From molecular noise to behavioural variability in a single bacterium

The chemotaxis network that governs the motion of Escherichia coli has long been studied to gain a general understanding of signal transduction. Although this pathway is composed of just a few components, it exhibits some essential characteristics of biological complexity, such as adaptation and response to environmental signals. In studying intracellular networks, most experiments and mathematical models have assumed that network properties can be inferred from population measurements. However, this approach masks underlying temporal fluctuations of intracellular signalling events. We have inferred fundamental properties of the chemotaxis network from a noise analysis of behavioural variations in individual bacteria. Here we show that certain properties established by population measurements, such as adapted states, are not conserved at the single-cell level: for timescales ranging from seconds to several minutes, the behaviour of non-stimulated cells exhibit temporal variations much larger than the expected statistical fluctuations. We find that the signalling network itself causes this noise and identify the molecular events that produce it. Small changes in the concentration of one key network component suppress temporal behavioural variability, suggesting that such variability is a selected property of this adaptive system.     

小型浅水湖泊氨氧化细菌分布特征及其对氮素垂向分布的响应

以淮河流域里下河地区小型浅水湖泊为研究对象,采用分子生物学方法和细菌反硝化稳定同位素技术研究氨氧化细菌(AOB)的生物多样性和群落特征,探究不同类型的污染物对AOB丰度和群落特征的影响。结果表明,得胜湖AOB的生物多样性和丰度最高,而大纵湖北部最低,究其原因,认为是得胜湖较为复杂的污染来源和周围环境以及大纵湖湖心密集的水生植物造成的。amoA基因的系统发育分析表明,研究区内丰度最高的是亚硝化单胞菌属,占92.3%,亚硝化螺菌属占7.7%;硝氮含量与AOB丰度具有一致性,AOB丰度高的采样点上覆水中硝氮较高。同位素溯源分析表明污染物的来源差异导致了δ¹⁵N的不同,长期的围网养殖会导致δ¹⁵N降低,而腐烂植物的长期过度累积则会导致δ¹⁵N增大。     

Temporal response properties to second-order visual stimuli in the LGN of cats

Visual stimuli occurring naturally are rich in instances of objects delineated from the backgrounds only by differences in luminance,which is called first-order stimuli,as well as those defined by differences of contrast or texture,referred to as second-order stimuli. The neuronal mechanism for processing second-order stimuli is still unclear. In this study,we compared the responses of cat LGN (lateral geniculate nucleus) cells to second-order stimuli at five temporal frequencies to their responses to first-order stimuli. Our results showed that most LGN cells can be evoked by second-order stimuli,and their firing rates to second-order stimuli decreased relative to first-order stimuli as temporal frequency increased from 0.5 to 8 Hz; moreover the ratio of a nonlinear to linear factor had a higher value in the responses to second-order stimuli than to first-order stimuli. We also found that the responses of Y-cells to second-order stimuli were significantly higher than the responses of X-cells,suggesting the Y-cells have a more important role in the processing of second-order stimuli. All these results reveal that first-order and second-order signals might be processed in separate 'streams' of the visual sys-tem.     

Changes in fossil-fuel carbon emissions in response to interannual and interdecadal temperature variability

Relationships on interannual and interdecadal timescales among global mean air temperature,CO2 concentrations and fossil-fuel carbon emissions in four major developed countries (the United States,the United Kingdom,France,and Germany) were analyzed.On an interannual timescale,the United States fossil-fuel carbon emissions tend to increase during cold winters and decrease during warm winters,which is opposite to the situation in summer.On an interdecadal timescale,cold (warm) periods both in the United States and globally agree with high (low) periods of fossil-fuel carbon emissions,with the temperature variability leading by 5–7 years.The leading correlation on the interdecadal timescale and the asymmetry in seasonal correlation on the interannual timescale indicate that temperature variability is a possible cause of changes in fossil-fuel carbon emissions.     

6kaBP中东亚气候对植被变化的响应

选取PMIP2计划中ECBilt-CLIO-VECODE模式的结果,对比中全新世(6 kaBP)气候对于现代气候的变化,探讨了植被在中全新世气候变化中的意义.中东亚干旱区受西风环流影响,而东亚地区6 kaBP季风深入,不同大气环流的影响导致两区域大尺度气候特征差异大,同时该时期植被的变化增强了气候系统对轨道参数变化的响应:一系列气候要素对植被的动态响应导致气温、降水都因植被反馈而发生较大变化,但是该模式的结果存在低估6 kaBP升温幅度的缺陷,尤其是对冬季温度的模拟;即使耦合植被后有所改善,但对6 kaBP气候变化的驱动因子及其相互关系的研究仍需深入,同时对局地气候变化的物理机制还需改进.     

互花米草根际细菌相对丰度及其与环境因子的关系

对黄河三角洲受堤坝影响区域和不受堤坝影响区域互花米草(SpartinsalternifloraLoisel)的根际细菌及环境因子进行了为期2年的监测. 受堤坝影响区域根际细菌相对丰度值显著低于不受堤坝影响区域根际细菌相对丰度值, 同一区域不同季节互花米草根际细菌相对丰度值也存在显著差异. 并且在受堤坝影响区域中,根际细菌相对丰度值最大值发生向海方向的位移,根际细菌相对丰度值与由海向陆的距离呈显著正相关(P<0.05),随着由海向陆的位移,根际细菌相对丰度值呈显著增加的趋势. 同时,随土壤深度增加,根际细菌相对丰度值逐渐降低. 根际细菌相对丰度值与总氮和有机质质量分数呈显著正相关(P<0.5),与盐质量浓度呈显著负相关(P<0.5),根际细菌相对丰度值随着盐质量浓度的降低呈显著增加的趋势,而根际细菌相对丰度值与总磷质量分数无显著相关性. 研究对黄河三角洲典型植被特别是入侵物种生态演替具有重要科学意义和应用价值,并为我国滨海地区互花米草的治理提供针对性措施和决策依据.      

Effects of age on latency and variability of visual response in monkeys

Visual function declines during normal aging. The neural mechanisms underlying age-related changes have just begun to be revealed. It has been demonstrated that retinal ganglion cells and cells in dorsal lateral geniculate nucleus (dLGN) in old monkeys are relatively normal. However, age-related functional degradations have been found at cellular level in mammalian visual cortex.     

相互依存与亚太地区的国家间合作

相互依存使亚太地区国家的共同利益不断增长，然而各个国家的个别利益并没有消失。基于此。亚太地区的国家间合作存在着无条件合作、竞争性合作和被动式协调三个层次和自助、政策协调和制度化安排三种类型。而正确地认识与维护国家利益以及完善制度化的安排将促进和巩固亚太地区的国家间合作。     

理科知识相互渗透教学初探

为培养学生的学科间综合能力,全面提高学生的综合素质,尝试了在化学教学中实施理科知识相互渗透教学,具体方法：（1）备课;了解学生现有理科知识状况,熟悉理科知识结构,精心选择教学素材,（2）上课：设计好问题情境,抓住渗透教学时机,将各科知识有机地融入化学学科中。     

Temporal and spatial variability response of groundwater level to land use/land cover change in oases of arid areas

This paper conducts a case study on the impacts of land use/cover change （LUCC） on the temporal and spatial variability of the groundwater level in an arid oasis in the Sangong River Watershed by using the geographical information system （GIS）, remote sensing （RS） and geostatistical methods. The temporal and spatial variability of the groundwater level in the watershed in 1978, 1987 and 1998 is regressed by using the＇semivariogram model and Kriging interpolation. The LUCC classification maps derived from the aerial images in 1978, Landsat TM image in 1987 and Landsat ETM image in 1998 are used to superpose and analyze the conversion relationship of LUCC types in the regions with different isograms of the groundwater depth. The results show that the change of groundwater recharge was not so significant in the whole oasis, but the temporal and spatial LUCC was significant either in the normal flow periods or in the high flow periods during the 20-year period from 1978 to 1998, and there was a close correlation between them. There is generally a moderate spatial correlation of groundwater level （33.4%） and the spatial autocorrelation distance is 17.78 km. The regions where the groundwater level is sharply changed are also the regions where the land resources are increasingly exploited, which include mainly the exploitation of farmlands, woodlands, and building, industrial and mining lands. The study reveals that the LUCC affects strongly the temporal and spatial variability of the groundwater level in the arid oasis. The study results are of direct and practical significance for rationally utilizing shallow groundwater resources and maintaining the stability of the arid oasis.     

小流域尺度下土壤有机碳和全氮空间变异特征

以小流域为尺度,通过Kriging插值用Surfer 8.0软件绘制南京邓下小流域土壤有机碳(SOC)和全氮(TN)等值线图,研究了土壤有机碳和全氮空间变异特征.结果表明:(1)研究区土壤有机碳和全氮平均值分别为1.60%和0.15%,变异系数分别为44.43%和30.73%,属于中等强度变异,有机碳的变异性较强.经Kolmogorov.Smirnov检验,土壤有机碳和全氮都符合正态分布.(2)选择球状模型、指数模型分别为土壤有机碳和全氮的半方差函数理论模型,土壤有机碳和全氮的C0/(C0 c)值均小于25%,表明在变程内具有强烈的空间相关性;以小流域尺度进行土壤有机碳和全氮空间分布研究能得到较准确的结果.(3)研究区土壤有机碳和全氮分布规律是有机碳在北部较高,东南部较低,呈自北部向东南递减趋势,最低处以岛状分布在中南部,全氮空间分布和有机碳的空间分布趋势大致相同.