Filtration increases the correlation between water extractable organic carbon and soil microbial activity

A study was carried out in order to establish the relationship between the water extractable organic carbon (WEOC) content of soils and soil microbial activity, and to determine how variations in the extraction procedure might influence the quantity of WEOC recovered. Concentrations of WEOC were determined in soils taken from 12 different sites in the south east of Scotland, using a procedure in which samples were shaken with distilled water, centrifuged at 5000g and then filtered through 0.45 μm Millipore filters. Filtration resulted in between 30 and 400 μg C g⁻¹ being extracted using this procedure and the concentration of WEOC in the resultant extracts correlated with soil microbial production of CO₂ and dehydrogenase activity (P<0.001). Without filtration, although more WEOC was extracted (between 31 and 716 μg C g⁻¹), there was no significant correlation with biological activity. There was also no correlation between WEOC and nitrous oxide release during the incubations. Centrifugation at 20,000g for at least 10 min prior to filtration was required to remove particulate organic materials. Storage of samples at 4 °C or for up to 1 week or freezing for up to 3 months was not found to have a large influence on the concentration of WEOC in extracts, although amounts increased with soil:extractant ratio and increasing extraction time (from 15 to 60 min).     

浅谈农科专业计算机课程教学方法

本文从研讨计算机课程教学方法的必要性出发,探讨了如何改进教学方法的问题,并举例分析了让绝大多数学生在有限的时间内迅速掌握课程的基本概念、基本技能和应用的具体教学措施。     

用扫描电镜观察不镀导电膜对大肠杆菌损伤和图像的影响

[目的]为利用扫描电镜进行科学研究提供参考与借鉴。[方法]以脱水干燥的大肠杆菌为材料,对其不镀金在扫描电镜下进行观察,并与镀金样品图像进行对比。最后阐述了选择不同样品的镀膜材料与镀膜厚度的方法。[结果]未镀金的样品图片亮暗不均,局部有闪烁亮斑,且随着观察时间的延长,样品逐渐被热电子烤焦。[结论]样品不镀金,发射电子会损伤样品,图像清晰度比镀金样品的差。     

基于DEA分析和样点调查的工业企业用地效率研究

基于长春市76家汽车及零部件企业实地调查，应用DEA中的c。R模型，以工业企业宗地为评价单元，进行土地利用有效性分析。结果表明，土地投入量过大是用地效率DEA无效的企业中最突出的问题；产出指标中上缴利税的不足也造成了企业用地效率低下；劳动力过剩的企业也占到了1／4，说明劳动力配置的不合理也会导致企业用地效率偏低。     

Sample handling substantially affects Johne's ELISA

Detection methods for Mycobacterium avium subsp. paratuberculosis (MAP) are imperfect, yet crucial for diagnosis of Johne's disease. Our purpose was to test for significant and biologically relevant changes in Johne's ELISA results associated with how field-collected blood samples were transported to the laboratory, prepared and stored prior to testing, while removing potential confounding by test kit and laboratory variables. Blood samples were collected from 21 cows that previously had MAP ELISA scores ranging from negative to highly positive. Samples for immediate laboratory processing were subjected to different transportation temperatures (on ice, 26 °C) and preparation methods (serum separated, hemolyzed and serum separated, clotted whole blood), but were tested using the same ELISA kit in the same laboratory. Samples for laboratory processing after one week of storage were subjected to different storage temperatures (4 °C, −20 °C) and preparation methods (serum separated, hemolyzed and serum separated, clotted whole blood), and again were tested using the same ELISA kit in the same laboratory. Finally, samples were evaluated by time to processing (one day, one week) and storage temperature (4 °C, −20 °C). Data were checked for normality and analyzed with repeated measures ANOVAs. Significantly (P = 0.027) higher MAP ELISA scores were recorded for whole blood and hemolyzed samples transported at 26 °C than serum separated samples. Sample storage for one week at −20 °C resulted in significantly (P < 0.001) lower MAP ELISA scores, regardless of handling method, compared to samples stored at 4 °C for one week. Method of sample preparation, as well as transportation temperature and medium-term storage temperature, affects MAP ELISA results. Such discrepancies will inevitably result in improper classification of MAP-infected cattle, impeding both biosecurity measures on uninfected farms and MAP control programs.     

低温预处理与植物生长调节剂对结缕草愈伤组织诱导的影响

以结缕草Zoysia japanica的茎尖、茎基、根尖为外植体材料,研究了低温预处理、不同激素配比对结缕草诱导愈伤的影响,结果表明：10 ℃低温预处理3次（即累积30 d）为最佳低温预处理时间;经过3次处理后,3种外植体的愈伤诱导率都明显提高,其中茎基最好,愈伤诱导率达94%,较对照提高了38%,芽分化率为74.47％;以此为基础,在配方为MS+2,4 D(2 mg/L)+6 BA(0.1 mg/L)的培养基上,3种外植体均获得最高的愈伤诱导率,其中茎基最好,为94％;外植体材料中最佳为茎基,出愈容易,且出愈率高。     

土壤微量节肢动物组织中镉测定方法的改进

Highly precise and reliable determination of heavy metals in soil micro-arthropod tissues remains a challenge because of the small size of the animals and their typical low abundance in metal-contaminated agricultural soils. The present study sought to develop a method for cadmium(Cd) determination in soil micro-arthropods by optimizing the sample digestion procedure, reducing sample weight, modifying sample pre-treatment and validating the methodology with field samples. The optimized digestion conditions comprised a sample mass of 50–150 μg, digestion reagent of nitric acid:hydrogen peroxide(3:1), digestion temperature of 105℃,digestion period of 3 h and digestion volume of 30 μL. Defecation of the standard Collembola Folsomia candida(92 h) and the indigenous Collembola Onychiurus yodai(42 h) and ultrasonic cleaning of F. candida increased the accuracy of Cd determination.The recovery of Cd using the refined procedure was 98.9% and the limits of detection and quantification were 0.002 and 0.008 μg L~(-1), respectively. The within-batch precision values were 3%. The Cd concentrations in the tissues of the Collembola Isotoma sp.collected from a range of metal-contaminated fields determined by the improved method were consistent with the Cd concentrations in the field soils. The results indicate that the optimized method can be used for more accurate or reliable determination of Cd concentrations in soil micro-arthropod tissues.     

超声辅助液相微萃取-气相色谱法检测饮用水中有机磷农药残留

建立超声辅助分散液相微萃取(USALPME)结合气相色谱火焰光度检测器的新方法,应用于饮用水中的3种有机磷农药(杀螟硫磷、毒死蜱和苯线磷)残留的检测。对可能影响萃取效率的因素,本试验进行优化。结果为:取一只装有5mL水样的离心试管,用移液枪迅速注入30μL氯苯(萃取剂)超声10min,冰浴10min,以3 500r/min离心5min,用微量进样器吸取沉淀相1μL进样分析。在最优条件下,说明3种有机磷农药杀螟硫磷、毒死蜱和苯线磷的检出限为0.41～0.83μg/mL,相对标准偏差为11.94%～16.73%,线性的变化范围(浓度0.5～100μg/mL)在0.995 7～0.999 7之间,此方法检测饮用水中有机磷农药残留结果较满意。     

UASB工艺系统设计方法探讨

本文全面介绍了UASB系统的设计问题。重点介绍了厌氧预处理工艺和UASB反应器的负荷设计原则和设计方法，混凝土结构矩形UASB反应器各个部分尺寸的计算和确定原则。对UASB的进水配水系统和布水方式作了详细介绍。对三相分离器和UASB建筑材料等问题也进行了讨论。     

森林生物量建模样本采集有关技术问题的实践与思考

通过总结连续两年开展样本采集工作的感受与体会,指出了从工作准备到样本采集等过程中的关键环节及应注意的问题,并介绍了山西省在实践过程中的一些具体做法,旨在进一步完善森林生物量建模技术方案,为做好今后的样本采集工作提供参考和借鉴。