Effects of microplastics on carbon release and microbial community in mangrove soil systems

Stable isotope probing and oligotyping reveal the impact of organophosphorus pesticides on the carbon fixation related bacterioplankton lineage

Freshwater bacterioplankton communities play a pivotal role in global carbon fixation and energy exchange. However, establishing direct linkages between environmental stressors like organophosphorus pesticides (OPPs) and the ecological functions, such as carbon-fixing related microorganisms (CFMs), remains challenging. This study investigated the effects of four OPPs - two phosphates (dichlorvos, monocrotophos) and two phosphorothioates (omethoate, parathion) - on bacterioplankton communities using stable isotope probing, high-throughput sequencing and oligotyping analysis. Seven CFMs were identified. All OPPs significantly reduced total biomass (from 7.87 ×104 to 2.30-4.11 ×104 cells/mL) but stimulated CFMs proliferation. Notably, phosphorothioates induced a greater increase in CFMs abundance (36.84 %-57.18 %, up from 21.1 %) compared to phosphates (23.85 %-37.10 %; p < 0.05). Principal coordinate analysis (PCoA) revealed that phosphorothioates exerted stronger effects on microbial community and CFMs oligotypes structure compared to phosphates (p < 0.05). Variance partitioning analysis (VPA) identified pesticide type as the dominant driver of community structure. PICRUSt2 prediction demonstrated that OPPs suppressed oxidoreductase pathways linked to energy metabolism while activating transferase pathways associated with microbial stress resistance. Phosphorothioates depleted 64 pathways and enhanced 208 pathways, far exceeding phosphate impacts (2 depleted, 22 enhanced), indicating the phosphorothioates played a more important role on bacterioplankton communities than phosphate. Additionally, OPPs exposure reduced functional redundancy and destabilized community stability in bacterioplankton, potentially granting CFMs a long-term competitive advantage and elevating algal bloom risks. These findings provide insights into active CFMs in aquatic systems and their responses to diverse OPPs, offering new perspectives for managing organophosphorus pesticide contamination.

Deciphering the effects of long-term exposure to conventional and biodegradable microplastics on the soil microbiome

Despite recent advances in the understanding of the impacts of microplastics (MPs) on the soil microbiome under short-term exposure, little information is known regarding the long-term ecological effects of MPs in soil, especially biodegradable MPs (BMPs). Here, we systematically compared the effects of four prevalent microplastics, including two conventional MPs (CMPs) and two BMPs, on the soil microbiome over short- and long-term exposure durations. The soil microbial community were not significantly affected by the MP addition under short-term exposure; however, the soil microbial composition was obviously impacted by MP exposure under long-term exposure, some MP-adapted microbes (e.g., the phyla Protobacteria and Actinobacteria) were enriched but the phyla Acidobacteriota declined. These results indicated that the effects of the MP exposure on the soil microbiome were time dependent. PERMANOVA analysis demonstrated that the exposure time played a more important role in the variation in soil microbiome than the polymer type. The soil microbes which were reshaped by MPs were specialized in genetic potential of lipid metabolism and xenobiotics degradation and metabolism and weakened in microbial genetic information process. The carbon metabolic capacity and nitrogen transformation of soil microbes were disturbed by MPs under long-term exposure. Compared with CMPs, many more MPs derivatives, such as dissolved organic matter and low molecular-weight oligomers, were released from BMPs during the long-term degradation process in soil; thus, BMPs had a stronger effect on the soil microbiome than CMPs under long-term exposure. This study underscores the potential risk of the replacement of conventional plastics with biodegradable plastics.

Coupling of sulfate reduction and dissolved organic carbon degradation accelerated by microplastics in blue carbon ecosystems

Microplastics have increasingly accumulated in sulfate- and organic matter-rich mangrove ecosystems, yet their effects on microbially mediated carbon and sulfur cycling in sediments remains poorly understood. In this study, we performed a 70-day anaerobic microcosm experiment to examine the effects of polylactic acid (PLA) microplastics with different sizes on sulfate reduction and dissolved organic carbon (DOC) degradation in mangrove sediments. Our results demonstrated that millimeter-scale PLA (mm-PLA) more effectively enhanced sulfate reduction, sulfur isotope fractionation, reduced sulfide production, and carbon dioxide (CO2) emission compared to micrometer-scale PLA (m-PLA). These results suggested that mm-PLA had a more pronounced impact on the carbon and sulfur cycles. Integrated 16S rRNA gene amplicon sequencing and metagenomic analyses revealed that mm-PLA preferentially enriched key functional microorganisms, including acetate-producing bacteria (e.g., Acetobacteroides), completely oxidizing sulfate-reducing bacteria (e.g., Desulfobacter), and incompletely oxidizing sulfate-reducing bacteria (e.g., Desulfobulbus). These microorganisms exhibited higher abundances and greater genetic potential for carbon metabolism and sulfate reduction under mm-PLA treatment. Their relative abundances showed positive correlations with sulfate reduction rates, sulfur isotope fractionation, and CO2 emission, identifying them as crucial drivers of coupled carbon-sulfur cycling. Furthermore, the synergistic interactions among Acetobacteroides, Desulfobacter, and Desulfobulbus facilitated the oxidation of sediment-derived DOC, highlighting significant implications for carbon sequestration in blue carbon ecosystems.

Aging behaviors intensify the impacts of microplastics on nitrate bioreduction-driven nitrogen cycling in freshwater sediments

Microplastics (MPs) inevitably undergo aging processes in natural environments; however, how aging behaviors influence the interactions between MPs exposures and nitrate bioreduction in freshwater sediments remains poorly understood. Here, we explored the distinct impacts of virgin and aged MPs (polystyrene (PS) and polylactic acid (PLA)) on nitrate bioreduction processes in lake sediments through a long-term microcosm experiment utilizing the 15N isotope tracing technique and molecular analysis. Compared to virgin MPs, aged PLA significantly increased the rates of denitrification, anaerobic ammonium oxidation (anammox), and dissimilatory nitrate reduction to ammonium (DNRA) (p < 0.05), facilitating sediment nitrogen loss, while aged PS only significantly improved the rates of DNRA by 272-297 % and contributed to nitrogen retention in sediments. Metagenomic sequencing demonstrated that a more significant enrichment of functional genes responsible for nitrate bioreduction pathways occurred with aged MPs exposures than with virgin MPs. By combining analyses of MPs aging traits and the key drivers of nitrate bioreduction, we revealed that aging behaviors directly regulated sediment nutrient status (e.g., DOC/NOx- ratio) and microbiological properties (from genes to bacteria), thereby further determining the activity of nitrate bioreduction. This work provides new insights into the impacts of aged MPs on sediment nitrate reduction and highlights the role of MPs aging in future assessments of long-term MPs pollution in freshwater ecosystems.

Microplastic diversity stimulates N2O emission during NO3--N transformation by altering microbial interaction and electron consumption in eutrophic water

Microplastic mixtures, consisting of various types, are widespread in aquatic ecosystems. However, the role of microplastic diversity in influencing N2O emission during NO3--N transformation remains unclear, particularly in eutrophic water bodies. To address this, we established 10 microcosms with microplastic diversity of 0, 1, 3, and 5 and explored the effects of microplastic diversity on NO3--N transformation, N2O emission, microbial communities, co-occurrence networks, and electron transfer. Results showed that microplastic diversity slightly impacted NO3--N transformation rates, but remarkably enhanced N2O emission. Although elevated microplastic diversity caused notable variations in microbial community, bacterial abundance had insignificant correlations with NO3--N transformation or N2O emission rates. Notably, the increased microplastic diversity made microbial networks more complex and stable, indirectly promoting N2O emission by altering electron transfer and consumption during NO3--N transformation. Especially, electron consumption had the most direct effect on N2O emission. Furthermore, the increasing microplastic diversity slightly affected NOR activity, while significantly decreasing NOS activity and raising (nirK+nirS)/nosZ ratio, which suggested that microplastic diversity primarily enhanced N2O emission by inhibiting its further reduction. Our findings provide deeper insight into the nitrogen transformation and greenhouse gas emission influenced by microplastic mixtures in eutrophic aquatic environments.

Depth-dependent response of soil microbial community and greenhouse gas efflux to polylactic acid microplastics and tidal cycles in a mangrove ecosystem

The impacts of microplastics (MPs) on greenhouse gas emissions from mangrove soil remain poorly understood. Previous studies mostly focused on the topsoil in stable inundation state, ignoring the effects of natural tidal cycle and deep soil under different soil oxygen conditions. In this study, we analyzed soil microbial communities and greenhouse gas emissions from mangrove soils across various depths and tidal conditions (by adding seawater to create different inundation durations) in response to polylactic acid (PLA) MP exposure. Results indicated that PLA MPs addition enhances CO2 and CH4 release from the continuously anaerobic subsoil (100-120 cm). With increasing submersion duration, PLA MPs facilitate the emission of CH4 from the topsoil (0-5 cm). An elevated C:N ratio may promote microbial nitrogen mining and organic carbon mineralization, indicating the threat of PLA MPs to soil carbon and nitrogen pools. PLA MPs addition significantly altered the bacterial community structure and reduced bacterial diversity in the subsoil. Increases in the abundance and functioning of communities associated with methanogenesis and sulfate reduction contributed to the release of CO2 and CH4. The duration of inundation had no significant impact on the microbial community structure in the topsoil. These findings demonstrate the accelerating effect of PLA MPs on organic carbon mineralization and carbon release, which was critically regulated by the soil depth and tidal inundation.

Plastic pollution in mangrove ecosystems: A global meta-analysis

Mangrove ecosystems play a crucial role in blue carbon sequestration, coastal flood protection, and biodiversity conservation, while also serving as nursery habitats for threatened and economically important species. Due to their complex root structures, mangroves act as natural plastic traps, making them vulnerable to marine plastic contamination. In this study, we conducted a meta-analysis synthesising available global data on macroplastic and microplastic pollution in mangrove ecosystems, assessing their prevalence and the environmental partitioning of plastics both within and outside Marine Protected Areas (MPAs). We reviewed 44 primary studies and conducted statistical analyses to compare plastic abundance in the sediment, water, and biota. Our results show that mangrove ecosystems experience significant plastic pollution. Macroplastic abundance within the studied mangroves varied by five orders of magnitude, averaging 23.73 ± 8.80 items m-2, comparable to the highest levels recorded on beaches and underscoring the plastic-trapping capacity of mangroves. Mangroves globally had a mean contamination of 1122.98 ± 150.17 microplastics kg-1 in sediment and 16.00 ± 11.04 microplastics L-1 in seawater, both approximately double estimated safe limits. Our analyses found a 45.5 % reduction in microplastic within mangrove sediments and an 83.3 % reduction in macroplastic contamination in protected mangrove ecosystems. However, seawater microplastic levels were higher within MPAs, particularly near urbanized areas. These findings emphasize the need for integrated mitigation strategies that combine MPAs with targeted plastic waste reduction measures. Our analyses also highlight that the ecological impacts of this plastic accumulation within mangrove ecosystems remains a key knowledge gap.

Geospatial distribution and anthropogenic litter impact on coastal mangrove ecosystems from the Saudi Arabia coast of the Gulf

Mangrove ecosystems are significantly impacted by marine litter pollution, an increasingly important environmental problem. These ecosystems, situated at the interface between sea and land, serve as critical habitats and act as traps for plastic pollution. This study investigated the concentration, source, and composition of marine litter on both the mangrove bottom and canopy along the Saudi Arabia coast in the Gulf. The observed concentration of surface litter ranged from 0.98 ± 0.05 to 2.96 ± 0.25 items/m², with a mean concentration of 1.4 ± 0.61 items/m² (SD; N = 9). The mean trapped litter was 0.79 ± 0.45 items/tree, ranging from 0 to 7 items/tree. Plastic litter dominates the mangrove environment, accounting for 80% of debris items on the floor and 43% of those entangled in the canopy. Single-use plastics were the most prevalent type of litter detected across all surveyed locations. The sediments within the mangrove ecosystem serve as long-term repositories for plastic litter, evaluated through various indices, such as General Index, Clean Coast Index, Pollution Load Index, and Hazardous Litter Index, to assess the cleanliness of the mangrove floor. The Pollution Load Index shows a "Hazard level I," indicating that the mangrove floor is less contaminated. A higher concentration of litter was observed in urban areas with greater population density, likely originating from terrestrial activities like urban runoff and marine activities, particularly fishing.

Microbial colonization and succession on polylactic acid microplastics (PLA MPs) in mangrove forests - the role of environmental conditions and plastic properties

The concerns about possible risks of biodegradable plastics have increased in recent years. In this study, two types of biodegradable polylactic acid (PLA) MPs, 604 (low molecular weight) and 801 (high molecular weight), were incubated in-situ in mangrove ecosystems, across four different environmental matrix - mangrove sediment, mangrove water, mangrove air and beach air for 90 days. The fluorescence staining combined with scanning electron microscopy (SEM) results revealed that microbial colonization (both algae and bacteria) tended to be in the areas of depressions and cavities on MPs, which presumably showed signs of microbial degradation on the surface of the plastics. Over the 90-day incubation period, microbial colonization and succession on the plastics was significantly influenced by both environmental conditions and the properties of the MPs. Microbial colonization on plastic samples in mangrove sediment progressed more rapidly than that in mangrove water. Correspondingly, microbial communities on plastics in sediment showed high similarity to those in the surrounding environment, whereas the opposite was observed in water. Environmental disturbances and nutrient availability in different matrices also led to distinct microbial succession pathways for the two types of MPs. In sediment, which provided the most stable and nutrient-rich environment, divergent succession patterns were observed between 604 and 801 PLA MPs. Conversely, in flowing water and air, where environmental pressures were higher, convergent succession patterns were found. It is worth noting that the relatively stable environmental conditions and limited nutrient sources in mangrove air resulted in the highest enrichment of potential PLA-degrading microorganisms on both types of PLA MPs. Our findings highlighted the critical role of environmental conditions and MP properties in shaping microbial colonization and succession on PLA MPs. These results provided valuable scientific insights into the environmental degradation processes and long-term ecological risks of biodegradable plastics in mangrove coastal ecosystems.

Soil nitrogen deficiency aggravated the aging of biodegradable microplastics in paddy soil under the input of organic substances with contrasting C/N ratios

The application of organic substances to the agricultural field has effectively enhanced soil nutrient levels and crop yields. Biodegradable microplastics (bio-MPs), a pervasive emerging contaminant, may potentially impact the soil ecosystem through their aging process. Here, a 150-day dark incubation experiment was conducted to elucidate the disparities in the aging process of polylactic acid bio-MPs (PLA-MPs) in soils with contrasting C/N ratios of organic substances, as the mechanisms underlying this process remain unclear. The study found that PLA-MPs resulted in an increase in soil pH, nutrient levels, and organic carbon content in soil-straw system. Additionally, PLA-MPs significantly influenced bacterial community composition and microbial metabolic activity in soil-straw system. Notably, more pronounced aging features of PLA-MPs was observed in soil-straw system (lower soil nitrogen environment) compared to soil-fertilizer system (higher soil nitrogen environment). Under lower soil nitrogen conditions, microorganisms may accelerate the aging process of PLA-MPs due to their preference for readily available energy sources; conversely, under higher soil nitrogen conditions, the aging of PLA-MPs may be decelerated as microorganisms preferentially utilize substances with easily accessible energy sources. Our findings provide valuable insights into the interaction between PLA-MPs and soil amended with the organic substances of contrasting C/N ratios.

Ecological and Health Risk Mediated by Micro(nano)plastics Aging Process: Perspectives and Challenges

Aged micro(nano)plastics (MNPs) are normally the ultimate state of plastics in the environment after aging. The changes in the physical and chemical characteristics of aged MNPs significantly influence their environmental behavior by releasing additives, forming byproducts, and adsorbing contaminants. However, a systematic review is lacking on the effects of aged MNPs on ecological and human health regarding the increasing but scattered studies and results. This Review first summarizes the unique characteristics of aged MNPs and methods for quantifying their aging degree. Then we focused on the potential impacts on organisms, ecosystems, and human health, including the "Trojan horse" under real environmental conditions. Through combining meta-analysis and analytic hierarchy process (AHP) model, we demonstrated that, compared to virgin MNPs, aged MNPs would result in biomass decrease and oxidative stress increase on organisms and lead to total N/P decrease and greenhouse gas emissions increase on ecosystems while causing cell apoptosis, antioxidant system reaction, and inflammation in human health. Within the framework of ecological and human health risk assessment, we used the risk quotient (RQ) and physiologically based pharmacokinetic (PBK) models as examples to illustrate the importance of considering aging characteristics and the degree of MNPs in the process of data acquisition, model building, and formula evaluation. Given the ecological and health risks of aged MNPs, our urgent call for more studies of aged MNPs is to understand the potential hazards of MNPs in real-world environments.

The long-term straw return resulted in significant differences in soil microbial community composition and community assembly processes between wheat and rice

Introduction

Straw return is widely promoted as an environmentally sustainable practice to enhance soil health and agricultural productivity. However, the impact of varying straw return durations on soil microbial community composition and development remains insufficiently understood within a rice-wheat cropping system.

Methods

In this study, soil samples were collected during the wheat and rice harvesting periods following seven straw return durations: no straw return (NR) or 1, 3, 5, 7, 9, 11 years of straw return (SR1, 3, 5, 7, 9, 11), and microbial sequencing was performed.

Results

The results revealed a biphasic pattern in alpha diversity (Chao1 and Shannon) of soil microbial communities with increasing straw return duration, characterized by an initial increase followed by a subsequent decrease. Specifically, SR9 in the rice group exhibited the highest Chao1 and Shannon values, while SR3 in the wheat group showed the highest values. PCoA indicated significant shifts in microbial communities due to straw return, particularly in the wheat group compared to NR. Straw return obvious changed six bacterial phyla (Verrucomicrobiota, Proteobacteria, Desulfobacterota, MBNT15, Actinobacteriota, and Gemmatimonadota) during the rice and wheat harvesting periods, especially Proteobacteria. Correlation analysis between environmental factors and bacterial communities demonstrated a significant impact on these factors, particularly pH and total organic carbon (TOC) (p < 0.05), on the soil bacterial community during rice harvest, indicating the microbial enrichment after straw return may be related to the accumulation of TOC. Furthermore, the bacterial community network in the rice harvesting period was found to be more complex, with lower network stability compared to the wheat harvesting period. This complexity is closely associated with TOC accumulation in rice fields. Deterministic processes, including homogeneous and heterogeneous selection, were found to play a crucial role in shaping the soil bacterial communities in both rice and wheat systems. Environmental factors significantly influenced microbial community assembly during straw return and recycling.

Discussion

Our study enhances understanding of the impact of straw return on the diversity and assembly of soil microbial communities in the rice-wheat cropping system, which provide valuable insights for studying the mechanisms by which managing microbial communities after straw return can promote soil fertility restoration.

Carbon Cycling in Wetlands Under the Shadow of Microplastics: Challenges and Prospects

Wetlands are one of the most crucial ecosystems for regulating carbon sequestration and mitigating global climate change. However, the disturbance to carbon dynamics caused by microplastics (MPs) in wetlands cannot be overlooked. This review explores the impacts of MPs on the carbon cycles within wetland ecosystems, focusing on the underlying physicochemical and microbial mechanisms. The accumulation of MPs in wetland sediments can severely destabilize plant root functions, disrupting water, nutrient, and oxygen transport, thereby reducing plant biomass development. Although MPs may temporarily enhance carbon storage, they ultimately accelerate the mineralization of organic carbon, leading to increased atmospheric carbon dioxide emissions and undermining long-term carbon sequestration. A critical aspect of this process involves shifts in microbial community structures driven by selective microbial colonization on MPs, which affect organic carbon decomposition and methane production, thus posing a threat to greenhouse gas emissions. Notably, dissolved organic matter derived from biodegradable MPs can promote the photoaging of coexisting MPs, enhancing the release of harmful substances from aged MPs and further impacting microbial-associated carbon dynamics due to disrupted metabolic activity. Therefore, it is imperative to deepen our understanding of the adverse effects and mechanisms of MPs on wetland health and carbon cycles. Future strategies should incorporate microbial regulation and ecological engineering techniques to develop effective methodologies aimed at maintaining the sustainable carbon sequestration capacity of wetlands affected by MP contamination.

Different wetting states in riparian sediment ecosystems: Response to microplastics exposure

Climate change alters the wetting state of riparian sediments, impacting microbial community response and biogeochemical processes. Microplastics (MPs) invade nearly all ecosystems on earth, posing a significant environmental risk. However, little is known about the response mechanism of MP exposure in sediment ecosystems with different wetting states under alternating seasonal rain and drought conditions. In this study, sediments with three different wetting states were selected to explore the differential response of ecosystems to PLA MP exposure. We observed that PLA MP exposure directly affected biogeochemical processes in sediment ecosystems and induced significant changes in microbial communities. PLA MP exposure was found to alter the composition of key species and microbial functional groups in the ecosystem, resulting in a more complex, interconnected, but less stable microbial network. Our findings showed that PLA MP exposure enhances the contribution of stochastic processes, for example the dispersal limitation increasing from 7.41 % to 54.32 %, indicating that sediment ecosystems strive to buffer disturbances from PLA MP exposure. In addition, 87 pathogenic species were detected in our samples, with PLA MPs acting as vectors for their transmission, potentially amplifying ecosystem disturbance. Importantly, we revealed that submerged sediments may present a greater environmental risk, while alternating wet and dry sediments demonstrate greater resistance and resilience to PLA MPs pollution. Overall, this study sheds light on how sediment ecosystems respond to MP exposure, and highlights differences in sediment response mechanisms across wetting states.

Unveiling the impact of anthropogenic wastes on greenhouse gas emissions from the enigmatic mangroves of Indian Sundarban

The greenhouse gas (GHG) emissions from the mangrove ecosystem due to climate change have been an emerging environmental issue in the present scenario. However, the GHGs, emitted through anthropogenic causes in these vulnerable regions are often neglected. The level of soil pollution has increased due to the uncontrolled disposal of wastes from ports, ferry services, plastics, and metals, emitting huge amounts of GHGs. Here, a novel dynamic model on GHG emission was proposed for the simulation of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) emissions using R programming language, where, anthropogenic and environmental drivers were considered. The CO2 emission was sensitive to HMeff2 (impact rate of heavy metals on microbial respiration process) and MPeff3 (impact rate of microplastics on microbial respiration process). The CH4 dynamics was sensitive to HMeff1 (impact rate of heavy metal on methanogenesis process) and MPeff1 (impact rate of microplastics on methanogenesis process) and the N2O pool was sensitive to N2O dif rt. (N2O diffusion rate). Fish waste, heavy metals, and microplastics are the prime emitters of GHG in the Sundarbans. Control and monitoring of plastics, fish wastes, and heavy metals, and strategic implementation of no-plastic or no-waste zones in line with the Sustainable Development Goals (SDGs) would ensure solutions to the present problem.

The combined effects of microplastics and their additives on mangrove system: From the sinks to the sources of carbon

Mangrove ecosystems, a type of blue carbon ecosystems (BCEs), are vital to the global carbon cycle. However, the combined effects of microplastics (MPs) and plastic additives on carbon sequestration (CS) in mangroves remain unclear. Here, we comprehensively review the sources, occurrence, and environmental behaviors of MPs and representative plastic additives in mangrove ecosystems, including flame retardants, such as polybrominated diphenyl ethers (PBDEs), and plasticizers, such as phthalate esters (PAEs). Mangrove ecosystems have a complex influence on the behaviors of MPs and additives. Under the action of natural and unnatural factors, these pollutants exhibit complex behaviors including migration, interception, deposition and transformation, that are closely linked to those of particulate carbon, particularly carbon sequestration processes. MPs and additives hinder the CS function of mangroves by harming the growth of flora and fauna, influencing microbial nitrogen and sulfur cycles, and enhancing the degradation of organic matter in the sediment. The increasing accumulation and widespread occurrence of MPs and additives will greatly influence the carbon cycle. Future work is encouraged on systematic investigation of new alternatives to plastics and additives, and research methods to uncover the impact mechanisms of MPs and additives on BCEs. The developments of management measures and engineering technologies are also required to enhance pollutant control and mangrove CS.

Microplastics in agricultural soil: Unveiling their role in shaping soil properties and driving greenhouse gas emissions

Microplastics (MPs) contamination is pervasive in agricultural soils, significantly influencing carbon and nitrogen biogeochemical cycles and altering greenhouse gas (GHG) fluxes. This review examines the sources, status, mechanisms, and ecological consequences of MPs pollution in agricultural soils, with a focus on how MPs modified soil physicochemical properties and microbial gene expression, ultimately impacting GHG emissions. MPs were found to reduce soil water retention, decreasing soil respiration and increasing emissions of CO2, CH₄, and N2O. They also enhanced soil aggregate stability and influenced soil organic carbon (SOC) sequestration, contributing further to GHG emissions. MPs-induced increases in soil pH were associated with suppressed CH₄ and N2O emissions, whereas the abundance of genes encoding enzymes for cellulose and lignin decomposition (e.g., abfA and mnp) stimulated enzyme activity, intensifying N2O release. Additionally, a reduced soil C/N ratio promoted denitrification processes. Changes in microbial communities, including increases in Actinomycetes and Proteobacteria, were observed, with a rise in genes associated with carbon cycling (abfA, manB, xylA) and nitrification-denitrification (nifH, amoA, nirS, nirK), further exacerbating CO2 and N2O emissions. This review provides valuable insights into the complex roles of MPs in GHG dynamics in agricultural soils, offering perspectives for improving environmental management strategies.

The dual role of coastal mangroves: Sinks and sources of microplastics in rapidly urbanizing areas

Mangrove ecosystems are vital for coastal protection, biodiversity, and pollution interception, yet their interactions with microplastics in rapidly urbanizing regions remain underexplored. This study investigated the microplastic dynamics in the Maozhou River and Dasha River, along with the coastal Xiwan Mangrove Park in the Pearl River Estuary, the second largest estuary in China. Samples were collected from mangrove and surrounding areas, identifying microplastics using Fourier-transform infrared spectroscopy (FTIR) and Laser Direct Infrared (LDIR) techniques. Microplastic concentrations ranged from 245.8 to 1562.4 n/m³ in water and 374.3 to 7475.3 n/kg in sediments. The Maozhou River exhibited consistent microplastic levels across varying hydrological conditions, while the Dasha River and Xiwan Mangrove showed greater sensitivity to water flow changes influenced by urban land use. During high-flow periods, urban river microplastic concentrations decreased due to dilution, whereas mangrove areas experienced elevated levels in water from urban runoff, upstream retention, and sediment resuspension, suggesting a potential for outward release. Weaker water dynamics led to increased microplastic accumulation in mangrove sediments. The distribution of microplastic types was influenced by multiple urban pollution sources, with synthetic rubbers linked to urban transportation comprising over 50 % of some samples, peaking at 79 %. These findings underscore the dual role of mangroves as microplastic sinks and potential sources, highlighting the significant impact of hydrological conditions on their function. This study offers new insights into microplastic pollution in urban mangrove ecosystems and emphasizes the urgent need for improved management strategies in coastal areas facing rapid urbanization.

Mechanisms underpinning microplastic effects on the natural climate solutions of wetland ecosystems

Wetland ecosystems are vital carbon dioxide (CO2) sinks, offering significant nature-based solutions for global climate mitigation. However, the recent influx of microplastic (MP) into wetlands substantially impacts key drivers (e.g., plants and microorganisms) underpinning these wetland functions. While MP-induced greenhouse gas (GHG) emissions and effects on soil organic carbon (SOC) mineralization potentially threaten the long-term wetland C-climate feedbacks, the exact mechanisms and linkage are unclear. This review provides a conceptual framework to elaborate on the interplay between MPs, wetland ecosystems, and the atmospheric milieu. We also summarize published studies that validate possible MP impacts on natural climate solutions of wetlands, as well as provide extensive elaboration on underlying mechanisms. We briefly highlight the relationships between MP influx, wetland degradation, and climate change and conclude by identifying key gaps for future research priorities. Globally, plastic production, MP entry into aquatic systems, and wetland degradation-related emissions are predicted to increase. This means that MP-related emissions and wetland-climate feedback should be addressed in the context of the UN Paris Climate Agreement on net-zero emissions by 2050. This overview serves as a wake-up call on the alarming impacts of MPs on wetland ecosystems and urges a global reconsideration of nature-based solutions in the context of climate mitigation.

Distinct impacts of microplastics on the carbon sequestration capacity of coastal blue carbon ecosystems: A case of seagrass beds

Seagrass beds, as an important coastal blue carbon ecosystem, are excellent at storing organic carbon and mitigating the impacts of global climate change. However, seagrass beds are under threat due to increased human activities and ubiquitous presence of microplastics (MPs) in marine environments. Bibliometric analysis shows that the distribution and accumulation of microplastics in seagrass beds has been widely documented worldwide, but their impacts on seagrass beds, particularly on carbon sequestration capacity, have not been given sufficient attention. This review aims to outline the potential impacts of MPs on the carbon sequestration capacity of seagrass ecosystems across five key aspects: (1) MPs act as sources of organic carbon, contributing to direct pollution in seagrass ecosystems; (2) Impacts of MPs on seagrasses and their epiphytic algae, affecting plant growth and net primary productivity; (3) Impacts of MPs on microorganisms, influencing production of recalcitrant dissolved organic carbon and greenhouse gas; (4) Impacts of MPs on seagrass sediments, altering the quality, structure, properties and decomposition processes of plant litters; (5) Other complex impacts on the seagrass ecosystems, depending on different behaviors of MPs. Latest progress in these fields are summarized and recommendations for future work are discussed. This review can provide valuable insights to facilitate future multidisciplinary investigations and encourage society-wide implementation of effective conservation measures to enhance the carbon sequestration capacity of seagrass beds.

Insights into effects of conventional and biodegradable microplastics on organic carbon decomposition in different soil aggregates

The impacts of microplastics on soil ecological functions such as carbon recycling and soil structure maintenance have been extensively focused. However, the mechanisms underlying the impacts of microplastics on soil carbon transformation and soil microbial community at soil aggregate scale have not been clarified yet. In this work, the effects and action mechanisms of traditional microplastic polypropylene (PP) and degradable microplastic polylactic acid (PLA) on carbon transformation in three sizes of soil aggregates were investigated. The results showed that both PP and PLA promoted CO2 emission, and the effect depended on the type and content of microplastics, and the size of soil aggregates. Changes in soil carbon stocks were mainly driven by changes in organic carbon associated with macroaggregates. For macroaggregates, PP microplastics decreased soil organic carbon (SOC) as well as dissolved organic carbon (DOC). These changes were reversed in microaggregates and silt and clay. Interestingly, PLA increased the SOC, DOC and CO2 emissions in bulk soil and all three aggregates with a dose-effect response. These changes were associated with soil microbes, functional genes and enzymes associated with the degradation of labile and recalcitrant carbon fractions. Furthermore, PP and PLA reduced bacterial community diversities and shifted bacterial community structures in both the three aggregates and in bulk soil. Alterations of functional genes induced by microplastics were the key driving factors of their impacts on carbon transformation in soil aggregates. This research opened up a new insight into the mechanisms underlying the impacts of microplastics on soil carbon transformation, and helped us make rational assessments of the risks and the disturbances of microplastics on soil carbon cycling.

Effects of polypropylene films and leached dissolved organic matters on bacterial community structure in mangrove sediments

Over the past decades, the accumulation of plastics in mangrove ecosystems has emerged as a significant environmental concern, primarily due to anthropogenic activities. Polypropylene (PP) films, one of the plastic types with the highest detection rate, tend to undergo intricate aging processes in mangrove ecosystems, leading to the release of dissolved organic matter (DOM) that may further influence the local bacterial communities. Yet, the specific effects of new and weathered (aged) plastic films and the associated leached DOM on bacterial consortia in mangrove sediments remain poorly understood. In this study, an incubation experiment was conducted to elucidate the immediate effects and mechanisms of the new and relatively short-term (45 or 90 days) aged PP films, as well as their leached DOM (PDOM), on characteristics of DOM and the bacterial community structure in mangrove sediments under different tidal conditions. Surface morphology and functional group analyses showed that both new and aged PP films exhibited comparable degradation profiles under different tidal conditions over the incubation period. As compared to the new PP film treatments, the introduction of the short-term aged PP films significantly affected the content of humic-like compounds in sediments, and such effects were partially ascribed to the release of PDOM during the incubation. Although the addition of PP films and PDOM showed minor effects on the overall diversity and composition of bacterial communities in the sediments, the abundance of some dominant phyla exhibited a growth or reduction tendency, possibly changing their ecological functions. This study was an effective attempt to investigate the relationship among plastic surface characteristics, sedimentary physicochemical properties, and bacterial communities in mangrove sediments. It revealed the ecological ramifications of new and short-term plastic pollution and its leachates in mangrove seedtimes, enhancing our understating of their potential impacts on the health of mangrove ecosystems.

Ecotoxicological effects of polyethylene microplastics and lead (Pb) on the biomass, activity, and community diversity of soil microbes

Microplastics and heavy metals are ubiquitous and persistent contaminants that are widely distributed worldwide, yet little is known about the effects of their interaction on soil ecosystems. A soil incubation experiment was conducted to investigate the individual and combined effects of polyethylene microplastics (PE-MPs) and lead (Pb) on soil enzymatic activities, microbial biomass, respiration rate, and community diversity. The results indicate that the presence of PE-MPs notably reduced soil pH and elevated soil Pb bioavailability, potentially exacerbated the combined toxicity on the biogeochemical cycles of soil nutrients, microbial biomass carbon and nitrogen, and the activities of soil urease, sucrase, and alkaline phosphatase. Soil CO2 emissions increased by 7.9% with PE-MPs alone, decreased by 46.3% with single Pb, and reduced by 69.4% with PE-MPs and Pb co-exposure, compared to uncontaminated soils. Specifically, the presence of PE-MPs and Pb, individually and in combination, facilitated the soil metabolic quotient, leading to reduced microbial metabolic efficiency. Moreover, the addition of Pb and PE-MPs modified the composition of the microbial community, leading to the enrichment of specific taxa. Tax4Fun analysis showed the effects of Pb, PE-MPs and their combination on the biogeochemical processes and ecological functions of microbes were mainly by altering amino acid metabolism, carbohydrate metabolism, membrane transport, and signal transduction. These findings offer valuable insights into the ecotoxicological effects of combined PE-MPs and Pb on soil microbial dynamics, reveals key assembly mechanisms and environmental drivers, and highlights the potential threat of MPs and heavy metals to the multifunctionality of soil ecosystems.

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

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

Freeze-thaw aged polyethylene and polypropylene microplastics alter enzyme activity and microbial community composition in soil

In cold regions, microplastics (MPs) in the soil undergo freeze-thaw (FT) aging process. Little is known about how FT aged MPs influence soil physico-chemical properties and microbial communities. Here, two environmentally relevant concentrations (50 and 500 mg/kg) of 50 and 500 µm polyethylene (PE) and polypropylene (PP) MPs treated soils were subjected to 45-day FT cycles (FTCs). Results showed that MPs experienced surface morphology, hydrophobicity and crystallinity alterations after FTCs. After 45-day FTCs, the soil urease (SUE) activity in control (MPs-free group that underwent FTCs) was 33.49 U/g. SUE activity in 50 µm PE group was reduced by 19.66 %, while increased by 21.16 % and 37.73 % in 500 µm PE and PP groups compared to control. The highest Shannon index was found in 50 µm PP-MPs group at 50 mg/kg, 2.26 % higher than control (7.09). Compared to control (average weighted degree=8.024), all aged MPs increased the complexity of network (0.19-1.43 %). Bacterial biomarkers of aged PP-MPs were associated with pollutant degradation. Aged PP-MPs affected genetic information, cellular processes, and disrupted the biosynthesis of metabolites. This study provides new insights into the potential hazards of MPs after FTCs on soil ecosystem in cold regions.