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The texture of the soil profile determines the movement and distribution of soil water and also affects plant growth and development. Most studies have focused on the movement of water in homogeneous or layered soil profiles such as coarse sand or gravel as a capillary barrier. Few studies have used loess as an interlayer of sand to study the water distribution characteristics of soil profiles. Here, a layered sand-loess-sand soil profile was constructed in indoor soil columns to explore the effects of different thicknesses of loess interlayer (0, 10 and 20 cm) on water transport. The advancing height of the sand wetting front followed a power function with time in different loess interlayer thickness treatments and the loess interlayer promoted the advancing height of the wetting front. Loess interlayer treatment significantly increased the soil volumetric water content in the corresponding treatment layer (40-60 cm). The thicker the loess interlayer the higher the soil volumetric water content. After two months of soil drainage the volumetric water content in the treatment layer (40-60 cm) corresponding to the loess interlayer treatment did not decline but the control declined by 1.36%. These results may provide a scientific basis and theoretical support for the artificial reconstruction of soil profiles in arid and semi-arid coal mining areas to optimize sand moisture content. [ABSTRACT FROM AUTHOR]

Bacterial type IV secretion systems (T4SSs) are a versatile family of macromolecular translocators, collectively able to recruit diverse DNA and protein substrates and deliver them to a wide range of cell types. Presently, there is little understanding of how T4SSs recognize substrate repertoires and form productive contacts with specific target cells. Although T4SSs are composed of a number of conserved subunits and adopt certain conserved structural features, they also display considerable compositional and structural diversity. Here, we explored the structural bases underlying the functional versatility of T4SSs through systematic deletion and subunit swapping between two conjugation systems encoded by the distantly-related IncF plasmids, pED208 and F. We identified several regions of intrinsic flexibility among the encoded T4SSs, as evidenced by partial or complete functionality of chimeric machines. Swapping of VirD4-like TraD type IV coupling proteins (T4CPs) yielded functional chimeras, indicative of relaxed specificity at the substrate—TraD and TraD—T4SS interfaces. Through mutational analyses, we further delineated domains of the TraD T4CPs contributing to recruitment of cognate vs heterologous DNA substrates. Remarkably, swaps of components comprising the outer membrane core complexes, a few F-specific subunits, or the TraA pilins supported DNA transfer in the absence of detectable pilus production. Among sequenced enterobacterial species in the NCBI database, we identified many strains that harbor two or more F-like plasmids and many F plasmids lacking one or more T4SS components required for self-transfer. We confirmed that host cells carrying co-resident, non-selftransmissible variants of pED208 and F elaborate chimeric T4SSs, as evidenced by transmission of both plasmids. We propose that T4SS plasticity enables the facile assembly of functional chimeras, and this intrinsic flexibility at the structural level can account for functional diversification of this superfamily over evolutionary time and, on a more immediate time-scale, to proliferation of transfer-defective MGEs in nature. Author summary: Mobile genetic elements (MGEs) comprise a diverse group of extrachromosomal plasmids or integrated DNA fragments that are widely distributed among many bacterial species. MGEs typically encode conjugation systems dedicated to their transmission to other bacteria, and also code for resistance to antibiotics or virulence or other fitness traits. The conjugation systems, along with an equally medically important group of translocators devoted to the interkingdom delivery of protein effectors by pathogenic species, comprise the superfamily of type IV secretion systems (T4SSs). Recent studies have defined many mechanistic and structural features of the T4SSs, yet there remains little understanding of how T4SSs recruit specific DNA or protein substrates, elaborate functional channels, and in some cases build attachment organelles termed conjugative pili. We explored the mechanics of T4SS machine function by systematically exchanging individual components between two distinct conjugation systems functioning in enterobacterial species. Through construction of chimeric machines, and further mutational analyses, we identified subunits or protein domains of conjugation machines specifying recruitment of different DNA substrates or selectively contributing to assembly of translocation channels or conjugative pili. Such features of T4SSs are prime targets for development of inhibitory strategies aimed at blocking T4SS functions for therapeutic intervention. [ABSTRACT FROM AUTHOR]

Dark septate endophytes (DSE) are widespread colonizers of plant roots and have important ecological functions such as the regulation of plant growth and nutrient uptake. The mechanisms by which DSE mycelium and its extracellular metabolites promote plant growth have not yet been determined. Here, the growth‐promoting effects of DSE mycelium (H) and extracellular metabolites (M) on alfalfa (Medicago sativa L.) were investigated. Treatments H, M and HM increased the total biomass of alfalfa by 23.9%, 47.2% and 47.1%, respectively. H and M modified root structure by increasing root volume and reducing root tissue density, and promoting nutrient uptake. Metabolomic analysis indicates that alfalfa root exudates contained 204 metabolites of different types, mainly lipids and lipid‐like molecules, organic acids and derivatives, benzenoids. There were more organoheterocyclic compounds and fewer organic acids and derivatives in root exudates in treatment H than in treatment M. Pathway analysis shows that DSE and its extracellular metabolites had greater effects on glycerophospholipid metabolism and N‐glycan biosynthesis pathway. The results provide information on the mechanisms involved in the metabolic regulation of plant growth promotion by DSE. [ABSTRACT FROM AUTHOR]

Tidal wetlands sequester vast amounts of organic carbon (OC) and enhance soil accretion. The conservation and restoration of these ecosystems is becoming increasingly geared toward "blue" carbon sequestration while obtaining additional benefits, such as buffering sea‐level rise and enhancing biodiversity. However, the assessments of blue carbon sequestration focus primarily on bulk SOC inventories and often neglect OC fractions and their drivers; this limits our understanding of the mechanisms controlling OC storage and opportunities to enhance blue carbon sinks. Here, we determined mineral‐associated and particulate organic matter (MAOM and POM, respectively) in 99 surface soils and 40 soil cores collected from Chinese mangrove and saltmarsh habitats across a broad range of climates and accretion rates and showed how previously unrecognized mechanisms of climate and mineral accretion regulated MAOM and POM accumulation in tidal wetlands. MAOM concentrations (8.0 ± 5.7 g C kg−1) (±standard deviation) were significantly higher than POM concentrations (4.2 ± 5.7 g C kg−1) across the different soil depths and habitats. MAOM contributed over 51.6 ± 24.9% and 78.9 ± 19.0% to OC in mangrove and saltmarsh soils, respectively; both exhibited lower autochthonous contributions but higher contributions from terrestrial or marine sources than POM, which was derived primarily from autochthonous sources. Increased input of plant‐derived organic matter along the increased temperature and precipitation gradients significantly enriched the POM concentrations. In contrast, the MAOM concentrations depended on climate, which controlled the mineral reactivity and mineral–OC interactions, and on regional sedimentary processes that could redistribute the reactive minerals. Mineral accretion diluted the POM concentrations and potentially enhanced the MAOM concentrations depending on mineral composition and whether the mineral accretion benefited plant productivity. Therefore, management strategies should comprehensively consider regional climate while regulating sediment supply and mineral abundance with engineering solutions to tap the OC sink potential of tidal wetlands. [ABSTRACT FROM AUTHOR]

Summary: Supporting food security while maintaining ecosystem sustainability is one of the most important global challenges for humanity. Optimization of cropping systems is expected to promote the ecosystem services of agroecosystems. Yet, how and why cropping system influences the trade‐offs between economic profitability and multiple ecosystem services remain poorly understood.We investigate the influence of six cropping systems on trade‐offs between economic profitability and multiple ecosystem services after considering 36 agricultural ecosystem properties using field experiment data from 2020 to 2022.We show that designing cropping system is a critical tool to closing the gap between ecosystem sustainability and commercial profitability. Cropping system with three harvests within 2 yr had higher performance in overall ecosystem multiple services through enhancement of supporting, regulating, and economic performance without compromising provisioning compared with four other systems. These systems diminished the trade‐off among multiple services, resulting in a 'win‐win' situation for economics and multiple services. By contrast, the monoculture and double cropping systems lead to a strong trade‐off between pairwise services including ecosystem health and profitability.Our work illustrates the substantial potential of rotation systems with three harvests within 2 yr in enforcing ecosystem services and closing the trade‐offs among multiple agricultural ecosystem services. [ABSTRACT FROM AUTHOR]

[Display omitted] • The proportion and OC content of large aggregates were affected by vegetation types. • The direction of carbon flows was from small aggregates to silt + clay size classes. • Tree plantation slowed carbon flows of aggregates. • Roots are more likely to be the starting point of carbon flow at 15–30cm depth. The vegetation restoration of land post‑mining can promote soil structure development and increase organic carbon storage. The response of soil carbon sequestration pathways to different recovery modes is poorly understood, especially in soils of reclaimed surface-mine areas. Here, long-term carbon dynamics were characterized by examining aggregate-associated carbon contents and carbon flow pathways following vegetation restoration of reclaimed land near a surface mine. Six long-term restoration areas were represented by Populus alba trees, Amorpha fruticosa shrubs, and grassland. During the long-term restoration process the contribution of aggregates to SOC (12.5 to 46.1%), δ13C values (-25.91 to –23.65‰) and percentages of particulate organic carbon in large soil aggregates of tree plantations showed the maximum increase and shrubland showed the minimum. The direction of carbon flows was from small aggregates to silt + clay size classes, and tree plantations slowed the carbon flows of aggregates. With increasing soil depth, roots were more likely to be the starting point of carbon flow in aggregates. This analysis of the natural δ13C signature reveals the mechanism of organic carbon stabilization under long-term vegetation restoration near a surface mine in a semi-arid region. [ABSTRACT FROM AUTHOR]

BACKGROUND: Maintaining or improving soil chemical quality is critical for sustainable agricultural productivity and environmental safeguards. Organic fertilizer application, a common agricultural practice in banana cultivation, is often associated with greater microbial biomass and activity, which are linked to improvements in soil chemical quality. However, the effect of the duration of organic fertilizer application on soil chemical quality and whether it is microbially driven still needs to be investigated. We collected soil samples from banana plantations consistently applying organic fertilizers for 1 (Y1), 4 (Y4), 7 (Y7) and 10 (Y10) years. Soil chemical quality is expressed as total data set (TDS) and minimum data set (MDS) based on chemical indicators, and soil microorganisms are characterized by phospholipid fatty acid (PLFA). RESULTS: Based on TDS and MDS, the soil chemical quality indices in Y7 and Y10 treatments were significantly higher than that in Y1 and Y4 treatments. Soil total PLFA concentrations and the proportional abundance of fungi and arbuscular mycorrhizal fungi increased with prolonged banana cultivation. Total PLFA concentrations were significantly positive correlation with the soil chemical quality index. Soil gram‐positive bacteria (G+), bacteria, protozoa and ratio of G+ to gram‐negative bacteria (G–) were major drivers of soil chemical quality. CONCLUSION: The organic fertilizer application can significantly improve soil chemical quality, which is regulated by soil bacteria. Regular application of organic fertilizers is important in promoting soil quality and soil biological properties need to be incorporated into the assessment of soil health in banana plantations. © 2022 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Dark septate endophytes (DSE) colonize plant roots extensively and increase host plant growth and nutrition. However, the development of DSE-produced metabolites as plant biostimulants has been largely ignored. DSE growth curves and extracellular metabolite components were analyzed and the growth-promoting effects of DSE extracellular metabolites on alfalfa (Medicago sativa L.) grown for 4, 8 12, 16 and 20 days were evaluated. The growth curve of the DSE strain Alternaria sp. shows days 0-8 in the growth phase, days 8-16 in the stable phase, and days 16-20 in the senescent phase. The extracellular metabolite components of DSE were significantly different at different growth stages. The biomass of alfalfa was increased significantly by DSE extracellular metabolites (P < 0.05). Biomass of alfalfa inoculated with DSE extracellular metabolites more than doubled after growth for 8 days and nutrient availability also increased significantly compared with the uninoculated control. Six DSE extracellular metabolites, calycosin 7-galactoside, 1-[(5-amino-5-carboxypentyl)amino]-1-deoxyfructose, N2-fructopyranosylarginine, 2-(4-methyl-5-thiazolyl)ethyl hexanoate, kenposide B, and medinoside E, were significantly positively correlated with alfalfa biomass (P < 0.01). This study combines the DSE extracellular metabolites with plant and soil traits to provide a theoretical basis for the use of DSE metabolites in the product development of plant biostimulants. • The time factor significantly affects the growth and metabolism of DSE. • The major components of DSE extracellular metabolites are amino acids and peptides. • The addition of DSE metabolites can promote alfalfa growth and nutrient uptake. • DSE metabolites promote plant growth and nutrient uptake through multiple pathways. [ABSTRACT FROM AUTHOR]

Biodegradation is difficult at high temperatures due to the limited capacity of microorganisms to survive and function outside their optimum temperature range. Here, a thermophilic petroleum-degrading consortium was enriched from compost at a temperature of 55 °C. 16S rDNA and metagenomic techniques were used to analyze the composition of the consortium and the mechanisms of degradation. The consortium degraded 17000 mg total petroleum hydrocarbons (TPHs) L−1 with a degradation efficiency of 81.5% in 14 days. The consortium utilized a range of substrates such as n-hexadecane, n-docosane, naphthalene and pyrene and grew well over a wide range of pH (4–10) and salinity (0–90 g L−1). The hydrocarbon-degrading extremophilic consortium contained, inter alia , (relative abundance >1%) Caldibacillus , Geobacillus , Mycolicibacterium , Bacillus , Chelatococcus , and Aeribacillus spp. Metagenomic analysis was conducted to discover the degradation and environmental tolerance functional genes of the consortium. Two alkane hydroxylase genes, alk B and lad A, were found. A microcosm study shows that the consortium promoted the bioremediation of soil TPHs. The results indicate that the consortium may be a good candidate for the high-temperature bioremediation of petroleum-contaminated soils. [Display omitted] • The strain composition of the consortium was stable during degradation. • Bacterial taxa with smaller relative abundances had higher contribution coefficients. • The bacterial consortium promoted the bioremediation of petroleum-contaminated soils. [ABSTRACT FROM AUTHOR]

Contamination of groundwater with chlorinated aliphatic hydrocarbons (CAHs) has become increasingly widespread. Enhanced reductive dechlorination (ERD) by emulsified vegetable oil (EVO) is an environmentally friendly, low-carbon and sustainable technology that effectively eliminates the threat from CAHs. To improve the permeability and bioavailability of EVO in the low-permeability substratum, nano-emulsified vegetable oil (nanoEVO) can be synthesized using a modified phase inversion composition method (MPIC) by increasing the emulsification temperature that reduces the shear force required for the formation of nanodroplets and the interfacial tension between the mixed phase and water. The emulsification temperature of 60 °C, the water content of 40–70%, the droplet diameter (DD) of nanoEVO prepared by MPIC is ∼200 nm, and had good monodispersion (≤0.2). The high molecular weight and low solubility of vegetable oil, and similar size of droplet make nanoEVO remains homogeneous after storage for > one year. NanoEVO can effectively biostimulate indigenous bacteria in CAHs-contaminated groundwater to dechlorinate 1,1,2-trichloroethane (1,1,2-TCA) to ethene via vinyl chloride (VC). The maximum dihaloelimination rate of 1,1,2-TCA was ∼66.06 μM·Cl−·day−1 and the maximum hydrogenolysis rate of VC was ∼35.67 μM·Cl−·day−1. NanoEVO effectively increased the relative abundance of Dehalococcoides from <0.10 to 9.61%. The abundances of Dhc 16S rRNA gene and dehalogenase gene vcr A increased by 102 and 103, respectively. Biostimulation shaped the structure of microbial communities and promoted hydrolytic acidification and anaerobic fermentation. Moreover, the syntrophic VFA-oxidizing bacteria participated in secondary fermentation and were closely correlated with H 2 consumption metabolism. By providing carbon sources and maintaining an anaerobic environment with stable pH and ORP, nanoEVO biostimulated the hydrolytic acidification led by fermentative bacteria, secondary fermentation with syntrophic VFA-oxidizing bacteria and reductive dechlorination carried out by dechlorinator, thus greatly increasing the CAH-dechlorinating ability of indigenous microbial communities. [Display omitted] • The MPIC method can prepared highly stable nanoEVO. • Biostimulation increased the abundance of Dehalococcoides by 102 times and increased the VC dechlorination rate. • Syntrophic VFA-oxidizing bacteria were important in biostimulated dechlorination community. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) play an important role in crop productivity, but their response to different fertilization regimes is variable. Understanding the mechanisms governing mycorrhizal responses under various fertilization regimes is key to maximizing the mycorrhizal contribution to ecosystem functioning. Indigenous AMF communities and soil were collected from long-term field experiments with various fertilization regimes. A greenhouse bioassay was carried out to identify the key regulators of the mycorrhizal response to inorganic and organic fertilization. Different fertilization regimes generated continuous gradients for most soil properties and a full spectrum of mycorrhizal phenotypes. Mycorrhizal growth response (MGR) in particular showed complex shifts from positive to neutral to negative, while mycorrhizal phosphorus (P) response was consistently positive and mycorrhizal nitrogen (N) response was consistently negative in fertilized treatments. Soil available P and available N to P (N:P) ratio appeared to be key soil predictors of the mycorrhizal response. Also, the nutrient status of non-mycorrhizal (NM) plants, namely shoot N concentration, shoot P concentration and shoot N:P ratio, were plant predictors of mycorrhizal response. A positive MGR occurred when NM plants were P-limited, and neutral and negative MGR occurred when NM plants were N-limited or co-limited by N and P. Further, the thresholds of soil available P (c. 13 mg kg-1), NM shoot N concentration (c. 14 g kg-1), NM shoot P concentration (c. 0.7 g kg-1) and NM shoot N:P ratio (c. 18), respectively, were estimated to predict mycorrhizal response. We conclude that the relative availability of N and P in soil and NM plants are good predictors of mycorrhizal response in different fertilization regimes. The existing nutrient thresholds combining soil and plant allowed more accurate prediction of mycorrhizal response and this has important implications for optimizing the mycorrhizal association in some important crops by managing soil nutrients. • A wide spectrum of mycorrhizal phenotypes was observed in multiple fertilization regimes. • Soil P availability and N:P ratio were key soil predictors of mycorrhizal response. • N and P status of non-mycorrhizal plants were key plant predictors of mycorrhizal response. • Nutrient thresholds in soil and plants in predicting mycorrhizal response were identified. [ABSTRACT FROM AUTHOR]

The Porphyromonas gingivalis type IX secretion system (T9SS) promotes periodontal disease by secreting gingipains and other virulence factors. By in situ cryoelectron tomography, we report that the P. gingivalis T9SS consists of 18 PorM dimers arranged as a large, caged ring in the periplasm. Near the outer membrane, PorM dimers interact with a PorKN ring complex of ∼52 nm in diameter. PorMKN translocation complexes of a given T9SS adopt distinct conformations energized by the proton motive force, suggestive of different activation states. At the inner membrane, PorM associates with a cytoplasmic complex that exhibits 12-fold symmetry and requires both PorM and PorL for assembly. Activated motors deliver substrates across the outer membrane via one of eight Sov translocons arranged in a ring. The T9SSs are unique among known secretion systems in bacteria and eukaryotes in their assembly as supramolecular machines composed of apparently independently functioning translocation motors and export pores. [ABSTRACT FROM AUTHOR]

F plasmids circulate widely among the Enterobacteriaceae through encoded type IV secretion systems (T4SSFs). Assembly of T4SSFs and associated F pili requires 10 VirB/VirD4‐like Tra subunits and eight or more F‐specific subunits. Recently, we presented evidence using in situ cryoelectron tomography (cryoET) that T4SSFs undergo structural transitions when activated for pilus production, and that assembled pili are deposited onto alternative basal platforms at the cell surface. Here, we deleted eight conserved F‐specific genes from the MOBF12C plasmid pED208 and quantitated effects on plasmid transfer, pilus production by fluorescence microscopy, and elaboration of T4SSF structures by in situ cryoET. Mutant phenotypes supported the assignment of F‐specific subunits into three functional Classes: (i) TraF, TraH, and TraW are required for all T4SSF‐associated activities, (ii) TraU, TraN, and TrbC are nonessential but contribute significantly to distinct T4SSF functions, and (iii) TrbB is essential for F pilus production but not for plasmid transfer. Equivalent mutations in a phylogenetically distantly related MOB12A F plasmid conferred similar phenotypes and generally supported these Class assignments. We present a new structure‐driven model in which F‐specific subunits contribute to distinct steps of T4SSF assembly or activation to regulate DNA transfer and F pilus dynamics and deposition onto alternative platforms. [ABSTRACT FROM AUTHOR]

• Drought stress affected soybean growth and physiology. • Leaf temperature reflected the effect of AMF on plant water status under drought stress. • AMF regulated leaf temperature to affect other physiological activities. The influence of arbuscular mycorrhizal fungi (AMF) on plant water status and growth under drought stress were investigated using soybean subjected to drought stress (40% of soil water-holding capacity (WHC)) and control conditions (60% WHC) either inoculated with AMF or uninoculated controls. Leaf temperature (T leaf) and stomatal conductance (gs) were determined at 10:00, 12:00 and 18:00 on the harvest day. The effects of AMF on the water physiological status and growth of soybeans under drought stress were examined using thermal infrared imaging technology (TIIT). AMF inoculation under drought stress increased plant above- and below-ground biomass, nutritional status, and nitrogen, phosphorus and potassium uptake rates, and reduced plant root/shoot ratio. Monitoring T leaf reflected the effect of AMF on plant water physiological status under drought stress. AMF inoculation resulted in a decline in T leaf of 0.1–0.4 °C as water uptake proceeded compared with an increase of 0.2–1.4 °C in uninoculated controls. Thus, the effects of AMF on soybean drought resistance changed from positive to negative. AMF reduced plant T leaf , promoted the accumulation of photosynthetic products, reduced malondialdehyde accumulation, and increased stomatal regulation and T leaf. These preliminary results provide a basis for further studies on the effects of AMF on the water and growth status of plants under drought stress in arid areas. [ABSTRACT FROM AUTHOR]

Thermal infrared imaging technology was used to understand the effects of arbuscular mycorrhizal fungi (AMF) and dark septate endophytic (DSE) fungi, both separately and together, on plant growth and physiological status, and to screen and develop efficient microbial agents in a pot experiment design. Eight treatments comprised the control (CK), AMF inoculation alone, DSE fungal treatments (DSE20%, DSE40% and DSE80%; 2, 4, 8 × 105 CFU mL−1) and combined inoculation treatments (DSE20% + AMF, DSE40% + AMF, and DSE80% + AMF). Canopy temperature (Tcanopy) and stomatal conductance (gs) were monitored at different growth stages, and plant biomass-related indicators were obtained at harvest. These indicators were used to assess plant growth and the physiological status resulting from the different inoculation treatments. During plant growth, the plant Tcanopy decreased following inoculation. Differences in Tcanopy between control and inoculated plants were detected by thermal infrared imaging technology and were −3.8 to + 9.3 °C (control–inoculation treatment). Growth index and Tcanopy monitoring indicate that the growth-promoting effect of combined inoculation was higher than that of either fungal type alone, with DSE80% + AMF producing the highest growth promotion. During the growth process of inoculated maize, the effect of inoculated AMF on the physiological condition of maize growth can be better monitored by thermal infrared at 10 a.m., 12 p.m., 2 p.m. and 4 p.m. on the 31st–57th days of the growth period. The method and results of this experiment are conducive to the rapid and efficient monitoring of the effects of microorganisms on plant growth and physiological status and can be applied to the screening, application, and promotion of microbial agents. [ABSTRACT FROM AUTHOR]

Water-dispersible colloids (WDCs) are vital for trace element migration, but there is limited information about the abundance, size distribution and elemental composition of WDC-bound thallium (Tl) and arsenic (As) in mining-contaminated soils and sediments solutions. Here, we investigated the potential mobilization of WDC-bound Tl and As in soils and sediments in a typical Tl/As-contaminated area. Ultrafiltration results revealed on average > 60% of Tl and As in soil solution (< 220 nm) coexisted in colloidal form whereas Tl and As in sediment solution primarily existed in the truly dissolved state (< 10 kDa) due to increased acidity. Using AF4-UV-ICP-MS and STEM-EDS, we identified Fe-bearing WDCs in association with aluminosilicate minerals and organic matter were main carriers of Tl and As. SAED further verified jarosite nanoparticles were important components of soil WDC, directly participating in the migration of Tl and As. Notably, high pollution levels and solution pH promoted the release of Tl/As-containing WDCs. This study provides quantitative and visual insights into the distribution of Tl and As in WDC, highlighting the important roles of Fe-bearing WDC, soil solution pH and pollution level in the potential mobilization of Tl and As in contaminated soils and sediments. [Display omitted] • > 60% of Tl and As in soil solution occurred in water-dispersible colloids (WDCs). • Tl/As-bearing WDCs comprised Fe oxides, aluminosilicates and OM. • Jarosite was an important component of WDCs involved in Tl/As migration. • High pollution levels and solution pH promoted the release of Tl/As-bearing WDCs. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal (AM) fungi contribute to the revegetation of degraded ecosystems such as coal mining areas and may indirectly affect the development of biological soil crusts (biocrusts). However, bacterial diversity and microbial nutrient cycling in the soil underlying biocrusts are seldom considered when assessing ecological restoration effects. Bacterial community composition was quantified and compared using 16S rRNA gene sequencing, metabolic limitation of microbes via extracellular enzymatic stoichiometry and their association with carbon use efficiency (CUE) in soil underlying moss biocrusts in vegetated areas inoculated with an AM fungus or uninoculated and in uninoculated unvegetated areas. The AM fungal inoculum significantly influenced bacterial community composition and diversity, extracellular enzyme activities and CUE in soil underlying moss biocrusts mainly by affecting soil nutrients. Correlation analysis revealed that Actinobacteria, Armatimonadetes, Bacteroidetes, Chlorobi, Cyanobacteria, Saccharibacteria, and Verrucomicrobia were positively correlated with soil nutrients carbon (C), nitrogen (N) and phosphorus (P). A vector analysis of extracellular enzyme activity indicates that soil microbial communities underlying moss biocrusts were limited by P but microbial communities in areas inoculated with the AM fungus had the lowest relative P limitation. The alleviation of microbial P limitation increased the microbial CUE and bacterial phylum community and alpha diversity, leading to an increase in subsoil C content underlying moss biocrusts. This indicates that microbial communities in soil underlying moss biocrusts under in restoration areas containing the AM fungus were more stable under environmental stress, and the inclusion of AM fungal inoculation may be recommended as the preferred option for ecosystem restoration in arid and semi-arid coal mining areas. • Soil microbial communities under moss biocrusts were P-limited. • AM fungal inoculum increased microbial CUE and bacterial biodiversity under biocrusts. • Microbial P limitation was minimum in areas inoculated with the AM fungus. • More diverse soil bacterial communities had higher microbial CUE values. [ABSTRACT FROM AUTHOR]

Summary: Hotspots of N2O emissions are generated from legume residues during decomposition. Arbuscular mycorrhizal fungi (AMF) from co‐cultivated intercropped plants may proliferate into the microsites and interact with soil microbes to reduce N2O emissions. Yet, the mechanisms by which or how mycorrhizal hyphae affect nitrifiers and denitrifiers in the legume residues remain ambiguous. Here, a split‐microcosm experiment was conducted to assess hyphae of Rhizophagus aggregatus from neighbouring maize on overall N2O emissions from stubbles of nodulated or non‐nodulated soybean. Soil microbes from fields intercropped with maize/soybean amended with fertilizer nitrogen (SS‐N1) or unamended (SS‐N0) were added to the soybean chamber only. AMF hyphae consistently reduced N2O emissions by 20.8%–61.5%. Generally, AMF hyphae promoted the abundance of N2O‐consuming (nosZ‐type) denitrifiers and altered their community composition. The effects were partly associated with increasing MBC and DOC. By contrast, AMF reduced the abundance of nirK‐type denitrifiers in the nodulated SS‐N0 treatment only and that of AOB in the non‐nodulated SS‐N1 treatment. Taken together, our results show that AMF reduced N2O emissions from soybean stubbles, mainly through the promotion of N2O‐consuming denitrifiers. This holds promise for mitigating N2O emissions by manipulating the efficacious AMF and their associated microbes in cereal/legume intercropping systems. [ABSTRACT FROM AUTHOR]

Designing an environmentally benign bio-adsorbent for the removal of heavy metal ions from aqueous medium was a sustainable strategy to ensure water safety. Herein, three-dimensional macroscopic aminosilyated nanocellulose aerogels (APTM S -modified TO-NFC) for the removal of heavy metal ions in water were successfully synthesized from bamboo-derived TEMPO-oxidized nanofibrillated cellulose (TO-NFC) and aminopropyltrimethoxysilane (APTMs) via a facile freeze-drying process. Owing to a relatively high BET surface area (129.32 m2 g−1), high porosity (99.14%) as well as high substitution degree of amino groups (0.41), the resulting APTM S -modified TO-NFC aerogel exhibited good adsorption capacity of 99.0, 124.5, and 242.1 mg g−1 for Cu2+, Cd2+ and Hg2+, respectively. Furthermore, the crosslinked and three-dimensionally porous architecture imparted it with relatively high compression strength, good excellent stability in water, and ease of recyclability from water after the usage. The pH value of the solution had a great influence on adsorption efficiency of the aerogel adsorbent, and optimal adsorption efficiency could be achieved at pH 3–7. Thermodynamic parameters suggested the spontaneous and endothermic nature of adsorption process. This work provides a facile method for preparing sustainable bio-adsorbent for effective heavy metal ions removal from aqueous medium. A novel and sustainable APTMs-modified NFC aerogel bio-adsorbent for effective removal of Cu2+, Cd2+ and Hg2+ ions was prepared via a facile freeze-drying of TEMPO oxidized NFC suspension in the presence of APTMs. [Display omitted] [ABSTRACT FROM AUTHOR]

Aims: The rhizosphere microbiome plays an important role in plant growth and behavior during phytoremediation. This work aims to explore how hyperaccumulating plant performance (shoot biomass and Cd uptake) and rhizosphere bacterial community are driven by plant development under a Cd concentration gradient and their relationship during plant growth. Methods: A pot experiment was conducted using the Cd hyperaccumulator Sedum plumbizincicola grown in soil spiked with 0, 5 and 20 mg Cd kg−1 for 13 weeks. Plant performance (shoot biomass and Cd uptake) was determined and the rhizosphere bacterial community was examined by weekly Illumina sequencing. Biomarker genera were identified by the Random Forest model and the functions were predicted by PICRUSt2. Results: The rhizospheres bacterial community tended to stabilize from the 6th or 7th week regardless of the soil Cd concentration, coinciding with the vigorous growth stage of the hyperaccumulator. Biomarker genera Paenibacillus and Streptacidiphilus enriched in the stable stage showed significant positive correlations with Cd uptake. In addition, some predicted gene abundances of enzymes related to plant growth promotion by the rhizosphere bacterial community were influenced to various degrees by plant development and soil Cd concentration. Conclusion: There exists a stable bacterial community in the rhizosphere of S. plumbizincicola during phytoremediation and biomarker taxa enriched at this stage were positively correlated with Cd uptake. Selecting microorganisms that match the developmental stages might further enhance phytoremediation. This provides some theoretical basis for modulating rhizosphere microbes at the appropriate time during phytoextraction to optimize the phytoremediation technique. [ABSTRACT FROM AUTHOR]

Background: Effects on maize were assessed of dual inoculation with arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE) isolated from other plant species. Methods: Suspensions of DSE isolated from Stipa krylovii were prepared at different densities (2, 4, and 8 × 105 CFU mL− 1) and inoculated separately (AMF or DSE) or together (AMF + DSE), to explore their effects on maize growth. Results: Inoculation with AMF or medium and high densities of DSE and combined inoculation (AMF + DSE) increased plant above-ground growth and altered root morphology. Differences in plant growth were attributable to differences in DSE density, with negative DSE inoculation responsiveness at low density. AMF promoted plant above-ground growth more than DSE and the high density of DSE promoted root development more than AMF. Combined inoculation might lead to synergistic growth effects on maize at low density of DSE and competitive effects at medium and high DSE densities. Conclusions: AMF and DSE co-colonized maize roots and they had positive effects on the host plants depending on DSE density. These findings indicate the optimum maize growth-promoting combination of AMF and DSE density and provide a foundation for further exploration of potentially synergistic mechanisms between AMF and DSE in physiological and ecological effects on host plants. [ABSTRACT FROM AUTHOR]

Aims: There is little information available on the potential influence of soil micro-arthropods on the phytoremediation of metal-contaminated soils using hyperaccumulator plants. We hypothesized that soil micro-arthropods may promote organic matter decomposition, thereby releasing nitrogen and enhancing the growth of and metal uptake by hyperaccumulators and thereby increase phytoextraction efficiency. Methods: Four highly contaminated soils with a range of metal contents were used in a pot experiment to study the effects of the collembolan Folsomia candida and the mite Hypoaspis aculeifer on phytoextraction by Sedum plumbizincicola, a cadmium (Cd) and zinc (Zn) hyperaccumulator. Results: Both micro-arthropods survived when the hyperaccumulator grew in the four soils. F. candida slightly increased the growth of S. plumbizincicola and shoot metal concentrations increased significantly in the presence of F. candida with or without H. aculeifer. Soil fauna increased shoot Cd accumulation by 27.9–66.3% compared to corresponding control soils. Similar shoot 15N abundances across treatments and decreasing shoot N content in two of the soils with addition of F. candida indicate that the promotion of phytoextraction was not associated with increasing plant nitrogen uptake from organic matter by F. candida. Conclusions: The mechanism of plant growth promotion might be an interaction between the soil fauna and the roots of the hyperaccumulator and this merits further investigation. This work highlights for the first time a potential role of soil micro-arthropods in the phytoextraction of metal-polluted soils. [ABSTRACT FROM AUTHOR]

Soil particle size may significantly affect metal distribution and stable isotopic behavior. Here, two soils were separated into four particle size fractions, namely fine sand, silt, fine silt, and colloidal particles and used to determine cadmium (Cd) and zinc (Zn) concentrations and isotope compositions. Concentrations of Cd and Zn were generally enriched in the finer particles and positively correlated with the iron (Fe) and manganese (Mn) oxide contents. However, Cd concentration in the fine sand was higher than in the silt fraction due to the higher soil organic matter contents in the former particle fraction. The maximum δ114/110Cd value was found in the colloidal particles (−0.02 and 0.01‰) of both soils while the minimum was in the silt particles (−0.12 and 0.06‰). Incorporation into the mineral lattice of Fe and Mn oxides is suggested to explain the slight enrichment of heavy Cd isotopes in the colloidal fraction. The similar δ66Zn values of the four particle fractions (0.20–0.29‰ with a mean of 0.25‰) indicate similar Zn sources in different particle sizes. Metal isotopic fingerprint of different soil particle size fractions provides further insight into the underlying metal retention mechanisms within soil micro-zones and helps in tracing metal sources and biogeochemical processes. [Display omitted] • Cd and Zn isotopic ratios in four particle size fractions were determined. • Fe and Mn oxides enhanced Cd and Zn retention in the finer particles. • Similar Zn isotope compositions in different particles indicate similar sources. • Incorporation of Cd into Fe/Mn oxides enriched heavy Cd isotopes in the colloidal particles. [ABSTRACT FROM AUTHOR]

Blue carbon ecosystems (BCEs), located at the land-sea interface, provide critical ecological services including the buffering of anthropogenic pollutants. Understanding the interactions between trace element (TE) loads in BCEs and socioeconomic development is imperative to informing management plans to address pollution issues. However, the identification of anthropogenic TE pollution in BCEs remains uncertain due to the complex geochemical and depositional processes and asynchronous socioeconomic development along continental coastlines. Here, priority-controlled TE (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) concentrations in the mangrove, saltmarsh and seagrass soils and plant tissues along the coastline of China were investigated while taking bare flat and upland soils as corresponding references. We demonstrate that blue carbon (BC) soils accumulated markedly higher concentrations of anthropogenic TEs than the reference soils, mainly due to the effective trapping of fine-grained particles and higher binding capacities. We identify the time course of TE changes over the last 100 years which shows increasing anthropogenic TE accumulation resulting from military activities (1930–1950) and the growth of industrial and agricultural activities (1950–1980), then reaching a maximum after national economic reform (1980–2000). Since the 2000s, decreases in TE discharges driven by socioeconomic reform and strengthened environmental regulations have led to a widespread reversal of anthropogenic TE concentrations in BC soils. Based on the current TE flux we estimate that BCEs can filter over 27.3–100 % of the TEs emitted in industrial wastewaters from Chinese coastal provinces annually. However, the uptake of these TEs by plants can be substantially reduced through various mechanisms offered by edaphic properties such as organic carbon, clay, and sulfur contents. Therefore, enhancing TE filtering while preventing TEs from entering food webs through the conservation and restoration of BCEs will greatly aid in achieving the sustainable development goal of the coastal zone under intensified anthropogenic activities. [ABSTRACT FROM AUTHOR]

Chlorinated aliphatic hydrocarbons (CAHs) are potentially toxic substances that have been detected in various contaminated environments. Biological elimination is the main technique of detoxifying CAHs in the contaminated sites, but the soil bacterial community at CAH-contaminated sites have been little investigated. Here, high-throughput sequencing analysis of soil samples from different depths (to 6 m depth) at an aged CAH-contaminated site has been conducted to investigate the community composition, function, and assembly of soil bacteria. The alpha diversity of the bacterial community significantly increased with increasing depth and bacterial community also became more convergent with increasing depth. Organohalide-respiring bacteria (OHRB) is considered keystone taxa to reduce the environmental stress of CAHs by reductive dechlorinate CAHs into nontoxic products, increases the alpha diversity of bacterial community and improves the stability of bacterial co-occurrence network. The high concentration of CAHs in deep soil and the stable anaerobic environment make deterministic processes dominate bacterial community assembly, while the topsoil is dominated by dispersal limitation. In general, CAHs at contaminated sites have a great impact on bacterial community, but the CAHs metabolic community acclimated in deep soil can reduce the environmental stress of CAHs, which provides foundation for the monitored natural attenuation technology in CAHs-contaminated sites. [Display omitted] • Alpha-diversity increased with increasing depth at aged CAHs-contaminated site. • Obligate organohalide respiration played a vital role in bacterial community function. • The complexity and stability of bacterial co-occurrence network increased with increasing depth. • Deterministic processes gradually dominated bacterial community assembly with increasing depth. [ABSTRACT FROM AUTHOR]

[Display omitted] • PCB77 biodegradation efficiency increased significantly in soils treated with endogenous H 2. • Endogenous H 2 selected bacteria harboring PCB degradation genes. • Different taxa conducting successive metabolic steps of PCB metabolism. • Enriched hydrogenotrophic taxa encoding biphenyl oxidation genes drove PCB biodegradation through endogenous H 2. Endogenous hydrogen (H 2) is produced through rhizobium-legume associations in terrestrial ecosystems worldwide through dinitrogen fixation. In turn, this gas may alter rhizosphere microbial community structure and modulate biogeochemical cycles. However, very little is understood about the role that this H 2 leaking to the rhizosphere plays in shaping the persistent organic pollutants degrading microbes in contaminated soils. Here, we combined DNA-stable isotope probing (DNA-SIP) with metagenomics to explore how endogenous H 2 from the symbiotic rhizobium-alfalfa association drives the microbial biodegradation of tetrachlorobiphenyl PCB 77 in a contaminated soil. The results showed that PCB77 biodegradation efficiency increased significantly in soils treated with endogenous H 2. Based on metagenomes of 13C-enriched DNA fractions, endogenous H 2 selected bacteria harboring PCB degradation genes. Functional gene annotation allowed the reconstruction of several complete pathways for PCB catabolism, with different taxa conducting successive metabolic steps of PCB metabolism. The enrichment through endogenous H 2 of hydrogenotrophic Pseudomonas and Magnetospirillum encoding biphenyl oxidation genes drove PCB biodegradation. This study proves that endogenous H 2 is a significant energy source for active PCB-degrading communities and suggests that elevated H 2 can influence the microbial ecology and biogeochemistry of the legume rhizosphere. [ABSTRACT FROM AUTHOR]

Surfactant-enhanced bioremediation (SEBR) is frequently employed to clean up soil polluted with petroleum hydrocarbons, but few studies have focused on how surfactants affect microbial communities and different fractions of petroleum hydrocarbons, particularly in the field. Here, the surfactants sodium dodecyl benzene sulfonate (SDBS), alpha olefin sulfonate (AOS), Triton X-100 (TX-100), Tween80, and rhamnolipid were combined with the oil-degrading bacterium Pseudomonas sp. SB to remediate oil-contaminated soil in the laboratory. AOS gave the highest removal efficiency (65.1%) of total petroleum hydrocarbons (TPHs). Therefore, AOS was used in a field experiment with Pseudomonas sp. SB and the removal efficiency of TPHs and long-chain hydrocarbons C21–C40 reached 57.4 and 53.0%, respectively, significantly higher than the other treatments. During bioremediation the addition of Pseudomonas sp. SB significantly stimulated the growth of bacterial genera such as Alcanivorax , Luteimonas , Parvibaculum , Stenotrophomonas , and Pseudomonas and AOS further stimulated the growth of Sphingobacterium , Pseudomonas and Alcanivorax. This study validates the feasibility of surfactant-enhanced bioremediation in the field and partly reveals the mechanism of surfactant-enhanced bioremediation from the perspective of changes in different fractions of petroleum and microbial community dynamics. [Display omitted] • Surfactant-enhanced bioremediation succeeded in the field. • Surfactant promoted biodegradation of petroleum hydrocarbons, especially C21–C40 fractions. • Surfactant promoted the growth of oil-degrading bacteria. [ABSTRACT FROM AUTHOR]

Layered double hydroxides (LDHs) and their composites are a promising platform for a wide range of applications, especially in the environmental field. However, the facile and efficient synthesis of high-quality LDHs and their composites remains a challenge. Here, an improved co-pyrolysis method has been developed to synthesize LDH/biochar composites. A composite material was prepared by directly anchoring MgFe-LDH on corn stover by co-precipitation with FeCl 3 and Mg(OH) 2 , and then through pyrolysis. The main features of this improved method are the use of the solubility product Mg(OH) 2 to maintain the pH of the mixture at ∼10 (the optimum for LDH precipitation), eliminating the cumbersome pH control steps of the traditional co-precipitation method, and the low rate of solid-liquid reaction to obtain high LDH crystallinity and purity. This produces improved properties of the MgFe-LDH/biochar composite after pyrolysis: higher loading of MgFe-LDH, larger specific surface area of the composite, a more stable layered structure, and a more customizable LDH. The theoretical maximum adsorption capacity of phosphorus for the composite was 379.4 mg L−1 according to an adsorption isotherm study, and the dominant adsorption mechanism is chemical adsorption accompanied by physical adsorption. In actual wastewater applications, >80% of total phosphorus in biogas slurry was removed via adsorption, indicating that the composite is highly efficient in phosphorus selectivity in wastewaters with complex components. Here, a more sustainable synthesis method of LDH/biochar composite has been developed with high application potential. [Display omitted] • A facile innovative method for the synthesis of MgFe-LDH/biochar composites is proposed. • Mg(OH) 2 was used to spontaneously adjust the co-precipitation pH. • MgFe-LDH anchored on biomass using the new method has higher crystallinity and purity. • The derived MgFe-LDH/biochar exhibits an excellent phosphorus removal capability. [ABSTRACT FROM AUTHOR]

Metal pollution of agricultural soils is currently an issue of major concern in China and many soils require remediation. Photovoltaic (PV) power generation is a useful source of renewable energy but solar power plants often require large areas of land. Combining PV power generation with phytoextraction on contaminated arable land is therefore a novel and potential option if these processes can work effectively together. A three-year-long continuous field study was conducted to test the feasibility of phytoextraction using a metal hyperaccumulator species growing under arrays of PV panels. Meteorological data were collected and the growth and cadmium (Cd) and zinc (Zn) uptake of the Cd/Zn hyperaccumulator Sedum plumbizincicola were determined. Shading by the PV panels reduced the annual solar irradiance by 58.4% but this showed no inhibitory effect on plant growth or metal uptake by S. plumbizincicola. Phytoextraction under the PV panels gave high removal efficiencies of Cd and Zn and the hyperaccumulator took up Cd and Zn at rates of 3.40 and 96.2 kg ha−1, respectively, for three seasons. It is concluded that soil phytoextraction and PV electricity generation can be combined to realize soil remediation and energy production. [Display omitted] • Combined phytoextraction with solar power generation is an emerging land-use type. • Cd/Zn hyperaccumulator Sedum plumbizincicola grew well under photovoltaic panels. • Shading by the panels did not inhibit the growth of the hyperaccumulator. • Phytoextraction of polluted soil under PV panels gave high Cd removal efficiencies. [ABSTRACT FROM AUTHOR]

Wheat is the second most important staple food crop, therefore safe and environmentally friendly production of wheat is essential for human safety and health. Southern Jiangsu province is a very important wheat producing region that is highly industrialized with many soils polluted with potentially toxic metals, especially cadmium (Cd). Wheat varieties with low Cd bioconcentration factors (BCF) are often used to decrease Cd accumulation and increase the safety of products in field practice. In addition, the development of local soil safety thresholds, the main focus of soil health management, is also necessary to protect agricultural soil health and agricultural production. However, there is no published literature describing low-Cd-accumulating wheat varieties and soil safety thresholds in this region. Field plot experiments and field investigations at multiple experimental sites in southern Jiangsu province have therefore been conducted for several years to screen low-Cd-accumulating wheat varieties and to derive soil Cd safety thresholds. The varieties Yangmai 25, Zhengmai 12 and Yangmai 12 had stable and low Cd BCF. The deduced safe thresholds of total soil Cd concentrations for protecting 95 % of wheat varieties were 0.17, 0.18, and 0.31 mg kg−1 at 4.5 < pH ≤ 6.5, 6.5 < pH ≤ 7.5 and 7.5 < pH ≤ 9.0, stricter levels than the Chinese national risk screening values. The deduced thresholds were validated to increase the protection rates of wheat by field investigations. In conclusion, wheat varieties with low Cd BCF and soil thresholds can contribute to local soil health management and safe wheat production in southern Jiangsu province. [Display omitted] • Local low-Cd wheat varieties were screened by several years of field experiments. • Deduced safety thresholds of total soil Cd for wheat were stricter than the Chinese national risk screening values. • The deduced safety thresholds increase the protection rates of wheat in southern Jiangsu. • This study contributes to local soil health management and safe wheat production. [ABSTRACT FROM AUTHOR]

[Display omitted] • The CAST model well simulated the effect of fertilization practices on carbon dynamics in a chronosequence; • Free microaggregates in the Fluvaquent were the primary C sequestration fraction under RCP2.6 scenarios; • MNPK treatment promotes C storage in the study soil under current and future climates. Quantifying soil structural dynamics and aggregate turnover is important in understanding soil organic carbon (SOC) stocks, particularly over decadal and larger time scales. Until now it has remained unclear clear how soil aggregate size and its associated carbon respond to both long-term soil fertility and climate change. Here, we explore changes in soil structure and aggregate organic C (OC) stocks under different fertilization practices by combining field chronosequence SOC measurements with dynamic and process modeling in a long-term wheat-maize field experiment on the North China Plain. The fertilization practices comprise no fertilization (CK), chemical fertilization (NPK), and combined manure and NPK treatments (MNPK). The experimental measurements included the mass of OC stocks in different soil aggregate size classes. We used this information to calibrate parameters of the Carbon, Aggregation, and Structure Turnover (CAST) model and to predict future changes in aggregate structure and the resulting OC stocks using the RCP2.6 scenarios that were defined by the outputs of five future climate models from IPCC projection. With trends towards a wetter climate and increasing soil moisture under the RCP2.6 scenarios for the region, soil OC stocks will increase in all three treatments, with the strongest increase under MNPK due to exogenous C inputs. The CAST model output further suggests that changes in microaggregate (250–53 μm) OC stocks in the NPK and MNPK treatments accounted for 78.6 % and 75.3 % of the calculated change in total SOC stocks between the early and late 21st century. In conclusion, our combined data and modeling approach describes changes in soil aggregate C, identifies the primary soil aggregate size class of microaggregates involved in C sequestration in an agricultural soil, and predicts the role of Fluvaquent soils on the North China Plain as a future C sink. [ABSTRACT FROM AUTHOR]

Particulate cadmium (Cd) and zinc (Zn) are ubiquitous in agricultural soils of Pb–Zn mining regions. Water management serves as an important agronomic measure altering the bioavailability of Zn and Cd in soils, but how this affects particulate Cd and Zn and the underlying mechanisms remain largely unknown. Microcosm soil incubation combined with spectroscopic and microscopic characterization was conducted. During a two-year-long incubation period we observed that the concentrations of soil CaCl 2 -extractable Zn and Cd increased 3–10 times in sphalerite-spiked soils and 1–2 times in smithsonite-spiked soils under periodic flooding conditions due to the long-term dissolution of sphalerite (SP) and smithsonite (SM). However, the increase in the concentration of CaCl 2 -extractable metals (Zn: from 0.607 mg kg−1 to 1.051 mg kg−1 and Cd: from 0.047 mg kg−1 to 0.119 mg kg−1) was found only in SP-treatment under continuous flooding conditions, indicating the mobilization of metals. Ultrafiltration analysis shows that the nanoparticulate fraction of Zn and Cd in soil pore water increased 5 and 7 times in SP-treatments under continuous flooding conditions, suggesting the increment of metal pools in soil pore water. HRTEM-EDX-SAED further reveals that these nanoparticles were mainly crystalline ZnS and Zn-bearing sulfate nanoparticles in the SP-treatment and amorphous ZnCO 3 and ZnS nanoparticles in the SM-treatment. Therefore, the formation of the stable crystalline Zn-bearing nanoparticles in the SP-treatment may explain the elevation of the concentration of soil CaCl 2 -extractable Zn and Cd under continuous flooding. The potential mobility of particulate metals should therefore be expected in scenarios of continuous flooding such as paddy soils and wetland systems. • CaCl 2 -extractable Cd and Zn increased in SP-spiked soils under continuous flooding. • Formation of Cd- and Zn-bearing nano-colloids enhanced the extractability of Cd and Zn in soils. • More stable metal-bearing nano-crystals were abundant in SP- than in SM-spiked soil pore water. [ABSTRACT FROM AUTHOR]

Chemical weathering of carbonate-hosted Pb–Zn mines via acid-promoted or oxidative dissolution generates metal-bearing colloids at neutral mine drainage sites. However, the mobility and bioavailability of the colloids associated with metals in nearby soils are unknown. Here, we monitored the mobility of metal(loid)s in soils affected by aeolian deposition and river transport in the vicinity of a carbonate-hosted Pb–Zn mine. Using chemical extraction, ultrafiltration, and microscopic and spectroscopic analysis of metals we find that contamination levels of the soil metals cadmium (Cd), lead (Pb) and zinc (Zn) were negatively correlated with metal extractability. However, nano-scale characterization indicates that colloid-metal(loid) interactions induced potential mobilization and increased risk from metal(loid)s. Dynamic light scattering (DLS) and HRTEM-EDX-SAED analysis further indicate that organic matter (OM)-rich nano-colloids associated with calcium (Ca), silicon (Si) and iron (Fe) precipitates accounted for the majority of the dissolved metal fractions in carbonate-hosted Pb–Zn mine soils. More stable nano-crystals (ZnS, ZnCO 3 , Zn-bearing sulfates, hematite and Al–Si–Fe compounds) were present in the pore water of aeolian-impacted upland soils rather than in river water-impacted soils. Our results suggest that future work should consider the possibility that potential mobilization of metal(loid)s induced by the weathering and transformation of these metal-bearing nano-crystals to metal-bearing amorphous colloids, potentially elevating metal mobility and/or bioavailability in river water-impacted agricultural soils. [Display omitted] • Soil metal levels were negatively correlated with soil metal extractability. • More water-dispersive colloids are bound to trace metals than base metals. • Abundant nano-colloids promoted the mobilization of metals in mine-impacted soils. • Formation of nanocrystals induced sequestration of metals in aeolian-impacted soil. • Formation of amorphous colloids induced metal mobilization in river-impacted soils. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal (AM) fungi form potentially symbiotic associations with most crop species and potentially increase crop phosphorus (P) uptake in intensive cropping systems. Their widespread use, however, remains restrained by our limited understanding of the processes that determine the outcome of the associations. Here, we have used 32P to quantify the delivery of P to maize (Zea mays L.) and wheat (Triticum aestivum L.) via indigenous AM fungi in compartmented pots under high- and low-P conditions. Soil P level was important in driving shoot P uptake via the direct root pathway (DP) or the mycorrhizal pathway (MP). The MP contribution reached 81.8 and 75.8%, respectively, in maize and wheat at low P status but declined to 40.6 and 9.1% at high P. The abundance of intraradical and extraradical colonization and the relative abundance of Rhizophagus and shoot P utilization efficiency (PUE) significantly impacted the MP contribution. Larger mycorrhizal P and growth responses were closely related to a higher MP contribution and shoot PUE in maize but only P response was significantly related to the latter in wheat. These results suggest that crops can acquire considerable amounts of P via the MP with indigenous AM fungi, especially at low P levels, and highlight the importance of plant and AM fungal identity in regulating the relationship between hidden P uptake and symbiotic outcomes. Therefore, manipulation of fertilizer P application rates to optimize the abundance and assemblage of the indigenous AM fungi and crop PUE to increase MP activity and symbiotic outcomes may contribute to the efficient utilization of AM fungi in intensive cropping systems. • Crops took up considerable amounts of P via AM fungi but were regulated by P level. • AMF colonization, Rhizophagus abundance and shoot PUE affected the MP contribution. • The relationship between MP contribution and MGR differed between maize and wheat. [ABSTRACT FROM AUTHOR]

Two phylogenetically distantly-related IncF plasmids, F and pED208, serve as important models for mechanistic and structural studies of F-like type IV secretion systems (T4SS F s) and F pili. Here, we present the pED208 sequence and compare it to F and pUMNF18, the closest match to pED208 in the NCBI database. As expected, gene content of the three cargo regions varies extensively, although the maintenance/leading regions (MLRs) and transfer (Tra) regions also carry novel genes or motifs with predicted modulatory effects on plasmid stability, dissemination and host range. By use of a Cre recombinase assay for translocation (CRAfT), we recently reported that pED208-carrying donors translocate several products of the MLR (ParA, ParB1, ParB2, SSB, PsiB, PsiA) intercellularly through the T4SS F. Here, we extend these findings by reporting that pED208-carrying donors translocate 10 additional MLR proteins during conjugation. In contrast, two F plasmid-encoded toxin components of toxin-antitoxin (TA) modules, CcdB and SrnB, were not translocated at detectable levels through the T4SS F. Remarkably, most or all of the pED208-encoded MLR proteins and CcdB and SrnB were translocated through heterologous T4SSs encoded by IncN and IncP plasmids pKM101 and RP4, respectively. Together, our sequence analyses underscore the genomic diversity of the F plasmid superfamily, and our experimental data demonstrate the promiscuous nature of conjugation machines for protein translocation. Our findings raise intriguing questions about the nature of T4SS translocation signals and of the biological and evolutionary consequences of conjugative protein transfer. • pED208 genome comparisons underscores mosaicism of F plasmids • Diversification of conjugation systems influences plasmid transfer and host range • Leading region proteins are co-translocated with the F plasmid during conjugation • Leading region proteins are translocated through heterologous conjugation systems • Conjugation systems translocate a large repertoire of proteins substrates [ABSTRACT FROM AUTHOR]

Zero-valent iron (ZVI) is widely used to mitigate environmental pollutants such as chlorinated pesticides through reductive reactions accompanied by extensive impacts on the soil microbial community. However, whether and how ZVI changes the biodegradation of target compounds remain poorly understood. Here, we monitor the fate of lindane using a 14C-labled tracer and evaluate the growth and functions of the bacterial community in ZVI-stressed conditions in a historically γ-hexachlorocyclohexane (lindane)-contaminated soil using a combination of isotopic (18O-H 2 O) and metagenomic methods. ZVI promoted the biomineralization of lindane in a dose-dependent manner. Soil bacteria were inhibited by amendment with ZVI during the initial stages of incubation (first three days) but recovered during the subsequent six weeks. Metagenomic study indicates that the todC1 / bedC1 genes involved in the oxidation of dechlorinated lindane intermediates were upregulated in the 18O-labeled bacterial community but the presence of the lin genes responsible for lindane dechlorination was not confirmed. In addition, the benzoate biodegradation pathway that links to downstream catabolism of lindane was enhanced. These findings indicate successive chemical and biological degradation mechanisms underlying ZVI-enhanced lindane mineralization and provide a scientific basis for the inclusion of an extended bioremediation stage in the environmental application of ZVI materials. [Display omitted] • ZVI enhanced lindane removal by increasing mineralization and NER formation. • ZVI promoted the biomineralization of lindane in a dose-dependent manner. • Bacterial growth was inhibited by ZVI in the initial stage but recovered later. • Lin gene responsible for lindane dechlorination was not confirmed. • Pathway that links to downstream catabolism of lindane was enhanced by ZVI. [ABSTRACT FROM AUTHOR]

Cadmium (Cd)-bearing sphalerite and smithsonite ore particles are ubiquitous in soils near metal-mining areas. Previous studies indicate that smithsonite is more readily dissolved in acidic waters and soils than sphalerite but the mobility of Cd and zinc (Zn) derived from these ores in soils is unknown. Using microcosm incubation experiments and microscopic and spectroscopic analysis, we found that the mobility of Cd and Zn derived from smithsonite is higher than from sphalerite. The mobilization rates of Cd (16.6%) and Zn (13.7%) released from smithsonite in soils after 30-day incubation experiments were higher than those from sphalerite (Cd, ~ 1.42%; Zn, ~ 0.75%). Moreover, the percentages of Cd2+ and Zn2+ in soil pore water showed a dynamic increase in smithsonite-spiked treatments but a decrease in sphalerite-spiked treatments. HRTEM-EDX-SAED analysis further indicates the occurrence of dynamic transformation of amorphous Cd and Zn species in soil pore water to crystalline ZnS and iron oxides in sphalerite-spiked soil but crystalline ZnCO 3 nanoparticles were dynamically transformed to amorphous metal-bearing species in smithsonite-spiked soil. The opposite transformation trends in pore water of Zn ore-spiked soils provide new insights into the Cd environmental risks in soils affected by Zn mining. [Display omitted] • High mobility or bioavailability of Cd and Zn were found in SM-spiked soils. • First-order kinetic well-fitted the release of Cd and Zn derived from Zn ores. • Crystalline Zn-bearing nanoparticle dynamic transformed to amorphous colloids in SM-spike soil pore water. • Zn-bearing amorphous colloids dynamic transformed to nano-crystals in SP-spiked soil pore water. • The formation of metal-bearing nano-crystals may be frequent in the karst soil pore water. [ABSTRACT FROM AUTHOR]

The remediation effects of hydrogen peroxide (H 2 O 2) oxidation and surfactant-leaching alone or in combination on three typical oilfield sludges were studied. The removal efficiency of total petroleum hydrocarbons (TPHs) of Jidong, Liaohe and Jiangsu oil sludges by hydrogen peroxide oxidation alone was very poor (6.5, 6.8, and 3.4 %, respectively) but increased significantly (p < 0.05), especially of long-chain hydrocarbons, by combining the use of H 2 O 2 with surfactants (80.0, 79.8 and 82.2 %, respectively). Oxidation combined with leaching may impair microbial activity and organic manure was therefore added to the treated sludges for biostimulation and the composition and function of the microbial community were studied. The addition of manure rapidly restored sludge microbial activity and significantly increased the relative abundance of some salt-tolerant and alkali-tolerant petroleum-degrading bacteria such as Corynebacterium , Pseudomonas , Dietzia and Jeotgalicoccus. Moreover, the relative abundance of two classic petroleum-degrading enzyme genes, alkane 1-monooxygenase and catechol 1, 2-dioxygenase, increased significantly. • Peroxide combined with surfactant leaching enhanced C16–C40 fraction of TPH removal. • Manure application can rapidly restore the ecological function of treated sludges. • Relative abundances of two petroleum degradation genes increased significantly in treated sludge. [ABSTRACT FROM AUTHOR]