POLLINATION AND POLLEN ENERGETICS IN MEDITERRANEAN ECOSYSTEMS

Most plants in Mediterranean ecosystems are insect pollinated, with pollen being the main reward to pollinators. The great majority of pollinators (70%) are bees and flies. We measured the energy content of pollen from 40 plant species in these ecosystems that represent abiotic and biotic pollination modes as well as the number of species of their pollinators. Pollen energy content correlates with pollinator diversity. Pollen of wind-pollinated plants contained less energy than that of insect-pollinated plants; there was no difference between insect-pollinated dicots and insect-pollinated monocots. The median date of flowering (from 1 January) estimated for each of the plant species did not vary significantly either with the number of pollinator species or with the energy content of pollen. The reasons for the differing values of pollen energy content are discussed; in particular, its relation to the type of pollen reserves, length of the flower style, and pollination enhancement.     

NUTRIENTS IN AQUATIC ECOSYSTEMS: AN INTRODUCTION TO SIMILARITIES BETWEEN FRESHWATER AND MARINE ECOSYSTEMS

Summary

Biologists in the aquatic sciences are often guilty of numerous errors in the presentation of their chemical data. This paper reviews the use of units in the representation of the inorganic constituents of aquatic solutions for their benefit. It explains the relationship between salinity, total dissolved solids and conductivity, and between the amount of substance and concentration, and specifies conditions in which each can be used. Methods for the mathematical verification of analytical results are briefly discussed. Tables of recommended units, conversion factors and molar conductivities are provided. It is concluded that chemical data can easily be reported correctly and that both authors and referees have a duty to ensure that this is done.     

城市生态系统的模拟方法：灵敏度模型及其改进

评估城市生态系统的持续发展能力,探讨其持续发展对策是一个复杂的动态问题,需要运用动态的模拟方法进行。由德国著名生态控制论专家Ｆ．Ｖｅｓｔｅｒ和Ａ．Ｖ．Ｈｅｓｌｅｒ教授提出的“灵敏度模型”方法,将系统科学思想、生态控制论方法及城市规划融为一体,解释、模拟、评价和规划城市复杂的系统关系,是模拟城市生态系统很好的方法。本文对该方法进行了改进。改进后的“灵敏度模型”为评价城市持续发展能力、探讨其持续发展对策提供了新的思路。     

陆地生态系统磷素循环及其影响因素

 磷是生命系统的重要组成成分,其在生态系统内的迁移转化是生态系统结构和功能的决定性因素之一。近20年来,磷在陆地生态系统内的重要性受到越来越多的关注。该文总结了国内外磷循环研究的成果,从磷的来源、在土壤中的存在形态和固定特性、影响因素的复杂性等方面分析了磷素循环的特点;系统阐述了磷在陆地生态系统各库之间及其内部,主要是植被-土壤亚系统内的迁移转化规律及影响因素。陆地生态系统磷素循环主要是系统内部的生物化学循环,由植物自身的遗传特性和土壤的生物、理化性质共同控制,不同控制因素的相对重要性因生态系统类型、时间和空间尺度而异。文章简述了磷循环研究方法的发展及存在的局限性;另外,分析了干旱、半干旱地区磷循环研究的重要性和意义;干旱区生态系统的脆弱性及其植被、土壤特性决定了其磷素循环有其自身的特点及研究的必要性。最后指出了当前陆地生态系统磷循环研究的发展趋势。     

林木树干呼吸变化及其影响因素研究进展

树干呼吸是森林生态系统碳平衡的重要组成部分,它每年消耗碳同化总量(NPP)的11%~33%。受测定技术所限,过去对树干呼吸的研究未能引起足够的重视。近十几年来,由于大气CO₂温室气体浓度的持续升高,树干呼吸已成为研究的热点。测定树干呼吸的方法较多,早期一般采用气体交换法和密闭方法,最近利用便携式光合测定系统(Li-Cor6400)或土壤碳通量测量系统(Li-8100)对树干呼吸采用开路系统测定方法。大量研究结果表明: 1)树干呼吸的日变化呈双峰型曲线,即从早晨开始,树干呼吸速率随温度的上升而增加,到午间有所降低,之后逐渐增加,达到峰值后又逐渐降低。2)树干呼吸的季节动态为:生长季的树干呼吸速率明显高于非生长季,即从春季到夏季树干呼吸速率呈持续升高态势,高峰值出现在7或8月,尔后逐渐下降。树干呼吸活动是一个复杂的生物学过程,其影响因子较多。直接影响因子有气象因子(如温度、湿度和CO₂浓度)和生物因子(如树种、树龄、径阶、边材积和树干氮含量等);而纬度、海拔和地形因子通过影响气象因子或生物因子而间接影响树干呼吸。诸多因子中,树干温度对树干呼吸的贡献最大(Q₁₀可描述树干呼吸对温度升高的敏感性)。树干呼吸机理及其影响因子乃是今后研究的主要内容,一方面要采用统一的测量方法和技术,另一方面要综合考虑影响树干呼吸的内外因素,建立树干呼吸的相关模型,为构建森林生态系统碳循环模型、了解森林生态系统碳收支状况及其对大气CO₂浓度变化的贡献和对全球变化的响应提供理论依据。     

DECOMPOSITION IN ESTUARINE ECOSYSTEMS

SUMMARY

The varied sources of estuarine plant detritus and the processes and organisms involved in its decomposition are discussed in this review. In the case of emergent and peripheral vegetation, microbial decomposition commences in the phylloplane, with fairly rapid leaching of DOM occurring soon after immersion. Residual POM, largely cellulose, is decomposed more slowly by cellulolytic micro-organisms. Phytoplankton start contributing to the DOM pool before senescence by excreting soluble substances during normal metabolism and interesting regulatory mechanisms are Involved in the bacterial utilization of this material. Bacteria play a more important role than fungi in decomposition and the latter appear to be prominent only in the breakdown of mangrove litter. Predaceous microflagellates and other protists occur in association with the bacteria and feed on them, enhancing decomposition by maintaining optimal bacterial growth rates. They appear to play a more important role in mineralization than do the bacteria, which are more effective in the conservation of nutrients upon which their efficiency of detritus incorporation Is dependent. Aerobic decomposition tends to terminate in complete mineralization, whereas under anaerobic conditions incomplete oxidation yields organic end products such as volatile fatty acids. A comparison of this process with the functioning of the herbivore rumen leads to the conclusion that the latter is more cost-effective in energy terms. Contrary to earlier published statements that estuaries are major exporters of energy in the form of detritus, many export very little of this material, or are net importers. Finally, the methods for studying decomposition in estuaries must be carefully chosen because of the environmental diversity of these systems. This is particularly true of radio-labelled substrates used for uptake and turnover studies; there appears to be no universal substrate or approach.     

复杂性与脑功能

EEG代表了大脑活动的一种电信号,但是用它来研究脑的功能活动是非常困难的.近年来由于非线性动力学的新发展,为我们提供了从一维EEG的时间序列提取脑的多维动力系统的信息,其中一个重要的方法是测量“关联维数”,但发现EEG是非平稳的混沌态,分维的知识只能给出系统的几何特征.而非平稳性表现出的是动态特性.因此我们对EEC的“复杂性”进行了研究,并与其它已知的标准的奇异吸引子做了比较.     

热带雨林退化生态系统生物多样性消失与修复探讨

热带雨林退化生态系统的主要类型有：（１）人工生态系统;（２）次生森林生态系统和（３）片断森林生态系统等。在退化生态系统中,物种多样性的损失与人类干扰程度、频率和持续时间密切相关;而在片断的热带雨林中则随着环境变化强度的加大和持续时间的延长而增加。退化生态系统的修复主要在于减少人类的干扰、改善地区性的环境和在保护与发展相结合的原则下,采取多种有效的综合措施。尊重当地民族生物多样性传统管理经验,实行封     

中国农田生态系统土壤呼吸作用研究与展望

 农田生态系统是陆地生态系统的重要组成部分,占全球陆地面积的10.5%,其CO₂排放量占人为温室气体排放量的21%～25%;由于农田生态系统 受到强烈的人为干扰,因此农田生态系统土壤呼吸作用及其影响因素对准确评估陆地生态系统碳收支具有重要的意义。中国是个有悠久历史的 农业大国,不仅为农田土壤作用的研究提供了天然的实验室, 而且中国农田土壤呼吸作用的研究对全球的碳循环研究及碳收支准确评估具有非 常重要的示范与指导意义。该文综述了近10年来中国农田生态系统土壤呼吸作用研究进展,指出水热因子、作物生物学特性和农业管理活动是 造成中国农田生态系统土壤呼吸作用时空变异 的主要因素;作物根系呼吸作用占土壤作用的比例在13%～77.2%之间,存在极大的不确定性;合 理施肥、秸秆还田和免耕有助于农田生态系统土壤呼吸作用减排和固碳。指出了中国农田生态系统土壤呼吸作用拟重点加强不同区域典型农田 生态系统土壤呼吸作用的比较、空间异质性、影响因素模拟及减排对策等方面的研究。     

SPATIAL ORDER IN MICROBIAL ECOSYSTEMS

(1) It is suggested that microbiologists are concentrating too much at present on homogeneous laboratory models such as the chemostat to simulate natural microbial ecosystems, which are not usually homogeneous but structured in time and space. (2) Natural microbial ecosystems that are spatially heterogeneous are reviewed and discussed. (3) Microbial interactions are briefly discussed in so far as they are relevant to spatially organized ecosystems. (4) Concepts such as ‘niche’ and ‘habitat’ are defined and discussed in terms of their applicability to microorganisms growing at specific points in solute gradient systems. The definitions currently accepted lack precision because they do not take into account the importance of spatial and temporal coordinates. Use of the words ‘compartment’ and ‘domain’ is advocated. The former corresponds to a cell, the latter to a region around it where the compartment has some influence, acting either as a source or as a sink for particular solutes. The terms ‘niche’ and ‘habitat’ are redefined for the activity domains of a compartment and the habitat domains of the ecosystem. The importance of the vectorial flow of solutes is stressed. (5) Current methodology in microbial ecology is briefly reviewed. (6) Methods specifically designed for investigating heterogeneous ecosystems are described, These include: (i) The gradostat, a system of interlinked culture vessels allowing the establishment of steady-state bidirectional solute gradients. (ii) Percolating columns. (iii) Capillary methods. (iv.) The thin film fermenter. (v) The use of two-dimensional diffusion plates or stopped time-dependent gradient plates. (vi) Gel-stabilized diffusion models established vertically in glass containers such as beakers. (vii) The use of one-dimensional gradient-plate techniques to determine the habitat characteristics of different microbial species. (viii) Investigations into naturally structured systems such as the bacterial colony.     

离散广义Logistic模型的稳定性和浑沌现象

文[1]提出了单种生长的连续性文广义Logistic dx/dt=γx({K-x}/(K+px))其中γ>ο为种群的内禀生长率,K>0为环境容纳量,ν>-1表示种群对环境(包括营     

离散广义LOGISTIC模型的渐进性态和混沌现象

1引言自Li－Yorke的著名论文《3一周期意味混饨》问世以来,人们对一维离散模型进行了大量细致的研究工作,其中Logistic模型研究的最为彻底,并由此得到一系列普遍适用的理论结果［‘’2］文【3jIw接地对广义LOgistiC模型的稳定性及其吸引域进行了细致的研究,但其结论尚有不完善之处．在研究其周期解及混炖现象时,仅在IUI＜1时对其近似模型进行了初步讨论·这里参数C＞0为种群内禀生长率,U＞一1表示种群对环境（包括营养资源等）利用率程度的参数．显然,当U—0时,模型（2）可化为LOgistiC模型（1）．本文将直接对模型（2）进行…     

暖温带两种针叶林生态系统中茎流和穿透雨的养分特征研究

通过对暖温带地区两种典型人工针叶林生态系统内树干茎流和穿透雨的收集,对其中Ｎ、Ｐ、Ｋ、Ｃａ、Ｍｇ、Ｓ和Ａｌ等７种元素进行了测定。研究发现这些养分元素在树干茎流和穿透雨中的含量在年内有明显的时间动态变化,这些变化主要受元素在水分中的含量和它们在植物生命活动中的活跃程度等影响,甚至在不同的针叶林生态系统之间都有一定的差异,其中表现为明显的是Ｎ、Ｋ和Ｓ。