稻草—凤尾菇—蚯蚓—肉鸡食物链的氮流与能流研究

稻草养菇、菇渣喂蚓、以蚂喂鸡是通过营养关系将三个生产过程有机地连接起来,形成农业生态系统特有的食物链。关于这三个环节各自的经济效益及栽培技术方面的研究工作已经做了很多,而作为一条食物链的整体状况,主要是能流和物流状况。尚未见到更深入具体的报道。作者试图通过实验定量分析和评价该食物链中每一链节上以及整体上的氮流和能流状况,进而对其生产应用价值做一初步探讨。     

喀左县农业生态系统能流的研究

本文根据辽宁省西部一个典型具(喀左县)农业生态系统的调查,分析该系统八十年代初期基本特征,进而提出改善该农业生态系统的措施。 整个系统由七个组分(或亚系统)组成(农田、牲畜、果园、人工林、人工草地、天然灌丛草地、当地居民)。作者根据有关统计数据和调查资料估算出该系统1981—1983年期间年平均流量,其中包括流入和流出能量以及系统内各组分之间的能流量。最后讨论了调整畜牧业结构,提高工业能量、生物质能量利用率和林分改造等问题。     

一个农户庭院经济的效益及其能流分析

一个农户庭院经济的效益及其能流分析方达福（湖北省阳新县农业环境保护站４３５２００）ＡｎａｌｙｓｉｓｏｆｔｈｅＥｃｏｎｏｍｉｃＢｅｎｅｆｉｔｓａｎｄＥｎｅｒｇｙＣｙｃｌｉｎｇｏｆｔｈｅＥｃｏｌｏｇｉｃａｌａｎｄＥｃｏｎｏｍｉｃＹａｒｄｉｎａＦａｒｍｅｒ...     

重金属在海洋食物链中的传递

近年来 ,金属在不同海洋食物链中摄食富集的定量研究得到越来越多的关注。自然环境中生物体内金属的浓度并不一定和生物在食物链中所处的营养级有相关关系 ,金属在生物体内的富集还受到生物的同化、排出等过程以及其它生理生化因子的影响。在经典的海洋浮游生物食物链中 (浮游植物→桡足类→鱼类 ) ,桡足类往往可以很有效地排出体内的金属 ,同时鱼类的金属同化率又很低 ,所以该食物链中金属的浓度随食物链水平增加而减少。目前研究发现只有甲基汞和铯 Cs会被食物链所放大。在以腹足动物为顶级捕食者的底栖食物链中 ,因为生物结合金属的效率很高 ,高同化率和低排出率导致金属浓度在生物体内得到放大。重金属在生物体内的可利用性可以通过测定同化率、排出率等参数、并结合考虑生物对该金属的消化行为 ,运用一个简易的动态模型来估算。已有的研究中人们多考虑金属的化学性质对食物链传递的影响。着重介绍了近年来国外对金属在不同海洋食物链 (底栖和浮游 )中的传递的研究成果 ,强调在金属的生物可利用性评估中 ,要充分考虑到动物的生理、生化过程的影响 ,同时也必须认识到不同的海洋生物有着复杂且不同的金属代谢机制     

"蒲公英-蝌蚪-鳝鱼"食物链的物流与能流分析

本文对食物链“蒲公英—蝌蚪—鳝鱼”的物质流和能量流作了定量分析。结果表明：该食物链经济产品的物质、能量转化效率较低,生物量转化效率为1.1％,能量转化效率为0．8％,N、P转化效率分别为3．1％、1．5％。但该食物链刺激鳝鱼食欲,有利于鳝鱼繁殖。     

稻田生物群落的能流参数

为了从能流动态来研究稻田生物群落,本文用田间调查和实验室测定等方法,取得了晚稻田生物群落的物种数量、生物量、热值、呼吸量、生产力、同化效率、摄食量等数据。据此,进一步估算了晚稻田生物群落的能量流动参数。根据其能量收支,用能量金字塔总结了晚稻田生物群落各类种群间的能量关系。     

稻田生物群落的能流参数

为了从能流动态来研究稻田生物群落,本文用田间调查和实验室测定等方法,取得了晚稻田生物群落的物种数量、生物量、热值、呼吸量、生产力、同化效率、摄食量等数据。据此,进一步估算了晚稻田生物群落的能量流动参数。根据其能量收支,用能量金字塔总结了晚稻田生物群落各类种群间的能量关系。     

一个预测核事故后果的动态食物链模式与程序

描述了一个新过建立与开发的能预测核事故后果的动态食物链模式与程序,它既适用于西方饮食谱,也适用于中国居民的饮食谱,此模式考虑了干,湿沉积截获和初始滞留,易位,入渗,根部吸收,耕作等过程对事故释放导致的植物可食用部位中核素浓度的影响,也考虑了动物对核素的摄入,食品加工的影响及人体食入途径对核素的摄入率,在干沉积中考虑了有效叶面积指数对干沉积量的影响,在湿沉积中考虑了事故期间不同时期不同降雨强度对湿沉     

关于调整竹林生态系统食物链的研究

关于调整竹林生态系统食物链的研究李昌荣,屠六邦,吴继林（南京林业大学,２１００３７）（福建省永安市大湖林业站,３６６０１５）王进荣,黄文培（江苏省溧水县秋湖林场,２１１２００）（四川省长宁万岭楠竹研究所,６４４３０４）ＳｔｕｄｙｏｎＲｅｇｕｌａｔｉｎ...     

A new photobioreactor for continuous microalgal production in hatcheries based on external-loop airlift and swirling flow

This study deals with the scale of a new photobioreactor for continuous microalgal production in hatcheries. The combination of the state-of-art with the constraints inherent to hatcheries has turned the design into a closed, artificially illuminated and external-loop airlift configuration based on a succession of elementary modules, each one being composed of two transparent vertical interconnected columns. The liquid circulation is ensured pneumatically (air injections) with respect to a swirling motion (tangential inlets). A single module of the whole photobioreactor was built-up to scale its geometry (diameter and length) and to optimize its design (air sparger, tangential inlets). The volumetric productivities were predicted by modeling radiative transfer and growth of Isochrysis affinis galbana (clone Tahiti). The hydrodynamics of the liquid phase was modeled in terms of global flow behavior (circulation and mixing times, Péclet number) and of swirling motion decay along the column (Particle Image Velocimetry). The aeration performances were determined by overall volumetric mass transfer measurements. Continuous cultures of Isochrysis affinis galbana (clone Tahiti) were run in two geometrical configurations, generating either an axial or a swirling flow. Lastly, the definitive options of design are presented as well as a 120-L prototype, currently implemented in a French mollusk hatchery and commercialized.     

Joint effects of nutrients and contaminants on the dynamics of a food chain in marine ecosystems

We analyze the joint effect of contaminants and nutrient loading on population dynamics of marine food chains by means of bifurcation analysis. Contaminant toxicity is assumed to alter mortality of some species with a sigmoidal dose-response relationship. A generic effect of pollutants is to delay transitions to complex dynamical states towards higher nutrient load values, but more counterintuitive consequences arising from indirect effects are described. In particular, the top predator seems to be the species more affected by pollutants, even when contaminant is toxic only to lower trophic levels.     

Peak-to-peak dynamics in food chain models

We show in this paper that the chaotic regimes of many food chain models often enjoy a very peculiar property, known as peak-to-peak dynamics. This means that the maximum (peak) density of the populations of any trophic level can be easily forecasted provided the last two peaks of the same population are known. Moreover, extensive simulation shows that only the last peak is needed if the forecast concerns the population at the top of the food chain and that peaks variability often increases from bottom to top. All these findings bring naturally to the conclusion that top populations should be sampled in order to have higher chances to detect peak-to-peak dynamics. The analysis is carried out by studying ditrophic food chain models with seasonally varying parameters, tritrophic food chain models with constant parameters, and more complex food chain and food web models.     

Homoclinic and heteroclinic orbits to a cycle in a tri-trophic food chain

 The asymptotic behavior of a tri-trophic food chain model is studied. The analysis is carried out numerically, by finding both local and global bifurcations of equilibria and limit cycles. The existence of transversal homoclinic orbits to a limit cycle is shown. The appearance of homoclinic orbits, by moving through a homoclinic bifurcation point, is associated with the sudden disappearance of a chaotic attractor. A homoclinic bifurcation curve, which bounds a region of extinction, is continued through a two-dimensional parameter space. Heteroclinic orbits from an equilibrium to a limit cycle are computed. The existence of these heteroclinic orbits has important consequences on the domains of attraction. Continuation of non-transversal heteroclinic orbits through parameter space shows the existence of two codimension-two bifurcations points, where the saddle cycle is non-hyperbolic. The results are summarized by dividing the parameter space in subregions with different asymptotic behavior. Received: 25 February 1998 / Revised version: 19 August 1998     

土壤—小麦食物链硒转移模式及其应用

利用~(75)Se为示踪剂,研究了土壤-小麦系统中Se的迁移和分布规律。土壤Se植物可利用系数SA=0.3—1.9,土壤不同,SA值也不同。土壤固液两相中Se的分配系数Kd=141—395,说明土壤对Se有强烈的吸附作用,Kd大小顺序为:暗棕色森林土>黑土>草甸棕壤。小麦对土壤Se的浓集系数CF=0.09—0.14,小麦不是浓集Se的作物;Se在小麦各器官间CF值>1,表明其在小麦体内运转比较容易。作者提出了一个食物链Se转移模式,评价了土壤有效Se水平,指出草甸棕壤有效Se充足,黑土和暗棕色森林土则不足。估算了病区每人每天摄Se量为26.6μg,远低于我国成人安全摄Se量建议值40—240μg/人·日的下限值。     

食物链中抗生素耐药性基因的转移

抗生素的使用,一方面起到预防和治疗疾病的作用,另一方面,饲料、食品和环境中抗生素残留增加,使抗生素耐药性菌产生并进化,从而导致将来治疗某些疾病时无有效抗生素可用,比如,结核病已经卷土重来,而且现在就有许多患者就不能用抗生素治愈。随着人们生活水平的提高,安全、健康问题受到人们广泛的关注和重视。本文初步对耐药性基因在食物链中怎样产生和转移进行综述。     

Factors controlling eicosapentaenoic acid production in semicontinuous cultures of marine microalgae

Three marine microalgal species with a high content of eicosapentaenoic acid (EPA), Phaeodactylum tricornutum, Isochrysis galbana and Porphyridium cruentum, were cultured semicontinuously in order to study the effect of renewal rate on EPA productivity. The percentage of EPA in total fatty acids increased with increasing renewal rates in nitrogen limited cultures, but while for Phaeodactylum tricornutum and Isochrysis galbana a plateau around 20–25% of total fatty acids was reached with renewal rates that were not nitrogen-limiting, in Porphyridium cruentum EPA percentage increased continuously with increasing renewal rate even for those cultures that were nitrogen sufficient. Maximal EPA productivities of4.6 mg L^-1 day^-1 for Isochrysis galbana and 5.2 mg L^-1 day^-1 for Phaeodactylum tricornutum were achieved with renewal rates of 20% and 30% respectively. On the other hand for Porphyridium cruentum maximal EPA productivity, 5.3 mg L^-1 day^-1, was obtained with the maximal renewal rate tested. Results indicate that different culture strategies should be adopted for the production of a particular polyunsaturated fatty acid depending on the microalgal species being used. This revised version was published online in August 2006 with corrections to the Cover Date.     

Dinosterol side chain biosynthesis in a marine dinoflagellate, Crypthecodinium cohnii

The heterotrophic dinofiagellate, Crypthecodinium cohnii, cultured in a nutrient medium containing methionine-[CD₃] incorporated deuterium into the newly synthesized 4α-monomethyl compound dinosterol (4α,23,24-trimethylcholest-22-en-3β-ol). The MS fragmentation pattern indicated that the C-23 methyl group contained three deuterium atoms and was introduced intact by transmethylation from methionine. The C-24 methyl group contained only two deuterium atoms which is consistent with the production of a 24-methylenesterol intermediate which is subsequently reduced to give the 24-methyl side chain. Mechanisms are proposed to account for the production of the dinosterol side chain.     

Species coexistence and chaotic behavior induced by multiple delays in a food chain system

In this paper, we present a food chain system composed of three species (resource, consumer and predator). Food digested periods corresponding to consumer-eat-resource and predator-eat-consumer are introduced for more realistic consideration, which are called resource digested delay (RDD) and consumer digested delay (CDD), respectively. In order to explore the combined influence of multiple delays on population dynamics, two different scenarios were explored, i.e. the intrinsic growth rate of resource is less/more than consumer and predator. In case 1, some types of species coexistence characterized by RDD and CDD independent are illustrated by the corresponding characteristic equation. Multiple delays can promote and suppress the recurrent bloom of species population, which is called the stability switching of species coexistence. In case 2, using RDD and CDD as the varying parameters, complex dynamical behaviors including multiple periodic motion and chaotic behavior are exhibited in detail by employing some numerical simulations, such as phase trajectory, power spectra, and bifurcation diagram. The population dynamics exhibit chaos behavior and then evolve into system collapse for species outbreak. Further, greater RDD and CDD make system population enter into system collapse easier.     

Trends in research on shallow water food webs

Making sense of the spider–web networks of interactions between species in food webs has been a major pre-occupation of ecologists over the last 60 years. This review describes the early attempts to reduce this complexity through the grouping of individual taxa into functional categories (such as trophic levels), through adopting the energy flow or systems approach as epitomised by the International Biological Programme, and most recently by the derivation of web statistics by food web theorists. The strengths and weaknesses of these approaches are discussed in relation to empirical field experiments for unravelling the processes responsible for organising communities and an assessment made of the representation of these approaches in the marine biological literature.