Influence of polyethylene terephthalate microplastic and biochar co-existence on paddy soil bacterial community structure and greenhouse gas emission

Nano- and Microplastics Increase the Occurrence of Bacterial Wilt in Tomato (Solanum lycopersicum L.)

Concern over nano- and microplastic contamination of terrestrial ecosystems has been increasing. However, little is known about the effect of nano- and microplastics on the response of terrestrial ecosystems already under biotic stress. Here, nano- and microplastics at 150-500 mg·kg-1 were exposed to tomatoes (Solanum lycopersicum L.), and the results demonstrate that the presence of nano- and microplastics increased the occurrence of bacterial wilt caused by Ralstonia solanacearum in tomatoes as a function of contaminant concentration, surface modification, and size. Our work shows that nanoplastics (30 nm, 250 mg·kg-1) increased the disease incidence by 2.19-fold. The disease severities in amino- and carboxyl-modified nanoplastic treatments were 30.4 and 21.7% higher than that in unmodified nanoplastic treatment, respectively. The severity of disease under the influence of different-sized nano- and microplastic treatments followed the order 30 > 100 nm > 1 > 50 μm. Mechanistically, nanoplastics disrupted the structure of the tomato rhizosphere soil bacterial community and suppressed the induced systemic resistance in tomato; nanoplastics in planta decreased the salicylic acid and jasmonic acid content in tomatoes, thus inhibiting systemic acquired resistance; and microplastics increased the soil water retention, leading to increased pathogen abundance in the rhizosphere. Additionally, the leachates from nano- and microplastics had no effect on disease occurrence or the growth of tomatoes. Our findings highlight a potential risk of nano- and microplastic contamination to agriculture sustainability and food security.

Effects of microplastics and combined pollution of polystyrene and di-n-octyl phthalate on photosynthesis of cucumber (Cucumis sativus L.)

Photosynthesis provides carbon sources and energy for crop growth and development, and the widespread presence of microplastics and plastic plasticisers in agricultural soils affects crop photosynthesis, but the mechanism of the effect is not clear. This study aims to investigate the effects of different microplastics and plasticizers on cucumber photosynthesis. Using polyvinyl chloride (PVC), polyethylene (PE), polystyrene (PS), and di-n-octyl phthalate (DOP) as representative microplastics and plasticizers, we assessed their impact on cucumber photosynthesis. Our results reveal significant alterations in key parameters: intercellular CO2 concentration (Ci) and transpiration rate (Tr) increased across all treatments, whereas stomatal limit value (Ls) and water use efficiency (WUE) decreased. Notably, PS + DOP treatment led to a significant reduction in the maximum efficiency of photosystem II (Fv/Fm) and ATP accumulation. Furthermore, PE and PS + DOP treatments decreased lycopene and ɛ-carotene synthesis rates, as well as abscisic acid (ABA) accumulation. All treatments inhibited the conversion of β-carotene into strigolactone (SL) and decreased chlorophyll synthesis rates, with PS + DOP exhibiting the most severe impact. Regarding chlorophyll degradation pathways, PVC and PE treatments reduced chlorophyll decomposition rates, whereas DOP with PS promoted degradation. PE and PS treatments also impaired light energy capture, electron transport, and the structural stability of photosystems I and II, as well as photosynthetic capacity and NADPH and ATP synthesis rates. Our findings underscore the differential impacts of microplastics and plasticizers on cucumber photosynthesis, with PS + DOP having the most detrimental effect. These results shed light on the complex interactions between microplastics and plant physiology, highlighting the urgent need for mitigation strategies in agricultural practices to safeguard crop productivity and environmental sustainability.

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.

Exploring the potential of biochar for the remediation of microbial communities and element cycling in microplastic-contaminated soil

The detrimental effects of microplastics (MPs) on soil microbial and elemental raise significant environmental concerns. The potential of remediation with biochar to mitigate these negative impacts remains an open question. The remediation effects of biochar derived from corn and cotton straw on MPs concerning soil microorganisms and element cycling were investigated. Specifically, biochar induced substantial remediations in microbial community structure following MP exposure, restoring and fortifying the symbiotic network while exerting dominance over microbial community changes. A combined treatment of biochar and MPs exhibited a noteworthy increase in the abundance of NH4+, NO3-, and available phosphorous by 0.46-2.1 times, reversing the declining trend of dissolved organic carbon, showing a remarkable increase by 0.36 times. This combined treatment also led to a reduction in the abundance of the nitrogen fixation gene nifH by 0.46 times, while significantly increasing the expression of nitrification genes (amoA and amoB) and denitrification genes (nirS and nirK) by 22.5 times and 1.7 times, respectively. Additionally, the carbon cycle cbbLG gene showed a 2.3-fold increase, and the phosphorus cycle gene phoD increased by 0.1-fold. The mixed treatment enriched element-cycling microorganisms by 4.8 to 9.6 times. In summary, the addition of biochar repaired the negative effects of MPs in terms of microbial community dynamics, element content, gene expression, and functional microbiota. These findings underscore the crucial role of biochar in alleviating the adverse effects of MPs on microbial communities and elemental cycling, providing valuable insights into sustainable environmental remediation strategies.

Microplastics in agroecosystems: Soil-plant dynamics and effective remediation approaches

Increasing microplastic (MP) pollution, primarily from anthropogenic sources such as plastic film mulching, waste degradation, and agricultural practices, has emerged as a pressing global environmental concern. This review examines the direct and indirect effects of MPs on crops, both in isolation and in conjunction with other contaminants, to elucidate their combined toxicological impacts. Organic fertilizers predominantly contain 78.6% blue, 9.5% black, and 8.3% red MPs, while irrigation water in agroecosystems contains 66.2% white, 15.4% blue, and 8.1% black MPs, ranging from 0-1 mm to 4-5 mm in size. We elucidate five pivotal insights: Firstly, soil MPs exhibit affinity towards crop roots, seeds, and vascular systems, impeding water and nutrient uptake. Secondly, MPs induce oxidative stress in crops, disrupting vital metabolic processes. Thirdly, leachates from MPs elicit cytotoxic and genotoxic responses in crops. Fourthly, MPs disrupt soil biotic and abiotic dynamics, influencing water and nutrient availability for crops. Lastly, the cumulative effects of MPs and co-existing contaminants in agricultural soils detrimentally affect crop yield. Thus, we advocate agronomic interventions as practical remedies. These include biochar input, application of growth regulators, substitution of plastic mulch with crop residues, promotion of biological degradation, and encouragement of crop diversification. However, the efficacy of these measures varies based on MP type and dosage. As MP volumes increase, exploring alternative mitigation strategies such as bio-based plastics and environmentally friendly biotechnological solutions is imperative. Recognizing the persistence of plastics, policymakers should enact legislation favoring the mitigation and substitution of non-degradable materials with bio-derived or compostable alternatives. This review demonstrates the urgent need for collective efforts to alleviate MP pollution and emphasizes sustainable interventions for agricultural ecosystems.

Effects of micro-nano plastics on the environmental biogeochemical cycle of nitrogen: A comprehensive review

Micro-nano plastics (MNPs; size <5 mm), ubiquitous and emerging pollutants, accumulated in the natural environment through various sources, and are likely to interact with nutrients, thereby influencing their biogeochemical cycle. Increasing scientific evidences reveal that MNPs can affect nitrogen (N) cycle processes by affecting biotopes and organisms in the environmental matrix and MNPs biofilms, thus plays a crucial role in nitrous oxide (N2O) and ammonia (NH3) emission. Yet, the mechanism and key processes behind this have not been systematically reviewed in natural environments. In this review, we systematically summarize the effects of MNPs on N transformation in terrestrial, aquatic, and atmospheric ecosystems. The effects of MNPs properties on N content, composition, and function of the microbial community, enzyme activity, gene abundance and plant N uptake in different environmental conditions has been briefly discussed. The review highlights the significant potential of MNPs to alter the properties of the environmental matrix, microbes and plant or animal physiology, resulting in changes in N uptake and metabolic efficiency in plants, thereby inhibiting organic nitrogen (ON) formation and reducing N bioavailability, or altering NH3 emissions from animal sources. The faster the decomposition of plastics, the more intense the perturbation of MNPs to organisms in the natural ecosystem. Findings of this provide a more comprehensive analysis and research directions to the environmentalists, policy makers, water resources planners & managers, biologists, and biotechnologists to do integrate approaches to reach the practical engineering solutions which will further diminish the long-term ecological and climatic risks.

Effects of microplastics on soil microorganisms and microbial functions in nutrients and carbon cycling - A review

The harmful effects of microplastics (MPs) pollution in the soil ecosystem have drawn global attention in recent years. This paper critically reviews the effects of MPs on soil microbial diversity and functions in relation to nutrients and carbon cycling. Reports suggested that both plastisphere (MP-microbe consortium) and MP-contaminated soils had distinct and lower microbial diversity than that of non-contaminated soils. Alteration in soil physicochemical properties and microbial interactions within the plastisphere facilitated the enrichment of plastic-degrading microorganisms, including those involved in carbon (C) and nutrient cycling. MPs conferred a significant increase in the relative abundance of soil nitrogen (N)-fixing and phosphorus (P)-solubilizing bacteria, while decreased the abundance of soil nitrifiers and ammonia oxidisers. Depending on soil types, MPs increased bioavailable N and P contents and nitrous oxide emission in some instances. Furthermore, MPs regulated soil microbial functional activities owing to the combined toxicity of organic and inorganic contaminants derived from MPs and contaminants frequently encountered in the soil environment. However, a thorough understanding of the interactions among soil microorganisms, MPs and other contaminants still needs to develop. Since currently available reports are mostly based on short-term laboratory experiments, field investigations are needed to assess the long-term impact of MPs (at environmentally relevant concentration) on soil microorganisms and their functions under different soil types and agro-climatic conditions.

Non-negligible impact of microplastics on wetland ecosystems

There has been much concern about microplastic (MP) pollution in marine and soil environments, but attention is gradually shifting towards wetland ecosystems, which are a transitional zone between aquatic and terrestrial ecosystems. This paper comprehensively reviews the sources of MPs in wetland ecosystems, as well as their occurrence characteristics, factors influencing their migration, and their effects on animals, plants, microorganisms, and greenhouse gas (GHG) emissions. It was found that MPs in wetland ecosystems originate mainly from anthropogenic sources (sewage discharge, and agricultural and industrial production) and natural sources (rainfall-runoff, atmospheric deposition, and tidal effects). The most common types and forms of MPs identified in the literature were polyethylene and polypropylene, fibers, and fragments. The migration of MPs in wetlands is influenced by both non-biological factors (the physicochemical properties of MPs, sediment characteristics, and hydrodynamic conditions) and biological factors (the adsorption and growth interception by plant roots, ingestion, and animal excretion). Furthermore, once MPs enter wetland ecosystems, they can impact the resident microorganisms, animals, and plants. They also have a role in global warming because MPs act as unique exogenous carbon sources, and can also influence GHG emissions in wetland ecosystems by affecting the microbial community structure in wetland sediments and abundance of genes associated with GHG emissions. However, further investigation is needed into the influence of MP type, size, and concentration on the GHG emissions in wetlands and the underlying mechanisms. Overall, the accumulation of MPs in wetland ecosystems can have far-reaching consequences for the local ecosystem, human health, and global climate regulation. Understanding the effects of MPs on wetland ecosystems is essential for developing effective management and mitigation strategies to safeguard these valuable and vulnerable environments.

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 enhance nitrogen loss from a black paddy soil by shifting nitrate reduction from DNRA to denitrification and Anammox

Microplastics (MPs) are frequently detected emerging pollutants in soil that can endanger farmland ecosystems; however, little is known about their impacts on dissimilatory nitrate reduction processes in paddy soil. Here, using the 15N-tracer and microbial molecular techniques, we investigated the effects of MPs (200-400 μm) made of polystyrene (PS), polyvinyl chloride (PVC), and polyethylene (PE) on denitrification, anaerobic ammonium oxidation (Anammox), and dissimilatory nitrate reduction to ammonium (DNRA) and the associated microbial community in a black paddy soil. All MPs increased the Anammox rate by 6.6 %-745 % and decreased the DNRA rate by 15.1 %-74.2 %, while MPs of PS and PE significantly increased the denitrification rate by 79.3 %-102.3 % and 34.8 %-62.1 %, respectively. The MPs promoted the partitioning of NO3- towards denitrification and Anammox while inhibiting DNRA, as suggested by the decreased relative contributions of DNRA from 24.1 % to 5.4 %-14.2 % following MPs amendment. This was attributed to the increased denitrification gene abundance and the enriched specific denitrifier taxa, as well as the decreased DNRA gene abundance. Our findings suggest that the stimulated denitrification and Anammox by MPs, accompanied by the suppression of DNRA, may lead to substantial nitrogen loss in paddy fields, underscoring the need to further evaluate the environmental behaviors of MPs in agricultural ecosystems.

Effects of biochar on soil microbial communities: A meta-analysis

Changes in soil microbial communities may impact soil fertility and stability because microbial communities are key to soil functioning by supporting soil ecological quality and agricultural production. The effects of soil amendment with biochar on soil microbial communities are widely documented but studies highlighted a high degree of variability in their responses following biochar application. The multiple conditions under which they were conducted (experimental designs, application rates, soil types, biochar properties) make it difficult to identify general trends. This supports the need to better determine the conditions of biochar production and application that promote soil microbial communities. In this context, we performed the first ever meta-analysis of the biochar effects on soil microbial biomass and diversity (prokaryotes and fungi) based on high-throughput sequencing data. The majority of the 181 selected publications were conducted in China and evaluated the short-term impact (<3 months) of biochar. We demonstrated that a large panel of variables corresponding to biochar properties, soil characteristics, farming practices or experimental conditions, can affect the effects of biochar on soil microbial characteristics. Using a variance partitioning approach, we showed that responses of soil microbial biomass and prokaryotic diversity were highly dependent on biochar properties. They were influenced by pyrolysis temperature, biochar pH, application rate and feedstock type, as wood-derived biochars have particular physico-chemical properties (high C:N ratio, low nutrient content, large pores size) compared to non-wood-derived biochars. Fungal community data was more heterogenous and scarcer than prokaryote data (30 publications). Fungal diversity indices were rather dependent on soil properties: they were higher in medium-textured soils, with low pH but high soil organic carbon. Altogether, this meta-analysis illustrates the need for long-term field studies in European agricultural context for documenting responses of soil microbial communities to biochar application under diverse conditions combining biochar types, soil properties and conditions of use.

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.

Effects of plastic contamination on carbon fluxes in a subtropical coastal wetland of East China

Coastal wetlands are recognized as carbon sinks that play an important role in mitigating global climate change because of the strong carbon uptake by vegetation and high carbon sequestration in the soil. Over the last few decades, plastic waste pollution in coastal zones has become increasingly serious owing to high-intensity anthropogenic activities. However, the influence of plastic waste (including foam waste) accumulation in coastal wetlands on carbon flux remains unclear. In the Yangtze Estuary, we investigated the variabilities of vegetation growth, carbon dioxide (CO2) and methane (CH4) fluxes, and soil properties in a clean Phragmites australis marsh and mudflat and a plastic-polluted marsh during summer and autumn. The clean marsh showed a strong CO2 uptake capacity (a carbon sink), and the clean mudflat showed a weak CO2 sink during the measurement period. However, polluted marshes are a significant source of CO2 emissions. Regardless of the season, the gross primary production and vegetation biomass of the polluted marshes were on average 9.5 and 1.1 times lower than those in the clean marshes, respectively. Ecosystem respiration and CH4 emissions in polluted marshes were significantly higher than those in clean marshes and mudflats. Generally, the soil bulk density and salinity in polluted marshes were lower, whereas the median particle size was higher at the polluted sites than at the clean sites. Increased soil porosity and decreased salinity may favor CO2 and CH4 emissions through gas diffusion pathways and microbiological behavior. Moreover, the concentrations of heavy metals in the soil of plastic-polluted marshes were 1.24-1.49 times higher than those in the clean marshes, which probably limited vegetation growth and CO2 uptake. Our study highlights the adverse effects of plastic pollution on the carbon sink functions of coastal ecosystems, which should receive global attention in coastal environmental management.

Reviewing the role of biochar in paddy soils: An agricultural and environmental perspective

The main challenge of the twenty-first century is to find a balance between environmental sustainability and crop productivity in a world with a rapidly growing population. Soil health is the backbone of a resilient environment and stable food production systems. In recent years, the use of biochar to bind nutrients, sorption of pollutants, and increase crop productivity has gained popularity. This article reviews key recent studies on the environmental impacts of biochar and the benefits of its unique physicochemical features in paddy soils. This review provides critical information on the role of biochar properties on environmental pollutants, carbon and nitrogen cycling, plant growth regulation, and microbial activities. Biochar improves the soil properties of paddy soils through increasing microbial activities and nutrient availability, accelerating carbon and nitrogen cycle, and reducing the availability of heavy metals and micropollutants. For example, a study showed that the application of a maximum of 40 t ha-1 of biochar from rice husks prior to cultivation (at high temperature and slow pyrolysis) increases nutrient utilization and rice grain yield by 40%. Biochar can be used to minimize the use of chemical fertilizers to ensure sustainable food production.

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.

Interactions between white and black carbon in water: A case study of concurrent aging of microplastics and biochar

Microplastics and biochar, as particulate matter that is prevalent in the water environment, will inevitably encounter and interact with each other during environmental aging. The potential interaction of microplastics and biochar, and the associated impact on their environmental behavior remains largely unknown. In this study, we exposed microplastics and biochar concurrently to ultraviolet light to mimic the aging process, investigated the release and fluorescence characteristics of dissolved organic matter (DOM) in water, and analyzed the effects of co-existing microplastics and biochar on their sorption of organic contaminants. We demonstrate that early-stage interactions of microplastics and biochar could entangle to promote the release of DOM from biochar, while their long-term interactions after light irradiation resulted in the sorption of hydrophobic and small molecules of microbial byproduct-like DOM. Simultaneously, early-stage interactions of microplastics and biochar showed a promotion for sorption of organic contaminants with an increase of 5.3-17.7%. After aging, however, long-term interactions between microplastics and biochar made it no longer promote the sorption of organic contaminants due to the influence of heterogeneous aggregation. Our results provide new insights into the time-dependent interactions between microplastics and biochar and highlight the need to incorporate their interactions into future environmental risk assessments for microplastics in the water environment.

Revealing the response of microbial communities to polyethylene micro(nano)plastics exposure in cold seep sediment

To date, multiple studies have shown that the accumulation of microplastics (MPs)/nanoplastics (NPs) in the environment may lead to various problems. However, the effects of MPs/NPs on microbial communities and biogeochemical processes, particularly methane metabolism in cold seep sediments, have not been well elucidated. In this study, an indoor microcosm experiment for a period of 120 days exposure of MPs/NPs was conducted. The results showed that MPs/NPs addition did not significantly influence bacterial and archaeal richness in comparison with the control (p > 0.05), whereas higher levels of NPs (1 %, w/w) had a significant adverse effect on bacterial diversity (p < 0.05). Moreover, the bacterial community was more sensitive to the addition of MPs/NPs than the archaea, and Epsilonbacteraeota replaced Proteobacteria as the dominant phylum in the MPs/NPs treatments (except 0.2 % NPs). With respect to the co-occurrence relationships, network analysis showed that the presence of NPs, in comparison with MPs, reduced microbial network complexity. Finally, the presence of MPs/NPs decreased the abundance of mcrA, while promoting the abundance of pmoA. This study will help elucidate the responses of microbial communities to MPs/NPs and evaluate their effects on methane metabolism in cold seep ecosystems.

The co-occurrent microplastics and nano-CuO showed antagonistic inhibitory effects on bacterial denitrification: Interaction of pollutants and regulations on functional genes

The wide occurrence of microplastics (MPs) and nanoparticles resulted in their inevitable coexistence in environment. However, the joint effects of these two types of particulate emerging contaminants on denitrification have seldomly been investigated. Herein, non-biodegradable polyvinyl chloride, polypropylene, polyethylene and biodegradable polyhydroxyalkanoate (PHA) MPs were chosen to perform the co-occurrent effects with nano copper oxide (nano-CuO). Both the nano-CuO and MPs inhibited the denitrification process, and biodegradable PHA-MPs showed severer inhibition than non-biodegradable MPs. However, the presence of MPs significantly alleviated the inhibition of nano-CuO, suggesting an antagonistic effect. Other than MPs decreasing copper ion release from nano-CuO, MPs and nano-CuO formed agglomerations and induced lower levels of oxidative stress compared to individual exposure. Transcriptome analysis indicated that the co-occurrent MPs and nano-CuO induced different regulation on denitrifying genes (e. g. nar and nor) compared to individual ones. Also, the expressions of genes involved in denitrification-associated metabolic pathways, including glycolysis and NADH electron transfer, were down-regulated by nano-CuO or MPs, but exhibiting recovery under the co-occurrent conditions. This study firstly discloses the antagonistic effect of nano-CuO and MPs on environmental process, and these findings will benefit the systematic evaluation of MPs environmental behavior and co-occurrent risk with other pollutants.

Micro and nanoplastics ravaging our agroecosystem: A review of occurrence, fate, ecological impacts, detection, remediation, and prospects

Micro-and nanoplastics (MNPs) are particles that are smaller than a millimeter in size and have infiltrated both terrestrial and aquatic ecosystems. MNPs pollution have become a widespread problem causing severe adverse effects on human health and the environment worldwide. Once in the environment, these polymers are not easily degradable due to their recalcitrant nature and small size and are easily consumed by aquatic organisms and transported through the food chain, at great risk to human health. Substantial evidence demonstrates the negative effects of MNPs residues on aquatic organisms' reproductive and developmental defects. Similarly, soil flora, soil quality, and plant height have been severely impacted by their presence in the agroecosystem. This is evident in the inhibition of water absorption by blocked seed pores, delayed germination, and the dramatic decline in transpiration rates and growth of plant roots, inevitably leading to drop in biomass and crop production, posing an overall threat to global food security. In this review, we present the impact of MNPs in agroecosystems around the globe, including their sources, occurrence, distribution, transport, and ultimate fate. We recommend using bio-based plastics, eco-friendly remediation strategies, reformed agricultural practices, non-single-use synthetic plastic legislation, and increased plastic waste disposal awareness campaigns as effective tools to mitigate this problem.

Adsorptive behavior of micro(nano)plastics through biochar: Co-existence, consequences, and challenges in contaminated ecosystems

The abundance of micro(nano)plastics in natural ecosystems is a crucial global challenge, as these small-sized plastic particles originate from land-based and marine-based activities and are widely present in marine, freshwater, and terrestrial ecosystems. Micro(nano)plastics can significantly be reduced through various methods, such as biological, chemical, and physical techniques. Biochar is a low-cost adsorbent and is considered an efficient material and its application is ecologically effective carbon-negative for remediation of organic and inorganic pollutants. Therefore, this review critically discusses the fate and transport of micro(nano)plastics and their interactions with different biochar in aqueous and column porous media. This review outlines the implications of biochar with the co-existence of micro(nano)plastics in efforts to understand their coupled effects on soil physicochemical properties, microbial communities, and plant growth, along with the removal of heavy metals and other toxic contaminants. In batch experiments, biochar synthesized from various biomasses such as corn straw, hardwood, pine and spruce bark, corncob, and Prosopis juliflora had shown high level of removal efficiency (>90 %) for microplastic adsorption under varying environmental conditions viz., pH, temperature, ionic strength, particle size, and dose due to chemical bonding and electrostatic attractions. Increased temperature of the aqueous solutions encouraged higher adsorption, while higher pH and dissolved organic matter and nutrients may show decreased adsorption capacities for micro(nano)plastics using biochar. Compared to other available physical, chemical, and biological methods, biochar-amended sand filters in column experiments have been very efficient in removing micro(nano)plastics. In saturated column porous media, various microplastics could be inhibited using biochar due to decreased electrostatic repulsion, steric hindrance, and competitive sorption due to humic acid, ionic strength, and cations. Finally, this review provides in-depth insights on further investigations and recommendations for overall micro(nano)plastics removal using biochar-based materials.

Effects of microplastics on cadmium accumulation by rice and arbuscular mycorrhizal fungal communities in cadmium-contaminated soil

Both microplastics (MPs) and cadmium (Cd) are common contaminants in soil-rice systems, but their combined effects remain unknown. Thereby, we explored the effects of three MPs, i.e., polyethylene terephthalate (PET), polylactic acid (PLA), and polyester (PES), on Cd accumulation in rice and the community diversity and structure of arbuscular mycorrhizal fungi (AMF) in soil spiked with or without Cd. Results showed that 2% PLA decreased shoot biomass (-28%), but PET had a weaker inhibitive effect. Overall, Cd alone did not significantly change shoot and root biomass and increased root biomass in combination with 0.2% PES. MPs generally increased soil Cd availability but decreased Cd accumulation in rice tissues. Both MPs and Cd improved the bioavailability and uptake of Fe and Mn in rice roots. MPs altered the diversity and community composition of AMF, depending on their type and dose and co-existing Cd. Overall, 2% PLA caused the most distinct changes in soil properties, plant growth and Cd accumulation, and AMF communities, but showed no synergistic interactions with Cd. In conclusion, MPs can mediate rice performance and Cd accumulation via altering soil properties, nutrient uptake, and root mycorrhizal communities, and biodegradable PLA MPs thought environment-friendly can exhibit higher phytotoxicity than conventional MPs.

Role of polyamide microplastic in altering microbial consortium and carbon and nitrogen cycles in a simulated agricultural soil microcosm

Microplastics (MPs) are persistent organic pollutants globally, with a continuous increase in MP wastes near and away from the regions of human activities. Studies to date aimed to explore the impact of MPs on ecosystems, but the area of research could not go beyond environmental pollution caused by MPs. To address the menace of MPs, scientists need to pay enough attention to the biogeochemical cycles, microbial communities, and functional microorganisms. Hence, this study aimed to evaluate the impact of adding 0.3% (mass ratio) [low-concentration (LC) group] and 1% [high-concentration (HC) group] of polyamide (PA) MP to the soil microenvironment with regard to the aforementioned parameters. PA MP decreased the soil microbial diversity (Shannon and Simpson indices, P < 0.05). At the phylum level, PA MP increased the abundance of Acidobacteria, Firmicutes, and Crenarchaeota (P < 0.05); at the genus level, it enhanced that of Geobacter, Thiobacillus, Pseudomonas, and Bradyrhizobium (P < 0.01) while decreased that of Bacillus, Flavisolibacter, Geothrix, and Pseudarthrobacter (P < 0.05). PA MP affected the carbon (C) cycle. PA MP accelerated the soil C fixation by enhancing the abundance of the genes accA and pccA. The LC PA MP accelerated organic C degradation and methane metabolism by changing the abundance of mnp, chiA, mcrA, pmoA, and mmoX genes, while the HC PA MP inhibited them with increasing the experimental time. Regarding the effects of PA on the nitrogen (N) cycle, the PA MP promoted N assimilation and ammonification by increasing the abundance of the genes gdh and ureC, the impact of PA MP on N fixation and denitrification depended on its concentration and treating time. This study showed that PA MP impacted the microbial consortium, it also affected the C and N cycles and its effect depended on its concentration and the treating time.

The weathering process of polyethylene microplastics in the paddy soil system: Does the coexistence of pyrochar or hydrochar matter?

This study is based on a particular test site to simulate the weathering process of microplastics (MPs) in paddy soil. A substantial amount of plastic waste, especially MPs, inevitably accumulates in agricultural soil due to the high consumption and short average use of plastics. Recently, MP pollution has become a global environmental concern. However, insight into the soil weathering process of MPs in paddy soil, particularly in the presence of biochar, is lacking. In this study, the physicochemical properties of polyethylene (PE) MPs were determined through a 24-week weathering system conducted in paddy soil, paddy soil with pyrochar, or hydrochar. Moreover, the sorption of original and weathered PE MPs toward three typical pollutants (cadmium/Cd, bisphenol A/BPA, and dimethyl phthalate/DMP) was investigated. The surface of PE MPs was fractured, 1.1-fold rougher, yellow-colored (11.7 units), and 1.8-fold more oxidized after paddy soil weathering. In addition, the crystallinity, negative charge, and stronger hydrophilicity of weathered PE MPs increased compared to original PE MPs. Weathering in a pyrochar or hydrochar system caused fissures, extensive destruction of amorphous areas, and accelerated chemical or bio-oxidation processes for PE MPs, resulting in a more noticeable change in roughness (1.4-2.2-fold), yellow color (12.7-13.7), crystallinity (1.2-1.5-fold), and oxygen content (2.5-3.6-fold). Weathered PE MPs facilitated the sorption with Cd and BPA, attributed to larger specific surface area, abundant polar functional groups, and increased negatively charged sites. However, sorption of DMP to PE MPs was highly influenced by their hydrophobicity, resulting in decreased hydrophobic partition sorption on weathered PE MPs. Overall, paddy soil weathering affected the properties of PE MPs and enhanced sorption of Cd and BPA but reduced sorption of DMP. The coexistence of biochar exacerbated the paddy soil weathering effect. The insight gained from this study assists in better understanding the weathering process of PE MPs in agricultural soils.

Every coin has two sides: Continuous and substantial reduction of ammonia volatilization under the coexistence of microplastics and biochar in an annual observation of rice-wheat rotation system

Microplastics (MPs) are verified to affect the fate of ammonia (NH₃) in agricultural soils. However, the impacts and mechanisms of MPs coupled with biochar (BC), a widely used agricultural conditioner, on NH₃ losses are mostly untapped. The aim of this study was to investigate the mechanisms of common MPs (i.e., polyethylene, polyester, and polyacrylonitrile) and straw-derived BC on NH₃ volatilization in rice-wheat rotation soils. Results showed that BC alone and MPs with BC (MPs + BC) reduced 5.5 % and 11.2-26.6 % cumulative NH₃ volatilization than the control (CK), respectively, in the rice season. The increased nitrate concentration and soil cation exchange capacity were dominant contributors to the reduced soil NH₃ volatilization in the rice season. BC and MPs + BC persistently reduced 44.5 % and 60.0-62.6 % NH₃ losses than CK in the wheat season as influenced by pH and nitrate concentration. Moreover, BC and MPs + BC increased humic acid-like substances in soil dissolved organic matter by an average of 159.1 % and 179.6 % than CK, respectively, in rice and wheat seasons. The increased adsorption of soil NH₄⁺ and the promotion of crop root growth were the main mechanisms of NH₃ reduction. Our findings partially revealed the mechanisms of the coexistence of MPs and BC on NH₃ mitigation in rice-wheat rotational ecosystems.

Effects of organic fertilization on functional microbial communities associated with greenhouse gas emissions in paddy soils

Soil microbial communities play a key role in the biochemical processes and nutrient cycles of the soil ecosystem and their byproducts, including greenhouse gases (GHGs). Organic fertilization influences bacterial soil biodiversity and is an essential emission source of GHGs in paddy soil ecosystems. However, the impact of organic fertilization on the functional microorganisms associated with the GHGs methane and nitrous oxide remains unknown. We conducted paddy soil field experiments under three different treatments (no fertilization, base fertilization, and organic fertilization) to investigate the contribution of organic fertilization to soil nutrients and the functional microorganisms associated with GHG emissions. We found that organic fertilization effectively increased the soil organic matter (P < 0.001), soil organic carbon (P < 0.001), and total nitrogen (P < 0.05) as well as the richness (operational taxonomic units and abundance-based coverage estimators) of the methanogenic communities. Correlation analyses showed that methanogenic communities that were present in abundance were more vulnerable to perturbations in soil properties compared to nitrifying bacterial communities. Partial least squares path model analyses elucidated that organic fertilization directly affected both methanogenic communities and nitrifying bacterial communities (P < 0.05), thereby accelerating methane emissions. Strong co-occurrence networks were observed within the soil-dominant phyla Acidobacteria, Bacteroidetes, and Proteobacteria. Our findings highlight the impact of organic fertilization on soil nutrients and functional microorganisms and guide mitigating GHG emissions from paddy soil agroecosystems.

Interactive effects of microplastics, biochar, and earthworms on CO2 and N2O emissions and microbial functional genes in vegetable-growing soil

Soil carbon dioxide (CO₂) and nitrous oxide (N₂O) emissions are two main greenhouse gases that play important roles in global warming. Studies have shown that microplastics, biochar, and earthworms can significantly affect soil greenhouse gas emissions. However, few studies have explored how their interactions affect soil CO₂ and N₂O emissions. A mesocosm experiment was conducted to investigate their interactive effects on soil greenhouse gases and soil microbial functional genes in vegetable-growing soil under different incubation times. Biochar alone or combined with microplastics significantly decreased soil CO₂ emissions but had no effect on soil N₂O emissions. Microplastics and biochar inhibited CO₂ emissions and promoted N₂O emissions in the soil with earthworms. The addition of microplastics, biochar, and earthworms had significant effects on soil chemical properties, including dissolved organic carbon, ammonia nitrogen, nitrate nitrogen, total nitrogen, and pH. Microplastics and earthworms selectively influenced microbial abundances and led to a fungi-prevalent soil microbial community, while biochar led to a bacteria-prevalent microbial community. The interactions of microplastics, biochar, and earthworms could alleviate the reduction of the bacteria-to-fungi ratio and the abundance of microbial functional genes caused by microplastics and earthworms alone. Microplastics significantly inhibited microorganisms as well as C and N cycling functional genes in earthworm guts, while biochar obviously stimulated them. The influence of the addition of exogenous material on soil greenhouse gas emissions, soil chemical properties, and functional microbes differed markedly with soil incubation time. Our results indicated that biochar is a promising amendment for soil with microplastics or earthworms to simultaneously mitigate CO₂ emissions and regulate soil microbial community composition and function. These findings contribute to a better understanding of the interaction effects of microplastics, biochar, and earthworms on soil carbon and nitrogen cycles, which could be used to help conduct sustainable environmental management of soil.

Differences, links, and roles of microbial and stoichiometric factors in microplastic distribution: A case study of five typical rice cropping regions in China

Microplastics (MPs), as new pollutants in agroecosystems, have already attracted widespread attention from scientists. However, our understanding of MP geographic distribution and its influencing factors across spatial scales remains poor. Here, a regional-scale field investigation was conducted to assess the distribution characteristic of MPs in five major rice-growing regions of China, and we explored the roles of biological and abiotic factors, especially stoichiometry and microbial influences on MP distribution. MPs were observed in all sampling sites, averaging 6,390 ± 2,031 items⋅kg^–1. Sizes less than 0.5 mm and black and transparent MPs dominated. Fiber, classified as one of the MP shapes, occurred most frequently. MP community analysis, firstly used in paddy soil, revealed more black MPs abundance in Henan (HE), more rayon, blue, and other colors MPs in Hunan (HN), more transparent MPs in Tianjing (TJ), and more PE MPs in Heilongjiang (DB). Higher MP community diversity was found in most south paddy soils of this study, due to a broader range of sources. C/N showed a positive relationship with pellet-shaped MP abundance and MPs of size between 2 and 5 mm (P < 0.05). Chao1 index of soil microbial communities was positively correlated with the MP abundance, MPs of size less than 0.5 mm, and fiber abundance. The minimum temperature was positively correlated with MP abundance (P < 0.05), implying the potential effects of the freeze-thaw process might exist. The regression analysis highlighted the important role of population quantity in determining MP abundance (R = 0.421, P = 0.02). This study confirmed the wide distribution of MPs in different soil depths of paddy lands in China and demonstrated that its distribution was influenced by population quantity and environmental variables, such as microbiology. These findings could provide a basis for the toxicological behavior of MPs and the potential risk to human health.

Effects of microplastics on greenhouse gas emissions and microbial communities in sediment of freshwater systems

Microplastics can regulate greenhouse gas emissions from environmental systems and affect microbes in the environment. However, the effect of microplastics in freshwater sediment system is still not well studied. In this paper, polyethylene terephthalate (PET) particles with six different diameters of 5-2000 µm were added to freshwater sediment, PET exposing for 90 days was carried out and its effect on greenhouse gas emissions, nutrients cycle and microbial communities were studied. In the 5 µm experimental group, carbon dioxide (CO₂) emissions were significantly promoted in the 7-30 days and nitrogen monoxide (N₂O) emissions were significantly promoted in the 7 days after cultivation. Microplastics in the range of 300-800 µm significantly promoted CO₂ emissions after three days of culture. In addition, microplastics increased the total organic carbon (TOC) content in freshwater sediment and changed microbial diversity, especially increased the microorganisms capable of degrading complex organics such as Saprospiraceae. There was a positive correlation between N₂O emission and nitrate (NO₃^-) content in sediment after 3 days of culture, while greenhouse gas emission was mainly related to TOC content after 90 days of culture. These results showed that microplastics could affect the carbon and nitrogen cycling process of shallow lake ecosystem.

Effects of Microplastics on Higher Plants: A Review

Microplastics pose great risks to terrestrial systems owing to their large quantity and strong persistence. Higher plants, an irreplaceable part of the terrestrial ecosystem, are inevitably exposed to microplastics. This review highlights the effects of microplastics on higher plant growth and performance. The tested microplastics, plant species, and cultural methods used in existing studies were summarized. We discussed the reasons why these microplastics, plants, and methods were selected. The various responses of higher plants to microplastics in both soils and waters were critically reviewed. We also highlighted the influencing mechanisms of microplastics on higher plants. Conclusively, more than 13 types of common microplastics and more than 30 species of higher plants have been selected and studied by the published literatures. Soil culture tests and hydroponic experiments are almost equally divided. The effects of microplastics on higher plants varied among microplastic properties, plant species, and environmental factors. Microplastics had no or positive effects on higher plants under certain experimental conditions. However, more studies showed that microplastics can inhibit higher plant growth and performance. We reduced the inhibitory mechanisms into direct and indirect mechanisms. The direct mechanisms include blocking pores or light, causing mechanical damage to roots, hindering genes expression, and releasing additives. The indirect mechanisms contain changing soil properties, affecting soil microbes or soil animals, and affecting bioavailability of other pollutants. This review improves the understanding of effects and influencing mechanisms of microplastics on higher plants.

Transport and retention patterns of fragmental microplastics in saturated and unsaturated porous media: A real-time pore-scale visualization

The environmental behaviors of microplastics (MPs) have garnered ever-increasing attention globally. To overcome the limitations of commonly used "black box", a real-time pore-scale visualization system including microscope, charge coupled device (CCD) microscope camera, and flow cell (connected with pump and sample collector) was used to unravel the transport and retention mechanisms of fragmental microplastics (FMPs) in saturated and unsaturated porous media. The breakthrough curves (BTCs) of effluent concentrations from the flow cells were used to quantitatively analyze FMPs transport. The videos gathered from different transport scenarios indicated that FMPs can move along with the bulk flow in porous media, but also move around the sand surfaces via sliding, rolling, and saltating patterns. The FMPs were retained in porous media mainly via deposition and straining in saturated porous media. Interestingly, little FMPs were captured by the air-water interface in unsaturated conditions. The mobility of FMPs varied with environmental factors, which became lower at higher solution ionic strength (IS), smaller grain size, and lower water content in porous media. Flow rate barely affected the transport of FMPs under 0.1 mM IS with the mass recovery rate ranging between 65.8 and 67.5%, but significantly enhanced FMPs mobility under 10 mM IS through reducing the moving rate. The IS and grain size showed a more significant effect on the transport of FMPs in unsaturated porous media. Our findings, for the first time, visually deciphered the transport and retention patterns of MPs with fragmental shapes on pore-scale, expanding our current knowledge of the fate and transport of more realistic MPs in the environment.