柏木低效林不同改造模式优势草本植物多样性及其生态位

草本层对森林生态系统具有重要的作用,其对于环境的变化比乔木层和灌木层更为敏感,在较短的时间内更容易反映改造带来的影响。为了分析林分改造后草本植物多样性的变化和揭示草本群落间的关系,以川中丘陵区改造4 a后的11种模式:不同密度(株行距1.5 m×4 m与1.5 m×2 m)的桤木(Alnus cremastogyne)、香椿(Toona sinensis)、银木(Cinnamomum septentrionale)纯林模式和株行距为1.5 m×2 m的银木+桤木模式、香椿+银木模式、香椿+桤木模式、桤木+香椿+银木模式以及采伐迹地作为研究对象,柏木(Cupressus funebris)纯林为对照,对柏木低效林不同改造模式的优势草本植物多样性、生态位宽度及生态位重叠进行研究。结果表明:(1)除高低密度香椿模式、低密度银木模式和桤木+香椿+银木模式外,其他模式的草本植物多样性均优于柏木纯林,其中以香椿+银木模式(Shannon-Wiener指数、Simpson指数、均匀度和丰富度指数分别为(1.82、0.83、0.94和1.30),与香椿+桤木模式(1.83、0.83、0.93和1.33)的生物多样性显著高于柏木纯林(1.48、0.69、0.82和1.27),为最优的改造模式。(2)改造前铁线蕨(Adiantum capillus-veneris)生态位宽度最广为2.365,喜阴植物占有优势地位,改造后林下光照环境发生变化,喜阳植物五节芒(Miscanthus floridulus)在低密度的纯林模式中迅速占据林下生长空间,生态位宽度较大,随改造模式郁闭度的增加,薹草(Carex tristachya)、地果(Ficus tikoua)、竹叶草(Oplismenus compositus)等喜阴植物逐渐占据优势地位,喜阳植物逐渐被淘汰。生态位宽度的大小与重要值呈极显著正相关关系(r=0.916),但也与资源位呈极显著正相关关系(r=0.977)。(3)生态位宽度较大的物种间既有较大的生态位重叠,也有较小的生态位重叠,不能仅凭生态位宽度来判定生态位重叠值,而生态位宽度较小的鼠麴草(Gnaphalium affine)(0.647)与蛇莓(Duchesnea indica)(2.152)之间拥有最大的生态位重叠(0.123),可能是因为它们有相似的资源利用方式或相近的生态学特性。总体来说所有模式中草本植物物种间生态位重叠值都较低(0.2),生态位分化明显,种间竞争并不激烈,这可能与改造时间较短有关系。     

Three-dimensional chromatin ensemble reconstruction via stochastic embedding

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昆虫嗅觉神经的计算机三维重建

基于激光扫描共聚焦显微镜平台的计算机三维重建在昆虫嗅觉神经研究中发挥了重要作用。对经荧光标记的神经组织采集系列光学切片并进行三维重建,在双翅目、鳞翅目、膜翅目、蜚蠊目昆虫中均有进展。触角叶是昆虫的初级嗅觉中心,触角叶的解剖学图谱是识别不同种和雌雄虫间嗅球体特定功能的先决条件。了解构成嗅觉传输途径的主要神经元的形态和空间关系是理解气味信息在中枢神经系统编码的基础。三维重建昆虫的嗅觉神经,对于探讨昆虫嗅觉在其寄主选择、觅食以及寻找配偶等行为中的作用具有非常重要的意义。     

Single particle analysis of relaxed and activated muscle thin filaments

The movement of tropomyosin from actin's outer to its inner domain plays a key role in sterically regulating muscle contraction. This movement, from a low Ca2+ to a Ca2+-induced position has been directly demonstrated by electron microscopy and helical reconstruction. Solution studies, however, suggest that tropomyosin oscillates dynamically between these positions at all Ca2+ levels, and that it is the position of this equilibrium that is controlled by Ca2+. Helical reconstruction reveals only the average position of tropomyosin on the filament, and not information on the local dynamics of tropomyosin in any one Ca2+ state. We have therefore used single particle analysis to analyze short filament segments to reveal local variations in tropomyosin behavior. Segments of Ca2+-free and Ca2+ treated thin filaments were sorted by cross-correlation to low and high Ca2+ models of the thin filament. Most segments from each data set produced reconstructions matching those previously obtained by helical reconstruction, showing low and high Ca2+ tropomyosin positions for low and high Ca2+ filaments. However, approximately 20% of segments from Ca2+-free filaments fitted best to the high Ca2+ model, yielding a corresponding high Ca2+ reconstruction. Conversely, approximately 20% of segments from Ca2+-treated filaments fitted best to the low Ca2+ model and produced a low Ca2+ reconstruction. Hence, tropomyosin position on actin is not fixed in either Ca2+ state. These findings provide direct structural evidence for the equilibration of tropomyosin position in both high and low Ca2+ states, and for the concept that Ca2+ controls the position of this equilibrium. This flexibility in the localization of tropomyosin may provide a means of sterically regulating contraction at low energy cost.     

Methanol-free biosynthesis of fatty acid methyl ester (FAME) in Synechocystis sp. PCC 6803

To meet the increasing global demand of biodiesel over the next decades, alternative methods for producing one of the key constituents of biodiesel (e.g. fatty acid methyl esters (FAMEs)) are needed. Algal biodiesel has been a long-term target compromised by excessive costs for harvesting and processing. In this work, we engineered cyanobacteria to convert carbon dioxide into excreted FAME, without requiring methanol as a methyl donor. To produce FAME, acyl-ACP, a product of the fatty acid biosynthesis pathway, was first converted into free fatty acid (FFA) by a thioesterase, namely ’UcFatB1 from Umbellularia californica. Next, by employing a juvenile hormone acid O-methyltransferase (DmJHAMT) from Drosophila melanogaster and S-adenosylmethionine (SAM) as a methyl donor, FFAs were converted into corresponding FAMEs. The esters were naturally secreted extracellularly, allowing simple product separation by solvent overlay as opposed to conventional algae biodiesel production where the algae biomass must first be harvested and processed for transesterification of extracted triacylglycerols (TAGs). By optimizing both the promoter and RBS elements, up to 120 mg/L of FAMEs were produced in 10 days. Quantification of key proteins and metabolites, together with constructs over-expressing SAM synthetase (MetK), indicated that ’UcFatB1, MetK, and DmJHAMT were the main factors limiting pathway flux. In order to solve the latter limitation, two reconstructed ancestral sequences of DmJHAMT were also tried, resulting in strains showing a broader methyl ester chain-length profile in comparison to the native DmJHAMT. Altogether, this work demonstrates a promising pathway for direct sunlight-driven conversion of CO₂ into excreted FAME.     

An ostracod-based calibration function for electrical conductivity reconstruction in lacustrine environments in Patagonia,Southern South America

In the Patagonian region (∼37–56°S) E of the Andes, the salinity and solute composition of lakes is strongly related to their location along the marked W-E decreasing precipitation gradient that is one of the main climatic features of the area. A calibration function (n = 34) based on 12 ostracod species (Ostracoda, Crustacea) was developed by WA-PLS to quantitatively reconstruct electrical conductivity (EC) values as a salinity proxy. The selected one component model had a r² = 0.74 and RMSEP and maximum bias equal to 16% and 31% of the sampled range, respectively, comparable to other published ostracod-based calibration functions. This model was applied to the ostracod record of the closed lake Laguna Cháltel (49°58′S, 71°07′W), comprising seven species and dominated by two species of the genus Limnocythere. In order to evaluate the calibration function’s robustness, the obtained EC values were compared with qualitative lake level and salinity variations inferred through a multiproxy hydrological reconstruction of the lake. Both reconstructions show good overall agreement, with reconstructed EC values in the oligo-mesohaline range (average: 11 060 ± 680 μS/cm) between 4570 and 3190 cal BP, corresponding to the ephemeral and shallow lake phases, and a marked decrease in EC concurrent with a lake level rise, reaching an average EC of 1140 ± 90 μS/cm during the deep lake phase (1720 cal BP to present). The variability in the reconstructed EC values for the ephemeral lake phase showed some inconsistency with the expected trend, which was attributed to time-averaging effects; for its part, the pace of the decrease in EC during the medium-depth phase (3190–1720 cal BP) differed from the expected, which could be due to autigenic effects (redissolution of salts) at the onset of this phase. This comparison not only lends support to the adequacy of the calibration function, but also suggests that its application in the context of a multiproxy study can greatly contribute to distinguish between autigenic and climatic-related controls of paleosalinity in closed lakes, allowing performing more accurate paleoenvironmental inferences on the basis of paleohydrological reconstructions.     

Land surface phenology as an indicator of biodiversity patterns

With the rapid decline in biodiversity worldwide it is imperative to develop procedures for assessing changes in biodiversity across space. The synoptic view provided by imaging remote sensors constitutes a suitable approach for analyzing biodiversity from local to regional scales. A procedure based on the close relationship between floristic similarity and the similarity in land surface phenology was recently developed and successfully applied to assess diversity patterns using time series imagery acquired by the Moderate Resolution Imaging Spectro-radiometer (MODIS). However, as it depends on high temporal resolution remotely sensed data (e.g., MODIS), the procedure is constrained by the coarse spatial resolution characterizing these high temporal resolution data. Using an optimized technique for image fusion, we combined high temporal resolution data acquired by the MODIS sensor system with moderate spatial resolution data acquired by the Landsat TM/ETM+ sensor systems. Our results show that the MODIS/Landsat data fusion allows the characterization of land surface phenology at higher spatial resolutions, which better corresponded with information acquired within vegetation survey plots established in temperate montane forests located in Wolong Nature Reserve, Sichuan Province, China. As such, the procedure is useful for capturing changes in biodiversity induced by disturbances operating at large spatial scales and constitutes a suitable tool for monitoring and managing biodiversity.     

16层螺旋CT三维重建与DR平片检查对外伤性肋骨骨折的诊断价值比较研究

目的:研究16层螺旋电子计算机断层扫描(CT)三维重建与数字化摄影(DR)平片检查对外伤性肋骨骨折的诊断价值,为临床诊治提供参考。方法:将2017年6月至2018年6月期间于本院接受诊治的82例外伤性肋骨骨折患者作为研究对象,所有患者均接受16层螺旋CT三维重建与DR平片检查,观察并记录患者的骨折发生部位,并比较两种诊断方法对外伤性肋骨骨折诊断的准确率、灵敏度、特异性、阳性预测值、阴性预测值以及漏诊情况。结果:82例外伤性肋骨骨折患者经影像学与临床诊断明确发生骨折179处,多发性骨折发生率为62.20%,单发性骨折发生率为37.80%,骨折肋骨段位中4-10段骨折发生率最高为69.83%,骨折肋骨水平阶段中腋肋骨折发生率最高为59.78%。相较于DR平片,16层螺旋CT三维重建诊断外伤性肋骨骨折的准确率、灵敏度、特异性、阳性预测值、阴性预测值更高,漏诊率更低,差异有统计学意义(P0.05)。结论:相较于DR平片检查,应用16层螺旋CT三维重建检查外伤性肋骨骨折能明显提高临床诊断的准确率、灵敏度和特异性,减少漏诊,可为临床诊治提供更可靠的信息,值得临床推广。