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 CO, CH₄, and NO. 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 NO emissions, whereas the abundance of genes encoding enzymes for cellulose and lignin decomposition (e.g., abfA and mnp) stimulated enzyme activity, intensifying NO 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 CO and NO 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.

Sediment plays a pivotal role in deep-sea ecosystems by providing habitats for a diverse range of microorganisms and facilitates the cycling processes of carbon, sulfur and nitrogen. Beyond the normal seafloor (NS), distinctive geographical features such as cold seeps (CS) and hydrothermal vent (HV) are recognized as life oases harboring highly diverse microbial communities. A global atlas of microorganisms can reveal the notable association between geological processes and microbial colonization. However, a comprehensive understanding of the systematic comparison of microbial communities in sediments across various deep-sea regions worldwide and their contributions to Earth's elemental cycles remains limited. Analyzing metagenomic data from 163 deep-sea sediment samples across 73 locations worldwide revealed that microbial communities in CS sediments exhibited the highest richness and diversity, followed by HV sediments, with NS sediments showing the lowest diversity. The NS sediments were predominantly inhabited by , a type of ammonia-oxidizing archaea (AOA). In contrast, CSs and HVs were dominated by , a family of anaerobic methane-oxidizing archaea (ANME), and , a family of sulfate-reducing bacteria (SRB), respectively. Microbial networks were established for each ecosystem to analyze the relationships and interactions among different microorganisms. Additionally, we analyzed the metabolic patterns of microbial communities in different deep-sea sediments. Despite variations in carbon fixation pathways in ecosystems with different oxygen concentrations, carbon metabolism remains the predominant biogeochemical cycle in deep-sea sediments. Benthic ecosystems exhibit distinct microbial potentials for sulfate reduction, both assimilatory and dissimilatory sulfate reduction (ASR and DSR), in response to different environmental conditions. The presence of nitrogen-fixing microorganisms in CS sediments may influence the global nitrogen balance. In this study, the significant differences in the taxonomic composition and functional potential of microbial communities inhabiting various deep-sea environments were investigated. Our findings emphasize the importance of conducting comparative studies on ecosystems to reveal the complex interrelationships between marine sediments and global biogeochemical cycles.

Extreme climate events, such as marine heatwaves (MHWs), are expected to occur more frequently and intensely in the future, resulting in a substantial impact on marine life. The way that diatoms respond to MHWs may have crucial effects on global primary production and biogeochemical cycles. Euplanktonic diatoms appear to benefit from MHWs directly, but this phenomenon needs an explanation. As concerns tychoplanktonic and benthic diatoms, no studies have been addressed on their thermal response strategies. To address this, we investigated the responses and underlying mechanisms of three typical growth forms of diatoms, Pseudo-nitzschia multiseries (euplanktonic), Paralia guyana (tychoplanktonic) and Navicula avium (benthic), under heat stress by combining a growth experiment with transcriptomic analysis. Our results showed that the physiological responses of diatoms to MHWs and underlying molecular mechanisms are largely related to their growth forms. The euplanktonic diatom was first depressed, but then had a distinct increase in the growth rate accompanied by inducing zeatin and unsaturated fatty acid biosynthesis and repressing substance assimilation and energy metabolism. Contrarily, the benthic diatom showed elevated substance and energy demands for macromolecules accumulation by reducing cell division and increasing photosynthesis and nitrogen assimilation. The tychoplanktonic diatom exhibited higher physiological plasticity to maintain growth and cellular homeostasis. Our results indicate the increased rate of cell division in euplanktonic diatoms under heat stress is likely an emergency response strategy promoting diatom dispersal for survival, but at the cost of disturbances of metabolic balance.

Organic fertilizer application in agricultural land is known to improve soil microbial processes, fertility, and yield. In particular, the changes in soil chemical composition due to multi-year application of organic fertilizers are thought to alter the microbial community. Here, the effects of organic fertilization with oil-cake amendments (OC) on soil bacterial diversity, community profile, and enzyme activity were evaluated and compared to those amended with chemical fertilizer (NPK). Diversity indices show that the application of organic fertilizer potentially increases microbial diversity as well as the number of different microbial groups. The ordination plot distinguished and clustered both treatments, showing the differential effects of soil chemical factors on the microbial communities in each treatment. Proteobacteria, Verrucomicrobia, and Bacteriodetes were significantly more abundant in OC-amended soil than in the NPK soil, indicating alterations in community structure, composition, and diversity, concurrent to the changes in the pH, Ca, and Mg contents of the soil. These shifts in bacterial community structure and composition, partially explained by differences in soil chemical factors, could be observed from the phylum to the genus level in NPK and OC-amended soils. The OC soil contained a significantly higher abundance of predicted genes corresponding to enzymes related to biogeochemical cycling, decomposition, and plant growth promotion. Collectively, these results support the use of an unconventional organic fertilizer positively altering bacterial populations in jujube orchards. The application of an unconventional organic fertilizer improved microbial diversity and enhanced ecosystem functions related to biogeochemical cycles, mineralization, and plant growth promotion.

This review explores the potential impact of microplastic-derived dissolved organic matter (MP-DOM) on biogeochemical processes associated with global carbon and nitrogen cycles, with consideration given to the possible influence of irregular climate changes. We synthesize literature on MP-DOM leaching behaviors during various natural aging processes, such as heavy rainfall, heat waves, and UV irradiation, which may be intensified by climate change. MP-DOM release varies with plastic type and conditions, with organic additives significantly influencing leaching under UV exposure. Increased turbulence from hydrological events and rising temperatures also enhances MP-DOM release. While most research has focused on specific additive releases, the broader effects of polymer degradation and subsequent impacts on microbial communities and biogeochemical cycles are only recently recognized. These disruptions may affect cellular processes in algae and plant roots, enhance microbial utilization of dissolved organic carbon, and potentially increase greenhouse gas production. Our review highlights overlooked roles of MP-DOM exacerbated by climatic stressors and calls for further research to understand its broader biogeochemical impacts. We also emphasize the importance of distinguishing between polymers and commercial plastics when assessing MP-DOM's effects on biogeochemical processes associated with carbon and nitrogen cycles and recommend investigating additional aging processes influencing MP-DOM release.

Photosynthetic dinoflagellates are one of the major microalgal taxa, playing essential roles in biogeochemical cycles and food webs in aquatic environments. Some freshwater dinoflagellates are known to be sensitive to environmental conditions, like water quality and contaminants; however, their molecular toxicological responses are insufficiently discovered. In the present study, we evaluated the physiological and transcriptomic responses of the freshwater dinoflagellate Palatinus apiculatus exposed to cadmium (Cd), focusing on stress-responsive genes. The cell number of P. apiculatus decreased significantly at Cd concentrations above 0.25 mg/L after 72 h, with an estimated EC value of 1.35 mg/L. In addition, we constructed 87,207 transcriptomic contigs from the P. apiculatus cells exposed to the Cd. Differential expression gene analysis showed that 21.0 % of total contigs were statistically significant, including 8647 up-regulated and 4195 down-regulated genes. Gene Ontology enrichment results revealed that genes responsive to stress and external stimuli were highly expressed in Cd-treated cells. Moreover, Cd significantly induced reactive oxygen species (ROS) production in P. apiculatus cells, and their patterns were similar to the expressions of certain antioxidant genes. Among the selected genes, GR expression levels were down-regulated, which may lead to the failure of cell defense against heavy metals. These results showed molecular defense pathways of the freshwater dinoflagellate P. apiculatus against the heavy metal that could be served as potential sensitive biomarkers for evaluating molecular toxicity in freshwater ecosystems.

Marine phytoplankton community composition influences the production and export of biomass and inorganic minerals (such as calcite), contributing to core marine ecosystem processes that drive biogeochemical cycles and support marine life. Here we use morphological and assemblage data sets within a size-trait model to investigate the mix of cellular biogeochemical traits (size, biomass, calcite) present in high latitude calcareous nannoplankton communities through the Oligocene (ca. 34-26 Ma) to better understand the biogeochemical consequences of past climate variability on this major calcifying phytoplankton group. Our record from IODP Site U1553 in the southwest Pacific reveals that nannoplankton communities were most size diverse during the earliest Oligocene, which we propose is linked to evidence for increased nutrient availability in the region across the Eocene-Oligocene transition. In addition to driving changes in community size structure, early Oligocene extinctions of the largest species combined with an increasing dominance of heavily calcified, small-medium-sized cells through time also led to an overall increase in community inorganic to organic carbon ratios (PIC:POC) throughout the Oligocene. Crucially, genus-level cellular PIC:POC diversity meant that abundance was not always the best indicator of which species were the major contributors to community biomass and calcite. As shifts in plankton size structure and calcareous nannoplankton PIC:POC have previously been highlighted as important in biological carbon pump dynamics, our results suggest that changes in community composition that are coupled to changes in community biogeochemical trait diversity have the potential to significantly alter the role of calcareous nannoplankton in marine biogeochemical processes.

The Southern Ocean is rich in highly dynamic mesoscale eddies and substantially modulates global biogeochemical cycles. However, the overall surface and subsurface effects of eddies on the Southern Ocean biogeochemistry have not been quantified observationally at a large scale. Here, we co-locate eddies, identified in the Meta3.2DT satellite altimeter-based product, with biogeochemical Argo floats to determine the effects of eddies on the dissolved inorganic carbon (DIC), nitrate, and dissolved oxygen concentrations in the upper 1,500 m of the ice-free Southern Ocean, as well as the eddy effects on the carbon fluxes in this region. DIC and nitrate concentrations are lower in anticyclonic eddies (AEs) and increased in cyclonic eddies (CEs), while dissolved oxygen anomalies switch signs above (CEs: positive, AEs: negative) and below the mixed layer (CEs: negative, AEs: positive). We attribute these anomalies primarily to eddy pumping (isopycnal heave), as well as eddy trapping for oxygen. Maximum anomalies in all tracers occur at greater depths in the subduction zone north of the Antarctic Circumpolar Current (ACC) compared to the upwelling region in the ACC, reflecting differences in background vertical structures. Eddy effects on air-sea exchange have significant seasonal variability, with additional outgassing in CEs in fall (physical process) and additional oceanic uptake in AEs and CEs in spring (biological and physical process). Integrated over the Southern Ocean, AEs contribute 0.01 Pg C (7 ) to the Southern Ocean carbon uptake, and CEs offset this by 0.01 Pg C (2 ). These findings underscore the importance of considering eddy impacts in observing networks and climate models.

Marine soft sediments play crucial roles in global biogeochemical cycles and biodiversity. Yet, with organisms often hidden in the sediment, they pose challenges for effective monitoring and management. This study introduces a novel approach utilizing sediment microtopography as a proxy for ecosystem functioning and biodiversity. Combining field sampling, benthic chamber incubations, and advanced Structure-from-Motion photogrammetry techniques, we investigated the relationships between microtopographic features and various ecological parameters across diverse subtidal habitats. Our findings reveal strong associations between sediment microtopography and environmental variables, benthic fluxes, biodiversity metrics, and community functional traits, with microtopography consistently explaining more than 50% of the variance in the data. This research demonstrates the potential of sediment microtopography as a cost-effective and scalable tool for assessing soft-sediment ecosystem dynamics and informing conservation strategies. By providing insights into the links between habitat structure and ecological processes, this study advances our understanding of marine benthic ecology and opens new possibilities for habitat assessment applications worldwide.

The Jiaozhou Bay (JZB) intertidal zone is a significant carbon reservoir that plays a crucial role in transporting and accumulating organic matter; however, quantitative studies of organic matter sources are scarce. In this study, we present bulk parameters of total organic carbon (TOC), TOC/TN, δC, and biomarker contents in 36 surface sediment samples from the JZB intertidal zones to quantify the contribution of organic carbon (OC) derived from terrestrial/marine sources, such as C plants, C plants, estuarine productivity, sewage outlets, and marine productivity. The results demonstrated that a two-end-member model based on the traditional indicators of TOC/TN or δC is not appropriate for quantifying the OC source. The presence of C plants, C plants, and sewage outlets in the JZB intertidal zone could lead to errors in determining OC contribution when solely using TOC/TN or δC. A classical mixing diagram (three-end-member model) utilizing TOC/TN and δC values revealed that OC contribution was dominated by marine productivity throughout the intertidal zone. In the west, the average OC contribution from marine productivity, estuarine productivity, and C plants was 73.8 %, 14.2 %, and 12.0 %, respectively. In the east, the average OC contribution from marine productivity, estuarine productivity, and sewage outlets was 57.6 %, 24.9 %, and 17.4 %, respectively. The higher OC contribution from marine productivity in the west was attributed to the occurrence of Spartina alterniflora, while the OC contribution from estuarine productivity in the east was primarily due to the presence of more rivers flowing into the JZB compared to the west. By combining biomarkers and OC contents, a significant positive relationship verified the suitability of the end-member values selected for the three-end-member mixing model in the west and east intertidal zones of JZB. This finding was further supported by principal component analysis (PCA) analyses of these proxies. This study demonstrated that OC sources in intertidal zones varied among contrasting coastal environmental conditions and addressed the knowledge gap regarding biogeochemical cycles and ecological protection in the JZB intertidal zones.