武汉月湖水生植被重建过程中浮游植物的动态变化

2004年12月-2005年5月武汉市月湖水生植被重建过程中,对浮游植物进行逐月调查.结果表明,在营养盐浓度较高的条件下,浮游植物仍保持较低的生物量和密度,浮游植物的生长与温度保持一定的相关性,但与湖水营养盐浓度并不存在相关关系.菹草和伊乐藻能使水体的透明度保持较高的状态.浮游植物主要由隐藻和硅藻组成,能形成水华的一些常见种类并未随温度升高而出现,可能与这两种沉水植物的存在改变了浮游植物的群落结构有关.因此,在水温较低的冬季和春季进行水生植被重建是富营养化湖泊治理的有效途径

淡水湖泊浮游藻类对富营养化和气候变暖的响应

水体富营养化和气候变暖是淡水生态系统面临的两大威胁。文章分别阐述了富营养化和气候变暖对淡水湖泊浮游藻类直接和间接效应，并总结气候变暖可能通过影响水体理化性质、水生植物组成、食物链结构从而直接或间接改变浮游藻类生物量或群落结构。作者重点分析了气候变暖下湖泊生态系统蓝藻水华暴发机制，比较了不同湖泊蓝藻对气候变暖和富营养化响应的异同点，发现气候变暖和富营养化对湖泊生态系统影响存在相似性，表现在均促进湖泊由清水．浊水稳态转变、增加蓝藻水华发生频率和强度。然而二者对湖泊浮游藻类影响的相对重要性取决于分层型湖泊和混合型湖泊的差异性、不同营养型湖泊和不同类群蓝藻组成差异性。作者认为，开展气候变暖和富营养化下，湖泊浮游藻类功能群响应研究亟待进行

淡水湖泊浮游藻类对富营养化和气候变暖的响应

水体富营养化和气候变暖是淡水生态系统面临的两大威胁。文章分别阐述了富营养化和气候变暖对淡水湖泊浮游藻类直接和间接效应，并总结气候变暖可能通过影响水体理化性质、水生植物组成、食物链结构从而直接或间接改变浮游藻类生物量或群落结构。作者重点分析了气候变暖下湖泊生态系统蓝藻水华暴发机制，比较了不同湖泊蓝藻对气候变暖和富营养化响应的异同点，发现气候变暖和富营养化对湖泊生态系统影响存在相似性，表现在均促进湖泊由清水．浊水稳态转变、增加蓝藻水华发生频率和强度。然而二者对湖泊浮游藻类影响的相对重要性取决于分层型湖泊和混合型湖泊的差异性、不同营养型湖泊和不同类群蓝藻组成差异性。作者认为，开展气候变暖和富营养化下，湖泊浮游藻类功能群响应研究亟待进行

不同氮、磷浓度对穗花狐尾藻生长及酚类物质含量的影响

为揭示解营养物质对穗花狐尾藻生长及其体内酚类物质的影响,研究了不同氮、磷浓度下穗花狐尾藻体内可溶性糖、可溶性蛋白和总酚含量的变化及与酚类代谢相关酶——苯丙氨酸裂解酶(Pheny lalanine ammonia-lyase,PAL)的活性.结果表明,不同氮、磷条件下,穗花狐尾藻顶端组织中可溶性蛋白含量没有明显变化,低氮、低磷水平下顶端组织中可溶性糖含量分别为50.91、38.25mg.g-1(以干重计),均高于对照组,表明穗花狐尾藻体内可溶性糖对氮、磷胁迫的响应较可溶性蛋白敏感.不同氮浓度(0.875、7.0、56.0mg.L-1)和磷浓度(0.194、1.55、12.4mg.L-1)下,穗花狐尾藻顶端组织中总酚含量分别为44.74、24.42、29.73mg.g-1和37.77、30.60、36.05mg.g-1(以干重计),对应PAL酶活性的变化趋势与酚类物质变化趋势一致,而生物量增长率与酚类物质变化趋势相反,即过高和过低的氮、磷胁迫均会导致穗花狐尾藻生物量增长率的降低及体内酚类物质含量的升高

基于化感物质释放特性的沉水植物抑藻作用模式研究进展

沉水植物对藻类的化感抑制作用,是沉水植物获取竞争优势和维持清水稳态的重要机制之一。化感物质是由植物产生并释放到水环境中的次生代谢产物,化感物质的有效释放和作用是实现沉水植物化感抑藻作用的关键环节。因此,在化感物质释放水平阐明沉水植物化感抑藻的作用模式、过程和机制具有重要意义。通过比较沉水植物化感物质释放到水环境中的种类、含量和常规急性毒性测试中化感物质的抑藻效果,发现沉水植物化感物质在释放水平上的作用模式不同于常规急性毒性试验中的单次作用。为了回答沉水植物化感物质在释放水平如何高效抑藻的问题,结合化感物质的释放特性,重点从化感物质的联合作用和持续作用等角度探讨沉水植物化感抑藻的作用模式,提出沉水植物可能通过多种化感物质低剂量持续释放的方式,实现对目标藻类的持续协同控制。今后有必要进一步结合沉水植物与目标藻类的共存系统与原位实验,借助分析化学、植物化学、细胞和分子生物学的技术手段,从生态学水平加强沉水植物化感抑藻作用机制研究

基于化感物质释放特性的沉水植物抑藻作用模式研究进展

沉水植物对藻类的化感抑制作用,是沉水植物获取竞争优势和维持清水稳态的重要机制之一。化感物质是由植物产生并释放到水环境中的次生代谢产物,化感物质的有效释放和作用是实现沉水植物化感抑藻作用的关键环节。因此,在化感物质释放水平阐明沉水植物化感抑藻的作用模式、过程和机制具有重要意义。通过比较沉水植物化感物质释放到水环境中的种类、含量和常规急性毒性测试中化感物质的抑藻效果,发现沉水植物化感物质在释放水平上的作用模式不同于常规急性毒性试验中的单次作用。为了回答沉水植物化感物质在释放水平如何高效抑藻的问题,结合化感物质的释放特性,重点从化感物质的联合作用和持续作用等角度探讨沉水植物化感抑藻的作用模式,提出沉水植物可能通过多种化感物质低剂量持续释放的方式,实现对目标藻类的持续协同控制。今后有必要进一步结合沉水植物与目标藻类的共存系统与原位实验,借助分析化学、植物化学、细胞和分子生物学的技术手段,从生态学水平加强沉水植物化感抑藻作用机制研究

A weighty dilemma

n all ACP countries, growth in urban populations has already outstripped or very soon will that of rural areas. In Caribbean and Latin America, 75% of people live in towns. According to FAO, that figure will rise to 83% by 2030. In the Pacific and Asia, the percentage is set to increase from 37 to 53%, and in Africa it will rise from 38 to 55%. In coastal countries on the Gulf of Guinea, the urban population increased nine-fold between 1960 and 2000, while the rural population fell from 80% to 50%. Feeding towns which often have more than a million inhabitants is a considerable challenge for the governments of countries in the South. For a long time now, their main concern has been how to supply sufficient quantities of food for these people. In many countries, local farmers have dramatically stepped up production in order to supply the new urban demand. Food crops have become cash crops . Agriculture has also developed rapidly in and around the major cities, and this contributes to the supply of fresh vegetables, eggs, and poultry, among other products, for people living there. But in spite of the efforts of producers, local agriculture simply cannot keep pace with the growing requirements of these towns, which are forced to resort to imports. Rice, wheat, meat, oil, industrial agro-alimentary products imported merchandise is flooding the markets, often selling for less than local products. Countries vary in the extent to which they depend on these imports. In the Pacific, urban populations now rely almost entirely on imported products made by agro-alimentary industries. In the Caribbean, consumption levels of such products differ from one island to another. The cost of imports In sub-Saharan Africa, per capita imports have remained unchanged for the past 20 years, but according to recent studies, the overall figure has increased substantially due to the growth of urban populations. The fall in world commodity prices, together with trade liberalisation and agricultural subsidies to Organisation for Economic Co-operation and Development (OECD) countries have led to a steady rise in cheap imports to countries of the South. FAO figures show that between 1995 and 2002, the volume of cereal imports to African countries rose by 58.2% while the price per tonne of rice fell by 35.2% (see Spore 115). Likewise, poultry imports have increased threefold while the price has dropped by more than 40% (see Spore 114). Mauritius, sick of junk food The mobile health missions which have been plying through the towns and villages of Mauritius for the past two years have made an alarming discovery: 40% of adults over 30 are obese, 30% suffer from high blood pressure and 20% are diabetic. In Mauritius, one out of every two deaths is linked to a "non-communicable disease" (NCD). Forever pushed for time, the islanders buy frozen and ready-to-eat food or eat street food. As part of the price of modern-day life, no one has time anymore to prepare meals or exercise not even walking. These bad habits became more widespread around 1995/1996, 5 or 6 years after the onset of Mauritius economic miracle. Traditionally, the people of this island ate large quantities of vegetables and very little meat. These days, however, junk food is the norm for town and rural dwellers alike, and no one is spared its effects. Thanks to these imports, food security for urban populations has not been a major worry for governments and the international community over the past decade, in contrast with the rural areas. But the cost of importing food has placed a heavy burden on a number of countries, which are forced to devote a growing share often more than half of their export revenues to feeding their people. Dependent on world prices, Africa is finding it increasingly difficult to pay for the imports needed to supply its urban growth. The recent rise in import prices is threatening to upset the balance of supplies for the towns and to leave the poorest sectors of urban populations to go hungry. Local products cannot replace them the supply is inadequate and they are usually more expensive than imported products. Since 2001, Africa has seen a deficit in its agriculture and food trade sectors. Food imbalances However, even though the towns in the South may not actually experience food shortages, the nutritional status of the people who live there is still far from satisfactory. A significant proportion of urban dwellers suffer from malnutrition. In the Pacific islands, no one dies of hunger, but there are high levels of anaemia and deficiencies in vitamin A and in trace elements. The same is true in West Africa, where one symptom of urban poverty is the rising level of micronutrient deficiency, especially in children. Lacking the means or even a place to cook meals, the poorest households often have no choice but to buy street food which just fills their stomachs as opposed to feeding themselves in any balanced way. Senegal: a vegetable garden on your balcony Tomatoes, salad leaves, cucumbers all these vegetables grow in profusion in Senegalese towns, planted in hydroponic "micro-gardens" set up in courtyards or on balconies. Launched by the Centre de Développement Horticole (CDH), an NGO in Cambérene, near Dakar, the "micro-garden" project was designed to help combat the malnutrition that affects many of the poorest families in the Senegalese capital who cannot afford fresh vegetables. The scheme also helps the gardeners earn extra income. The vegetables are grown in wooden tubs or polystyrene boxes. Instead of earth, the substratum is made up of peanut shells, rice husks and clay pellets and watered with a solution containing micro-nutrients. n many towns of the South, there are now two categories of people living side by side those suffering from serious nutritional deficiencies and those who have a diet that is much richer, but which is often far from balanced. The eating habits of urban populations has in fact changed dramatically over the past few decades. In the big cities, traditional food based on dishes which take a long time to prepare are being increasingly replaced by processed foods made by agro-alimentary industries, which often contain too much fat, sugar and salt. High consumption levels of sugary, carbonated drinks, fast food and food additives all take a toll on people s health. Families no longer sit down to eat together; instead, people eat on the run, relying on pre-packed food, a tendency which encourages snacking. A study carried out in 133 developing countries revealed that urban migration could result in a doubling of consumption levels of cheap, ready-to-eat food with a high fat and sugar content, in preference to more costly traditional dishes, which take longer to prepare and which are often also rich in fat. Added to these strictly nutritional factors is the problem of changing lifestyles more time spent sitting down, more use of transport, the mechanisation of the workplace, more passive leisure activities and the effects are beginning to make themselves felt. Researchers refer to a nutritional transition , a phenomenon which is very marked in towns which, depending on the country, have either undergone, or are undergoing a change from food insecurity to a situation where diseases associated with excessive nutrition are common conditions which are linked to unbalanced diets and urban life. The pace of this transition is more rapid than was thought as studies now show that babies born to malnourished mothers develop mechanisms in the womb to save on both energy and nutrients. Once they become well nourished adults, they have a stronger tendency than others to succumb to obesity. The problem of excess weight, and the string of diseases that it generates mainly diabetes and cardiovascular diseases is causing havoc in many towns of the South. Although this was originally an issue affecting the better-off social classes, it is now rapidly becoming a problem for the poorest sectors of the population, who have less choice about the food they eat. Non-communicable diseases Studies show that in Pacific states such as the Cook Islands, Nauru, Samoa and Tonga, 75% of inhabitants suffer from obesity. Diseases linked to obesity cause almost six out of every ten deaths in the western Pacific region. In these islands, rice, sugar and canned fruit and vegetables have taken the place of fresh fish, fruit and local vegetables. In the Caribbean, the fight against obesity, which, for example, now affects one in three Jamaicans, has become a key health priority for governments. In South Africa, which has the highest obesity rates on the continent, almost 20% of all adults and 30% of black women are affected. These non-communicable diseases are becoming increasingly common throughout Africa, where the percentage of deaths caused by cardio-vascular disease is already higher than in the West. In Cameroon, one out of every two men, and one out of every three women are overweight. And while such figures give cause for considerable concern, it must also be said that most people have very little understanding of the negative implications of excess weight. In Africa, being overweight is often seen as a sign of prosperity. In women, stoutness is considered a sign of good health (especially at a time when AIDS is rife), fertility and material well-being. These days, as participants at a recent CTA seminar in Belize noted, governments primary concern should certainly be to ensure that people have food in sufficient quantity. But they should also be concerned about the quality, so that people can lead healthy lives, work and be productive. A trio of CTA seminars Food and nutrition security is an important theme for CTA, which has arranged three seminars on the subject, covering the three ACP regions. The first was held in Maputo in November 2004. The second took place in Belize in March 2005. The final workshop, for the Pacific region, will be held in Apia. Farmers should strive for similar goals. Locally produced, high-quality products will always be popular, provided they do not cost too much and are quickly prepared. Increasing the supply of locally produced food is a vital issue for many city dwellers in the South. Do everything in your power to make sure your traditional diet remains as varied as possible , advises Francis Delpeuch, who heads a nutritional research team at the Institut de Recherche pour le Développement (IRD), the French science and technology institute. If you forget these different ways of preparing food, which help to make up a varied diet, the imbalances are going to get worse. For most people living in the cities of the South, however, the main priority remains eating their fill.Feeding the growing towns of the South is a hefty challenge for ACP countries, already forced to import massive quantities of food at the expense of local production. To limit deficiencies, and the already alarming levels of obesity in many regions, the

水生植物化感抑藻作用机制研究进展

富营养化引起的藻华问题是当前许多水体面临的重大环境问题。化感抑藻现象的发现为这一问题的解决提供了一种新思路。目前,已发现很多水生植物具有化感抑藻效应,通过恢复受污染水体的水生植被群落来进行水体修复的工程案例逐渐增多,但对水生植物抑藻机制的研究还不够深入,化感作用机理的揭示对于藻生理生态研究和水华的控制有重要意义。文章主要从生理生化的角度介绍最近几年水生植物及其化感物质的抑藻机制研究进展,指出化感物质可能的抑藻机制,包括:化感物质对细胞膜,呼吸作用和光合系统Ⅱ(PSⅡ)造成影响,化感胁迫后胞内活性氧(ROS)水平升高而导致藻氧化胁迫,NO作为化感作用的信号分子,介导藻细胞的程序性死亡。不同化感物质作用靶点的探寻,化感物质在胞内转化途径,化感物质介导信号分子调控网络以及化感物质诱导的程序性死亡的研究将会是今后化感抑藻机理研究的重要方面

三种水鳖科沉水植物释放的脂肪酸类化感物质的分离与鉴定

沉水植物是水生态系统的重要组成部分,在维持水生态系统结构和功能方面具有重要作用[1],其中的一个重要机制就是通过释放化感物质抑制藻类生长,从而保持水体的清水稳态[2]