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精研植物护理配方翻译成英文Plant Care Formulation Research and Development1. IntroductionPlant care is an essential aspect of maintaining healthy and thriving plants. It involves understanding the specific needs of different plant species and providing the necessary nutrients, treatments, and care to promote their growth and well-being. Plant care formulations play a crucial role in providing plants with the required nutrients and treatments. Through extensive research and development, we have been working on perfecting plant care formulations to meet the diverse needs of various plant species. In this report, we present our findings on plant care formulation research and development.2. Research MethodologyUsing the knowledge gained from our analysis, we formulated different plant care solutions and conducted laboratory experiments to test their effectiveness in meeting the plants' needs. These experiments involved monitoring plant growth, health, and response to treatments. Promising formulations were further tested through field trials to evaluate their performance on a larger scale.3. Key FindingsThrough our research and development efforts, we have made significant progress in developing effective plant care formulations. Some of our key findings include:3.1 Nutrient Balance:We identified the importance of maintaining a proper balance of nutrients in plant care formulations. Different plants have varying nutrient requirements, and providing them with the right balance of macronutrients and micronutrients is crucial fortheir growth and development. Our formulations have been designed to meet these specific requirements.3.2 Targeted Treatments:We found that certain plant species are prone to specific pests, diseases, or environmental stresses. By incorporating targeted treatments into our formulations, we can effectively address these issues. For example, our formulations for roses contain ingredients specifically targeted to prevent black spot and powdery mildew.3.3 Organic Solutions:In response to the growing demand for organic plant care products, we have also focused on developing organic formulations. These formulations utilize natural and sustainable ingredients, ensuring that plants receive the necessary care without the use of synthetic chemicals.3.4 Growth Promotion and Stress Resistance:Our formulations have been designed to not only promote plant growth but also enhance the plants' natural defense mechanisms against stressors. Through the incorporation of bio-stimulants and stress-tolerance enhancers, our formulations strengthen the plants' ability to withstand adverse conditions.4. ConclusionIn conclusion, our research and development efforts in plant care formulation have yielded promising results. We have focused on formulating nutrient-balanced solutions, targeted treatments, organic alternatives, and growth-promoting formulations. Our findings have contributed to the development of effective plant care products that cater to the diverse needs of different plant species. Moving forward, we will continue to refine our formulations and explore new avenues to enhance plant care practices. By striving to provide the best plant care solutions, we aim to contribute to healthier and greener environments.。
新托福TPO5阅读原文(一):Minerals and PlantsTPO-5-1：Minerals and PlantsResearch has shown that certain minerals are required by plants for normal growth and development. The soil is the source of these minerals, which are absorbed by the plant with the water from the soil. Even nitrogen, which is a gas in its elemental state, is normally absorbed from the soil as nitrate ions. Some soils are notoriously deficient in micro nutrients and are therefore unable to support most plant life. So-called serpentine soils, for example, are deficient in calcium, and only plants able to tolerate low levels of this mineral can survive. In modern agriculture, mineral depletion of soils is a major concern, since harvesting crops interrupts the recycling of nutrients back to the soil.Mineral deficiencies can often be detected by specific symptoms such as chlorosis (loss of chlorophyll resulting in yellow or white leaf tissue), necrosis (isolated dead patches), anthocyanin formation (development of deep red pigmentation of leaves or stem), stunted growth, and development of woody tissue in an herbaceous plant. Soils are most commonly deficient in nitrogen and phosphorus. Nitrogen-deficient plants exhibit many of the symptoms just described. Leaves develop chlorosis; stems are short and slender, and anthocyanin discoloration occurs on stems, petioles, and lower leaf surfaces. Phosphorus-deficient plants are often stunted, with leaves turning a characteristic dark green, often with the accumulation of anthocyanin. Typically, older leaves are affected first as the phosphorus is mobilized to young growing tissue. Iron deficiency is characterized by chlorosis between veins in young leaves.Much of the research on nutrient deficiencies is based on growing plants hydroponically, that is, in soilless liquid nutrient solutions. This technique allows researchers to create solutions that selectively omit certain nutrients and then observe the resulting effects on the plants. Hydroponics has applications beyond basic research, since it facilitates the growing of greenhouse vegetables during winter. Aeroponics, a technique in which plants are suspended and the roots misted with a nutrient solution, is another method for growing plants without soil.While mineral deficiencies can limit the growth of plants, an overabundance of certain minerals can be toxic and can also limit growth. Saline soils, which have high concentrations of sodium chloride and other salts, limit plant growth, and research continues to focus on developing salt-tolerant varieties of agricultural crops. Research has focused on the toxic effects of heavy metals such as lead, cadmium, mercury, and aluminum; however, even copper and zinc, which are essential elements, can become toxic in high concentrations. Although most plants cannot survive in these soils, certain plants have the ability to tolerate high levels of these minerals.Scientists have known for some time that certain plants, called hyperaccumulators, can concentrate minerals at levels a hundredfold or greater than normal. A survey of known hyperaccumulators identified that 75 percent of them amassed nickel, cobalt, copper, zinc, manganese, lead, and cadmium are other minerals of choice. Hyperaccumulators run the entire range of the plant world. They may be herbs, shrubs, or trees. Many members of the mustard family, spurge family, legume family, and grass family are top hyperaccumulators. Many are found in tropical and subtropical areas of the world, where accumulation of high concentrations of metals may afford some protection against plant-eating insects and microbial pathogens.Only recently have investigators considered using these plants to clean up soil and waste sites that have been contaminated by toxic levels of heavy metals–an environmentally friendly approach known as phytoremediation. This scenario begins with the planting of hyperaccumulating species in the target area, such as an abandoned mine or an irrigation pond contaminated by runoff. Toxic minerals would first be absorbed by roots but later relocated to the stem and leaves. A harvest of the shoots would remove the toxic compounds off site to be burned or composted to recover the metal for industrial uses. After several years of cultivation and harvest, the site would be restored at a cost much lower than the price of excavation and reburial, the standard practice for remediation of contaminated soils. For examples, in field trials, the plant alpine pennycress removed zinc and cadmium from soils near a zinc smelter, and Indian mustard, native to Pakistan and India, has been effective in reducing levels of selenium salts by 50 percent in contaminated soils.译文：TPO-5-1 矿物质和植物研究表明，某些矿物质是植物正常生长发育所必需的。
PlantPhysiology综述：植物基因组编辑和脱靶变化的相关性用于靶向基因组编辑的定点核酸酶（SDN）是强大的新工具，可将精确的遗传变化引入植物。
像常规杂交和诱导诱变等传统方法一样，基因组编辑旨在提高作物产量和营养。
下一代测序研究表明，农作物物种的整个基因组通常携带数百万个单核苷酸多态性以及许多拷贝数和结构变异。
自发突变以每代每个位点约10-8至10-9的速率发生，而化学处理或电离辐射引起的变异导致更高的突变率。
图 1 比较不同育种策略导入番茄的每个基因组（单个）的SNP和插入缺失的平均数。
数据代表在S.lycopersicum（Heinz 1706参考基因组）的基因组序列与已用于现代番茄品种育种的其他品种或野生近缘种之间的大约SNP数量。
在SDN中，脱靶更改或编辑是发生在与目标编辑区域具有序列相似性的位点上的意外，非特异性突变。
与自然发生在育种种群中或通过诱变方法引入的SDN变异相比，SDN介导的脱靶变异可以导致少量其他遗传变异。
最近的研究表明，使用计算算法设计基因组编辑试剂可以减轻植物的脱靶编辑。
最后，农作物必须经过强有力的选择，才能通过成熟的多代育种，选择和商业品种开发实践来淘汰异型植物。
图2 来自前20个番茄育种国家的官方发布的突变品种数量，显示了用作育种材料的改良品种(橙条)和突变品种(蓝条)的直接释放。
星号表示欧盟国家。
数据来源：突变品种数据库().在这种情况下，与其他育种实践相比，作物的脱靶编辑不会带来新的安全问题。
已经证明，当前一代的基因组编辑技术对于开发具有消费者和农民利益的新植物品种很有用。
基因组编辑可能会伴随着SDN交付的新发展以及基因组表征的增加而提高编辑特异性，从而进一步改善试剂设计和应用。
Site-directed nucleases (SDNs) used for targeted genome editing are powerful new tools to introduceprecise genetic changes into plants. Like traditional approaches, such as conventional crossing and induced mutagenesis, genome editing aims to improve crop yield and nutrition. Next-generation sequencing studies demonstrate that across their genomes, populations of crop species typically carry millions of single nucleotide polymorphisms and many copy number and structural variants. Spontaneous mutations occur at rates of ∼10−8 to 10−9 per site per generation, while variation induced by chemical treatment or ionizing radiation results in higher mutation rates. In the context of SDNs, an off-target change or edit is an unintended, nonspecific mutation occurring at a site with sequence similarity to the targeted edit region. SDN-mediated off-target changes can contribute to a small number of additional genetic variants compared to those that occur naturally in breeding populations or are introduced by induced-mutagenesis methods. Recent studies show that using computational algorithms to design genome editing reagents can mitigate off-target edits in plants. Finally, crops are subject to strong selection to eliminate off-type plants through well-established multigenerational breeding, selection, and commercial variety development practices. Within this context, off-target edits in crops present no new safety concerns compared to other breeding practices. The current generation of genome editing technologies is already proving useful to develop new plant varieties with consumer and farmer benefits. Genome editing will likely undergo improved editing specificity along with new developments in SDN delivery and increasing genomic characterization, further improving reagent design and application.版权作品，未经PaperRSS书面授权，严禁转载，违者将被追究法律责任。
《Plant Physiology》（双语）教学教案任课教师：王晓峰教授单位：生命科学学院植物学系授课班级：生科丁颖班、农学丁颖班等Introduction计划学时：2 h一.教学目的了解植物生理学的对象、内容、产生和发展及发展趋势。
二.教学重点植物生理学的内容及发展趋势，植物生理学与分子生物学的关系。
三.教学难点植物生理学的发展趋势四.教学方法采用以多媒体教学法为主。
五.教学用具多媒体硬件支持。
六.教学过程●Introduction of my research work briefly (5 min)●Concept of plant physiology and main contents and chapters of this course (20 min) ●Tasks of plant physiology（20 min）Some examples: Photoperiod, Solution culture, Water culture, Senescence, Ethylene, Tissue culture, Plant growth substance, Photomorphogenesis, Etiolation.●Establishment and development of plant physiology（30 min）In ancient China and western countries→Experimentally/scientifically→J.von Liebig’s work→Modern plant physiology. Establishment and development of plant physiology in China.●Perspectives of plant physiology（10 min）Five problems of human beings : Food, Energy, Environment, Resources, Population ●Summary of the contents of introduction（5 min）Chapter 1 Water Metabolism教学章节：植物对水分的需要、植物细胞对水分的吸收、植物根系对水分的吸收、蒸腾作用、植物体内水分的运输、合理灌溉的生理基础计划学时：3 h一、教学目的通过本章学习，主要了解植物对水分吸收、运输及蒸腾作用的基本原理，认识维持植物水分平衡的重要性，为合理灌溉提供理论基础。
建议一种方法处理水污染的英语作文Title: A Proposed Method for Treating Water PollutionIntroduction:Water pollution has become a significant concern worldwide, affecting both human health and the environment. It is crucial to address this issue by implementing effective methods to treat and prevent water pollution. This essay suggests a comprehensive approach to tackle water pollution, focusing on sustainable and eco-friendly solutions.Body:1. Identification of Pollutants:The first step in treating water pollution is to identify the sources and types of pollutants present in the water. This can be achieved through water quality analysis, which helps in understanding the specific contaminants and their concentration levels.2. Source Control:To effectively treat water pollution, it is essential to control the sources of pollution. This can be achieved through the following measures:a. Industrial Waste Treatment: Implementing strict regulations for industries to treat their wastewater before disposal. Encouraging the use of advanced treatment technologies such as reverse osmosis, biological treatments, and chemical precipitation.b. Agricultural Runoff Management: Promoting sustainable farming practices, including precision agriculture and the use of cover crops, to minimize the use of chemical fertilizers and pesticides. Implementing buffer zones and contour farming techniques to reduce soil erosion and nutrient runoff.c. Sanitary Waste Management: Upgrading sewage treatment plants to ensure proper treatment of domestic wastewater. Encouraging the use of decentralized wastewater treatment systems in areas with inadequate infrastructure.3. Remediation Techniques:For water bodies already contaminated, remediation techniques should be employed to restore water quality. Some effective methods include:a. Bioremediation: Utilizing microorganisms to degrade or transform pollutants into less harmful substances. This eco-friendly approach is effective for treating organic contaminants.b. Phytoremediation: Using plants to absorb and accumulate pollutants from the water. This method is particularly useful for removing metals and organic contaminants from soil and sediment.c. Nanoremediation: Employing nanotechnology to remove pollutants from water. Nanoparticles can be designed to target specific contaminants, enhancing the removal efficiency.4. Public Awareness and Education:Raising public awareness about the importance of water conservation and pollution prevention is crucial. Education programs should be implemented to inform communities about the impact of their actions on water quality. Encouraging sustainable practices such as rainwater harvesting, water reuse, and reducing plastic waste can significantly contribute to preventing water pollution.5. Monitoring and Regulation:Establishing a robust monitoring system to regularly assess water quality is essential. Governments should enforce strict regulations and standards to control pollution levels. Regular inspections and penalties for non-compliance can act as deterrents for potential polluters.Conclusion:Addressing water pollution requires a multi-pronged approach, focusing on source control, remediation techniques, public awareness, and strict regulation. By implementing the suggested method, we can significantly improve water quality, ensuring a sustainable water supply for future generations. It is essential for governments, industries, and individuals to work together in order to achieve a cleaner and healthier water environment.。
八年级英语作文,介绍一种植物本身的特点全文共3篇示例，供读者参考篇1The Mighty Oak TreeHave you ever really stopped to look at a tree? I mean, really look at one and appreciate all of its amazing qualities and characteristics? Well, after my English teacher assigned our class the task of choosing a plant and writing about its special features, I decided to observe and learn all about the mighty oak tree. Let me tell you, these trees are pretty incredible!To start, oak trees belong to the plant genus Quercus which contains around 600 different species. However, the two main oak varieties are the red oak and the white oak. Red oaks get their name from having reddish-colored wood with pointed lobed leaves, while white oaks have lighter colored wood with rounded lobed leaves. Both types of oak start off with green leaves that change to red, brown or yellow in the fall before dropping off for the winter. This cycle of losing and re-growing leaves each year is a key characteristic of oak trees and all deciduous trees.Another really cool fact about oaks is just how huge they can grow! The overall size and height achieved by an oak depends on the species, but some varieties can reach towering heights of over 100 feet tall with massive trunk circumferences over 20 feet around. The branches tend to grow outward in a spreading pattern, creating a broad, dense crown of foliage that provides excellent shade coverage. In fact, oak trees are one of the biggest contributors of shade in our forests and urban environments.Have you ever noticed small brown nuggets scattered around the base of an oak tree? Those are acorns, the fruit produced by oak trees which serves as a seed for new growth. Each acorn consists of a nutty kernel surrounded by a tough outer shell. When the acorns drop to the ground, the outer shell can split apart and the kernel inside germinates into a new oak seedling if the conditions are right. A squirrel's favorite snack, acorns are also an important food source for other forest creatures like deer, turkeys, and bears. But watch out, the tannins in acorns can make them slightly toxic if consumed in large quantities!In terms of their bark, oak trees develop very thick, rough, and furrowed gray-brown bark as they mature. This rugged barkhelps protect the tree from damage, insects, and even wildfire due to its fire-resistant properties. The bark also contains many small crevices and grooves which provide shelter and homes for all sorts of critters like insects, birds, bats and small mammals. So you could say that oak bark helps sustain entire ecosystems of forest wildlife!As for the wood itself, oak is one of the most valuable and sought-after hardwood timber species in the world. Its density, strength, and resistance to fungus and insects make oak wood ideal for use in construction, flooring, furniture, cabinets, wine barrels, and much more. People have been utilizing oak wood for thousands of years due to its practicality and aesthetic beauty when polished and stained.Speaking of aesthetics, oak trees are truly magnificent to behold, especially older, mature specimens. With their thick, twisting branches, furrowed gray bark, and expansive crowns of green foliage, oaks have an almost regal, commanding presence. That's likely why they are such a popular choice for planting in parks, yards, and public spaces - they literally stand out as colossal works of natural art. In autumn, the yellow, red and orange hues of oak leaves create breathtaking displays that draw admiration from all.But beyond their impressive physical attributes, oak trees provide environmental benefits that are just as valuable. Their massive size and canopy help filter air pollutants, generate oxygen, control soil erosion with their extensive root systems, and aid in water filtration. Oak trees are also prime habitats for countless species of birds, mammals, insects, fungi, and other plants that call them home. In essence, the survival of entire forest ecosystems is dependent on oak trees flourishing.After thoroughly researching and observing these arboreal giants up close, I've gained such an immense appreciation for the humble oak tree. From their colossal size and unique characteristics to their environmental importance and practical value to humans, oak trees have proven themselves as true wonders of the natural world. While they may often get taken for granted as just another tree, I now see oak trees with a profound sense of respect and awe. The mighty oak is so much more than just a tree - it is a living embodiment of strength, resilience, and nature's supreme magnificence.篇2The Magnificent SunflowerHave you ever really looked at a sunflower? I mean really studied one closely? They are one of the most fascinating plants in nature. With their vibrant yellow petals, fuzzy brown centers, and tall stalks, sunflowers demand attention. But there is so much more to these cheerful flowers than meets the eye. Let me tell you about some of the amazing traits and characteristics of the sunflower.First off, the name "sunflower" is quite appropriate, as the heads of these plants actually track the sun across the sky from east to west each day. This movement is known as heliotropism. It allows the sunflower to soak up as much direct sunlight as possible to fuel its growth through photosynthesis. Crazy, right? The huge blossoms act like a solar panel, pivoting to face the sun.As the sunflower matures, the blooming head stops moving once it sets sunflower seeds and faces permanently eastward. But in its budding stage, you can watch the sunflower's head turn gradually from morning until evening, following the path of the sun. Just one of its many awesome sun-worshipping behaviors!The main flower head is quite large, typically between 6-12 inches across when fully bloomed. But the entire sunflower plant can tower over humans, some varieties growing well over 10 feettall on their rough, hairy stems. The leaves are pretty gargantuan too, with the bigger ones reaching over a foot in length.Up close, a sunflower's center is a striking geometric masterpiece, made up of gorgeous spiral patterns. The precisely arranged seeds twist in opposing circular spirals that meet in perpendicular directions. These sun-soaked seed spirals show really neat mathematical properties related to the Fibonacci sequence and sacred geometry found throughout nature.While they look pretty delicate, sunflowers are actually quite hardy and resilient plants in many ways. They can shake off minor frosts and keep on blooming. Their root systems are immensely strong too - a single sunflower can anchor itself with a taproot extending over 6 feet into the soil! That's how they remain firmly upright and resist winds, storms, and other intense conditions.Let's talk about the many uses and benefits of sunflowers. Most people are familiar with sunflower seeds as a healthy, nutrient-rich snack full of vitamin E, minerals, and unsaturated fats. But the oil extracted from sunflower seeds has tons of applications in cooking, as a base for soaps and cosmetics, in paints and lubricants, and even as biodiesel fuel.The large showy blooms have ornamental value in gardens and flower arrangements. Plus, sunflowers provide tons of nectar that bees love to feast on. Some people even use the thick sunflower stalks and heads for crafting after the seeds have been removed. You can make all sorts of rustic ornaments, wreaths, birdhouses, and more.But one of the coolest characteristics of sunflowers is how they can help clean up contaminated soils through a process called phytoremediation. It turns out sunflowers have the special ability to extract nas篇3The Fascinating World of the Venus FlytrapHave you ever heard of a plant that can eat insects? It may sound like something straight out of a sci-fi movie, but it's a real-life phenomenon! The Venus flytrap (Dionaea muscipula) is a truly remarkable plant species that has captured the imagination of plant enthusiasts and curious minds alike. As an eighth-grader with a keen interest in biology, I find this carnivorous plant utterly fascinating, and I'm excited to share with you some of its unique characteristics.Appearance and StructureThe Venus flytrap is a small perennial plant native to the subtropical wetlands of North and South Carolina in the United States. It has a rosette of flat, tongue-shaped leaves that grow close to the ground, with each leaf consisting of two lobes hinged together in the middle. The lobes are edged with sharp, teeth-like spines that interlock when the trap is closed, forming a prison for unsuspecting prey.What sets the Venus flytrap apart from other plants is its highly specialized leaf structure that allows it to capture and digest insects. The inner surface of each lobe is lined with three to seven hair-like triggers, known as "trichomes." When an insect or other small creature touches these trichomes, it initiates a series of events that lead to the trap's closure.The Trapping MechanismThe trapping mechanism of the Venus flytrap is a marvel of evolutionary adaptation. When an insect or other small animal brushes against the trichomes, it triggers the lobes to slowly close, trapping the prey inside. However, the trap won't close completely until the trichomes are touched a second time, ensuring that the plant doesn't waste energy on false alarms caused by wind or rain.Once the trap is fully closed, the interlocking spines create a sealed chamber, preventing the prey from escaping. The plant then produces digestive enzymes that break down the trapped insect, allowing the Venus flytrap to absorb the nutrients it needs to survive.Adaptation to Nutrient-Poor EnvironmentsSo, why does the Venus flytrap need to consume insects in the first place? The answer lies in the nutrient-poor environments where it thrives. The Venus flytrap is adapted to grow in nutrient-deficient soils, such as those found in the boggy areas of North and South Carolina. By supplementing its diet with insects, the plant can obtain the nitrogen, phosphorus, and other essential nutrients it needs to thrive in these harsh conditions.While the Venus flytrap does undergo photosynthesis like other plants, it relies on its carnivorous behavior to compensate for the lack of nutrients in the soil. This adaptation has allowed the Venus flytrap to flourish in environments where other plants struggle to survive.Fascinating Facts and MisconceptionsAs an enthusiast of this remarkable plant, I've learned some fascinating facts and dispelled a few common misconceptions along the way. For instance, contrary to popular belief, the Venus flytrap does not actively seek out prey. Instead, it relies on insects and other small creatures to wander into its trap by chance.Another interesting fact is that the Venus flytrap has a "memory" of sorts. If the trap closes without capturing any prey, it will reopen within a day or two, ready to try again. However, if it successfully captures and digests an insect, the trap will remain closed for several weeks or even months, allowing the plant to fully absorb the nutrients before reopening.Despite its carnivorous nature, the Venus flytrap is not a threat to humans or larger animals. Its traps are simply too small to capture anything larger than a small insect or spider. In fact, the plant is more likely to be harmed by curious individuals trying to trigger the trap with their fingers or other objects.Conservation EffortsUnfortunately, the Venus flytrap is currently classified as a vulnerable species due to habitat loss and overcollection from the wild. Its native range is limited to a small area in North andSouth Carolina, and its wetland habitats are under threat from urban development, drainage, and fire suppression.Conservation efforts are underway to protect the remaining populations of Venus flytraps in their natural habitats. Many organizations and individuals are also working to raise awareness about the importance of preserving this unique plant species and its delicate ecosystem.ConclusionThe Venus flytrap is truly a remarkable example of the wonders of nature. Its ability to trap and digest insects, coupled with its adaptation to nutrient-poor environments, makes it a fascinating subject of study for biologists and plant enthusiasts alike.As an eighth-grader, I find myself captivated by the intricate mechanisms and evolutionary strategies of this remarkable plant. Learning about the Venus flytrap has not only deepened my appreciation for the complexity of the natural world but has also inspired me to explore other fascinating plant species and their adaptations.Whether you're a fellow student, a nature lover, or simply someone with a curiosity for the extraordinary, I encourage youto learn more about the Venus flytrap and its incredible story of survival. Who knows, you might just find yourself drawn into the captivating world of carnivorous plants!。
植物可利用态养分英文Plants require several essential nutrients for their growth and development. These nutrients can be broadly classified into two categories: macronutrients and micronutrients. Macronutrients are needed in large quantities, while micronutrients are required in very small amounts. In their usable forms, these nutrients play vital roles in various physiological and biochemical processes within plants.One of the most important macronutrients for plants is nitrogen. Nitrogen is a major component of proteins, nucleic acids, and chlorophyll, which are all essential for plant growth. It is primarily taken up by plants in the form of nitrate (NO3-) or ammonium (NH4+). Nitrogen is responsible for promoting vegetative growth, enhancing leaf and stem development, and increasing overall plant size and yield. Nitrogen deficiency can lead to stunted growth, yellowing of leaves, and reduced flowering and fruiting.Phosphorus is another macronutrient that is critical for plant growth. It plays a vital role in energy transfer and storage, cell division, and root development. Phosphorus is absorbed by plants in the form of phosphate (PO43-). It is particularly important during the early stages of plant growth, as it promotes root establishment and improves flowering and fruiting. Phosphorus deficiency can result in reduced growth, poor root development, and delayed maturity.Potassium is a macronutrient that is involved in many physiological processes in plants, including photosynthesis, water and nutrient uptake, and regulation of stomatal openings. It is taken up by plants in the form of potassium ions (K+). Potassium helps plants to tolerate environmental stresses, such as drought and disease, and improves overall plant health and vigor. Potassium deficiency can lead to weakened stems, discoloration of leaves, and reduced resistance to pests and diseases.Apart from the macronutrients, plants also require several micronutrients for their proper growth and development. Iron is one such micronutrient that is necessary for chlorophyll synthesis and electron transport. Although required in small amounts, iron deficiency can cause chlorosis, a condition where the leaves turn yellow due to the lack of chlorophyll production.Zinc is another important micronutrient that plays a crucial role in enzyme activation and protein synthesis. It is involved in several biochemical processes, such as carbohydrate metabolism and hormone synthesis. Zinc deficiency can lead to stunted growth, reduced flowering, and distorted leaves.Other important micronutrients for plants include manganese, copper, boron, molybdenum, and chlorine. Manganese is necessary for photosynthesis and activation of enzymes, while copper is involved in several redox reactions. Boron is required for cell wall synthesis and calcium uptake, while molybdenum is essential for nitrogen fixation. Finally, chlorine is involved in photosynthesis and osmotic regulation.In conclusion, plants require a variety of nutrients for their growth and development. These nutrients can be broadly classified into macronutrients and micronutrients. Macronutrients such as nitrogen, phosphorus, and potassium are required in large quantities and play important roles in variousphysiological processes. Micronutrients, including iron, zinc, and manganese, are needed in small amounts and are essential for specific biochemical reactions within plants. Understanding and maintaining the optimal nutrient levels in the soil is crucial for promoting healthy plant growth and maximizing crop yields.。
植物生长调节剂英语Plant growth regulators are pretty cool. They're like the secret weapons in the plant kingdom, helping plants grow faster, stronger, and sometimes even changing their appearance. You know, some farmers use them to make sure their crops are ready for market on time.Talking about how they work, it's fascinating. These regulators mimic natural hormones in plants, giving them a boost when needed. They can be applied as sprays, powders, or even injected directly into plant tissue.One interesting thing about plant growth regulators is that they're not all the same. There are growth promoters that speed things up, and there are also inhibitors that slow down or stop certain processes. It's all about finding the right balance for each plant and its needs.You might be wondering if using these regulators is safe. Well, when used correctly, they're considered safefor humans, animals, and the environment. But of course, there are always risks, so farmers and gardeners need to follow the instructions carefully.In the future, I think we'll see even more innovative uses of plant growth regulators. Maybe we'll be able to grow crops in harsher environments or even produce plants with new and improved traits. It's an exciting field of science that's constantly evolving.。
Chapter17Plant Nutrient Phytoremediation Using Duckweed Louis Landesman,Clifford Fedler,and Runbin DuanAbstract Over the last40years a great deal of research has been published on the use of duckweed to treat wastewater both from point sources(feedlots, food processing plants)and from non-point sources. These plants can recover nutrients such as nitrogen and phosphorus from contaminated waters in those agricultural practices.They can also remove or accu-mulate metals,radionuclides,and other pollutants in their tissues.In addition,the duckweed can be used as a feed source for livestock and poultry as well as an energy source for biofuel production.A summary of some of the published work done using duckweed species to phytoremediate natural,domestic,industrial, and agricultural wastewaters is presented. Keywords Duckweed·Plant nutrients·Phytoremediation·Lemnaceae·Lemna·Wolffia 17.1Introduction and Backgroundof DuckweedDuckweeds belong to the arum family Araceae,sub-family Lemnoideae,a family offloating,aquatic plants.This family consists offive genera with at least40species identified as of1997(Les et al. 2002).Duckweeds are among the smallest and sim-plestflowering plants,consisting of an ovoid frond a ndesman( )Virginia Cooperative Extension,Virginia State University, Petersburg,V A23806,USAe-mail:llandesman@ few millimeters in diameter and a short root usually less than1–cm long(Fig.17.1).The frond represents a fusion of leaves and stems and represents the max-imum reduction of an entire vascular plant(Landolt 1986).Some species of the genus Wolffia are only 2mm or less in diameter;other Lemna spp.have frond diameters of about5–8mm.The largest species of Lemnaceae have fronds measuring up to20mm in diameter(Spirodela sp.).The minuteflowers are rarely found in most species.Under adverse conditions such as low temperatures or desiccation,modified fronds called turions appear which sink to the bottom of the water body.These turions can resurface at the onset of favorable conditions of light,moisture and temperature to start new generations of duckweed plants(Hillman 1961,Perry1968).Becauseflowering in Lemnaceae is rare,reproduction normally occurs by budding from mature fronds.The tolerance of Lemnaceae fronds and turions to desiccation allows a wide dispersal of Lemnaceae species.This low level of geneflow and infrequent sexual reproduction has produced substan-tial levels of genetic divergence among populations, despite an absence of morphological differentiation (Cole and V oskuil1996).However,asexual reproduc-tion in Lemnaceae allows for rapid reproduction in this family.Occasionally extreme weather events,such as unusually high summer temperatures,can cause mass flowering(Bramley1996).Usuallyflowering has to be induced with plant hormones or photoperiod manip-ulation(Cleland and Tanaka1979).All Lemnaceae flowers are minute and barely discernable without magnification(Landolt1986).Due to its ease of culture and worldwide distribu-tion,a tremendous literature exists on duckweed ecol-ogy,physiology,production,and ndolt and Kandeler’s two monographs on Lemnaceae are the341A.A.Ansari et al.(eds.),Eutrophication:Causes,Consequences and Control,DOI10.1007/978-90-481-9625-8_17,©Springer Science+Business Media B.V.2011342ndesman etal.Fig.17.1Spirodela (large ),Wolffia (small ),and Lemna (intermediate )most comprehensive works on Lemnaceae and list vir-tually all published works up to 1986(Landolt 1986,Landolt and Kandeler 1987).In addition there are sev-eral web sites that have more updated information on duckweed biology and applications (Cross 2007,Landesman 2008).The genera Lemna ,Spirodela ,and Wolffia of the family Lemnaceae play an important ecological role in lakes,ponds,and wetlands.They often are an impor-tant source of food for waterfowl (Krull 1970)and aquatic invertebrates.The outer margins of duckweed fronds (phyllosphere)support dense populations of diatoms,green algae,rotifers,and bacteria (Coler and Gunner 1969).Associated with this epiphytic commu-nity is an assortment of insects,including beetles,flies,weevils,aphids,and water striders (Scotland 1940).Some of these insects may become abundant enough to affect the duckweed population.Together with the frond biomass this microfauna enhances the nutritive value of duckweed to grazing animals such as ducks,geese,nutria,turtles,coots,fish,and snails,all of which have been recorded as feeding on duckweed.Duckweed populations are limited mostly by light,nutrients,and temperature (Hillman 1961).Duckweed populations can grow very densely in nutrient-rich environments,so much so that layers of fronds grow one on top of another to form a mat that can be up to 6–cm thick.This thick mat creates an anaerobic envi-ronment in the water body on which this mat floats,thus promoting anaerobic digestion and denitrification of the water body in which the duckweed grows.Since duckweed floats freely on water surfaces,strong winds can sweep fronds from the water surface.The presence of duckweed in an aquatic envi-ronment has both direct and indirect effects on that environment.When duckweed is abundant enough to completely cover a pond,ditch,or canal,this layer of opaque fronds can shade out rooted aquatic macro-phytes (Janes et al.1996)as well as reduce phyto-plankton abundance.In eutrophic environments such as the polders of Holland,Lemna sp.can form a climax community that prevents Chara and other submerged macrophytes from getting established (Portielje and Roijackers 1994).A complete cover of duckweed on the water surface can lead to the creation of an anaero-bic environment in the water column,which in turn can make that water body inhospitable to fish and aquatic insects (Pokorny and Rejmankova 1983,Leng et al.2004).The presence of duckweed can contribute to the organic matter present in a water yers of Lemna minor L.excrete amino acids and humic substances into the aquatic environment which can provide nutrients to other organisms such as bacte-ria,epiphytic algae,and indirectly to snails,spring-tails,isopods (Asellus sp.),and other microdetrivores (Thomas and Eaton 1996).Dead and dying duck-weed fronds fall to the bottom of the water column where their decay contributes organic matter,nitro-gen,phosphorus,and other minerals to the benthos (Laube and Wohler 1973).In addition cyanobacteria residing in the phyllosphere of duckweed fronds can17Plant Nutrient Phytoremediation Using Duckweed343fix atmospheric nitrogen,providing a nitrogen input in oligotrophic environments(Tran and Tiedje1985). This can be an important source of nutrients in aquatic environments.Duckweeds are among the fastest growing aquatic angiosperms in the world,frequently doubling their biomass under optimum conditions in2days or less (Culley et al.1981).Based on growth rates recorded in the literature,duckweeds can grow at least twice as fast as other higher plants(Hillman1978).Depending on the genus,duckweed daughter fronds are produced vegetatively in pairs(Lemna and Spirodela)or as a daughter frond from the basal end of the mother frond (Wolffia).Each daughter frond repeats the budding history of its clonal parents,resulting in exponential growth(Landolt1987).Lemna,Spirodela,and Wolffia, three important genera of Lemnaceae,are all subject to self-shading(intra-specific competition)and reach a steady–state condition where frond death equals frond multiplication.Hence Lemnaceae is subject to density-dependent growth(Ikusima1955,Ikusima et al.1955). Once essential nutrients are depleted or waste products build up,the growth rate declines.When duckweed was cultured in axenic(ster-ile)conditions using chemically defined media under artificial lights,growth rates were recorded that far exceeded growth rates measured under natural con-ditions(Hillman1961).Excessively high light lev-els(more than200Wm–2),nutrient shortages,and the presence of herbivores,parasites,and commen-sal organisms antagonistic to duckweed populations greatly reduce the growth rates of duckweeds in natural environments(Landesman2000).Duckweed growing in wastewater treatment plants,however,is under less pressure from herbivores because the high ammonia and low dissolved oxygen levels prevalent in wastew-ater may exclude potential grazers such asfish and turtles.Wastewater environments also have abundant supplies of nitrogen and phosphorus as compared to natural aquatic environments.17.2Duckweed for Phytoremediationof Contaminated Waters Phytoremediation is defined as the method to utilize higher plants to alter contaminated envi-ronments.It is a cost-effective,low-impact,and environmentally sound remediation technology (Cunningham and Ow1996).And phytoremedia-tion includesfive different mechanisms,which are rhizofiltration,phytostabilization,phytoextraction, phytovolatilization,and phytotransformation(Ghosh and Singh2005).Rhizofiltration is that plants are used to absorb,concentrate,and precipitate contami-nants from polluted aquatic environment by their roots; phytostabilization involves the stabilization of contam-inated soils by sorption,precipitation,complexation, or metal valence reduction rather than the removal of contaminants;phytoextraction,also referred as phytoaccumulation,is the process that plants absorb, concentrate,and precipitate the contaminants in the biomass;phytovolatilization is the mechanism that plants extract certain contaminants in nearby roots and then transpire them into the atmosphere;phy-totransformation,also referred as phytodegradation, is the process that plants remove contaminants from environment by their metabolism.More detailed infor-mation on thesefive different mechanisms is listed into Table17.1.17.2.1As an Alternative Meansof Wastewater Treatment Duckweed has been utilized in the treatment of munic-ipal and industrial wastewaters for more than two decades,which can be traced back to before1990 (Oron et al.1988).Duckweed is widely and effectively used for phytoremediation of contaminated water due to its ability to grow at wide ranges of temperature,pH, and nutrient level(Landolt and Kandeler1987)in areas where land is available for its application(Krishna and Polprasert2008).Considerable work was done in the 1970s and1980s on the use of duckweed genera,espe-cially Lemna,as a means of treating wastewater of both agricultural and domestic origin.When Lemna is grown in wastewater treatment ponds thefloating mat of fronds is held in place by partitions and baffles that prevent wind from blowing fronds to one side off or completely off the surface of the treatment pond.These partitions and baffles are usually made of polyethy-lene in industrialized countries but may be made of bamboo or other natural materials in developing countries.ndesman et al.Table17.1Contaminant removal processes and mechanisms by phytoremediationRhizofiltration Phytostabilization Phytoextraction Phytovolatilization PhytotransformationMechanism Rhizosphereaccumulation,absorption,concentration,precipitation Complexation,sorption,precipitation,metal valencereductionHyper-accumulation,absorption,concentration,precipitationV olatilization Degradation by plantmetabolismContaminant Organics/inorganics,Pb,Cd,Cu,Zn,Cr,Ni Inorganics,heavymetalsInorganics,heavymetalsOrganics/inorganics,Hg,SeOrganics,ammunitionwastes,chlorinatedsolvents,herbicidesEnvironment Industrialdischarge,agriculturalrunoff,acidmine drainage Soil,sediment,sludgeDiffusely pollutedareasSoil,water,sedimentSoil,water,groundwaterReference Chaudhry et al.(1998),USEPA(2000),Ghoshand Singh(2005)Mueller et al.(1999),USEPA(2000),Ghoshand Singh(2005)Rulkens et al.(1998),USEPA(2000),Ghoshand Singh(2005)Bañuelos(2000),Henry(2000),Ghosh and Singh(2005)Black(1995),Ghoshand Singh(2005)As part of a facultative treatment system,duckweed can cover treatment ponds and reduce the growth of algae in these ponds as well as reduce nitrogen in the effluent from these ponds through ammonia uptake and denitrification(Alaerts et al.1996;Hammouda et al.1995).Duckweed can also be part of constructed wetland systems,either as a component of a wetland receiving wastewater or as plants that polish nutrients from wetland-treated effluents(Ancell1998,Fedler et al.1999,WEF2001).Harvesting wastewater-grown duckweed helps to remove surplus nutrients,which might otherwise be released into aquatic environments by wastewater treatment plants(Harvey and Fox1973,Oron et al. 1988).Duckweeds,like other plants,take up nutri-ents from their surrounding environment(Landesman 2000).This ability has been exploited to remove sur-plus nutrients from swine lagoon effluents(Cheng et al.2002b).The growing plants can then be harvested to remove surplus nitrogen and phosphorus.However, the application of duckweed in recovery(Cheng et al.2002a)and removal of nitrogen and phosphorus in swine lagoon water was found to be subject to the water concentrations and seasonal climate since the primary mechanism is assimilation of those nutri-ents in environment;therefore,the appropriate light intensity and preferable temperature are key param-eters for duckweed in removal of surplus nutrients (Cheng et al.2002b),and duckweed prefers to take up NH4+than NO3-by both roots and fronds(Fang et al.2007).Duckweed populations can remove nutrients from stormwater ponds.A monoculture of L.minor con-sistently removed a large amount of ammonia from stormwater while a mixture of L.minor and Spirodela polyrhiza removed the largest amount of phospho-rus from stormwater within8weeks of treatment (Perniel et al.1998).Recently,Drenner et al.(1997) have described a system for culturing periphyton on eutrophic effluents and raisingfish that graze on this wastewater-grown periphyton.In this way,surplus nutrients are concentrated infishflesh.A similar sys-tem could be designed using duckweed as the nutrient stripping plant(van der Steen et al.1998).Duckweed systems can remove50–60%of nitro-gen and phosphorus(Vatta et al.1994)from domestic wastewater or even73–97%of total Kjeldahl nitrogen and63–99%of total phosphorus in duckweed-covered domestic wastewater(Körner and Vermaat1998). The removal of chemical oxygen demand(COD)is faster in duckweed-covered domestic wastewater than uncovered wastewater,and organic degradation can be improved by additional oxygen supply and addi-tional surface in duckweed-covered domestic wastew-ater(Körner et al.1998).The removal efficiencies can be reached at high to84,88,68,58,and87%17Plant Nutrient Phytoremediation Using Duckweed345for COD,BOD5,NH3-N,TN,and TSS,respec-tively,in duckweed-based wastewater treatment sys-tem under optimum operating and environmental con-ditions(Krishna and Polprasert2008).Furthermore duckweed systems evaporate20%less water com-pared to other open water wastewater treatment systems(Oron et al.1986,Borrelli et al.1998). The reduced evaporation of duckweed-covered sur-faces in wastewater treatment is an asset in arid climates.Guidelines for the use of duckweed to remove ammonia and phosphorus from effluent from an algae culture system were given by Koles et al.(1987). Researchers at the Politecnico di Milano,Italy,have developed models for duckweed-based wastewater treatment plants(Boniardi et al.1994,Rota et al. 1995).These models will greatly assist in the design and management of duckweed-based wastewater treat-ment systems(Landesman et al.2005).Duckweed-based treatment systems have their limitations.They require large areas of land that may not be avail-able near urban areas.In temperate climates duckweed growth slows in the winter.This may restrict the use of such treatment systems in cooler climates unless a greenhouse system is utilized.Duckweedbased treat-ment systems may be most useful in treating secondary effluents from small communities where land costs are low(Bonomo et al.1997).A series of investigations on duckweed application in restoration of eutrophic water were done in the past decades.Eutrophic water is associated with exces-sive nitrogen and phosphorus in water input by dis-charge from agricultural wastewater,industrial water, and domestic water.Eutrophic water had the risk of eutrophication defined as the negative effects of the excessive growth of phytoplanktons(Khan and Ansari 2005),degradation of water ecosystems,or even dis-appearance of the water body involved in.Duckweed was used to remove the targeted nutrients in eutrophic water due to its ability to survive in nutrient-laden envi-ronments and its rapid growth(Li et al.2009)so that those nutrients can be removed by harvesting duck-weed biomass(Li et al.2007)and eutrophic water can be recovered by combining other technologies.The duckweed L.minor is suitable for phytoremediation of eutrophic waters at acidic pH and at temperature from20to30◦C(Ansari and Khan2008);however, the duckweed S.polyrhiza cannot be used to recover the eutrophic waters at low temperature of10–12◦C (Song et al.2006).Many mathematical models have been developed for duckweed systems to describe its phytoremediation of eutrophic waters(Frédéric et al. 2006);those models incorporated duckweed growth parameters including temperature,photoperiod,nitro-gen concentration,phosphorus concentration,and mat density(Lasfar et al.2007).17.2.2As a Means of Removing HeavyMetals and Other Toxic Elementsin WatersHeavy metals are readily accumulated and transported in aquatic environment in the form of dissolved or solid wastes from domestic,industrial,and agricultural runoff(Megateli et al.2009).Heavy metal contami-nation in environment can be cost-effectively removed by phytoremediation.Such a technology is most suit-able for developing countries(Ghosh and Singh2005). Generally,heavy metal cannot degrade or decompose as other contaminants;therefore,their removal by phytoremediation mainly depends on phytoextraction mechanism.In recent years,there were manyfindings reported on the removal of heavy metals by duckweed phytoremediation.Khellaf and Zerdaoui(2009)addressed that the duckweed Lemna gibba L.can be successfully employed to remove Zn from contaminated water by 61–71%.Another research found that the duckweed L.gibba could remove Zn and Cu rapidly in thefirst 2days with concentration reduction higher than60% and then slowly in the following8days with reduc-tion of10–20%;however,the removal of Cd was linear and determined by initial Cd concentration and the removal was about90%after6or8days with initial concentrations of0.1or0.001mgL–1(Megateli et al. 2009).Duckweed phytoremediation has its limitation in heavy metal removal due to heavy metal’s toxicity. Hou et al.(2007)stated that Cd2+was more toxic than Cu2+for the duckweed L.minor;the tolerance levels of Cd and Cu were smaller than0.5and10mgL–1, respectively,and L.minor was recommended to phy-toremediate low-level contaminated waterbody by Cu and Cd.S.polyrhiza was found to have a large capability for the uptake and accumulation of heavy metals,surpass-ing that of algae and other angiosperms.For example,ndesman et al.the zinc concentration in frond tissue was2,700times higher than that of its medium(Sharma and Gaur 1995).Under experimental conditions L.minor proved to be a good accumulator of cadmium and copper and a moderately good accumulator of chromium. Duckweed can accumulate other toxic elements such as selenium(Ornes et al.1991),technetium(Hattink 2000),lead(Jain et al.1990,Kruatrachue et al.2002), uranium,and arsenic(Mkandawire et al.2004).The growth rates and ease of harvest make duckweed species useful for phytoremediation of certain heavy elements as compared to many algal species that require much more extensive harvesting equipment (Zayed et al.1998).Duckweed can therefore prove useful in treating effluents from mining operations. However,heavy metal concentrations can depress duckweed growth reducing its effectiveness in remov-ing toxic elements from the water body in which it grows(Boniardi et al.1999).The duckweeds L.minor (Alvarado et al.2008),L.gibba(Marín and Oron2007, Sasmaz and Obek2009),and S.polyrhiza L.(Rahman et al.2007)investigated for their phytoremediation ability to remove arsenic,boron,and uranium in water; L.gibba was found to be a suitable candidate used for the treatment of water containing boron with con-centration lower than2mgL-1(Marín and Oron2007) and to accumulated arsenic(133%),uranium(122%), and boron(40%)(Sasmaz and Obek2009);L.minor had good treatment of water with arsenic lower than 0.15mgL–1(Alvarado et al.2008);Spirodela polyrhiza L.was identified as a good arsenic phytofiltrator by physico-chemical adsorption mechanism(Rahman et al.2007).17.2.3As a Means of Removing ToxicOrganic Compounds fromWastewaterDuckweed species can accumulate toxic organic com-pounds such as phenols,chlorinated phenols,phar-maceuticals,and surfactants.Duckweed species can do this directly or indirectly through microbiota liv-ing on frond surfaces.For example,surfactants like alkylbenzene sulfonate and alcohol ethoxylate are mineralized by duckweed microbiota(Federle et al. 1989).Duckweed can take upfluorinated agricultural chemicals(Reinhold2006)and detoxify chlorinated phenols(Barber et al.1995).The duckweed S.olig-orrhiza L.wash proven to have the ability to uptake and transform DDT and organophosphorus pesti-cides(Gao et al.2000a,b).The ability of duck-weed to perform reductive dechlorination can be used in phytoremediation of industrial wastewaters (Ensley et al.1997).Duckweed species definitely have the potential to contribute to natural systems of bioremediation.17.3Duckweed’s Other PracticalApplicationIn addition to the application for phytoremediation of contaminated waters,duckweed has been devel-oped for other applications.Duckweed can be used as livestock food,toxicity testing,and raw material for biofuel production.17.3.1As a Source of Livestock FeedThe value of duckweed as a source of feed forfish and poultry has been promoted by the World Bank,espe-cially in developing countries(Skillicorn et al.1993). Research at Louisiana State University demonstrated the value of using dried duckweed fronds as a feed source for dairy cattle and poultry(Culley et al.1981). Research at Texas Tech University has shown that duckweed species have potential as a feed ingredient for cattle,sheep,and pigs(Johnson1998,Moss1999). Duckweed also has potential as a feed ingredient infish farming(Gaigher et al.1984).A great deal of work has been done on the nutri-tional value(Table17.2)of species of Lemnaceae, especially Lemna,Spirodela,and Wolffia(Rusoff et al.1980,Landesman et al.2004).Duckweed has Table17.2Chemical composition of L.gibba meal(%dry matter)Chemical composition Dry matter(%)Dry matter 3.5Crude protein41.7Crude fat 4.4Acid detergentfiber15.6Non-fiber carbohydrate17.6Ash16.217Plant Nutrient Phytoremediation Using Duckweed347 Table17.3Amino acidcomposition of dried L.gibba(g amino acid/100g dry L.gibba)Amino acidg amino acid/100g dryL.gibba Amino acidg amino acidper/100g dry L.gibbaTaurine0.03Methionine0.64Aspartic acid 3.51Isoleucine 1.66 Threonine 1.68Leucine 2.89Serine 1.39Tyrosine 1.27 Glutamic acid 3.67Phenylalanine 1.75Proline 1.42Histidine0.73Glycine 1.93Ornithine0.05Alanine 2.30Lysine 1.85 Cysteine0.44Arginine 2.14Valine 2.12Tryptophan0.40been fed to pigs,cattle,sheep,chickens,ducks,and fish and can substitute for soybean meal in animal feed rations(Robinette et al.1980,Haustein et al. 1994,Bell1998,Moss1999,Johnson1999,Leng 2004).Wolffia arrhiza is collected for human food in Thailand and Laos and is sold at local markets in these countries(Bhanthumnavin and McGarry1971). Its amino acid composition(Tables17.3and17.4) is more like that of animal protein than plant pro-tein having a high lysine and methionine content, two amino acids normally deficient in plant products (Dewanji1993).Finally,dried duckweed can provide vitamins,minerals,and pigments such as beta-carotene in livestock diets,reducing the need to add these compounds to rations and thus reducing the cost of producing feed.Research was conducted at Texas Tech University to utilize duckweed species as part of a system for recy-cling cattle wastes from feedlots(Fedler and Parker 1998).Duckweed growing in a series of ponds receiv-ing wastewater from a cattle feedlot concentrated nitro-gen,phosphorus,and other elements,both purifying this wastewater and providing an ingredient for cattle feed.Since the protein content of duckweed was found to be almost as high as that of soybean meal,duckweed production provided both a means of water purifica-tion and a source of livestock feed as well(Allen1997, Johnson1998,Moss1999).It was found that a level of up to11%of the protein requirements for cattle could be supplied by duckweed and provide added growth benefits as compared to soybean meal as the protein source(Johnson1998).Mature poultry can utilize dried duckweed as a par-tial substitute for vegetable protein such as soybean meal in cereal grain-based diets(Islam et al.1997). Duckweed used at a level of up to15%in broiler diets can represent an important alternative source of pro-tein for poultry feeds in countries where soybean or fish meal is unavailable(Haustein1994).When dried Lemna spp.Nex fed to crossbred meat ducks as a sub-stitute for soybean meal there was no significant dif-ference in the carcass traits between treatments(Bui et al.1995).The protein from duckweed has a biological value equivalent to that of soya beans in diets formu-lated for ducklings(Nguyen et al.1997).Duckweed has a high organic matter and protein content but has a low digestibility for ducks.When duckweed was used to replace half the ration in diets for ducks resulted in a reduced feeding costs by up to half(Khanum et al. 2005).Diets formulated for pigs can substitute duckweed for soybean meal(Leng et al.1995).Duckweed has Table17.4Essential amino acid composition of dried L.gibbameal(g amino acid/100g dry L.gibba)g amino acid/100g Essential amino acid dry L.gibba Leucine 2.89Arginine 2.14Valine 2.12Lysine 1.85 Phenylalanine 1.75Threonine 1.68Isoleucine 1.66Tyrosine 1.27Histidine0.73Methionine0.64Cysteine0.44 Tryptophan0.40ndesman et al.been ensiled with other feed crops such as corn or cassava leaves to produce an alternative diet for pigs raised on small farms in Vietnam and that fresh duckweed(providing5%of the diet dry mat-ter)has a stimulating effect on weight gain(Du 1998).The addition of duckweed(Spirodela sp.) to corn significantly increased both the pre-ensiled and the postensiled protein content of the silage (Eversull1982).What has not been found are articles published on the effect of incorporating duckweed meal into penaeid shrimp diets.Fresh and decomposed duck-weed(Spirodela sp.)has been used as feed for the Australian red claw crayfish(Cherax quadricar-inatus)(Fletcher and Warburton1997).They found that decomposed Spirodela species supported cray-fish growth as well as commercial pellets did.The abundance of carotenoids and pigments can stimu-late crustacean growth(Hertampf and Piedad-Pascual 2000).Perhaps the most promising use of duckweed is as a feed for pondfish such as carp and tilapia(Landesman et al.2002).Ponds for duckweed production can be located next tofish culture ponds,eliminating the need for expensive drying to produce a dried feed.Nile tilapia and a polyculture of Chinese carps fed read-ily on fresh duckweed added to their ponds,and the nutritional requirements of tilapia appear to be met by duckweed(Saber2004).W.arrhiza L.alone sup-ported the growth of two species of Indian carp and four species of Chinese carp as well as one species of barb Puntius javanicus(Bikr.)(Naskar1986).The her-bivorous grass carp(Ctenopharyngodon idella)digests duckweed species such as Lemna and Wolffia quite well and it could,by itself,support production of thisfish(Cassani et al.1982,Van Dyke and Sutton 1977).Duckweed has also been tested as a compo-nent in the diet of catfish(Robinette et al.1980), silver barb(Azim et al.2003),and tilapia(Hassan and Edwards1992;Fasakin et al.1999)where it was also able to be substituted for soybean meal.A system for combining duckweed andfish culture was developed in Bangladesh for use by small farmers in develop-ing countries by the non-governmental organization PRISM(Skillicorn et al.1993).This system could sus-tain a dry weight production of duckweed in excess of 20–35metric tons a year,(Leng1999).Hence,duck-weed can become a competitive source of plant protein especially in tropical countries.17.3.2As an Inexpensive and AccurateWay of Toxicity TestingDue to its small size and ease of growth,duck-weed species make useful organisms for toxicity test-ing(Lakatos et al.1993).Duckweed species offer many advantages for the testing of toxic compounds. Duckweed fronds assimilate chemicals directly from their aquatic media into their leaf tissue,allowing for toxicant application in a controlled manner.The growth assay for toxicant assessment is rapid and can be performed without special equipment by counting leaves.Since Lemna and Spirodela are inexpensive to maintain and the fronds are small,multiple treatments are easy to do simultaneously(Greenberg et al.1992). Duckweed species have been used to test the toxicity of oils(King and Coley1985),herbicides(Nitschke et al. 1999),phenol(Barber et al.1995),and polycyclic aro-matic hydrocarbons(Huang et al.1992),among other toxicants.A new company in Germany has devised a Lemna toxicity test that has been approved by the European Commission(Lemna Tec1999),and the use of duck-weed for toxicity testing is mentioned in Standard Methods(1995).Duckweed can be used in both static and the dynamic test procedures(Davis1981,Wang 1990,Taraldsen and Norberg-King1990).17.3.3Miscellaneous UsesThe ease and convenience of culturing duckweed species under both natural and artificial lights make this species an ideal teaching tool,both at the uni-versity and at the primary school level.An example of an experiment using duckweed that can be per-formed by elementary school students was published in the Journal of Biological Education by a Japanese teacher and two research workers(Kawakami et al. 1997).Since duckweed is so quick and easy to grow, students can learn how to study concepts of exponen-tial growth,heavy metal toxicity,photosynthesis,and asexual reproduction.The effect of environmental vari-ables like light and temperature can also be studied using duckweed(Robinson1988).An allelopathic effect of duckweed on mosquito lar-vae may have public health significance.Extracts of L.minor caused significant mortality in the larvae of。
