鼎湖山针阔叶混交林冠层下方CO2通量及其环境响应

精确估算典型森林生态系统冠层下方CO₂通量（Fcb）对验证陆地生态系统碳平衡模型具有重要意义。采用开路涡度相关法对鼎湖山针阔叶混交林Fcb进行定位测定,根据1周年数据分析Fcb及其对环境要素的响应特征,结果表明：(1) 白天Fcb呈下降趋势表明地表植被全年具有光合能力,但总体上地表植被和土壤表现为CO2排放源;(2) Van’t Hoff方程、Arrhenius方程和Lloyd-Taylor方程均可以较好反映土壤温度(Ts)与Fcb的关系,其中仅Lloyd-Talor方程能够反映温度因子敏感性指标Q10随温度的变异性特征;(3) Lloyd-Talor方程模拟的Fcb完全由Ts控制,而连乘模型由Ts和土壤水分(Ms)控制,可以反映水热条件的综合影响,对Fcb具有更强的拟合能力;(4)在Ms较大时连乘模型对Fcb的估算高于Lloyd-Talor方程,反之在干旱时段连乘模型模拟结果低于Lloyd-Talor方程,表明当存在水分胁迫时,Ms可以成为影响Fcb的主导因子;(5) 2003年鼎湖山针阔叶混交林Fcb总量((787.4±296.8)gCm^-2a^-1)比静态箱-气相色谱法测得的土壤呼吸偏低17%。与箱式法相比,涡度相关法通量测定结果普遍存在偏低估算现象。     

鼎湖山针阔叶混交林冠层下方CO2通量及其环境响应

精确估算典型森林生态系统冠层下方CO2通量（Fcb）对验证陆地生态系统碳平衡模型具有重要意义。采用开路涡度相关法对鼎湖山针阔叶混交林Fcb进行定位测定,根据1周年数据分析Fcb及其对环境要素的响应特征,结果表明：（1）白天Fcb呈下降趋势表明地表植被全年具有光合能力,但总体上地表植被和土壤表现为CO2排放源;（2）Van’tHoff方程、Arrhenius方程和Lloyd-Taylor方程均可以较好反映土壤温度（Ts）与Fcb的关系,其中仅Lloyd-Talor方程能够反映温度因子敏感性指标Q10随温度的变异性特征;（3）Lloyd-Talor方程模拟的Fcb完全由Ts控制,而连乘模型由Ts和土壤水分（Ms）控制,可以反映水热条件的综合影响,对Fcb具有更强的拟合能力;（4）在Ms较大时连乘模型对Fcb的估算高于Lloyd-Talor方程,反之在干旱时段连乘模型模拟结果低于Lloyd-Talor方程,表明当存在水分胁迫时,Ms可以成为影响Fcb的主导因子;（5）2003年鼎湖山针阔叶混交林Fcb总量（（787.4±296.8）gCm^-2a^-1）比静态箱-气相色谱法测得的土壤呼吸偏低17%。与箱式法相比,涡度相关法通量测定结果普遍存在偏低估算现象。     

长江安庆段河流湿地生态系统呼吸及其影响因子

研究湿地生态系统呼吸(Reco)对评价湿地生态系统碳汇功能具有重要的意义.采用涡度相关法对位于长江中游河流湿地的杨树人工林生态系统进行了长期的定位观测,根据2005-07-23～2007-12-15的数据对Reco进行估算,并分析Reco对主要环境因子的响应特征.结果表明:(1)Reco具有明显的季节变化,每年的最大值出现在8月份,最小值出现在1月份,Reco受空气温度、土壤温度和土壤含水量共同影响,总体上看空气温度是驱动Reco的主要因子;(2)在几种模拟生态系统呼吸的模型中,Van't Hoff方程、Arrhenius方程、Lloyd-Talor方程在统计意义上具有同等的能力,由空气温度和土壤含水量共同驱动的连乘模型对Reco的拟合效果最好;(3)使用连乘模型估算的2006年生态系统呼吸总量为1074.7 gC·m-2·a-1,2007年为1127.0 gC·m-2·a-1,与亚热带和温带的森林站点的测定值相接近.     

珠三角城市绿地CO2通量的季节特征

城市绿地是城市碳循环的重要组成部分,利用长期定位观测资料估算珠三角典型城市绿地的CO2通量,可以为应对气候变化、评价区域碳源汇提供参考。应用2009、2010年,东莞市植物园内的涡度相关法CO2通量定位观测资料,分析了净生态系统交换量(NEE)的年变化及其与气象要素的关系,结果表明:(1)年平均NEE总量为-104.2 gC.m-.2a-1,表明城市绿地生态系统具有固碳能力。(2)NEE随光温条件变化呈现明显的季节动态,12至3月表现为碳源,其他月份表现为碳汇。(3)根据白天NEE与光合有效辐射(PAR)逐月拟合Michaelis-Menten方程,得到年平均表观初始光能利用率(α)为(0.00134±0.00035)mgCO.2μmol-1光子,年平均光饱和生态系统生产力(Pmax)为(1.006±0.283)mgCO.2m-.2s-1。(4)利用夜间呼吸(Reco)与5 cm土壤温度(Ts)拟合指数方程,得到年平均Reco总量为1378.1 gC.m-.2a-1。(5)NEE与PAR、气温(Ta)和饱和水压差(VPD)的相关性分析显示,NEE与PAR偏相关系数的绝对值大于Ta和VPD,表明PAR对NEE的影响最大。     

珠三角城市绿地CO2通量的环境响应特征

城市绿地的净生态系统CO2交换量(NEE)受多种环境因素控制,定量分析NEE的环境响应机制对评估绿地生态系统固碳效益、优化城市绿地布局有重要意义。本文应用2009、2010年位于东莞市植物园内的涡度相关CO2通量定位观测资料,分析了光合有效辐射(PAR)、土壤温度(Ts)、饱和水汽压差(VPD)、降水及周边不同下垫面类型对NEE的影响。结果表明:NEE绝对值随PAR的升高而增加,PAR超过光饱和点(约为1500μmol photons·m-2·s-1)后,NEE绝对值呈回落趋势;生态系统呼吸(Reco)随Ts升高而增加,在温度较低时,Reco对Ts的敏感性较强(10℃时,Lloyd-Taylor方程的Q10=1.8),随着温度升高,敏感性下降(30℃时,Q10=1.43);VPD通过影响植物气孔导度对CO2交换产生作用,相同温度下,随着VPD升高,气孔导度增大,呼吸释放与光合固定的CO2量均增加;降水能增加土壤湿度进而使Reco增大,25℃时,降水后的Reco比降水前增加15.8%;测站东北和西南方的绿地范围较大,当东北和西南部是主要贡献区时,NEE绝对值较大,表明增加城市绿地能有效提高城市固碳效益。     

数据处理方法不确定性对CO_2通量组分估算的影响

基于中国陆地生态系统通量观测研究网络(ChinaFLUX)4个站点(2个森林站和2个草地站)的涡度相关通量观测资料,分析了CO2通量数据处理过程中异常值剔除参数设置、夜间摩擦风速(u*)临界值(u*c)确定及数据插补模型选择对CO2通量组分估算的影响.结果表明:3种数据处理方法均对净生态系统碳交换量(NEE)年总量估算有显著影响,其中u*c确定是影响NEE估算的重要因子;异常值剔除、u*c确定及数据插补模型选择导致NEE年总量估算偏差分别为0.62～21.31 g C.m-2.a-1(0.84%～65.31%)、4.06～30.28 g C.m-2.a-1(3.76%～21.58%)和0.69～27.73 g C.m-2.a-1(0.23%～55.62%),草地生态系统NEE估算对数据处理方法参数设置更敏感;数据处理方法不确定性引起的总生态系统碳交换量和生态系统呼吸年总量估算相对偏差分别为3.88%～11.41%和6.45%～24.91%.     

仪器的加热效应校正对生态系统碳水通量估算的影响

涡度相关技术的广泛应用为获取生态系统碳、水通量提供了可能,但在开路式涡度相关系统中,仪器的加热效应增大了观测数据的不确定性。为了衡量仪器的加热效应,以ChinaFLUX3个典型生态系统(长白山温带针阔混交林(CBS)、海北灌丛草甸(HBGC)、鼎湖山亚热带常绿阔叶林(DHS))为研究对象,就仪器的加热效应校正对碳、水通量估算的影响进行分析。结果表明:加热校正没有改变生态系统的能量闭合特征,也没有对水汽通量的估算产生影响,但显著减小了CBS和HBGC非生长季的净生态系统生产力(NEP),进而减少了NEP的年总量,对DHS没有显著影响。NEP减小幅度受到温度的强烈影响,CBS为7.7%～10.4%,远小于HBGC的76.6%～85.2%,HBGC的NEP大幅降低主要是由夜间NEP的改变导致生态系统呼吸(RE)的增大而引起。因而,在温带生态系统中,充分考虑加热校正对于准确估算生态系统的碳收支具有重要作用。     

太湖流域典型稻麦轮作农田生态系统碳交换及影响因素

利用涡度相关技术观测太湖流域典型稻麦轮作农田生态系统2a净生态系统碳交换(NEE)变化过程,分析其碳交换特征及影响机理,结果表明:太湖流域典型稻麦轮作农田年NEE为-749.49—-785.38 g C m-2a-1,考虑作物籽粒碳和秸秆还田后净吸收88.12 g C m-2a-1,为弱碳汇;稻/麦季日均NEE和白天NEE季节变化直接受作物植被生长影响;麦季夜间NEE与10 cm土壤温度呈显著指数关系,2012/2013年温度敏感系数(Q10)分别为3.03和2.67;当土壤水分低于田间持水量时,麦季夜间NEE主要受土壤温度影响,反之,夜间NEE受土壤温度和水分双重影响;降水对麦季夜间NEE有短时的激发效应;稻季淹水对土壤呼吸产生较明显的阻滞效应,降低了夜间NEE对土壤温度的敏感性,2012和2013年分别为1.88和1.39,稻季淹水与烤田交替变化对土壤呼吸产生明显的抑制或激发的短时效应。     

中国东部森林最大总初级生产力的时空分布特征及其影响因子

生态系统碳循环对温度的响应是全球变化生态学的重要研究内容之一。总初级生产力(GPP)随着温度的升高而升高,在最适温下达到最大值(GPP_(max)),之后随温度的升高而保持不变甚至下降,因此GPP_(max)代表着最适温度下的植被光合潜力。然而,关于森林生态系统GPP_(max)的时空分布和影响因子仍不清楚。本文以中国东部南北森林样带(NSTEC)上的长白山温带针阔混交林、会同亚热带杉木人工林、千烟洲亚热带常绿针叶人工林、鼎湖山亚热带常绿针阔混交林和西双版纳热带季雨林等5种典型生态系统为对象,利用涡度相关技术分析森林GPP_(max)的时空规律及其主要影响因素。结果表明:在所有森林生态系统中,GPP对温度的响应模式均为单峰曲线,最适温下的GPP_(max)表现为长白山温带针阔混交林千烟洲亚热带常绿针叶人工林西双版纳热带季雨林会同亚热带杉木人工林鼎湖山亚热带常绿针阔混交林。在所有的站点中,温度是引起GPP_(max)空间变异的最主要因素,GPP_(max)随温度的增加而减少。此外,太阳辐射、降水和饱和蒸汽压差也显著影响GPP_(max)。在时间尺度上,对每个森林生态系统GPP_(max)年际变异的对比分析发现,温度是长白山温带针阔混交林GPP_(max)年际变化的主要控制因子,5 cm土壤含水量是影响会同、千烟洲和鼎湖山通量观测系统GPP_(max)年际变异的主要因子,未发现影响西双版纳热季雨林年际变异的主要因子。本研究有助于理解未来气候变暖背景下GPP的变化趋势,并为中国碳循环的准确模拟提供实验证据和参数依据。     

中亚热带人工针叶林生态系统碳通量拆分差异分析

涡度通量观测可直接获取陆地生态系统与大气之间CO2净交换量(NEE),但深入认识碳循环过程和校验生态系统模型需要不同时间尺度总初级生产力(GPP)和生态系统呼吸(Re)等碳通量数据。利用中国陆地生态系统通量观测与研究网络(ChinaFLUX)中亚热带人工针叶林生态系统2003—2009年的涡度通量和气象观测数据,分析了两种NEE拆分方法对不同时间尺度GPP和Re评估的影响,结果表明:(1)两种拆分方法得到的生态系统碳通量组分(GPP和Re)的季节动态变化一致,都在生长季7、8月份达到峰值;(2)非线性回归模型拆分得到的全年Re和GPP相较于光响应曲线模型分别高出2%—28.6%和1.6%—23%,最大高出317.6 gC·m-2·a-1(2006年),逐月最大差值主要发生在8、9月份;(3)不同时间尺度上,两种方法拆分得到的GPP和Re之间差值的环境响应因子不同。在广泛采用非线性回归模型进行拆分时,如果当月光合有效辐射接近到905mol·m-2·月-1,月平均空气饱和水汽压差接近1.18 kPa时,需要考虑使用光响应曲线模型拆分该月通量,结合两种拆分方法以减小全年的误差。     

Race and Racism in America and in Anthropology

Race in North America: Origin and Evolution of a Worldview . Audrey Smedley
Anthropology and Race . Eugenia Shanklin     

Degradation and conversion of somatostatin in normal and diabetic rats in vivo and in vitro

Plasma somatostatin-like immunoreactivity in the portal and jugular veins of streptozotocin diabetic rats was compared with that in normal control rats. In the diabetic group, somatostatin levels in the portal (p less than 0.05) and jugular (p less than 0.01) veins were both elevated compared with those in the control group. Moreover, the degree of elevation was greater in the jugular vein than in the portal vein. To further investigate the role of the liver in the clearance of somatostatin-28 in vivo, 2 micrograms of somatostatin-28 was administered as a bolus into the external jugular vein of intact and functionally hepatectomized rats. The mean half-time of somatostatin-28 was significantly longer in intact diabetic rats than in controls (p less than 0.05). The functional hepatectomy did not cause a significant difference in the half-time in diabetic rats but made it longer in control rats. These results suggest that the longer half-time of somatostatin-28 in diabetic rats in vivo is due to its slower hepatic clearance. The hepatic clearance of somatostatin-28 and somatostatin-14 was further studied in vitro using a recirculating liver perfusion method. The hepatic clearance of 1.2 nM of either somatostatin-28 or somatostatin-14 was significantly lower in diabetic rats than in controls (p less than 0.01). This indicates that elevated plasma somatostatin levels in diabetic rats are caused at least in part by decreased hepatic clearance of somatostatin.(ABSTRACT TRUNCATED AT 250 WORDS)     

Variation in infectivity and aggressiveness in space and time in wild host-pathogen systems: causes and consequences

Variation in host resistance and in the ability of pathogens to infect and grow (i.e. pathogenicity) is important as it provides the raw material for antagonistic (co)evolution and therefore underlies risks of disease spread, disease evolution and host shifts. Moreover, the distribution of this variation in space and time may inform us about the mode of coevolutionary selection (arms race vs. fluctuating selection dynamics) and the relative roles of G × G interactions, gene flow, selection and genetic drift in shaping coevolutionary processes. Although variation in host resistance has recently been reviewed, little is known about overall patterns in the frequency and scale of variation in pathogenicity, particularly in natural systems. Using 48 studies from 30 distinct host–pathogen systems, this review demonstrates that variation in pathogenicity is ubiquitous across multiple spatial and temporal scales. Quantitative analysis of a subset of extensively studied plant–pathogen systems shows that the magnitude of within‐population variation in pathogenicity is large relative to among‐population variation and that the distribution of pathogenicity partly mirrors the distribution of host resistance. At least part of the variation in pathogenicity found at a given spatial scale is adaptive, as evidenced by studies that have examined local adaptation at scales ranging from single hosts through metapopulations to entire continents and – to a lesser extent – by comparisons of pathogenicity with neutral genetic variation. Together, these results support coevolutionary selection through fluctuating selection dynamics. We end by outlining several promising directions for future research.     

Electroejaculation in chimpanzees and gorillas and artificial insemination in chimpanzees

Electroejaculation was performed in 3 chimpanzees, 1 pygmy chimpanzee, and 2 gorillas with an instrument that delivers a modified sine wave current with a frequency of 24 Hz. The current stimuli were applied by a rectal probe with longitudinal electrodes. The electrical parameters varied from 6 to 12 V and from 30 to 40 mA for response of erection and lay between 8 and 18 V and between 40 and 145 mA during semen emission. Eleven chimpanzee semen samples showed the following data (x ± SD): total volume 1.9 ± 1.3 ml, volume of the liquid fraction 0.3 ± 0.2 ml, spermatozoa per ejaculate 743 ± 376 × 10⁶, sperm motility 52.7 ± 9.6%, morphologically abnormal spermatozoa 12.2 ± 7.5%. From an adult gorilla, three semen samples were collected, in each case without spermatozoa. The electrostimulation of a 6-year-old gorilla led to an erection, but not to semen emission. Three female chimpanzees were inseminated with fresh or frozen semen, each of them within three different estrous cycles. None of these inseminations led to a pregnancy.     

Aminoacylation in Sulfolobus acidocaldarius and in methanogenic and halophilic archaebacteria

Abstract Phenylalanyl-tRNA synthetase (PRS) from the sulphur-metabolizing thermoacidophilic archaebacterium Sulfolobus acidocaldarius has been purified 150-fold using different chromatographic steps. The enzyme has a M _r of 270 000 and exhibits considerable thermostability in a temperature range up to 90°C with optimal activity at 70°C. Conservation of antigenic determinants could not be detected by antibodies against various PRS of all primary kingdoms. As a further means to detect traits of phylogenetic relationship, the cross-species reactivity between PRS and tRNAs of organisms from the three branches of archaebacteria and from all primary kingdoms reveals the group character of all 3 branches of the archaebacterial domain, the sulphur-metabolizing, methanogenic and halophilic archaebacteria.     

Advances in purine and pyrimidine metabolism in health and diseases

ABSTRACT

In June, 2015, the Purine and Pyrimidine Society organized the 16th biennial symposium on Purine and Pyrimidine metabolism at the Faculty House of Columbia University, New York City. This exciting meeting focused on these important molecules, new developments in inborn errors of metabolism; therapeutic analogs. In addition, the biochemistry of mammalian and non-mammalian systems were discussed. Due to significant advances in molecular medicine, the boundaries between clinical and basic sciences have merged into exciting translational research, of which a small portion was highlighted in the presymposium.     

MPD and DNA Bending in Crystals and in Solution

Bending of 15 to 24° is observed within crystal structures ofB-DNA duplexes, is strongly sequence-dependent, and exhibits no correlation with the concentration of MPD (2-methyl-2,4-pentanediol) in the crystallizing solution. Two types of bends are observed: facultative bends or flexible hinges at junctions between regions of G·C and A·T base-pairs, and a persistent and almost obligatory bend at the center of the sequence R-G-C-Y. Only A-tracts are characteristically straight and unbent in every crystal structure examined to date. A detailed examination of normal vector plots for individual strands of a double helix provides an explanation, in terms of the stacking properties of guanine and adenine bases. The effect of high MPD concentrations, in both solution and crystal, is to decrease local bending somewhat without removing it altogether. MPD gel retardation experiments provide no basis for choosing among the three models that seek to explain macroscopic curvature of DNA by means of microscopic bending: junction bending, bent A-tracts, or bent general- sequence DNA. Crystallographic data on the straightness of A-tracts, the bendability of non-A sequences, and the identity of inclination angles in A-tract and non-A-tractB-DNA support only the general-sequence bending model. The pre-melting transition observed in A-tract DNA probably represents a relaxation of stiff adenine stacks to a flexible conformation more typical of general-sequence DNA.