Search

[Display omitted] • Electrons rapidly transfer through Fe-O-Bi electronic channels at the interface. • The internal electric field promotes the separation and transfer of charge carriers. • DFT calculation reveals the effect of pollutant structure on photocatalysis rate. • Photolysis rate of FQs is positively correlated with ƒ0 of main active carbon atoms. • MIL-53(Fe)/Bi 4 O 5 I 2 achieves efficient LEV photolysis at different water matrix. Building a heterojunction is a fascinating option to guarantee sufficient carrier separation and transfer efficiency, but the mechanism of charge migration at the heterojunction interface has not been thoroughly studied. Herein, MIL-53(Fe)/Bi 4 O 5 I 2 photocatalyst with a Z-scheme heterojunction structure is constructed, which achieves efficient photocatalytic decontamination under solar light. Driven by the newly-built internal electric field (IEF), the formation of Fe-O-Bi electron migration channel allows for rapid separation and transfer of charge carriers at the heterojunction interface, confirmed by the material characterization and density functional theory (DFT) calculation. The narrower band gap and improved visible light response also contribute to the enhanced photocatalytic activity of composite materials. With levofloxacin as the target pollutant, the optimal MIL-53(Fe)/Bi 4 O 5 I 2 achieves complete removal of pollutant within 150 min, the photocatalysis rate of which is ca. 4.4 and 26.0 times that of pure Bi 4 O 5 I 2 and MIL-53(Fe), respectively. Simultaneously, the optimal composite material exhibits satisfactory photodegradation of seven fluoroquinolones, and the photocatalysis rates are as follows: lomefloxacin > ciprofloxacin > enrofloxacin > norfloxacin > pefloxacin > levofloxacin > marbofloxacin. DFT calculations reveal a positive relationship between degradation rate and Fukui index (ƒ0) of main carbon atoms in seven fluoroquinolones. This study sheds light on the existence of electron migration channels at Z-scheme heterojunction interface to ensure sufficient photoinduced carrier transfer, and reveals the influence of pollutant structure on photolysis rate. [ABSTRACT FROM AUTHOR]

An induction brazing method for joining Al 2 O 3 ceramic to 316L stainless steel (SS) was developed in this study. The Sn–Ti alloy was rapidly melted by induction heating, which enabled the active element Ti to react with O in Al 2 O 3. Consequently, a metallurgical bonding formed between and Al 2 O 3 and 316L SS. The microstructure of the joint was mainly composed of Fe 2 SnTi layer, FeSn 2 , Ti 6 Sn 5 particles and TiO layer. The maximum shear strength of 20 MPa was obtained at 260 A/140 s. The induction heating exhibited a higher heating rate compared to traditional resistance heating, as evidenced by the brazing process with only approximately 140 s. The proof-of-concept study on the induction brazing of Al 2 O 3 ceramic to 316L SS with high efficiency provides insights in the further development of ceramic/metal joining. [ABSTRACT FROM AUTHOR]

In this study, the bonding of a TZM alloy/graphite-brazed joint was improved by fabricating a striped structure on a graphite surface, effectively increasing the surface area ratio and surface roughness of graphite. The typical interfacial microstructure of the joint was TZM/(Ti, Mo)ss/TiNi/TiC/graphite. The shear strength of the joint increased and then decreased with an increase in laser scan distance, reaching a maximum value of 18.1 MPa at a laser scan distance of 90 μm. FEM simulations indicated that the formation of the striped structure optimised the residual stress distribution in the joint, with the stress state at the interface transformed from unilateral tensile stress to alternating tensile-compressive stress. Hence, the formation of the striped structure increased the joining area and optimised the stress distribution of the joints, thereby improving the mechanical properties of the TZM/ graphite-brazed joints. • The bonding of TZM/graphite joint was improved by fabricating striped structure. • Laser scan distance effects on the microstructure and properties were studied. • The striped structure optimised the residual stress distribution in the joint. [ABSTRACT FROM AUTHOR]

Soil microorganisms are important bioactive components of wetland ecosystems. Their abundances and enzyme activities directly influence biogeochemical cycle processes and are strongly associated with vegetation type. Our study aims to investigate the changes in microbial gene abundances and enzyme activities in Sanjiang Plain wetlands under different vegetation types, namely, Carex lasiocarpa , Deyeuxia purpurea , Glyceria acutiflora subsp. japonica , Oryza sativa , and Phragmites australis. Our results demonstrated that soil microbial gene abundances and enzyme activities were greatly affected by changes in vegetation type and soil chemical properties. The abundances of the carbon fixation gene (cbbL) and activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) in topsoil and subsoil were higher in C. lasiocarpa and D. purpurea wetlands than in other wetlands. This result indicated that the C. lasiocarpa and D. purpurea wetlands have stronger carbon fixation capacity than other wetlands. The highest nif H, nir K, and nir S gene abundances in subsoil were found in the D. purpurea wetland, indicating that soil microorganisms in subsoil under D. purpurea have stronger nitrogen fixation capacity and denitrification potential compared with those in subsoils under other vegetation types. The significantly higher nif H, nir K, and nir S gene abundances in topsoil than in subsoil in the C. lasiocarpa and G. acutiflora wetlands illustrated that topsoil has higher nitrogen fixation and denitrification capacity than subsoil. Redundancy analysis revealed that the cumulative interpretation rates of ammonia-N and dissolved organic carbon (DOC) for soil microbial gene abundances and enzyme activities were 73.1 % and 85.4 %, respectively, showing that ammonia-N and DOC are crucial drivers inducing alterations in soil microbial gene abundances and enzyme activities. Overall, our research clarified the mechanism underlying the linkage among plants, soil, and microorganisms in wetlands and improved the theoretical basis for predicting the effect of wetland vegetation changes on microbial function under the influence of future climate change and human activities. • Microbial abundances and enzyme activities were vegetation type-dependent. • Topsoil microbial abundances were higher than subsoil in C. lasiocarpa wetland. • Soil enzyme activities were strongly associated with soil carbon components. • Microbial abundances and enzyme activities were affected by ammonia-N and DOC. [ABSTRACT FROM AUTHOR]

Plant species composition influences belowground ecosystem function. However, there are few data on the interactive effects of plant diversity and soil function. We surveyed plant species diversity, and determined soil carbon (C), nitrogen (N) fractions and enzyme activity in five peatlands with different vegetation-types. We also investigated the interactions between plant species diversity and richness, and soil biochemical properties. We found a close relationship between plant species diversity and total carbon (TC) in both surface (0–15 cm) and subsoil (15–30 cm) layers. Plant diversity and richness positively correlated with soil dissolved organic carbon (DOC), NH 4 +-N in both soil layers and subsoil moisture and total nitrogen (TN), as well as topsoil pH. Plant species diversity and richness were also positively correlated with subsoil moisture, pH, protease, acid phosphatase activity and topsoil urease activity. Soil β-glucosidase, invertase, urease, protease, and acid phosphatase activity positively correlated with soil TC, TN, DOC, available N and soil moisture. Our findings demonstrate that plant community diversity is linked with soil C and N turnover through soil enzyme activity. These results will improve our ability to more fully understand the linkages between aboveground and belowground components in peatland ecosystems. • Plant species diversity and richness positively correlated with soil DOC and NH 4 +-N. • Soil moisture and pH affected plant distribution, species diversity and richness. • Soil TC, TN, DOC, and moisture were important factors influencing enzyme activity. • Plant community diversity is linked with soil C and N turnover through soil enzyme. [ABSTRACT FROM AUTHOR]

[Display omitted] • C/Bi 3 O 4 I achieved 100% pyrene elimination within 20 min. • Carbon doping dramatically elevated internal electric field and photolysis activity. • Effect of halogen type on photocatalytic activity of Bi 3 O 4 X was thoroughly studied. • Doped C implanted into [X] layers and induced impurity state formation above VB. • Formation rate of free radicals and their contribution on degradation were measured. A series of C-doped Bi 3 O 4 X (X = Cl, Br, I) photocatalysts with layer-stacked structure was synthesized using glucose as carbon source, and the carbon doping and halogen species on harvesting broader solar spectrum and promoting charge carrier separation were systematically investigated. For pyrene photolysis, the photodegradation rate of pristine materials followed the order of Bi 3 O 4 I > Bi 3 O 4 Br > Bi 3 O 4 Cl, which was attributed to the difference in electronegativity of the halogen elements. The doped carbon boosted photocatalytic performance and the optimal C/Bi 3 O 4 I achieved 100% pyrene removal within 20 min, which primarily benefited from the dramatic improvement of the internal electric field (IEF). The improved IEF further increased the separation and transfer efficiency of photogenerated charge carriers. XRD and XPS characterizations confirmed that the doped carbon implanted into the lattice of [X] layers, and mainly affected the X np states. The X np orbitals contributed to the valence band (VB) of Bi 3 O 4 X, thus the local occupied states induced by doped carbon formed above VB and significantly decreased the VB potential. Meanwhile, the doped carbon narrowed the band gap and greatly improved visible light utilization. The O 2 −, h+ and OH were identified as dominant active species for pyrene degradation, and the generation rate of O 2 − and OH was further measured by the probe technique. Moreover, the photodegradation pathways of pyrene were proposed and the ecotoxicity of intermediates was assessed. This study reveals the effect of halogen species on photocatalytic activity and provides guidance for enhancing IEF by doping inorganic element. [ABSTRACT FROM AUTHOR]

In the present work, a reliable TZM/graphite heterogeneous joint was prepared by vacuum brazing with Ti-35Ni alloy. The influence of brazing temperature on the interfacial microstructure, shear strength, and fracture characteristics of the joints were analyzed. The formation mechanism of the joints was also investigated in detail. TiC layer was formed on graphite during the vacuum brazing process, characterized by SEM and TEM analysis. The interfacial microstructure of the joints brazed at 1200 °C was TZM/Ti(s,s)/TiNi + Ti 2 Ni/TiC/graphite. The thickness of TiC layer gradually increased with the increase in brazing temperature. In addition, the shear strength of TZM/graphite heterogeneous joints increased first and then decreased, reaching the peak value of 14.5 MPa at 1300 °C. Under optimal vacuum brazing temperature, the fracture path of the joint started in the TiC layer and then extended to the interior of the graphite substrate. • Reliable TZM/graphite joint was prepared by vacuum brazing with Ti-35Ni alloy. • The thickness of the TiC layer gradually increased with the elevated temperature. • The formation mechanism of the brazed joint was investigated in detail. [ABSTRACT FROM AUTHOR]

Abstract A two-step process involving, first, the pre-metallization of the SiC ceramic, followed by the vacuum brazing using graphene nanoplatelets (GNPs) reinforced AgCuTi composite filler was developed to join SiC ceramic and GH99 superalloy. The metallization characteristics, joint microstructure and fracture behavior were investigated. Through pre-metallization, a smooth metallic coating formed on the SiC ceramic surface; the carbide layer adjacent to SiC ceramic had a semi-coherent interface with it. Brazing process showed that in situ synthesized TiC particles with fine-grains were evenly dispersed in the filler matrix due to GNPs acting as nucleation sites, promoting the refinement of microstructure of the joint. Moreover, the effect of GNPs in retarding the diffusion of metal atoms limited the reaction of Ti with Cu and Ni, thereby reducing the negative impact induced by the brittle compounds. The maximum shear strength of 26.4 MPa was obtained at AgCuTi-1%GNPs, which was ∼151.4% higher than the joint brazed using AgCuTi filler. [ABSTRACT FROM AUTHOR]

Abstract Graphene nanoplatelets (GNPs) were used as reinforcement in AgCuTi filler for brazing SiC ceramic. Ti from the filler reacted with SiC ceramic to form TiC and Ti 5 Si 3 adjacent to the SiC ceramic. According to the TEM and HRTEM results, TiC layer exhibited good lattice matching with SiC substrate. TiC particles synthesized by the reaction between Ti and GNPs in situ promoted the heterogeneous nucleation of TiCu and Cu(s,s), and contributed to the refinement of microstructure. Shear tests results indicated that the adoption of GNPs affected the joint property significantly. The TiC particles and an appropriate TiC + Ti 5 Si 3 layer thickness both relieved the residual stress of the brazed joint and thereby increased the joint strength. The shear strength of the joint reached the maximum value of 38 MPa when using AgCuTi/GNPs (GNPs reinforced AgCuTi) composite filler containing 1% GNPs, which was ∼139% higher than that of the joint brazed with AgCuTi filler. [ABSTRACT FROM AUTHOR]

Approximately one-third of northern peatlands are within permafrost regions. Soil organic matter (SOM) and plant root biomass in permafrost peatlands are vulnerable to future global warming. However, previous studies have primarily focused on the response of SOM mineralization to increases in temperature without analysing the potential interaction effects of increased plant root biomass. This study investigated the influence of temperature and root additions on soil carbon and nitrogen mineralization as well as the mechanisms driving mineralization in a high latitude permafrost peatland in the Da Xing'an Mountains, Northeast China. We investigated changes in shallow soil (0–15 cm) and deep soil (15–30 cm) carbon mineralization, available N contents, microbial biomass carbon (MBC), dissolved organic carbon (DOC), and enzyme activities in response to increasing temperature and Eriophorum vaginatum root additions by using an incubation experiment. Our results indicate that elevated temperature significantly increased soil carbon mineralization. The Q 10 values of the carbon mineralization rates in the shallow soil and deep soil were 3.95 and 2.91, respectively. In contrast, the soil MBC and DOC decreased significantly, confirming that labile carbon is the main driving force of microbial mineralization activities under warming conditions. Elevated temperature significantly increased the shallow soil net N mineralization rates and increased the net nitrification rates in both soil layers. At high temperatures, ammonification rates increased in the shallow soil but decreased in the deep soil. The increase in the incubation temperature resulted in significantly increased shallow soil β-glucosidase activity and decreased invertase activity. This suggests the increased production of complex substrate enzymes, and decreased production of simple substrate-acquiring enzymes. The root additions significantly increased the soil C mineralization and stimulated the secretion of invertase by soil microorganisms. These findings indicate that future climate warming in the northern high latitude will significantly stimulate soil carbon and nitrogen mineralization in permafrost peatlands. Furthermore, increases in plant roots will enhance C accumulation and may even enhance the response of soil C mineralization to temperature, significantly impact the soil C balance in high latitude permafrost peatlands. [ABSTRACT FROM AUTHOR]

Nitrogen (N) availability affects litter decomposition and nutrient dynamics, especially in N-limited ecosystems. We investigated the response of litter decomposition to N additions in Eriophorum vaginatum and Vaccinium uliginosum peatlands. These two species dominate peatlands in Northeast China. In 2012, mesh bags containing senesced leaf litter of Eriophorum vaginatum and Vaccinium uliginosum were placed in N addition plots and sprayed monthly for two years with NH 4 NO 3 solution at dose rates of 0, 6, 12, and 24 g N m − 2 year − 1 (CK, N1, N2 and N3, respectively). Mass loss, N and phosphorus (P) content, and enzymatic activity were measured over time as litter decomposed. In the control plots, V. uliginosum litter decomposed faster than E. vaginatum litter. N1, N2, and N3 treatments increased the mass losses of V. uliginosum litter by 6%, 9%, and 4% respectively, when compared with control. No significant influence of N additions was found on the decomposition of E. vaginatum litter. However, N and P content in E. vaginatum litter and V. uliginosum litter significantly increased with N additions. Moreover, N additions significantly promoted invertase and β-glucosidase activity in E. vaginatum and V. uliginosum litter. However, only in V. uliginosum litter was polyphenol oxidase activity significantly enhanced. Our results showed that initial litter quality and polyphenol oxidase activity influence the response of plant litter to N additions in peatland ecosystems. Increased N availability may change peatland soil N and P cycling by enhancing N and P immobilization during litter decomposition. [ABSTRACT FROM AUTHOR]

In this work, alumina ceramic was bonded to itself with composite foils (Ti/Cu/Ni/Cu/Ti). The thermodynamics analysis indicates that Ti-Cu liquid firstly formed and reacted with alumina to produce Ti 3 Cu 3 O reaction layer. Meanwhile, the consumption of element Ti within the Ti-Cu liquid by Ni interlayer optimized the microstructure of the joint. By thickening Ni interlayer from 0 µm to 100 µm at 1020 ℃, the joints' strength could be significantly improved by 130.6%. While the joints' strength decreased with the decomposition of reaction layer at the brazing temperature higher than 1020 ℃. The FE simulations show that the high-level stress concentration within the reaction layer could be ameliorated by Ni interlayer effectively, which was in accordance with the corresponding fracture characteristics. Although the joint's strength could be improved to 203.9 MPa by using 300 µm Ni interlayer, its improvement rate was limited with Ni interlayer constantly thickening. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is a limiting nutrient in many peatland ecosystems. Enhanced N deposition, a major component of global climate change, affects ecosystem carbon (C) balance and alters soil C storage by changing plant and soil properties. However, the effects of enhanced N deposition on peatland ecosystems are poorly understood. We conducted a two-year N additions field experiment in a peatland dominated by Eriophorum vaginatum in the Da Xing’an Mountains, Northeast China. Four levels of N treatments were applied: (1) CK (no N added), (2) N1 (6 g N m −2 yr −1 ), (3) N2 (12 g N m −2 yr −1 ), and (4) N3 (24 g N m −2 yr −1 ). Plant and soil material was harvested at the end of the second growing season. N additions increased litter N and phosphorus (P) content, as well as β-glucosidase, invertase, and acid-phosphatase activity, but decreased litter C:N and C:P ratios. Litter carbon content remained unchanged. N additions increased available NH 4 + –N and NO 3 − –N as well as total Gram-positive (Gram+), Gram-negative (Gram−), and total bacterial phospholipid fatty acids (PLFA) in shallow soil (0–15 cm depth). An increase in these PLFAs was accompanied by a decrease in soil labile organic C (microbial biomass carbon and dissolved organic carbon), and appeared to accelerate decomposition and reduce the stability of the soil C pool. Invertase and urease activity in shallow soils and acid-phosphatase activity in deep soils (15–30 cm depth) was inhibited by N additions. Together, these findings suggest that an increase in N deposition in peatlands could accelerate litter decomposition and the loss of labile C, as well as alter microbial biomass and function. [ABSTRACT FROM AUTHOR]

[Display omitted] • The direct bonding of Si 3 N 4 and copper was achieved via laser surface modification. • Si with intergranular glass contained were formed on Si 3 N 4 via laser modification. • A robust bonding was obtained through mechanical locking and metallurgical bonding. • The facile bonding approach has great potential in developing high-power devices. A convenient and efficient approach for direct bonding of Si 3 N 4 ceramic to copper via laser surface modification is introduced in this work. Laser irradiation was capable of dissociating Si 3 N 4 to create a silicon metalloid layer that attained the metallurgical bonding with copper facilitated by the copper-silicon eutectic reaction. The analytical test results show that a strong Si 3 N 4 /copper bonded pair with the shear strength of 18.3 MPa, along with a low bonding defect density (0.4%) was obtained. The validity and reliability of the as-prepared Si 3 N 4 /copper structure were verified given ca. 99.4% bonded area maintained after 1000 cycles of thermal cycling testing. This proof-of-concept study on the Si 3 N 4 /copper bonding approach with laser modification provides insights to fabricate the metalized ceramic substrate. [ABSTRACT FROM AUTHOR]

The enhanced technology of laser surface modification was developed to improve the mechanical properties of Cu/Si 3 N 4 AMB joints in this work. The application of laser modification enabled the fabrication of periodic micro-grooves arrays with Si precipitates contained on the Si 3 N 4. The bonding behavior and strengthening mechanism of the joints with laser modification are investigated by means of thermodynamic analysis and finite element simulation. The introduction of Si precipitates on the laser-modified Si 3 N 4 surface could facilitate the atomic diffusion in the bonding and improve the kinetic behavior of the joints. Large amounts of Ti 5 Si 3 particles were produced at the interface adjacent to Si 3 N 4 preferentially. Finite element results demonstrated that the wave-like interfacial structure of the joints could decrease and redistribute the residual stress field in the interface, providing a method for improving the mechanical properties of the joint. The maximum shear strength of joints with the laser modification was 64.6 MPa, which was approximately 200% higher than that of the un-treated joints. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • The low-temperature bonding of Si 3 N 4 and Cu was achieved using Ti/Cu films. • It is an effective means of relieving stress caused by Si 3 N 4 /Cu CTE mismatch. • An efficient Cu-on-Si 3 N 4 structure for power devices is expected. A low-temperature bonding method of Si 3 N 4 /Si 3 N 4 homostructure and Si 3 N 4 /Cu heterostructure was developed in this work. The flawless interfaces were obtained by sputtered Ti/Cu thin films after bonding at 250 °C for 30 min under a uniaxial pressure of 20 MPa. The Ti film is able to improve the adhesion of the Cu film to Si 3 N 4 substrate, and the low-temperature bonding was achieved in view of high diffusion rates of Cu nanocrystalline film with (1 1 1) crystal plane. This proof-of-concept study on the low-temperature bonding of Si 3 N 4 ceramic to Cu is expected to address residual stress caused by ordinary active metal brazing (AMB) method, which provides insights for the further heterogeneous integrations of ceramics to metals. [ABSTRACT FROM AUTHOR]

In this paper, AlN ceramic was directly joined to copper without active brazing filler metal. By exerting the nanosecond laser irradiation on the AlN surface, the AlN ceramic was thermally decomposed to aluminum and the surface was metalized. The as-metalized AlN ceramic was successfully joined to copper through the eutectic reaction between aluminum and copper. The effect of the groove interface structure fabricated with various laser scanning speeds on the mechanical and heat transfer properties of AlN/Cu joints was investigated. The joints obtained optimal shear strength and thermal diffusivity of 10.64 MPa and 51.75 mm2/s at the scanning speed of 250 mm/s. The micro groove structures of the interface contributed to the enhancement of mechanical and heat transfer properties of joints. The approach of laser-irradiation assisted joining proposed in this paper provided a novel thought for the fabrication of metal/ceramic composite structures. [ABSTRACT FROM AUTHOR]

• The decomposition of E. vaginatum litter is faster than that of Sphagnum. • Warming could promote decomposition of E. vaginatum and Sphagnum litter. • N addition promoted the decomposition of Sphagnum (low N) and vascular litter. • High N concentration inhibited the decomposition of Sphagnum litter. • Microorganisms regulated warming and N addition impacts on litter decomposition. As one kind of the most important carbon (C) sink in the world, peatlands are sensitive to climate change. The decomposition of litter plays an important role in C fixation and nutrient utilization in peatlands. To reveal the mechanism of response of the litter decomposition to climate warming and the addition of nitrogen (N) in permafrost peatlands, we selected two typical plants, Eriophorum vaginatum and Sphagnum palustre , in the permafrost peatland of Da Xing'anling Mountains, China, as the research objects and conducted a 54-day litter decomposition experiment at 10 ℃ and 20 ℃. Three N addition treatments (CK: 0 mg N g−1, N1: 2.5 mg N g−1, and N2: 5 mg N g−1) were established. Our results showed that the E. vaginatum litter decomposed more quickly than that of Sphagnum , and an increase in temperature significantly promoted the litter decomposition and CO 2 emission of E. vaginatum and Sphagnum. The addition of N promoted the decomposition of E. vaginatum litter, whereas the decomposition of Sphagnum litter was promoted by the N1 treatment but was inhibited by the N2 treatment. The enzyme activity in both types of litter was inhibited with the increase in temperature. The abundances of bacteria and fungi positively correlated with the decomposition constant and mean CO 2 release rate by E. vaginatum and Sphagnum litter, indicating that the effects of temperature and N addition on the decomposition of plant litter were primarily regulated by microorganisms. This study provides a theoretical basis to understand and predict the effects of global climate change on the decomposition of plant litter in boreal peatlands. [ABSTRACT FROM AUTHOR]

• The decomposition of E. vaginatum litter is faster than that of Sphagnum. • Warming could promote decomposition of E. vaginatum and Sphagnum litter. • N addition promoted the decomposition of Sphagnum (low N) and vascular litter. • High N concentration inhibited the decomposition of Sphagnum litter. • Microorganisms regulated warming and N addition impacts on litter decomposition. As one kind of the most important carbon (C) sink in the world, peatlands are sensitive to climate change. The decomposition of litter plays an important role in C fixation and nutrient utilization in peatlands. To reveal the mechanism of response of the litter decomposition to climate warming and the addition of nitrogen (N) in permafrost peatlands, we selected two typical plants, Eriophorum vaginatum and Sphagnum palustre , in the permafrost peatland of Da Xing'anling Mountains, China, as the research objects and conducted a 54-day litter decomposition experiment at 10 ℃ and 20 ℃. Three N addition treatments (CK: 0 mg N g−1, N1: 2.5 mg N g−1, and N2: 5 mg N g−1) were established. Our results showed that the E. vaginatum litter decomposed more quickly than that of Sphagnum , and an increase in temperature significantly promoted the litter decomposition and CO 2 emission of E. vaginatum and Sphagnum. The addition of N promoted the decomposition of E. vaginatum litter, whereas the decomposition of Sphagnum litter was promoted by the N1 treatment but was inhibited by the N2 treatment. The enzyme activity in both types of litter was inhibited with the increase in temperature. The abundances of bacteria and fungi positively correlated with the decomposition constant and mean CO 2 release rate by E. vaginatum and Sphagnum litter, indicating that the effects of temperature and N addition on the decomposition of plant litter were primarily regulated by microorganisms. This study provides a theoretical basis to understand and predict the effects of global climate change on the decomposition of plant litter in boreal peatlands. [ABSTRACT FROM AUTHOR]

Abstract: Soil organic matter decomposition is regulated by nutrient availability. Adding nitrogen (N) and litter could affect the stability of soil organic carbon (SOC). An incubation experiment was conducted to examine the effects of ammonium nitrate (AN), urea (U), and litter amendment on activities of soil microbial extracellular enzyme, soil microbial biomass C (MBC), dissolved organic C (DOC), and C mineralization in freshwater marsh. The results showed that adding N including AN and U decreased soil urease activity, MBC, DOC, and soil pH. However, litter amendment and combined litter and N amendment increased the enzymes activities of urease and invertase, MBC and DOC concentrations. The response of soil C mineralization to N and litter additions was different, being inhibited with AN addition while stimulated with littler addition and the combined litter and N addition, initially stimulated but inhibited thereafter with urea addition. Our results suggest that adding N is helpful for improving marshland soil C stocks via decreasing soil cumulative CO2–C emissions, labile organic carbon concentration of MBC and DOC. However, adding litter could reduce C storage stability by stimulating soil C mineralization and increasing soil labile C fractions and enzyme activities. [Copyright &y& Elsevier]

Abstract: Nitrogen (N) is commonly a limited nutrient in wetland ecosystems. Nitrogen addition affects the ecosystem carbon (C) balance and alters soil C storage through soil chemical and biological changes. In the present study, the effects of N addition and vegetation removal after one growing season on soil properties were examined in a Calamagrostis angustifolia freshwater marsh in Northeast China. Specifically, available N (NH4 +–N and NO3 −–N), microbial biomass C (MBC), and dissolved organic C (DOC) concentrations in the soil were analyzed. In addition, activities of soil enzyme (β-glucosidase, invertase, and urease) were investigated. The results showed that N addition resulted in significant increase of NH4 +–N and NO3 −–N in both topsoil and subsoil, and vegetation removal enhanced these effects. Soil MBC concentrations increased after N addition and vegetation removal but DOC concentrations did not change significantly. As to soil enzyme activities, N addition stimulated the β-glucosidase activity in the topsoil and invertase and urease activities in both soil layers. Vegetation removal enhanced the effect of N addition on β-glucosidase and invertase activities but inhibited the effect on urease activity. These results suggested that N addition affects soil biochemical process indirectly through marshland vegetation. [Copyright &y& Elsevier]

Human activities can have dramatic effects on the environment so that evaluating the anthropogenic driving forces is an important issue in the consideration of how humans impact the world. In this paper, ecological footprint (EF) was used as an aggregate index of total human impacts in 31 provinces in mainland China during 2010. The STIRPAT model was employed to analyze the major anthropogenic drivers of EF. The empirical results demonstrate that great disparities of EF exist at the spatial scale. Provinces with the largest total EF are mostly distributed in the populated east coast of China, whereas provinces with the lowest total EF are mostly found in west China. Similar to EF, ecological deficit (ED) is a dominant characteristic of most municipal areas in China. The results of STIRPAT show that population has the largest potential effect on the Chinese environment at the provincial scale, followed by EF intensity, affluence, percentage of gross domestic product (GDP) from the industrial sector, age structure, and per capita land area. Urbanization has negative effects on EF disparities, but it is not an inevitable factor in this case. This study is helpful to recognizing the human effects on environment and helps to facilitate the management of sustainable development across China. [ABSTRACT FROM AUTHOR]

• Rising temperature accelerated the mineralization of SOC in permafrost peatlands. • Q 10 of SOC mineralization ranged from 2.24 to 4.22 among 7 permafrost peatlands. • SOC mineralization positively correlated with soil DOC, NH 4 +-N, NO 3 −-N contents. • Substrate availability and microbe drive SOC mineralization in permafrost peatlands. Permafrost peatlands are important pools of soil carbon. Soil organic carbon (SOC) mineralization and its temperature sensitivity in permafrost peatlands are crucial for predictions of soil carbon-climate feedback. However, little is known about the changes in SOC mineralization and its mechanism in response to environmental change in the permafrost peatlands of Northeastern China. We collected seven permafrost peatland soils from Greater and Lesser Khingan Mountains in Northeastern China to investigate how the responses of microbes and labile substrates control the mineralization of SOC in the laboratory incubation study. The results show that temperature and sampling sites affected the mineralization of SOC. Elevated temperatures significantly increased the rate of carbon mineralization across the peatland soils. The mean sensitivity of SOC mineralization to temperature (Q 10 value) was 2.96. The increase in substrate availability and microbial abundance in parallel with the increase in temperature is responsible for the high rates of decomposition of the organic carbon pools. We found that the mineralization of soil carbon positively correlated with the concentrations of soil dissolved organic carbon (DOC), NH 4 +-N, NO 3 −-N, as well as the abundances of bacteria, fungi, methanotrophs and nir K denitrifiers. Moreover, the content of DOC positively correlated with the abundances of soil bacteria, methanotrophs and nir K denitrifiers, indicating that the influences of soil microbial abundances on carbon mineralization were strongly mediated by the availability of carbon substrates. Our findings provide novel insights into the effects of increasing temperatures on the relationship between microbial communities and labile substrates and their roles in carbon decomposition in permafrost peatlands. [ABSTRACT FROM AUTHOR]

• Warming increases soil C cycling microbial abundance, which will result in C loss. • Soil nif H and nir K gene abundances exhibit insensitivity to 6 years of warming. • Soil β-glucosidase, inverse, and urease respond differently to 6 years of warming. • Warming accelerates DOC decomposition and leaching from shrub non-rhizosphere soil. • No warming effect is observed on soil TC, MBC, and NO 3 −–N content. Soil microbes and enzymes in permafrost peatland are sensitive to temperature changes, which might result in more potential loss of carbon and increase in available nitrogen from permafrost peatlands in a warming world. We previously demonstrated that 3-year warming could affect soil microbial abundance and enzymatic activity. However, soil microbial abundance and enzymatic activity in permafrost peatlands under long-term climate warming is not well understood. Therefore, a 6-year field manipulation experiment was used to assess the impact of long-term warming on soil microbial abundance and enzymatic activity in a permafrost peatland in northeastern China. Results showed that 6-year warming increased the abundance of bacteria in 0 to 15 cm soil under tussock and from shrub rhizosphere, fungi from shrub non-rhizosphere, and archaea under tussock and from the rhizosphere of shrub. These increased microbial abundances could stimulate soil carbon cycling and accelerate soil carbon loss in permafrost peatland under warming. Six-year warming increased methanogen abundance in 0 to 15 cm soil and methanotroph abundance in 15 to 30 cm soil under tussock, indicating that warming could enhance CH 4 cycling. Soil nir S-denitrifier abundance from the 0 to 15 cm shrub rhizosphere increased under warming, thereby suggesting that warming stimulated denitrification and N 2 O emission. β-Glucosidase activity in 0 to 15 cm soil under tussock and from shrub rhizosphere increased, but invertase activity in 15 to 30 cm soil under tussock and from shrub rhizosphere showed opposite tendency under warming. DOC content tended to increase in the 0 to 15 cm rhizosphere soil, but decreased in shrub non-rhizosphere soil. Warming increased NH 4 +–N content in both rhizosphere and non-rhizosphere soil. Positive correlations between abundances of bacteria, archaea, contents of DOC, and NH 4 +–N in 0 to 15 cm soil suggest that increases in bacterial and archaeal abundance could indicate higher carbon and nitrogen availability in topsoil of permafrost peatlands under warming. The results offer new insights into the response of plant–soil-microbe interactions in permafrost peatlands to climate change. [ABSTRACT FROM AUTHOR]

Natural wetlands are mostly nitrogen-limited ecosystems, while reclamation stimulates the loss of nitrogen (N) in soils by shifting the N regime. To investigate the microbial mechanisms of the N regime shift, we first conducted a global meta-analysis to quantify the wetland reclamation impacts on soil mineral N pools and then a field campaign to sample 24 soil cores up to 100 cm depth in a natural wetland and a 23-year cultivated soybean field from the Sanjiang Plain in northeastern China. After wetland reclamation, the N regime was shifted to cause a potential risk of massive N loss in soils; their microbial mechanisms were revealed through metagenomic data. In cropland, the relative abundance of genes involved in nitrification and assimilatory nitrate reduction to ammonia (ANRA) were enriched while those in N fixation, mineralization, denitrification, and dissimilatory nitrate reduction to ammonia (DNRA) were diminished. Wetland reclamation substantially enhanced the relative abundance of genes involved in nitrification (except for genes for ammonia oxidation to NH2OH) and denitrification in surface (0–30 cm) soils but decreased them in subsurface (30–100 cm) soils. After wetland reclamation, the relative abundance of genes involved in denitrification and DNRA significantly reduced in spring and summer, but such patterns were not found in autumn and winter. This change enhanced potential microbial-driven N loss in spring and summer. The metagenomic data serve as surrogate data sources for quantifying soil roles on soil N cycles under land use change. [ABSTRACT FROM AUTHOR]

Peatlands in permafrost region are large carbon pools sensitive to global warming. However, the effects of increased temperature on carbon emissions and associated microbial abundances of peatlands under anaerobic condition remain largely unknown, especially when considering depths. For supplementing the deficiency about this, we collected soil from 0 to 150 cm depth of a permafrost peatland in the Great Hing'an Mountain and incubated at 5 and 15 °C for 55 days under anaerobic condition. Soil CO 2 and CH 4 emissions were detected during incubation, and inorganic nitrogen, dissolved organic carbon, and carbon-cycling microbial abundances were analyzed at the end of incubation. Results showed that emission rates and cumulative emissions amount of CO 2 and CH 4 at 15 °C across all soil depths were higher than those observed at 5 °C. Specifically, 0–20 cm and 20–40 cm layers had the highest CO 2 emission rates and cumulative emission amounts, whereas the 40–60 cm and 60–80 cm layers had the highest CH 4 emission rates and cumulative emission amounts. Mean temperature sensitivity (Q 10) values of CO 2 and CH 4 were 2.39 and 55.49 respectively. Q 10 values of bacteria, fungi, archaea, methanogen, and methanotroph abundances were 1.17, 3.85, 1.75, 1.68, and 1.66 respectively, which were calculated by the abundance ratio of microbial functional gene at 15 °C and 5 °C. Similar to the trend of CO 2 emissions, high bacteria, fungi, archaea, methanogen, and methanotroph functional gene abundances were also observed in 0–20 cm and 20–40 cm layers, and such abundances increased along with temperature increasing. In sum, elevated temperature enhances the carbon emission of peatland in permafrost region, and the warming simulated CO 2 emission is linked to the abundances of carbon-cycling microorganisms. • Soil CO 2 and CH 4 emissions at 15 °C are higher than at 5 °C across all soil depths. • Active layer soil has the highest CO 2 emission amounts in permafrost peatland. • CH 4 emissions are highest in the transition layer and its adjacent active layer. • Warming stimulated CO 2 emission is linked to C-cycling related microbial abundance. [ABSTRACT FROM AUTHOR]

• Permafrost types affect soil microbial abundance distribution in peatlands. • NH 4 +-N, pH, and total C are crucial in changing soil microbial abundance. • Archaea are relatively stable in different types of permafrost peatlands. • pmo A, mcr A and nir S gene abundances can be used as TC and TN indicators in peatlands. Soil microbial abundance, which is related to soil characteristics and process rates, is an early indicator of changes in soil health and quality. However, microbial functional groups in permafrost peatland soils have rarely been studied. These soils are important C and N stores and possibly vulnerable to climate warming. We randomly gathered surface soils (0–15 cm and 15–30 cm soil layers) from 10 peatlands in sporadic island, discontinuous island, and continuous permafrost regions in Northeast China. The aim was to clarify the soil microbial abundance distribution in different types of permafrost peatlands. Results revealed different effects of permafrost types on different soil C- and N-cycling microbial abundances in peatlands. The bacteria, amo A, and nir K gene abundances in the two soil layers were the highest in discontinuous island permafrost peatlands. Soil mcr A and pmo A gene abundances in 0–15 cm soil were high in continuous and discontinuous island permafrost peatlands, respectively. The amo A gene abundance in both soil layers and nir S gene abundance in 15–30 cm soil were high in discontinuous island permafrost peatlands. The average nir K gene abundance in both soil layers was in the order: discontinuous island permafrost peatlands > continuous permafrost peatlands > sporadic island permafrost peatlands. No significant differences in archaeal abundance were observed in both soil layers among the different types of permafrost peatlands. Moreover, 42.5%, 15.9%, and 15.3% of the variation in soil microbial abundances could be explained by soil ammonia-N, pH, and total C, respectively. Our results imply that soil microbial abundance can be utilized as effective soil N availability, C pool, and pH indicators in permafrost peatlands. [ABSTRACT FROM AUTHOR]

This work designed a novel TiNiCuNb eutectic alloy for manufacturing C/C-SiC composite joints. By introducing Ti into the semi-solid TiNiCuNb alloy, low-temperature melting of this eutectic alloy was induced. Ti/TiNiCuNb/Ti composite interlayers were utilized to join C/C-SiC composite lower than the melting temperature of TiNiCuNb alloy. Effects of joining temperature on the microstructure evolution and mechanical property of joints were investigated. The melting range of this TiNiCuNb alloy was 944 °C to 1064 °C. During the initial melting of the TiNiCuNb alloy, a thin liquid layer formed on the alloy's surface, which provided a path for the rapid diffusion of elements. Without pressure, Ti could be easily introduced into the TiNiCuNb alloy, which induced the complete melting of this alloy at 950 °C. Based on this, we successfully brazed C/C-SiC composite using Ti/TiNiCuNb/Ti interlayers. It not only hindered the formation of brittle compounds in the joints, but also weakened the overreaction between filler and C/C-SiC composite. Due to the high solubility of Si in liquid filler, the joint microstructure was controlled by the interaction between filler and SiC at different temperatures. At 1010 °C for 10 min, the maximum shear strength of 28.5 MPa was obtained. This work contributed to preparing and repairing the C/C-SiC composite. • A novel TiNiCuNb eutectic alloy was designed. • Low-temperature melting of TiNiCuNb eutectic alloy was induced by introducing Ti into the semi-solid TiNiCuNb alloy. • The interaction between Ti/TiNiCuNb/Ti interlayers and C/C-SiC composite was characterized in detail. [ABSTRACT FROM AUTHOR]

Graphene nanoplates (GNPs) reinforced TiNiCu composite filler (TiNiCu G) developed with which the brazing of graphite to W was achieved in this study. The effects of the GNPs reinforcement and brazing temperature (1120–1200 °C) on the interfacial microstructure and mechanical properties of brazed joints were implemented in detail. Experimental results revealed that the bonding of graphite and filler material was achieved through the formation of a TiC reaction layer. A well bonded TiC/Ti(Ni,Cu) interface with lattice mismatch of 6.8% was observed by HRTEM. The FCC TiC and monoclinic Ti(Ni,Cu) taken the coherent orientation relations of [0 1 ̅ 1] fcc ║[331]. The typical interfacial microstructure of graphite/W joint using TiNiCu G at 1180 °C for 15 min was graphite/Ti(Ni,Cu)+ Ti 2 (Ni,Cu)+TiC /W(Ti)ss/W. The added GNPs reacted with Ti and in-situ synthesized TiC particles by reducing the residual stress to strengthen the brazed joint and increase the thickness of the brazing seam. The shear strength of the joint using composite filler reached the maximum value of 37.59 MPa, 132% higher than that joint without using GNPs. • GNPs were used as reinforcement in TiNiCu filler for brazing graphite to tungsten. • GNPs reduced the negative impact induced by the brittle compounds. • The TiC and Ti(Ni,Cu) taken the coherent orientation relations of [0 1 ̅ 1]║[331]. • The maximum shear strength was 132% higher than that joint without using GNPs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synergistic effect of Ce and Fe accelerates electron transfer and ROS generation. • Surface OH groups and OVs played important roles in the reactions. • •OH and •O 2 − are the dominant ROS while 1O 2 also play a role on AMX degradation. • The application potential of FC-0.3 catalyst on catalytic ozonation was evaluated. A Fe-doped CeO 2 was fabricated for catalytic ozonation of Amoxicillin (AMX), and the catalytic mechanisms were explored in this study. Under optimal conditions (the initial solution pH of 7.0, FC-0.3 dosage of 0.5 g/L, O 3 dosage of 4 mg/min), the AMX and TOC removal by the optimal material (FC-0.3, at Fe/Ce atomic ratio of 0.3) reached 98.1 % at 24 min and 55.2 % at 36 min, respectively. Improved the AMX mineralization efficiency by 3.7 times. The experiments and theoretical calculation reveal the mechanisms of promoted catalytic ozonation by FC-0.3: 1) Highly abundant surface-active sites (i.e., –OH) enabled the adsorption of H 2 O and O 3 , which was favorable to the generation of reactive oxygen species (ROS) and improved the reaction probability for ROS and contaminants. 2) The synergistic effect between Ce4+/Ce3+ and Fe3+/Fe2+ redox couples accelerated the electron transfer and formation of ROS. More than 42 % of •OH was generated in the presence of FC-0.3, and the •OH, •O 2 − and 1O 2 were the main ROS that contributed to AMX degradation. The surface OH groups played a key role in the catalytic ozonation. The oxygen vacancies (OVs) played an important role in electron transfer, Ce and Fe were the active sites of electrons transfer following the sequence of (Ce3+ + Fe2+) → (Ce4+ + Fe3+) → (Ce3+ + Fe2+) redox reaction. The degradation pathway investigation and toxicity evaluation revealed that some more toxic intermediates were generated during the ozonation process, and sufficient mineralization is required to meet safe discharge. This study provides reference for the synthesis of new catalysts and insight into the reaction mechanisms in the heterogeneous catalytic ozonation process. [ABSTRACT FROM AUTHOR]

Underwater wet flux-cored arc welding of Q460 steel using specially developed Ni-based filler and commercially obtained ER308 were investigated. Wet welded joints using Ni-based filler were of high performance with high ultimate tensile strength (518 MPa) and impact toughness of the weld metal (128.9 J/cm 2 ). ER308 failed to acquire sound welded joints due to extensive slag remained in the bottom of groove. The highest microhardness (450 HV) was recorded on the coarse-grained heat-affected zone of the base metal for both joints. TypeⅡboundaries existed in the interfaces between austenitic weld metal and ferritic base metal. Compared to austenitic stainless steel weld metal, nickel-based weld metal possessed the ability to be significantly diluted by Q460 base metal. [ABSTRACT FROM AUTHOR]

• New method was proposed to modify the Si 3 N 4 surface by nanosecond laser. • A recast silicon layer formed on the Si 3 N 4 surface after laser irradiation. • Defect-free Si 3 N 4 /Al joints were obtained by surface modification of Si 3 N 4. In this study, a nanosecond laser was conducted to modify the Si 3 N 4 surface to realize the bonding of Si 3 N 4 to Al. The effects of nanosecond laser irradiation on the surface morphology and chemical compositions of Si 3 N 4 ceramic together with the bonding of Si 3 N 4 ceramic to Al were investigated. The laser irradiation induced the thermal decomposition of Si 3 N 4 ceramic, resulting in the formation of a recast silicon layer upon the ceramic surface. Then bonding of Si 3 N 4 ceramic and Al was achieved by the eutectic reaction between the recast silicon layer and Al at a bonding temperature of 600 °C under a uniaxial pressure of 10 MPa for 60 min. The nanosecond laser irradiation method proposed in this study provided a new idea to realize the direct bonding of ceramic to metal. [ABSTRACT FROM AUTHOR]

Natural wetlands store 20–30% of soil organic carbon (C) in terrestrial ecosystems. Wetlands conversion to croplands has caused a massive loss of soil organic C; however, the microbial contribution to this C loss remains elusive. In this study, we took 24 soil cores from a natural wetland and a 23-year cultivated cropland over four seasons to compare the abundance of functional genes encoding 138 enzymes for ten C-cycling pathways classified as organic C degradation, catabolic and anabolic processes. We found that land use-induced C loss was primarily driven by enhanced organic C degradation (∼24% increase) but suppressed microbial C assimilation efficiency, represented by shifted catabolism and declined anabolism (∼22% decrease). The enhanced organic C degradation was advocated by the enriched genes encoding organic C degradation enzymes; the suppressed microbial C assimilation efficiency was upheld by the shifted catabolic processes and inhibited anabolic processes. Compared with natural wetlands, the croplands showed substantial shifts in catabolic processes - 22% suppression of the Embden-Meyerhof-Parnas pathway, 27% decline in the Citrate Cycle, 22% increase in Entner-Doudoroff, and 25% stimulation in pentose phosphate pathways. Meanwhile, the anabolic process, especially the Wood-Ljungdahl pathway, was significantly suppressed (∼55%) in the cropland. The shifts in organic C degradation, catabolism, and anabolism were stronger in spring and summer than in winter and autumn. At the ecosystem level, microbial metabolic quotient was suppressed by 44%, while microbial biomass carbon was boosted by 5% after wetland conversion to cropland, indicating a faster microbial growth rate but lower C use efficiency. Differentiating microbial metabolic processes explained the C loss after wetland cultivation, indicating an urgency to represent microbial metabolism in soil C models. • The organic C degradation was enhanced after wetland conversion. • The catabolic process was shifted to energetically less efficient after conversion. • The anabolic process was depressed in cultivated cropland. • C loss after cultivation was driven by microbial metabolism differentiation. [ABSTRACT FROM AUTHOR]

Abstract: Anthropogenic activities have increased phosphorus (P) inputs to wetland ecosystems. However, little is known about the effect of P enrichment on soil respiration in these ecosystems. To understand the effect of P enrichment on soil respiration, we conducted a field experiment in Calamagrostis angustifolia-dominated freshwater marshes, the Sanjiang Plain, Northeast China. We investigated soil respiration in the first growing season after P addition at four rates (0, 1.2, 4.8 and 9.6 g P m−2 year−1). In addition, we also examined aboveground biomass, soil labile C fractions (dissolved organic C, DOC; microbial biomass C, MBC; easily oxidizable C, EOC) and enzyme activities (invertase, urease and acid phosphatase activities) following one year of P addition. P addition decreased soil respiration during the growing season. Dissolved organic C in soil pore water increased after P addition at both 5 and 15 cm depths. Moreover, increased P input generally inhibited soil MBC and enzyme activities, and had no effects on aboveground biomass and soil EOC. Our results suggest that, in the short-term, soil respiration declines under P enrichment in C. angustifolia-dominated freshwater marshes of Northeast China, and its extent varies with P addition levels. [Copyright &y& Elsevier]

Abstract: Natural wetlands play an important role in the global carbon cycle, and loss of dissolved carbon through water has been indicated as one of the most important carbon sources for riverine ecosystems. During the last century, a large natural wetland area was reported to be converted to other land use types such as rice paddy land around the world. In this study, we explored the dynamics of dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) in two natural freshwater wetlands and a rice paddy field, which was reclaimed from the natural wetlands in the Sanjiang Plain, Northeastern China, during the growing season (May–October) of 2009. The DOC and DIC concentrations in the two ecosystems were significantly different (P <0.05). The mean DOC concentrations during the growing season in the surface water of the Deyeuxia angustifolia and Carex lasiocarpa wetlands were 49.88±5.44 and 27.97±1.69mg/L, respectively, while it was only 8.63±2.54mg/L in the rice paddy field. Specific ultra-violet light absorption at 254nm (SUVA254) of DOC increased by an average of 19.54% in the surface water from the natural wetlands to rice paddy, suggesting that DOC mobilized in the natural wetlands was more aromatic than that in the rice paddy field. The mean DIC concentration in surface water of the rice paddy was 5.25 and 5.04 times higher than that in the natural D. angustifolia and C. lasiocarpa wetlands, respectively. The average ratio of DIC to dissolved total carbon (DTC) for the water sampled from the artificial drainage ditch in the rice paddy field was 61.82%, while it was 14.75% from the nearby channel of natural wetlands. The significant differences in dissolved carbon concentration in surface water and channels originating from different land use types suggested that reclamation of natural wetlands to rice paddy field would reduce DOC runoff and increase the DIC concentration to adjacent watersheds. Our study results for the changed pattern in dissolved carbon after the natural wetland was transformed to paddy field could have important implications for studying the impacts of the large-scale land use change to carbon cycle and management. [Copyright &y& Elsevier]

In this paper, a novel approach was proposed to achieve the joining of AlN and Cu by nanosecond laser pre-irradiation of AlN. The effects of the speed of laser scanning on the morphology, chemical compositions, and properties of the surface of AlN ceramic and the mechanism of laser-assisted joining of AlN and Cu were investigated. With the increase of the speed of laser scanning, the surface roughness of AlN decreased. After nanosecond laser irradiation, element Al was detected on the surface of AlN. When nanosecond laser irradiation was applied, the hydrophilicity and the surface energy of the ceramic surface were improved. The modified AlN was successfully joined to Cu at the temperature of 620 °C with a speed of laser scanning of 500 or 1000 mm/s. The results of TEM confirmed the presence of Al 4 Cu 9 , indicating the metallurgical combination of Cu and AlN. Also, the method presented in this paper was supposed to be of great reference significance for the joining of ceramics and metals. [ABSTRACT FROM AUTHOR]

• W90 and Mg alloy were firstly bonded by ultrasonic-assisted soldering at 250 °C. • A semi-coherent interface was formed between Sn and W. • The joint strength treated with the ultrasonication time of 2 s reached 10.4 MPa. W90 tungsten heavy alloy (W90) and AZ31B Mg alloy were firstly bonded by ultrasonic-assisted soldering using Sn in atmospheric environment. The wetting angle of Sn on W90 decreased to 130.7° under the action of ultrasound. The microstructure of W90/Sn/Mg joint treated with 2 s of ultrasounication time was W90/Mg 2 Sn + Sn/Mg 2 Sn layer/Mg. As the ultrasonication time increased to 4 s, the joint width reduced and the thickness of Mg 2 Sn layer increased. The joint strength decreased from 10.4 MPa to 5.1 MPa as the ultrasonication time increased from 2 s to 4 s. A semi-coherent interface formed at the Sn/W interface as the ultrasound was applied. [ABSTRACT FROM AUTHOR]

Aims: Soil dissolved organic carbon (DOC) is a primary form of labile carbon in terrestrial ecosystems, and therefore plays a vital role in soil carbon cycling. This study aims to quantify the budgets of soil DOC at biome and global levels and to examine the variations in soil DOC and their environmental controls. Location: Global. Time period: 1981–2019. Methods: We compiled a global dataset and analysed the concentration and distribution of DOC across 10 biomes. Results: Large variations in DOC are found among biomes across space and the soil DOC concentration declines exponentially along soil depths. Tundra has the highest soil DOC concentration in 0–30 cm soils [453.75 (95% confidence interval: 324.95–633.5) mg/kg], whereas tropical and temperate forests have relatively lower DOC concentrations, ranging from 30.20 (24.78–36.80) to 54.54 (49.77–59.77) mg/kg. DOC generally accounts for < 1% of total organic carbon in soils, and DOC in 0–30 cm contributes more than half of the total DOC in the 0–100 cm soil profile. Furthermore, variations in DOC are primarily controlled by soil texture, moisture, and total organic carbon. Main conclusions: A global synthesis is combined with an empirical model to extrapolate the DOC concentration along soil profiles across the globe, and global budgets of DOC are estimated as 7.20 Pg C in the top 0–30 cm and 12.97 Pg C in the 0–100 cm soil profile, respectively, with a considerable variation among biomes. The strong soil texture control but weak total organic carbon (TOC) control on DOC variations suggest that the investigation of physical protection of soil organic carbon might need to expand to consider the labile C in soils. The global maps of DOC concentration serve as a benchmark for validating land surface models in estimating carbon storage in soils. [ABSTRACT FROM AUTHOR]

In this work, carbon fiber was introduced into the Ag-26.7Cu-4.5Ti (wt%) filler to optimize brazed joints by participating in brazing reaction process. The interfacial microstructure was analyzed by SEM and TEM, the effects of carbon fiber content on the microstructure and mechanical property of brazed joints were studied, the formation of brazing interface was systematically discussed, and the action mechanism of carbon fiber was illustrated. Experimental results demonstrated that carbon fiber reacted with Ti to generate TiC during the brazing process, and formed a structure of carbon fiber wrapped by TiC and Ti-Cu compounds (TiCu+Ti 3 Cu 4). Due to competitive reaction between carbon fiber and Cu to Ti, the formation of bulk Ti 3 Cu 4 and TiCu 4 was inhibited, while the formation of Cu-based solid solution was promoted. The microstructure of joints was dispersed as the increase of carbon fiber. The maximum shear strength of 27.8 MPa was achieved when 0.3 wt% carbon fiber was added into AgCuTi filler. The reinforcing effects of carbon fiber were mainly to relieve the residual stress generated by CTE mismatch and reduce the thickness of brittle TiC layer close to C/C composite. However, excessive carbon fiber would deteriorate the joints because of the insufficient reaction between filler and C/C composite. • The intermetallic compounds formed on carbon fiber were characterized in detail. • The formation of brazing interface was systematically discussed. • The effects of carbon fiber content on the microstructure evolution and mechanical property of the joints were investigated. • The strengthening mechanism of carbon fiber during the brazing process was illustrated. [ABSTRACT FROM AUTHOR]

Joining ceramics and metals is important to expand their application scope in the nuclear industry. The brazing of SiC and Mo was conducted using a Nb 0.74 CoCrFeNi 2 eutectic high-entropy alloy filler. The microstructure and mechanical properties of the joints were examined at different brazing temperatures. As the temperature increased, the eutectic structure gradually disappeared, and a layered structure was formed at the brazed joint. An increase in the MoNi phase content can improve joint strength owing to differences in the thermal expansion coefficient and lattice mismatch between phases. The joints exhibited a maximum shear strength of 62 MPa at 1300 °C. Finite element analysis results demonstrated that the presence of a Cr 0.46 Mo 0.4 Si 0.14 phase causes the concentration of residual stress. Brittle fracture occurred mainly in the Cr 0.46 Mo 0.4 Si 0.14 phase, causing the rupture of the joint. This study provides valuable insights into the use of eutectic high-entropy alloys as fillers to establish a strong and reliable connection between ceramics and metals. • The eutectic high-entropy Nb 0.74 CoCrFeNi 2 alloy was used to join a SiC and Mo. • The presence of Cr 0.46 Mo 0.4 Si 0.14 phase causes concentration of residual stress. • Amorphous regions appear at the interface between FCC and MoNi. • The existence of dislocations in FCC phase storage plays a stress-relieving role. [ABSTRACT FROM AUTHOR]

Methane (CH 4) is a potent greenhouse gas, and it is well established that low nitrogen (N) stimulates- and high N suppresses CH 4 oxidation in grassland ecosystems. In this study, we examined the response of CH 4 uptake to long-term (>10 years) multi-level N additions in a temperate steppe of northern China. The N impacts on CH 4 uptake transitioned from positive to negative at the N addition rate of 4 g N m−2 y−1. However, the high-N suppression on CH 4 uptake was partially relieved when the continuous (>10 years) high N inputs (16 g N m−2 y−1 to 64 g N m−2 y−1) caused soil pH drop to < 5.7. Further experiments revealed that continuous high-N inputs acidified soil to pH < 5.7 that released metal ions to stimulate monooxygenase enzyme activity; therefore, the CH 4 oxidation suppression was partially relieved under continuous N loading. Structural equation model results confirmed that metal ions, such as Iron (Fe3+), Manganese (Mn4+), and Copper (Cu) desorbed by soil particles, were negatively correlated with soil pH while positively correlated with CH 4 oxidation under high N inputs. These analyses suggested that continuous high N inputs-induced soil acidification can release previously bounded metal elements that partially alleviated the N suppression on CH 4 uptake. The N-induced soil acidification impacts on CH 4 uptake might play a critical role in global CH 4 cycling and deserve further investigation as external N inputs continue climbing. • N suppression on CH 4 uptake shifted after 10 years of continuous high N addition. • The high-N suppression was partially relieved when N inputs caused soil pH to drop to 5.7. • The N-induced soil acidification released previously bounded metal ions, partially alleviating the N suppression. [ABSTRACT FROM AUTHOR]

The wetting behavior of Sn0.3Ag0.7Cu (SAC) filler with the addition of Ti on SiC ceramic was investigated using sessile drop method. SiC/SiC was brazed by SAC‐Ti filler with different Ti content at 1223 K (950°C) for 10 minutes. The wettability of SAC‐Ti filler on SiC was significantly enhanced with the addition of Ti. The contact angle decreased at first and then increased with increasing Ti content. The lowest contact angle of 9° was obtained with SAC‐1.5Ti (wt%) filler. When Ti content further increased to 2.0 wt%, the contact angle increased, due to the intense reaction of Ti–Sn. The reaction between Ti and SiC controlled the wetting behavior of SAC‐Ti on the SiC substrate and the reaction products such as TiC and Ti5Si3 were formed. The wetting of SAC‐Ti on SiC was reaction‐controlled. Interfacial reaction products TiC and Ti5Si3 were observed. The wetting activation energy in spreading stage was calculated to be 129.3 kJ/mol. Completely filled SiC/SiC joints were obtained using the filler with Ti content higher than 0.5 wt%. The fillet height increased firstly then decreased with mounting Ti content. The shear strength of joints increased first with the addition of Ti then decreased with Ti content increasing to 2.0 wt%. The highest shear strength of 35.7 MPa was obtained with SAC‐1.5 Ti (wt%) filler. The wettability of Sn0.3Ag0.7Cu on SiC was enhanced by the introduction of Ti, which results from the interfacial reaction between Ti and SiC forming TiC and Ti5Si3. [ABSTRACT FROM AUTHOR]

Diurnal freeze-thaw cycles (FTCs) occur in the spring and autumn in boreal wetlands as soil temperatures rise above freezing during the day and fall below freezing at night. A surge in methane emissions from these systems is frequently documented during spring FTCs, accounting for a large portion of annual emissions. In boreal wetlands, methane is produced as a result of syntrophic microbial processes, mediated by a consortium of fermenting bacteria and methanogenic archaea. Further research is needed to determine whether FTCs enhance microbial metabolism related to methane production through the cryogenic decomposition of soil organic matter. Previous studies observed large methane emissions during the spring thawed period in the Sanjiang seasonal frozen marsh of Northeast China. To investigate how FTCs impact the soil microbial community and methanogen abundance and activity, we collected soil cores from the Sanjiang marsh during the FTCs of autumn 2014 and spring 2015. Methanogens were investigated based on expression level of the methyl coenzyme reductase ( mcrA ) gene, and soil bacterial and archaeal community structures were assessed by 16S rRNA gene sequencing. The results show that a decrease in bacteria and methanogens followed autumns FTCs, whereas an increase in bacteria and methanogens was observed following spring FTCs. The bacterial community structure, including Firmicutes and certain Deltaproteobacteria , was changed following autumn FTCs. Temperature and substrate were the primary factors regulating the abundance and composition of the microbial communities during autumn FTCs, whereas no factors significantly contributing to spring FTCs were identified. Acetoclastic methanogens from order Methanosarcinales were the dominant group at the beginning and end of both the autumn and spring FTCs. Active methanogens were significantly more abundant during the diurnal thawed period, indicating that the increasing number of FTCs predicted to occur with global climate change could potentially promote CH 4 emissions in seasonal frozen marshes. [ABSTRACT FROM AUTHOR]

Carbon/carbon (C/C) composite and Ti6Al4V alloy (wt%) were successfully brazed with graphene nanosheets strengthened AgCuTi filler (AgCuTiG). Graphene nanosheets (GNSs) with low CTE and high strength were dispersed into AgCuTi filler by ball milling. The interfacial microstructure was systematically characterized by varieties of analytical means including transmission electron microscopy (TEM). Results show that typical interfacial microstructure of the joint brazed at 880 °C for 10 min is a layer structure consisting of (Ti6Al4V/diffusion layer/Ti2Cu + TiCu + Ti3Cu4 + TiCu4/GNSs + TiCu + TiC + Ag(s,s) + Cu(s,s)/TiC/C/C composite). The interfacial microstructure and mechanical properties of brazed joints changed significantly as temperature increased. High temperature promoted the growth of TiCu and TiC phases, which were attached to GNSs. Meanwhile, the diffusion layer and primary reaction layers thickened as temperature increased, while the thickness of brazing seam decreased. The maximum shear strength of 30.2 MPa was obtained for the joint brazed at 900 °C for 10 min. GNSs decreased the thickness of brittle reaction layers and promoted the formation of TiCu and TiC phases in brazing seam, which caused the strengthening effect and decreased the CTE mismatch of brazed joints. The fracture modes are also discussed in this paper. [ABSTRACT FROM AUTHOR]