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

Unveiling the mechanism of micro-and-nano plastic phytotoxicity on terrestrial plants: A comprehensive review of omics approaches

Micro-and-nano plastics (MNPs) are pervasive in terrestrial ecosystems and represent an increasing threat to plant health; however, the mechanisms underlying their phytotoxicity remain inadequately understood. MNPs can infiltrate plants through roots or leaves, causing a range of toxic effects, including inhibiting water and nutrient uptake, reducing seed germination rates, and impeding photosynthesis, resulting in oxidative damage within the plant system. The effects of MNPs are complex and influenced by various factors including size, shape, functional groups, and concentration. Recent advancements in omics technologies such as proteomics, metabolomics, transcriptomics, and microbiomics, coupled with emerging technologies like 4D omics, phenomics, spatial transcriptomics, and single-cell omics, offer unprecedented insight into the physiological, molecular, and cellular responses of terrestrial plants to MNPs exposure. This literature review synthesizes current findings regarding MNPs-induced phytotoxicity, emphasizing alterations in gene expression, protein synthesis, metabolic pathways, and physiological disruptions as revealed through omics analyses. We summarize how MNPs interact with plant cellular structures, disrupt metabolic processes, and induce oxidative stress, ultimately affecting plant growth and productivity. Furthermore, we have identified critical knowledge gaps and proposed future research directions, highlighting the necessity for integrative omics studies to elucidate the complex pathways of MNPs toxicity in terrestrial plants. In conclusion, this review underscores the potential of omics approaches to elucidate the mechanisms of MNPs-phytotoxicity and to develop strategies for mitigating the environmental impact of MNPs on plant health.

Forest management impacts on soil phosphorus cycling: Insights from metagenomics in Moso bamboo plantations

Bamboo forests are crucial ecosystems and provide essential ecological and economic services in both tropical and subtropical regions. Soil phosphorus (P), a vital nutrient for plant growth, is fundamental to the productivity and health of bamboo forests. However, the microbial mechanisms through which management practices affect soil P processes in bamboo forests remain poorly understood. This study employed metagenomics to examine alterations in microbial P cycling in Moso bamboo plantations under three distinct management conditions. The results revealed that intensive management (M2, annual fertilization, selective harvesting, and understory vegetation removal) significantly increased soil inorganic P (Pi) by 61.76% and 87.39% compared to extensive management (M1, selective bamboo trunk and shoot harvesting every two years) and non-management (M0), respectively, while decreasing soil organic P (Po) by 50.41% and 41.05%. Forest management significantly altered the bacterial communities: Firmicutes, WPS-2, and Acidobacteriales were represented in M2, Xanthobacteraceae in M1, and Chloroflexi AD3, Acidothermus, and Subgroup_2 in M0. M2 significantly increased the community-level habitat niche breadth and weakened the deterministic process of bacterial community assembly relative to M1 and M0 (p ≤ 0.05). Furthermore, functional metagenomics showed that the total abundance of genes related to Po mineralization, P transportation, and P regulation was significantly lower (p ≤ 0.05) in M2 than in M0 and M1. pstA, pstB, and pstC were more abundant in M2 (p ≤ 0.05), whereas phnN, phnI, phnG, phoA, phoD, phnC, phnD, and phnE were more abundant in M1 (p ≤ 0.05), and phnF was significantly abundant in M0 (p ≤ 0.05). A partial least squares path model indicated that soil bacterial community and P cycling genes had direct effects on Pi and Po, respectively. These findings enhance our understanding of the links between forest management practices and P cycling, providing insights for improving soil functionality and nutrient balance.

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

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

Effects of manure and nitrogen fertilization on soil microbial carbon fixation genes and associated communities in the Loess Plateau of China

The effects of long-term fertilization on soil carbon (C) cycling have been a key focus of agricultural sustainable development research. However, the influences of different fertilization treatments on soil microbial C fixation profiles are still unclear. Metagenomics technology and multivariate analysis were employed to inquire changes in soil properties, soil microbial C fixation genes and associated bacterial communities, and the influence of dominant soil properties on C fixation genes. The contents of soil C and nitrogen fractions were signicficantly higher in manure or combined with nitrogen fertilization (NM) than other treatments. The composition of soil microbial C fixation genes and associated bacterial communities varied among different fertilization treatments. Compared with other treatments, the total abundance of microbial C fixation genes and the abundance of Proteobacteria were significantly higher in NM than in other treatments, as well as the abundances of C fixation genes involved in dicarboxylate/4-hydroxybutyrate cycle and reductive citrate cycle. Key functional genes and main bacterial communities presented in the middle of the co-occurrence network. Soil organic carbon, total nitrogen, and microbial biomass nitrogen were the dominant soil properties influencing microbial C fixation genes and associated bacterial communitis. Fertilization increased the abundance of C fixation genes by affecting the changes in bacterial communities abundance mediated by soil properties. Overall, elucidating the responses of soil microbial C fixation genes and associated communities to different fertilization will enhance our understanding of the processes of soil C fixation in farmland.

Microplastics in tea from planting to the final tea product: Traceability, characteristics and dietary exposure risk analysis

Tea, sold as tea bags or loose tea, is a popular drink worldwide. We quantified microplastics in loose tea during various stages of production, from planting to processing and brewing. The quantity of microplastics in tea ranged from (70-3472 pcs/kg), with the highest abundance detected during processing, mainly in the rolling stage (2266 ± 1206 pcs/kg tea). Scanning electron microcopy revealed scratches and pits on the surface of microplastics fibers from tea plantation soil and processed tea, and their degradation was characterized by cracks and fractures. Exposure risks, based on an estimated dietary intake of 0.0538-0.0967 and 0.0101-0.0181 pcs /kg body weight /day for children and adults, respectively, are considered very low. This study not only evaluates the extent of research on microplastics pollution in tea, but also assess the risk of people's exposure to microplastics through drinking tea.

Mitigating the detrimental impacts of low- and high-density polyethylene microplastics using a novel microbial consortium on a soil-plant system: Insights and interactions

The accumulation of polyethylene microplastics (PE-MPs) in soil has raised considerable concerns; however, the effects of their persistence and mitigation on agroecosystems have not been explored. This study aimed to assess the detrimental effects of PE-MPs on a soil-plant system and evaluate their mitigation using a novel microbial consortium (MC). We incorporated low-density polyethylene (LDPE) and high-density polyethylene (HDPE) at two different concentrations, along with a control (0 %, 1 %, and 2 % w/w) into the sandy loam soil for a duration of 135 days. The samples were also treated with a novel MC and incubated for 135 days. The MC comprised three bacterial strains (Ralstonia pickettii (MW290933) strain SHAn2, Pseudomonas putida strain ShA, and Lysinibacillus xylanilyticus XDB9 (T) strain S7-10F), and a fungal strain (Aspergillus niger strain F1-16S). Sunflowers were subsequently cultivated, and physiological growth parameters were measured. The results showed that adding 2 % LDPE significantly decreased soil pH by 1.06 units compared to the control. Moreover, adding 2 % HDPE resulted in a more significant decrease in soil electrical conductivity (EC) relative to LDPE and the control. A dose-dependent increase in dissolved organic carbon (DOC) was observed, with the highest DOC found in 2 % LDPE. The addition of higher dosages of LDPE reduced soil bulk density (BD) more than HDPE. The addition of 2 % HDPE increased the water drop penetration time (WDPT) but decreased the mean weight diameter of soil aggregates (MWD) and water-stable aggregates (WSA) compared to LDPE. The results also revealed that higher levels of LDPE enhanced soil basal respiration (BR) and microbial carbon biomass (MBC). The interaction of MC and higher MP percentages considerably reduced soil pH, EC, BD, and WDPT but significantly increased soil DOC, MWD, WSA, BR, and MBC. Regarding plant growth, incorporating 2 % PE-MPs significantly reduced physiological responses of sunflower: chlorophyll content (Chl; -15.2 %), Fv/Fm ratio (-25.3 %), shoot dry weight (ShD; -31.3 %), root dry weight (RD; -40 %), leaf area (LA; -38.4 %), and stem diameter (StemD; -25 %) compared to the control; however, the addition of novel MC considerably reduced and ameliorated the harmful effects of 2 % PE-MPs on the investigated plant growth responses.

Differential impacts of polyethylene microplastic and additives on soil nitrogen cycling: A deeper dive into microbial interactions and transformation mechanisms

The impact of microplastics and their additives on soil nutrient cycling, particularly through microbial mechanisms, remains underexplored. This study investigated the effects of polyethylene microplastics, polyethylene resin, and plastic additives on soil nitrogen content, physicochemical properties, nitrogen cycling functional genes, microbial composition, and nitrogen transformation rates. Results showed that all amendments increased total nitrogen but decreased dissolved total nitrogen. Polyethylene microplastics and additives increased dissolved organic nitrogen, while polyethylene resin reduced it and exhibited higher microbial biomass. Amendments reduced or did not change inorganic nitrogen levels, with additives showing the lowest values. Polyethylene resin favored microbial nitrogen immobilization, while additives were more inhibitory. Amendment type and content significantly interacted with nitrogen cycling genes and microbial composition. Distinct functional microbial biomarkers and network structures were identified for different amendments. Polyethylene microplastics had higher gross ammonification, nitrification, and immobilization rates, followed by polyethylene resin and additives. Nitrogen transformation was driven by multiple functional genes, with Proteobacteria playing a significant role. Soil physicochemical properties affected nitrogen content through transformation rates, with C/N ratio having an indirect effect and water holding capacity directly impacting it. In summary, plastic additives, compared to polyethylene microplastics and resin, are less conducive to nitrogen degradation and microbial immobilization, exert significant effects on microbial community structure, inhibit transformation rates, and ultimately impact nitrogen cycling.

Biodegradable Microplastic-Driven Change in Soil pH Affects Soybean Rhizosphere Microbial N Transformation Processes

The potential impacts of biodegradable and nonbiodegradable microplastics (MPs) on rhizosphere microbial nitrogen (N) transformation processes remain ambiguous. Here, we systematically investigated how biodegradable (polybutylene succinate, PBS) MPs and nonbiodegradable (polyethylene, PE) MPs affect microbial N processes by determining rhizosphere soil indicators of typical Glycine max (soybean)-soil (i.e., red and brown soils) systems. Our results show that MPs altered soil pH and dissolved organic carbon in MP/soil type-dependent manners. Notably, soybean growth displayed greater sensitivity to 1% (w/w) PBS MP exposure in red soil than that in brown soil since 1% PBS acidified the red soil and impeded nutrient uptake by plants. In the rhizosphere, 1% PBS negatively impacted microbial community composition and diversity, weakened microbial N processes (mainly denitrification and ammonification), and disrupted rhizosphere metabolism. Overall, it is suggested that biodegradable MPs, compared to nonbiodegradable MPs, can more significantly influence the ecological function of the plant-soil system.

Global Responses of Soil Carbon Dynamics to Microplastic Exposure: A Data Synthesis of Laboratory Studies

Microplastics (MPs) contamination presents a significant global environmental challenge, with its potential to influence soil carbon (C) dynamics being a crucial aspect for understanding soil C changes and global C cycling. This meta-analysis synthesizes data from 110 peer-reviewed publications to elucidate the directional, magnitude, and driving effects of MPs exposure on soil C dynamics globally. We evaluated the impacts of MPs characteristics (including type, biodegradability, size, and concentration), soil properties (initial pH and soil organic C [SOC]), and experimental conditions (such as duration and plant presence) on various soil C components. Key findings included the significant promotion of SOC, dissolved organic C, microbial biomass C, and root biomass following MPs addition to soils, while the net photosynthetic rate was reduced. No significant effects were observed on soil respiration and shoot biomass. The study highlights that the MPs concentration, along with other MPs properties and soil attributes, critically influences soil C responses. Our results demonstrate that both the nature of MPs and the soil environment interact to shape the effects on soil C cycling, providing comprehensive insights and guiding strategies for mitigating the environmental impact of MPs.

Mycorrhizosphere bacteria inhibit greenhouse gas emissions from microplastics contaminated soil by regulating soil enzyme activities and microbial community structure

Microplastics (MPs) accumulation in terrestrial ecosystems can affect greenhouse gases (GHGs) production by altering microbial and soil structure. Presently, research on the MPs effect on plants is not consistent, and underlying molecular mechanisms associated with GHGs are yet unknown. For the first time, we conducted a microcosm study to explore the impact of MPs addition (Raw vs. aged) and Trichoderma longibrachiatum and Bacillus subtilis inoculation (Sole vs. combination) on GHGs emission, soil community structure, physiochemical properties, and enzyme activities. Our results indicated that the addition of aged MPs considerably enhanced the GHGs emissions (N2O (+16%) and CO2 (+21%), respectively), C and N cycling gene expression, microbial biomass carbon, and soil physiochemical properties than raw MPs. However, the soil microbial community structure and enzyme activities were enhanced in raw MPs added treatments, irrespective of the MPs type added to soil. However, microbial inoculation significantly reduced GHGs emission by altering the expression of C and N cycling genes in both types of MPs added treatments. The soil microbial community structure, enzymes activities, physiochemical properties and microbial biomass carbon were enhanced in the presence of microbial inoculation in both type of MPs. Among sole and combined inoculation of Trichoderma and Bacillus subtilis, the co-applied Trichoderma and Bacillus subtilis considerably reduced the GHGs emission (N2O (-64%) and CO2 (-61%), respectively) by altering the expression of C and N cycling genes regardless of MPs type used. The combined inoculation also enhanced soil enzyme activities, microbial community structure, physiochemical properties and microbial biomass carbon in both types of MPs treatment. Our findings provide evidence that polyethylene MPs likely pose a high risk of GHGs emission while combined application of Trichoderma and Bacillus subtilis significantly reduced GHGs emission by altering C and N cycling gene expression, soil microbial community structure, and enzyme activities under MPs pollution in a terrestrial ecosystem.

Combined effects of mulch film-derived microplastics and pesticides on soil microbial communities and element cycling

Pesticides and microplastics (MPs) derived from mulch film in agricultural soil can independently impact soil ecology, yet the consequences of their combined exposure remain unclear. Therefore, the effects of simultaneous exposure to commonly used pesticides (imidacloprid and flumioxazin) and aged mulch film-derived MPs on soil microorganisms and element cycles in cotton fields were investigated. The combined exposure influenced soil microorganisms, alongside processes related to carbon, nitrogen, and phosphorus cycles, exhibiting effects that were either neutralized or enhanced compared to individual exposures. The impact of pesticides in combined exposure was notably more significant and played a dominant role than that of MPs. Specifically, combined exposure intensified changes in soil bacterial community and symbiotic networks. The combined exposure neutralized NH4+, NO3-, DOC, and A-P contents, shifting from 0.33 % and 40.23 % increase in MPs and pesticides individually to a 40.24 % increase. Moreover, combined exposure resulted in the neutralization or amplification of the nitrogen-fixing gene nifH, nitrifying genes (amoA and amoB), and denitrifying genes (nirS and nirK), the carbon cycle gene cbbLG and the phosphorus cycle gene phoD from 0.48 and 2.57-fold increase to a 2.99-fold increase. The combined exposure also led to the neutralization or enhancement of carbon and nitrogen cycle functional microorganisms, shifting from a 1.53-fold inhibition and 10.52-fold increase to a 6.39-fold increase. These findings provide additional insights into the potential risks associated with combined pesticide exposure and MPs, particularly concerning soil microbial communities and elemental cycling processes.