张北地区退化杨树防护林的水分利用特征

在张北地区,以杨树为主的防护林出现不同程度的退化现象,水分是干旱区植物生存的主要限制因子,为揭示水分与防护林退化的关系,本文基于稳定氢氧同位素技术,通过对比小叶杨枝条水与潜在水源的同位素值,探究不同退化程度下小叶杨的水分来源及其对各水源的利用比率.结果表明:不同退化程度的杨树林水分来源不同,随退化程度的加深,小叶杨的水分来源从深层逐渐向表层转移.无退化的小叶杨主要利用320~400 cm的土壤水,利用率为25.1%;轻度退化的小叶杨主要利用120~180、180~240和240~320 cm的土壤水,对这3层的利用率总和将近50.0%,而对其他土壤水利用较少;中度退化的小叶杨主要利用20~40、40~60和60~80 cm的土壤水,对这3层土壤水每层利用率在17.5%~20.9%范围,对120 cm及其以下的土壤水利用率均低于10.0%;而重度退化的小叶杨主要利用0~20 cm的表层土壤水分,利用率为30.4%,明显高于其他水源.杨树防护林在衰退过程中的水分来源逐渐变浅,而林地浅层土壤较低的土壤含水量无法满足杨树的正常水分需求,加速了杨树林的退化和死亡.     

北美CHIHUAHUAN荒漠啮齿动物群落动态：Ⅲ.变量的频次分布和预测

本文用Ｘ＾２方和柯尔莫哥洛夫检验分析了北美Ｃｈｉｈｕａｈｕａｎ荒漠啮齿动物群落６个生态学变量的频次分布,并用移动平均和指数平滑方法拟合了这些变理的动态变化。结果显示：１）结合种群密度、生物量、物种均匀性和生物量均匀性服从正态分布;２）物种数和物种多样性的频次为向右偏斜的分布,无法用常见的理论分布来近似表示;３）单移动平均和双移动平均分别较好地描述了和的种多样性和物种均匀性;４）其余４个变量可用单指     

非同位素PCR-SSCP方法的初步临床应用

单链构象多态性检测法 (PCR-SSCP)是近年发展起来的一项检测人类基因组 突变的新技术。然而,在该技术中需要使用放射性同位素标记的核苷酸或引物,从而限制 了其广泛临床研究及诊断方面的应用。本文报告一种改进的PCR-SSCP方法, 该方法不用 同位素标记引物,而直接在溴乙啶染色的聚丙烯酰胺凝胶上显示SSCP。用该方法对55例 平滑肌肉瘤p53基因第7外显子突变的检测表明,38%的瘤组织DNA存在异常的SSCP。其中10例有HaeⅢ和MspⅠ酶切位点的突变(18%), 19例有突变型p53蛋白的过度表达(9例同时有异常SSCP改变)。而p53质粒D NA,平滑肌瘤及Alzheimer病患者基因组DNA无p53基因第7外显子扩增片段的异常SSCP改变。同时,还使用该方法对临床诊断的20例Alzheimer病患者和8例健康对照进行了β-淀粉样蛋白前体基因第16和17外显子的扩增及分析,均未发现有异常SSCP改变及EcoRⅠ,BclⅠ酶切位点的突变。本研究结果提示,该非同位素PCR-SSCP方法可靠、敏感、简便、快速,具有潜在的推广价值。     

福建畲族苯硫脲味盲频率的分析

我国畲族总人口约６６万,主要分布在福建、浙江等省,其中福建有３６万人,宁德地区占１７万人。我国已对２０多个民族的ＰＴＣ尝味能力进行了调查,其中包括浙江畲族〔１〕,但福建畲族未见报道。我们用阈值法〔２〕测定宁德地区民族中学学生的苯硫脲味盲频率,其中畲族...     

Crystal structure determination of an acidic neurotoxin (BmK M8) from scorpion Buthm martensii Karsch at 0.25nm resolution

The crystal structure of an acidic neurotoxin, BmK M8, from Chinese scorpion Buthus martensii Karsch was determined at 0.25 nm resolution. The X-ray diffraction data of BmK M8 crystals at 0.25nm resolution were collected on a Siemens area detector. Using molecular replacement method with a basic scorpion toxin AaH II in a search model, the cross-rotation function, PC-refinement and translation function were calculated by X-PLOR program package. The correct orientation and position of BmK M8 molecule in crystal were determined in a resolution range of 1.5 - 0.35nm, The oystallographic refinement was further performed by stereo-chemical restrict least-square technique, followed by simulated annealing, slow-cooling protocols. The final crystallographic R-factor at 0.8-0.25 nm is 0.171. The standard deviations of bond length and bond angle from ideality are 0.001 7nm and 2.24° , respectively. The final model of BmK M8 structure is composed of a dense core of secondary structure elements by a stretch of α-     

Plant water balance with tritiated water-tracing dynamical method

The conception of "metabolic pool" is introduced and an ecosystem model consisting of sand body metabolic pool, plant metabolic pool, atmospheric pool and their corresponding channels is established. In addition, the input and output terms of water balance including plant transpiration etc. are measured by tritiated water-tracing dynamical method, etc. and thus a water balance table is obtained. Finally, the plant water balance in the steppified desert environment of the Shapotou area at southeastern fringe of Tengger Desert in China is comprehensively analysed.     

Experimental studies on extremely low frequency pulsed magnetic field inhibiting sarcoma and enhancing cellular immune functions

The previous observation with an electron microscope showed that extremely low frequency (ELF) pulsed magnetic field (PMF) (with the maximum intensity of 0. 6-2. 0 T, gradient of 10-100 T. M-1, pulse width of 20-200 ms and frequency of 0. 16-1. 34 Hz) inhibited the growth of S-180 sarcoma in mice and enhanced the ability of immune cell's dissolving sarcoma cells. In this study, the DNA contents of nuclei were assayed by using Faulgen Staining method. With an electron microscope and cell stereoscopy technology it was observed that magnetic field affected the sarcoma cell's metabolism, lowered its malignancy, and restrained its rapid and heteromorphic growth. The magnetic field enhanced the cellular immune ability and the reaction of lymphocytes and plasma. Since ELF pulsed magnetic fields can inhibit the growth of sarcomas and enhance the cellular immune ability, it is possible to use it as a new method to treat cancer.     

温泉蛇的染色体组型及Ag-NORs的研究

本文首次报道了温泉蛇(Thermophis baileyi)的染色体组型及Ag-NORs,其核型模式可表达为2n=36=14M+2T+20m, ZW型性决定,Z和W分别为中及亚端部着丝点染色体。该结果与游蛇属种类的核型有较大差异,从而旁证了将温泉蛇从游蛇属中分出的观点。仅一对NOR于No.9染色体长臂并与其次溢痕位置相当,该NOR与锦蛇属种类一致而与游蛇类不同。根据染色体特征,认为温泉蛇在游蛇亚科中处于较为原始的地位。     

广西食植瓢虫属五新种：鞘翅目：瓢虫科

本文记述采自广西的食植瓢虫属Ｅｐｉｌａｃｈｎａ５新种,即花端食植瓢虫Ｅｐｉｌａｃｈｎａ ａｎｔｈｏｄｅａ,ｓｐ．ｎｏｖ。,短叶食植瓢虫Ｅ．ｂｒａｃｈｙｌｏｄｂ,ｓｐ．ｎｏｖ。浪平食植瓢虫Ｅ．ｌａｎｇｐｉｎｇｅｎｓｉｓ,ｓｐ．ｎｏｖ．,靴管食植瓢虫Ｅ．ｏｃｒｅａｔａ,ｓｐ．ｎｏｖ．和管刺食植瓢虫Ｅ;ｓｉｐｏｎｅｃｈｉｎｕｌａｔａ,ｓｐ．ｎｏｖ．。     

热带山地雨林生态系统的水分生态效应——冠层对暴雨势能的消减、暴雨养分贮存

基于对尖峰岭热带山地雨林集水流域的定位研究,分析了３年间该群落冠层对大雨、暴雨及大暴雨势能的消减、缓冲耗能效应以及年暴雨携带养分在系统中贮存效应,其冠层消减大雨、暴雨及大暴雨势能占年总消减势能在６１．８％～７１．８％之间,其中消减（≥２００ｍｍ）大暴雨势能量占年总消减势能的４３．９％;大雨、暴雨及大暴雨雨水的年均养分含量为５５．１２２ｋｇ／ｈｍ２,其产流流失为４２．９１７ｋｇ／ｈｍ２,年均净积累为１２．２０５ｋｇ／ｈｍ２,除取Ｓｉ外,年净积累量达３２．６７４ｋｇ／ｈｍ２,充分体现出热带山地雨林生态系统具有的环境生态效应。