Enhanced carbon emission driven by the interaction between functional microbial community and hydrocarbons: An enlightenment for carbon cycle

Key Role of Vegetation Cover in Alleviating Microplastic-Enhanced Carbon Emissions

Microplastics (MPs) are considered to influence fundamental biogeochemical processes, but the effects of plant residue-MP interactions on soil carbon turnover in urban greenspaces are virtually unknown. Here, an 84-day incubation experiment was constructed using four types of single-vegetation-covered soils (6 years), showing that polystyrene MP (PSMP) pollution caused an unexpectedly large increase in soil CO2 emissions. The additional CO2 originating from highly bioavailable active dissolved organic matter molecules (<380 °C, predominantly polysaccharides) was converted from persistent carbon (380-650 °C, predominantly aromatic compounds) rather than PSMP derivatives. However, the priming effect of PSMP derivatives was weakened in plant-driven soils (resistivity: shrub > tree > grass). This can be explained from two perspectives: (1) Plant residue-driven humification processes reduced the percentage of bioavailable active dissolved organic matter derived from the priming effects of PSMPs. (2) Plant residues accelerated bacterial community succession (dominated by plant residue types) but slowed fungal community demise (retained carbon turnover-related functional taxa), enabling specific enrichment of glycolysis, the citric acid cycle and the pentose phosphate pathway. These results provide a necessary theoretical basis to understand the role of plant residues in reducing PSMP harm at the ecological level and refresh knowledge about the importance of biodiversity for ecosystem stability.

Spatio-temporal dynamics of land use transitions associated with human activities over Eurasian Steppe: Evidence from improved residual analysis

We presented a framework to evaluate the land use transformations over the Eurasian Steppe (EUS) driven by human activities from 2000 to 2020. Framework involves three main components: (1) evaluate the spatial-temporal dynamics of land use transitions by utilizing the land change modeler (LCM) and remote sensing data; (2) quantifying the individual contributions of climate change and human activities using improved residual trend analysis (IRTA) and pixel-based partial correlation coefficient (PCC); and (3) quantifying the contributions of land use transitions to Leaf Area Index Intensity (LAII) by using the linear regression. Research findings indicate an increase in cropland (+1.17 % = 104,217 km2) over EUS, while a - 0.80 % reduction over Uzbekistan and - 0.16 % over Tajikistan. From 2000 to 2020 a slight increase in grassland was observed over the EUS region by 0.05 %. The detailed findings confirm an increase (0.24 % = 21,248.62 km2) of grassland over the 1st half (2000-2010) and a decrease (-0.19 % = -16,490.50 km2) in the 2nd period (2011-2020), with a notable decline over Kazakhstan (-0.54 % = 13,690 km2), Tajikistan (-0.18 % = 1483 km2), and Volgograd (-0.79 % = 4346 km2). Area of surface water bodies has declined with an alarming rate over Kazakhstan (-0.40 % = 10,261 km2) and Uzbekistan (-2.22 % = 8943 km2). Additionally, dominant contributions of human activities to induced LULC transitions were observed over the Chinese region, Mongolia, Uzbekistan, and Volgograd regions, with approximately 87 %, 83 %, 92 %, and 47 %, respectively, causing effective transitions to 12,997 km2 of cropland, 24,645 km2 of grassland, 16,763 km2 of sparse vegetation in China, and 12,731.2 km2 to grassland and 15,356.1 km2 to sparse vegetation in Mongolia. Kazakhstan had mixed climate-human impact with human-driven transitions of 48,568 km2 of bare land to sparse vegetation, 27,741 km2 to grassland, and 49,789 km2 to cropland on the eastern sides. Southern regions near Uzbekistan had climatic dominancy, and 8472 km2 of water bodies turned into bare soil. LAII shows an increasing trend rate of 0.63 year-1, particularly over human-dominant regions. This study can guide knowledge of oscillations and reduce adverse impacts on ecosystems and their supply services.

Elucidating response mechanisms at the metabolic scale of Eisenia fetida in typical oil pollution sites: A native driver in influencing carbon flow

Previous investigations on the stress response patterns of earthworms (Eisenia fetida) in practical petroleum hydrocarbon (PH) contamination systems were less focused. Therefore, this study investigated the ecotoxicological effect of PH contamination on earthworms based on metabonomics and histological observation, followed by correlation analysis between the earthworm metabolism, PH types and concentrations, soil physicochemical characteristics, and the microbial community structures (i.e., diversity and abundance) and functions. The results showed that due to the abundant PH organics, the cell metabolism of earthworms shifts under PH contamination conditions, leading them to use organic acids as alternative energy sources (i.e., gluconeogenesis pathway). Simultaneously, biomarker metabolites related to cellular uptake, stress response, and membrane disturbance were identified. In addition, when compared to the controls, considerable epicuticle and cuticle layer disruption was observed, along with PH internalization. It was demonstrated that PH pollution preferentially influences the physiological homeostasis of earthworms through indirect (i.e., microbial metabolism regulation) than direct (i.e., direct interaction with earthworms) mechanisms. Moreover, the varied CO2 releasement was verified, which highlights the potential role of earthworms in influencing carbon transformation and corresponds with the considerably enriched energy metabolism-related pathway. This study indicated that PH contamination can induce a strong stress response in earthworms through both direct and indirect mechanisms, which in turn, substantially influences carbon transformation in PH contamination sites.

Long-term aged fibrous polypropylene microplastics promotes nitrous oxide, carbon dioxide, and methane emissions from a coastal wetland soil

Microplastics (MPs) has been suggested that it can greatly affect soil greenhouse gases (GHGs) emissions via altering soil physical, chemical, and biological properties. However, the difference in GHGs emissions, especially for those from coastal wetland soils, between varied aged MPs was rarely explored and the underlying mechanisms of GHGs emissions affected by the aged MPs were poorly understood. Therefore, the implications of fibrous polypropylene MPs (FPP-MPs) exposure on N2O, CO2, and CH4 emissions were examined by a 60-day soil incubation experiment. Compared with the control, the additions of un-aged FPP-MPs with both two rates (0.2 and 2 %) and aged FPP-MPs with a low rate (0.2 %) showed an insignificant effect on N2O emission, while the aged FPP-MPs added with a high rate (2 %) resulted in a remarkably increase in N2O emission, especially for those of the 30-day-aged FPP-MPs. A significant increase in CO2 emission was only observed in the 30-day-aged FPP-MPs treatments, compared with the control, and a higher addition rate produced a higher increase of CO2 emission. Regarding CH4 emission, it was significantly increased by adding aged FPP-MPs, and a longer aging period or/and a higher addition rate generated a higher degree of promotion of CH4 emission. However, compared with the CO2 emission, the quantity of CH4 emission was extremely low. These increased GHGs emissions can be ascribed to the improvements in soil physical structure and other chemical properties (e.g., pH and contents of soil organic matter and dissolved organic carbon) and enhancements in the abundances of denitrification- and carbon mineralization-related microorganisms. Overall, our results highlight the risk of elevated GHGs emissions from the soil polluted with 30-day-aged FPP-MPs, which should not be ignored as long-term aged FPP-MPs continue to increase in coastal wetland soils.

Effects of livestock grazing on the relationships between soil microbial community and soil carbon in grassland ecosystems

Livestock grazing of grassland ecosystems may induce shifts in microbe community traits and soil carbon (C) cycling; however, impacts of grassland management (grazing) on soil C- microbe community trait (microbial biomass, diversity, community structure, and enzyme activity) relationships are unclear. To address this, we conducted a global meta-analysis of 95 articles of livestock grazing studies that vary in grazing intensities (light, moderate, and high) and durations (<5 years, 5-10 years, and > 10 years). We found that gazing decreased soil organic carbon content (SOC; 10.1 %), and activities of the enzymes of saccharase (SA; 31.1 %), urease (UA; 7.0 %), and acid phosphatase (11.9 %) in topsoil. Meanwhile, the SOC, soil microbial biomass and enzyme activities consistently decreased as grazing intensity and duration prolonged. Furthermore, we observed strong linear relationships of microbe community traits with SOC (p < 0.05), but weak relationships with soil N or P (p > 0.05) in grasslands, which also depends on the grazing intensity and duration. In conclusion, our results indicate that traits of soil carbon content, soil microbe community, and in particular their relationships in global grasslands are overall significantly affected by livestock grazing, but the effects strongly depend on the grazing intensity and duration.

Utilization of-Omic technologies in cold climate hydrocarbon bioremediation: a text-mining approach

Hydrocarbon spills in cold climates are a prominent and enduring form of anthropogenic contamination. Bioremediation is one of a suite of remediation tools that has emerged as a cost-effective strategy for transforming these contaminants in soil, ideally into less harmful products. However, little is understood about the molecular mechanisms driving these complex, microbially mediated processes. The emergence of -omic technologies has led to a revolution within the sphere of environmental microbiology allowing for the identification and study of so called 'unculturable' organisms. In the last decade, -omic technologies have emerged as a powerful tool in filling this gap in our knowledge on the interactions between these organisms and their environment in vivo. Here, we utilize the text mining software Vosviewer to process meta-data and visualize key trends relating to cold climate bioremediation projects. The results of text mining of the literature revealed a shift over time from optimizing bioremediation experiments on the macro/community level to, in more recent years focusing on individual organisms of interest, interactions within the microbiome and the investigation of novel metabolic degradation pathways. This shift in research focus was made possible in large part by the rise of omics studies allowing research to focus not only what organisms/metabolic pathways are present but those which are functional. However, all is not harmonious, as the development of downstream analytical methods and associated processing tools have outpaced sample preparation methods, especially when dealing with the unique challenges posed when analyzing soil-based samples.