球囊霉素及其在土壤生态系统中的作用

球囊霉素(Glomalin)是一种在土壤中大量存在的、由丛枝菌根真菌(Arbuscular mycorrhizal fungi, AMF)产生的具有良好热稳性的特殊糖蛋白。球囊霉素因其在促进土壤团聚体形成,保持团聚体稳定性,增加土壤有机碳库,提高植物抗逆能力以及降低重金属在土壤中的毒性等方面的作用备受人们关注。目前由于提取方法的原因,人们一般将球囊霉素的命名改为球囊霉素相关土壤蛋白(Glomalin related soil protein, GRSP)。随着研究的不断深入,人们对GRSP在生态系统中的作用展开了广泛的研究。GRSP对土壤颗粒有较强的胶结作用,其胶结能力为其他胶结物质的3～10倍;作为有机碳库的重要组成部分对土壤有机碳的贡献率为6.98%～31.3%,并且在土壤中周转时间较长为6～42年;GRSP还可以螯合不同的重金属,减少它们在土壤中的毒害作用以及降低潜在毒性。但想要更为深入的了解GRSP在生态系统中的作用需要对其结构进行进一步的了解、提取测定方法进行进一步的优化。本文重点总结了国内外研究中GRSP对土壤团聚体、土壤有机碳库的作用,GRSP研究中存在的主要问题以及未来...     

Glomalin in aggregate size classes from three different farming systems

Glomalin was measured in soil from farming systems managed for 8 years by chisel tillage (CT), more intensive tillage for organic (ORG) production, and no tillage (NT) on Acrisols (FAO Soil Units) in the Mid-Atlantic region of the U.S. Whole soil and aggregate size classes of >2.00, 0.50–2.00 and 0.21–0.50 mm (macroaggregates), 0.05–0.21 mm (microaggregates), and <0.05 mm (fine material) were examined. Glomalin-related soil protein (GRSP) was extracted from 1-g samples (four plots per treatment) with 100 mM sodium pyrophosphate, pH 9.0, at 121 °C in three extraction cycles. Extracts were pooled and quantified by using the Bradford protein assay. Concentrations of GRSP and total carbon (C) in aggregates were linearly related across aggregate size classes for all treatments (GRSP = 0.101C + 0.56, r² = 0.95). No tillage had significantly greater whole soil GRSP than did CT or ORG (P = 0.01). Mean values for GRSP in aggregates of NT were higher than for CT or ORG aggregates by 0.53 and 0.66 mg g⁻¹ aggregates, respectively. There were no differences among treatments in GRSP concentrations in fine material. In NT the concentration of GRSP increased as aggregate size increased in contrast to the disturbed treatments, CT or ORG, where there were no differences in GRSP concentration across aggregate size fractions. Larger proportions of GRSP were distributed in macroaggregates of NT compared to CT and ORG in contrast to larger proportions in microaggregates of CT and ORG than in NT. Although soil disturbance in ORG farming is greater than for CT farming, both treatments had similar GRSP concentrations and distributions.     

土壤中有机磷农药的提取纯化和气相色谱-氮磷检测器测定

The objectives of this study were to optimize instrumental parameters and conditions for analysis of selected organophosphorus pesticides (OPPs) by gas chromatography (GG) with nitrogen-phosphorus detection (NPD) (GG-NPD); to select an appropriate solvent system; to conduct a comparison of sonication and shaking extractions; and to select an appropriate procedure for extracting organophosphorus pesticides from soils. Procedure Ⅰ consisted of n-hexane or petroleum ether together with acetone used as solvents, while Procedure II contained several solvents including acetone,methanol, dichloromethane, and n-hexane or petroleum ether. Experimental results indicated that a mixture of petroleum ether/acetone (2:1, v/v) could be used in place of n-hexane/acetone (2:1, v/v) as it was a less expensive solvent system.In addition, shaking under a water bath at 20℃ was more effective than sonication. Also, Procedure Ⅰ was more effective,safer, and more timesaving than Procedure Ⅱ. Procedure Ⅰ was applied to three soil types of different organic matter content, with recoveries of the OPPs from the yellow-brown soils, which had a higher organic matter content, being lower than those from the yellow and red soils.     

球囊霉素在土壤团聚体中的分布特征及影响因素的Meta分析

为充分认识球囊霉素在维持土壤有机碳平衡和土壤团聚体稳定性中的重要作用,建立改善土壤结构 和提升土壤质量的管理策略,通过收集整理近些年来已发表的19篇文献中的332组数据,定量分析球囊霉素在不同粒径土壤团聚体中的分布特征,系统解析其影响因素,并比较了不同土地利用方式下球囊霉素在土壤团聚体中的分配差异。结果表明：无论是总球囊霉素还是易提取球囊霉素,在大团聚体（>2 000 μm）和小团聚体（2 000~250 μm）中的质量百分比（分别约占30%）均显著高于微团聚体（250~53 μm）和黏粉粒级微团聚体（<53 μm）（分别约占15%）。易提取球囊霉素占总球囊霉素的比例在粉黏粒级微团聚体（<53 μm）中更低,约为20%,其他粒径均在30%以上。球囊霉素中碳占土壤有机碳的比例在各团聚体中无显著差异,不同粒径团聚体中易提取球囊霉素约占有机碳的2%左右,而总球囊霉素约占有机碳的8%左右。大于250 μm团聚体中球囊霉素随温度和降水的增加而增加,而随着pH的增加而降低。在小于250 μm团聚体中未发现显著相关性,但发现球囊霉素随土壤有机碳增加而增加,呈显著正相关。通过比较不同利用方式的土壤,本研究还发现林地土壤各粒径团聚体中的球囊霉素均不低于耕地和草地土壤,这说明林地土壤较其他类型土壤更有利于球囊霉素的积累。     

钼矿开采对球囊霉素相关土壤蛋白和土壤化学计量特性的影响

以不同开采程度钼矿区根际土壤为研究对象，探索了钼矿开采对土壤球囊霉素相关土壤蛋白、化学计量特性及其两者之间关系的影响。结果表明，开采区土壤碳、氮含量分别为25.30和1.00 g/kg，显著低于恢复区和未开采区土壤的碳、氮含量。开采区土壤的碳氮比达到29.36，分别是恢复区和未开采区的2.02倍和1.30倍。恢复区和未开采区土壤的总提取球囊霉素含量为2.81和3.64 mg/g，易提取球囊霉素含量为1.22和2.02 mg/g，分别是开采区土壤总提取和易提取球囊霉素的2.08倍、2.70倍和1.97倍、3.26倍。此外，土壤碳、氮含量对丛枝菌根真菌分泌球囊霉素相关土壤蛋白有显著的影响。可见，钼矿开采主要导致了土壤碳、氮的大量流失，并对丛枝菌根真菌分泌球囊霉素相关土壤蛋白具有明显的抑制作用。     

Extraction of Glomalin and Associated Compounds with Two Chemical Solutions in Cultivated Tepetates of Mexico

Glomalin is a glycoprotein produced by the hyphae of arbuscular mycorrhizal fungi (AMF). The chemical methods usually employed to extract glomalin from the soil obtain something more than this pure glycoprotein, and therefore it would be better to call this fraction soil protein related to glomalin (SPRG) or glomalin associated with humic substances (GAHS). On this account, its isolation is controversial. The SPGR or GAHS has a significant influence on the physical, chemical, and biological properties of soils and could then be considered as an indicator of soil use change. In the present study, the storage of SPRG was evaluated, as well as carbon (C) associated with the latter (CG) and the content of soil organic C (SOC) in cultivated tepetates in the State of Mexico. Tepetates are hardened volcanic tuffs of the fragipan type, ameliorated for agricultural production. The specific objectives of the present study were (1) to evaluate the SPRG levels in tepetates, (2) measure the contribution of carbon (C) made by the SPRG to soil organic C (SOC), and (3) compare the extraction of SPRG with sodium pyrophosphate and sodium citrate. The samples used in this experiment came from 87 tepetate-cultivated plots (0–20 cm) located in the Texcoco River basin, State of Mexico. The levels of SPRG were observed among traces, 2.3 mg g^–1 for citrate and up to 5.6 mg g^–1 for pyrophosphate. The latter reactive allowed us to extract nearly three times more SPRG and two times more C-SPRG than sodium citrate (P?=?0.05) in the tepetates having about 4% of SOC; yet when the latter was less than 0.5%, the extraction levels with both solutions were similar. The SPRG and CG were closely correlated with SOC (r > 0.90). Tepetates have levels of SPRG similar to those observed in arid soils.     

Freeze-dried soil extraction method for the measurement of microbial biomass C

A new method for the measurement of microbial biomass C by direct extraction of freeze-dried soil with either 0.5M K₂SO₄ or 0.5M NaHCO₃ was evaluated. The underlying principle of the method is that rehydrating a freeze-dried soil releases cytoplasmic organic compounds from desiccated and disrupted microbial cells. Nineteen soils under various management regimes were sampled to test the proposed method, in which each soil sample was split into two subsamples. One subsample was kept in the field-moist condition at 4°C. The other subsample was brought to 100% water-holding capacity and frozen at –20°C for 24h. The frozen soil was then freezedried. Both subsamples were extracted with 0.5M K₂SO₄ or 0.5M NaHCO₃ at a soil-to-extractant ratio of 1-to-4 (w/v) and organic C determined in the extract (C_{K2 SO4} or C_NaHCO3). The net freeze-dry stimulated increase in extracted C was correlated (r ²=0.98 for C_{K2 SO4} or 0.93 for <$>\rm C_{NaHCO_3})<$> more closely with microbial biomass C (C_MB) measured as net evolution of CO₂–C by chloroform fumigation incubation (CFI) than with total C (r ²=0.42 for C_{K2 SO4} or 0.47 for C_NaHCO3). Based on linear regression equations, extraction efficiency coefficients (K _EC) were used to calculate C_MB from C_{K2 SO4} or C_NaHCO3 as follows: C_MB=C_{K2 SO4}/0.152±0.004 C_MB=C_NaHCO3/0.257±0.01 The relationship between the C_MB and the flushes of C extracted after rehydration of freeze-dried soil showed that the K _EC values were more consistent for C_{K2 SO4} than C_NaHCO3. The freeze-dried soil extraction was a fast, precise, reliable and safe method for measuring microbial biomass C in soil. Received: 27 May 1996     

接种丛枝菌根真菌的种植紫花苜蓿土壤中球囊霉素含量与去除的关系

以菲和芘为多环芳烃（PAHs）代表物,以紫花苜蓿（Medicago sativa L.）为宿主植物,选用幼套球囊霉（Glomus etunicatum, Ge）、摩西球囊霉（Glomus mosseae,Gm）和层状球囊霉（Glomus lamellosum,Gla）3种丛枝菌根真菌（AMF）,研究了接种AMF下土壤中AMF菌丝密度、球囊霉素含量与PAHs去除率的关系。35~75 d,接种Ge、Gm、Gla处理的土壤中菌丝密度、总球囊霉素含量、易提取球囊霉素含量均随时间延长而显著增大,与不接种对照相比,75 d时接种Ge、Gm、Gla处理的土壤中易提取球囊霉素含量提高了48.58%、55.99%和50.23%,总球囊霉素含量则提高了38.75%、50.95%和46.12%。接种AMF促进了土壤中菲和芘的去除,随着时间（35~75 d）延长,接种Ge、Gm、Gla处理的土壤中菲去除率分别高达83.4%~92.7%、82.1%~93.8%、86.9%~93.4%,芘去除率达42.2%~63.5%、43.7%~69.2%、44.6%~66.4%。接种Ge、Gm和Gla处理土壤中AMF菌丝密度、总球囊霉素含量均与土壤中菲和芘的去除率之间存在极显著正相关关系,表明接种AMF提高了土壤中AMF菌丝密度和总球囊霉素含量,并促进了土壤中PAHs的去除。研究结果为阐明丛枝菌根修复PAHs污染土壤的规律及机理提供了依据。     

Glomalin amount and compositional variation,and their associations with soil properties in farmland,northeastern China

Glomalin‐related soil protein (GRSP) is well‐known for its soil conditioning functions, but compositional traits are rarely considered. Farmland in northeastern China is the most important commercial grain basis, and soil degradation becomes the bottleneck for keeping crop productivity. The objective of this study was to uncover the possible associations between GRSP (amount and composition) and soil properties, and make suggestions for soil improvement from soil glomalin rehabilitation in northeastern China. Here, spatial variation in GRSP amount (Easily‐extractable‐GRSP, EE‐GRSP; Total‐GRSP, T‐GRSP) and its compositional traits from infrared spectroscopy, UV‐absorbance, X‐ray diffraction (XRD) and 3‐D fluorescence spectroscopy were surveyed in 360 soil samples across northeastern China, and their association with 11 soil properties were also analyzed for finding the possible influence of soil properties on GRSP composition in farmland. There about 3‐fold spatial variation in GRSP amount was observed, while functional group variations were ranged from 1.2‐fold (O–H & N–H stretching) to 2.4‐fold (C–O stretching & O–H bending of –COOH) in different locations. The XRD showed that grain size was 113–180Å and crystallinity was 0.71–1.42%, and GRSP contained seven fluorescent compounds of tyrosine‐like, tryptophan‐like, fulvic acid‐like, soluble microbial byproduct, humic acid‐like, nitrobenzoxadidole‐like, and calcofluor white‐like. Both, EE‐GRSP and T‐GRSP positively associated with soil organic carbon (SOC), soil N (SON), soil P (SOP), alkali‐hydrolyzed N (AN), available P (AP), available K (AK), and soil water, while negatively associated with soil pH and soil bulk density. Structural equation model (SEM) analysis indicates that direct effects on GRSP amounts were mainly from soil bulk density (coefficient: –0.27), soil pH (coefficients: –0.51 to –0.57), SOC (coefficients: 0.51 to 0.69) and AP (coefficients: 0.18 to 0.26), while all other soil properties had indirect effects on GRSP amounts via their close associations with these four parameters. Compared with the GRSP amounts, soil properties laid fewer effects on GRSP compositional traits. Of 16 compositional traits, five of them showed possible regulations from soil properties, which were three infrared functional groups (IR‐II: aliphatic C–H stretching; IR‐V: C–O stretching & O–H bending of –COOH; IR‐VII: O–H binding) and two fluorescent compounds (tyrosine‐like and humic acid‐like). SEM analysis indicates that soil water, pH and EC could directly affect IR‐II, IRV, tyrosine‐like and humic acid‐like, while available nutrients showed more evident influences on infra‐red functional groups than total amounts of N, P and K. Moreover, SOC, as a media of various soil nutrients, gave the strongest influence on GRSP compositional traits. As a supplement to previous studies, we found that GRSP is a mixture of different fluorescent compounds with different functional groups. Our findings highlight that soil properties could strongly change both GRSP accumulation in soil and their compositional traits, and the definition of the most probable soil properties in regulating glomalin amount and composition in this paper could favor good soil management in farmland at northeastern China.     

基于Landsat TM图像棉花面积提取中线状地物的扣除方法研究

在新疆棉花遥感监测中，发现各种线状地物对TM影像图中的棉花面积提取精度产生影响，直接对图像进行处理和分类这种影响难以消除。经实际调查，新疆某一农场的各种线状地物占到总耕地面积的12．8％。为提高作物面积提取精度，完善农业部全国棉花遥感监测运行系统，进行了线状地物扣除方法的试验研究。阐述了试验研究方法的理论依据、技术路线与实施过程。并经验证可消除绝大部分线状地物对作物面积提取精度产生的影响。     

红壤区林下侵蚀劣地土壤碳氮及球囊霉素对接种AM真菌的响应

南方红壤区林下侵蚀劣地近地表植被覆盖度低,导致林下水土流失严重.接种AM真菌能够促进植被生长,改善土壤肥力,进而可以减少土壤侵蚀.以马尾松退化林地为对象,设置引种灌木(S)和引种灌木并接菌(S+AMF)2个处理,研究AM真菌接种对林下侵蚀劣地土壤碳氮及球囊霉素的影响.结果表明:接菌近1年后,菌根侵染率(MCR)在S+A...     

Analysis of swainsonine: extraction methods, detection, and measurement in populations of locoweeds (Oxytropis spp.)

An analytical method has been developed to measure the locoweed toxin, swainsonine, in locoweed plant material. Dry ground plant samples were extracted using a small-scale liquid/liquid extraction procedure followed by isolation of the swainsonine by solid phase extraction with a cation-exchange resin. Detection and quantitation of the swainsonine were accomplished using reversed phase high-performance liquid chromatography coupled to atmospheric pressure chemical ionization tandem mass spectrometry (LC-MS(2)). The limit of quantitation was estimated to be 0.001% swainsonine by weight in dry plant material, which corresponds to the lower threshold for toxicity of locoweeds. The method of analysis was applied to the analysis of Oxytropis sericea (white locoweed) and Oxytropis lambertii (Lambert locoweed) plant samples to measure the variability of individual plant swainsonine levels within populations and within species. Individual plant variability was found to be highly significant for both O. sericea and O. lambertii populations. The combined three-year mean swainsonine values taken from three populations of O. sericea ranged from 0.046% in Utah to 0.097% in a New Mexico population. Sixteen individual populations of O. lambertii were sampled from eight different U.S. states. Swainsonine was detected at levels >0.001% in only 5 of the 16 collection sites. Those populations of O. lambertii found to contain higher swainsonine levels were restricted to the most southern and western portion of its distribution, and all were identified as belonging to var. bigelovii, whereas var. articulata and var. lambertii samples contained swainsonine at levels <0.001%.     

Total lipid extraction of homogenized and intact lean fish muscles using pressurized fluid extraction and batch extraction techniques

The reliability and efficiency of pressurized fluid extraction (PFE) technique for the extraction of total lipid content from cod and the effect of sample treatment on the extraction efficiency have been evaluated. The results were compared with two liquid-liquid extraction methods, traditional and modified methods according to Jensen. Optimum conditions were found to be with 2-propanol/n-hexane (65:35, v/v) as a first and n-hexane/diethyl ether (90:10, v/v) as a second solvent, 115 degrees C, and 10 min of static time. PFE extracts were cleaned up using the same procedure as in the methods according to Jensen. When total lipid yields obtained from homogenized cod muscle using PFE were compared yields obtained with original and modified Jensen methods, PFE gave significantly higher yields, approximately 10% higher (t test, P < 0.05). Infrared and NMR spectroscopy suggested that the additional material that inflates the gravimetric results is rather homogeneous and is primarily consists of phospholipid with headgroups of inositidic and/or glycosidic nature. The comparative study demonstrated that PFE is an alternative suitable technique to extract total lipid content from homogenized cod (lean fish) and herring (fat fish) muscle showing a precision comparable to that obtained with the traditional and modified Jensen methods. Despite the necessary cleanup step, PFE showed important advantages in the solvent consumption was cut by approximately 50% and automated extraction was possible.     

耦合浮珠-超声辅助溶剂萃取法用于微藻采收及油脂提取

为了优化微藻生物柴油生产工艺,开发高效低耗的微藻采收与油脂提取技术,该研究使用优化浮珠浮选工艺对小球藻进行采收,随后选取小球藻-表面层状聚合物浮珠聚集体进行破壁提油处理,并通过响应面优化破壁工艺,建立一种新型耦合浮珠-超声辅助溶剂萃取工艺。结果表明,在超声时间为13 min,正己烷：异丙醇体积比例为4,微藻质量浓度为13.6 g/L,超声功率为254 W时,油脂提取效率较高,为18.91%。相比传统气浮法与超声辅助溶剂萃取法,该法采收效率、细胞破壁效率和饱和脂肪酸含量都达到了较高水平,分别为98.36%、90.19%和37.03%。因此,耦合浮珠-超声辅助溶剂萃取工艺是一种有效提取小球藻细胞中油脂的工艺。研究结果为微藻生物柴油制备工艺的发展提供科学依据。     

Fat extraction from acid- and base-hydrolyzed food samples using accelerated solvent extraction

This paper describes a new in-cell method for pursuing accelerated solvent extraction (ASE) prior to lipid analysis from food samples. It is difficult to pursue direct ASE with acid- or base-hydrolyzed samples due to the corrosive nature of the reagents and material limitations. In this study ion exchange based materials were used to remove acid or base reagents in-cell without compromising the recovery of lipids. The performance data are presented here for the new methods for lipid extraction for a variety of food samples and compared to the Mojonnier method. NIST Standard Reference Materials (SRM-1546 and SRM-1849) were used to validate the ASE methods. Excellent fat recoveries were obtained for the ASE methods. The new methods presented here enhance the utility of ASE and eliminate labor intensive protocols.     

适宜提取方法提高美藤果油提取率及油品质

为了提高美藤果油的提取率以及油的品质,该文以美藤果为原料,比较了水酶法、超临界CO2萃取法、超声波辅助有机溶剂萃取法和低温冷榨法这4种不同的提取方法对美藤果油提取率和油品质的影响;并采用气相色谱-质谱联用法（gas chromatograph-mass spectrometer-computer, GC-MS）和高效液相色谱法（high performance liquid chromatography, HPLC）测定美藤果油的营养组成,以及以1,1-二苯基-2-三硝基苯肼（1,1-Diphenyl-2-picrylhydrazyl radical 2,2-Diphenyl-1-(2,4,6-trinitrophenyl) hydrazyl,DPPH?自由基）清除率为指标比较了美藤果油与其他植物油的体外抗氧化活性。结果表明：4种提取方法中,水酶法和超声波辅助有机溶剂提取法油脂提取率较高,分别为95.1%和92.7%,其次为超临界萃取法,为86.44%。但超临界CO2萃取法提取出的油脂综合理化指标优于其他３种提取方法,其中水酶法提取出的油不溶性杂质、酸价、过氧化值和黄色值都低于超声波辅助有机溶剂萃取法和低温冷榨法,但感官品质最差。综合考虑得出：超临界萃取法为美藤果油较佳的提取方法。此方法提取的美藤果油中富含不饱和脂肪酸和生育酚、多酚等活性成分,不饱和脂肪酸质量分数高达92.37%,总生育酚和总多酚质量分数分别为59.2 mg/(100 g)、10.2 mg/(100 g),但不含有维生素A;美藤果油对DPPH·自由基的半数抑制率IC50为1.148 mg/mL,明显低于橄榄油、茶油、亚麻籽油和紫苏油（P<0.01）,说明美藤果油体外抗氧化能力较强。研究结果可为美藤果油进一步开发提供参考。     

传统与微波辅助工艺提取苹果果胶品质比较

该研究比较了传统工艺（CSE）与微波辅助工艺（MAE）所提取苹果果胶的品质差异,微波工艺[pH=1.0,提取时间20.8 min,功率499 W,料液比=1︰14.5（m/V）]提取的苹果果胶其得率、纯度和总离子含量均显著高于传统工艺[pH=2.0,提取时间1.5 h,温度85℃,料液比=1︰13],动态模式下对果胶溶液凝胶性能分析发现,传统工艺提取的苹果果胶凝胶温度为94℃,微波工艺提取的温度为82℃,但其酯化度和黏均分子质量显著小于传统工艺;传统工艺提取的苹果果胶溶液褐变指数、屈服应力、表观黏度、活化能显著高于微波工艺,总酚含量显著低于微波工艺;传统工艺提取苹果果胶溶液的亮度值和色调角均高于微波工艺,彩度值低于微波工艺提取的苹果果胶;频率扫描发现,传统工艺提取的果胶溶液具有更加稳定的三维结构,分子间相互结合得更加紧密,具有更好的凝胶特性。     

Combination of total solids determined by oven drying and fat determined by Mojonnier extraction for measurement of solids-not-fat content of raw milk: collaborative study

Each of 9 laboratories analyzed 9 pairs of blind duplicate raw milk samples for fat, using the Mojonnier ether extraction method (16.E13-16.E17), and for total solids, using a new direct forced air oven method. Solids-not-fat was determined by subtracting percent fat from percent total solids. The solids-not-fat content of the samples tested in the collaborative study ranged from 8.48 to 9.36%. The average repeatability standard deviation (sr) and the average reproducibility standard deviation (SR) for the solids-not-fat method were 0.019 and 0.041, respectively. Average repeatability (RSDr) and reproducibility (RSDR) relative standard deviations were 0.218 and 0.466%, respectively. The mean repeatability value (r) was 0.055; the mean reproducibility value (R) was 0.117. The difference between milk total solids determined by direct forced air oven drying and milk fat determined by Mojonnier ether extraction has been approved for interim official first action for determination of solids-not-fat content of milk.     

Modification of the original chloroform fumigation extraction technique to allow measurement of δC of soil microbial biomass carbon

In studies of the soil microbial biomass C by the chloroform fumigation extraction (CFE) technique, biomass C is routinely extracted using 0.5 M K₂SO₄ solution. The excessive amounts of salts contained in the extracting solution pause a significant challenge in using ¹³C isotope techniques to study the nature of C in the soil microbial biomass. This is because the salts can affect the oxidation process and therefore hamper accurate mass spectromic analysis of dried extracts. In spite of this, no standard protocol exists for preparing the K₂SO₄ extracts for ¹³C isotope analysis. We have modified the original CFE method to allow measurement of the δ¹³C of soil microbial biomass C by using 2 M KCl instead of the usual 0.5 M K₂SO₄ solution to extract biomass C. Excess salts were removed by dialysis in 100 molecular weight cut off membranes, after which the extracts were freeze-dried and their δ¹³C measured using a mass spectrometer. The soil microbial biomass C and δ¹³C of 2 M KCl extracts were compared with those of 0.5 M K₂SO₄ extracts. There was excellent agreement between organic C and δ¹³C estimates for dialyzed 2 M KCl and 0.5 M K₂SO₄ extracts, but the speed of dialysis for the latter was very slow, making use of the former more rapid. These results suggest that in procedures where oxidation with potassium dichromate is not critical to analysis of soluble C, 2 M KCl may be used in place of 0.5 M K₂SO₄ to extract soil microbial biomass C for δ¹³C measurements. The new procedure is relatively easy and rapid for obtaining indices for both pool sizes and turnover rates of soil microbial biomass C and provides a promising approach to study soil organic C.     

Comparison of solvent extraction and microwave extraction for release of dimethyl sulfide from cereals and canola

Natural levels of dimethyl sulfide (DMS) in newly harvested wheat, barley, paddy, and canola were determined by gas chromatography using a flame photometric detector in sulfur mode. The two methods involved determination of DMS in the headspace of cereal or oilseed samples (1) after extraction with microwaves and (2) after a traditional approach using 25% KBr solution. Quantitative results from each method were similar, and therefore both methods are suitable for the determination of DMS in grains and oilseeds. However, the microwave procedure has several advantages; for example, results are obtained very quickly, and only a small amount of sample is required.