西南峡谷型喀斯特坡地土壤微生物量C、N、P空间变异特征

土壤微生物是陆地生态系统中最活跃的成分,它推动着生态系统的能量和物质循环,被公认为土壤生态系统变化的预警及敏感指标。以西南峡谷型喀斯特坡地为研究对象,基于网格法取样,结合经典统计学和地统计学方法,揭示了土壤微生物生物量的空间分布与格局及其主要影响因子。结果表明,西南峡谷型喀斯特坡地土壤微生物生物量碳(MBC)、氮(MBN)、磷(MBP)、碳氮比(MBC/MBN)、碳磷比(MBC/MBP)适宜,MBC、MBN、MBP变异均很大;空间自相关性明显,除MBP最佳拟合模型为球状模型外,其他指标均为指数模型。C0/(C0+C)均25%(4.9%—6.2%),呈强烈的空间相关,这主要由结构性变异引起。Kriging等值线图表明,MBC、MBN的高值区集中在坡中上部;MBP的格局明显不同,高值区集中在坡脚;MBC/MBN斑块较大,变化缓和;MBC/MBP的空间分布规律不明显,斑块多而破碎。西南峡谷型喀斯特坡地土壤微生物量空间分布的影响因子很多,其中,影响土壤微生物量碳和氮的主要因子有土层厚度、pH、碱解氮。西南峡谷型喀斯特坡地土壤微生物不仅存在着小尺度的空间分布格局,而且不同土壤微生物属性的空间分布不同。因此,应采取适宜措施,激活土壤微生物活性。     

乙酰胆碱酯酶的构效关系研究进展

乙酰胆碱酯酶是胆碱能神经传导中的一种关键酶．对其构效关系的研究一直是生命科学的重要课题,目前主要研究手段有X线衍射晶体学、分子生物学、电子顺磁共振等。本文重点介绍应用这些方法研究乙酰胆碱酯酶构效关系所取得的新进展,包括芳香族引导、后门开放、环的纳秒机制与高效催化的关系等。     

长江三峡工程湖北库区药用植物引种栽培

长江三峡工程湖北库区药用植物引种栽培林刚,康宁,刘启宏（中国科学院武汉植物研究所武汉４３００７４）关键词植物引种,药用植物,长江三峡工程湖北库区ＴＨＥＩＮＴＲＯＤＵＣＴＩＯＮＡＮＤＣＵＬＴＩＶＡＴＩＯＮＯＦＴＨＥＭＥＤＩＣＩＮＡＬＰＬＡＮＴＳＦＲＯＭ...     

Seasonal inventory and status of flying insects, in Kihansi Gorge, Tanzania

Sampling of flying insects in Kihansi Gorge was conducted in six micro-habitats namely Lower, Upper, Main, Mid-Gorge and Mhalala Spray Wetlands and adjacent forest. The four traps used were, malaise, pitfall, light and artificial substrate sampler, besides sweep netting and beating. In the wet season, 65,549 flying insects (65.13%) were recorded when compared to 35,633 flying insects (34.87%) in dry season. At its peak, 29,783 flying insects (29.15%) were recorded at the start of wet season (December 2004). The abundance value was significant ( χ ² = 1794.98, d.f. = 5, P  ≤ 0.001). The favourable weather condition at the beginning of the wet season might have triggered emergence of high numbers of winged insects like ants, to facilitate migration through dispersal and reproduction, and some aquatic insects (Plecoptera, Odonata and Trichoptera) moulted and entered into terrestrial life to raise terrestrial abundance. No association was recorded between abundance of flying insects and amphibians (Kihansi Spray Toad; Nectophynoides asperginis ), for Mid-Gorge and Main Spray Wetlands (r = −0.71, n = 4, P  = 0.147 and r = −0.69, n = 5, P  = 0.201) respectively.     

Rapid binding of a cationic active site inhibitor to wild type and mutant mouse acetylcholinesterase: Brownian dynamics simulation including diffusion in the active site gorge

It is known that anionic surface residues play a role in the long-range electrostatic attraction between acetylcholinesterase and cationic ligands. In our current investigation, we show that anionic residues also play an important role in the behavior of the ligand within the active site gorge of acetylcholinesterase. Negatively charged residues near the gorge opening not only attract positively charged ligands from solution to the enzyme, but can also restrict the motion of the ligand once it is inside of the gorge. We use Brownian dynamics techniques to calculate the rate constant k_on for wild type and mutant acetylcholinesterase with a positively charged ligand. These calculations are performed by allowing the ligand to diffuse within the active site gorge. This is an extension of previously reported work in which a ligand was allowed to diffuse only to the enzyme surface. By setting the reaction criteria for the ligand closer to the active site, better agreement with experimental data is obtained. Although a number of residues influence the movement of the ligand within the gorge, Asp74 is shown to play a particularly important role in this function. Asp74 traps the ligand within the gorge, and in this way helps to ensure a reaction. © 1998 John Wiley & Sons, Inc. Biopoly 46: 465–474, 1998     

西南峡谷型喀斯特区坡地土壤矿物质的空间分布特征

探明峡谷型喀斯特土壤矿物质的分布规律可以为喀斯特地区植被恢复和生态重建提供参考。基于动态监测样地(200 m×300 m)的网格取样,采用经典统计分析和地统计学方法分析土壤矿物质(SiO2、Fe2O3、CaO、MgO、Al2O3、MnO)的空间分布特征。结果表明,研究区土壤矿物质含量差异较大,但变异系数不大,SiO2和Al2O3占了土壤矿物质总量的85.99%;SiO2、Al2O3、MgO、MnO均服从正态分布,Fe2O3、CaO分别经过平方和倒数转换后也服从正态分布。土壤各矿物质半变异函数的最佳拟合模型均为指数模型,块金值与基台值比C0/(C0+C)均较小,具有中等或强烈的空间相关性,表明空间变异主要由结构性因素引起;Al2O3和MnO的变程较大,空间连续性较好,其它矿物质的变程较小且相近,空间依赖性较强;Kriging等值线图表明峡谷型喀斯特区土壤SiO2和MnO具有相似的空间分布,受坡位和人为干扰共同影响,基本呈现坡顶高、坡脚低的分布格局;Fe2O3、CaO和MgO的空间分布也相似,斑块较破碎,主要受地形的影响;Al2O3的空间格局呈单峰分布,沿海拔的升高而升高。因此,减少干扰、增加植被覆盖对土壤矿物质具有良好的保持和调控作用。     

试论三峡工程对农业生态系统的影响

本文探讨了三峡工程对长江流域农业生态系统的影响。这些影响可分为2类:(1)淹没土地,移民搬迁,在已脆弱的库区生态环境中又增加了环境压力,属突变性;(2)随着水文水势的改变,可增加中下游地区低洼稻田的沼泽化与潜育化潜在威胁,三角洲地区土壤盐渍亦有加重趋势。为此,需封山育林,保水保土,合理安排农林用地,强化治水改土,以及防治土壤沼泽化潜育化等措施,方能改善流域生态系统,提高土地承载能力。     

NEUROTOXICOLOGY OF bis(n)‐TACRINES ON Blattella germanica AND Drosophila melanogaster ACETYLCHOLINESTERASE

A series of bis(n)‐tacrines were used as pharmacological probes of the acetylcholinesterase (AChE) catalytic and peripheral sites of Blattella germanica and Drosophila melanogaster, which express AChE‐1 and AChE‐2 isoforms, respectively. In general, the potency of bis(n)‐tacrines was greater in D. melanogaster AChE (DmAChE) than in B. germanica AChE (BgAChE). The change in potency with tether length was high in DmAChE and low in BgAChE, associated with 90‐fold and 5.2‐fold maximal potency gain, respectively, compared to the tacrine monomer. The optimal tether length for Blattella was 8 carbons and for Drosophila was 10 carbons. The two species differed by only about twofold in their sensitivity to tacrine monomer, indicating that differential potency occurred among dimeric bis(n)‐tacrines due to structural differences in the peripheral site. Multiple sequence alignment and in silico homology modeling suggest that aromatic residues of DmAChE confer higher affinity binding, and the lack of same at the BgAChE peripheral site may account, at least in part, to the greater overall sensitivity of DmAChE to bis(n)‐tacrines, as reflected by in vitro assay data. Topical and injection assays in cockroaches found minimal toxicity of bis(n)‐tacrines. Electrophysiological studies on D. melanogaster central nervous system showed that dimeric tacrines do not readily cross the blood brain barrier, explaining the observed nonlethality to insects. Although the bis(n)‐tacrines were not good insecticide candidates, the information obtained in this study should aid in the design of selective bivalent ligands targeting insect, pests, and disease vectors.     

云南纵向岭谷区道路网络对生态系统影响的阈值分析

云南纵向岭谷区由于受到人类活动,尤其是道路网络的影响,使得该地区生态系统退化日益严重.通过云南纵向岭谷区路网密度与生态系统转换(1980～2000年期间)的多尺度空间相关分析,研究了路网的对生态系统的影响及其阈值.研究结果表明,路网是导致有林地向疏林地、有林地向中覆盖度草地、灌木林地向疏林地转变的主要影响因子.路网导致有林地向疏林地转变的路网密度均值为0.8381～0.8800 km/km2,导致有林地向中覆盖度草地转变的路网密度均值为0.6984～0.8124 km/km2,导致灌木林地向疏林地转变的路网密度均值为1.2770～3.6426 km/km2.随着尺度的增大,路网密度的变化不显著.路网影响阈值的研究,开始从定量的角度探索道路网络对生态系统的影响,对公路建设、规划和管理具有一定的理论和应用价值.     

Mouse acetylcholinesterase unliganded and in complex with huperzine A: A comparison of molecular dynamics simulations

A 1 ns molecular dynamics simulation of unliganded mouse acetylcholinesterase (AChE) is compared to a previous simulation of mouse AChE complexed with huperzine A (HupA). Several common features are observed. In both simulations, the active site gorge fluctuates in size during the 1 ns trajectory and is completely pinched off several times. Many of the residues in the gorge that formed hydrogen bonds with HupA in the simulation of the complex now form hydrogen bonds with other protein residues and water molecules in the gorge. The opening of a “backdoor” entrance to the active site that was found in the simulation of the complex is also observed in the unliganded simulation. Differences between the two simulations include overall lower structural rms deviations for residues in the gorge in the unliganded simulation, a smaller diameter of the gorge in the absence of HupA, and the disappearance of a side channel that was frequently present in the liganded simulation. The differences between the two simulations can be attributed, in part, to the interaction of AChE with HupA. © 1999 John Wiley & Sons, Inc. Biopoly 50: 35–43, 1999