A GC/MS method for the assessment of N and C incorporation into soil amino acid enantiomers

Identifying the transformation process of amino acid enantiomers was essential to probe into the fate, turnover and aging of soil nitrogen due to their important roles in the biogeochemical cycling. If this can be achieved by differentiating between the newly biosynthesized and the inherent compounds in soil, then the isotope tracer method can be considered most valid. We thereby developed a gas chromatography/mass spectrometry (GC/MS) method to trace the ¹⁵N or ¹³C isotope incorporation into soil amino acid enantiomers after being incubated with ¹⁵NH₄⁺ or U-¹³C-glucose substrates. The most significant fragments (F) as well as the related minor ions were monitored by the full scan mode and the isotope enrichment in amino acids was estimated by calculating the atom percentage excess (APE). ¹⁵NH₄⁺ incorporation was evaluated according to the relative abundance increase of m/z F+1 to F for neutral and acidic amino acids and F+2 to F (mass 439) for lysine. The assessment of ¹³C enrichment in soil amino acids was more complicated than that of ¹⁵N due to multi-carbon atoms in amino acid molecules. The abundance ratio increment of m/z F+n to F (n is the original skeleton carbon number in each fragment) indicated the direct conversion from the added glucose to amino acids, but the total isotope incorporation from the added ¹³C can only be calculated according to all target isotope fragments, i.e. the abundance ratio increment summation from m/z (Fa+1) through m/z (Fa+T) represented the total incorporation of the added ¹³C (Fa is the fragment containing all original skeleton carbons and T is the carbon number in the amino acid molecule). This method has a great advantage especially for the evaluation of high-abundance isotope enrichment in organic compounds compared with GC/C/IRMS. And in principle, this technique is also valid for amino acids besides enantiomers if stereoisomers are not concerned. Our assessment approach could shine a light on investigating the biochemical mechanism of microbial transformation of N and C in soils of terrestrial ecosystem.     

Comparison of modeling approaches to quantify residue architecture effects on soil temperature and water

RZ-SHAW is a hybrid model, comprised of modules from the Simultaneous Heat and Water (SHAW) model integrated into the Root Zone Water Quality Model (RZWQM) that allows more detailed simulation of different residue types and architectures that affect heat and water transfer at the soil surface. RZ-SHAW allows different methods of surface energy flux evaluation to be used: (1) the SHAW module, where evapotranspiration (ET) and soil heat flux are computed in concert with a detailed surface energy balance; (2) the Shuttleworth–Wallace (S–W) module for ET in which soil surface temperature is assumed equal air temperature; and (3) the PENFLUX module, which uses a Penman transformation for a soil slab under incomplete residue cover. The objective of this study was to compare the predictive accuracy of the three RZ-SHAW modules to simulate effects of residue architecture on net radiation, soil temperature, and water dynamics near the soil surface. The model was tested in Akron, Colorado in a wheat residue-covered (both standing and flat) no-till (NT) plot, and a reduced till (RT) plot where wheat residue was incorporated into the soil. Temperature difference between the soil surface and ambient air frequently exceeded 17 °C under RT and NT conditions, invalidating the isothermal assumption employed in the S–W module. The S–W module overestimated net radiation (R_n) by an average of 69 Wm⁻² and underestimated the 3-cm soil temperature (T_s3) by 2.7 °C for the RT plot, attributed to consequences of the isothermal assumption. Both SHAW and PENFLUX modules overestimated midday T_s3 for RT conditions but underestimated T_s3 for NT conditions. Better performances of the SHAW and PENFLUX surface energy evaluations are to be expected as both approaches are more detailed and consider a more discretized domain than the S–W module. PENFLUX simulated net radiation slightly better than the SHAW module for both plots, while T_s3 was simulated the best by SHAW, with a mean bias error of +0.1 °C for NT and +2.7 °C for RT. Simulation results for soil water content in the surface 30 cm (θ_v30) were mixed. The NT conditions were simulated best by SHAW, with mean bias error for θ_v30 within 0.006 m³ m⁻³; RT conditions were simulated best by the PENFLUX module, which was within 0.010 m³ m⁻³.     

实体水-虚拟水"二维三元"耦合流动理论基本框架

在变化环境下,区域水资源系统演变规律正在发生深刻变化。解决新形势下出现的水问题单单依靠传统的实体水资源规划、调度和调控手段还不够。虚拟水概念和理论的提出拓展了水文水资源的认知范畴,丰富了水问题的解决手段。然而,如何搭建虚拟水理论与传统水文水资源认知体系的统一框架,认识自然-经济-社会连续系统中水资源演化的新规律,目前学界还没有成熟统一的看法。该文首先提出了实体水-虚拟水耦合流动效应的基本理论框架,指出实体水-虚拟水耦合流动是现代环境下自然-经济-社会水资源系统呈现的新特征。其次,从文明进步和生产力发展角度,论述了人类社会水文水资源系统的演化历史,将水文水资源系统演进大体分为三个阶段:早期的实体水"一维一元"自然循环阶段,近现代的实体水"二元"水循环阶段和当前的实体水-虚拟水"二维三元"耦合流动阶段。最后,该文详细论述了实体水-虚拟水耦合流动过程的路径结构,并针对其流动过程和状态表征提出了定量表达方程,初步构建了实体水-虚拟水耦合流动基本理论框架。     

~(60)Coγ射线对甘薯黑斑病(Ceratocystis fimbriata)的抑制效果

用60~(Co)γ射线25—400krad的不同剂量辐照甘著黑斑病菌及带病甘薯(Ipomoeabatatas Lam.)薯块,发现200及400krad剂量的辐照对菌丝体和子囊孢子有一定的抑制作用,对分生孢子、厚垣孢子抑制作用甚微;200krad在20天内基本抑制薯块上病斑的发生和发展,薯块外观良好,接种发病率比对照低75％,病斑平均直径不及对照的五分之一;400krad的抑茵效果更高,但尚不能完全杀死病菌孢子,并对薯块外表有伤害,使其色泽变暗,贮藏后期易产生干腐。本试验表明,200krad剂量的辐照处理对甘著贮藏有实践意义。     

Composition,distribution and sources of polycyclic aromatic hydrocarbons in sediments of the western harbour of alexandria,egypt

Aim and Background  Little data are available on the levels of polycyclic aromatic hydrocarbons (PAHs) in the sediments of the Mediterranean Sea Coast of Egypt in general and the Alexandria coastal zone in particular. It was therefore deemed necessary to set up a monitoring programme to determine the current concentrations of PAHs in bottom sediments, and to identify any area where high concentrations of these potential hazardous contaminants were present in the Western Harbour of Alexandria. Methods  The composition, distribution and the source of PAHs in surficial sediments of the harbour were investigated. To document the spatial PAH input, surficial sediment samples from 23 locations throughout the harbour were analysed. as]Results and Discussion The total PAH load determined in the surficial sediment samples ranged from 8 to 131150 ng g¹ dry wt, generally with most of the samples having total concentrations of PAHs greater than 5000 ng g¹ dry weight. The highest concentration of total PAHs was recorded in sediments of the inner harbour. Ratio values of specific compounds such as phenanthrene to anthracene, fluoranthrene to pyrene, methyl-phen-anthrene to phenanthrene, methyl-dibenzothiophenes to dibenzothiophenes, alkylated to non-alkylated and high molecular weight to low molecular weight PAH, were calculated to evaluate the possible source of PAH contamination in the harbour sediments. Conclusions  Two main sources of PAH in the study area have been found: pyrolytic and petrogenic. Interferences of rather petrogenic and pyrolytic PAH contaminations were noticed for most samples. The dominant sources of PAH appear to be the combustion processes through run-off, industrial and sewage discharges, and atmospheric input. The concentrations of PAHs were generally above levels expected to cause adverse biological effects. Recommendations and outlook  Information from this study and any other relevant studies should be useful in designing future strategies for environmental protection and management of the harbour.     

A non-ACC pathway for ethylene biosynthesis in Botrytis cinerea

Premature softening and tissue senescence occur in kiwifruit infected with Botrytis cinerea. While ethylene production is enhanced in infected fruit and B. cinerea produces ethylene on defined media in vitro the source of ethylene in this pathosystem is unclear. Ethylene production by B. cinerea was enhanced when methionine or ∝-keto-methylthiobutyric acid (KMBA) was added to a defined (modified Pratts) medium. Although 1-aminocyclopropane-1-carboxylic acid (ACC) did not stimulate ethylene production, ∝-aminooxyacetic acid (AOA) was inhibitory suggesting a role for a pyridoxal phosphate mediated enzyme reaction down stream from the methionine/KMBA stimulated ethylene biosynthetic pathway. Cobalt chloride (Co²⁺) was inhibitory, but after a 4-d lag period ethylene production from B. cinerea cultures containing methionine and Co²⁺ reached the same level as those without Co²⁺. [U ¹⁴C] methionine was converted to ¹⁴C-ethylene with high efficiency indicating that it is a direct precursor, while [2,3 ¹⁴C]-ACC did not yield radioactively labelled ethylene. These results suggest that the ethylene biosynthetic pathway in B. cinerea does not involve ACC as a precursor and that the enzyme responsible for synthesising ethylene is similar to, but different from, ACC oxidase from higher plants. The ethylene biosynthetic pathway in B. cinerea is yet to be determined.     

一个新的水稻窄叶突变体的遗传分析和基因定位

水稻叶片形态相关突变体是水稻功能基因组学研究和株型改良的重要材料.本研究以新的窄叶突变体MR11为研究材料,发现该突变体在整个生育期表现为窄叶、叶长变短和植株矮化.叶片组织结构观察发现由于叶脉数减少和叶脉问宽度减小,导致突变体倒二叶叶片宽度不及野牛型的1/2.F2和BC1F1两个群体分离结果表明该窄叶突变体表型受一对隐...     

Image denoising using HMT in PDTDFB domain

Based on the dependency of the PDTDFB coefficients across the interscale and interdirection and the statistical properties of HMT for the correlation properties, a new HMT in PDTDFB domain was put forward. Compared with the other typical denoising methods, the experimental results demonstrate that the proposed method shows better performance in image denoising, especially in edge maintenance.     

Comparative study of low voltage ride-through techniques for doubly-fed induction generator wind turbines under asymmetrical grid faults

Asymmetrical grid faults occur more frequently and have more adverse effects on the doubly fed induction generator (DFIG) than symmetrical grid faults in the transmission system. The transient response of DFIG under asymmetrical grid faults is analyzed firstly. Meanwhile, operation behaviors of several low voltage ride-through (LVRT) techniques under severe asymmetrical grid faults are given by simulation with the Matlab/Simulink software. Then the characteristics of these LVRT techniques are further researched and analyzed based on the simulation results. Finally, the economies of these LVRT techniques are discussed. The conclusion lays a certain foundation for engineering development of these LVRT techniques.