禹城地区陆气相互作用耦合模式和观测研究

论述了陆气相互作用研究在人类生存环境与发展区域经济中的重要意义与研究现状。在原有研究工作基础上,针对中国科学院禹试验城站地区麦田陆气水热传输过程,提出了一个多层陆气耦合模式。对植被内部湍流交换的物理过程作了深入研究,特别考虑了叶片气孔为非饱和水汽条件下的交换情况,并且给出了修正后的根系吸水模式。陆气耦俣模式分别对大气、植被、土壤作多层划分,以助于细致了解沿高度分布的各种物理量。利用本模式对中国科学     

沙漠人工植被的生态学取向及其途径

水是干旱沙漠植物生态系统中的最重要的限制因子。在干旱沙漠生境中建造人工植被的正确方向是要建造沙漠人工植被 ,就必须以提供额外的水资源为前提 ;在不能增加额外水资源的情况下不应增加沙漠人工植被 ;增加沙漠植被应保护现有植被和建造半人工植被为主。考察种群生态适应性的一般过程 :一是目前有无这种植物的天然种群 ,二是历史上是否有过这种植物的种群 ,三是目前的生境条件是否满足这种种群或群落的需要 ,四是有无人工提供生态资源的可能性。封育保护和建造半人工植被是建造沙漠植被的主要途径 ,保护地下水资源是根本途径。     

塔克拉玛干沙漠腹地人工植被土壤肥力变化

在极端干旱的塔克拉玛干沙漠腹地,利用地下咸水（矿化度4-5g/L)灌溉建立人工植被后,不仅改善了当地的生态环境。也促进了风沙土的成土发育,使土壤内部发生了一系列的变化。通过分析测定。结果表明人工植被建立对流沙的固定和成土发育产生了深刻的影响,它使土壤内部的各个性质都发生了显著的变化。土支离破碎中物理化学性质得到改善,土壤的肥力提高,这种变化是随着植被建立时间的延长而逐渐增大的,同时由于受到不同植被类型和人为措施的影响,使得相同种植时间的不同样地,土壤性质的变化有差异。另外从土壤物理,化学和生物因子等方面出发,建立了土壤肥力综合评价指标体系,并利用多元统计方法,对塔克拉马干沙漠腹地人工植被建立过程中土壤肥力的变化特征进行综合评价。结果表明,随着人工植被建立时间的延长,土壤肥力呈增长趋势,但由于植被类型和人为措施的不同,相同种植时间的植被样地,土壤肥力的变化不同,变化最为显著的是蔬菜地,花卉地和草地,IFI值分别为0.689,0.729和0.773。     

河西走廊沙漠人工植被区土壤种子库特征

土壤种子库作为地上植被更新的重要的种源储备库,在植被自然恢复和演替过程以及生态系统建设中起着重要作用。以河西走廊不同区域沙漠人工植被为研究对象,研究了土壤种子库物种组成、时空分布和数量变化特征。结果表明：河西走廊沙漠人工林土壤种子库共出现27种植物,分属8科22属,以藜科植物最多,生活型以草本植物种子比例最高,占到90.6%—95.06%;土壤种子库密度介于19.29粒/m~2—858.57粒/m~2之间,从东到西呈水平地带性分布,土壤种子库分布主要集中在0—2cm土层中,不同样地土壤种子库密度均呈明显的垂直分布,在0—10cm土层内,随着土层深度增加,种子库密度先减小后增大;土壤种子库多样性(Simpson指数)在河西走廊东段沙漠人工植被区最高,在0.671—0.812之间,河西走廊中段沙漠人工植被区为0.417—0.809之间,河西走廊西段沙漠人工植被区为0.256—0.707之间,从东到西呈下降趋势,Shannon-Wiener指数、Margalett丰富度指数、Peilow均匀度指数也表现出相同的趋势,说明由于生境的植被的异质性程度高,使土壤种子库之间的差异性显著;河西走廊沙漠...     

我国干旱沙漠地区人工植被与环境演变过程中植物多样性的研究

 以我国干旱沙漠区流沙治理的成功模式包兰铁路沙坡头地段人工植被防护体系作为研究对象,研究了区域人工植被与环境演变过程中植物多样性的变化特点。研究表明：该区人工植被经过40余年的演变其植物种的组成趋于动态平衡;植物多样性在时间尺度上的变化表现为随群落演替的进行而增大,42年前(1956年)建立的人工植被多样性指数达到D＝0.706～0.822或H′＝1.393～1.893,10年前(1987年)建立的人工植被其多样性仅为D＝0.501～0.702或H′＝0.819～1.074;β多样性的测度表明,沙坡头地区人工植被在其演变的历程中经历了2次物种周转速率相对较快的阶段,这一特点与植被演替密切相关,对干旱沙漠地区的生态恢复和人工绿洲建设与管理具有重要的参考价值。本文还进一步研究了土壤基质条件等变化对植物多样性的影响。     

腾格里沙漠沙坡头地区荒漠地衣与生物地毯工程

文章论述了荒漠地衣与“沙漠生物地毯工程”。在沙坡头结皮微型生物中发现了23种地衣,其中两个新种已发表,一属6种为中国新记录。对于在腾格里沙漠东南角沙坡头地区人工植被固沙防护体系建成后的生态演替进行了分析。由于人工植被为形成结皮的微型生物提供了适宜的生长环境而导致微型生物结皮的形成和发育。在水分平衡规律的作用下漫长生态演替过程中,具有抽水机效应的人工植被使沙土深层水分消耗殆尽,从而导致人工植被自身逐年衰退。然而,与此相反的是无抽水机效应而具有固沙、固碳和抗旱功能的结皮微型生物却逐年形成并发育。这一结果为借助于结皮微型生物的接种技术在干旱沙漠构建“沙漠生物地毯工程”的可行性提供了科学依据。为了优化“沙漠生物地毯工程”利用荒漠地衣耐旱基因以构建转基因草地植物的研究也正在进行中。该研究是“沙漠生物地毯工程”基础研究的组成部分。     

黄土高原植被建设与土壤干燥化:问题与展望

黄土高原大规模植被建设有效减少了水土流失、改善了区域生态环境,大规模人工植被种植也造成了土壤水分的过度消耗,导致了土壤干燥化,成为当前黄土高原生态恢复的重要制约因素,威胁区域生态系统健康与稳定。系统综述了黄土高原地区人工植被恢复对土壤干燥化的作用机制,植被群落特征与土壤干燥化的耦合关系,多尺度土壤干燥化时空分异规律及其影响因素,明确了当前大规模人工植被恢复过程中土壤水分持续利用面临的问题与挑战。建议今后加强植被动态对水文过程影响的研究,明确多尺度植被格局与土壤干燥化时空分异的耦合关系,系统开展变化环境下不同尺度植被与土壤水分相互作用的模拟研究,探讨基于植被格局优化的土壤水分调控机制,维护黄土高原地区土壤安全,提升区域生态系统服务功能。     

我国北方风沙危害区生态重建与恢复:腾格里沙漠土壤水分与植被承载力的探讨

我国北方风沙危害的主要防治区包括贺兰山以东沙地和以西的沙漠、绿洲和沙漠与荒漠草原过渡区,约3.2×105 km2.植被重建与恢复是该区遏制风沙危害的重要手段和有效的途径.基于腾格里沙漠沙坡头地区50余年的长期生态学研究,发现重建植被通过对土壤水分的利用和时空再分配改变了原来沙丘系统的水循环特征,在给定的区域降水条件下,土壤水的时空动态与重建植被动态密切相关;指出沙区水文过程的长期改变驱动着人工植被的演替;探讨了降水小于200 mm风沙区土壤水分的植被承载力和植物固沙的模式.     

包兰铁路沙坡头段人工植被区生境与植被变化研究

综合土壤、气体、植被等诸多因子,结合时间尺度上的环境变迁对植被的变化进行了研究。结果表明,（1）沙子水分随着人工植被建立时间延长而线性地减少,30a后人工植被的水分得以稳定,对降水量增加的响应也变弱。（2）虽然人工植被盖度有所下降,但以油蒿为建群种的群落能够适应沙坡头环境的变化,不断的自我繁衍,保持可持续性。（3）随着环境的变化,该地的生物多样性增加了;藻类、藓类以及浅根性植物和动物等的侵入,使简单的人工植被已演变到多层次的复杂的人工＋自然生态系统,该生态系统能够维持草原化荒漠条件下较高的盖度,有利于沙面形成结皮并向在土过程发育,从而可保持固沙系统较长时期的稳定。     

沙坡头人工植被演替过程的土壤呼吸特征

为探讨人工植被演替过程对土壤呼吸速率的影响,本文利用碱液吸收法同步测定了腾格里沙漠东南缘1956、1964、1981、1987、1989、2007年始植的人工植被区和2007年新铺设的草方格固沙区及流沙区的土壤呼吸速率变化,同时分析了土壤水分和温度对上述不同样地土壤呼吸的影响。结果表明:1) 总体而言,土壤呼吸速率随着人工植被演替时间的延长而逐渐增大。当土壤含水量较高时,不同始植年代人工植被区的土壤呼吸速率具有显著的差异(P<0.05);当土壤含水量较低时,不同始植年代植被区的土壤呼吸速率没有显著的差异(P>0.05)。2)土壤呼吸速率与土壤含水量呈正相关关系,且相关系数随着人工植被演替时间的延长而逐渐增大。3)利用土壤呼吸速率-土壤温度指数函数关系计算得到不同人工植被演替阶段土壤呼吸速率的Q₁₀值均较低(平均值仅为1.02)。土壤温度对1987、1989年人工植被区内的土壤呼吸速率产生了显著影响(P<0.05),而对其他样地的土壤呼吸速率影响不显著 (P>0.05)。综合说明,人工植被的演替过程改变了土壤呼吸速率大小及其对土壤水分和温度的响应。     

Local ecosystem feedbacks and critical transitions in the climate

Global and regional climate models, such as those used in IPCC assessments, are the best tools available for climate predictions. Such models typically account for large-scale land-atmosphere feedbacks. However, these models omit local vegetation-environment feedbacks that may be crucial for critical transitions in ecosystems at larger scales. In this viewpoint paper, we propose the hypothesis that, if the balance of feedbacks is positive at all scales, local vegetation-environment feedbacks may trigger a cascade of amplifying effects, propagating from local to large scale, possibly leading to critical transitions in the large-scale climate. We call for linking local ecosystem feedbacks with large-scale land-atmosphere feedbacks in global and regional climate models in order to improve climate predictions.     

Molecular dynamics simulation of the cooperative adsorption of barley lipid transfer protein and cis-isocohumulone at the vacuum-water interface

Molecular dynamic simulations have been carried out on systems containing a mixture of barley lipid transfer protein (LTP) and cis-isocohumulone (a hop derived iso-alpha-acid) in one of its enol forms, in bulk water and at the vacuum-water interface. In solution, the cis-isocohumulone molecules bind to the surface of the LTP molecule. The mechanism of binding appears to be purely hydrophobic in nature via desolvation of the protein surface. Binding of hop acids to the LTP leads to a small change in the 3-D conformation of the protein, but no change in the proportion of secondary structure present in helices, even though there is a significant degree of hop acid binding to the helical regions. At the vacuum-water interface, cis-isocohumulone shows a high surface activity and adsorbs rapidly at the interface. LTP then shows a preference to bind to the preadsorbed hop acid layer at the interface rather than to the bare water-vacuum interface. The free energy of adsorption of LTP at the hop-vacuum-water interface is more favorable than for adsorption at the vacuum-water interface. Our results support the view that hop iso-alpha-acids promote beer foam stability by forming bridges between separate adsorbed protein molecules, thus strengthening the adsorbed protein layer and reducing foam breakdown by lamellar phase drainage. The results also suggest a second mechanism may also occur, whereby the concentration of protein at the interface is increased via enhanced protein adsorption to adsorbed hop acid layers. This too would increase foam stability through its effect on the stabilizing protein layer around the foam bubbles.     

The structural basis of signal transduction for the response regulator PrrA from Mycobacterium tuberculosis

The structure of the two-domain response regulator PrrA from Mycobacterium tuberculosis shows a compact structure in the crystal with a well defined interdomain interface. The interface, which does not include the interdomain linker, makes the recognition helix and the trans-activation loop of the effector domain inaccessible for interaction with DNA. Part of the interface involves hydrogen-bonding interactions of a tyrosine residue in the receiver domain that is believed to be involved in signal transduction, which, if disrupted, would destabilize the interdomain interface, allowing a more extended conformation of the molecule, which would in turn allow access to the recognition helix. In solution, there is evidence for an equilibrium between compact and extended forms of the protein that is far toward the compact form when the protein is inactivated but moves toward a more extended form when activated by the cognate sensor kinase PrrB.     

Numerical simulation of the insertion process of an uncemented hip prosthesis in order to evaluate the influence of residual stress and contact distribution on the stem initial stability

The long-term success of a cementless total hip arthroplasty depends on the implant geometry and interface bonding characteristics (fit, coating and ingrowth) and on stem stiffness. This study evaluates the influence of stem geometry and fitting conditions on the evolution and distribution of the bone–stem contact, stress and strain during and after the hip stem insertion, by means of dynamic finite element techniques. Next, the influence of the mechanical state (bone–stem contact, stress and strain) resulted from the insertion process on the stem initial resistance to subsidence is investigated. In addition, a study on the influence of bone–stem interface conditions (friction) on the insertion process and on the initial stem stability under physiological loading is performed. The results indicate that for a stem with tapered shape the contact in the proximal part of the stem was improved, but contact in the calcar region was achieved only when extra press-fit conditions were considered. Changes in stem geometry towards a more tapered shape and extra press fit and variation in the bone–stem interface conditions (contact amount and high friction) led to a raise in the total insertion force. A direct positive relationship was found between the stem resistance to subsidence and stem geometry (tapering and press fit), bone–stem interface conditions (bone–stem contact and friction interface) and the mechanical status at the end of the insertion (residual stress and strain). Therefore, further studies on evaluating the initial performance of different stem types should consider the parameters describing the bone–stem interface conditions and the mechanical state resulted from the insertion process.     

Coupling dTTP hydrolysis with DNA unwinding by the DNA helicase of bacteriophage T7

The DNA helicase encoded by gene 4 of bacteriophage T7 assembles on single-stranded DNA as a hexamer of six identical subunits with the DNA passing through the center of the toroid. The helicase couples the hydrolysis of dTTP to unidirectional translocation on single-stranded DNA and the unwinding of duplex DNA. Phe(523), positioned in a β-hairpin loop at the subunit interface, plays a key role in coupling the hydrolysis of dTTP to DNA unwinding. Replacement of Phe(523) with alanine or valine abolishes the ability of the helicase to unwind DNA or allow T7 polymerase to mediate strand-displacement synthesis on duplex DNA. In vivo complementation studies reveal a requirement for a hydrophobic residue with long side chains at this position. In a crystal structure of T7 helicase, when a nucleotide is bound at a subunit interface, Phe(523) is buried within the interface. However, in the unbound state, it is more exposed on the outer surface of the helicase. This structural difference suggests that the β-hairpin bearing the Phe(523) may undergo a conformational change during nucleotide hydrolysis. We postulate that upon hydrolysis of dTTP, Phe(523) moves from within the subunit interface to a more exposed position where it contacts the displaced complementary strand and facilitates unwinding.     

Biophysical Characterization of the Dimer and Tetramer Interface Interactions of the Human Cytosolic Malic Enzyme

The cytosolic NADP⁺-dependent malic enzyme (c-NADP-ME) has a dimer-dimer quaternary structure in which the dimer interface associates more tightly than the tetramer interface. In this study, the urea-induced unfolding process of the c-NADP-ME interface mutants was monitored using fluorescence and circular dichroism spectroscopy, analytical ultracentrifugation and enzyme activities. Here, we demonstrate the differential protein stability between dimer and tetramer interface interactions of human c-NADP-ME. Our data clearly demonstrate that the protein stability of c-NADP-ME is affected predominantly by disruptions at the dimer interface rather than at the tetramer interface. First, during thermal stability experiments, the melting temperatures of the wild-type and tetramer interface mutants are 8–10°C higher than those of the dimer interface mutants. Second, during urea denaturation experiments, the thermodynamic parameters of the wild-type and tetramer interface mutants are almost identical. However, for the dimer interface mutants, the first transition of the urea unfolding curves shift towards a lower urea concentration, and the unfolding intermediate exist at a lower urea concentration. Third, for tetrameric WT c-NADP-ME, the enzyme is first dissociated from a tetramer to dimers before the 2 M urea treatment, and the dimers then dissociated into monomers before the 2.5 M urea treatment. With a dimeric tetramer interface mutant (H142A/D568A), the dimer completely dissociated into monomers after a 2.5 M urea treatment, while for a dimeric dimer interface mutant (H51A/D90A), the dimer completely dissociated into monomers after a 1.5 M urea treatment, indicating that the interactions of c-NADP-ME at the dimer interface are truly stronger than at the tetramer interface. Thus, this study provides a reasonable explanation for why malic enzymes need to assemble as a dimer of dimers.     

Interactions controlling the membrane binding of basic protein domains: phenylalanine and the attachment of the myristoylated alanine-rich C-kinase substrate protein to interfaces.

Basic residues are known to play a critical role in the attachment of protein domains to membrane interfaces. Many of these domains also contain hydrophobic residues that may alter the binding and the position of the domain on the interface. In the present study, the role of phenylanine in determining the membrane position, dynamics and free energy of a peptide derived from the effector domain of the myristoylated alanine-rich C-kinase substrate (MARCKS) protein was examined. Deuterium NMR in membranes containing phosphatidylcholine (PC) and phosphatidylserine (PS) indicates that this peptide, MARCKS(151-175), partially penetrates the membrane interface when bound and alters the effective charge density on the membrane interface by approximately 2 charges per bound peptide. However, a derivative of this peptide in which the five phenylalanines are replaced by alanine, MARCKS-Ala, does not penetrate the interface when membrane-bound. This result was confirmed by depth measurements by electron paramagnetic resonance spectroscopy on several spin-labeled derivatives of the Phe-less derivative. In contrast to nitroxides on MARCKS(151-175), nitroxides on the derivative lacking Phe do not reside within the bilayer but are in the aqueous phase when the peptide is bound to the membrane. The Phe to Ala substitutions shift the position of the labeled side chains by approximately 10-15 A. The side-chain dynamics of MARCKS-Ala are strongly influenced by membrane charge density and indicate that this peptide is drawn closer to the membrane interface at higher charge densities. As expected, MARCKS-Ala binds more weakly to membranes composed of PS/PC (1:9) than does the native MARCKS peptide; however, each phenylalanine contributes only 0.2 kcal/mol to the binding energy difference, far less than the 1.3 kcal/mol expected for the binding of phenylalanine to the membrane interface. This energetic discrepancy and the differences in membrane position of these peptides can be accounted for by a dehydration energy that is encountered as the peptide approaches the membrane interface. This energy likely includes a Born repulsion acting between the charged peptide and the low dielectric membrane interior. The interplay between the long-range attractive Coulombic force, the short-range repulsive force and the hydrophobic effect controls the position and energetics of protein domains on acidic membrane interfaces.     

Anchoring of phospholipase A2: the effect of anions and deuterated water, and the role of N-terminus region

The effect of anions and deuterated water on the kinetics of action of pig pancreatic phospholipase A2 is examined to elaborate the role of ionic interactions in binding of the enzyme to the substrate interface. Anions and deuterated water have no significant effect on the hydrolysis of monomeric substrates. Hydrolysis of vesicles of DMPMe (ester) is completely inhibited in deuterated water. The shape of the reaction progress curve is altered in the presence of anions. The nature and magnitude of the effect of anions depends upon the nature of the substrate as well as of the anion. Substantial effects of anions on the reaction progress curve are observed even at concentrations below 0.1 M and the sequence of effectiveness for DMPMe vesicles is sulfate greater than chloride greater than thiocyanate. Apparently, anions in the aqueous phase bind to the enzyme, and thus compete with the anionic interface for binding to the enzyme. Binding of the enzyme to anionic groups on the interface results in activation and increased accessibility of the catalytic site possibly via hydrogen bonding network involving water molecule. In order to elaborate the role of the N-terminus region in interfacial anchoring, the action of several semisynthetic pancreatic phospholipase A2s is examined on vesicles of anionic and zwitterionic phospholipids. The first-order rate constant for the hydrolysis of DMPMe in the scooting mode by the various semisynthetic enzymes is in a narrow range: 0.7 +/- 0.15 per min for phospholipase A2 derived from pig pancreas and 0.8 +/- 0.4 per min for the enzymes derived from bovine pancreas. In all cases a maximum of about 4300 substrate molecules are hydrolyzed by each phospholipase A2 molecule. If anions are added at the end of the first-order reaction progress curve, a pseudo-zero-order reaction progress curve is observed due to an increased intervesicle exchange of the bound enzyme. These rates are found to be considerably different for different enzymes in which one or more amino acids in the N-terminus region have been substituted. Steady-state and fluorescence life-time data for these enzymes in water, 2H2O and in the presence of lipids is also reported. The kinetic and binding results are interpreted to suggest that the N-terminus region of phospholipase A2 along with some other cationic residues are involved in anchoring of phospholipase A2 to the interface, and the catalytically active enzyme in the interface is monomeric.     

Factors that control the reactivity of the interface cysteine of triosephosphate isomerase from Trypanosoma brucei and Trypanosoma cruzi

The amino acid sequences and X-ray structures of homodimeric triosephosphate isomerase from the pathogenic parasites Trypanosoma brucei (TbTIM) and Trypanosoma cruzi (TcTIM) are markedly similar. In the two TIMs, the side chain of the only interface cysteine (Cys14) of one subunit docks into loop 3 of the other subunit. This portion of the interface is also markedly similar in the two enzymes. Nonetheless, Cys14 of TcTIM is nearly 2 orders of magnitude more susceptible to the thiol reagent methylmethane thiosulfonate (MMTS) than Cys14 of TbTIM. The causes of this difference were explored by measuring the second-order rate constant of inactivation by MMTS (k(2)) under various conditions. At pH 7.4, k(2) in TcTIM is 70 times higher than in TbTIM. The difference decreases to 30 when the amino acid sequence of loop 3 and adjoining residues of TbTIM are conferred to TcTIM (triple mutant). The pK(a) values of the thiol group of the interface cysteine of TcTIM and the triple mutant were 0.7 pH unit lower than in TbTIM. Because this difference could account for the different sensitivity of the enzymes to thiol reagents, we determined the k(2) of inactivation at equal levels of ionization of their interface cysteines. Under these conditions, the difference in k(2) between TcTIM and TbTIM became 8-fold, whereas that of the triple mutant to TbTIM was 1.5 times. The substrate analogue phosphoglycolate did not modify the pK(a) of the thiol group of the interface, albeit it diminished the rate of its derivatization by MMTS. In the presence of phosphoglycolate, under conditions in which the interface cysteines of the enzymes had equal levels of protonation, the difference in k(2) of TcTIM and TbTIM became smaller, whereas k(2) of the triple mutant was almost equal to that of TbTIM. Thus, from measurements of the reactivity of the interface cysteine in various conditions, it was possible to obtain information on the factors that control the dynamics of a portion of the dimer interface.     

RNA interference for the study and genetic manipulation of ticks

Ticks are ectoparasites of wild and domestic animals, and humans. A more comprehensive understanding of tick function and the tick-pathogen interface is needed to formulate improved tick-control methods. RNA interference (RNAi) is the most widely used gene-silencing technique in ticks where the use of other methods of genetic manipulations has been limited. In the short time that RNAi has been available, it has proved to be a valuable tool for studying tick gene function, the characterization of the tick-pathogen interface, and the screening and characterization of tick protective antigens. This review considers the applications of RNAi to tick research and the potential of this technique for tick functional studies, and to elucidate the tick-pathogen and tick-host interface. It is probable that the knowledge gained from this experimental approach will contribute to development of vaccines to control tick infestations and the transmission of tick-borne pathogens.