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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.。
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托福TPO5阅读真题文本Part1Minerals 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 ofanthocyanin. 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. Manymembers 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.Paragraph 1: Research 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 serpentinesoils, 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.托福TPO5阅读真题题目Part11. According to paragraph 1, what is true of plants that can grow in serpentine soil?○ They absorb micronutrients unusually well.○ They require far less calcium than most plants do.○ They are able to absorb nitrogen in its elemental state.○ They are typically crops raised for food.Paragraph 2: 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.2. The word "exhibit" in the passage is closest in meaning to○ fight off○ show○ cause○ spread3. According to paragraph 2, which of the following symptoms occurs in phosphorus-deficient plants but not in plants deficient in nitrogen or iron?○ Chlorosis on leaves○ Change in leaf pigmentation to a dark shade of green○ Short, stunted appearance of stems○ Reddish pigmentation on the leaves or stem4. According to paragraph 2, a symptom of iron deficiency is the presence in young leaves of○ deep red discoloration between the veins○ white or yellow tissue between the veins○ dead spots between the veins○ characteristic dark green veinsParagraph 3: 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 facilitatesthe growing of greenhouse vegetables during winter. Aeroponics, a technique in which plants aresuspended and the roots misted with a nutrient solution, is another method for growing plants without soil.5. The word "facilitates" in the passage is closest in meaning to○ slows down○ affects○ makes easier○ focuses on6. According to paragraph 3, what is the advantage of hydroponics for research on nutrient deficiencies in plants?○ It allows researchers to control what nutrients a plant receives.○ It allows researchers to observe the growth of a large number of plants simultaneously.○ It is possible to directl y observe the roots of plants.○ It is unnecessary to keep misting plants with nutrient solutions.7. The word "suspended" in the passage is closest in meaning to○ grown○ protected○ spread out○ hungParagraph 5: 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.8. Why does the author mention "herbs", "shrubs", and "trees"?○ To provide examples of plant types that cannot tolerate high levels of harmful minerals.○ To show why so many plants are hyperaccumulators.○ To help explain why hyperaccumulators can be found in so many different places.○ To emphasiz e that hyperaccumulators occur in a wide range of plant types.9. The word "afford" in the passage is closest in meaning to○ offer○ prevent○ increase○ removeParagraph 6: 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.10. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.○ Before considering phytoremediation, hyperaccumulating species of plants local to the target area must be identified.○ The investigation begins with an evaluation of toxic sites in the target area to determine the extent of contamination.○ The first step in phytoremediation is the planting of hyperaccumulating plants in the area to be cleaned up.○ Mines and irrigation ponds can be kept from becoming contaminated by planting hyperaccumulating species in targeted areas.11. It can be inferred from paragraph 6 that compared with standard practices for remediation of contaminated soils, phytoremediation○ does not allow for the use of the removed minerals for industrial purposes○ can be faster to implement○ is equally friendly to the environment○ is less suitable for soils that need to be used within a short period of time12. Why does the author mention "Indian mustard"?○ To warn about possible risks involved in phytoremediation ○ To help illustrate the potential of phytoremediation○ To show that hyperaccumulating plants grow in many regions of the world○ To explain how zinc contaminati on can be reducedParagraph 5: Scientists have known for some time that certain plants, called hyperaccumulators, can concentrateminerals 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.13. Loo k at the four squares [■] that indicate where the following sentence could be added to the passage.Certain minerals are more likely to be accumulated in large quantities than others.Where could the sentence best fit?14. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some answer choices do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.Plants need to absorb certain minerals from the soil in adequate quantities for normal growth and development.●●●Answer Choices○Some plants are able to ac cumulate extremely high levelsof certain minerals and thus can be used to clean up soils contaminated with toxic levels of these minerals.○Though beneficial in lower levels, high levels of salts, other minerals, and heavy metals can be harmful to plants.○When plants do not absorb sufficient amounts of essential minerals, characteristic abnormalities result.○Because high concentrations of sodium chloride and other salts limit growth in most plants, much researchhas been done in an effort to develop salt-tolerant agricultural crops.○Some plants can tolerate comparatively low levels of certain minerals, but such plants are of little use for recycling nutrients back into depleted soils.○Mineral deficiencies in many plants can be cured by misting their roots with a nutrient solution or by transferring the plants to a soilless nutrient solution托福TPO5阅读真题答案Part1参考答案：1.○22.○23.○24.○25.○36.○17.○48.○49.○110.○311.○412.○213.○114. Some plants are able toThough beneficial in lower…When plants do not…托福TPO5阅读真题文本翻译Part1参考翻译：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。
DOI:10.7524/j.issn.0254-6108.2023102601李云捷, 李佳, 陈振国, 等. 石蜡与氨基酸废母液粉配施对烟草重金属Cd吸附的阻控效应[J]. 环境化学, 2024, 43（4）: 1365-1373.LI Yunjie, LI Jia, CHEN Zhenguo, et al. Blocking effect of paraffin wax and amino acid waste mother liquor powder on the adsorption heavy metal Cd of tobacco[J]. Environmental Chemistry, 2024, 43 （4）: 1365-1373.石蜡与氨基酸废母液粉配施对烟草重金属Cd吸附的阻控效应 *李云捷1 李 佳1 陈振国2 李建平2 喻雪婧1 云月利1 孙光伟2 朱 蓉1 李亚东1 **（1. 湖北大学生命科学学院，武汉，430062；2. 湖北省烟草科学研究院，武汉，430033）摘 要 烟草是强富集镉（Cd）的重要经济作物. 为降低烟草对Cd的吸收，以矿区污染土壤（Cd含量为0.678 mg·kg−1）为种植基质，烟草专用肥（硝态氮）为对照，氨基酸母液粉为新型氮肥（氨基氮），并分别配施作为土壤微生物碳源的食品级石蜡，以期促进土壤微生物种群与数量的持续增加（石蜡降解速度缓慢），通过微生物的生化调控达到降低土壤有效态Cd含量，从而减少烟叶对镉的吸收. 结果表明：（1）石蜡和氨基酸废母液粉配施（T4处理）显著（P<0.05）提高土壤微生物丰富度，ACE指数达到4464.47，Chao1指数达到3888.30，氨基酸废母液粉（T3处理）土壤微生物多样性最好，Shannon指数达到6.4066；（2）施加氨基酸废母液粉（T3、T4处理）可显著（P<0.05）提高土壤pH值，3个时期（烟叶旺长期、打顶期、成熟期）最大提高量分别为0.23、0.49和0.35；（3）石蜡和氨基酸废母液粉显著（P<0.05）降低土壤有效态Cd含量，3个时期较烟草专用肥组（T1处理）分别降低了14.8%—20.7%、18.6%—34.5%、20.5%—36.7%；（4）石蜡和氨基酸废母液粉显著（P<0.05）降低烟叶Cd含量，3个时期较烟草专用肥（T1处理）分别降低了0.6%—10.2%、8.2%—26.2%、13.8%—38.9%. 因此，石蜡和氨基酸废母液粉配施能够有效提高土壤微生物丰富度和多样性，降低土壤有效态Cd含量，减少烟草对Cd的吸收.关键词 石蜡，氨基酸废母液粉，土壤微生物，烟草，镉.Blocking effect of paraffin wax and amino acid waste mother liquor powder on the adsorption heavy metal Cd of tobaccoLI Yunjie1 LI Jia1 CHEN Zhenguo2 LI Jianping2 YU Xuejing1 YUN Yueli1 SUN Guangwei2 ZHU Rong1 LI Yadong1 **（1. School of Life Science, Hubei University, Wuhan, 430062, China；2. Hubei Provincial Tobacco Research Institute,Wuhan, 430033, China）Abstract Tobacco is an important cash crop with strong enrichment of cadmium (Cd). In order to reduce the absorption of Cd by tobacco, the contaminated soil in mining area (Cd content is0.678 mg·kg−1) is used as planting substrate. In this experiment, tobacco special fertilizer (nitratenitrogen) was used as control, the amino acid waste mother liquor powder was a new nitrogen fertilizer (amino acid nitrogen), and paraffin wax (food-grade) as soil microbial carbon source was2023 年 10 月 26 日 收稿（Received：October 26，2023）．* 湖北省烟草公司科技项目（027Y2021-024）资助.Supported by the Science and Technology Program of Hubei Tobacco Company （027Y2021-024）.* * 通信联系人 Corresponding author，E-mail：*****************1366环 境 化 学43 卷applied separately. The purpose is to promote the continuous increase of soil microbial population and quantity (the degradation rate of paraffin wax is slow.), and reduce the soil available Cd content through biochemical regulation of microorganisms, thereby reducing the absorption of Cd by tobacco leaves. The results showed that: (1) Paraffin wax and amino acid waste mother liquor powder (T4 treatment) significantly (P<0.05) increased the soil microbial richness, the ACE reached 4464.47, the chao1 reached 3888.30, the amino acid waste mother liquor powder (T3 treatment) soil microbial Shannon diversity was the best, and the Shannon reached 6.4066; (2) the application of amino acid waste mother liquor powder (T3, T4 treatment) could significantly increase soil pH (P<0.05), and the maximum increases in the three periods were 0.23、0.49 and 0.35 units. (3) Paraffin wax and amino acid waste mother liquor powder significantly (P<0.05) reduced the soil effective Cd content, which was reduced by 14.8%—20.7%, 18.6%—34.5% and 20.5%—36.7%compared with the tobacco special fertilizer group (T1 treatment) in the three periods. (4) Paraffin wax and amino acid waste mother liquor powder significantly (P<0.05) reduced the Cd content of tobacco leaves, and decreased by 0.6%—10.2%, 8.2%—26.2% and 13.8%—38.9% compared with tobacco special fertilizer (T1 treatment) in the three periods. Therefore, the combination of paraffin wax and amino acid waste mother liquor powder can effectively improve the richness and diversity of soil microorganisms and reduce the soil effective Cd content. Finally, the absorption of Cd by tobacco is reduced.Keywords paraffin wax，amino acid waste mother liquor powder，soil microorganisms，tobacco，cadmium.镉（Cd）可通过食物链逐层积累，对生态环境和生物生命健康存在威胁[1]. 据2021年生态环境部发布简况，影响农用地土壤环境质量的主要污染物是重金属，其中镉为首要污染物. 烟草极易吸收Cd[2]，Cd胁迫对烟草整个生长周期和生理指标均产生影响，严重降低烟叶口感和产量，且Cd通过烟气进入人体，威胁人体健康[3]，因此如何降低烟草吸收Cd是烟草行业亟需解决的问题. 阻控烟草吸收Cd已有不少研究，如李晓锋等[4]发现, 生物有机类钝化剂提高烟草生物量且降低Cd吸收最显著；杜甫等[5]利用新型丙烯酰胺/羧甲基纤维素/生物炭复合水凝胶，提高了烟草在Cd胁迫下的耐受性；吕怡颖等[6]发现镉浓度50—200 μmol·L−1对烟苗生长发育具有显著抑制作用，外源褪黑素（一种小分子吲哚胺类）可显著缓解烟草镉毒害. 但相关研究尚未得到广泛应用，有可能是成本较高或对土壤存在二次污染[7]；与此同时，土壤微生物阻控植物吸收重金属已卓有成效[8].本研究以曾应用于氨基酸、有机酸发酵工业的石蜡（食品级，碳原子13—18）[9]作为土壤微生物生长碳源，以期在氨基酸废母液粉作为氮肥的基础上，通过配施石蜡，促进石蜡降解菌群增加，全面提高土壤微生物种群数量，利用土壤微生物对镉离子的络合、螯合、沉淀等作用[10]，降低Cd的迁移能力和有效态Cd含量，从而减少烟草对镉的吸收，为轻度镉污染土壤种植合格烟叶提供新的栽培技术.1 材料与方法（Materials and methods）1.1 实验材料实验于2022年11月22日在湖北大学生命科学学院全智能温室开展，供试烟草品种为云烟87，土壤取自黄石市矿区，其中含镉0.678 mg·kg−1，pH为5.15.1.2 实验设计施肥量纯氮97.5 kg·hm−2，m（N）∶m（P2O5）∶m（K2O）=1∶1∶1.5，移栽前一个月将肥料与土混合均匀，于2022年11月22日移栽烟苗至塑料盘内，塑料盘尺寸为32 cm×30 cm（直径×高）. 实验设置4个处理，如表1所示其具体施肥方案：T1（只添加烟草专用肥）、T2（添加烟草专用肥＋石蜡）、T3（只添加氨基酸废母液）、T4（添加氨基酸废母液＋石蜡）. 其中，石蜡采购自荆门市维佳实业有限公司，维佳58#食品级石蜡；氨基酸废母液粉为实验室自主研发的有机肥料，含氮≥14%；烟草专用肥购自烟台云天化肥公司，货号复合肥料（硫酸钾型/含硝态氮），含氮≥24%. 按比例配施磷钾肥，充分粉碎，在移栽前30天和移栽后45 d分两次施入土壤. 每个处理9株烟苗作为重复，遵循完全随机原则，其他所有处理栽培条件按照优质烟草生产方式进行.表 1 具体施肥方案Table 1 The specific fertilization scheme处理Treatment烟草专用肥Tobacco special fertilizer氨基酸废母液粉Amino acid mother liquor powder石蜡Paraffin waxT1406.2 kg·hm−2——T2406.2 kg·hm−2—300 kg·hm−2 T3—696.45 kg·hm−2—T4—696.45 kg·hm−2300 kg·hm−21.3 样品采集1.3.1 土壤样品采集烟苗移栽后45 d、75 d、105 d利用“S”形5点取样法采集根际土壤样品，近烟株根部10 cm、直径3 cm、深度12 cm的根际土壤样品，重复3次. 取移栽后75 d的根际土壤样品100 g装入无菌袋中迅速放入干冰盒中，-80℃保存，待测根际土壤微生物；其他样品风干粉碎后过200目筛，遵循土壤检测标准进行制备[11]，待测土壤pH值、土壤有效态Cd含量.1.3.2 烟叶及烟株根茎样品采集烟苗移栽后45 d、75 d、105 d采集烟叶样品，其中移栽后45 d取第6叶位；移栽后75 d取上部叶（第4、5叶位）、中部叶（第10、11叶位）、下部叶（第15、16叶位）；待烟叶均匀落黄后，移栽后105 d同移栽后75 d取样，叶位均为从上往下数，取样时随机选取一株两片烟叶样品混合为1个生物学重复，重复3次. 烟叶用蒸馏水洗净、擦干，105 ℃杀青30 min，65 ℃烘干至恒重，剔去主脉，剩余叶片粉碎后过200目筛，待测烟叶Cd含量. 烟叶全部采摘后，取烟株茎部上中下3个部位混合为一个生物学重复，重复3次，蒸馏水洗净擦干，烘干至恒重，粉碎后过200目筛，待测茎部镉含量；取烟株根部须根，每3株作为一个生物学重复，重复3次，蒸馏水洗净擦干，烘干至恒重，粉碎后过200目筛，待测根部Cd含量.1.4 测定项目与方法1.4.1 根际土壤微生物的测定采集好的根际土壤样品委托上海美吉生物科技股份有限公司进行微生物测序，其中，对细菌的16rRNA的V3-V4区进行PCR扩增，具体引物序列见表2，采用Vsearch[12]方法对序列进行处理，从而对样本中的所包含的高质量系列进行统计. 通过稀疏的方法对OTU丰度进行抽样[13]，获得每个样本中的微生物群落各分类水平的具体组成数据.表 2 土壤微生物实时定量 PCR 分析基因及引物Table 2 Real-time quantitative PCR analysis of genes and primers by soil microorganisms区域Region引物名称Primer name引物序列（5’-3’）Primer sequences （5'-3'）V3＋V4341F CCTAYGGGRBGCASCAG 806R GGACTACNNGGGTATCTAAT1.4.2 根际土壤pH值测定参照《中华人民共和国国家环境保护标准（土壤 pH 值的测定电位法）》 （HJ 962—2018）[14]中土壤pH值测定方法，土水比为1:2.5（m:V），200 r·min−1振荡2 min，静置30 min，pH计（德国赛多利斯Sartoriu，PB-10）测定.1.4.3 根际土壤有效态Cd含量的测定土壤有效态Cd含量测定参照《土壤质量：有效态铅和镉的测定-原子吸收法》（GB/T 23739—2009）[15]测定.4 期李云捷等：石蜡与氨基酸废母液粉配施对烟草重金属Cd吸附的阻控效应13671.4.4 烟叶及烟株茎、根部Cd含量的测定烟叶及烟株茎、根部Cd含量测定参照《食品安全国家标准：食品中镉的测定》（GB/T 17141—1997）[16]测定.1.5 数据分析采用Microsoft Excel 2019进行数据处理和作图，采用SPSS 26.0进行数据分析，采用GraphPad Prism 9作图.2 结果与讨论（Results and discussion）2.1 不同处理对植烟土壤微生物群落组成的影响2.1.1 根际土壤微生物OTU丰度和α多样性在97%相似水平条件下得到土壤微生物群落物种多样性指数如表3所示，所有处理的覆盖率均大于0.95，说明测序能力能够真实反映土壤微生物群落特征. T1、T2、T3、T4处理下土壤微生物Sobs、ACE、Chao1指数均表现为T4>T3>T2>T1，T4处理组ACE指数达到4464.47，Chao1指数达到3888.30，Shannon指数表现为T3>T4>T1>T2，T3处理组Shannon指数达到6.4066. Simpson指数表现为T2>T1>T4>T3. 由α多样性可以看出，T4处理土壤微生物丰富度最高，T3处理土壤微生物多样性最好.表 3 不同处理根际土壤微生物α多样性指数Table 3 α Diversity index of soil microorganisms with different treatments处理Treatment Sobsα多样性指数α diversity index覆盖率Coverage Shannon Simpson ACE Chao1T12643.00b 6.3583a0.0098a3851.65b3571.71a0.9548T22714.33b 6.3359a0.0099a3864.72b3638.19a0.9551T32891.33a 6.4066a0.0086b4118.76b3787.24a0.9597T42914.00a 6.3752a0.0092ab4464.47a3888.30a0.9515 注：同列不同小写字母表示组间差异达显著水平（P<0.05）水平. Note: Different lowercase letters in the same column indicate a significant difference between groups （P<0.05） level.2.1.2 不同处理对根际土壤微生物群落组成的影响图1展示了门水平上平均相对丰度前五的类群（放线菌门、绿弯菌门、变形菌门、酸杆菌门和厚壁菌门），其中放线菌门（Actinobacteriota）在各处理中均占绝对优势，其次是绿弯菌门（Chloroflexi）和变形菌门（Proteobacteria）. 放线菌门的相对丰度表现为T4>T2>T3>T1，其平均丰度与添加石蜡呈正相关；绿弯菌门的相对丰度表现为T3>T4>T1>T2，其平均丰度与添加氨基酸废母液粉呈正相关；变形菌门的相对丰度表现为T1>T2>T3>T4，与增施氨基酸废母液和石蜡均呈负相关.图 1 不同处理的微生物门水平上的相对丰度柱状图Fig.1 Histogram of relative abundance at the level of microbial phylums with different treatments 属分类水平上，根据所有样品的物种注释及丰度信息，选取根际土壤微生物丰度排名前20的物种，并按照其丰度信息绘制热图（图2），结果表明T1与T2、T3与T4处于同一分支，2组土壤微生物群1368环 境 化 学43 卷4 期李云捷等：石蜡与氨基酸废母液粉配施对烟草重金属Cd吸附的阻控效应1369落结构相似，说明氨基酸废母液粉是影响微生物群落结构的主要原因. 其中戈登式菌属（Gordonia）、分枝杆菌属（Mycobacterium）受是否添加石蜡影响较大，在T2和T4处理中的相对丰度较高，与其他两个处理存在极显著性差异；节杆菌属（Aothrobacter）、芽孢杆菌属（Bacillus）受是否添加氨基酸废母液粉影响较大，在T3和T4处理中的相对丰度较高，与其他两个处理存在显著性差异；而戴氏菌属（Dyella）受烟草专用肥影响较大，在T1和T2处理中的相对丰度较高，较其他两个处理相对丰度显著升高.图 2 不同处理的微生物属水平上优势菌属的层次聚类分析热图.注：颜色变化可以反映不同处理间在属水平上群落组成的相似性和差异性；右侧图为颜色梯度代表的数值Fig.2 Hierarchical clustering analysis heat map of dominant genera at the level of microorganisms with different treatments. Note: Color variations can reflect similarities and differences in community composition at genera levels between treatments；the graph on theright shows the numerical values represented by the color gradient随着微生物种群数量的增加，微生物细胞壁、胞外物质和胞内细胞器均起到降低重金属有效态作用，减少植物吸收，从而达到生态学方向的原位钝化作用. 本研究中发现增施氨基酸废母液粉和石蜡可提高根际土壤微生物丰富度和多样性（表3），这是由于氨基酸废母液粉作为有机肥提供小分子氮源，石蜡作为烃类物质提供碳源，两者相互促进微生物的生长繁殖，这与张慧、万连杰等证明氮肥和有机肥可有效提高土壤微生物丰富度的结果一致[17 − 19]，且石蜡的存在会提高分解石蜡的烃类微生物. 在属水平上，节杆菌属和芽孢杆菌已被证明对重金属有钝化作用，尤其对重金属镉[20 − 21]；戈登式菌属具备生物降解烃类物质的能力[22]，且戈登式菌属和分枝杆菌属细胞壁中富含霉菌酸，使得细胞表面疏水性和渗透性极差，进而阻止重金属离子的渗透，可在重金属胁迫的环境下正常生长繁殖[23]. 可见，氨基酸废母液粉和石蜡可有效提高土壤微生物丰富度和多样性，从而降低土壤中有效态Cd含量，但对于是胞外物质还是胞内细胞器或各种酶对吸附、包埋重金属起作用还有待进一步研究.2.2 不同处理对各时期根际土壤pH值和土壤有效态Cd含量不同处理对各时期土壤pH值变化如图3a所示. 在烟株的各个生育期土壤pH均表现为氨基酸废母液粉组大于烟草专用肥组，表明增施氨基酸废母液粉可提高土壤pH值，但添加石蜡对土壤pH值无显著影响，其中移栽后45 d时pH提高量最高可达0.23，移栽后75 d时pH提高量最高可达0.49，移栽后105 d时pH提高量最高可达0.35，均具有显著性差异（P<0.05），而且所有施肥处理的土壤pH值都随着烟株的生长呈先升高后降低的变化. 不同处理对各时期植烟土壤有效态镉的影响如图3b所示. 移栽后45 d土壤有效态镉含量表现为T1>T3>T2>T4，T2、T3和T4处理较T1处理显著降低了16.6%、14.8%、20.7%，其他处理间无显著性差异；移栽后75 d土壤有效态镉含量表现为T1>T2>T4>T3，T2、1370环 境 化 学43 卷T3和T4处理较T1处理显著降低了18.6%、34.5%、31.5%，T3和T4处理较T2处理显著降低了13.4%、13.5%，在数值上T4>T3，但两处理间无显著性差异；移栽后105 d土壤有效态镉含量表现T1>T2> T3>T4，T2、T3和T4处理较T1处理显著降低了20.5%、36.6%、36.7%，T3和T4处理较T2处理显著降低了13.4%、13.5%，T3和T4处理间无显著性差异.图 3 不同处理对不同时期根际土壤pH值变化（a）和土壤有效态Cd含量变化（b）注：同组不同小写字母表示组间差异达显著水平（P<0.05）水平；其中45 d、75 d、105 d表示烟苗移栽后45 d、75 d、105 dFig.3 Changes of rhizosphere soil pH value （a） and changes of soil available Cd content at different periods of treatment （b）Note: Different lowercase letters in the same group indicate that the difference between groups reaches a significant level （P<0.05） level;Among them, 45 d, 75 d and 105 d indicated that 45 d, 75 d, 105 d after transplanting tobacco seedlings,土壤pH值对土壤中镉的形态影响较大[24]，Wang等[25]研究表明，土壤pH较高时，镉主要以氧化物结合态及残留态形式存在，土壤pH较低时，氧化络合物中的镉会溶解，镉离子被释放，游离镉浓度上升. 本研究中氨基酸废母液粉可有效提高土壤pH值，3个生长时期可提高0.23—0.49，这是因为，氨基酸废母液粉是本实验室自主研发的有机肥料，由动物废毛发、骨头等动物蛋白通过氢氧化钾高温水解将蛋白质水解为小分子的氨基酸，肥料整体呈碱性，其次本研究减施磷肥可有效提高土壤pH值，防止土壤酸化，与龚玲婷结果一致[26].2.3 不同处理对各时期烟株镉含量2.3.1 对移栽后45 d烟叶镉含量不同处理对移栽45 d后烟叶Cd含量变化如图4（a）所示，在数值上Cd含量表现为T1>T2> T3>T4，但并无显著性差异，较T1分别降低了0.6%、7.1%和10.2%，表明在烟草生长前期各处理间对烟草吸收Cd的阻控并无太大差异.2.3.2 对移栽后75 d烟叶镉含量不同处理对移栽后75 d烟叶的Cd含量测定结果见图4（b）. 移栽后75 d时各部位烟叶Cd含量均表现为T2>T1>T3>T4. 对于烟株下部叶，T4处理烟叶Cd含量显著低于T1处理，降低了26.2%；对于烟株中部叶，T3和T4处理显著低于T1和T2处理，较T1处理分别降低了8.2%、16.2%，较T2处理降低了6.8%、14.6%，且T3和T4处理间存在显著性差异；对于烟株上部叶，T3和T4处理显著低于T1处理，较T1处理分别降低了15.6%、18.7%，其他处理间无显著性差异. 结果表明，移栽后75 d氨基酸废母液粉可有效阻控烟草吸收Cd，且石蜡和氨基酸废母液粉配施对中部叶降Cd最为显著.2.3.3 对移栽后105 d烟叶、茎和根镉含量不同处理对移栽后105 d烟叶Cd含量测定结果见图4（c）. 移栽后105 d时下部叶和中部叶Cd含量均表现为T1>T2>T3>T4，其中烟株下部叶，T3和T4处理显著低于T1和T2处理，较T1处理分别降低了23.0%、27.0%，较T2处理降低了19.0%、23.7%，且T3和T4处理间存在显著性差异；对于烟株中部叶，T2、T3和T4处理显著低于T1，较T1处理分别降低了14.3%、32.5%、38.9%，较T2处理降低了16.0%、21.6%，其他处理间无显著性差异；对于烟株上部叶，Cd含量表现为T2>T1>T3>T4，其中T3和T4处理显著低于T1处理和T2处理，较T1处理分别降低了13.8%、31.4%，较T2处理降低了23.7%、18.9%，且T3和T4处理间存在显著性差异.图 4 移栽后45 d(a)、75 d(b)和105 d(c)烟叶Cd 含量变化图注：同组不同小写字母表示组间差异达显著水平（P <0.05）水平;Fig.4 Changes of Cd content of tobacco leaves at 45 d(a), 75d(b) and 105 d(c) aftertransplanting with different treatmentsNote: Different lowercase letters in the same group indicate that the difference between groups reaches a significant level （P <0.05） level 不同处理对移栽后105 d 烟株茎部Cd 含量测定结果见图5（a ），茎部Cd 含量表现为T1>T2>T3>T4，T2、T3和T4处理显著低于T1，较T1处理分别降低了30.9%、38.1%、39.4%；不同处理对移栽后105 d 烟株根系Cd 含量测定结果见图5（b ），根系镉含量表现为T1>T3>T2>T4，T2、T3和T4处理均显著降低烟株根系Cd 含量，较T1分别降低了28.5%、27.9%和31.2%，但3个处理之间无显著性差异.图 5 不同处理对移栽后105 d 烟草茎部Cd 含量变化（a ）和烟草根部Cd 含量变化（b ）注：同组不同小写字母表示组间差异达显著水平（P <0.05）水平Fig.5 Changes of Cd content of tobacco stems （a ） and changes of Cd content of tobacco roots （b ）at 105 days aftertransplanting with different treatmentsNote: Different lowercase letters in the same group indicate that the difference between groups reaches a significant level （P <0.05） level结果表明，石蜡和氨基酸废母液配施对烟草阻控Cd 是有效地，尤其在移栽后105 d 即烟草成熟期，烟叶降低率最高可达39.0%，烟茎部降低率达到39.4%，烟根部降低率达到31.2%. 这可能是因为增施石蜡后，石蜡缓慢的被微生物分解，持续提供微生物碳源，使土壤微生物对镉离子持续吸附，从而达到降低烟叶中Cd 的效果. Cd 在烟叶中的分布呈现上部叶>中部叶>下部叶，烟茎部>烟根部，这可能是因为烟株有强的蒸腾作用，在由下而上的运输过程中镉元素逐步向烟株上部积累，这与李晓忠的研究结果一致[27].4 期李云捷等：石蜡与氨基酸废母液粉配施对烟草重金属Cd 吸附的阻控效应13713 结论（Conclusion）（1） 本研究通过增施石蜡（食品级）不仅增加了常规微生物种群数量而且新增戈登式菌属（Gordonia ）微生物种群（石蜡降解专属菌群），因此与氨基酸废母液粉作为肥料配施时，为微生物吸附、结合、沉淀重金属建立生态学基础，也表明石蜡作为碳源提高土壤微生物种群数量的可行性.（2） 本研究通过配施石蜡和氨基酸废母液粉，提高土壤pH 值，改变Cd 的存在形态，降低土壤中有效态Cd 含量，从而阻控烟草对Cd 的吸收，为实现轻度镉污染土壤条件下烟草的安全种植提供新的栽培措施.参考文献(References)陈世宝, 王萌, 李杉杉, 等. 中国农田土壤重金属污染防治现状与问题思考[J ]. 地学前缘, 2019, 26（6）: 35-41.CHEN S B, WANG M, LI S S, et al. Current status of and discussion on farmland heavy metal pollution prevention in China [J ]. Earth Science Frontiers, 2019, 26（6）: 35-41 (in Chinese).［ 1 ］杨佳蒴. 氯化钠诱导根系木质化对烟草镉吸收的影响[D ]. 北京: 中国农业科学院, 2020.YANG J S. Effects of the sodium chloride induced root lignification on cadmium accumulation by tobacco [D ]. Beijing: Chinese Academy of Agricultural Sciences, 2020 (in Chinese).［ 2 ］SIEMIANOWSKI O, BARABASZ A, KENDZIOREK M, et al. 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增加植物的方法英语作文Increasing plant growth is essential for maintaining a healthy and beautiful environment. There are several methods to increase plant growth, which can be implemented in gardens, farms, and landscapes. In this article, we will discuss some effective methods to enhance plant growth.Firstly, providing the necessary nutrients is crucial for plant growth. Plants require essential nutrients such as nitrogen, phosphorus, potassium, and micronutrients like iron, magnesium, and zinc to thrive. One way to provide these nutrients is by using fertilizers. Organic fertilizers, like compost and manure, can add nutrients to the soil and improve its fertility. Chemical fertilizers are also effective in providing essential nutrients to plants, but they should be used cautiously to prevent soil and water pollution.Secondly, proper watering is important for plant growth. Plants need water to survive and grow, so it is essential to water them adequately. Over-watering or under-watering can stress plants and hinder their growth. The frequency and amount of water needed by plants vary depending on the species, soil type, and weather conditions. Using drip irrigation systems or soakerhoses can ensure that plants receive water directly at their roots, promoting healthier growth.Furthermore, ensuring proper sunlight exposure is crucial for plant growth. Sunlight is essential for photosynthesis, the process by which plants convert light energy into chemical energy. Most plants require at least six hours of sunlight per day to thrive. Inadequate sunlight exposure can lead to stunted growth and poor flowering or fruiting. Therefore, it is important to place plants in locations where they can receive sufficient sunlight throughout the day.In addition to providing nutrients, water, and sunlight, controlling pests and diseases is also essential for increasing plant growth. Pests like insects, mites, and rodents can damage plants by feeding on their leaves, stems, and fruits. Diseases caused by fungi, bacteria, and viruses can also weaken plants and inhibit their growth. Using organic pest control methods, like neem oil or insecticidal soap, can help mitigate pest problems without harming the environment. Proper sanitation, like removing diseased plant material and disinfecting tools, can prevent the spread of diseases among plants.Moreover, pruning and trimming plants can stimulate growth and improve their overall health. Pruning removes deador diseased branches, allowing plants to redirect their energy towards new growth. Trimming helps maintain the shape and size of plants, promoting better airflow and light penetration. Regular pruning and trimming can also increase flowering and fruit production, making plants more attractive and productive.Lastly, creating healthy soil is vital for increasing plant growth. Soil provides plants with essential nutrients, water, and support for their roots. Adding organic matter, like compost or mulch, can improve soil structure and fertility. Testing soil pH and nutrient levels can help determine the specific needs of plants and enable gardeners to make informed decisions about fertilization and soil amendments. Using cover crops and crop rotation can also help replenish nutrients in the soil and prevent erosion.In conclusion, there are multiple methods to increase plant growth, ranging from providing nutrients and water to controlling pests and diseases. By implementing these strategies, gardeners, farmers, and landscape designers can create thriving and sustainable plant environments. Following best practices for plant care can lead to healthier, more vibrant plants that enhance the beauty and productivity of any garden or landscape. By nurturing plants with the right nutrients, water, sunlight, andcare, everyone can contribute to a greener and more sustainable world.。
写想发明植物生长药水的作文英文回答：As an aspiring inventor, I have been working on a new invention that I believe has the potential to revolutionize the agriculture industry. My invention is a plant growth potion that can significantly enhance the growth and yield of various crops.The idea for this invention came to me when I was conducting research on the various factors that affect plant growth. I discovered that certain natural compounds and nutrients can have a profound impact on the development of plants. This led me to develop a unique formula that combines these compounds in a way that maximizes their effectiveness.The plant growth potion works by providing plants with a concentrated dose of essential nutrients and growth-promoting compounds. When applied to the soil or sprayeddirectly onto the plants, it is absorbed by the roots and leaves, stimulating rapid growth and increased productivity. The potion is designed to be safe for the environment and non-toxic to humans and animals.I believe that this invention has the potential to address some of the key challenges facing modern agriculture, such as the need to increase crop yields to feed a growing global population. By using the plant growth potion, farmers can boost the productivity of their crops without relying on harmful chemical fertilizers and pesticides.In addition to its potential impact on food production, the plant growth potion could also have significant implications for sustainable agriculture and environmental conservation. By promoting healthier and more resilient plants, it could help reduce the need for intensive farming practices that degrade the soil and contribute to pollution.I am excited about the possibilities that thisinvention holds and am currently seeking partnerships andfunding to further develop and commercialize the plant growth potion. I am confident that this invention has the potential to make a meaningful contribution to the futureof agriculture and the well-being of our planet.中文回答：作为一个有抱负的发明家，我一直致力于研发一种新的发明，我相信这个发明有潜力彻底改变农业产业。
营养液的英语单词Nutrient-rich solutions are essential for the growth of plants, especially in hydroponic systems where they replace soil.These solutions contain a balanced mix of essential elements, including nitrogen, phosphorus, and potassium, which are vital for plant development.The English term for such a solution is "nutrient solution" or "hydroponic nutrient solution," which is aliquid mixture specifically formulated to provide plants with all the nutrients they need to thrive.In a hydroponic setup, a nutrient solution is circulated through the system, ensuring that each plant receives an adequate amount of the necessary nutrients for its growth and health.Understanding the composition of a nutrient solution is crucial for gardeners, as it allows them to tailor the mix to the specific needs of their plants, resulting in lush, healthy growth.For beginners, it's important to start with a pre-mixed solution and gradually learn how to adjust the ratios of nutrients as they gain more experience.Over time, one can experiment with different nutrient solutions to optimize plant health and yield, adapting to the unique requirements of various plant species and growing conditions.。
植物养分吸收转换流程英文回答：Plant Nutrient Uptake and Translocation.Nutrient Uptake.1. Absorption by roots: Plants absorb nutrients from the soil solution through their roots. The root system consists of a network of root hairs that increase the surface area for nutrient uptake.2. Translocation to vascular tissues: Once nutrients are absorbed into the roots, they are transported to the vascular tissues (xylem and phloem) for transport to the rest of the plant.3. Active transport: Active transport is a process that requires energy (ATP) to move nutrients across cell membranes against a concentration gradient.Nutrient Translocation.4. Xylem transport: Water and dissolved minerals are transported from the roots to the leaves through the xylem vessels.5. Phloem transport: Organic compounds, such as sugars, amino acids, and proteins, are transported from the leavesto other parts of the plant through the phloem vessels.6. Redistribution: Nutrients can be redistributedwithin the plant as needed. This process involves the transport of nutrients from one organ to another, such as from leaves to fruits or roots.Factors Affecting Nutrient Uptake and Translocation.Soil pH.Soil moisture.Temperature.Nutrient availability.Plant species.Root health.Importance of Nutrient Uptake and Translocation.Nutrients are essential for plant growth and development.Proper nutrient uptake and translocation ensure that plants receive the necessary nutrients to carry out various physiological processes.Efficient nutrient management practices can improve plant growth, yield, and quality.中文回答：植物养分吸收转换流程。
水培植物的劳动课英语作文英文回答：Hydroponics, a revolutionary method of growing plants without soil, has captivated the attention of gardeners and plant enthusiasts alike. In this unique approach, plants are suspended in a nutrient-rich water solution, allowing them to absorb essential elements directly from their immediate environment. This technique offers numerous advantages, making it a viable alternative to traditional soil-based gardening.One of the key benefits of hydroponics is its space efficiency. Vertical farming, a popular hydroponic technique, utilizes vertical space to maximize plant growth within limited areas. This method is particularlybeneficial in urban settings where land is scarce or expensive. Additionally, hydroponics allows for precise control over nutrient delivery, ensuring that plants receive the optimal balance of elements for optimal growthand development.Hydroponic systems can be customized to suit different plant species and growing conditions. The most common type of hydroponic system is the nutrient film technique (NFT), where a thin film of nutrient-rich water flows over the roots of plants. Other systems include deep water culture (DWC), where plants are submerged in a reservoir ofnutrient solution, and aeroponics, where plant roots are suspended in a mist of nutrient-rich water.While hydroponics offers numerous advantages, it also has its drawbacks. The initial setup can be expensive, requiring specialized equipment and materials. Furthermore, hydroponic systems are more susceptible to power outages and equipment malfunctions, which can disrupt nutrient delivery and potentially harm plants. Despite these challenges, the benefits of hydroponics often outweigh the potential drawbacks, making it a viable choice for growers seeking efficient and controlled plant cultivation.中文回答：水培，一种无需土壤即可种植植物的革命性方法，吸引了园丁和植物爱好者的关注。
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。
