Occurrence of nitrification-denitrification and gaseous nitrogen loss process in flooded rice soil

Flooding in wetland rice fields soon after transplanting results in displacement of soil air (including O2). Thus any dissolved O2 in the pore water is consumed out by microbial respiration in a short period. Supply of O2 to the flooded rice soil is by diffusion of O2 through the standing floodwater and consumption at the soil-water interface, and by exudation of O2 by rice roots and subsequent diffusion of O2 into the rhizosphere. The greater potential consumption of O2 compared to the renewal rate results in the development of distinct soil layers: oxidized soil layers under soil-water interface and in the rhizosphere, and reduced soil layers or reduced bulk soil. Nitrification in oxidized soils and denitrification in reduced soils have been known. Currently, denitrification in oxidized soils, even in standing floodwater, has also been identified. In this article, we present a modified nitrification and denitrification occurring mechanism in flooded rice soil.     

Effects of nitrogen sources and glucose on the consumption of ethylene and methane by temperate volcanic forest surface soils

There is limited knowledge with regard to the consumption of ethylene (C2H4) and methane (CH4) in volcanic forest soils containing low microbial carbon-to-organic carbon ratio, and to the responses of both consumptions to nitrogen and carbon additions. Temperate volcanic forest surface soils under three forest stands (e.g. Pinus sylvestris L., Cryptomeria japonica and Quercus serrata) were used to compare CH4 and C2H4 consumption by forest soils, and to study the effects of nitrogen sources and glucose on both consumptions. There was a good parallel between CH4 and C2H4 consumption by for- est soils, but mineralization reduced CH4 consumption rather than C2H4 consumption in forest soils, particularly in a Pinus forest soil. The stimulatory effect of glucose addition on both CH4 and C2H4 consumption by forest soils was increased by increasing the pre-incubation period after glucose addi- tion, and a largest stimulation occurred in the Pinus forest soil. The addition of KNO3-N at the rate of 100 μg·g1 significantly reduced the consumptions of both C2H4 and CH4 by forest soils (P≤0.05). In the presence of urea plus dicyandiamide, the consumption rates of C2H4 and CH4 by forest soils were higher than those in the KNO3-N and urea-N treated soils at the same N rate (P≤0.05), but were similar to those of the control. Hence, under experimental conditions, there was a strong inhibitory effect of NO3 rather than NH4 addition on the CH4 and C2H4 consumption in these forest soils. When amount of the added NO3-N increased up to more than 2―3 times the soil initial NO3-N concentrations, both C2H4 and CH4 consumption rates were reduced to 10%―20% of the rates in soils without nitrate addition. By comparing the three forest stands, it was shown that there was a smallest effective concentration of the added nitrate that could inhibit C2H4 and CH4 consumption in the Pinus forest soil, which indicated that C2H4 and CH4 consumption of the soil was more sensitive to NO3-N addition.     

Burn-resistant behavior and mechanism of Ti14 alloy

The direct-current simulation burning method was used to investigate the burn-resistant behavior of Ti14 titanium alloy. The results show that Ti14 alloy exhibits a better burn resistance than TC4 alloy (Ti–6Al–4V). Cu is observed to preferentially migrate to the surface of Ti14 alloy during the burning reaction, and the burned product contains Cu, Cu₂O, and TiO₂. An oxide layer mainly comprising loose TiO₂ is observed beneath the burned product. Meanwhile, Ti₂Cu precipitates at grain boundaries near the interface of the oxide layer, preventing the contact between O₂ and Ti and forming a rapid diffusion layer near the matrix interface. Consequently, a multiple-layer structure with a Cu-enriched layer (burned product)/Cu-lean layer (oxide layer)/Cu-enriched layer (rapid diffusion layer) configuration is formed in the burn heat-affected zone of Ti14 alloy; this multiple-layer structure is beneficial for preventing O₂ diffusion. Furthermore, although Al can migrate to form Al₂O₃ on the surface of TC4 alloy, the burn-resistant ability of TC4 is unimproved because the Al₂O₃ is discontinuous and not present in sufficient quantity.     

Microstructure characterization of a pressureless infiltrating oxidized SiCp preform by Al-8Mg

The microstructure of a pressureless infiltrating 55vol% oxidized SiC preform by Al-8Mg alloy was characterized by transmission electron microscopy (TEM), high resolution TEM (HRTEM), field emission scanning electron microscopy (FE-SEM), and X-ray diffraction. The TEM image of the interface between Al and SiC shows that the surface of SiC is covered by a rough nanocrystal layer of MgAl₂O₄, Al₂O₃, and Si, produced by the interfacial reaction of Al, Mg, and SiO₂ on the surface of SiC. The Al-SiC interface is also examined by HRTEM to be better understood how MgAl₂O₄ and Al₂O₃ are produced. Dendritic Al₂O₃ crystals are embedded in the pores of the composite generated from the mutual bonding of SiO₂ on the surface of SiC. Columnar AlN crystals of about 250 nm in length are bunched vertically on the SiC particle surface.     

Immobilization of arsenic in soils by stabilized nanoscale zero-valent iron, iron sulfide (FeS), and magnetite (Fe3O4) particles

Arsenic is a widespread contaminant in soils and groundwater. While various iron-based materials have been studied for immobilizing arsenic in contaminated soils, the feasibility of stabilized iron-based nanoparticles has not been reported. This study investigates the effectiveness of using three types of starch-stabilized iron-based nanoparticles, including zero-valent iron (ZVI), iron sulfide (FeS), and magnetite (Fe₃O₄), for immobilization of arsenic in two representative As-contaminated soils (an orchard soil and a fire range soil). To test the effect of the nanoparticles on the arsenic leachability, As-contaminated soils were amended with the nanoparticles at various Fe/As molar ratios (5:1–100:1) and contact time (3 and 7 d). After three days’ treatments of a field-contaminated sandy soil, the PBET-based bioaccessibility of As decreased from an initial (71.3±3.1)% (mean±SD) to (30.9±3.2)% with ZVI, (37.6±1.2)% with FeS, and (29.8± 3.1)% with Fe₃O₄ at an Fe/As molar ratio of 100:1. The TCLP-based leachability of arsenic in a spiked fire range soil decreased from an initial (0.51±0.11)% to (0.24±0.03)%, (0.27±0.04)% and (0.17±0.04)% by ZVI, FeS, and Fe₃O₄ nanoparticles, respectively. The Fe₃O₄ nanoparticles appeared to be more effective (5% or more) than other nanoparticles for immobilizing arsenic. When the two soils were compared, the treatment is more effective on the orchard soil that has a lower iron content and higher initial leachability than on the range soil that already has a high iron content. These results suggest that these innocuous iron-based nanoparticles may serve as effective media for immobilization of As in iron-deficient soils, sediments or solid wastes.     

Temperature effects on ethylene and methane production from temperate forest soils

Change in temperature affects the activity of soil microorganisms.However,there is limited knowledge about temperature effects on ethylene(C2H4) and methane(CH4) production from forest soils.Topsoil samples(0―5 cm) collected from different temperate forest stands(e.g.,Pinus sylvestris L.,Cryptomeria japonica,and Quercus serrata) were used to compare C2H4 and CH4 production from soils at temperature from 5 to 35℃ under oxic and anoxic conditions.The rates of C2H4 and CH4 production from soils under oxic cond...     

Effects of acetylene at low concentrations on nitrification, mineralization and microbial biomass nitrogen concentrations in forest soils

Temperate forest surface soils at the varying distances from main trunks (e.g., Pinus koraiensis and Quercus mongolica) were used to study the effects of acetylene (C₂H₂) at low concentrations on nitrification, mineralization and microbial biomass N concentrations of the soils, and to assess the contribution of heterotrophic nitrification to nitrous oxide (N₂O) emissions from soils. The use of acetylene at partial pressures within a range from 10 to 100 Pa C₂H₂ in headspace gas gave a significant decrease in N₂O emission at soil moisture of c. 45% water-filled porosity space, and the decrease was almost the same in each soil after exposure of C₂H₂ at low concentrations. Heterotrophic nitrification could account for 21%―48% of total N₂O emission from each soil; the contribution would increase with increasing distances from the Pinus koraiensis trunks rather than from the Quercus mongolica trunks. Under the experimental conditions, the use of C₂H₂ at low concentrations showed no significant influence on soil microbial biomass N, net N mineralization and microbial respiration. However, 100 Pa C₂H₂ in headspace gas could reduce carbon dioxide (CO₂) emissions from soils. According to the rapid consumption of 10 Pa C₂H₂ by forest soils and convenience for laboratory incubations, 50 Pa C₂H₂ in headspace gas can be used to study the origin of N₂O emissions from forest soils under aerobic conditions and the key associated driving mechanisms. The N₂O and CO₂ emissions from the soils at the same distances from the Quercus mongolica trunks were larger than those from the Pinus koraiensis trunks, and both emissions decreased as the distances from trunks increased. The stepwise regression analysis showed that 95% of the variability in soil CO₂ emissions could be accounted for by the concentrations of soil total C and water soluble organic C and soil pH, and that 72% of the variability in soil N₂O emissions could be accounted for by the concentrations of soil total N, exchangeable NH⁺₄-N and microbial biomass N and 25% of the variability in heterotrophic nitrification by the soil microbial biomass N concentration. The emissions of N₂O and CO₂ from forest soils after exposure of C₂H₂ at low concentrations were positively related to the net nitrification of the soils.     

Interface bond mechanisms of ceramic-cemented carbide compact insert

Conclusion Ceramic-cemented carbide compact inserts have been developed by hot-pressing sintering techniques, the upper part of the compact insert is of Al₂O₃ + TiB₂ ceramic material, while the base part of the compact insert is of WC + Co cemented carbide. The compact insert makes full use of the advantages of the high hardness of ceramic materials and the high strength of cemented carbide, and its mechanical properties are just between that of Al₂O₃ + TiB₂ and WC + Co. SEM, XRD and electron microprobe analysis showed that element diffusion and formation of new phases are the main causes for the bond of Al₂O₃ + TiB₂ with WC + Co in the interface.     

铁氨氧化在环境系统中的研究进展及其应用性探究

近年来,厌氧氨氧化耦合Fe(III)还原过程(Feammox)作为一种新型的脱氮技术,在环境系统中被广泛发现和研究。Feammox从热力学角度分析在不同环境中(高地土壤、水稻土、河岸沉积物、湿地沉积物)的代谢产物不同(N₂、NO_2^-、NO_3^-)。环境因素影响着Feammox脱氮效果,本文从铁电极、pH、溶解氧(DO)、温度、Fe(III)浓度等方面探讨Feammox的过程控制。对于Feammox过程中的作用微生物还缺乏统一定论,其中尤以铁还原菌、Acidimicrobiaceae bacterium A6、厌氧氨氧化菌属为主要代表。本文就Feammox反应机理、影响因素、微生物多样性及工程适用性分析角度来归纳总结近年来的研究进展及应用型探究,并对未来发展和应用进行展望。     

低温域湿地植物根际氮转化强度

在低温条件下(0 ～15℃),对菖蒲、芦苇、香蒲等10种湿地植物根际土壤的氮转化强度进行对比分析.结果表明,湿地植物根际氨化、反硝化作用强度随温度下降而逐渐降低,硝化作用强度在10℃左右出现大幅下降;低温域植物根际反硝化作用强度明显高于硝化作用强度;植物种类对根际土壤氨化、硝化作用强度影响较大,其中香蒲氨化作用强度最大...     

微生物在温室气体排放与吸收中的多样性

对N2O和CH4两种重要的温室气体进行了研究．结果表明它们的生物排放源主要来自土壤微生物过程．其中土壤微生物的硝化和反硝化作用是N2O的重要排放源,厌氧土壤通过反硝化作用能将N2O还原为N2,是N2O的弱的汇．CH4主要由土壤中甲烷产生菌在厌氧条件下产生．在好氧条件下,甲烷氧化菌将厌氧土壤产生的甲烷进行氧化,成为土壤甲烷的汇．由此可见土壤微生物在温室气体N2O和CH4的产生与消耗中起着十分重要的作用,体现了微生物在温室气体产生与排放中的多样性．     

天然盐碱化湿地土壤水分扩散率的分析

运用水平土柱入渗法模拟研究了盐碱化湿地土壤的水分扩散过程以及水分扩散率和土壤含水量之间的关系,结果表明：盐碱化可降低土壤的水分渗透性能,湿地10～20 cm内土层水分渗透速度较其它两层小得多,下部土壤层次的水分扩散率高于上部土壤层,湿地土壤水扩散率随土壤含水量的增加呈指数增长变化的趋势,且表层土壤的增长曲线相对较陡.     

铜胁迫下菌株CL01促进紫云英生长的研究

从湖北某矿区植物根际土壤中筛选到了一株多种重金属抗性菌株CL01.根据形态学特征和16S rDNA序列比较了结果,鉴定其为Achromobacter xylosoxidans.当土壤所含铜浓度为75 mg/kg时,接种菌株CL01可以促进紫云英根延长,增加植株高度,提高紫云英的生物量.菌株CL01通过减少根际土壤可吸收的铜含量,减少了铜在紫云英根部的聚集,说明该细菌提高了植物的抗铜能力.     

A kinetic approach to evaluate salinity effects on carbon mineralization in a plant residue-amended soil

The interaction of salinity stress and plant residue quality on C mineralization kinetics in soil is not well understood. A laboratory experiment was conducted to study the effects of salinity stress on C mineralization kinetics in a soil amended with alfalfa, wheat and corn residues. A factorial combination of two salinity levels (0.97 and 18.2 dS/m) and four levels of plant residues (control, alfalfa, wheat and corn) with three replications was performed. A first order kinetic model was used to describe the C mineralization and to calculate the potentially mineralizable C. The CO₂-C evolved under non-saline condition, ranged from 814.6 to 4842.4 mg CO₂-C/kg in control and alfalfa residue-amended soils, respectively. Salinization reduced the rates of CO₂ evolution by 18.7%, 6.2% and 5.2% in alfalfa, wheat and corn residue-amended soils, respectively. Potentially mineralizable C (C ₀) was reduced significantly in salinized alfalfa residue-treated soils whereas, no significant difference was observed for control treatments as well as wheat and corn residue-treated soils. We concluded that the response pattern of C mineralization to salinity stress depended on the plant residue quality and duration of incubation.     

Studies of several systems with air electrode electro-synthesizing H<Subscript>2</Subscript>O<Subscript>2</Subscript> on the spot for degrading aniline in aqueous

A gas diffusion electrode (air electrode) with a high current efficiency of electro-synthesizing H₂O₂ using O₂ in air was prepared. The several systems with air electrode as cathode of electro-synthesizing H₂O₂ on the reaction spot for degrading aniline in aqueous—electro-Fenton system, photo-excitation electro-H₂O₂ system and photo-electro-Fenton system, were developed. The rates of decomposition of H₂O₂ and mineralization of aniline were experimentally measured respectively under different conditions, and the results indicated there has an excellent parallel relation between decomposition rate of H₂O₂ and mineralization rate of aniline. Especially, photo-electro-Fenton system, where H₂O₂ is decomposed the fastest, is the best system of oxidizing and degrading organic toxicants. Compared photo-electro-Fenton system with photo-Fenton system, important role is revealed in the interface of air electrode. In this paper, the mineralization mechanism of aniline in the photo-electro-Fenton system was also discussed. Foundation item: Supported by the National Natural Science Foundation of China (200710026) and Foundation of Environmental Sciences Academy of Jiangsu Province. Biography: Cao xiao-yu (1979-), male, Master candidate, research direction: Electrochemistry     

基于土水特征曲线的非饱和土强度预测研究

土水特征曲线反映了非饱和土体中的基质吸力与含水量,或者饱和度之间的关系,在非饱和土的渗流、强度、扩散等诸多方面的研究都会涉及土水特征曲线的相关理论。在前人研究的基础上,分析了土水特征曲线产生滞回效应的微观机理,将基质吸力产生的负压力对应于土颗粒间所产生正应力的增量,将体积含水量引入抗剪强度增量公式。认为非饱和土的强度分为土体处在饱和状态时的强度以及由于基质吸力所引起的强度增量两个部分,提出了非饱和土的强度预测公式;并通过定义等效含水率对公式进行修正。通过选取的四种材料参数对所提出的公式进行验证,结果表明强度预测公式与实际情况吻合良好,所提公式具有一定的适用性。在此基础上较为系统地分析了基质吸力对非饱和土体强度的贡献。     

First-principles studies of the adsorption of O2 on Al （001）

Oxidationisaubiquitousphenomenonofnature.Theeconomiclossduetooxidationisverylargeeveryyear.Theinvestigationoftheadsorptionofoxygenonthesur-facesofmetalsisofgreatimportanceforbetterunder-standingoftheoxidationmechanismbecauseitistheverybeginningstageofoxidationofmetals.Itisgenerallybe-lievedthattheprocessofO2adsorptiononmetalsisinanorderofO2?O?O-?O2-,andthefollowingstagesareoxidenucleation,growthandtheoxidefilmformation.Astheprocessofadsorptionistooquicktobeobservedbyexperiments,atheoreticals…     

变化的淹水条件对土壤磷素释放影响

为了研究农业磷引起的水体富营养化机理,选择太湖流域宜兴稻麦轮作土,模拟了变化的淹水深度、水土比、不同酸度上覆淹水等,进行了淹水土壤磷释放研究.实验表明:土壤释磷量随淹水深度成比例增加,同一淹水深度土壤吸附/释放磷量出现周期性变化规律;实验得到一个临界水土比4:1,水土比小于4:1时,淹水中没有Fe2 溶出,且土壤磷释放缓慢,而水土比大于4:1时,磷释放强度增大,上覆淹水中开始出现Fe2 ,且随水土比增大而增加;碱性淹水条件时土壤释磷量大于酸性淹水条件时的释磷鼍,其中上覆水pH9.78时土壤释磷量最大,而pH3.7时土壤总铁和Fe2 释放量最大,但此时释磷量很低,表明淹水中水-土体系Fe2 -Fe2 氧化物氢氧化物胶体一定程度上抑制土壤磷的释放.     

龙江河河岸带撑篙竹根际与非根际土壤细菌群落特征

为探究龙江河河岸带撑篙竹(Bambusa pervariabilis McClure)根际与非根际土壤细菌群落组成特征,揭示土壤细菌群落的相互作用与功能特征,以及影响细菌群落组成的环境因素,本研究开展该区域土壤理化环境因子调查,并进行土壤细菌群落高通量测序分析。结果表明,撑篙竹根际土壤pH值、氨氮(NH₄⁺-N)、硝氮(NO^-₃-N)和速效磷(Available Phosphorus, AP)均低于非根际土壤,水分含量(Moisture Content, MC)和土壤有机质(Soil Organic Matter, SOM)含量则高于非根际土壤,部分理化指标之间存在显著相关性。α多样性分析表明,撑篙竹根际土壤细菌群落丰富度较非根际土壤高,而多样性较非根际土壤低;放线菌门(Actinobacteriota, 26.93%)、变形菌门(Proteobacteria, 17.63%)、Patescibacteria(4.28%)、黏球菌门(Myxococcota, 3.25%)和蓝藻门(Cyanobact...     

用于45#钢丝拉拔加工的叠层陶瓷拉拔模具磨损分析

为研究45#钢丝拉拔加工过程中受力和Al₂O₃-TiC/Al₂O₃-TiC-CaF₂叠层陶瓷拉拔模具磨损情况,采用真空热压烧结方式制备Al₂O₃-TiC/Al₂O₃-TiC-CaF₂叠层陶瓷拉拔模具,并将其固定在万能拉伸试验机上进行钢丝拉拔实验。 采用三维造型软件SolidWorks建立钢丝坯料和拉拔模具的有限元模型,通过有限元模拟软件对钢丝拉拔成形过程进行仿真分析,得到45#钢丝在变形过程中的轴向应力、应变以及拉拔力的变化情况。 扫描电镜（SEM）及能量弥散X射线谱（EDS）观察拉拔模具磨损后的微观形貌。 结果表明:叠层陶瓷拉拔模具工作区的Al₂O₃-TiC-CaF₂材料层比Al₂O₃-TiC材料层磨损严重,Al₂O₃-TiC-CaF₂材料层的固体润滑膜被拖覆到Al₂O₃-TiC材料层,模具整体具有自润滑性能。 实际测量拉拔力与公式计算所得拉拔力相吻合,模拟所得拉拔力比实际测量拉拔力小。