriched by MPs regardless of polymer type. The emissions of CO2 and N2O were suppressed by MPs in most cases, which in combination led to a decline in global warming potential. LDPE and 1 - 1.5 % of PLA MPs significantly improved the multifunctionality of the soil ecosystem, while PP and 0.5 % of PLA MPs exerted an opposite effect. Soil total organic carbon, pH, DOM molecular mass and condensation degree, and CO2 emissions were identified as the most important variables for predicting soil ecosystem multifunctionality. Results of this study can extend the current understanding of the impacts of MPs on soil biogeochemical cycling and ecosystem functionality.

Microplastic effects on carbon cycling in terrestrial soil ecosystems: Storage, formation, mineralization, and microbial mechanisms

Soil is the largest environmental reservoir of microplastics (MPs) on the earth. Incremental accumulation of MPs in the soil can cause significant changes in soil physicochemical and microbial traits, which may in turn interfere with soil biogeochemical processes such as carbon cycling. With published research regarding MPs impacts on soil carbon cycling growing rapidly, a systematic review summarizing the current knowledge and highlighting future research needs is warranted. As carbon-rich polymers, MPs can contribute to soil organic carbon (SOC) storage via degradation and leaching. MPs can also affect the humification of dissolved organic matters (DOM), consequently influencing the stability of SOC. Exposure to MPs can cause substantial impacts on the growth performance, litter decomposition, and root secretion of terrestrial plants as well as soil microbial carbon turnover, inducing changes in the formation of SOC. The presence of MPs has contrasting effects on the emissions of both CO2 and CH4 from the soil. The diverse effects of MPs on soil carbon metabolism could be partly attributed to the varying changes in soil microbial community structure, functional gene expression, and enzyme activity under MPs exposure. Further research is still highly needed to clarify the pathways of MPs impacts on soil carbon cycling and the driving biological and physicochemical factors behind these processes.

The bifunctional impact of polylactic acid microplastics on composting processes and soil-plant systems: Dynamics of microbial communities and ecological niche competition

Although extensive research has been conducted on the environmental impact of microplastics (MPs), their effects on microorganisms during the composting process and on the compost-soil system remain unclear. Our research investigates the microbial response to polylactic acid microplastics (PLAMPs) during aerobic composting and examines how compost enriched with PLAMPs affects plants. Our findings reveal that PLAMPs play a dual role in the composting process, influencing microorganisms differently depending on the composting phase. PLAMPs reduce the relative abundance of sensitive bacterial ASVs, specifically those belonging to Limnochordaceae and Enterobacteriaceae, during composting, while increasing the relative abundance of ASVs belonging to Steroidobacteriaceae and Bacillaceae. The impact of PLAMPs on microbial community assembly and niche width was found to be phase-dependent. In the stabilization phase (S5), the presence of PLAMPs caused a shift in the core microbial network from bacterial dominance to fungal dominance, accompanied by heightened microbial antagonism. Additionally, these intricate microbial interactions can be transferred to the soil ecosystem. Our study indicates that composting, as a method of managing PLAMPs, is also influenced by PLAMPs. This influence is transferred to the soil through the use of compost, resulting in severe oxidative stress in plants. Our research is pivotal for devising future strategies for PLAMPs management and predicting the subsequent changes in compost quality and environmental equilibrium.

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.

Characteristics of biofilms on polylactic acid microplastics and their inhibitory effects on the growth of rice seedlings: A comparative study of petroleum-based microplastics

Increasing evidence highlights the negative effects of microplastics (MPs) on crops and bio-based plastics offer an alternative to conventional plastics. However, there is limited knowledge on the impacts and mechanisms of bio-based MPs on crop physiology. In this study, bio-based polylactic acid (PLA) and petroleum-based MPs [polyamide (PA) and polypropylene (PP)] were added to hydroponic cultures planted with rice (Oryza sativa L.) seedlings to assess their toxicity. Compared to PA and PP MPs, PLA MPs experienced greater aging after 28 days of exposure, and their surfaces were loaded with more rod-shaped microorganisms with potential plastic degradation ability, such as Proteobacteria and Bacteroidota, which competed with rice seedlings for carbon and nitrogen sources for self-multiplication, thus altering the carbon fixation and nitrogen cycling processes during rice seedling growth. Down-regulation of amino acid and lipid metabolisms in the PLA treatment inhibited the normal synthesis of chlorophyll in rice seedling leaves. Consequently, decreases in the biomass and height of rice seedling roots and shoots were observed in the PLA MP treatment. This study provides evidence that bio-based MPs may have a more severe impact on crop growth than petroleum-based MPs.

Effect of jujube orchard abandonment time on soil properties and enzyme activities at soil profile in the Loess Plateau

In the Loess Plateau, the impact of abandoned farmland on soil properties and enzyme activity, along with its temporal variations and potential driving factors, remains a mystery. This study was designed to systematically and comprehensively examine the variations in soil enzyme activities, particle size distribution, and stability of soil aggregates at different stages of ecological recovery in the Loess Plateau. Our findings reveal a nuanced temporal pattern: with the progression of cropland abandonment, there is a notable decrease in soil bulk density. Concurrently, a dynamic trend in enzyme activities is observed-initially exhibiting a decline, followed by an increase over extended periods of recovery. Notably, prolonged abandonment leads to marked enhancements in soil structure. Parameters such as the mean weight diameter (MWD) and geometric mean diameter (GMD) of soil aggregates show an overall increasing trend. In terms of the Relative Dissipation Index (RSI), our data indicate a sequence of control > 2 years of abandonment > 4 years > 6 years > 14 years. From this, it can be seen that fallowing may be an effective natural restoration strategy for improving the physical structure of soils in the Loess Plateau and restoring soil nutrients. However, positive changes may take a long time to become evident.

Earthworms improve the rhizosphere micro-environment to mitigate the toxicity of microplastics to tomato (Solanum lycopersicum)

Microplastics (MPs) are widespread in agricultural soil, potentially threatening soil environmental quality and plant growth. However, toxicological research on MPs has mainly been limited to individual components (such as plants, microbes, and animals), without considering their interactions. Here, we examined earthworm-mediated effects on tomato growth and the rhizosphere micro-environment under MPs contamination. Earthworms (Eisenia fetida) mitigated the growth-inhibiting effect of MPs on tomato plant. Particularly, when exposed to environmentally relevant concentrations (ERC, 0.02% w/w) of MPs, the addition of earthworms significantly (p < 0.05) increased shoot and root dry weight by 12-13% and 13-14%, respectively. MPs significantly reduced (p < 0.05) soil ammonium (NH4+-N) (0.55-0.69 mg/kg), nitrate nitrogen (NO3--N) (7.02-8.65 mg/kg) contents, and N cycle related enzyme activities (33.47-42.39 μg/h/g) by 37.7-50.9%, 22.6-37.2%, and 34.2-48.0%, respectively, while earthworms significantly enhanced (p < 0.05) inorganic N mineralization and bioavailability. Furthermore, earthworms increased bacterial network complexity, thereby enhancing the robustness of the bacterial system to resist soil MPs stress. Meanwhile, partial least squares modelling showed that earthworms significantly influenced (p < 0.01) soil nutrients, which in turn significantly affected (p < 0.01) plant growth. Therefore, the comprehensive consideration of soil ecological composition is important for assessing MPs ecological risk.

Ecological effect of microplastics on soil microbe-driven carbon circulation and greenhouse gas emission: A review

Soil organic carbon (SOC) pool, the largest part of terrestrial ecosystem, controls global terrestrial carbon balance and consequently presented carbon cycle-climate feedback in climate projections. Microplastics, (MPs, <5 mm) as common pollutants in soil ecosystems, have an obvious impact on soil-borne carbon circulation by affecting soil microbial processes, which play a central role in regulating SOC conversion. In this review, we initially presented the sources, properties and ecological risks of MPs in soil ecosystem, and then the differentiated effects of MPs on the component of SOC, including dissolved organic carbon, soil microbial biomass carbon and easily oxidized organic carbon varying with the types and concentrations of MPs, the soil types, etc. As research turns into a broader perspective, greenhouse gas emissions dominated by the mineralization of SOC coming into view since it can be significantly affected by MPs and is closely associated with soil microbial respiration. The pathways of MPs impacting soil microbes-driven carbon conversion include changing microbial community structure and composition, the functional enzyme's activity and the abundance and expression of functional genes. However, numerous uncertainties still exist regarding the microbial mechanisms in the deeper biochemical process. More comprehensive studies are necessary to explore the affected footprint and provide guidance for finding the evaluation criterion of MPs affecting climate change.

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.

Influence of microplastics on the availability of antibiotics in soils

Microplastics (MPs) and antibiotics, as two major types of emerging pollutants, inevitably coexist in the soil environment due to agricultural film residue, sewage irrigation and sludge application. However, the impact of MPs on antibiotic availability in soils with varying characteristics has not been extensively studied. Therefore, in this study, an interference experiment was conducted using three types of MPs (polyethylene (PE), polyvinyl chloride (PVC) and polypropylene (PP)) in red soil, paddy soil and cinnamon soil. The available antibiotics in soils were evaluated using diffusive gradients in thin-films (DGT). Results showed that MPs had a significant impact on the amount of antibiotics adsorbed on soil solid (Cs) by providing additional binding sites or altering soil characteristics (e.g., pH and dissolved organic carbon). The most significant effects on Cs were observed in cinnamon soil, and the Cs values were dependent on concentration of MPs. The available antibiotics, as measured by DGT significantly decreased after the addition of MPs. This decrease was influenced by the soil characteristics. However, the concentration of antibiotics in soil solutions (Cd) was only slightly impacted by MPs. Therefore, the influence of MPs on the migration of antibiotics was reflected by their impact on the soil/water partition coefficient (Kd), while the resupply ability (R) from the soil solid phase was less influential. Moreover, the dosage of MPs had a significant effect on the availability of antibiotics in CS by promoting the adsorption of antibiotics on the solid phase, while in RS and PS, the soil properties played a dominate role in the changes in antibiotic availability after MP addition. These results indicate that the impact of MPs on available antibiotics mainly depends on soil properties. In addition, DGT measurement is more sensitive than soil solution to investigate the effects of coexisting pollutants on the behavior of antibiotics in soil.

Effects of farmland residual mulch film-derived microplastics on the structure and function of soil and earthworm Metaphire guillelmi gut microbiota

Microplastics derived from polyethylene (PE) mulch films are widely found in farmland soils and present considerable potential threats to agricultural soil ecosystems. However, the influence of microplastics derived from PE mulch films, especially those derived from farmland residual PE mulch films, on soil ecosystems remains unclear. In this study, we analyzed the bacterial communities attached to farmland residual transparent PE mulch film (FRMF) collected from peanut fields and the different ecological effects of unused PE mulch film-derived microplastics (MPs) and FRMF-derived microplastics (MPs-aged) on the soil and earthworm Metaphire guillelmi gut microbiota, functional traits, and co-occurrence patterns. The results showed that the assembly and functional patterns of the bacterial communities attached to the FRMF were clearly distinct from those in the surrounding farmland soil, and the FRMF enriched some potential plastic-degrading and pathogenic bacteria, such as Nocardioidaceae, Clostridiaceae, Micrococcaceae, and Mycobacteriaceae. MPs substantially influenced the assembly and functional traits of soil bacterial communities; however, they only significantly changed the functional traits of earthworm gut bacterial communities. MPs-aged considerably affected the assembly and functional traits of both soil and earthworm gut bacterial communities. Notably, MPs had a more remarkable effect on nitrogen-related functions than the MPs-aged in numbers for both soil and earthworm gut samples. Co-occurrence network analysis revealed that both MPs and MPs-aged enhanced the synergistic interactions among operational taxonomic units (OTUs) of the composition networks for all samples. For community functional networks, MPs and MPs-aged enhanced the antagonistic interactions for soil samples; however, they exhibited contrasting effects for earthworm gut samples, as MPs enhanced the synergistic interactions among the functional contents. These findings broaden and deepen our understanding of the effects of FRMF-derived microplastics on soil ecosystems, suggesting that the harmful effects of aged plastics on the ecological environment should be considered.