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

Metabolite-mediated responses of phyllosphere microbiota to powdery mildew infection in resistant and susceptible black currant cultivars

Plant-metabolite-microbe interactions play essential roles in disease suppression. Most studies focus on the root exudates and rhizosphere microbiota to fight soil-borne pathogens, but it is poorly understood whether the changes in phyllosphere metabolites can actively recruit beneficial microbes to enhance disease resistance. In this study, the differences of phyllosphere microbial communities and key leaf metabolites were systematically explored in resistant and susceptible black currant cultivars related to powdery mildew (PM) by integrating microbiome and metabolomic analyses. The results showed that the diversity and composition of microbiome changed, as highlighted by a reduction in microbial alpha-diversity and beta-diversity of susceptible cultivars. An increasing fungal network complexity and a decreasing bacterial network complexity occurred in resistant cultivar. Bacillus, Burkholderia (bacteria), and Penicillium (fungi) were identified as keystone microorganisms and resistance effectors in resistant cultivar. Metabolites such as salicylic acid, trans-zeatin, and griseofulvin were more abundant in resistant cultivar, which had a positive regulatory effect on the abundance of bacterial and fungal keystones. These findings unravel that resistant cultivar can enrich beneficial microorganisms by adjusting leaf metabolites, thus showing the external disease-resistant response. Moreover, the reduced stomatal number and increased tissue thickness were observed in resistant cultivar, suggesting inherent physical structure also provides a basic defense against PM pathogens. Therefore, resistant black currant cultivar displayed multilevel defense responses of physical structures, metabolites, and microorganisms to PM pathogens. Collectively, our study highlights the potential for utilizing phyllosphere microbiome dynamics and metabolomic adjustments in agricultural practices, plant breeding, and microbiome engineering to develop disease-resistant crops.

Occurrence and environmental consequences of microplastics and nanoplastics from agricultural reuse of wastewater and biosolids in the soil ecosystem: A review

The contamination of soil and groundwater ecosystems by plastic particles (micro- and nanoplastics) was discussed, focusing on wastewater and biosolids recycled into agricultural soils. The impact of these contaminants was critically examined. Livestock (average: 18; min.: 8 - max.: 42 MP/L) and municipal (average: 2226; min: 0.08 - máx: 31,400 MP/L) wastewater, vinasse, and biosolids (>30,000 MP/L) from wastewater treatment plants are the most frequently reported in the literature for their nutritional potential in agricultural reuse. However, aside from municipal wastewater and biosolids, plastic particles in these other matrices are still largely unexplored, posing a potential threat to soil quality due to the limited understanding of their contribution to soil contamination. The particles accumulate in deeper layers, altering the hydraulic conductivity, fertility, organic matter availability, greenhouse gas emissions, and soil fauna and microorganisms. Nanoplastics have a more pronounced impact than microplastics and represent a greater threat. Due to their vertical mobility, nanoplastics have a greater capacity to accumulate in deep layers, including in groundwater. Different from what is observed for microplastics, current detection and quantification methodologies for nanoplastics are broad and nonspecific. It currently considers extensive size ranges (0-5000 μm), making it difficult to accurately identify these compounds, highlighting the need for more suitable methods for detecting nanoplastics. Given the recognized impacts on soil, it is essential to advance studies to ensure the benefits of reusing wastewater and organic soil amendments while effectively eliminating plastic particles from these matrices to prevent critical contamination scenarios.

Discarded floral foam as a source for green preparation of sustainable adsorbent for quick and efficient removal of phenoxyacetic acid herbicides from waters

Due to the high toxicity and increasing consumption, efficient removal of phenoxyacetic acid herbicides (PAAHs) from water is imperative. In current study, a new adsorbent was prepared by modifying porous carbon derived from disused floral foam with chitosan (CS) (ACFC). Density functional theory (DFT) calculation uncovered that the amino and hydroxyl groups in the introduced CS played a critical role in the efficient adsorption of ACFC towards PAAHs. Batch experiments were performed to study the adsorption behaviors and removal mechanism. Under the optimal adsorption conditions, the PAAHs residues in various environmental waters were efficiently removed within 20 min by the ACFC, the removal rates varied from 81.9 % to 93.8 %, which remarkably better than that achieved on unmodified carbon (32.5-56.5 %). The maximum adsorption capacities were in the range of 172-221 μg/g. In addition, the prepared adsorbent presented excellent preparation repeatability and acceptable reusability. In comparison with reported adsorbents, the ACFC displayed some merits such as low cost, green, short removal period and high removal rate. The current study not only supplies a cost-effective and sustainable adsorbent for the removal of PAAHs residues from waters, but also opens up a new route for the recycle utilization of disused floral foam.

Natural coagulants from chestnut shells: A sustainable approach for textile wastewater treatment

The textile industry contributes to 2-10% of global greenhouse gas emissions, water extraction, and biodiversity loss, consuming 93 billion cubic meters of water annually with low reuse rates. Coagulation/flocculation is commonly used for industrial wastewater treatment, typically using conventional coagulants. Recently, interest in natural alternatives, particularly tannin-based coagulants, has grown. Given Portugal's role as a major chestnut producer and textile exporter, this study developed chestnut shell-based coagulants for textile wastewater treatment. Ethanolamine (ETA) and diethanolamine (DEA) were tested in the Mannich reaction, but only ETA produced a coagulant with a positive zeta potential and higher charge density. Five coagulants (CE_1-CE_5) were synthesized using different ETA/tannin and formaldehyde (FA)/tannin ratios. Lower ETA concentrations (7.5 mol L-1) produced the coagulant with the highest charge density and zeta potential. Further testing of FA/tannin ratios (3.5, 6, and 7.5) showed that lower FA levels reduced color removal efficiency and increased toxicity. Comparing synthetic and real textile effluent performance, natural coagulants showed superior color removal, while FeCl3 was more effective for organic matter and nitrogen removal. All coagulants removed phosphorus, with CE_2 achieving nearly 70% removal. Toxicity tests revealed that only CE_5 inhibited V. fischeri bacteria by over 70%. Formaldehyde leaching into treated water was minimal (0.17-0.3 mg L-1), below WHO limits (2.6 mg L-1), but concentrations in sludge were higher, especially in CE_3 and Tanfloc. These findings highlight chestnut shells as a promising source for producing natural, effective coagulants.

Exploring the response of bacterial community functions to microplastic features in lake ecosystems through interpretable machine learning

Microplastics (MPs) are ubiquitous and have various characteristics. However, their impacts on bacterial community functions in lakes remain elusive. In this study, we identified 33 different MPs features including their abundance, shape, color, size, and polymer type, from Taihu Lake, China. These features were used to construct 48 machine learning models, utilizing four types of machine learning regression algorithms, to investigate how different MP features influence human health, carbon/nitrogen cycling, and energy source-related functions of bacterial communities. The XGBoost models provided the best performance with an average R2 of 0.85 in explaining the abundance of functions. Yellow-, fragment-, and polyethylene terephthalate (PET) MPs were the most important features by Shapley values. Yellow- and PET-MPs mainly had primarily negative impacts on human pathogens pneumonia and chemoheterotrophy, respectively. Fragment-MPs had a primarily positive impact, which shifted from positive to negative at a proportion of 0.5 for methanol oxidation. Moreover, MPs may affect community structure by filtering for functional traits. These findings are important for understanding the effects of MP pollution on bacterial community function and its role in the global carbon and nitrogen cycling and human health and help us to determine the potential impacts of MP pollution on ecosystems.

Modulated use of high-concentration invasive biochar in waste-to-energy strategies: Impact analysis on microbial communities

As a potential amendment, biochar has attracted considerable attention for its impact on soil microbial communities. However, there is little consensus regarding the impacts of biochar derived from invasive plants on microbial communities in coastal saline wetland soils. In this study, we used Juglans regia biochar (JBC) and two other invasive plant biochar, Spartina alterniflora biochar (SBC) and Flaveria bidentis biochar (FBC) to saline soils at rates of 1%, 3%, and 5% (w/w). The results demonstrated that the application of biochar led to a reduction in microbial community diversity, particularly evident in the 5% SBC and FBC treatments. Furthermore, the 5% FBC treatment resulted in a notable decline in community richness. With regard to species composition, the addition of SBC and FBC resulted in a notable impact on the relative abundance of Acidobacteria in comparison to JBC. Additionally, 5% SBC led to a reduction in the relative abundance of Bacteroidetes by 21.49%-23.90%, and 5% FBC reduced the relative abundance of Nitrospirae by 14.71%-17.86%. The addition of biochar enhanced the overall complexity of the community. Specifically, adding 5% SBC boosted the complexity of the microbial network and encouraged cooperative relationships among microorganisms. However, this community became more vulnerable to environmental changes and exhibited weaker anti-interference capabilities. Moreover, 5% JBC and 5% SBC altered the community assembly process from deterministic to stochastic. We emphasize the importance of carefully selecting biochar types during soil remediation, with particular attention to the application of high concentrations of biochar. This paper lays the groundwork for long-term practice in soil remediation through the approach of "treating waste with waste".

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.

Impact of phenolic-formaldehyde resin microplastics on anaerobic granular sludge: EPS interaction mechanisms and impacts on reactor performance

This paper investigates the effects of phenolic-formaldehyde resin microplastics (PF-MPs) with different particle sizes on anaerobic granular sludge (AnGS) and reveals the complex interaction mechanisms between extracellular polymeric substances (EPS) and PF-MPs through the combination of molecular dynamics simulations and spectroscopy. PF-MPs provide a new ecological niche for microorganisms. Microorganisms and EPS can adhere and accumulate on the surface of PF-MPs, producing highly active floc sludge inside the reactor, thereby increasing the chemical oxygen demand (COD) removal rate and methane production of the reactor. However, the high metabolic activity of floc sludge consumes the biodegradable components in EPS, resulting in loose rupture of the sludge particles and reduced particle size. In addition, small particle size S-PF can adhere to the sludge surface，which caused mass transfer barriers and reduced the expression of genes and enzyme activities for the sludge acidification process and the main methanogenic processes. Insufficient internal nutrients lead to endogenous metabolism within the granules, causing internal hollowing, which affects the density and settling performance of the sludge. Monolayer physical adsorption plays a major role in the adsorption of EPS on PF-MPs. 2D-COS and FTIR spectroscopy were used to elucidate the preferential binding of polysaccharides to PF-MPs. This paper explores the fate of PF-MPs in anaerobic systems and demonstrates the important role of EPS in the capture of microplastics by granular sludge, providing a theoretical basis for understanding the migration of microplastics in wastewater treatment.

Bioremediation Potential of Rhodococcus qingshengii PM1 in Sodium Selenite-Contaminated Soil and Its Impact on Microbial Community Assembly

Soil microbial communities are particularly sensitive to selenium contamination, which has seriously affected the stability of soil ecological environment and function. In this study, we applied high-throughput 16S rRNA gene sequencing to examine the effects of low and high doses of sodium selenite and the selenite-degrading bacterium, Rhodococcus qingshengii PM1, on soil bacterial community composition, diversity, and assembly processes under controlled laboratory conditions. Our results indicated that sodium selenite and strain PM1 were key predictors of bacterial community structure in selenium-contaminated soils. Exposure to sodium selenite initially led to reductions in microbial diversity and a shift in dominant bacterial groups, particularly an increase in Actinobacteria and a decrease in Acidobacteria. Sodium selenite significantly reduced microbial diversity and simplified co-occurrence networks, whereas inoculation with strain PM1 partially reversed these effects by enhancing community complexity. Ecological modeling, including the normalized stochasticity ratio (NST) and Sloan's neutral community model (NCM), suggested that stochastic processes predominated in the assembly of bacterial communities under selenium stress. Null model analysis further revealed that heterogeneous selection and drift were primary drivers of community turnover, with PM1 inoculation promoting species dispersal and buffering against the negative impacts of selenium. These findings shed light on microbial community assembly mechanisms under selenium contamination and highlight the potential of strain PM1 for the bioremediation of selenium-affected soils.

Unveiling the impacts of microplastic pollution on soil health: A comprehensive review

Soil contamination by microplastics (MPs) has emerged as a significant global concern. Although traditionally associated with crop production, contemporary understanding of soil health has expanded to include a broader range of factors, including animal safety, microbial diversity, ecological functions, and human health protection. This paradigm shifts underscores the imperative need for a comprehensive assessment of the effects of MPs on soil health. Through an investigation of various soil health indicators, this review endeavors to fill existing knowledge gaps, drawing insights from recent studies conducted between 2021 and 2024, to elucidate how MPs may disrupt soil ecosystems and compromise their crucial functions. This review provides a thorough analysis of the processes leading to MP contamination in soil environments and highlights film residues as major contributors to agricultural soils. MPs entering the soil detrimentally affect crop productivity by hindering growth and other physiological processes. Moreover, MPs hinder the survival, growth, and reproductive rates of the soil fauna, posing potential health risks. Additionally, a systematic evaluation of the impact of MPs on soil microbes and nutrient cycling highlights the diverse repercussions of MP contamination. Moreover, within soil-plant systems, MPs interact with other pollutants, resulting in combined pollution. For example, MPs contain oxygen-containing functional groups on their surfaces that form high-affinity hydrogen bonds with other pollutants, leading to prolonged persistence in the soil environment thereby increasing the risk to soil health. In conclusion, we succinctly summarize the current research challenges related to the mediating effects of MPs on soil health and suggest promising directions for future studies. Addressing these challenges and adopting interdisciplinary approaches will advance our understanding of the intricate interplay between MPs and soil ecosystems, thereby providing evidence-based strategies for mitigating their adverse effects.

Microplastic-contamination can reshape plant community by affecting soil properties

Microplastics, as emerging contaminants, pose a serious threat to terrestrial ecosystems, yet their impact on plant communities remains largely unexplored. This study utilized the soil seed bank to establish naturally germinated plant communities and investigated the effects of polyethylene (PE) and polypropylene (PP) on community characteristics. Additionally, the study aimed to elucidate the mechanisms by which variations in soil properties influenced plant community. The results indicated that microplastics led to a significant increase in soil available potassium (AK), likely due to alterations in soil microorganism proliferation. Furthermore, microplastics caused a decrease in soil salinity, total phosphorus (TP), and ammonium nitrogen (AN). Additionally, plant community composition shifted, resulting in reduced stability and niche breadth of dominant species. Microplastics also impacted niche overlap and interspecific associations among dominant species, possibly due to the reduced accessibility of resources for dominant species. Salinity, AK, and TP were identified as major drivers of changes in niche breadth, niche overlap, and community stability, with TP exerting the strongest impact on plant community composition. These findings provide valuable insights for the restoration of plant communities in coastal saline-alkali wetland contaminated by microplastics.

Microplastic pollution promotes soil respiration: A global-scale meta-analysis

Microplastic (MP) pollution likely affects global soil carbon (C) dynamics, yet it remains uncertain how and to what extent MP influences soil respiration. Here, we report on a global meta-analysis to determine the effects of MP pollution on the soil microbiome and CO2 emission. We found that MP pollution significantly increased the contents of soil organic C (SOC) (21%) and dissolved organic C (DOC) (12%), the activity of fluorescein diacetate hydrolase (FDAse) (10%), and microbial biomass (17%), but led to a decrease in microbial diversity (3%). In particular, increases in soil C components and microbial biomass further promote CO2 emission (25%) from soil, but with a much higher effect of MPs on these emissions than on soil C components and microbial biomass. The effect could be attributed to the opposite effects of MPs on microbial biomass vs. diversity, as soil MP accumulation recruited some functionally important bacteria and provided additional C substrates for specific heterotrophic microorganisms, while inhibiting the growth of autotrophic taxa (e.g., Chloroflexi, Cyanobacteria). This study reveals that MP pollution can increase soil CO2 emission by causing shifts in the soil microbiome. These results underscore the potential importance of plastic pollution for terrestrial C fluxes, and thus climate feedbacks.

Could soil microplastic pollution exacerbate climate change? A meta-analysis of greenhouse gas emissions and global warming potential

Microplastics pollution and climate change are primarily investigated in isolation, despite their joint threat to the environment. Greenhouse gases (GHGs) are emitted during: the production of plastic and rubber, the use and degradation of plastic, and after contamination of environment. This is the first meta-analysis to assess underlying causal relationships and the influence of likely mediators. We included 60 peer-reviewed empirical studies; estimating GHGs emissions effect size and global warming potential (GWP), according to key microplastics properties and soil conditions. We investigated interrelationships with microbe functional gene expression. Overall, microplastics contamination was associated with increased GHGs emissions, with the strongest effect (60%) on CH4 emissions. Polylactic-acid caused 32% higher CO2 emissions, but only 1% of total GWP. Phenol-formaldehyde had the greatest (175%) GWP via 182% increased N2O emissions. Only polystyrene resulted in reduced GWP by 50%, due to N2O mitigation. Polyethylene caused the maximum (60%) CH4 emissions. Shapes of microplastics differed in GWP: fiber had the greatest GWP (66%) whereas beads reduced GWP by 53%. Films substantially increased emissions of all GHGs: 14% CO2, 10% N2O and 60% CH4. Larger-sized microplastics had higher GWP (125%) due to their 9% CO2 and 63% N2O emissions. GWP rose sharply if soil microplastics content exceeded 0.5%. Higher CO2 emissions, ranging from 4% to 20%, arose from soil which was either fine, saturated or had high-carbon content. Higher N2O emissions, ranging from 10% to 95%, arose from soils that had either medium texture, saturated water content or low-carbon content. Both CO2 and N2O emissions were 43%-56% higher from soils with neutral pH. We conclude that microplastics contamination can cause raised GHGs emissions, posing a risk of exacerbating climate-change. We show clear links between GHGs emissions, microplastics properties, soil characteristics and soil microbe functional gene expression. Further research is needed regarding underlying mechanisms and processes.

Nitrogen supply neutralizes the nanoplastic-plant interaction in a coastal wetland

The presence of nanoplastics posed a potential threat to coastal saline-alkaline wetlands where nitrogen (N) fertilizer is being implemented as an important ecological restoration measure. Notwithstanding, the effects of N inputs on plant community in polypropylene-nanoplastics (PP-NPs) coexistence environments are largely unknown. To address this, we investigated the effects of PP-NPs addition alone or combined N supply on community aboveground biomass, morphological traits, diversity, composition, niche differentiation, interspecific interactions, and assembly. Our results showed that the PP-NPs addition alone reduced community aboveground biomass and morphological traits. However, the addition of high concentration (0.5%) PP-NPs alone favored community α-diversity and reduced community stability, which could be weakened through combined N supply. Overall, the effect of PP-NPs addition alone on plant community composition was greater than that of combined N supply. We also demonstrated PP-NPs addition alone and combined N supply reduced the niche breadth of the plant community and affected the niche overlap of dominant species. In the assembly of plant communities, stochastic processes played a dominant role. We conclude that N fertilization can amend the terrestrial nanoplastics pollution, thus mitigating the effects of PP-NPs on the plant community.

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.

The impacts of microplastics on the cycling of carbon and nitrogen in terrestrial soil ecosystems: Progress and prospects

As contaminants of emerging concern, microplastics (MPs) are ubiquitously present in almost all environmental compartments of the earth, with terrestrial soil ecosystems as the major sink for these contaminants. The accumulation of MPs in the soil can trigger a wide range of effects on soil physical, chemical, and microbial properties, which may in turn cause alterations in the biogeochemical processes of some key elements, such as carbon and nitrogen. Until recently, the effects of MPs on the cycling of carbon and nitrogen in terrestrial soil ecosystems have yet to be fully understood, which necessitates a review to summarize the current research progress and propose suggestions for future studies. The presence of MPs can affect the contents and forms of soil carbon and nitrogen nutrients (e.g., total and dissolved organic carbon, dissolved organic nitrogen, NH4+-N, and NO3--N) and the emissions of CH4, CO2, and N2O by altering soil microbial communities, functional gene expressions, and enzyme activities. Exposure to MPs can also affect plant growth and physiological processes, consequently influencing carbon fixation and nitrogen uptake. Specific effects of MPs on carbon and nitrogen cycling and the associated microbial parameters can vary considerably with MP properties (e.g., dose, polymer type, size, shape, and aging status) and soil types, while the mechanisms of interaction between MPs and soil microbes remain unclear. More comprehensive studies are needed to narrow the current knowledge gaps.

Microplastics induced the differential responses of microbial-driven soil carbon and nitrogen cycles under warming

The input of microplastics (MPs) and warming interfere with soil carbon (C) or nitrogen (N) cycles. Although the effects of warming and/or MPs on the cycles have been well studied, the biological coupling of microbial-driven cycles was neglected. Here, the synergistic changes of the cycles were investigated using batch incubation experiments. As results, the influences of MPs were not significant at 15, 20, and 25 °C, and yet, high temperature (i.e., 30 °C) reduced the respiration of high-concentration MPs-amended soil by 9.80%, and increased dissolved organic carbon (DOC) by 14.74%. In contrast, high temperature did not change the effect of MPs on N. The decrease of microbial biomass carbon (MBC) and the constant of microbial biomass nitrogen (MBN) indicated that microbial N utilization was enhanced, which might be attributed to the enrichments of adapted populations, such as Conexibacter, Acidothermus, and Acidibacter. These observations revealed that high temperature and MPs drove the differential response of soil C and N cycles. Additionally, the transcriptomic provided genomic evidence of the response. In summary, the high temperature was a prerequisite for the MPs-driven response, which underscored new ecological risks of MPs under global warming and emphasized the need for carbon emission reduction and better plastic product regulation.

Phosphorus fertiliser application mitigates the negative effects of microplastic on soil microbes and rice growth

Soil microplastics (MPs) have attracted widespread attention recently. Most studies have explored how soil MPs affect the soil's physicochemical parameters, matter circulation, and soil microbial community assembly. Similarly, a key concern in agricultural development has been the use of phosphorus (P) fertiliser, which is essential for plant health and development. However, the relationship between MPs and phosphate fertilisers and their effects on the soil environment and plant growth remains elusive. This study assessed the influence of adding low-density polyethylene MPs (1%) with different phosphate fertiliser application rates on microbial communities and rice biomass. Our results showed that MPs changed the structure of soil bacterial and phoD-harbouring microbial communities in the treatment with P fertiliser at the same level and suppressed the interactions of phoD-harbouring microorganisms. In addition, we found that MPs contamination inhibited rice growth; however, the inclusion of P fertiliser in MP-contaminated soils reduced the inhibitory action of MPs on rice growth, probably because the presence with P fertiliser promoted the uptake of NO3--N by rice in MP-contaminated soils. Our results provide further insights into guiding agricultural production, improving agricultural management, and rationally applying phosphate fertilisers in the context of widespread MPs pollution and global P resource constraints.

Toxicity factors to assess the ecological risk for soil microbial communities

The toxicity factor (TF), a critical parameter within the potential ecological risk index (RI), is determined without accounting for microbial factors. It is considerable uncertainty exists concerning its validity for quantitatively assessing the influence of metal(loid)s on microorganisms. To evaluate the suitability of TF, we constructed microcosm experiments with varying RI levels (RI = 100, 200, 300, 500, and 700) by externally adding zinc (Zn), chromium (Cr), copper (Cu), lead (Pb), nickel (Ni), cadmium (Cd), and mercury (Hg) to uncontaminated soil (CK). Quantitative real-time PCR (qPCR) and high-throughput sequencing techniques were employed to measure the abundance and community of bacteria and fungi, and high-throughput qPCR was utilised to quantify functional genes associated with CNPS cycles. The results demonstrated that microbial diversity and function exhibited significant alterations (p < 0.05) in response to increasing RI levels, and the influences on microbial community structure, enzyme activity, and functional gene abundances were different due to the types of metal(loid)s treatments. At the same RI level, significant differences (p < 0.05) were discerned in microbial diversity and function across metal(loid) treatments, and these differences became more pronounced (p < 0.001) at higher levels. These findings suggest that TF may not be suitable for the quantitative assessment of microbial ecological risk. Therefore, we adjusted the TF by following three steps (1) determining the adjustment criteria, (2) deriving the initial TF, and (3) adjusting and optimizing the TF. Ultimately, the optimal adjusted TF was established as Zn = 1.5, Cr = 4.5, Cu = 6, Pb = 4.5, Ni = 5, Cd = 22, and Hg = 34. Our results provide a new reference for quantitatively assessing the ecological risks caused by metal(loid)s to microorganisms.

Polyethylene microplastics alter soil microbial community assembly and ecosystem multifunctionality

Although pervasive microplastics (MPs) pollution in terrestrial ecosystems invites increasing global concern, impact of MPs on soil microbial community assembly and ecosystem multifunctionality received relatively little attention. Here, we manipulated a mesocosm experiment to investigate how polyethylene MPs (PE MPs; 0, 1%, and 5%, w/w) influence ecosystem functions including plant production, soil quality, microbial community diversity and assembly, enzyme activities in carbon (C), nitrogen (N) and phosphorus (P) cycling, and multifunctionality in the maize-soil continuum. Results showed that PE MPs exerted negligible effect on plant biomass (dry weight). The treatment of 5% PE MPs caused declines in the availability of soil water, C and P, whereas enhanced soil pH and C storage. The activity of C-cycling enzymes (α/β-1, 4-glucosidase and β-D-cellobiohydrolase) was promoted by 1% PE MPs, while that of β-1, 4-glucosidase was inhibited by 5% PE MPs. The 5% PE MPs reduced the activity of N-cycling enzymes (protease and urease), whereas increased that of the P-cycling enzyme (alkaline phosphatase). The 5% PE MPs shifted soil microbial community composition, and increased the number of specialist species, microbial community stability and networks resistance. Moreover, PE MPs altered microbial community assembly, with 5% treatment decreasing dispersal limitation proportion (from 13.66% to 9.96%). Overall, ecosystem multifunctionality was improved by 1% concentration, while reduced by 5% concentration of PE MPs. The activity of α/β-1, 4-glucosidase, urease and protease, and ammonium-N content were the most important predictors of ecosystem multifunctionality. These results underscore that PE MPs can alter soil microbial community assembly and ecosystem multifunctionality, and thus development and implementation of practicable solutions to control soil MPs pollution become increasingly imperative in sustainable agricultural production.

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

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

Low-density polyethylene microplastics and biochar interactively affect greenhouse gas emissions and microbial community structure and function in paddy soil

Paddy soils are susceptible to microplastics (MPs) contamination. As a common soil amendment, biochar (BC) has been extensively applied in paddy fields. The co-occurrence of MPs and BC may cause interactive effects on soil biogeochemical processes, which has yet been well studied. In this study, a 41-days of microcosm experiment was conducted using paddy soil added with 0.5-1.5 wt% of low-density polyethylene (LDPE) and 5 wt% of BC individually or jointly. Application of BC, LDPE, or their mixture into soil significantly increased the emission of methane (CH4), but suppressed the emission of carbon dioxide (CO2). LDPE addition lowered soil nitrous oxide (N2O) emissions, while BC exerted an opposite effect. Proteobacteria was the most dominant phylum with a relative abundance range of 35.1-51.0%, followed by Actinobacteria (19.3-30.9%) and Acidobacteria (7.5-23.5%). The abundances of the mcrA gene and pH values were increased in soils added with BC or/and LDPE, which were the possible reasons for the higher CH4 emissions in these treatments. The emission of N2O was positively related to the abundances of norB and narG genes, suggesting denitrification was a major pathway to produce N2O. Results of structural equation modeling demonstrated that addition of BC or/and LDPE MPs could affect greenhouse gas emissions from paddy soil by altering soil chemical properties, microbial community structure, and functional gene abundances.

Microplastics increase soil microbial network complexity and trigger diversity-driven community assembly

The widespread existence of microplastics (MPs) in soil has been extensively demonstrated, and their presence would ineluctably change soil physicochemical properties and microbial community composition. However, there is limited understanding of how MPs affect soil microbial assembly. In this study, three different polymer types of MPs, i.e., high-density polyethylene (HDPE), polystyrene (PS), and polylactic acid (PLA), with the same particle size (100 μm) and dose (2%) were applied under the planted and unplanted condition, Pennisetum alopecuroides was chosen as a model species. Plant growth parameters, soil physicochemical properties, and microbial communities (including bacteria and eukaryotes) were determined. The assembly and the co-occurrence network of microbial communities were analyzed. Results revealed that the effect of MPs on soil physicochemical properties was type-dependent and could influenced by the presence of P . alopecuroides. MPs could enrich bacterial genera related to nitrogen cycle and some pathogens of eukaryotes. The presence of MPs changed bacterial and eukaryotic community assembly, in which diversity drove the deterministic/stochastic assembly processes. MPs addition increased the complexity of bacterial network, while had a minor effect on eukaryotic network. The inhibition of MPs on P . alopecuroides growth decayed over time, HDPE MPs was more harmful to P . alopecuroides growth than PS and PLA MPs. Our findings enormously improved our comprehensions of MPs-induced ecological impacts and interactions of soil bacterial and eukaryotic communities .

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.

Dose effect of polyethylene microplastics on nitrous oxide emissions from paddy soils cultivated for different periods

The presence of microplastics (MPs) under flooded conditions is beneficial for nitrifiers and denitrifiers to produce nitrous oxide (N₂O), but their dose effect remains unclear. This study evaluated the impact of different doses of polyethylene (PE) MPs on the release of N₂O from paddy soils cultivated for different years. Compared with unpolluted soils, low doses of MPs (≤ 0.1%) had a negligible influence on N₂O emissions, and high amounts of MPs (≥ 0.5%) significantly (p < 0.05) increased N₂O emissions from the paddy soils cultivated for 3, 15 and 40 years by 2.5-4.3, 3.9-8.5 and 8.9-27.7 times, respectively. Moreover, an exponential model indicated that a 0.2% concentration of PE MPs appeared to be the dose threshold that accelerated the release of N₂O from the all soils. Increased MP concentrations accelerated N₂O emissions by affecting microbial functional genes involved in N₂O production and reduction, but microbial taxonomic attributes involved in nitrogen cycling played an insignificant role in controlling N₂O emissions. Overall, our results indicated that high doses (≥ 0.5%) of PE MPs essentially accelerated the emission of N₂O from rice soils, and a longer cultivation period (40 years) enhanced the positive effect of MPs on N₂O emissions.

Dopamine alleviates cadmium stress in apple trees by recruiting beneficial microorganisms to enhance the physiological resilience revealed by high-throughput sequencing and soil metabolomics

Dopamine has demonstrated promise as a stress-relief substance. However, the function of dopamine in Cd tolerance and its mechanism remains largely unknown. The current study was performed to investigate the mechanism of dopamine on alleviating apple Cd stress through regular application of CdCl2 and dopamine solution to potting soil. The results indicated that dopamine significantly reduced reactive oxygen species (ROS) and Cd accumulation and alleviated the inhibitory effect of Cd stress on the growth of apple plants through activation of the antioxidant system, enhancement of photosynthetic capacity, and regulation of gene expression related to Cd absorption and detoxification. The richness of the rhizosphere microbial community increased, and community composition and assembly were affected by dopamine treatment. Network analysis of microbial communities showed that the numbers of nodes and total links increased significantly after dopamine treatment, while the keystone species shifted. Linear discriminant analysis effect size indicated that some biomarkers were significantly enriched after dopamine treatment, suggesting that dopamine induced plants to recruit potentially beneficial microorganisms (Pseudoxanthomonas, Aeromicrobium, Bradyrhizobium, Frankia, Saccharimonadales, Novosphingobium, and Streptomyces) to resist Cd stress. The co-occurrence network showed several metabolites that were positively correlated with relative growth rate and negatively correlated with Cd accumulation, suggesting that potentially beneficial microorganisms may be attracted by several metabolites (L-threonic acid, profenamine, juniperic acid and (3β,5ξ,9ξ)-3,6,19-trihydroxyurs-12-en-28-oic acid). Our results demonstrate that dopamine alleviates Cd stress in apple trees by recruiting beneficial microorganisms to enhance the physiological resilience revealed. This study provides an effective means to reduce the harm to agricultural production caused by heavy metals.