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Both indigenous arbuscular mycorrhizal (AM) fungi and phosphate solubilizing bacteria (PSB) are involved in phosphorus (P) mobilization and turnover in agroecosystems. Understanding the diversity and community structure of AM fungi and PSB is important for potentially optimizing their role in mining P for sustainable agriculture. Yet the characteristics of both AM fungi and PSB in response to P input, in particular the influence of different indigenous microbial communities on plant growth has been little studied. Here, we collected soil samples from the top 20 cm of the profile of a soil receiving three fertilizer P rates, comprising nil, optimal (44 kg P ha −1 ) and excessive (131 kg P ha −1 ) P to evaluate the AM fungal community structure and abundance of relevant PSB groups at three sampling times (June, July and September) using 454 pyrosequencing and quantitative-PCR (q-PCR), respectively. In addition, a pot experiment was conducted to investigate the feedback effects of different fractions of indigenous soil microbes on maize seedling growth. The results showed that overall sampling time had a greater impact than P application rate on the community structure of AM fungi and PSB abundance. At each sampling time the AM fungal communities were significantly affected by the fertilizer P rate. The overall abundance of soil microbes and selected taxa were slightly affected by sampling time but not by fertilizer P. Shoot biomass and P nutrition were significantly affected by the microbial community fraction but not by the fertilizer P rate. Changes in AM fungal communities did not lead to significant differences in maize growth. However, long-term absence of P inputs tended to build up microbial communities which greatly suppressed maize growth. Shoot biomass showed a mean decline of 24.4% when grown in inoculated soil compared to sterilized soil. Our results indicate that current P management has not led to negative influences on soil microbial communities. Evidence highlights the need to understand the interactions between plants and microbiome in mining P in order to make maximum use of the most effective indigenous soil microbes for sustainable agriculture. [ABSTRACT FROM AUTHOR]

Abstract: The bacterial type IV secretion systems (T4SSs) translocate DNA and protein substrates to bacterial or eukaryotic target cells generally by a mechanism dependent on direct cell-to-cell contact. The T4SSs encompass two large subfamilies, the conjugation systems and the effector translocators. The conjugation systems mediate interbacterial DNA transfer and are responsible for the rapid dissemination of antibiotic resistance genes and virulence determinants in clinical settings. The effector translocators are used by many Gram-negative bacterial pathogens for delivery of potentially hundreds of virulence proteins to eukaryotic cells for modulation of different physiological processes during infection. Recently, there has been considerable progress in defining the structures of T4SS machine subunits and large machine subassemblies. Additionally, the nature of substrate translocation sequences and the contributions of accessory proteins to substrate docking with the translocation channel have been elucidated. A DNA translocation route through the Agrobacterium tumefaciens VirB/VirD4 system was defined, and both intracellular (DNA ligand, ATP energy) and extracellular (phage binding) signals were shown to activate type IV-dependent translocation. Finally, phylogenetic studies have shed light on the evolution and distribution of T4SSs, and complementary structure-function studies of diverse systems have identified adaptations tailored for novel functions in pathogenic settings. This review summarizes the recent progress in our understanding of the architecture and mechanism of action of these fascinating machines, with emphasis on the ‘archetypal’ A. tumefaciens VirB/VirD4 T4SS and related conjugation systems. This article is part of a Special Issue entitled: Protein trafficking and secretion in bacteria. Guest Editors: Anastassios Economou and Ross Dalbey. [Copyright &y& Elsevier]

Abstract: Nitrogen (N) is a crucial nutrient that requires careful management in intensive cropping systems because of its diverse beneficial and detrimental effects. Here we propose the concept of theoretical N rate (TNR) to answer the important question of how much fertilizer N should be applied to intensive systems based on the N fluxes due to transformation processes in the soil–crop–environment continuum. We define TNR as the theoretically calculated fertilizer N rate with the quantitative relationships of the core N fluxes among fertilizer N, soil N and crop uptake N in the crop root zone to obtain high target yield, maintain soil N balance and minimize environmental risk. We deduced one basic mathematical expression (Nfert =Nuptake −Nstraw +Nfert3) and two simplified expressions [Nfert =(Nuptake −Nstraw)/(1−Coeff); Nfert ≅Nuptake] for calculating the TNR. These expressions do not need much field experimentation or elaborate soil and plant testing to obtain information on crop N demand and soil N supply, and are simple to implement in farming practice to provide a very cost-effective approach. We consider this scheme to be a useful contribution to rational fertilizer practice, especially in developing countries where other N recommendation systems are usually not available and agricultural extension services are poorly developed or absent. [Copyright &y& Elsevier]

Abstract: Greenhouse field experiments on tomato were carried out at Shouguang, Shandong province, over four double cropping seasons between 2004 and 2008 in order to understand the effects of manipulating root zone N management (RN) on fruit yields, N savings and N losses under conventional furrow irrigation. About 72% of the chemical N fertilizer used in conventional treatment (CN) inputs could be saved using the RN treatment without loss of yield. The cumulative fruit yields were significantly higher in the RN treatment than in the CN treatment. Average seasonal N from irrigation water (118kgNha−1), about 59% of shoot N uptake, was the main nitrogen source in treatments with organic manure application (MN) and without organic manure or nitrogen fertilizer (NN). N losses in the RN treatment were lowered by 54% compared with the CN treatment. Lower N losses were found in the MN and NN treatments due to excessive inputs of organic manure and fruit yields were consequently substantially affected in the NN treatment. The critical threshold of Nmin supply level in the root zone (0–30cm) should be around 150kgNha−1 for sustainable production. April to May in the winter–spring season and September to October in the autumn–winter season are the critical periods for root zone N manipulation during crop growth. However, control of organic manure inputs is another key factor to further reduce surplus N in the future. [Copyright &y& Elsevier]

Abstract: A split-root experiment investigated the effects of inoculation with the arbuscular mycorrhizal fungus Glomus mosseae and arsenic (As) addition on As uptake by Pteris vittata L. Either part or all of the root system was inoculated with G. mosseae or exposed to As addition (50ml 1000μmolL−1 As 1 week before harvest). Mycorrhizal colonization substantially increased frond and root dry weight and P and As contents irrespective of As addition. Frond As contents in mycorrhizal plants were highest when the whole root system was exposed to As. Frond As concentrations and contents were higher when inoculation and As addition were in the same parts of the root system than when spatially separate. There were positive effects of arbuscular mycorrhiza inoculation on plant growth and As uptake, and inoculation of part of the roots seemed to be as effective as inoculation of the whole root system. [Copyright &y& Elsevier]

The translocation of DNA across biological membranes is an essential process for many living organisms. In bacteria, type IV secretion systems (T4SS) are used to deliver DNA as well as protein substrates from donor to target cells. The T4SS are structurally complex machines assembled from a dozen or more membrane proteins in response to environmental signals. In Gram-negative bacteria, the conjugation machines are composed of a cell envelope-spanning secretion channel and an extracellular pilus. These dynamic structures (i) direct formation of stable contacts—the mating junction—between donor and recipient cell membranes, (ii) transmit single-stranded DNA as a nucleoprotein particle, as well as protein substrates, across donor and recipient cell membranes, and (iii) mediate disassembly of the mating junction following substrate transfer. This review summarizes recent progress in our understanding of the mechanistic details of DNA trafficking with a focus on the paradigmatic Agrobacterium tumefaciens VirB/D4 T4SS and related conjugation systems. [Copyright &y& Elsevier]

[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]

Biochars and hyperaccumulators have been widely used for the remediation of trace metal contaminated soils through immobilization and phytoextraction. These two options have rarely been used simultaneously despite their potential to achieve a greater decline in trace metal availability and higher removal efficiency in polluted soils. This study investigated the combined effects of biochar and the cadmium/zinc (Cd/Zn) hyperaccumulator Sedum plumbizincicola in a pot experiment and examined the effect of an antibiotic (oxytetracycline, OTC) in an acid soil spiked with Cd/Zn alone and with OTC. Biochar amendment alone significantly decreased soil CaCl 2 -extractable Cd and Zn by 22.7 and 43.1%, respectively. Growing S. plumbizincicola alone resulted in 11.3% Cd and 3.88% Zn removal after ten weeks of phytoextraction. Growing S. plumbizincicola with biochar resulted in higher decreases in extractable Cd and Zn by 60.0% and 53.2%, respectively, and more than three times Cd and Zn removal efficiencies compared to growing S. plumbizincicola without biochar. The results indicate that biochar addition promoted plant growth and increased shoot trace metal concentrations, consequently increasing the removal efficiency and that soil trace metal removal by the hyperaccumulator further reduced the extractable trace metals in addition to immobilization by biochar. Biochar amendment decreased plant OTC concentrations. However, OTC showed no effect on trace metal phytoextraction. Results indicate that the simultaneous use of biochar and the hyperaccumulator can give high Cd/Zn phytoextraction efficiency in terms of both soil total and available trace metal concentrations in acid soils highly contaminated with trace metals or trace metals and OTC. [ABSTRACT FROM AUTHOR]

High-throughput quantitative polymerase chain reaction (PCR) of antibiotic resistance genes (ARGs) was used to profile the composition and diversity of ARGs in biosolid-amended soil and in lettuce roots and shoots. Biosolid application significantly increased the ARGs in soil and influenced the soil antibiotics resistome mainly through exogenous introduction. Four dominant ARGs occurred in sterilized and water-washed leaves, namely catB8 , php , vanB and str , which accumulated to >50% of total abundance. Nine subclasses of ARGs were determined in both sterilized and water-washed leaves, and they were shared ARGs among soil, roots and shoots. This suggests that the ARGs in ready-to-eat lettuce were mainly located in endophytes and the internal route may contribute more to the ARGs in routinely consumed raw lettuce. Moreover, a previously unsuspected shift in multridrug ARGs to root and shoot compartments due to biosolid application was discovered. These results reveal that biosolid application drives the evolution and dissemination of ARGs in the soil-plant system. [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]

Phthalate esters (PAEs) are suspected of having adverse effects on human health and have been frequently detected in soils and vegetables. The present study investigated their occurrence and composition in plastic film greenhouse soil–vegetable systems and assessed their potential health risks to farmers exposed to these widespread pollutants. Six priority control phthalates, namely dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate (DnBP), butyl benzyl phthalate (BBP), di-(2-ethylhexyl) phthalate (DEHP) and di-n-octyl phthalate (DnOP), were determined in 44 plastic film greenhouse vegetables and corresponding soils. Total PAEs ranged from 0.51 to 7.16 mg kg − 1 in vegetables and 0.40 to 6.20 mg kg − 1 in soils with average concentrations of 2.56 and 2.23 mg kg − 1 , respectively. DnBP, DEHP and DnOP contributed more than 90% of the total PAEs in both vegetables and soils but the proportions of DnBP and DnOP in vegetables were significantly ( p < 0.05) higher than in soils. The average concentrations of PAEs in pot herb mustard, celery and lettuce were > 3.00 mg kg − 1 but were < 2.50 mg kg − 1 in the corresponding soils. Stem and leaf vegetables accumulated more PAEs. There were no clear relationships between vegetable and soil PAEs. Risk assessment indicates that DnBP, DEHP and DnOP exhibited elevated non-cancer risk with values of 0.039, 0.338 and 0.038, respectively. The carcinogenic risk of DEHP was about 3.94 × 10 − 5 to farmers working in plastic film greenhouses. Health risks were mainly by exposure through vegetable consumption and soil ingestion. [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]

• 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]

Bacteria use type IV secretion (T4S) systems to deliver DNA and protein substrates to a diverse range of prokaryotic and eukaryotic target cells. T4S systems have great impact on human health, as they are a major source of antibiotic resistance spread among bacteria and are central to infection processes of many pathogens. Therefore, deciphering the structure and underlying translocation mechanism of T4S systems is crucial to facilitate development of new drugs. The last five years have witnessed considerable progress in unraveling the structure of T4S system subassemblies, notably that of the T4S system core complex, a large 1 MegaDalton (MDa) structure embedded in the double membrane of Gram-negative bacteria and made of 3 of the 12 T4S system components. However, the recent determination of the structure of ∼3 MDa assembly of 8 of these components has revolutionized our views of T4S system architecture and opened up new avenues of research, which are discussed in this review. [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]

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]

Abstract: The bacterial type IV secretion systems (T4SSs) comprise a biologically diverse group of translocation systems functioning to deliver DNA or protein substrates from donor to target cells generally by a mechanism dependent on establishment of direct cell-to-cell contact. Members of one T4SS subfamily, the conjugation systems, mediate the widespread and rapid dissemination of antibiotic resistance and virulence traits among bacterial pathogens. Members of a second subfamily, the effector translocators, are used by often medically-important pathogens to deliver effector proteins to eukaryotic target cells during the course of infection. Here we summarize our current understanding of the structural and functional diversity of T4SSs and of the evolutionary processes shaping this diversity. We compare mechanistic and architectural features of T4SSs from Gram-negative and -positive species. Finally, we introduce the concept of the ‘minimized’ T4SSs; these are systems composed of a conserved set of 5–6 subunits that are distributed among many Gram-positive and some Gram-negative species. [Copyright &y& Elsevier]

Abstract: Phytoremediation of phthalic esters (PAE) polluted agricultural soils near electrical-waste dismantling areas in east China is a topic of much public concern. In this study, monocropping and intercropping of alfalfa (Medicago sativa L.), Elsholtzia splendens and Sedum plumbizincicola were compared for their potential in phytoremediation of contaminated soil. Regardless of whether alfalfa was cultivated in monoculture (A) or in combination with E. splendens (AE) or with S. plumbizincicola (AS), and also with all three (AES) in intercropping, concentrations of six PAEs in soil were significantly reduced (p < 0.01) by 87.2, 91.2, 87.2 and 89.4% compared to the control. Intercropping enhanced the decline in soil PAEs and increased soil microbial biomass and microbial functional diversity, and alfalfa shoots and roots took up more of the target pollutants than the other two plant species. DEHP was the most abundant of the target PAEs in soil, roots and shoots. The biological concentration factors (BCFs) of alfalfa in monoculture were relatively high, but the transfer factor (TF) and phytoextraction efficiency, which ranged from 1.16 to 1.69 %, were higher in intercropping systems. Thus, rhizospheric remediation by intercropping of the three-species contributed to PAE removal from the soil and may represent a promising in situ bioremediation strategy for PAE contaminated soils. [Copyright &y& Elsevier]

Abstract: The effects of repeated synthetic fertilizer or cattle slurry applications at annual rates of 50, 100 or 200m3 ha−1 yr−1 over a 38 year period were investigated with respect to herbage yield, N uptake and gross soil N dynamics at a permanent grassland site. While synthetic fertilizer had a sustained and constant effect on herbage yield and N uptake, increasing cattle slurry application rates increased the herbage yield and N uptake linearly over the entire observation period. Cattle slurry applications, two and four times the recommended rate (50m3 ha−1 yr−1, 170kgNha−1), increased N uptake by 46 and 78%, respectively after 38 years. To explain the long-term effect, a 15N tracing study was carried out to identify the potential change in N dynamics under the various treatments. The analysis model evaluated process-specific rates, such as mineralization, from two organic-N pools, as well as nitrification from NH4 + and organic-N oxidation. Total mineralization was similar in all treatments. However, while in an unfertilized control treatment more than 90% of NH4 + production was related to mineralization of recalcitrant organic-N, a shift occurred toward a predominance of mineralization from labile organic-N in the cattle slurry treatments and this proportion increased with the increase in slurry application rate. Furthermore, the oxidation of recalcitrant organic-N shifted from a predominant NH4 + production in the control treatment, toward a predominant NO3 − production (heterotrophic nitrification) in the cattle slurry treatments. The concomitant increase in heterotrophic nitrification and NH4 + oxidation with increasing cattle slurry application rate was mainly responsible for the increase in net NO3 − production rate. Thus the increase in N uptake and herbage yield on the cattle slurry treatments could be related to NO3 − rather than NH4 + production. The 15N tracing study was successful in revealing process-specific changes in the N cycle in relationship to long-term repeated amendments. [Copyright &y& Elsevier]

Iron plaque is ubiquitously formed on the root surfaces of rice. However, little is known about the role of iron plaque in Cd movement from soil to the plant aboveground parts. A pot experiment was conducted to investigate the influence of iron plaque in Cd uptake and accumulation by rice seedlings in soil. Rice seedlings were pre-cultivated in solution culture for 16 days. Two seedlings were transplanted in a nylon bag containing no substrate but surrounded by soil amended with Fe and Cd combined at rates of 0, 1, or 2 g Fe kg−1 and 0, 2.0, or 10 mg Cd kg−1 soil. Fe was added to induce different amounts of iron plaque, and Cd to simulate Cd-polluted soils. Plants were grown for a further 43 days and then harvested. The length of the longest leaf and SPAD values of the newly mature leaves were measured during plant growth. Fe and Cd concentrations were determined in dithionite–citrate–bicarbonate (DCB) soil extracts and in plant roots and shoots. Shoot and root dry weights were significantly affected by Fe supply level but not by added Cd. Root dry weight declined with increasing Fe supply but shoot dry weight decreased at 2 g Fe kg−1 and increased at 1 g Fe kg−1 (except at 2 mg Cd kg−1). The length of the longest leaf and SPAD values of the newly mature leaves were significantly affected by plant growth stage and added Fe and Cd. Fe tended to diminish the negative effect of Cd on these two parameters. Cd concentrations in DCB extracts increased with increasing Cd and Fe supply. In contrast, external Fe supply markedly reduced shoot and root Cd concentrations and there was generally no significant difference between the two Fe supply levels. Shoot and root Cd concentrations increased with increasing Cd addition. Root Cd concentrations were negatively correlated with root Fe concentrations. The proportion of Cd in DCB extracts was significantly lower than in roots or shoots. The results indicate that enhanced Fe uptake by plants can diminish the negative effects of Cd to some extent and that iron plaque on root surfaces is of little significance in affecting uptake and accumulation of Cd by rice plants. [Copyright &y& Elsevier]

Abstract: The effects of arbuscular mycorrhizal (AM) fungus (Glomus mosseae) and phosphorus (P) addition (100 mg/kg soil) on arsenic (As) uptake by maize plants (Zea mays L.) from an As-contaminated soil were examined in a glasshouse experiment. Non-mycorrhizal and zero-P addition controls were included. Plant biomass and concentrations and uptake of As, P, and other nutrients, AM colonization, root lengths, and hyphal length densities were determined. The results indicated that addition of P significantly inhibited root colonization and development of extraradical mycelium. Root length and dry weight both increased markedly with mycorrhizal colonization under the zero-P treatments, but shoot and root biomass of AM plants was depressed by P application. AM fungal inoculation decreased shoot As concentrations when no P was added, and shoot and root As concentrations of AM plants increased 2.6 and 1.4 times with P addition, respectively. Shoot and root uptake of P, Mn, Cu, and Zn increased, but shoot Fe uptake decreased by 44.6%, with inoculation, when P was added. P addition reduced shoot P, Fe, Mn, Cu, and Zn uptake of AM plants, but increased root Fe and Mn uptake of the nonmycorrhizal ones. AM colonization therefore appeared to enhance plant tolerance to As in low P soil, and have some potential for the phytostabilization of As-contaminated soil, however, P application may introduce additional environmental risk by increasing soil As mobility. [Copyright &y& Elsevier]

Bacteria use type IV secretion systems (T4SS) to translocate macromolecular substrates destined for bacterial, plant or human target cells. The T4SS are medically important, contributing to virulence-gene spread, genome plasticity and the alteration of host cellular processes during infection. The T4SS are ancestrally related to bacterial conjugation machines, but present-day functions include (i) conjugal transfer of DNA by cell-to-cell contact, (ii) translocation of effector molecules to eukaryotic target cells, and (iii) DNA uptake from or release to the extracellular milieu. Rapid progress has been made toward identification of type IV secretion substrates and the requirements for substrate recognition. [Copyright &y& Elsevier]

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]

The article presents reply to the researcher who has raised issues relating to article titled "Exposure of soil collembolans to microplastics perturbs their gut microbiota and alters their isotopic composition". Author replies that toxicology has to be followed in determining doseresponse relationships but objective of their study was not routine toxicology and they have used five replicates for comparing differences in the reproduction and growth between two treatments.

Changes in the biogeochemical cycling of mercury (Hg) and Hg species were investigated in a typical marine aquaculture area located at Zhoushan island, Zhejiang province, east China. Mercury species were analyzed in different environmental samples collected during a field survey and a simulation batch experiment. The field work comprised both summer and winter collection of water and sediment samples from marine aquaculture sites (MAS) in a field survey and from corresponding reference sites (CRS) located 2500 m from the MAS. THg concentrations in water were 91.3 ± 70.3 and 115 ± 22.6 pmol L−1 in summer and winter, respectively. Particulate Hg accounting for ˃60% of THg and positively correlated with total suspended solid content in water. Dissolved organic carbon in water was positively correlated with dissolved Hg. Significantly higher (p < 0.001, F = 102) total methylmercury (TMeHg) contents were observed in MAS (0.31 ± 0.26 ng g−1) than in CRS (0.06 ± 0.03 ng g−1) in the sediment solid phase. Moreover, MeHg formation rate in MAS was clearly higher than in CRS in the simulation experiment. Both the field survey and the simulation experiment highlighted the readier formation of MeHg in MAS than in CRS. TMeHg levels in blackhead seabream (Acanthopagrus schlegelii), red snapper (Lutjanus campechanus) and perch (Perca fluviatilis) were only 52.7 ± 5.74, 23.7 ± 2.51 and 24.3 ± 3.86 ng g−1, values significantly lower than the safety guideline (1000 ng g−1) established by the World Health Organization. Unlabelled Image • THg concentration in water was 91.3 pmol·L−1 and PHg account for 63.4% of THg. • Fish farming increased THg accumulation and MeHg formation in sediment. • Suspended solid influence the Hg distribution and sedimentation in water. • MeHg concentration in fish tissues was significantly lower than WHO guidelines. [ABSTRACT FROM AUTHOR]

Rapid industrialization and urbanization have accelerated the contamination of paddy soils with potentially toxic elements (PTEs). However, the status and the key factors responsible for the geographical variation in PTE concentrations in rice remain poorly understood. Here, a total of 113 pairs of soil and rice plant samples were collected from 19 provinces in four major rice producing areas of China to assess the geographical variation in total arsenic (As), cadmium (Cd) and lead (Pb) concentrations in the soil-rice system. Average total concentrations of As, Cd and Pb were 11.8, 0.45 and 25.7 mg kg−1, respectively, in the soils and 0.089, 0.087 and 0.036 mg kg−1 in the polished rice. The national maximum allowable concentrations of total soil As and Cd were exceeded in 6.19 and 33.6% of soils and that of Cd was exceeded in 7.96% of polished rice and no polished rice exceed the Pb limit. The As, Cd and Pb concentrations of rice were significantly and positively correlated (p < 0.05) with their corresponding soil available concentrations rather than with their soil total concentrations. Due to the combined effects of local rice varieties, cultivation of varieties with high Cd translocation factors and high Cd availability in acid soils, the highest rice Cd risk occurred in south China. The Cd concentrations in polished rice exceeded the maximum allowable by 4.0 and 15.8% in uncontaminated and contaminated soils, respectively. Results from 113 fixed samples may represent the actual current As, Cd and Pb status of rice in the main rice production areas nationally as they were very consistent with 574 random samples. In view of the high Cd contamination risk in acid soils of south China, countermeasures are needed to minimize Cd accumulation in rice crops in this region. Unlabelled Image • 113 paired paddy soil and rice samples collected from 19 Chinese provinces • High geographical variation in soil and rice PTEs (As, Cd and Pb) concentrations • Rice grown in acid unpolluted soils in south China at risk of Cd contamination • Soil properties, PTEs availabilities and rice genotypes influenced plant PTEs uptake. [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]

Abstract Diphenylarsinic acid (DPAA) is an organoarsenic compound derived from abandoned chemical weapons. DPAA sorption by iron (hydr)oxides is of considerable importance but remains largely unexplored. The current study aimed at investigating the sorption mechanisms of DPAA on ferrihydrite, goethite and hematite using both macroscopic sorption kinetics and sequential extraction procedure (SEP) as well as microscopic Fourier transformed infrared (FTIR) and extended X-ray absorption fine structure (EXAFS) spectroscopic techniques. Sorption kinetics studies show that >93% of added DPAA (4–100 mg L−1) was sorbed on ferrihydrite and hematite within 5 min, while only 84% of added DPAA (100 mg L−1) was sorbed on goethite after 24 h. The sequential extraction results and FTIR measurements reveal that DPAA formed simultaneously inner- and outer-sphere complexes on goethite and hematite, but predominantly inner-sphere complexes on ferrihydrite with limited formation of outer-sphere complexes (<15%). A combination of SEP, FTIR and EXAFS techniques further enables identification of the interfacial reactions between DPAA and solid surfaces of iron (hydr)oxides and the mechanisms involved. Results indicate that DPAA interacted with these iron (hydr)oxides via (1) electrostatic attraction or hydrogen bonding, (2) surface complexation and (3) complexation embedded inside the mineral particles. EXAFS studies further demonstrate that DPAA formed mainly bidentate binuclear corner-sharing (2 C) complexes regardless of the iron substrate, with As-Fe distances at 3.19–3.32 Å. Comparison of these results with available data in the literature on inorganic, methyl and phenyl arsenics (As) suggests that it is the phenyl group substitution that finally determines the predominance of 2 C complexes. Results from the present study will improve our knowledge of DPAA interaction with solid surfaces and may help in the prediction of the environmental fate and environmental risk management of DPAA in the soil-water system. Graphical abstract Unlabelled Image Highlights • We first investigated DPAA sorption on goethite and hematite. • DPAA formed both inner- and outer-sphere bonds on goethite and hematite. • DPAA formed predominantly inner-sphere bonds on ferrihydrite. • Inner-sphere bond was formed via complexation on the surface and embedded inside. • The dominant inner-sphere bonds of DPAA were identified as bidentate binuclear. [ABSTRACT FROM AUTHOR]

Abstract Two common organic wastes from agriculture (rice straw) and forestry (sawdust) were applied to a petroleum-contaminated soil to estimate their effectiveness in the removal of total petroleum hydrocarbons (TPHs) and polycyclic aromatic hydrocarbons (PAHs). Rice straw was the more effective amendment than the other treatments in reducing TPH contents and addition of sawdust resulted in a significant decrease in PAH removal, particularly high-molecular-weight (5–6 ring) PAHs. Principal coordinates analysis (PCoA) indicates that rice straw treatment separated only the bacterial community but sawdust greatly affected both the soil bacterial and fungal communities. Moreover, the abundance of some petroleum degraders such as the bacteria Sphingomonas , Idiomarina and Phenylobacterium and the fungi Humicola , Wallemia and Graphium was promoted by inputs of the two agricultural and forestry wastes. These results highlight the potential of waste applications in accelerating hydrocarbon biodegradation which may be attributed to the enrichment of keystone taxa that show strong positive associations with hydrocarbon degradation. Highlights • Rice straw and sawdust significantly enhance the TPHs and PAHs removal respectively. • Petroleum removal was irrelative with microbial community diversity. • Certain petroleum degraders play a vital role in petroleum removal. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Liming and organic fertilizer increased soil pH and decreased Al concentration. • Microbial communities were altered by lime and organic fertilizer. • Soil organic carbon and microbial activities were promoted by organic fertilizer. • Organic fertilizer may enhance synergistic microbial interactions. • Organic fertilizer, not heavy lime alone, effectively increased banana growth. Abstract Low soil pH and low soil organic matter content are major factors limiting banana production in acid soils. A pot experiment was conducted to determine whether liming or organic fertilizer is effective in mediating banana growth and soil health. The experiment comprised an unamended control and two treatments, lime and OF (organic fertilizer) and sampling was conducted twice, 65 and 280 days after planting. Soil nutrient concentrations, soil microbial communities and enzyme activities, and banana biomass and nutrient uptake were determined. As expected, the application of lime or organic fertilizer significantly increased soil pH and mineral nutrient concentrations and decreased Al3+ concentration. At both harvests an increase in bacterial and fungal diversity in the lime treatment and a shift in the soil bacterial and fungal communities did not translate into increased plant biomass. Organic fertilizer application significantly increased soil organic carbon content and enzyme activities, root length density down the soil profile, plant biomass and nutrient uptake compared to the lime treatment and the control. Changes in the soil microbial community in the organic fertilizer treatment compared to the control followed the same direction as in the lime treatment. However, the relative abundances of Actinobacteria and Ascomycota increased significantly 280 days after planting and potential pathogenic fungi including Fusarium decreased. Our results indicate that heavy liming alone may not be a viable approach to overcome the growth limiting factors in banana production on acid soils. In addition to the increased soil organic matter and nutrient availability, organic fertilizer may prime microbial activities and act as biologically active agent and/or enhance synergistic interactions within the soil microbiome in enhancing plant biomass. Increased soil biological activities after organic fertilizer application emphasize the importance of soil health in promoting the yield of banana crops. [ABSTRACT FROM AUTHOR]

Abstract Biodegradable plastics have been widely introduced into agricultural production, but their impacts on the soil ecosystem remain unclear. The present study investigated the impacts of a biodegradable seedling tray (BST) on the microbial communities in paddy soils. A 110-day rice culture experiment was conducted with three different paddy soils developed from black soil (BS, black chernozem soil), chao soil (CS, Fluvo-aquic) and red soil (RS, Alfisols) and three application rates of BST (0, 0.02 and 0.2 g kg−1). Soil phthalic acid ester (PAE) concentrations, physicochemical properties and enzyme activities were determined to evaluate the influence of BSTs on soil quality. 16S high-throughput sequencing was used to study bacterial community composition and the Biolog EcoPlate™ test was used to profile microbial activity and community function. Results show that the application of BSTs did not markedly affect soil quality, and the potential release of PAEs from BSTs was negligible. Interestingly, the microbial community was affected by BSTs in a soil-dependent and time-dependent pattern. The microbial community in RS was not significantly influenced by BSTs. Relative abundances of some predominant genera in BS (e.g. norank_f__BSV40) and CS (e.g. Norank_f__Nitrosomonadaceae) were significantly influenced by BSTs, and db-RDA results show that community composition in BS and CS was shaped mainly by BSTs. Community level profiling shows that BSTs significantly increased microbial activity and decreased functional diversity in BS after 55 days, but the impacts disappeared after 110 days. The results contribute to the knowledge of how biodegradable plastics influence microbial communities in paddy fields and provide information relevant to the practical use of BSTs under field condition. Graphical abstract Unlabelled Image Highlights • The use of biodegradable seedling trays (BSTs) neither increased PAE concentrations nor markedly affected soil quality. • The influence of BSTs on soil bacterial community composition was soil-dependent. • The use of BSTs increased microbial activity and reduced community functional diversity at early stages in certain soils. • The varied microbial communities in paddy soils might be due to the labile compounds leaching from BSTs. [ABSTRACT FROM AUTHOR]

Abstract Methylmercury (MeHg) can accumulate in rice and this has been demonstrated to be an important human MeHg exposure pathway. How to reduce MeHg concentrations in rice grains has therefore become a very important public health issue. Previous studies have investigated the role of plant biochars on Hg bioavailability in soils but knowledge of the influence of sewage sludge biochars (SSB) on MeHg formation and bioaccumulation in different soils is lacking. In the present study, SSB was applied to two Hg-contaminated soils, one acid and the other calcareous, in an attempt to stabilize MeHg in the soil and further mitigate MeHg accumulation in rice grains. The results indicate that the presence of SSB may promote Hg methylation in an acid soil. Moreover, MeHg concentrations increased gradually during rice growth, perhaps due to the release of root exudates. SSB can inhibit both MeHg and total Hg (THg) accumulation in different rice tissues. Both MeHg and THg decreased in the rice grains by up to 73.4 and 81.9%, respectively. However, the inhibitory effect was less pronounced in a calcareous soil. This study further demonstrates that biochar application can inhibit MeHg accumulation in soils despite the promotion of MeHg formation in soil by SSB application. However, an effect of biochar on MeHg accumulation was observed only in the acid soil. These results are useful in managing applications of biochars to Hg-contaminated paddy fields. Highlights • SSB application reduced MeHg accumulation in rice in acid soil. • SSB application resulted in the increase of MeHg concentration in acid soil. • MeHg accumulation in rice root decreased during rice growth period. • Release of rice root exudates lowered soil pH and further promoted MeHg formation. [ABSTRACT FROM AUTHOR]

Abstract Clay-enriched layers occurring in deltas are important as they reveal erosion, transportation and deposition of source materials from the basin to the coast. In the Yellow River Delta a red clay layer (RCL) with a thickness of 5–50 cm at 1 m depth in the soil profile occurs in the floodplain area dominated by fluvo-aquic soil derived from Yellow River sediments. The RCL typically has a median grain size of <20 μm, redness (a⁎) of >7, and relatively high contents of illite, calcite and iron oxides. In the Loess-Yellow River sediment-Yellow River Delta soil continuum a regime of weathering, mechanical sorting and dilution by carbonates and silica have been important factors altering the elemental geochemistry. The abundance of secondary minerals and deficiencies of silica and zircon in the RCL suggest that it was separated from a mixed source and was likely derived from highly weathered sediments (such as paleosol) from the basin. RCL samples show substantial accumulation of inorganic carbon with enhancement of the organic carbon content, indicating that increasing organic carbon in alkaline soils may lead to an increase in inorganic carbon in the subsoil. Large variations in elemental ratios have been found in the RCL characterized by excess nitrogen and trace metals and phosphorus deficiency due to adsorption and weathering effects. Implementation of the water-sediment regulation scheme (WSRS) may have altered the sedimentary environment and may have aggravated an elemental imbalance due to the occurrence of the yellow silt layer (YSL)-RCL sequence and thereby impacted biogeochemical cycling in the river-delta-coast continuum. Graphical abstract Unlabelled Image Highlights • The red clay layer (RCL) in the Yellow River Delta has unique characteristics. • Weathering, sorting and dilution are main factors altering elemental geochemistry. • Carbon, nitrogen and heavy metals are elevated but phosphorus is deficient in RCL. • Elemental imbalance may be aggravated by the RCL under anthropogenic perturbation. [ABSTRACT FROM AUTHOR]

Abstract Root exudates are the main media of information communication and energy transfer between plant roots and the soil. Understanding the response of root exudates to contamination stress is crucial in revealing the rhizoremediation mechanisms. Here, we investigate the response of alfalfa root exudates to bis(2-ethylhexyl) phthalate (DEHP) stress based on nontargeted metabolomic analysis. Alfalfa root exudates were collected using greenhouse hydroponic culture and analysed by gas chromatography-time of flight mass spectrometry (GC-TOFMS). A total of 314 compounds were identified in alfalfa root exudates of which carbohydrates, acids and lipids accounted for 28.6, 15.58 and 13.87%, respectively. Orthogonal partial least squares discriminant analysis (OPLS-DA) shows that DEHP exerted an important influence on the composition and quantity of root exudates. Fifty metabolites were clearly changed even at lower concentrations of DEHP, including common carbohydrates, fatty acids and some special rhizosphere signal materials, such as 4′,5-dihyrroxy-7-methoxyisoflavone. DEHP stress significantly suppressed carbohydrate metabolism but promoted fatty acid metabolism. However, amino acid metabolism, lipid metabolism and the tricarboxylic acid (TCA) cycle showed little change in response to DEHP stress. Graphical abstract Unlabelled Image Highlights • The main alfalfa root exudates were carbohydrates, acids, lipids, alcohols and amines. • DEHP significantly changed the composition and contents of root exudates. • DEHP stress suppressed carbohydrate metabolism but promoted fatty acid metabolism. • DEHP had little influence on amino acid and lipid metabolism and the TCA cycle. [ABSTRACT FROM AUTHOR]

Highlights • NSX2 inoculation significantly increased Cd accumulation in S. plumbizincicola. • NSX2 survived in the rhizosphere with a high relative abundance of 1.46%. • NSX2 reshaped the whole bacterial community structure in the rhizosphere. • NSX2 made the rhizosphere bacterial community network more complex. • Enhanced remediation by NSX2 strongly correlated with strengthened network topology. Abstract Hyperaccumulator plants combined with beneficial bacteria is a promising strategy for extracting trace metals from contaminated soils. We explored how the rhizosphere microbiome reshaped by exogenous functional bacteria and whether there is a relationship between the reshaped rhizosphere microbiome and Cadmium (Cd) accumulation in the hyperaccumulator plant during this process. A pot experiment was set up and the Cd hyperaccumulator Sedum plumbizincicola was planted with and without a plant beneficial bacterial strain Rhodococcus sp. NSX2. High-throughput sequencing and random matrix theory (RMT)-based network analysis were used to track the bacterial community in both the rhizosphere and the bulk soil. We found that NSX2 survived in the rhizosphere with a high relative abundance of 1.46% and reshaped the whole bacterial community structure in the rhizosphere. NSX2 inoculation significantly increased Cd accumulation in S. plumbizincicola and the phytoremediation efficiency strongly correlated with the reshaped bacterial network topology. Moreover, NSX2 made the bacterial network in the rhizosphere more complex through cooperating positively with the indigenous bacteria while the network in the bulk soil remained unchanged. We conclude that bacterial inoculation-enhanced phytoremediation did correlate with the beneficial bacterium inoculated itself and also with the subsequently changed indigenous rhizosphere bacterial community and their interactions at the whole community level. [ABSTRACT FROM AUTHOR]

Mixed soil microbiomes were established by introducing aliquots of a paddy soil into a red soil. The new mixed microbiomes effectively metabolized high-molecular-weight polycyclic aromatic hydrocarbons (PAHs, pyrene) in the soil mixtures. The pyrene removal efficiencies were 19% and 98%, respectively, in the original red soil and the paddy soil. The pyrene removal effectiveness by the mixed microbial community was enhanced by increasing the amount of paddy soil inoculant and the pyrene removal rates were 93%, 58% and 27% in paddy soil/red soil mixtures of 1:1, 3:7 and 1:9 (w/w), respectively. Supplementation with sterile paddy soil and nutrients changed the soil environment but the pyrene removal efficiency was not enhanced, indicating that the microbial composition largely determined the extent of pyrene removal. Moreover, the pyrene removal rate was positively related to the pyrene dioxygenase gene ( nidA ) abundance. The greater the percentage of the paddy soil in the soil mixture the greater the similarity of the mixed microbiome to that of the original paddy soil itself. The community of the inoculated sterile paddy soil was similar to that of the red soil and the community diverged from those of the red soil and the paddy soil with increasing culture time. After culture for 42 days, some enriched genera were responsible for PAH degradation, notably Nevskia , Ralstonia , Gemmatimonas and Lysobacter , while some genera have no clear classification information or category name at the genus level, such as f__Acidobacteriaceae and o__JG30-KF-AS9. This study is very important in recognizing the role of natural soil in the formation of a mixed microbiome to stimulate the degradation of PAHs in a soil with low intrinsic PAH degradation capability. [ABSTRACT FROM AUTHOR]

Highlights • Complexation of Hg with the antibiotics resulting in the dissolution of Hg compounds from the sediment. • Hg ions in the sediment can also promote the degradation of antibiotics. • The degradation of TC/OTC radicals generates CH3+ groups which can react with Hg° to form MeHg. Abstract The role of antibiotics commonly used in fish culture activities in methylmercury (MeHg) formation in mariculture sediments (MS) and in reference sediments (RS) was studied using simulation microcosms. MS and RS were split into three equal batches. Two batches were spiked with Hg(NO 3) 2 aqueous solution at levels of 2 and 8 mg kg−1 (dry weight basis) and the remainder served as a control batch. Tetracycline (TC) and oxytetracycline (OTC) (2.5 g and 10 g of each) were added to each treatment. Sediment THg concentration decreased during the culture period possibly due to complexation of Hg with the antibiotics resulting in the dissolution of Hg compounds from the sediment. More importantly, the MeHg concentration increased after 32 days together with a decrease in the concentrations of the antibiotics in the sediment. The complexation of TC or OTC with Hg resulted in the transport of electrons from TC or OTC to Hg2+ due to the high electronegativity of Hg2+. Subsequently, Hg2+ was reduced to Hg° which reacted with CH 3 + derived from TC or OTC. The use of antibiotics may therefore promote the formation of MeHg in sediments. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Decreasing the cell viability by strong interaction and ROS generation. • Nano-SIMS could prove the contribution of hematite to intracellular iron, directly. • Restricting the BaP bioaccessibility to the bacterium. Abstract Iron oxides are reactive inorganic soil components that play an important role in the fate and transport of organic pollutants. Here, hematite was selected to investigate its effect on the biodegradation of benzo[a]pyrene (BaP) by Paracoccus sp. strain HPD-2. Approximately 60% of the total BaP was degraded in the absence of hematite after 7 days but only 30.8 and 20.8% of that was degraded after the addition of 10 and 20 mg mL–1 hematite, respectively, indicating that the addition of hematite could significantly inhibit the biodegradation of BaP (P < 0.05). The hematite also lowered bacterium activity by coating the cells and by generating reactive oxygen species that destroyed the cells. Two-photon confocal laser scanning microscope images showed that the addition of hematite substantially decreased the amount of BaP combined with the bacterium, and this also enabled us to observe directly the migration and regression of BaP in the interaction between HPD-2 and hematite. Higher death ratio of HPD-2 might lower the BaP access to live cells because dead cells have a higher adsorption affinity for BaP than live cells. These observations enhance our understanding of the mechanisms by which metal oxides, organic pollutants and degrading-bacteria interact during the biodegradation process. [ABSTRACT FROM AUTHOR]

Estimating the bioavailability and predicting the uptake of metals to hyperaccumulators is very important in developing the field application of phytoextraction. A pot experiment was conducted using 108 agricultural soils covering a wide range of soil properties by the cadmium (Cd) hyperaccumulator Sedum plumbizincicola . The contributions of a range of soil properties to Cd uptake were quantified. Soil total, soluble, CaCl 2 -extractable and diffusive gradients in thin films (DGT)-extractable Cd concentrations (Cd total , Cd soln , Cd CaCl 2 and Cd DGT ) were used to estimate Cd bioavailability and predict shoot Cd concentration (Cd shoot ) using a piecewise function. Cd total and pH were the two major contributors to Cd uptake. Cd shoot showed a logarithmic increase with Cd total from 0.30 to 10.0 mg kg −1 but no further increase when Cd levels exceeded 10 mg kg −1 . Soil pH had a discernible negative effect on Cd bioavailability from pH 5.5 to 7.5 but a weak influence at pH < 5.5 or pH > 7.5. This indicates that the optimum pH for phytoextraction with S . plumbizincicola was ~5.5 and lower pH produced little increase in shoot Cd uptake. DGT gave the best estimation of Cd bioavailability across all the data. When Cd total  > 10 mg kg −1 , none of the four measures was accurate enough to predict Cd shoot but when pH > 7.5 all the four measures were well correlated with Cd shoot . Piecewise equations in different ranges of Cd total or pH significantly improved the prediction of Cd shoot compared with the global equations derived from all the data. Compared with the piecewise equations, when pH > 7.5 Cd shoot was greatly overestimated with the global equation of Cd total . Our study provides useful information on the soils in which phytoextraction with S . plumbizincicola is feasible in the field. Capsule Cd availability to S . plumbizincicola was estimated by a piecewise function in soils with wide ranges of total Cd concentration and pH. [ABSTRACT FROM AUTHOR]

Highlights • The transformation of PTEs in sewage sludge hydrochars was studied. • Effects of phosphoric acid activation on immobilization of PTEs were explored. • H 3 PO 4 in feed-water deactivated PTEs to reduce the sludge environmental risk. • High aromaticity caused high residual rates of PTEs in the hydrochars. • Large numbers of phosphate minerals effectively occluded PTEs in the hydrochars. Abstract The effect of phosphoric acid addition to the feed-water on the speciation and transformation behaviour of potentially toxic elements (PTEs) in the hydrothermal carbonisation (HTC) of sewage sludge was explored. Over 70% of each of the PTEs (As, Cd, Cr, Cu, Mn, Ni, Pb and Zn) was in the directly bioavailable and potentially bioavailable fraction in the raw sludge, and especially Cu and Zn at 97.5 and 98.6%, respectively. Through the HTC process the directly bioavailable and potentially bioavailable fractions of PTEs in the sludge hydrochar clearly decreased, and the residual fraction in the hydrochar showed an observable increase. Further stabilisation of PTEs in hydrochar occurred during HTC with the addition of phosphoric acid solution to the feed-water. As the concentration of phosphoric acid in the feed-water increased the percentages of the residual fraction of Cd, Cr, Ni, Pb and Zn in hydrochars each exceeded 80%, but different PTEs behaved differently with increasing phosphate molar ratio in the feed-water. When the molar ratio of phosphate was 15%, the percentages of the residual fractions of Cd, Mn and Zn reached their maximum values in accordance with the changing trend in aromaticity of the hydrochar. Moreover, a large number of phosphate mineral crystals effectively occluded the PTEs in hydrochar. In conclusion, the addition of phosphoric acid to the feed-water during HTC further deactivated PTEs leading to a substantial decline in the potential environmental risk associated with the land application of the sewage sludge. [ABSTRACT FROM AUTHOR]