pH-dependent distribution of soil ammonia oxidizers across a large geographical scale as revealed by high-throughput pyrosequencing

Purpose

Ammonia-oxidizing archaea (AOA) and bacteria (AOB) are ubiquitous and important for nitrogen transformations in terrestrial ecosystems. However, the distribution patterns of these microorganisms as affected by the terrestrial environments across a large geographical scale are not well understood. This study was designed to gain insights into the ecological characteristics of AOA and AOB in 65 soils, collected from a wide range of soil and ecosystem types.

Materials and methods

Barcoded pyrosequencing in combination with quantitative PCR was employed to characterize the relative abundance, diversity, and community composition of archaeal 16S rRNA gene, and AOA and AOB amoA genes in 65 soil samples.

Results and discussion

The operational taxonomic unit richness and Shannon diversity of Thaumarchaeota, AOA, and AOB were highly variable among different soils, but their variations were best explained by soil pH. Soil pH was strongly correlated with the overall community composition of ammonia oxidizers, as measured by the pairwise Bray–Curtis dissimilarity across all sites. These findings were further corroborated by the evident pH-dependent distribution patterns of four thaumarchaeal groups (I.1a-associated, I.1b, I.1c, and I.1c-associated) and four AOB clusters (2, 3a.1, 10, and 12). The ratios of AOA to AOB amoA gene copy numbers significantly decreased with increasing pH, suggesting a competitive advantage of AOA over AOB in acidic soils.

Conclusions

These results suggest that the distribution of ammonia oxidizers across large-scale biogeographical settings can be largely predicted along the soil pH gradient, thus providing important indications for the ecological characteristics of AOA and AOB in different soils.     

大孔吸附树脂分离纯化红小豆多酚工艺及效果

为开发利用红小豆加工副产物中的生理活性物质,该研究采用大孔树脂吸附法对煮制红小豆水的多酚类物质进行分离纯化,比较了5种不同型号大孔树脂对红小豆多酚的吸附分离效果,从中筛选出HPD 600型树脂作为理想的吸附剂;研究了 HPD 600树脂对红小豆多酚的吸附等温线,结果表明,该吸附等温线与 Langmuir、Freundlich函数曲线的拟合程度非常高,且采用Langmuir模型的拟合效果略优于Freundlich模型。静态和动态吸附、洗脱试验结果表明：样品液浓度、温度、pH值、乙醇浓度、上样流速及洗脱流速等因素均对HPD 600树脂吸附分离红小豆多酚有影响。较理想的工艺参数为：30℃是较适宜的静态吸附温度;保持煮制红小豆水本身的多酚浓度0.96 mg/mL和pH值6.8,上样体积200 mL,上样流速1.0 mL/min进行动态吸附;吸附饱和平衡后,采用50 mL 60%乙醇溶液,以1.5 mL/min的流速进行动态洗脱。依此得到的红小豆多酚纯化液,其总酚含量和总抗氧化能力均有显著提高,约为纯化前的2.2倍。     

基于Modelica语言建模的柴油机稳动态性能仿真与试验

针对传统柴油机建模效率不高、所建模型抽象不易理解、软件平台开放程度差、模型通用性低的问题,采用多领域统一物理建模规范Modelica语言和面向对象的建模思想建立了柴油机的仿真模型。以上柴D4114B型发电用柴油机为例,在解决上述问题的同时模拟了负荷特性下柴油机的稳态过程,最高压力、排温等稳态数据点的实测值与仿真值的最大相对误差为8.9%,证明了所建立的柴油机模型具有较好的稳态性能。在此基础上进行了动态仿真,模拟了转速、单缸循环油量等参数的动态变化规律,并将部分参数的仿真值与实测值进行比较,两者吻合得比较好,证明了所建立的柴油机模型能较好地预测其动态性能,可为后续的基于Modelica语言的柴油机建模提供参考。     

油料冷态预榨过程的油脂径向渗流模型及验证

为量化考察油料一维压榨过程中油脂的流动状态,针对直筒式冷态压榨制油过程,通过简化假设建立了一维压榨模型,并对油料微元进行受力分析;利用Darcy渗流定律与Terzaghi固结理论建立了油料压榨过程中的渗流模型,确定了影响压榨出油效果的因素主要为料筒内径、物料层高度、压榨压力、压榨时间、油脂黏度和物料孔隙度。在实际压榨过程中,压榨压力和压榨时间易控制,油脂黏度和孔隙度也可以通过设置压榨参数而改变,而压榨机的料筒规格不易改变,因此料筒半径的选取尤为重要。基于此,根据渗流模型推导出油率模型,分析了料筒半径对出油率的影响关系,指出料筒内径不宜过大。开展不同筒径时的出油率试验,并与模型预测值对照,其最大误差为2.10%。研究结果为油料直筒式低温预榨制油设备制造及工艺参数的优化及选取提供了参考。     

蛋壳作为吸附材料的研究进展

中国是禽蛋生产和消费大国,每年会产生大量废弃蛋壳。蛋壳往往被当作废弃物处理,不能得到及时回收和处理,浪费资源的同时污染环境。因蛋壳作为廉价易得的吸附材料在修复环境污染方面具有潜在的利用价值,国内外学者对其吸附特性进行了广泛的研究。该文对已有研究进行了归纳,从蛋壳结构与吸附性的关系,处理工艺,吸附的应用及效果、影响因素等方面进行了分析,以便读者了解蛋壳的吸附特性。同时,选取典型研究实例,介绍蛋壳的吸附特性以及加工工艺,从而引起人们对蛋壳潜在价值的重视,以促进蛋壳资源的再利用。     

不同发育阶段谷蠹侵害对储藏小麦蛋白结构的影响

为探索谷蠹在不同生长发育阶段对储藏小麦蛋白结构的影响,该文以谷蠹种虫感染后的小麦为研究对象,对谷蠹不同发育阶段(卵期、幼虫期、蛹期、成虫期)侵害后小麦中麦谷蛋白大聚合体(glutenin macropolymer,GMP)、沉降值、面筋蛋白持水力、蛋白二级结构、巯基(-SH)、二硫键(-S-S-)及面筋显微结构进行测定与分析。结果表明:在谷蠹发育的4个阶段,GMP、沉降值、β转角总体呈增加趋势,-SH、β折叠比例变化与之相反;面筋蛋白持水力、-S-S-和α螺旋比例总体呈先降后升趋势,无规卷曲比例变化则与之相反。卵期谷蠹危害较小,只有β转角和面筋蛋白持水力有显著变化(P0.05);幼虫期和蛹期谷蠹危害严重,与相同试验条件下相应时期的无虫小麦对照样相比,GMP、无规卷曲和β转角比例及沉降值均显著增加(P0.05),面筋蛋白持水力、-SH、-S-S-、α螺旋和β折叠显著减少(P0.05)。面筋蛋白显微结构显示:随着谷蠹在小麦籽粒内部发育,面筋表面粗糙程度加重,微纤维状丝增多,结构疏松散乱,断裂严重,至成虫期时,面筋结构已无法识别,因此在实际储藏过程中不仅要关注成虫的数量,还应注意及时控制谷蠹的生长发育。     

基于土地功能的农村居民点内部用地结构分类

科学合理的农村居民点内部用地功能结构分类是提升农村土地利用效率、实现用地结构优化配置的重要前提。该文在梳理农村居民点用地分类现状的基础上,从土地利用的功能角度出发,构建了涵盖农村居民点用地生产功能、生活功能、生态功能和潜在功能的分类体系,其中包含4个一级类、10个二级类和37个三级类;并以该分类方法为基础,通过实地调查典型农村居民点内部用地结构现状,从微观视角揭示内部用地结构。基于新的分类体系,大兴庄村用地类型可分为28种,农村居民点内部生产用地、生活用地和生态用地的比例分别为34.73%、53.53%和4.06%,可挖潜面积比例为占农村居民点总面积的13.09%。研究结果为中国农村居民点用地分类体系构建提供了基本思路和工作框架。     

单轨道山地果园运输机齿条齿形优选

为减小单轨道山地果园运输机能耗及提高运输效率,该文基于动力学理论建立了运输机驱动轮与轨道齿条啮合的动力学模型,并设计、加工制造了链轮齿形齿条、销轮齿形齿条、摆线齿形齿条。以运输机驱动轮旋转角速度、轨道坡度、齿条齿形为考察因素,以驱动轮与不同齿形齿条啮合时所需提供的驱动扭矩为评价指标,探究齿条齿形对单轨道山地果园运输机力学性能的影响,得到在相同条件下驱动轮与链轮齿形齿条啮合时的驱动扭矩最小,且波动幅度最小。在驱动轮转速为+88.08 rad/s、轨道坡度分别为+0?、+6?、+12?时,驱动轮与链轮齿形齿条啮合时的驱动扭矩均值较驱动轮与圆弧齿形齿条啮合时的驱动扭矩均值分别减小33.82%,33.45%,21.59%;在驱动轮转速为-88.08 rad/s、轨道坡度分别为-0?、-6?、-12?时,驱动轮与链轮齿形齿条啮合时的驱动扭矩均值较驱动轮与圆弧齿形齿条啮合时的驱动扭矩均值分别减小35.55%,27.24%,30.43%。试验结果表明,链轮齿形齿条综合性能最优,较圆弧齿形齿条更适宜用于单轨道山地果园运输机的轨道运输中。该研究为单轨道山地果园运输机轨道的结构优化设计提供了参考。     

Effects of temperature on soil organic carbon fractions contents,aggregate stability and structural characteristics of humic substances in a Mollisol

Purpose

Under a global warming scenario, understanding the response of soil organic carbon fractions and aggregate stability to temperature increases is important not only for better understanding and maintaining relevant ecosystem services like soil fertility and crop productivity, but also for understanding key environmental processes intimately related with the maintenance of other regulatory ecosystem services like global climate change mitigation through carbon sequestration. An increase in temperature would accelerate the mineralization of soil organic carbon. However, the properties of organic carbon remained in soil after mineralization is not well known.

Materials and methods

Mollisol was collected at 0–20-cm depth from maize (Zea mays L.) field in Northeast China. A 180-day incubation experiment was conducted at three different temperatures (10, 30, and 50 °C) under constant soil moisture (60 % water holding capacity). Soil samples were assayed for total organic carbon (TOC), water-soluble organic carbon (WSOC), easily oxidizable organic carbon (EOC), humic fractions carbon, aggregate-associated carbon, and water stability of aggregates. Elemental analysis and solid-state ¹³C nuclear magnetic resonance spectroscopy were used to characterize humic acid and humin fractions.

Results and discussion

The contents of soil TOC, EOC, humic fractions carbon, and aggregate-associated carbon decreased with the increase in temperature. The proportion of 2–0.25-mm macroaggregate and the mean weight diameter (MWD) of aggregates also decreased. The C, H, N, S, alkyl C, and O-alkyl C contents of humic acid and humin decreased, whereas the O, aromatic C, and carbonyl C contents increased. The H/C, aliphatic C/aromatic C, and O-alkyl C/aromatic C ratios in humic acid and humin fractions decreased.

Conclusions

The increase in temperature has a negative impact on soil organic carbon content, soil aggregation, and aggregate stability. Moreover, humic acid and humin molecules become less aliphatic and more decomposed with the increase in temperature.