Biochar, activated carbon, and carbon nanotubes have different effects on fate of (14)C-catechol and microbial community in soil

Influence of in situ biochar capping on microbial dynamics and ammonia nitrogen release in sediment

To study the influence of in situ biochar (BC) capping technique on the release of ammonia nitrogen (NH4+-N) from sediments, a field mesocosm experiment was conducted in Baiyangdian Lake (BYDL), a critical water body often referred to as the "kidney of North China" where sediment pollution poses a significant threat to water quality. This study also assessed the impact of BC on sediment microorganisms. The results showed that the NH4+-N concentration in the overlying water of the BC-treated mesocosms was the lowest among four treatments, decreasing to 0.051 mg L-1 by the 60th day. More importantly, the BC treatment showed the least increase in NH4+-N concentrations in sediments compared to other treatments. For sediments capped with a 4 cm layer of BC, the potential release flux of NH4+-N was reduced from 1.84 mg m-2 d-1 to -0.76 mg m-2 d-1. This reduction is likely due to the negatively charged surfaces of biochar, which enhance NH4+-N adsorption through electrostatic interactions. Additionally, BC modified the physical and chemical properties of the surface sediment, improving pH and increasing both organic content and the carbon/nitrogen (C/N) ratio. These changes influenced the microbial community structure within the sediments, enhancing NH4+-N removal. After 60 days, a significant alteration in the microbial community was observed in the BC-treated surface sediments. The addition of BC significantly increased the abundance of Proteobacteria and Firmicutes of the phyla in the sediments. Furthermore, BC enhanced the expression of functional genes including amoA, amoB, nirK, nirS, hzsB, nrfA and ureC, which are likely the primary microbial mechanisms promoting NH4+-N conversion in sediments for final removal.

Spatiotemporal distributions, co-occurrence networks, and assembly mechanisms of the bacterial community in sediments of the Yangtze River: comprehensive insights into abundant and rare taxa

Sediments are key reservoirs for rare bacterial biospheres that provide broad ecological services and resilience in riverine ecosystems. Compared with planktons, there is a lack of knowledge regarding the ecological differences between abundant and rare taxa in benthic bacteria along a large river. Here, we offer comprehensive insights into the spatiotemporal distributions, co-occurrence networks, and assembly processes of three divided categories namely always rare taxa (ART), conditionally rare taxa (CRT), and conditionally rare and abundant taxa (CRAT) in sediments covering a distance of 4,300 km in the Yangtze River. Our study demonstrated that ART/CRT contributed greatly to the higher Chao-1 index, Shannon-Wiener index, and phylogenetic alpha diversity of benthic bacteria in autumn than in spring. ART showed high overall beta diversity, and CRT/CRAT exhibited more significant distance-decay patterns than ART in both seasons, mainly corresponding to macroscopic landform types. CRT predominated the nonrandom co-occurrence network, with 97% of the keystone species mostly affiliated with Acidobacteriota flourishing in the lower-reach plain. Two selection processes had the greatest influences on the assembly of CRT (74.7-77.6%), whereas CRAT were driven primarily by dispersal limitation (74.9-86.8%) and ART were driven by heterogeneous selection (33.9-48.5%) and undominated stochasticity (32.7-36.5%). Natural factors such as river flow and channel slope exhibited more significant correlations with community variation than nutrients in all three groups, and total organic carbon mediated the balance among the distinct assembly processes of the ART and CRT in both seasons. Taken together, these results provide an improved ecological understanding of the discrepancy in biogeographic patterns between abundant and rare bacterial taxa in the sediments of Asia's largest river.

Ball milling nano-sized biochar: bibliometrics, preparation, and environmental application

Nano-sized biochar, which is a small structure prepared from biochar by grinding, has surpassed traditional biochar in performance, showing enhanced effects and potential for a wide range of environmental applications. Firstly, this paper visualizes and analyzes the literature in this field by CiteSpace to clarify the development trend of nano-sized biochar. The review intuitively shows the most influential countries, the most productive institutions, and the most concerned hot spots in the field of nano-sized biochar. Secondly, these hotspots in environment management are summarized by keywords and clustering: (1) The application of ball milling is a modification scheme that researchers have paid attention to, and it is also a key method for preparing biochar nanomaterials. It has a more dispersed structure and can support more modified materials. (2) Nano-sized biochar in the comprehensive utilization of water, soil, and plants was discussed and is a small range of application modification methods. (3) The bidirectional effects of nano-sized biochar on plants were analyzed, and the challenges in its application were listed. Finally, the economic management of nano-sized biochar and the relationship between microorganisms are the focus of the next research.

Spatiotemporal Variations in Co-Occurrence Patterns of Planktonic Prokaryotic Microorganisms along the Yangtze River

Bacteria and archaea are foundational life forms on Earth and play crucial roles in the development of our planet's biological hierarchy. Their interactions influence various aspects of life, including eukaryotic cell biology, molecular biology, and ecological dynamics. However, the coexistence network patterns of these microorganisms within natural river ecosystems, vital for nutrient cycling and environmental health, are not well understood. To address this knowledge gap, we systematically explored the non-random coexistence patterns of planktonic bacteria and archaea in the 6000-km stretch of the Yangtze River by using high-throughput sequencing technology. By analyzing the O/R ratio, representing the divergence between observed (O%) and random (R%) co-existence incidences, and the module composition, we found a preference of both bacteria and archaea for intradomain associations over interdomain associations. Seasons notably influenced the co-existence of bacteria and archaea, and archaea played a more crucial role in spring as evidenced by their predominant presence of interphyla co-existence and more species as keystone ones. The autumn network was characterized by a higher node or edge number, greater graph density, node degree, degree centralization, and nearest neighbor degree, indicating a more complex and interconnected structure. Landforms markedly affected microbial associations, with more complex networks and more core species found in plain and non-source areas. Distance-decay analysis suggested the importance of geographical distance in shaping bacteria and archaea co-existence patterns (more pronounced in spring). Natural, nutrient, and metal factors, including water temperature, NH4+-N, Fe, Al, and Ni were identified as crucial determinants shaping the co-occurrence patterns. Overall, these findings revealed the dynamics of prokaryotic taxa coexistence patterns in response to varying environmental conditions and further contributed to a broader understanding of microbial ecology in freshwater biogeochemical cycling.

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

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

Impact of lignin constituents on the bacterial community and polycyclic aromatic hydrocarbon co-metabolism in an agricultural soil

Lignin is a complex biopolymer comprising phenolic monomers with different degrees of methoxylation and may potentially enhance the degradation of soil pollutants such as polycyclic aromatic hydrocarbons (PAHs) through co-metabolism. However, the contribution of lignin constituents, including phenolic and methoxy subunits, to PAH biodegradation remains unclear. Here, p-hydroxybenzoate (pHBA), vanillate and methanol were selected to simulate phenolic units and methoxy groups of lignin. Soil microcosms receiving these compounds were established to evaluate their regulation on the bacterial community and PAH co-metabolism. There were different effects of different components on the biodegradation of a four-ring PAH, benzo(a)anthracene (BaA), as characterized using an isotopic tracer. Only vanillate significantly stimulated BaA mineralization to CO2, with pHBA and methanol leading to no appreciable change in the allocation of BaA in soil compartments. The lignin constituents had differential impacts on the soil bacterial community, with substantial enrichment of methylotrophs occurring in methanol-supplemented microcosms. Both vanillate and pHBA selected several aromatic degraders. Vanillate caused additional enrichment of methylotrophs, suggesting structure-dependent stimulation of bacterial functional guilds by lignin monomers. Compared with its constituents, lignin produced more extensive responses in terms of bacterial diversity and composition and the fate of BaA. However, it was difficult to link BaA co-metabolism to any specific bacterial taxa in the presence of lignin or its subunits. The results indicate that the co-metabolism effects of lignin may not be directly associated with phenolic or methoxy metabolism but with its regulation of the soil microbiome.

Meta-analytic evidence that allelopathy may increase the success and impact of invasive grasses

Background

In the grass family, a disproportionate number of species have been designated as being invasive. Various growth traits have been proposed to explain the invasiveness of grasses; however, the possibility that allelopathy gives invasive grasses a competitive advantage has attracted relatively little attention. Recent research has isolated plant allelochemicals that are mostly specific to the grass family that can breakdown into relatively stable, toxic byproducts.

Methods

We conducted a meta-analysis of studies on grass allelopathy to test three prominent hypotheses from invasion biology and competition theory: (1) on native recipients, non-native grasses will have a significantly more negative effect compared to native grasses (Novel Weapons Hypothesis); (2) among native grasses, their effect on non-native recipients will be significantly more negative compared to their effect on native recipients (Biotic Resistance Hypothesis); and (3) allelopathic impacts will increase with phylogenetic distance (Phylogenetic Distance Hypothesis). From 23 studies, we gathered a dataset of 524 observed effect sizes (delta log response ratios) measuring the allelopathic impact of grasses on growth and germination of recipient species, and we used non-linear mixed-effects Bayesian modeling to test the hypotheses.

Results

We found support for the Novel Weapons Hypothesis: on native recipients, non-native grasses were twice as suppressive as native grasses (22% vs 11%, respectively). The Phylogenetic Distance Hypothesis was supported by our finding of a significant correlation between phylogenetic distance and allelopathic impact. The Biotic Resistance Hypothesis was not supported. Overall, this meta-analysis adds to the evidence that allelochemicals may commonly contribute to successful or high impact invasions in the grass family. Increased awareness of the role of allelopathy in soil legacy effects associated with grass invasions may improve restoration outcomes through implementation of allelopathy-informed restoration practices. Examples of allelopathy-informed practices, and the knowledge needed to utilize them effectively, are discussed, including the use of activated carbon to neutralize allelochemicals and modify the soil microbial community.

Interactive effects of metals and carbon nanotubes in a microcosm agrosystem

Agricultural soils are exposed to multiple contaminants through the use of agrochemicals or sewage sludge, introducing metals, nanomaterials and others. Among nanomaterials, carbon nanotubes (CNTs) are known for their large surface area and adsorption capabilities, possibly modifying other element behavior. However, to date, very little is known about the impacts of such interactions in agrosystems. In this study, we aimed at understanding the transfer and toxicity of contaminants (Cd, Pb, Zn and CNTs) in microcosms including native soil bacteria, earthworms and lettuce. After a 6 week exposure, no effect of the addition of CNTs to metal contaminated soils was detected on bacterial concentration or earthworm growth. However, in lettuce, an interactive effect between CNTs and metals was highlighted: in the soil containing the highest metal concentrations the addition of 0.1 mg kg^-1 CNTs led to a biomass loss (-22%) and a flavonoid concentration increase (+27%). In parallel, the addition of CNTs led to differential impacts on elemental uptake in lettuce leaves possibly related to the soil organic matter content. For earthworms, the addition of 10 mg kg^-1 CNTs resulted in an increased body elemental transfer in the soil with the higher organic matter content (Pb: + 34% and Zn: + 25%).

Progress and prospects of applying carbon-based materials (and nanomaterials) to accelerate anaerobic bioprocesses for the removal of micropollutants

Carbon-based materials (CBM), including activated carbon (AC), activated fibres (ACF), biochar (BC), nanotubes (CNT), carbon xenogels (CX) and graphene nanosheets (GNS), possess unique properties such as high surface area, sorption and catalytic characteristics, making them very versatile for many applications in environmental remediation. They are powerful redox mediators (RM) in anaerobic processes, accelerating the rates and extending the level of the reduction of pollutants and, consequently, affecting positively the global efficiency of their partial or total removal. The extraordinary conductive properties of CBM, and the possibility of tailoring their surface to address specific pollutants, make them promising as catalysts in the treatment of effluents containing diverse pollutants. CBM can be combined with magnetic nanoparticles (MNM) assembling catalytic and magnetic properties in a single composite (C@MNM), allowing their recovery and reuse after the treatment process. Furthermore, these composites have demonstrated extraordinary catalytic properties. Evaluation of the toxicological and environmental impact of direct and indirect exposure to nanomaterials is an important issue that must be considered when nanomaterials are applied. Though the chemical composition, size and physical characteristics may contribute to toxicological effects, the potential toxic impact of using CBM is not completely clear and is not always assessed. This review gives an overview of the current research on the application of CBM and C@MNM in bioremediation and on the possible environmental impact and toxicity.

Synergy between fungi and bacteria promotes polycyclic aromatic hydrocarbon cometabolism in lignin-amended soil

Lignin enhanced biodegradation of polycyclic aromatic hydrocarbons (PAHs) in soil, but collaboration among soil microorganisms during this process remains poorly understood. Here we explored the relations between microbial communities and PAH transformation in soil microcosms amended with lignin. Mineralization of the four-ring benzo(a)anthracene (BaA), which was selected as a model, was determined by using an isotope-labeled tracer. The eukaryotic inhibitor cycloheximide and redox mediator ABTS were used to validate the fungal role, while microbial communities were monitored by amplicon sequencing. The results demonstrated that lignin significantly promoted BaA mineralization to CO₂, which was inhibited and enhanced by cycloheximide and ABTS, respectively. Together with the increased abundance of Basidiomycota, these observations suggested an essential contribution of fungi to BaA biodegradation, which possibly through a ligninolytic enzyme-mediated pathway. The enrichment of Methylophilaceae and Sphingomonadaceae supported bacterial utilization of methyl and aryl groups derived from lignin, implicating cometabolic BaA degradation. Co-occurrence network analysis revealed increased interactions between fungi and bacteria, suggesting they played synergistic roles in the transformation of lignin and BaA. Collectively, these findings demonstrate the importance of synergy between fungi and bacteria in PAH transformation, and further suggest that the modulation of microbial interplay may ameliorate soil bioremediation with natural materials such as lignin.

Anaerobic bacterial responses to carbonaceous materials and implications for contaminant transformation: Cellular, metabolic, and community level findings

Carbonaceous materials (CM) enhance the abundance and activity of bacteria capable of persistent organic (micro)pollutant (POP) degradation. This review synthesizes anaerobic bacterial responses to minimally modified CM in non-fuel cell bioremediation applications at three stages: attachment, metabolism, and biofilm genetic composition. Established relationships between biological behavior and CM surface properties are identified, but temporal relationships are not well understood, making it difficult to connect substratum properties and "pioneer" bacteria with mature microorganism-CM systems. Stark differences in laboratory methodology at each temporal stage results in observational, but not causative, linkages as system complexity increases. This review is the first to critically examine relationships between material and cellular properties with respect to time. The work highlights critical knowledge gaps that must be addressed to accurately predict microorganism-CM behavior and to tailor CM properties for optimized microbial activity, critical frontiers in establishing this approach as an effective bioremediation strategy.

Characterization of the bacterioplankton community and the influencing factors in the upper reaches of the Han River basin

The upper reaches of the Han River are the source region of water for the Middle Route of China's South-to-North Water Diversion Project, mainly for household, industrial, and irrigation purposes. Planktonic bacteria are more sensitive than macroorganisms to water physical and chemical properties and play a critical role in biogeochemical processes in river ecosystems. In November 2017 and April 2018, a systematic and methodical survey was carried out to evaluate the water quality and bacterial communities, on the mainstem of the Han River and its five main tributaries. In this study, high-throughput sequencing technology has been employed to investigate the bacterioplankton community composition. The results indicated the following: (1) diversity increased downstream, especially in the upper reaches of the Han River. (2) The relative abundance of Actinobacteria increased with the increase of river length, while that of Bacteroidetes decreased slightly. (3) Five tributaries were found to be importance sources of taxa to the Han River; however, in both months, a large proportion of operational taxonomic units (37.84% and 36.34%, respectively) had unknown sources. (4) Finally, redundancy analysis (RDA) and Bioenv analysis showed that environmental parameters (pH, TN, Cond, NH₄⁺-N, DO, NO₂^--N, Chl-a, and T) had a great influence (p ≤ 0.05) on the bacterioplankton community. These research results are beneficial for the managing the ecological system, protecting the tributary biodiversity, and conserving the mainstem and tributaries of the Han River basin.

Medium-term response of the natural grassland soil biota to multiwalled carbon nanotube contamination

Although the soil environment can potentially be exposed to contamination by carbon nanotubes (CNT), its impact on soil biology is poorly understood. In this study, we investigated the effect of the multiwalled CNT (MWCNT) contamination on different groups of soil organisms (microbial, micro- and mesofaunal communities) as well as the soil enzyme activity. The experimental mesocosms included the intact soil cores that were collected from a natural grassland. The MWCNTs that were pristine (pCNTs) and functionalised (fCNTs) at a concentration of 500 μg g^-1 of soil were applied in the form of water suspensions to the surface of the mesocosms, while ensuring the soil was not mixed after the treatment. Soil samples were taken at 3, 6, and 15 weeks after CNT application. The CNT soil contamination highlighted differences in the community dynamics within the studied groups when compared to the control (non-contaminated soil). Among the faunal groups, nematodes were found to be more sensitive to the CNT impact than mites. The most pronounced response of the nematodes was observed in the subsoil at week 6, when their numbers were 3- (pCNTs) and 4-fold (fCNTs) higher than the control mesocosms. Both types of CNTs influenced the relative abundance of the bacterial- and hyphal-feeding nematodes, where pCNTs significantly and negatively affected the predatory nematodes. Moreover, CNTs temporarily, but significantly, decreased the diversity of the nematode communities. In addition, the values of the nematode Structure Index confirmed a strong transitional disturbance effect of CNTs in the soil food web, while the Channel Index in the pCNTs indicated an increasing share of fungi in the decomposition pathway. Hence, we can infer that although the impact of CNTs seems to be temporary, the shifts in the soil community abundance and structure that it induced may have long-term consequences for soil functioning, including nutrient cycling.

Occurrence and distribution of PAHs and microbial communities in nearshore sediments of the Knysna Estuary, South Africa

This study investigated the polycyclic aromatic hydrocarbons (PAHs) occurrence, and their impact on the microbial community and PAH-degrading genera and genes in the Knysna Estuary of South Africa. The results reveal that the estuary exhibits low PAH levels (114.1-356.0 ng g^-1). Ignavibacteriae and Deferribacteres, as well as Proteobacteria and Bacteroidetes, are keystone phyla. Among measured environmental factors, total organic carbon (TOC), nutrients such as nitrite and nitrate, metals as Al, Cr, Cu, Ni, Pb and Zn, and environmental properties (pH and salinity) are primary contributors to structuring the bacterial community assemblage. The abundance of alpha subunit genes of the PAH-ring hydroxylating dioxygenases (PAH-RHDα) of Gram-negative bacteria lies in the range of (2.0-4.2) × 10⁵ copies g^-1, while that of Gram-positive bacteria ranges from 3.0 × 10⁵ to 1.3 × 10⁷ copies g^-1. The PAH-degrading bacteria account for up to 0.1% of the bacterial community and respond mainly to nitrate, TOC and salinity, while PAHs at low concentration are not significant influencing factors. PAH degraders such as Xanthomonadales, Pseudomonas, and Mycobacterium, which play a central role in PAH-metabolization coupled with other biogeochemical processes (e.g. iron cycling), may contribute to maintaining a healthy estuarine ecosystem. These results are important for developing appropriate utilization and protection strategies for pristine estuaries worldwide.

Transformation of catechol coupled to redox alteration of humic acids and the effects of Cu and Fe cations

Humic substances are reactive during redox alteration. However, the role of this reactivity in the transformation of organic compounds and in carbon cycling in the environment is still unclear. Here, we used ¹⁴C-radioactive tracer to study abiotic transformation and humification of catechol, a representative of naturally occurring monomeric phenols and phenolic pollutants, in suspensions of humic acids (HAs) at original and H₂/Pd-reduced redox states with flux of air (HA_org-Air and HA_red-Air, respectively) or N₂ (HA_org-N₂ and HA_red-N₂, respectively) for 20 min in absence and presence of Cu(II) and Fe(II). Both HA_org and HA_red can transform catechol in the absence of O₂ to 19% and 25% of the initially applied amount, respectively. The transformation of catechol strongly increased when air was introduced, amounting to 75% in HA_red-Air treatment and 43% in HA_org-Air treatment, owing to the generation of reactive oxygen species. Considerable amounts of catecholic carbons were incorporated into HAs (26% for HA_red-Air and 19% for HA_org-Air), constituting humification of catechol. The presence of Cu(II) strongly inhibited the overall transformation and humification of catechol, although it significantly increased humification at the start of incubation. The presence of Fe(II) overall enhanced both the transformation and humification. The results provide first insights into the impacts of redox alteration of humic substances together with the presence of metal ions with variable valences on the fate of phenolic compounds in the environment. This study points out that redox alteration-induced abiotic transformation may be one important process for dissipation of phenolic pollutants and humification of phenolic carbons in environments rich in HAs and subject to redox fluctuation.

Accumulation characteristics of endosulfan soil residues in soybean and reduction in their phytoavailability by treatment with powdered activated carbon

Powdered activated carbon (PAC) has been utilized for sorptive remediation of environmental sites contaminated with various organic chemicals. In the present study, time-dependent sorption/desorption characteristics of the α- and β-isomers and a sulfate-metabolite of endosulfan (ED) were investigated in PAC-amended soils to determine the optimal PAC amendment dosage. Subsequently, ED phytoavailability to soybean (Glycine max Merr.) plants were examined in the presence or absence of PAC under restricted laboratory conditions. Based on the results of sorption/desorption tests, the optimal dosage of PAC amendment for ED-contaminated soils was determined as 1% (w/w), and at this dosage, all ED residues were sorbed completely onto the PAC-amended soils without any desorption. In soil amended with 1% PAC, the extents of ED accumulated by soybean plants were reduced by 89.4-100.0% within 20 days compared to those extents observed in unamended controls. Moreover, PAC treatment precluded the formation of the toxic metabolite ED-sulfate in either the soil or soybean plants. Therefore, PAC amendment in ED-contaminated soils could be highly effective for limiting uptake of ED into plants from contaminated soil and may be useful as an alternative method to produce safe food resources from contaminated arable soils.

A comparative analysis of ball-milled biochar, graphene oxide, and multi-walled carbon nanotubes with respect to toxicity induction in Streptomyces

Ball-milled biochar has recently attracted a lot of attention due to the simplicity of its preparation and low cost. However, it is unknown if the biochar is environmentally safe. Here, the toxic effect of ball-milled biochar on Streptomyces was compared to that of pristine biochar and two other carbon nanomaterials of different shapes-graphene oxide and multi-walled carbon nanotubes. The effect of these different materials on antibiotic production was characterized. The results showed that even at concentrations of up to 10 mg/L, pristine biochar had a negligible effect on toxicity and antibiotic production in Streptomyces. However, after ball milling, the physical and chemical properties of biochar changed dramatically. Cells were severely damaged, and there was a significant increase in antibiotic production after the addition of ball-milled biochar. Exposure to 10 mg/L of ball-milled biochar caused massive cell disruption; the survival rate of Streptomyces coelicolor M145 cells was only 68.2% as compared to 90% after treatment with 10 mg/L graphene oxide and multi-walled carbon nanotubes. The secretion of the antibiotics- the red intracellular pigment undecylprodigiosin (RED) and blue diffusible pigment actinorhodin (ACT) was enhanced with the highest level in treatment with ball milled biochar, as compared to that with the other two carbon nanomaterials. This effect can be attributed to increased expression of pathway-specific regulatory genes redD, redZ and actⅡ-ORF4. Ball-milled biochar can be developed as an effective additive to increase antibiotic yield. However, we should restrict the large-scale use of ball-milled biochar before fully understanding its impact on the environment and human health.

Phage shock protein and gene responses of Escherichia coli exposed to carbon nanotubes

Two-dimensional electrophoretic, western blotting, and quantitative polymerase chain reaction analyses of Escherichia coli cells exposed to pristine single walled carbon nanotubes (SWCNTs), and hydroxyl and carboxylic functionalized SWCNTs (SWCNT-OHs and SWCNT-COOHs) were conducted. SWCNT concentration and length were experimental variables. Exposing E. coli cells to SWCNTs led to changes in protein and gene expressions. Several proteins altered their regulations at a low SWCNT concentration (10 μg/ml) and were shut down at a high SWCNT concentration (100 μg/ml). The expressions of the phage shock protein (psp) operon including pspA, pspB, and pspC genes responded to the membrane stressors, SWCNTs, were also examined. While pspA and pspC expressions were influenced by the length, concentration, and functional groups of SWCNTs, pspB expression was not induced by SWCNTs. The alterations in phage shock protein and gene expressions indicated that SWCNTs caused cell membrane perturbation.

The Charosphere Promotes Mineralization of 13C-Phenanthrene by Psychrotrophic Microorganisms in Greenland Soils

When soil is frozen, biochar promotes petroleum hydrocarbon (PHC) degradation, yet we still do not understand why. To investigate microbial biodegradation activity under frozen conditions, we placed 60-μm mesh bags containing 6% (v/v) biochar created from fishmeal, bonemeal, bone chip, or wood into PHC-contaminated soil, which was then frozen to -5°C. This created three soil niches: biochar particles, the charosphere (biochar-contiguous soil), and bulk soil outside of the bags. After 90 d, C-phenanthrene mineralization reached 55% in bonemeal biochar and 84% in bone chip biochar charosphere soil, compared with only 43% in bulk soil and 13% in bone chip biochar particles. Soil pH remained near neutral in bone chip and bonemeal biochar treatments, unlike wood biochar, which increased alkalinity and likely made phosphate unavailable for microorganisms. Generally, charosphere soil had higher aromatic degradative gene abundances than bulk soil, but gene abundance was not directly linked to C-phenanthrene mineralization. In bone chip biochar-amended soils, phosphate successfully predicted microbial community composition, and abundances of and increased in charosphere soil. Biochar effects on charosphere soil were dependent on feedstock material and suggest that optimizing the charosphere in bone-derived biochars may increase remediation success in northern regions.

Effects of multi-walled carbon nanotubes on pyrene adsorption and desorption in soils: The role of soil constituents

Once entering soil, carbon nanotubes (CNTs) can influence the fate of hydrophobic organic compounds (HOCs) in soil due to its strong adsorption capacity. This process may be influenced by the interactions between CNTs and soil constituents. The mechanisms therein were investigated in the present study by examining pyrene adsorption/desorption on one CNTs, two soils (black soil and paddy soil), and mixtures thereof. CNTs' amendment enhanced soil site heterogeneity and adsorption capacity of pyrene while it was less than that predicted by the sum of the individual adsorption on soils and CNTs, which was more obvious at low aqueous concentrations. This could be due to the interactions between soil constituents (dissolved organic matter (DOM) and clays) and CNTs. Modification of CNTs by DOM attenuated pyrene adsorption by 14.9%-66.1%, which was ascribed to occupying of surface adsorption sites, pore blockage of CNTs' aggregates, enhancement of surface polarity, and enhancement of pyrene solubility in aqueous phase. The coexistence of clay (kaolinite) also showed inhibition on pyrene adsorption onto CNTs with a reduction of 19.2%-40.2%. This could be ascribed to that the attachment of clay particles on CNTs' aggregates could cover the surface adsorption sites and enhance the surface polarity of CNTs. The effect of CNTs amendment on pyrene desorption hysteresis differed among soils. The hysteresis index of the black soil doubled after CNTs' amendment while that of paddy soil remained unchanged. The results of this study provide insights into the possible effects of CNTs on the fate of HOCs in real soil environment.

Toxicity of carbon nanomaterials to plants, animals and microbes: Recent progress from 2015-present

Nanotechnology has gained significant development over the past decades, which led to the revolution in the fields of information, medicine, industry, food security and aerospace aviation. Nanotechnology has become a new research hot spot in the world. However, we cannot only pay attention to its benefit to the society and economy, because its wide use has been bringing potential environmental and health effects that should be noticed. This paper reviews the recent progress from 2015-present in the toxicity of various carbon nanomaterials to plants, animals and microbes, and lays the foundation for further study on the environmental and ecological risks of carbon nanomaterials.

Carbonaceous Nanomaterials Have Higher Effects on Soybean Rhizosphere Prokaryotic Communities During the Reproductive Growth Phase than During Vegetative Growth

Carbonaceous nanomaterials (CNMs) can affect agricultural soil prokaryotic communities, but how the effects vary with the crop growth stage is unknown. To investigate this, soybean plants were cultivated in soils amended with 0, 0.1, 100, or 1000 mg kg-1 of carbon black, multiwalled carbon nanotubes (MWCNTs), or graphene. Soil prokaryotic communities were analyzed by Illumina sequencing at day 0 and at the soybean vegetative and reproductive stages. The sequencing data were functionally annotated using the functional annotation of prokaryotic taxa (FAPROTAX) database. The prokaryotic communities were unaffected at day 0 and were altered at the plant vegetative stage only by 0.1 mg kg-1 MWCNTs. However, at the reproductive stage, when pods were filling, most treatments (except 1000 mg kg-1 MWCNTs) altered the prokaryotic community composition, including functional groups associated with C, N, and S cycling. The lower doses of CNMs, which were previously shown to be less agglomerated and thus more bioavailable in soil relative to the higher doses, were more effective toward both overall communities and individual functional groups. Taken together, prokaryotic communities in the soybean rhizosphere can be significantly phylogenetically and functionally altered in response to bioavailable CNMs, especially when soybean plants are actively directing resources to seed production.

Plenty of room for carbon on the ground: Potential applications of biochar for stormwater treatment

Low impact development (LID) systems are increasingly used to manage stormwater, but they have limited capacity to treat stormwater-a resource to supplement existing water supply in water-stressed urban areas. To enhance their pollutant removal capacity, infiltration-based LID systems can be augmented with natural or engineered geomedia that meet the following criteria: they should be economical, readily available, and have capacity to remove a wide range of stormwater pollutants in conditions expected during intermittent infiltration of stormwater. Biochar, a carbonaceous porous co-product of waste biomass pyrolysis/gasification, meets all these criteria. Biochar can adsorb pollutants, improve water-retention capacity of soil, retain and slowly release nutrients for plant uptake, and help sustain microbiota in soil and plants atop; all these attributes could help improve removal of contaminants in stormwater treatment systems. This article discusses contaminant removal mechanisms by biochar, summarizes specific biochar properties that enhance targeted contaminants removal from stormwater, and identifies challenges and opportunities to retrofit biochar in LID to optimize stormwater treatment.

Integrated biogeography of planktonic and sedimentary bacterial communities in the Yangtze River

BACKGROUND

Bacterial communities are essential to the biogeochemical cycle in riverine ecosystems. However, little is presently known about the integrated biogeography of planktonic and sedimentary bacterial communities in large rivers.

RESULTS

This study provides the first spatiotemporal pattern of bacterial communities in the Yangtze River, the largest river in Asia with a catchment area of 1,800,000 km2. We find that sedimentary bacteria made larger contributions than planktonic bacteria to the bacterial diversity of the Yangzte River ecosystem with the sediment subgroup providing 98.8% of 38,906 operational taxonomic units (OTUs) observed in 280 samples of synchronous flowing water and sediment at 50 national monitoring stations covering a 4300 km reach. OTUs within the same phylum displayed uniform seasonal variations, and many phyla demonstrated autumn preference throughout the length of the river. Seasonal differences in bacterial communities were statistically significant in water, whereas bacterial communities in both water and sediment were geographically clustered according to five types of landforms: mountain, foothill, basin, foothill-mountain, and plain. Interestingly, the presence of two huge dams resulted in a drastic fall of bacterial taxa in sediment immediately downstream due to severe riverbed scouring. The integrity of the biogeography is satisfactorily interpreted by the combination of neutral and species sorting perspectives in meta-community theory for bacterial communities in flowing water and sediment.

CONCLUSIONS

Our study fills a gap in understanding of bacterial communities in one of the world's largest river and highlights the importance of both planktonic and sedimentary communities to the integrity of bacterial biogeographic patterns in a river subject to varying natural and anthropogenic impacts.

Contrasting effects of engineered carbon nanotubes on plants: a review

Rapid surge of interest for carbon nanotube (CNT) in the last decade has made it an imperative member of nanomaterial family. Because of the distinctive physicochemical properties, CNTs are widely used in a number of scientific applications including plant sciences. This review mainly describes the role of CNT in plant sciences. Contradictory effects of CNT on plants physiology are reported. CNT can act as plant growth inducer causing enhanced plant dry biomass and root/shoot lengths. At the same time, CNT can cause negative effects on plants by forming reactive oxygen species in plant tissues, consequently leading to cell death. Enhanced seed germination with CNT is related to the water uptake process. CNT can be positioned as micro-tubes inside the plant body to enhance the water uptake efficiency. Due to its ability to act as a slow-release fertilizer and plant growth promoter, CNT is transpiring as a novel nano-carbon fertilizer in the field of agricultural sciences. On the other hand, accumulation of CNT in soil can cause deleterious effects on soil microbial diversity, composition and population. It can further modify the balance between plant-toxic metals in soil, thereby enhancing the translocation of heavy metal(loids) into the plant system. The research gaps that need careful attention have been identified in this review.