Modelling Plant Disease Risk Areas Based on Brazilian Climate Change Scenarios
南充“PEP”2024年小学五年级上册第15次英语第三单元综合卷[有答案]
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南充“PEP”2024年小学五年级上册英语第三单元综合卷[有答案]考试时间：100分钟（总分:120）A卷一、综合题(共计100题共100分)1. 填空题：My friend loves __________ (参与社区服务).2. 听力题：An exothermic reaction releases ______ into the surroundings.3. 选择题：What is the name of the famous artist known for his "The Last Judgment"?A. MichelangeloB. RaphaelC. Leonardo da VinciD. Titian答案: A4. 选择题：What do we call the place where we learn?A. LibraryB. SchoolC. ParkD. Store答案:B5. 听力题：The dog is ___ the ball. (chasing, eating, sleeping)6. 填空题：My cat enjoys chasing after ______ (光点).7. 填空题：I like to go ______ (滑雪) in winter.The chemical formula for ethanol is ______.9. 填空题：The ________ were nomadic tribes that lived in Mongolia.10. Race was between the USA and _____. 填空题：The Span11. 选择题：What do you call a place where you can see many animals?A. ZooB. FarmC. ParkD. Aquarium答案:A12. 听力题：The _______ needs care and attention.13. 填空题：I enjoy _______ (写诗) in my notebook.14. 填空题：I can build a house with my ________ (玩具名称).15. 选择题：What is the capital of Slovenia?A. LjubljanaB. MariborC. CeljeD. Koper答案:A16. 填空题：My brother loves __________ (历史) and knows many facts.17. 选择题：What do we call the act of putting something in the correct place?A. OrganizingB. ArrangingC. SortingD. Categorizing答案：AA _______ (鳄鱼) has a powerful bite.19. 填空题：I see _____ flying around in the garden.20. 选择题：What is the sound of a horse?A. NeighB. WoofC. MeowD. Quack21. 选择题：What is the name of the famous composer known for his operas?A. Giuseppe VerdiB. Johann StraussC. Wolfgang Amadeus MozartD. Richard Wagner答案: A22. 填空题：A snail carries its _______ on its back.23. 听力题：The Earth’s ______ is responsible for its magnetic field.24. 选择题：What is the capital of the United Arab Emirates?A. DubaiB. Abu DhabiC. SharjahD. Ajman25. 听力题：The chemical symbol for iridium is _______.26. 听力题：An emulsion is a mixture of two ________ that do not usually mix.27. 选择题：What is the main job of a farmer?A. TeachB. Grow foodC. Fix carsD. Build housesMy brother is a ______. He loves to skateboard.29. 选择题：What is the main ingredient in sushi?A. RiceB. NoodlesC. FishD. Seaweed30. 听力题：Heat can speed up a ______.31. 听力题：The snow is _____ on the ground. (white)32. 听力题：The capital of the Cayman Islands is __________.33. 听力题：The ____ has a long tail and loves to swing from branches.34. 选择题：What is the name of the famous space telescope?A. HubbleB. James WebbC. KeplerD. Chandra35. 填空题：I enjoy feeding the ______ (小鸟) in my backyard. They are very ______ (可爱).36. 选择题：What is the capital of Honduras?A. TegucigalpaB. San Pedro SulaC. La CeibaD. Choluteca答案: A. Tegucigalpa37. 听力填空题：I think staying organized helps me manage my __________.38. 填空题：The cake is _______ (在桌子上).What is the name of the first man on the moon?A. Neil ArmstrongB. Buzz AldrinC. Yuri GagarinD. John Glenn40. 听力题：The capital of Belarus is _______.41. 选择题：What do we call a person who flies an airplane?A. PilotB. StewardessC. PassengerD. Engineer42. 填空题：I help my sister with her __________. (画画)43. 听力题：The Battle of Gettysburg was a turning point in the _______ War.44. 听力题：A dune is a hill of ______ formed by wind.45. 听力题：In ancient times, people used the stars for ______.46. 选择题：Which of these is a winter sport?A. SwimmingB. SkiingC. SurfingD. Running答案:B47. 填空题：The __________ was a famous ship that sank in 1912. (泰坦尼克号)48. 填空题：My favorite _____ is a cuddly bear.49. 听力题：My friend is a ______. He enjoys helping in the community.The invention of ________ allowed for faster communication.51. 填空题：The elephant is the largest _______ (动物).52. 选择题：What is the main purpose of a compass?A. Measure temperatureB. Tell timeC. Show directionD. Measure weight答案:C53. 选择题：What is 25 + 25?a. 40b. 50c. 60d. 70答案:b54. 听力题：I enjoy _____ (参加) community events.55. 填空题：I love _______ (和家人一起)去旅行。
小学上册第十二次英语第一单元测验试卷
小学上册英语第一单元测验试卷英语试题一、综合题(本题有100小题，每小题1分，共100分.每小题不选、错误，均不给分)1.The flowers are ______ in the garden. (blooming)2.The ______ is known for her supportive nature.3.I enjoy _____ (fishing/hunting) in the summer.4.On the farm, there are many ______ (动物). I like the ______ (小羊) because it is fluffy and soft.5.I like to _____ (制作) handmade gifts.6. A ________ (园艺) enthusiast loves planting.7.The _______ is home to various creatures.8.I like to ______ (玩) in the park after school.9.I love _____ (春天) flowers.10. A substance that can act as a reducing agent is called a ______ agent.11.The owl's feathers are designed for ________________ (静音) flight.12.How many teeth does an adult human have?A. 20B. 24C. 28D. 3213.I love _____ (spending/spent) time with friends.14.I like to ______ (参加) environmental activities.15.The leaves on the _______ turn red in autumn.16.The ant is very _________. (忙碌)17.I like to ride my ________ (摩托车) on weekends.18. A ______ is used to measure temperature.19.What do we call the area of land that is below sea level?A. BasinB. DepressionC. TrenchD. All of the above答案:D All of the above20. A ______ (青蛙) has webbed feet for swimming.21. A solution with a pH below is ______.22.What do you call the natural satellite that orbits the Earth?A. StarB. PlanetC. MoonD. Comet23.The mouse is very _______ (小心) when looking for food.24.The first successful human flight in space occurred in ________.25.There are ten _____ (students) in the class.26. A _______ is a type of mixture where the components are not evenly distributed.27.What do you use to draw?A. PencilB. ForkC. SpoonD. Plate28.The ______ (蚂蚁) works hard to gather food.29.My house has a big ______.30.My friend gave me a ______ (拼图) for my birthday. It has many pieces and is very ______ (有趣的) to do.31.I have a ___ (hobby/job) that I enjoy.32. A solution can be diluted by adding more ______.33.The chemical formula for potassium nitrate is ______.34.An endothermic reaction absorbs ______ from the environment.35.The ______ (气味) of flowers can be very pleasant.36.My mother is a _____ (护士) who loves her job.37.The __________ (历史的思考方式) shape our discourse.38.The Stone Age is known for the use of _______ tools.39.What do we call the study of living things?A. ChemistryB. BiologyC. PhysicsD. Geography答案:B40.What is the capital of Sweden?A. OsloB. CopenhagenC. StockholmD. Helsinki答案:C41.The discovery of ________ has drastically changed our approach to agriculture.42. A _______ (小海星) has five arms and lives in the sea.43. A _______ is a combination of two or more elements that are physically blended but not chemically combined.44.What do we call the place where we learn?A. SchoolB. HospitalC. OfficeD. Farm答案:A45.The fall of the Western Roman Empire occurred in ________ (公元476年).46.The _____ (peach) tree bears sweet fruit.47.I collect _____ (邮票).48.My sister loves to __________ (帮助) younger kids.49.Many cultures celebrate the __________ (植物的生长季节).50. A gas at high pressure can be compressed to form a ______.51.We have a ______ of friends at school. (group)52.The country famous for its fashion is ________ (法国).53.What is the term for a baby bird?A. ChickB. CalfC. PupD. Kit答案:A54.What do you call a baby kangaroo?A. JoeyB. CubC. PupD. Kit55.Sarah is my ______. We play together every day.56.Many plants are _____ (雌雄同体), meaning they have both male and female parts.57.The chemical formula for tartaric acid is ______.58.We had a _________ (玩具派对) where everyone brought their favorite toys.59.What is the name of a baby horse?A. CalfB. FoalC. KidD. Pup60.She is _______ (smiling/crying) because she is happy.61.What do we call the tall structures that touch the sky?A. MountainsB. TreesC. BuildingsD. Hills答案:C62.The ______ is a talented dancer.63.My grandpa is a very nice ____.64.My family celebrates every ____.65.I call my dad “.”66.What do you call the time when the sun goes down?A. SunriseB. SunsetC. NoonD. Midnight67. A compound that has both acidic and basic properties is called an ______.68.The firefighter saves _____ (生命) during emergencies.69.The butterfly emerges from its _________ (蛹).70.I like to _____ (读书) in my spare time.71.The ______ is a talented public speaker.72. A wave can carry energy and information through ______.73.The center of our solar system is the ______.74.Plants can grow in ______ (不同的) environments.75.What is the term for the sudden appearance of a new star in the sky?A. NovaB. SupernovaC. PulsarD. Variable Star76.What do we celebrate on the Fourth of July in the USA?A. ThanksgivingB. Independence DayC. ChristmasD. New Year答案:B77.Which tool is used to cut paper?A. ScissorsB. KnifeC. RulerD. Stapler78.The frog jumps from ______ to ______.79.The _____ (小鸟) fluffs its feathers in the cold.80.How many colors are in the rainbow?A. 5B. 6C. 7D. 881.I like to play with my _________ (拼图) while listening to music.82.What is the color of snow?A. WhiteB. BlackC. GrayD. Blue83.Metalloids have properties of both ________ and nonmetals.84.What do we call the movement of people from one place to another?A. MigrationB. TravelC. DisplacementD. Relocation答案:A85.The crab has a hard _______ (外壳).86.The ______ helps people stay fit.87.Understanding how plants interact with their ______ is essential for ecology. (了解植物如何与环境相互作用对生态学至关重要。
(2024年高考真题含解析)2024年普通高等学校招生全国统一考试英语试卷 新课标Ⅱ卷(含解析)
2024年普通高等学校招生全国统一考试新课标Ⅱ卷英语试卷养成良好的答题习惯，是决定成败的决定性因素之一。
做题前，要认真阅读题目要求、题干和选项，并对答案内容作出合理预测;答题时，切忌跟着感觉走，最好按照题目序号来做，不会的或存在疑问的，要做好标记，要善于发现，找到题目的题眼所在，规范答题，书写工整;答题完毕时，要认真检查，查漏补缺，纠正错误。
本试卷共12页。
考试结束后, 将本试卷和答题卡一并交回。
注意事项: 1. 答题前, 考生先将自己的姓名、准考证号码填写清楚, 将条形码准确粘贴在考生信息条形码粘贴区。
2. 选择题必须使用2B 铅笔填涂; 非选择题必须使用0.5 毫米黑色字迹的签字笔书写, 字体工整、笔迹清楚。
3. 请按照题号顺序在答题卡各题目的答题区域内作答, 超出答题区域书写的答案无效; 在草稿纸、试卷上答题无效。
4. 作图可先使用铅笔画出, 确定后必须用黑色字迹的签字笔描黑。
5. 保持卡面清洁, 不要折叠, 不要弄破、弄皱, 不准使用涂改液、修正带、刮纸刀。
第一部分听力（1—20 小题）在笔试结束后进行。
第二部分阅读（共两节, 满分50分）第一节（共15 小题; 每小题2.5 分, 满分37.5分）阅读下列短文, 从每题所给的A、B、C、D四个选项中选出最佳选项。
AChoice of Walks for Beginner and Experienced WalkersThe Carlow Autumn Walking Festival is a great opportunity for the beginner, experienced or advanced walker to enjoy the challenges of Carlow’s mountain hikes or the peace of its woodland walks.Walk 1 — The Natural WorldWith environmentalist Éanna Lamhna as the guide, this walk promises to be an informative tour. Walkers are sure to learn lots about the habitats and natural world of the Blackstairs.Date and Time: Saturday, 1st October, at 09:00Start Point: Scratoes BridgeWalk Duration: 6 hoursWalk 2 — Introduction to HillwalkingEmmanuel Chappard, an experienced guide, has a passion for making the great outdoors accessible to all. This mountain walk provides an insight into the skills required for hillwalking to ensure you get the most from future walking trips.Date and Time: Sunday, 2nd October, at 09:00Start Point: Deerpark Car ParkWalk Duration: 5 hoursWalk 3 — Moonlight Under the StarsWalking at night-time is a great way to step out of your comfort zone. Breathtaking views of the lowlands of Carlow can be enjoyed in the presence of welcoming guides from local walking clubs. A torch (手电筒) along with suitable clothing is essential for walking in the dark. Those who are dressed inappropriately will be refused permission to participate.Date and Time: Saturday, 1st October, at 18:30Start Point: The Town HallWalk Duration: 3 hoursWalk 4 — Photographic Walk in Kilbrannish ForestThis informative walk led by Richard Smyth introduces you to the basic principles of photography in the wild. Bring along your camera and enjoy the wonderful views along this well-surfaced forest path.Date and Time: Sunday, 2nd October, at 11:45Start Point: Kilbrannish Forest Recreation AreaWalk Duration: 1.5 hours1. Which walk takes the shortest time?A. The Natural World.B. Introduction to Hillwalking.C. Moonlight Under the Stars.D. Photographic Walk in Kilbrannish Forest.2. What are participants in Walk 3 required to do?A. Wear proper clothes.B. Join a walking club.C. Get special permits.D. Bring a survival guide.3. What do the four walks have in common?A. They involve difficult climbing.B. They are for experienced walkers.C. They share the same start point.D. They are scheduled for the weekend.BDo you ever get to the train station and realize you forgot to bring something to read? Yes, we all have our phones, but many of us still like to go old school and read something printed.Well, there’s a kiosk (小亭) for that. In the San Francisco Bay Area, at least.“You enter the fare gates (检票口) and you’ll see a kiosk that is lit up and it tells you can get a one-minute, a three-minute, or a five-minute story,” says Alicia Trost, the chief communications officer for the San Francisco Bay Area Rapid Transit —known as BART. “You choose which length you want and it gives you a receipt-like short story.”It’s that simple. Riders have printed nearly 20,000 short stories and poems since the program was launched last March. Some are classic short stories, and some are new original works.Trost also wants to introduce local writers to local riders. “We wanted to do something where we do a call to artists in the Bay Area to submit stories for a contest,” Trost says. “And as of right now, we’ve received about 120 submissions. The winning stories would go into our kiosk and then you would be a published artist.”Ridership on transit (交通) systems across the country has been down the past half century, so could short stories save transit?Trost thinks so.“At the en d of the day all transit agencies right now are doing everything they can to improve the rider experience. So I absolutely think we will get more riders just because of short stories” she says.And you’ll never be without something to read.4 Why did BART start the kiosk program?A. To promote the local culture.B. To discourage phone use.C. To meet passengers’ needs.D. To reduce its running costs.5. How are the stories categorized in the kiosk?A. By popularity.B. By length.C. By theme.D. By language.6. What has Trost been doing recently?A. Organizing a story contest.B. Doing a survey of customers.C. Choosing a print publisher.D. Conducting interviews with artists.7. What is Trost’s opinion about BART’s future?A. It will close down.B. Its profits will decline.C. It will expand nationwide.D. Its ridership will increase.CWe all know fresh is best when it comes to food. However, most produce at the store went through weeks of travel and covered hundreds of miles before reaching the tab le. While farmer’s markets are a solid choice to reduce the journey, Babylon Micro-Farm (BMF) shortens it even more.BMF is an indoor garden system. It can be set up for a family. Additionally, it could serve a larger audience such as a hospital, restaurant or school. The innovative design requires little effort to achieve a reliable weekly supply of fresh greens.Specifically, it’s a farm that relies on new technology. By connecting through the Cloud, BMF is remotely monitored. Also, there is a convenient app that provides growing data in real time. Because the system is automated, it significantly reduces the amount of water needed to grow plants. Rather than watering rows of soil, the system provides just the right amount to each plant. After harvest, users simply replace the plants with a new pre-seeded pod (容器) to get the next growth cycle started.Moreover, having a system in the same building where it’s eaten means zero emissions (排放) from transporting plants from soil to salad. In addition, there’s no need for pesticides and other chemicals that pollute traditional farms and the surrounding environment.BMF employees live out sustainability in their everyday lives. About half of them walk or bike to work. Inside the office, they encourage recycling and waste reduction by limiting garbage cans and avoiding single-use plastic. “We are passionate about reducing waste, carbon and chemicals in our environment,” said a BMF employee.8. What can be learned about BMF from paragraph 1?A. It guarantees the variety of food.B. It requires day-to-day care.C. It cuts the farm-to-table distance.D. It relies on farmer’s markets.9. What information does the convenient app offer?A Real-time weather changes. B. Current condition of the plants.C. Chemical pollutants in the soil.D. Availability of pre-seeded pods.10. What can be concluded about BMF employees?A. They have a great passion for sports.B. They are devoted to community service.C. They are fond of sharing daily experiences.D. They have a strong environmental awareness.11. What does the text mainly talk about?A. BMF’s major strengths.B. BMF’s general management.C. BMF’s global influence.D. BMF’s technical standards.DGiven the astonishing potential of AI to transform our lives, we all need to take action to deal with ourAI-powered future, and this is where AI by Design: A Plan for Living with Artificial Intelligence comes in. This absorbing new book by Catriona Campbell is a practical roadmap addressing the challenges posed by the forthcoming AI revolution (变革).In the wrong hands, such a book could prove as complicated to process as the computer code (代码) that powers AI but, thankfully, Campbell has more than two decades’ professional experience translating the heady into the understandable. She writes from the practical angle of a business person rather than as an academic, making for a guide which is highly accessible and informative and which, by the close, will make you feel almost as smart as AI.As we soon come to learn from AI by Design, AI is already super-smart and will become more capable, moving from the current generation of “narrow-AI” to Artificial General Intelligence. From there, Campbell says, will come Artificial Dominant Intelligence. This is why Campbell has set out to raise awareness of AI and its future now —several decades before these developments are expected to take place. She says it is essential that we keep control of artificial intelligence, or risk being sidelined and perhaps even worse.Campbell’s poin t is to wake up those responsible for AI-the technology companies and world leaders—so they are on the same page as all the experts currently developing it. She explains we are at a “tipping point” in history and must act now to prevent an extinction-level event for humanity. We need to consider how we want our future with AI to pan out. Such structured thinking, followed by global regulation, will enable us to achieve greatness rather than our downfall.AI will affect us all, and if you only read one book on the subject, this is it.12. What does the phrase “In the wrong hands” in paragraph 2 probably mean?A. If read by someone poorly educated.B. If reviewed by someone ill-intentioned.C. If written by someone less competent.D. If translated by someone unacademic.13. What is a feature of AI by Design according to the text?A. It is packed with complex codes.B. It adopts a down-to-earth writing style.C. It provides step-by-step instructions.D. It is intended for AI professionals.14. What does Campbell urge people to do regarding AI development?A. Observe existing regulations on it.B. Reconsider expert opinions about it.C. Make joint efforts to keep it under control.D. Learn from prior experience to slow it down.15. What is the author’s pur pose in writing the text?A. To recommend a book on AI.B. To give a brief account of AI history.C. To clarify the definition of AI.D. To honor an outstanding AI expert.第二节（共5小题; 每小题2.5分, 满分12.5分）阅读下面短文, 从短文后的选项中选出可以填入空白处的最佳选项。
高二生物学与环境保护英语阅读理解30题
高二生物学与环境保护英语阅读理解30题1<背景文章>The tropical rainforest is one of the most fascinating and important ecosystems on Earth. It is a place of extraordinary beauty and teeming with life. The rainforest is home to an incredibly diverse range of plant and animal species.The canopy of the rainforest is like a complex web of life. It is filled with colorful birds, agile monkeys, and countless insects. The understory is also rich in life, with unique plants and smaller animals. The forest floor is covered with fallen leaves and branches, providing a habitat for many organisms.However, the tropical rainforest is facing many threats. Deforestation is one of the major issues. Logging, agriculture, and urbanization are destroying large areas of rainforest. This not only leads to the loss of habitats for countless species but also has a significant impact on the global climate.Climate change is another threat to the rainforest. Rising temperatures and changing rainfall patterns can disrupt the delicate balance of the ecosystem.To protect the tropical rainforest, various measures need to be taken.Conservation efforts should be increased. Governments and organizations should work together to enforce laws against deforestation. Sustainable development practices should be promoted to ensure that economic growth does not come at the expense of the environment.1. The tropical rainforest is home to a ______ range of plant and animal species.A. limitedB. diverseC. fewD. similar答案：B。
高二英语询问植物界别单选题50题
高二英语询问植物界别单选题50题1. In the botanical garden, we saw a plant with seeds that are not enclosed in a fruit. Which type of plant is it?A. AngiospermB. GymnospermC. FernD. Moss答案：B。
解析：裸子植物（Gymnosperm）的种子是裸露的，不被果实包裹，这是裸子植物的重要特征。
被子植物（Angiosperm）的种子是被果实包裹的，蕨类植物（Fern）主要通过孢子繁殖，苔藓植物 Moss）也是通过孢子繁殖，所以A、C、D选项不符合。
2. A researcher in the plant laboratory is studying a plant that has flowers and produces seeds enclosed in a fruit. This plant is most likely to be a(n) _.A. GymnospermB. BryophyteC. AngiospermD. Pteridophyte答案：C。
解析：被子植物 Angiosperm）具有花朵，并且种子被包裹在果实内，这是被子植物区别于其他植物类群的典型特征。
裸子植物（Gymnosperm）种子裸露，苔藓植物（Bryophyte）没有种子，靠孢子繁殖，蕨类植物（Pteridophyte）也是靠孢子繁殖，所以A、B、D选项错误。
3. When we walked in the botanical garden, we noticed a plant without flowers but with cones. What kind of plant is it?A. AngiospermB. GymnospermC. AlgaeD. Fungi答案：B。
初三年级英文科普文章英语阅读理解20题
初三年级英文科普文章英语阅读理解20题1<背景文章>Artificial intelligence (AI) has been making remarkable strides in the medical field in recent years. AI - powered systems are being used for a variety of applications, from disease diagnosis to assisting in treatment and the development of medical robots.In the area of disease diagnosis, AI algorithms can analyze large amounts of medical data, such as patient records, symptoms, and test results. For example, they can detect patterns in X - ray or MRI images that might be difficult for human doctors to spot. This can lead to earlier and more accurate diagnoses of diseases like cancer. AI can also predict the likelihood of a patient developing a certain disease based on their genetic information, lifestyle factors, and family history.When it comes to assisting in treatment, AI can help doctors plan the best course of treatment for a patient. It can analyze the effectiveness of different drugs and therapies based on data from previous patients. This allows doctors to make more informed decisions and choose the treatment that is most likely to be successful for an individual patient.Medical robots are another area where AI is having a significant impact. Robots can be used in surgeries, providing more precisemovements than human hands. They can also be used to assist patients in rehabilitation, monitoring their progress and adjusting the rehabilitation program accordingly.However, the use of AI in medicine also brings some challenges. There are concerns about data privacy and security, as AI systems rely on large amounts of patient data. There are also ethical issues, such as who is responsible if an AI - based diagnosis or treatment goes wrong. Despite these challenges, the potential benefits of AI in the medical field are vast and are likely to continue to grow in the future.1. What can AI algorithms do in disease diagnosis according to the passage?A. Only analyze patient records.B. Detect patterns in medical images which are easy for human doctors.C. Predict the likelihood of a patient developing a disease based on some factors.D. Replace human doctors completely.答案：C。
木本植物应对干旱胁迫的响应机制：基于水力学性状视角
第４４卷第７期２０２４年４月生态学报ＡＣＴＡＥＣＯＬＯＧＩＣＡＳＩＮＩＣＡＶｏｌ．４４，Ｎｏ．７Ａｐｒ．，２０２４基金项目：国家自然科学基金项目（３２０７１８４５）；甘肃省科技计划资助（２３ＪＲＲＡ５７２）；内蒙古自治区科技重大专项（２０２１ＺＤ００１５）；甘肃省科技计划资助（２３ＪＲＲＡ６７１）收稿日期：２０２３⁃０５⁃２０；㊀㊀网络出版日期：２０２４⁃０１⁃１２∗通讯作者Ｃｏｒｒｅｓｐｏｎｄｉｎｇａｕｔｈｏｒ．Ｅ⁃ｍａｉｌ：ｌｉｙｌ＠ｌｚｂ．ａｃ．ｃｎＤＯＩ：１０．２０１０３／ｊ．ｓｔｘｂ．２０２３０５２０１０６５程莉，李玉霖，宁志英，杨红玲，詹瑾，姚博．木本植物应对干旱胁迫的响应机制：基于水力学性状视角．生态学报，２０２４，４４（７）：２６８８⁃２７０５．ＣｈｅｎｇＬ，ＬｉＹＬ，ＮｉｎｇＺＹ，ＹａｎｇＨＬ，ＺｈａｎＪ，ＹａｏＢ．Ｒｅｓｐｏｎｓｅｍｅｃｈａｎｉｓｍｓｏｆｗｏｏｄｙｐｌａｎｔｓｔｏｄｒｏｕｇｈｔｓｔｒｅｓｓ：ａｒｅｖｉｅｗｂａｓｅｄｏｎｐｌａｎｔｈｙｄｒａｕｌｉｃｔｒａｉｔｓ．ＡｃｔａＥｃｏｌｏｇｉｃａＳｉｎｉｃａ，２０２４，４４（７）：２６８８⁃２７０５．木本植物应对干旱胁迫的响应机制：基于水力学性状视角程㊀莉１，２，李玉霖１，２，３，∗，宁志英１，２，杨红玲１，２，詹㊀瑾１，２，姚㊀博１，２１中国科学院西北生态环境资源研究院，兰州㊀７３００００２中国科学院大学，北京㊀１０００４９３中国科学院西北生态环境资源研究院奈曼沙漠化研究站，通辽㊀０２８３００摘要：干旱最显著的影响表现在区域尺度的森林死亡事件中，可以在短时间内杀死数百万棵树木㊂鉴于未来极端干旱事件的频率和强度可能随温度的升高而增加，迫切需要明确树木对干旱胁迫的响应对策以及衰退死亡机理，揭示木本植物在干旱环境中存活和死亡的生理机制，了解树木在未来气候下的适应机制，提高预测树木对干旱反应的准确性㊂在常用植物功能性状的基础上，重点纳入与植物水分运输能力及耐旱性相关的水力学性状，系统总结了：１）植物木质部水分运输的物理机制；２）植物应对干旱胁迫的水力响应过程：３）干旱胁迫下木本植物水分利用对策；以及４）干旱胁迫下木本植物衰退／死亡机理㊂最后，提出３个尚待解决的主要问题：１）加强纳入水力性状阐明植物对干旱胁迫的响应和调节机制；２）加强从全株植物的角度考虑植物不同组织性状间的关系；３）深入探究树木干旱致死机理㊂关键词：木本植物；干旱胁迫；水力性状；水分运输策略；干旱致死机理Ｒｅｓｐｏｎｓｅｍｅｃｈａｎｉｓｍｓｏｆｗｏｏｄｙｐｌａｎｔｓｔｏｄｒｏｕｇｈｔｓｔｒｅｓｓ：ａｒｅｖｉｅｗｂａｓｅｄｏｎｐｌａｎｔｈｙｄｒａｕｌｉｃｔｒａｉｔｓＣＨＥＮＧＬｉ１，２，ＬＩＹｕｌｉｎ１，２，３，∗，ＮＩＮＧＺｈｉｙｉｎｇ１，２，ＹＡＮＧＨｏｎｇｌｉｎｇ１，２，ＺＨＡＮＪｉｎ１，２，ＹＡＯＢｏ１，２１ＮｏｒｔｈｗｅｓｔＩｎｓｔｉｔｕｔｅｏｆＥｃｏ⁃ＥｎｖｉｒｏｎｍｅｎｔａｎｄＲｅｓｏｕｒｃｅｓ，ＣｈｉｎｅｓｅＡｃａｄｅｍｙｏｆＳｃｉｅｎｃｅｓ，Ｌａｎｚｈｏｕ７３００００，Ｃｈｉｎａ２ＵｎｉｖｅｒｓｉｔｙｏｆＣｈｉｎｅｓｅＡｃａｄｅｍｙｏｆＳｃｉｅｎｃｅｓ，Ｂｅｉｊｉｎｇ１０００４９，Ｃｈｉｎａ３ＮａｉｍａｎＤｅｓｅｒｔｉｆｉｃａｔｉｏｎＲｅｓｅａｒｃｈＳｔａｔｉｏｎ，ＮｏｒｔｈｗｅｓｔＩｎｓｔｉｔｕｔｅｏｆＥｃｏ⁃ＥｎｖｉｒｏｎｍｅｎｔａｎｄＲｅｓｏｕｒｃｅｓ，ＣｈｉｎｅｓｅＡｃａｄｅｍｙｏｆＳｃｉｅｎｃｅｓ，Ｔｏｎｇｌｉａｏ０２８３００，ＣｈｉｎａＡｂｓｔｒａｃｔ：Ｔｈｅｍｏｓｔｎｏｔａｂｌｅｅｆｆｅｃｔｓｏｆｄｒｏｕｇｈｔａｒｅｍａｎｉｆｅｓｔｅｄｉｎｒｅｇｉｏｎａｌ⁃ｓｃａｌｅｆｏｒｅｓｔｍｏｒｔａｌｉｔｙｅｖｅｎｔｓ，ｗｈｉｃｈｃａｎｋｉｌｌｍｉｌｌｉｏｎｓｏｆｔｒｅｅｓｉｎａｓｈｏｒｔｔｉｍｅ，ｆｕｒｔｈｅｒａｆｆｅｃｔｉｎｇｒｅｇｉｏｎａｌｃｌｉｍａｔｅａｎｄｅｃｏｓｙｓｔｅｍｓｔｒｕｃｔｕｒｅａｎｄｆｕｎｃｔｉｏｎ．Ｇｉｖｅｎｔｈａｔｔｈｅｆｒｅｑｕｅｎｃｙａｎｄｉｎｔｅｎｓｉｔｙｏｆｅｘｔｒｅｍｅｄｒｏｕｇｈｔｅｖｅｎｔｓｉｎｔｈｅｆｕｔｕｒｅｍａｙｉｎｃｒｅａｓｅｗｉｔｈｉｎｃｒｅａｓｉｎｇｔｅｍｐｅｒａｔｕｒｅ，ｉｔｉｓｕｒｇｅｎｔｔｏｃｌａｒｉｆｙｔｈｅｒｅｓｐｏｎｓｅｓｔｒａｔｅｇｉｅｓｏｆｔｒｅｅｓｔｏｄｒｏｕｇｈｔｓｔｒｅｓｓａｎｄｔｈｅｍｅｃｈａｎｉｓｍｓｏｆｔｈｅｉｒｓｕｒｖｉｖａｌａｎｄｄｅａｔｈ，ｒｅｖｅａｌｔｈｅｐｈｙｓｉｏｌｏｇｉｃａｌｍｅｃｈａｎｉｓｍｏｆｗｏｏｄｙｐｌａｎｔｓｉｎａｒｉｄｅｎｖｉｒｏｎｍｅｎｔ，ｕｎｄｅｒｓｔａｎｄｔｈｅａｄａｐｔａｔｉｏｎｍｅｃｈａｎｉｓｍｏｆｔｒｅｅｓｉｎｆｕｔｕｒｅｃｌｉｍａｔｅｓ，ａｎｄｉｍｐｒｏｖｅｔｈｅａｃｃｕｒａｃｙｏｆｐｒｅｄｉｃｔｉｎｇｔｈｅｒｅｓｐｏｎｓｅｏｆｔｒｅｅｓｔｏｄｒｏｕｇｈｔｓｔｒｅｓｓ．Ｐｌａｎｔｆｕｎｃｔｉｏｎａｌｔｒａｉｔｓｒｅｆｅｒｔｏｔｈｅｍｏｒｐｈｏｌｏｇｉｃａｌ，ｐｈｙｓｉｏｌｏｇｉｃａｌ，ｏｒｐｈｅｎｏｌｏｇｉｃａｌｃｈａｒａｃｔｅｒｉｓｔｉｃｓｏｆｐｌａｎｔｓａｔｔｈｅｉｎｄｉｖｉｄｕａｌｌｅｖｅｌ，ｗｈｉｃｈｉｎｄｉｒｅｃｔｌｙａｆｆｅｃｔｔｈｅｐｅｒｆｏｒｍａｎｃｅｏｆｐｌａｎｔｓｂｙｄｉｒｅｃｔｌｙａｆｆｅｃｔｉｎｇｔｈｅｇｒｏｗｔｈ，ｓｕｒｖｉｖａｌｏｒｒｅｐｒｏｄｕｃｔｉｏｎｏｆｐｌａｎｔｓ，ａｎｄａｔｔｈｅｓａｍｅｔｉｍｅｒｅｆｌｅｃｔｔｈｅｌｏｎｇ⁃ｔｅｒｍａｄａｐｔａｔｉｏｎｏｆｐｌａｎｔｓｔｏｔｈｅｇｒｏｗｔｈｅｎｖｉｒｏｎｍｅｎｔ．Ｐｌａｎｔｆｕｎｃｔｉｏｎａｌｔｒａｉｔｓａｎｄｔｈｅｉｒｖａｒｉａｔｉｏｎｒｅｇｕｌａｔｉｏｎｓｃａｎｂｅｕｓｅｄｔｏｅｘｐｌａｉｎｔｈｅａｄａｐｔｉｖｅｍｅｃｈａｎｉｓｍａｎｄｆｕｎｃｔｉｏｎａｌｏｐｔｉｍｉｚａｔｉｏｎｍｅｃｈａｎｉｓｍｏｆｐｌａｎｔｓｔｏｔｈｅｅｎｖｉｒｏｎｍｅｎｔ，ａｎｄｈｅｌｐｔｏｐｒｅｄｉｃｔｔｈｅｒｅｓｐｏｎｓｅｏｆｔｒｅｅｓｔｏｄｒｏｕｇｈｔ．Ｃｏｍｐａｒｅｄｗｉｔｈｃｏｍｍｏｎｌｙｕｓｅｄｐｌａｎｔｆｕｎｃｔｉｏｎａｌｔｒａｉｔｓ，ｈｙｄｒａｕｌｉｃｔｒａｉｔｓｍａｙｂｅｔｔｅｒｄｅｓｃｒｉｂｅｔｈｅｒｅｓｐｏｎｓｅｏｆｔｒｅｅｓｔｏｄｒｏｕｇｈｔｓｔｒｅｓｓ．Ｏｎｔｈｅｂａｓｉｓｏｆｃｏｍｍｏｎｐｌａｎｔｆｕｎｃｔｉｏｎａｌｔｒａｉｔｓ，ｗｅｉｎｃｒｅａｓｅｄｔｈｅｈｙｄｒａｕｌｉｃｔｒａｉｔｓｗｈｉｃｈａｒｅｒｅｌａｔｅｄｔｏｗａｔｅｒｔｒａｎｓｐｏｒｔｃａｐａｃｉｔｙａｎｄｄｒｏｕｇｈｔｔｏｌｅｒａｎｃｅａｎｄｓｙｓｔｅｍａｔｉｃａｌｌｙｓｕｍｍａｒｉｚｅｄ：１）ｔｈｅｐｈｙｓｉｃａｌｍｅｃｈａｎｉｓｍｏｆｌｏｎｇ⁃ｄｉｓｔａｎｃｅｗａｔｅｒｔｒａｎｓｐｏｒｔｉｎｘｙｌｅｍ；２）ｐｈａｓｅｓｏｆｄｒｏｕｇｈｔｓｔｒｅｓｓａｎｄｔｈｅｒｅｓｐｏｎｓｅｏｆｐｌａｎｔｓ；３）ｐｌａｓｔｉｃｉｔｙｉｎｐｌａｎｔｆｕｎｃｔｉｏｎａｌｔｒａｉｔｓａｎｄｗａｔｅｒｒｅｇｕｌａｔｉｏｎｓｔｒａｔｅｇｉｅｓ：Ｉｓｏｈｙｄｒｉｃｒｅｇｕｌａｔｉｏｎｓｔｒａｔｅｇｙａｎｄａｎｉｓｏｈｙｄｒｉｃｒｅｇｕｌａｔｉｏｎｓｔｒａｔｅｇｙ，ｘｙｌｅｍｅｆｆｉｃｉｅｎｃｙ⁃ｓａｆｅｔｙｔｒａｄｅ⁃ｏｆｆｓｔｒａｔｅｇｙ，ｃｏｎｓｅｒｖａｔｉｖｅｗａｔｅｒｕｓｅｓｔｒａｔｅｇｙａｎｄｒｉｓｋ⁃ｔａｋｉｎｇｗａｔｅｒｕｓｅｓｔｒａｔｅｇｙ；ａｎｄ４）ｍｅｃｈａｎｉｓｍｓｏｆｄｒｏｕｇｈｔ⁃ｒｅｌａｔｅｄｍｏｒｔａｌｉｔｙ：ｈｙｄｒａｕｌｉｃｆａｉｌｕｒｅｈｙｐｏｔｈｅｓｉｓ，ｃａｒｂｏｎｓｔａｒｖａｔｉｏｎｈｙｐｏｔｈｅｓｉｓａｎｄｂｉｏｔｉｃａｇｅｎｔｓｈｙｐｏｔｈｅｓｉｓ．Ｆｉｎａｌｌｙ，ｔｈｒｅｅｍａｉｎｐｒｏｂｌｅｍｓｗｅｒｅｐｕｔｆｏｒｗａｒｄｔｏｂｅｓｏｌｖｅｄ：１）ｓｔｒｅｎｇｔｈｅｎｉｎｇｔｈｅｉｎｃｌｕｓｉｏｎｏｆｈｙｄｒａｕｌｉｃｔｒａｉｔｓｔｏｃｌａｒｉｆｙｔｈｅｒｅｓｐｏｎｓｅａｎｄｒｅｇｕｌａｔｉｏｎｍｅｃｈａｎｉｓｍｏｆｐｌａｎｔｓｔｏｄｒｏｕｇｈｔｓｔｒｅｓｓ，ｕｎｄｅｒｓｔａｎｄｉｎｇａｎｄｐｒｅｄｉｃｔｉｎｇｐｌａｎｔｓｕｒｖｉｖａｌ，ｇｒｏｗｔｈ，ｄｉｓｔｒｉｂｕｔｉｏｎａｎｄｄｅａｔｈｉｎｔｈｅｃｏｎｔｅｘｔｏｆｇｌｏｂａｌｃｈａｎｇｅ．２）ｓｔｒｅｎｇｔｈｅｎｉｎｇｔｈｅｃｏｎｓｉｄｅｒａｔｉｏｎｏｆｔｈｅｒｅｌａｔｉｏｎｓｈｉｐｂｅｔｗｅｅｎｄｉｆｆｅｒｅｎｔｐｌａｎｔｔｉｓｓｕｅｔｒａｉｔｓｆｒｏｍｔｈｅｐｅｒｓｐｅｃｔｉｖｅｏｆｔｈｅｗｈｏｌｅｐｌａｎｔ，ｒｅｖｅａｌｉｎｇｔｈｅｄｉｓｔｒｉｂｕｔｉｏｎｃｈａｒａｃｔｅｒｉｓｔｉｃｓｏｆｐｌａｎｔｓｉｎｔｈｅｅｃｏｓｙｓｔｅｍ，ａｎｄｐｒｅｄｉｃｔｉｎｇｃｏｍｍｕｎｉｔｙｃｏｍｐｏｓｉｔｉｏｎ；３）ｔｈｅｐｒｅｃｉｓｅｐｈｙｓｉｏｌｏｇｉｃａｌｍｅｃｈａｎｉｓｍｂｅｈｉｎｄｔｒｅｅｄｅａｔｈｉｓｓｔｉｌｌｕｎｃｌｅａｒ，ｆｕｔｕｒｅｓｔｕｄｉｅｓｎｅｅｄｔｏｆｕｒｔｈｅｒｅｘｐｌｏｒｅｔｈｅｍｅｃｈａｎｉｓｍｓｏｆｄｒｏｕｇｈｔ⁃ｒｅｌａｔｅｄｍｏｒｔａｌｉｔｙ．ＫｅｙＷｏｒｄｓ：ｗｏｏｄｙｐｌａｎｔｓ；ｄｒｏｕｇｈｔｓｔｒｅｓｓ；ｈｙｄｒａｕｌｉｃｔｒａｉｔｓ；ｗａｔｅｒｒｅｇｕｌａｔｉｏｎｓｔｒａｔｅｇｉｅｓ；ｄｒｏｕｇｈｔ⁃ｒｅｌａｔｅｄｍｏｒｔａｌｉｔｙｍｅｃｈａｎｉｓｍｓ㊀自工业革命以来，不断增强的人类活动导致了全球变暖［１ ２］㊂联合国政府间气候变化专门委员会（ＩＰＣＣ）评估报告表明，２０１１ ２０２０年全球地表温度比１８５０ １９００年高出１．１ħ，预计在２０２１ ２０４０年全球升温或将达到１．５ħ㊂随着气温上升，未来干旱肯定会恶化（当自然干旱发生时，它们会来的更快，强度更大）［３］㊂较高的温度通常会导致更大的蒸散，与温度较低时相比，土壤和植物会更快的干燥［４］㊂这种 全球变化型干旱 已经对生态系统产生了严重影响，比如大量树木死亡［５ ６］㊂区域尺度上的树木死亡事件改变了地表反照率以及地表⁃大气能量和潜热交换，对区域气候产生反馈［７］；广泛的树木死亡事件有能力在十年以下的时间尺度内从根本上改变区域尺度的景观，对生态系统结构和功能产生重大影响［８］㊂在此背景下，我们必须提高预测树木对干旱反应的准确性，以了解树木在未来气候制度下的适应能力［９］㊂植物功能性状是指植物在个体水平上的形态㊁生理或物候特征，它们通过直接影响植物的生长㊁存活或繁殖，从而间接影响植物的性能［１０ １１］，同时反映植物对生长环境的长期适应［１２］㊂植物功能性状有助于预测树木对干旱的响应［１２ １３］㊂近３０多年来，科研人员常使用植物功能性状及其变异规律来解释植物对环境的适应机制和功能优化机制㊂然而，随着研究的深入，人们逐步发现自然界生长的植物均是通过多个功能性状共同来完成其适应或功能优化，或者说任何一种功能均是通过多种功能性状来协同实现㊂准确量化这些多性状间的权衡和依赖关系，有助于我们更好地揭示植物的生境适应策略㊂然而，研究发现：１）常用植物功能性状的变异性与降水梯度并不一致，例如平均年降水量（Ｍｅａｎａｎｎｕａｌｐｒｅｃｉｐｉｔａｔｉｏｎ，ＭＡＰ）对全球尺度上自然生物群系比叶面积（Ｓｐｅｃｉｆｉｃｌｅａｆａｒｅａ，ＳＬＡ）变异的解释率不到１％；２）常用植物功能性状与干旱引起的树木死亡率的跨物种模式仅存在微弱的相关性，例如纳入ＳＬＡ和木材密度（Ｗｏｏｄｄｅｎｓｉｔｙ，ＷＤ）时，模型对物种死亡率的解释率从只考虑干旱的３０％增加到３７％［１４］㊂相比之下，水力性状可能更好地描述树木对干旱胁迫的响应㊂近年来发现反映植物水分运输能力或植物耐旱性的水力性状如叶片的最大导水率（Ｋｍａｘ）㊁膨压消失点叶水势（Ψｔｌｐ）㊁水力安全边际（Ｈｙｄｒａｕｌｉｃｓａｆｅｔｙｍａｒｇｉｎ，ＨＳＭ）等与降水梯度高度吻合［１５ １７］㊂因此纳入水力性状阐明植物对干旱的响应和调节机制，对于理解和预测全球变化背景下植物生存㊁生长㊁分布以及死亡有着重要意义㊂鉴于未来极端干旱事件的频率和强度可能随温度的升高而增加，迫切需要更好地了解植物对干旱胁迫的应对和调节机制以及不同植物的干旱致死机制，本文重点阐述了：１）植物木质部水分运输的物理机制；２）干旱胁迫下植物的水力响应过程；３）植物水分利用策略的多样性；以及４）植物干旱致死机理㊂９８６２㊀７期㊀㊀㊀程莉㊀等：木本植物应对干旱胁迫的响应机制：基于水力学性状视角㊀１㊀植物体内的水分传输与所有维管植物一样，木本植物通过一个复杂的中空死亡细胞（导管或管胞）管道系统，即木质部，将水分从土壤输送到叶片来防止干燥损伤［９］㊂植物木质部长距离水分运输是保证植物体内水分平衡㊁叶片气孔运动㊁光合作用以及其它各种代谢活动的主要纽带，被称为 植物生理学的支柱 ［１８］㊂综述植物体内木质部长距离水分运输过程，特别是了解防止植物蒸腾速率（Ｅ）超过临界速率（Ｅｃｒｉｔ）的结构和生理机制，有助于理解植物发生水力失败和碳饥饿的风险：１）临界蒸腾速率会导致与水力失败和共质体失败相关的木质部水势阈值（Ψｃｒｉｔ）的发生；２）此外，避免Ｅｃｒｉｔ（关闭气孔）对光合作用的影响以及随后对碳水化合物储备的影响对理解碳饥饿至关重要［１９ ２０］㊂为了维持组织的水合和光合作用，植物必须补充蒸腾作用损失的水分［８］㊂内聚力⁃张力假说（Ｃ⁃Ｔ理论）认为，蒸腾拉力是水分沿木质部上升的主要驱动力，叶面的蒸腾拉力将土壤中的水分通过植物木质部长距离运输提升到冠层并扩散到大气中［８，２１ ２２］，这样从根系到叶片的水就能补充蒸腾作用损失的水分［２３］㊂其中，蒸腾拉力（Ｅ）可以通过土壤⁃植物⁃大气水力连续体的稳态公式明确描述［８］：Ｅ＝Ｋ１（Ψｓ－Ψｌｅａｆ－ｈρｗｇ）式中，Ｅ为叶片蒸腾拉力，Ｋ１为叶片水力导度，Ψｓ是土壤水势，Ψｌｅａｆ是叶水势，ｈρｗｇ是高度为ｈ，密度为ρｗ的水柱的重力拉力㊂当Ｅ为０时，Ψｌｅａｆ＝Ψｓ（图１Ａ，ａ点）㊂随着Ｅ的增加，当Ｋ１保持不变时，导管并未发生空穴化，植物体内的张力差（Ψｓ－Ψｌｅａｆ）与Ｅ成正比，Ψｌｅａｆ逐渐下降（图１左，虚线ａ ｂ）㊂然而气种假说表明：木质部导管中的水柱在张力作用下处于亚稳定状态，导管中的亚稳态液流所承受的张力随Ｅ的增加而增加，此时空气经由木质部导管壁上的纹孔膜进入导管，导管开始发生空穴化，空穴化的发展逐渐加重木质部导管栓塞程度，Ｋ１逐渐下降㊂当Ｅ每增加一个单位时，由于Ｋ１的下降，会导致Ψｌｅａｆ的下降逐渐增大（图１左，实线ａ ｃ）㊂当Ｅ超过Ｅｃｒｉｔ时，木质部水势（Ψ）超过Ψｃｒｉｔ，则会发生水力失败㊂在干旱胁迫发生时，干旱降低了根区的Ψｓ，植物在Ｅ较低时便会发生水力失败（图１右，将实线ａ ｃ和实线ｄ ｅ进行比较）㊂在昼夜尺度上，植物通过关闭气孔保持Ｅ低于Ｅｃｒｉｔ（植物通过降低气孔导度（Ｇｓ）来响应增加的Ｅ［２４］，气孔闭合程度与导致栓塞的Ψｃｒｉｔ有关［２５］）㊂减少Ｇｓ的好处是减少水分损失，但他的代价是减少二氧化碳（ＣＯ２）从大气扩散到羧基化位点，从而限制光合作用对ＣＯ２的吸收［２０］，这种水分流失和ＣＯ２吸收之间的平衡可能会在干旱期间导致植物出现生存㊁水力衰竭和碳饥饿三种结果㊂图１㊀基于达西定律模型求解的蒸腾拉力（Ｅ）与叶水势（Ψｌｅａｆ）的变化Ｆｉｇ．１㊀Ｔｈｅｔｒａｎｓｐｉｒａｔｉｏｎｒａｔｅ（Ｅ）ｖｅｒｓｕｓｌｅａｆｗａｔｅｒｐｏｔｅｎｔｉａｌ（Ψｌｅａｆ）ｉｓｂａｓｅｄｏｎｔｈｅｍｏｄｅｌｓｏｌｕｔｉｏｎｏｆＤａｒｃｙᶄｓｌａｗΨｓ是土壤水势；Ｅｃｒｉｔ是最大蒸腾速率，取决于Ψｓ；Ψｃｒｉｔ是Ｅｃｒｉｔ处的Ψｌｅａｆ，也是允许水分吸收的最低Ψｓ２㊀植物应对干旱胁迫的水力响应过程植物应对干旱胁迫的响应过程主要分为两个阶段：１）干旱胁迫开始到气孔闭合期间；２）气孔闭合到木质０９６２㊀生㊀态㊀学㊀报㊀㊀㊀４４卷㊀部完全栓塞期间［２６］㊂在干旱期间，降水减少导致土壤湿度下降，这往往伴随着更高的温度和增加的大气蒸发需求，这些因素结合在一起引起植物的水分胁迫，导致植物Ψｘ下降（木质部水柱所受张力增加），因此植物关闭气孔以限制水分流失和延缓Ψｘ的下降㊂最近研究表明，尽管气孔关闭会造成一系列负面影响，但气孔仍旧会在木质部水势达到明显的气穴化形成阈值（气孔导度损失８８％对应的水势值，ｔｈｅｗａｔｅｒｐｏｔｅｎｔｉａｌａｔ８８％ｌｏｓｓｏｆｓｔｏｍａｔａｌｃｏｎｄｕｃｔａｎｃｅ，Ｐｇｓ８８）之前关闭［２６ ２８］㊂气孔关闭后，Ψｘ随着水分通过气孔渗漏［２９］以及表皮和树皮等其他组织损失而继续缓慢下降，植物通过释放内部储存水来缓冲Ψｘ的下降［３０］㊂与此同时，植物整个水力途径的水力导度通过一系列生物物理和生理机制而下降，比如叶脉的可逆塌缩［３１］㊁细胞膜水通道蛋白调节［３２］和细根皮层腔隙的形成［３３］等㊂这一阶段的失水速率通常比气孔完全打开时低１００ １０００倍［２９］㊂如果持续干旱，水势持续下降最终达到一个临界阈值（水力导度损失５０％对应的水势值，ｔｈｅｗａｔｅｒｐｏｔｅｎｔｉａｌａｔ５０％ｌｏｓｓｏｆｈｙｄｒａｕｌｉｃｃｏｎｄｕｃｔａｎｃｅ，Ｐ５０）时，栓塞开始在木质部中扩散［３４ ３５］，这一过程发生在包括植物根茎叶在内的整个水力系统中［３６ ３７］㊂由于栓塞大大减少了向冠层的水分输送，这种水力功能障碍导致了分支斑块性死亡和冠层叶面积显著减少［３８］㊂随着栓塞逐渐遍布整个输水网络，造成植物水力系统不可逆的损伤（水力导度损失８０％对应的水势值，ｔｈｅｗａｔｅｒｐｏｔｅｎｔｉａｌａｔ８８％ｌｏｓｓｏｆｈｙｄｒａｕｌｉｃｃｏｎｄｕｃｔａｎｃｅ，Ｐ８８），最终导致整株植株死亡㊂图２㊀植物对干旱胁迫的水力响应过程Ｆｉｇ．２㊀Ｐｈａｓｅｏｆｄｒｏｕｇｈｔｒｅｓｐｏｎｓｅｔｏｄｒｏｕｇｈｔｓｔｒｅｓｓｉｎｐｌａｎｔｓ随干旱胁迫增加，虚线代表气孔和表皮导度变化趋势，实线代表木质部水力导度损失率；Ｐｇｓ８８代表气孔关闭时的水势；Ｐ５０和Ｐ８８分别代表水力导度下降５０％和８８％的水势３㊀植物水分运输策略的多样性植物功能性状对植物的建立㊁存活㊁生长和繁殖有很大影响，可以很好地表征植物的生长策略［３９］㊂然而，在哪些性状可以用来评估生态耐旱性方面，我们的知识仍然有限㊂３．１㊀衡量植物抗旱性的性状３．１．１㊀压力⁃容积曲线（Ｐｒｅｓｓｕｒｅ⁃ｖｏｌｕｍｅｃｕｒｖｅ，简称Ｐ⁃Ｖ曲线）基于Ｐ⁃Ｖ曲线计算得到的参数（如膨压消失点叶水势（Ψｔｌｐ）㊁质壁分离时的相对含水量（ＲＷＣｔｌｐ）㊁饱和含水时的叶渗透势（π０）和细胞体积弹性模量（ε））在机制上均与耐旱性有关［４０ ４１］㊂其中，Ψｔｌｐ代表了引起萎蔫的叶片和土壤的干燥程度［４０］，被认为是最直接量化植物耐旱性的 更高级别 的性状［４２ ４３］㊂植物会改变其他Ｐ⁃Ｖ参数：１）渗透调节：积累溶质（减少π０）；２）质外体调节：通过将更多的水重新分配到细胞壁外部来减少共质体水分（增加ａｆ）；３）弹性调节：增加细胞壁的弹性（减少ε）以达到足够负的Ψｔｌｐ值［４１ ４３］，提高他们的耐１９６２㊀７期㊀㊀㊀程莉㊀等：木本植物应对干旱胁迫的响应机制：基于水力学性状视角㊀２９６２㊀生㊀态㊀学㊀报㊀㊀㊀４４卷㊀旱性㊂然而，由于这些参数通常是同时调整的，因此他们在影响Ψｔｌｐ方面的相对重要性仍然存在争议㊂前人的研究表明，Ψｔｌｐ与干旱指数呈显著正相关，湿润地区的生物群系比干旱区的生物群系具有更小的负值，这支持了膨压消失点叶水势在木本生物群系尺度上反映耐旱性的观点㊂尽管大多数人认为负值较大的Ψｔｌｐ有利于耐旱性，但也有人提出了相反的观点，认为负值较小的Ψｔｌｐ是有益的㊂当Ψｌｅａｆ下降时，负值较小的Ψｔｌｐ使叶片迅速失去膨压并关闭气孔，从而保持较高的ＲＷＣｔｌｐ㊂ＲＷＣｔｌｐ，也被认为是植物耐旱性的重要衡量标准㊂尽管大多数研究认为更负的Ψｔｌｐ有利于耐旱，一些研究则认为维持细胞水合比维持膨压更重要，因为脱水会导致细胞收缩，细胞壁结构损伤以及由于高离子浓度而产生的潜在渗透压，最终破坏代谢过程㊂除此之外，细胞总相对含水量低于７５％时会严重抑制ＡＴＰ，ＲＵＢＰ和蛋白质的产生［４４］㊂Ψｔｌｐ和ＲＷＣｔｌｐ作为耐旱性预测因子的重要性经常受到争议，但没有得到解决㊂一个最近的ｍｅｔａ分析表明Ψｔｌｐ而不是ＲＷＣｔｌｐ驱动物种与栖息地水分供应的关系［４１］㊂３．１．２㊀木质部栓塞脆弱性曲线（Ｖｕｌｎｅｒａｂｉｌｉｔｙｃｕｒｖｅｓ，简称ＶＣｓ）木质部栓塞抗性是决定植物抗旱性的最重要性状之一，也是解释近年来干旱导致植物死亡的重要性状之一［４５］㊂木质部栓塞抗性通常由ＶＣｓ决定，该曲线描述了当Ψｘ降低时，水力导度丧失百分比（Ｐｒｅｃｅｎｔｌｏｓｓｏｆｃｏｎｄｕｃｔｉｖｉｔｙ，ＰＬＣ）如何增加㊂ＶＣｓ可以提供有关特定植物干旱响应的有价值的信息，并已被用于量化植物抗旱性和生态适应性㊂例如，Ｐ５０或Ｐ８８以及水力安全范围被广泛用于量化抗旱性和水力失败的风险［４６］㊂大量研究表明，当Ψｘ降到Ｐ５０或Ｐ８８以下后，Ψｘ很小的变化将引起水分传导速率大幅下降，树木也因此面临严重栓塞及死亡风险㊂Ｐ５０是最常用的栓塞抗性指标㊂Ｌａｍｙ等对地中海松树的５１３种基因型的研究发现，气候差异明显的不同种群其Ｐ５０的遗传和表型变异均有限，Ｐ５０可能是松树固有特征［４５］㊂但是关于栓塞脆弱性的遗传变异和表型可塑性的研究仅限于少数物种，仍需进一步的研究来确定这一结论是否在所有树种中适用㊂物种水平上，对栓塞抗性在木本种中种间变异的ｍｅｔａ分析表明，不同树种木质部栓塞脆弱性存在巨大差异，植物木质部栓塞脆弱性与其生长环境的年平均降水量和干旱程度相关，来自干燥气候的物种比来自湿润气候的物种具有更大的Ｐ５０值，对干旱的忍耐力越强［４７ ４８］㊂然而在群落水平上，在较干燥的栖息地，植物脆弱性的变化往往很大，这表明脆弱性和干旱在某些情况下是解耦的［４９］㊂这种解耦是因为一些物种所使用的水分胁迫规避策略，如深根系植物或干旱落叶，这些策略使得它们在干旱时期保持较高的Ψｘ［９］㊂具有系统发生学差异的植物，其致死的水势临界点（即木质部导水性不能再恢复）与Ｐ５０或Ｐ８８的关系有所差异㊂裸子植物中的水势临界点与Ｐ５０具有很大正相关性，但被子植物的水势临界点却与Ｐ８８有更高的相关度［９］㊂水力安全范围有２种计算方式：１）ＨＳＭ：树种木质部最低水势（Ψｍｉｎ）与栓塞抗性（Ｐ５０或Ｐ８８）的差值（即Ψｍｉｎ－Ｐ５０或Ψｍｉｎ－Ｐ８８），是预测树木干旱死亡率的关键指标［５０］㊂ＨＳＭ值越小，说明树种面临水力失败的风险越大，反之树种面临水力失败的风险越小［５１］㊂然而，Ｃｈｏａｔ等针对全球８１个地点２２６种森林的研究结果发现，７０％的森林在应对干旱胁迫时的ＨＳＭ很窄（约＜１ＭＰａ），安全边际在很大程度上与年降水量无关，森林对干旱的脆弱性存在全球趋同：所有森林生物群落无论当前的降雨环境如何，都同样容易遭受水力失败［４８］㊂因为Ψｍｉｎ集成了与环境相关的植物结构（例如，生根深度）和生理（例如，气孔行为）性状的许多重要方面，在不同森林类型中发现的狭窄水力安全边际为植物生态学提供了一个重要视角，这表明植物的水力策略是根据其环境进行微调的，允许最大限度的碳获得，但在干旱期间将植物暴露在水力失败的风险中［９］㊂这也表明了一种普遍存在的 有风险 的策略，即植物对环境的快速变化做出反应的生理潜力有限［９］㊂这加剧了气候变化下极端干旱事件增加所构成的威胁［９］㊂２）气孔安全边际（Ｓｔｏｍａｔａｌｓａｆｅｍａｒｇｉｎ，ＳＳＭ）：气孔闭合时的水势（Ｐｇｓ８８）与抗栓塞能力（Ｐ５０或Ｐ８８）的差值（即Ｐｇｓ８８－Ｐ５０或Ｐｇｓ８８－Ｐ８８），用来反映树种的气孔调控策略［５２］，更直接地将气孔对水势的响应和木质部栓塞抗性结合起来㊂正的ＳＳＭ表明气孔关闭发生在茎严重栓塞之前，而负的ＳＳＭ表明气孔关闭发生在栓塞之后；ＳＳＭ宽的物种的耐旱时间更长㊂有明确证据表明，等水和非等水植物的部分死亡和完全死亡与水力失败有关，这进一步凸显了气孔调节和木质部栓塞抗性之间协调的重要性㊂总的来说，气孔安全边际随着栓塞抗性的增加而持续增加，并且气孔安全边际与水力安全边际相关［５３］㊂最重要的是，将气孔调节策略与木质部水力策略相结合有助于更全面地表达植物对干旱的适应［５４］㊂３．１．３㊀非结构性碳水化合物（ＮＳＣ）ＮＳＣ包括淀粉和可溶性糖［５５ ５６］，在树木的抗旱性中发挥重要作用［５７］㊂淀粉是一种长期的碳储存分子，它以一种紧凑的㊁不溶性的形式存在，允许植物在高光合速率的情况下储存碳水化合物㊂可溶性糖为植物提供能量和底物，同时也可充当中间代谢产物㊁信号分子或渗透物㊂植物通过光合作用将ＣＯ２固定为碳水化合物，然后用于呼吸㊁防御㊁生长㊁繁殖或在光合作用无法发生时（如夜间㊁休眠季节或环境压力时期）为植物提供能量储备［５８］㊂在干旱胁迫下，ＮＳＣ扮演着两种角色［５９］，缓冲了植物的碳供应不足［６０ ６１］：１）作为 碳饥饿 的缓冲㊂在 碳饥饿 过程中，光合作用受到干旱胁迫，植物缓慢地消耗他们储存的碳水化合物直到死亡［８］㊂因此，生活在炎热和干燥气候中的植物比生活在潮湿气候中的植物分配更多的碳储存，作为应对干旱胁迫的保守缓冲［６２］㊂２）作为渗透缓冲剂㊂当水分胁迫激活淀粉降解酶时，植物可以将不溶性淀粉转化回可溶性糖［６３］㊂这种从淀粉到糖的转化可以降低植物的渗透势，从而在干旱期间维持细胞膨压［６４ ６５］㊂因此，有人认为在干燥环境中进化或生长的植物将保持较高的ＮＳＣ储存量，并保持更大比例的可溶性糖储存，以防止细胞失水，保持细胞稳定，在干旱条件下生存更长时间［４１，６６ ６８］㊂３．１．４㊀结构性状结构性状可以很好地反映不同树种面对干旱胁迫时的适应能力㊂比如，叶片厚度（Ｌｅａｆｔｈｉｃｋｎｅｓｓ，ＬＴ）与植物获取㊁利用资源的策略紧密相关㊂具有较高ＬＴ的植物可以增强蓄水能力，避免环境胁迫造成伤害㊂叶干物质含量（Ｌｅａｆｄｒｙｍａｔｔｅｒｃｏｎｔｅｎｔ，ＬＤＭＣ）常用干重和鲜重的比值来表示，干旱地区的植物ＬＤＭＣ也较高，对环境胁迫有较强的抗性［６９］㊂比叶重（Ｌｅａｆｍａｓｓｐｅｒｕｎｉｔａｒｅａ，ＬＭＡ）和叶密度（Ｌｅａｆｄｅｎｓｉｔｙ，ＬＤ）是表示干旱容忍能力的重要叶片功能性状，因为ＬＭＡ较高和ＬＤ较高表明细胞壁较厚或者较密，从而能够较大程度地防止由于叶水势下降引起的变型诱导的损坏㊂ＬＭＡ常用叶片单位面积的干物质量来表示［７０］㊂ＬＭＡ高的植物因其较强的碳同化能力能够更好地生长㊂干旱地区的植物通过提高比叶重来提高植物固持资源（碳㊁氮）的效率，从而提高竞争力㊂ＬＤ反映叶片的紧实程度及植物对外界干旱环境的忍耐能力㊂具有较高ＬＤ的植物通常适应于干旱的生境㊂通常ＬＤ高，则叶片细胞小且细胞壁较厚，能够高效积累渗透物质同时减少水分损失，从而减弱水分可利用性低对叶片造成的破坏㊂胡伯尔值（ＡＬ：ＡＳ）与ＷＤ都是物种对不同水分可利用环境进行水力调节的重要性状㊂ＡＬ：ＡＳ表征枝条对叶片的供水能力，反映蒸腾叶面积与茎输导供水之间的权衡［７１ ７２］㊂低ＡＬ：ＡＳ可以避免蒸腾过程过度失水，促进叶片水平供水以适应干旱条件，降低水力紊乱的风险㊂ＷＤ常用植物对单位体积木材投资的生物量来表示，反应植物机械支撑㊁水分运输和生长速率［７３］㊂低ＷＤ意味着储水能力较高，有利于木质部再充水而修复栓塞；高ＷＤ意味着较厚的导管壁或较丰富的机械组织，结构紧密，相应的导管面积较小㊂在干旱胁迫的环境中，植物通常具有较高的ＷＤ，保护木质部避免空穴化［７２］㊂根系与土壤环境直接接触，负责吸收养分和水分，但由于其藏匿于地下，根系性状成为了植物对干旱响应的一个重要但被忽视的预测因子［７４］㊂有关根系性状对干旱反应的数据仅限于少数几种植物［７４］㊂因此，关于植物根性状响应策略的结论似乎很特殊，或者年代太久远［７４］㊂例如，有研究报告称，一些植物种因干旱而产生更细的根，具有高比根长（Ｓｐｅｃｉｆｉｃｒｏｏｔｌｅｎｇｔｈ，ＳＲＬ）和比根表面积（Ｓｐｅｃｉｆｉｃｒｏｏｔｓｕｒｆａｃｅａｒｅａ，ＳＲＳＡ），这一策略被解释为以低投资改善水资源获取［７５］㊂相比之下，其他研究报告称，植物种产生的根更粗，ＳＲＬ和ＳＲＳＡ较低，这已被证明可以降低水力失败的风险［７６］㊂更粗的根与通过真菌营养获得高养分和高水分有关［７７ ７８］，并与由于储存非结构性碳水化合物而产生的渗透调节有关［７９］㊂植物性状有助于预测树木对干旱的响应［７３］㊂相比于常用功能性状，现在已经出现了一套经过充分研究的与耐旱性机制相关的水力性状（表１），被寄予厚望用于预测植物对干旱胁迫的响应，这代表了未来研究的方向［９］㊂３９６２㊀７期㊀㊀㊀程莉㊀等：木本植物应对干旱胁迫的响应机制：基于水力学性状视角㊀表１㊀与树木耐旱性相关的植物水力性状列表Ｔａｂｌｅ１㊀Ｌｉｓｔｏｆｈｙｄｒａｕｌｉｃｔｒａｉｔｓ（ｐｈｙｓｉｏｌｏｇｉｃａｌ，ｍｏｒｐｈｏｌｏｇｉｃａｌ，ａｎｄａｎａｔｏｍｉｃａｌ）ａｓｓｏｃｉａｔｅｄｗｉｔｈｄｒｏｕｇｈｔｔｏｌｅｒａｎｃｅｉｎｔｒｅｅｓ性状Ｔｒａｉｔ性状描述Ｔｒａｉｔｄｅｓｃｒｉｐｔｉｏｎ参考文献Ｒｅｆｅｒｅｎｃｅｓ叶片Ｌｅａｖｅｓ气孔响应Ｓｔｏｍａｔａｌｒｅｓｐｏｎｓｅ气孔闭合速率和敏感性对ＶＰＤ和叶片水势变化［８０ ８７］膨压消失点和渗透调节Ｔｕｒｇｏｒｌｏｓｓｐｏｉｎｔ＆ｏｓｍｏｔｉｃｒｅｇｕｌａｔｉｏｎ叶片叶肉细胞失去膨压和叶片枯萎的水势，以及叶片叶肉细胞渗透含量的适应性调节［４１，４３，８８ ９８］最小气孔导度Ｍｉｎｉｍｕｍｓｔｏｍａｔａｌｃｏｎｄｕｃｔａｎｃｅ当气孔处于最小孔径时，叶片角质层的水分损失率［９９ １０１］木质部外通路Ｅｘｔｒａｘｙｌａｒｙｐａｔｈｗａｙｓ液体和蒸汽通过叶肉和支持组织的阻力变化［１０２ １０４］叶脱落Ｌｅａｆｓｈｅｄｄｉｎｇ在干旱期间通过叶片脱落减少叶面积可以减缓干燥速度，减轻水分对剩余叶片的压力［８７，１０５ １０６］气孔解剖结构Ｓｔｏｍａｔａｌａｎａｔｏｍｙ气孔的形状㊁大小和分布，影响失水相关的叶片生理性状［４２，１０７］根系Ｒｏｏｔｓ皮层空腔形成Ｃｏｒｔｉｃａｌｌａｃｕｎａｅｆｏｒｍａｔｉｏｎ根皮层细胞解体，使维管组织从表皮及周围干燥土壤分离［３３，１０８ １０９］细根损失Ｆｉｎｅｒｏｏｔｌｏｓｓ细根脱落，减少根系与土壤接触的总表面积，重新平衡根枝比［３３，１０８ １１１］根系深度Ｒｏｏｔｉｎｇｄｅｐｔｈ深层根系生长，获得更稳定的水源［１１２ １１８］组织性状Ｔｒａｉｔｓａｍｏｎｇｔｉｓｓｕｅｓ栓塞脆弱性Ｖｕｌｎｅｒａｂｉｌｉｔｙｔｏｃａｖｉｔａｔｉｏｎ木质部汁液的负压导致木质部最大水力导度损失５０％或８８％㊂如，裸子植物的生理临界点（Ｐ５０）；被子植物的生理临界点（Ｐ８８）［４７ ４８，１００，１１９ １３８］水容Ｃａｐａｃｉｔａｎｃｅ在木质部周围组织中储存的水分，可以缓冲导致空穴化事件的木质部汁液负液压［３０，１１３，１３９ １４１］细胞膜通透性Ｃｅｌｌｍｅｍｂｒａｎｅｐｅｒｍｅａｂｉｌｉｔｙ水通道蛋白的活性可以改变细胞膜的通透性，导致跨膜通路的水力导度降低［３２，１０３，１４２ １４３］木质部解剖性状Ｘｙｌｅｍａｎａｔｏｍｉｃａｌｔｒａｉｔｓ木质部导管尺寸㊁数量和连通性Ｘｙｌｅｍｃｏｎｄｕｉｔ木质部导管（管胞和导管）的直径㊁长度和连通性影响最大水力导度和空穴化脆弱性㊂［１３２，１４４ １４５］纹孔膜孔隙度／厚度Ｐｉｔｍｅｍｂｒａｎｅｐｏｒｏｓｉｔｙ／ｔｈｉｃｋｎｅｓｓ纹孔膜解剖结构决定了木质部导管之间的空气传播阈值，并影响水力导度和空穴化脆弱性㊂［１２１ １２２，１３１，１４６ １４７］木材密度Ｗｏｏｄｄｅｎｓｉｔｙ木材密度由木质部解剖性状决定，并与许多生理性状相关㊂［２８，１２７，１４８］连接性Ｓｅｃｔｏｒｉａｌｉｔｙ维管组织的空间分离，防止栓塞在分支间扩散［１４９ １５４］㊀㊀ＶＰＤ：饱和水汽压差Ｖａｐｏｒｐｒｅｓｓｕｒｅｄｅｆｉｃｉｔ３．２㊀植物水分利用策略鉴于植物在异质环境中争夺空间㊁阳光㊁水和养分的策略多种多样，任何单一植物功能性状均不足以表征植物在干旱胁迫下的生存力，常需结合一系列形态功能性状㊁生理功能性状㊁生物化学功能性状来阐明植物的水分调节对策及机制，进一步揭示植物对气候变化的响应和适应［１５５］㊂３．２．１㊀等水和非等水调节策略１９３６年，Ｂｅｒｇｅｒ提出等水／非等水概念，基于叶片水势或者蒸腾来描述植物昼夜水分调节关系㊂在昼夜转换间，等水植物会在正午来临时，及时关闭气孔，维持较高的正午叶片水势㊂而非等水植物气孔则持续张开，保持水碳交换，故而正午叶片水势较低㊂近期，研究者将等水／非等水概念用于长期干旱条件下的水分管理［８６］㊂即随着土壤水势的持续降低，等水植物的叶片水势会保持较高水平，然后缓慢降低，而非等水植物的叶片水势会持续降低㊂等水植物的叶片蒸腾随着土壤变干而迅速降低，而非等水植物则先缓慢降低而后加快４９６２㊀生㊀态㊀学㊀报㊀㊀㊀４４卷㊀。
小学上册第十一次英语第1单元期中试卷
小学上册英语第1单元期中试卷英语试题一、综合题(本题有50小题，每小题1分，共100分.每小题不选、错误，均不给分)1 The ancient Romans built ________ for entertainment.2 A __________ is a type of chemical bond formed through electrostatic attraction.3 Which animal is known for its long trunk?A. RhinoB. GiraffeC. ElephantD. Hippopotamus答案: C4 I found a _______ (小青蛙) near the pond.5 What do we call the part of a plant that absorbs water?A. StemB. LeafC. RootD. Flower答案:C6 What do we call a person who plays music?A. ArtistB. MusicianC. PainterD. Dancer答案:B7 I want to ________ (discover) new things.8 A _______ (小松鼠) gathers acorns for winter.9 The __________ (城市与乡村) have different lifestyles.10 The bear catches fish with its _______.11 What is the term for a baby sheep?A. KidB. LambC. CalfD. Foal答案:B12 During school breaks, I usually __________ with my family.13 A _______ is an area of land that is lower than the surrounding land.14 My brother collects ____ (coins) from around the world.15 ________ (花匠) take pride in their work.16 What is 5 + 2?A. 6B. 7C. 8D. 9答案: B17 In an acid-base reaction, the acid donates a _____ while the base accepts it.18 My brother is very ________.19 What is the capital of Saint Barthélemy?a. Gustaviab. Saint Martinc. Marigotd. Philipsburg答案:a20 The _____ (植物形态) can vary widely among species.21 The ________ is very lively.22 What is the name of the famous clock tower in London?A. Big BenB. Tower BridgeC. London EyeD. Buckingham Palace答案:A23 What is the name of the famous American holiday celebrated on the last Monday of May?A. Memorial DayB. Labor DayC. ThanksgivingD. Independence Day答案：A24 I enjoy planting seeds of ________.25 Astronomical units (AU) are used to measure distances within our ______.26 The Earth's atmosphere is vital for ______ life.27 What type of animal is a parrot?A. FishB. MammalC. BirdD. Reptile答案:C28 A __________ is a protective layer of minerals.29 My uncle tells great __________. (笑话)30 A _______ (小喜鹊) builds its nest in a tree.31 The book is on the _____ (table).32 A heterogeneous mixture has a ______ composition.33 What do you call a vehicle that flies in the air?A. CarB. TrainC. AirplaneD. Boat答案:C34 What do we call a scientist who studies the characteristics of living organisms?A. BiologistB. EcologistC. Environmental ScientistD. Geneticist35 The chemical formula for sodium sulfite is ______.36 My favorite movie star is _______ (名字). 她的表演很 _______ (形容词).37 Light travels fastest in a ______.38 Carta limited the power of the _______. (国王) The Magn39 I bought a new ______ (玩具车) that can go very fast. I love to race it with my______ (朋友).40 A __________ is a mixture of two or more gases.41 What do we call the small pieces of paper we use to write notes?A. NotebookB. Sticky NotesC. Index CardsD. Post-it Notes42 We will _______ (go) camping this weekend.43 I enjoy playing with my toy ________ (玩具名称) in the pool.44 What do we call a person who studies the weather?A. MeteorologistB. ClimatologistC. GeographerD. Environmentalist45 They are ___ a project together. (working on)46 A ________ (种植者) takes care of the plants.47 The __________ is a famous river in South America.48 What is the name of the hypothetical region containing icy bodies beyond Neptune?A. Kuiper BeltB. Oort CloudC. Asteroid BeltD. Heliosphere49 Rust is formed when iron reacts with ______.50 What is the capital of Thailand?A. BangkokB. Kuala LumpurC. HanoiD. Manila51 I think it's polite to call people ____. (我认为称呼人们为____是礼貌的。
高中英语植物保护单选题80题(带答案)
高中英语植物保护单选题80题(带答案)1.Protecting plants is important for maintaining ecological balance. What is the main reason for this?A.Because plants provide food for animals.B.Because plants produce oxygen.C.Because plants are beautiful.D.Because plants can be used for decoration.答案：B。
A 选项植物为动物提供食物也是重要的但不是维持生态平衡的主要原因。
B 选项植物产生氧气对于维持生态平衡至关重要，地球上的生物都需要氧气来生存。
C 选项植物美丽不是保护植物对于维持生态平衡的主要原因。
D 选项植物用于装饰也不是主要原因。
2.We should protect plants because they help in reducing pollution. Which of the following is the best way to protect plants?A.Stop using cars.B.Plant more trees.e plastic bags.D.Burn waste.答案：B。
A 选项停止使用汽车虽然能减少污染但不是保护植物的最好方式。
B 选项种植更多的树可以直接保护植物，同时树木也能吸收污染物等起到保护环境的作用。
C 选项使用塑料袋会污染环境不利于保护植物。
D 选项燃烧垃圾会污染空气不利于保护植物。
3.Protecting plants is crucial for the survival of many species. What does this mean?A.Plants provide homes for animals.B.Plants are not important for animals.C.Only animals are important for the ecosystem.D.Plants can survive without animals.答案：A。
18-Plant-Disease
❂Plant Disease18T opics in This chapTer❂By Jay W. Pscheidt, Extension Plant Pathologist, Oregon State University. Edited by Lindsey du Toit, Plant Diagnostician, Washington State University, Puyallup, and Warren Copes, Ornamental Plant Pathologist, Washington State University.Adapted by Michele Hébert, Extension Faculty, Agriculture and Horticulture, CooperativeExtension Service, University of Alaska Fairbanks.❂Pathogens❂Conditions necessary for biotic disease ❂The disease cycle ❂Disease diagnosis ❂Plant disease control ❂Fungicides for home gardenersEvery gardener has put in plants with hopes forwonderful flowers, fruits or vegetables, only to have those hopes dashed as the plants get sick and die. These plants are considered diseased. Many things can cause plants to become diseased, including biotic (living) agents, abiotic (nonliving) factors or a combination of the two. This chapter focuses only on living agents — fungi, bacteria, viruses, nematodes and parasitic plants. Other chapters discuss abiotic factors such as nutrient deficien -cies, lack of water, temperature stress and combinations of these problems as they relate to specific types of plants. Some plant diseases have had tremendous impacts on society. Perhaps foremost among these is Phytophthora late blight, a fungal disease that caused the Irish potato famine in 1845. Approximately 2 million people either starved or left Ireland, many for the United States. Powdery mildew and downy mildew are fungal diseases that devastated the French wine industry until Bordeaux mixture was found to control them.In the United States, the fungal disease chestnut blight was introduced accidentally into New York City in the late 1800s on imported Chinese chestnut trees. The Chinese trees were resistant to the blight, but American chestnut trees were not. In fewer than 40 years, 30 million acres of chestnut trees had died. Chestnut blight remains a problem in the eastern United States. Dutch elm disease also was in-troduced accidentally. It infects and kills elm trees through-out the nation.These examples are prominent because they caused so much damage. Plant diseases vary in how much trouble they cause, depending on a variety of conditions, including the susceptibility of the plant, and the organism’s disease cycle. Minimizing their impact requires correct diagnosis of332 • Plant Disease—Chapter 18Disease terminologyGeneral terms Disease—Abnormal and harmful physio-logical condition brought about by living(biotic) agents, such as fungi, bacteria,nematodes and viruses, or by nonliving(abiotic) factors, such as nutrient deficien-cies and water stress.Dodder—A parasitic seed plant lacking chlorophyll; its thread-like yellow bodytwines around its host, from which itwithdraws food and water.Downy mildew—A group of fungal patho-gens whose spore production looks likedowny growth on the undersides ofleaves.Exclusion—A process by which certain plants are not allowed in an area to pro-tect against pests and diseases from other areas.Haustoria—A modified hyphal branch that grows into a plant cell to absorb food and water.Host—A plant afflicted with a disease. Hypha—A single filament of a fungus. Immunity—A relationship between a plant and pathogen in which the plant does notbecome diseased.Incubation—A period of development dur-ing which a pathogen changes to a formthat can penetrate or infect a new hostplant. Some fungi, for instance, grow astructure called a penetration peg that can grow through a plant’s cell walls. Infection—The condition reached when a pathogen has invaded plant tissue and es-tablished a parasitic relationship between itself and its host. Inoculation—The introduction of a pathogen to a host plant’s tissue.Inoculum—The parts of a pathogen that infect plants.Powdery mildew—A group of fungal patho-gens whose spore production causeswhite to gray powdery mycelia on theoutside of their host. Quarantine—A regulation forbidding sale or shipment of plants or plant parts in anarea, usually to prevent disease, insect,nematode, or weed invasion. Resistance—Qualities in a host plant that make it retard the activities of a pathogen. Sanitation—The process of removing sourc-es of plant pathogens from a growing area (for example, by cleaning up plant debrisand sterilizing tools and growing media). Spore—(1) The reproductive body of fungi and other lower plants, containing one ormore cells. (2) A bacterial cell modified to survive in an adverse environment. Stylet—A nematode’s lance-like or hypoder-mic-needle-like mouthpart used to punc-ture and feed from plant cells. Tolerant—A crop plant that will produce a normal yield even if diseased. PathogensBacterium—A single-celled, microscopic organism having a cell wall but no chlo-rophyll; reproduces by cell division. Fungus—A plant organism with no chloro-phyll that reproduces via spores and usu-ally has filamentous growth. Examplesare molds, yeasts and mushrooms. Nematod e—A microscopic roundworm, usu-ally living in the soil; many feed on plantroots and can be disease pathogens. Parasitic seed plant—A higher plant that lives parasitically on other seed plants.An example is mistletoe.Chapter 18—Plant Disease • 333Disease terminology, continued Pathogen—A disease-producing organism. Phytoplasma—A microscopic, bacteria-like organism that lacks a cell wall. Virus—An infectious agent too small to see with a compound microscope; it multiplies only in living cells.Symptoms (external or internal physical dis-ease characteristics expressed by a host plant) Blight—Rapid, extensive discoloration, wilt-ing, and death of plant tissue. Blotch—A blot or spot (usually superficial and irregular in shape and size) on leaves, shoots or fruit.Canker—A dead place on the bark and cortex of twigs, stems or trunks; often discolored and either raised or sunken. Chlorosis—An abnormal yellowish-white or gray color of plant parts resulting fromincomplete destruction of chlorophyll. Damping-off—Decay of seeds in the soil or young seedlings shortly after they emerge;usually caused by Rhizoctonia, Pythium,or Fusarium fungi. Dieback—Progressive death of shoots, branch-es or roots, generally starting at the tips. Dwarfing—The underdevelopment of any plant organ. Enation—Epidermal outgrowths on leaves or stems.Epinasty—An abnormal downward-curving growth or movement of a leaf, leaf part or stem. Etiolation—Development of yellow, long, spindly growth as a result of insufficientlight.Fasciation—A distortion of a plant that results in thin, flattened and sometimescurved shoots.Flagging—Loss of turgor and drooping of plant parts, usually following a watershortage.Gall—An abnormal, localized swelling on leaf, stem or root tissue. Mosaic—Nonuniform foliage coloration with a more or less distinct intermingling of normal green and light green or yel-lowish patches.Mottle—An irregular pattern of light and dark areas.Necrosis—Death of plant tissue. Phyllody—A change from normal flower structures to leafy structures. Rot—Decomposition and destruction of tissue.Rugose—Wrinkled. Russet—Yellowish-brown or reddish-brown scar tissue on a fruit’s surface. Scab—A crust-like disease lesion.Water-soaked—Lesions that appear wet and dark and usually are sunken and/ortranslucent.Wilt—(1) Lack of freshness and turgor and drooping of leaves from lack of water. (2)A vascular disease that interrupts a plant’snormal uptake and distribution of water. Witches’ broom—Abnormal brush-like development of many weak shoots. Signs (physical evidence of a disease-causing agent)Bacterial slime—A gooey or dried mass of bacterial cells that oozes out of planttissues.Conk—A fungal fruiting structure (e.g., shelf or bracket fungi) formed on rotting woody plants.Cyst—The swollen, egg-containing female body of certain nematodes; can be seenon the outside of infected roots. Fruiting body—A fungal structure that con-tains or bears spores. Mycelia—Masses of fungal threads (hy-phae), which compose the vegetativebody of a fungus.334 • Plant Disease—Chapter 18the problem and an understanding of tech-niques for growing healthy plants.PathogensDisease causing organisms are pathogens. They are microscopic or very difficult to see or recognize without magnification. Fungi, bacteria, viruses, nematodes and even plants can be pathogenic on garden plants. Patho-gens generally get nutrients, water and ev-erything they need to reproduce from their host. Such a relationship is called parasitic. Some pathogens can infect several kinds of plants; others require a specific host. FungiThe largest group of plant pathogens, fungi come in a wide variety of forms. In general, they are multicellular organisms with a thread-like body. These threads, which are called hyphae, have cell walls. When many threads mass together, they form a mycelium. Further growth of a my-celium may produce fruiting bodies, where sexual or asexual spores are formed. The characteristics of the spores, fruiting bodies and mycelium are used to identifyand diagnose fungal problems.Some fungi can survive andgrow without a living host. Othersdie if they are not in close asso-ciation with a host.Fungi cause plant dis-eases by making toxinsthat kill plant cells, bygrowing within andplugging up a plant’svascular system, byrotting roots or bysending root-like struc-tures into plant cells.BacteriaBacteria are single-celled organisms that are much smaller and less complex than plant cells. Many are about the size of a plant chloroplast. Bacteria can build up to high numbers and ooze out of plant tissues. Some bacteria produce slime that may attract insects that spread the bacteria to healthy plants. Bacteria can survive unfavorable con-ditions in plant debris or even in seeds. Bacteria cause plant diseases by forming toxins or by producing enzymes that break down plant cell walls. Crown gall bacteria actually genetically engineer their host plant to make galls and amino acids, thus giving the bacteria a better place to live and the chemicals they need to grow and reproduce. VirusesVirus particles are composed of a few strands of DNA and are even smaller than bacteria. Electron microscopes reveal them to have many shapes, including long strands, short rods and multisided balls. Viruses utilize a host plant’s cell organ-elles to produce more viruses. The result can be strange plant colors, forms or struc-tures. Some viral infections, however, don’t result in any visible plant problems. Touching virus-infected plant material and then touching healthy plants can trans-mit some viruses. For example, a smoker can transmit tobacco mosaic virus from a cigarette to a plant. In Alaska, some viruses are transmitted by insects such as aphids, scales, leaf hoppers and whiteflies. Fungi, mites, nematodes and even parasitic plants also can transmit viruses. Some viruses also may infect a host plant’s seeds and thus be transmitted to the next generation. Potato virus X can be transferred from one garden potato to another by a contaminated garden tool or pant leg (anything that moves sap).Chapter 18—Plant Disease • 335 NematodesNematodes are multicellular roundwormsthat may be no larger than the letter “I” inthe word DIME on a U.S. coin. Because theyare clear and live in the soil, they are im-possible to see without magnification.All plant pathogenic nematodes have amouthpart called a stylet. The stylet is like alance or hypodermic needle that the nema-tode uses to puncture plant cells and feedfrom them.Some nematodes move from root to root,while others set up one feeding site in asingle root. Feeding may cause root lesionsor galls that restrict water and nutrient flowto the host plant. Other nematodes weakenthe plant through mass feeding. A few foliarnematodes attack above-ground plant parts.Movement of soil or infected plant parts can transmit nematode diseases.Parasitic plantsMany Alaskans notice moss and lichen growing in trees; this vegetation is not parasitic, it just uses the tree as a platform. Some plants are truly parasitic to other plants. Dodder, for example, produces flow-ers and seeds, but has no chlorophyll. Thus, it cannot manufacture its own food. It has a thread-like yellow body that twines around its host. Root-like haustoria penetrate the host plant and withdraw food and water. Some parasitic plants, such as mistletoe, manufacture chlorophyll but have no real roots and depend on their host (on hemlock in Southeast Alaksa) for water and nutri-ents. Seeds of parasitic plants are spread by birds or contaminated soil, or they may be shot out of plant structures like little bombs. Conditions necessary for biotic diseasesIn order for a biotic (pathogenic) plant disease to occur, three conditions must be met:• The host plant must be susceptible.• An active, living pathogen must be pres-ent.• The environment must be suitable or favorable for disease development.All three of these factors must occur simultaneously. If one or more is absent or unfavorable, disease does not occur. The relationship among a plant, a pathogen and the environment is shown in Figure 1. The more the circles overlap, the more severe the disease. This is referred to as disease triangle.A host plant’s genetic makeup determines its susceptibility to disease. This suscepti-bility depends on various physical and bio-chemical factors within the plant. Stature, growth habit, cuticle thickness and stomatal Figure 1.—Disease is a result of simultaneous interactions between the environment, host and pathogen.EnvironmentHost PathogenDisease336 • Plant Disease—Chapter 18The disease cycleThe sequence of events from a patho-gen’s survival to plant disease development and back to pathogen survival is called the disease cycle, or the pathogen’s life history. An understanding of the disease cycle is important when considering control options. Control measure are most effective when applied at the weakest link in the chain of events in the disease cycle.Most pathogens must survive a period of adverse conditions, usually winter, when they do not actively cause disease.shape are a few physical factors that influ -ence disease development. A plant’s de-velopmental stage also can have an effect. Stressful growing conditions can increase a plant’s susceptibility to diseases.Pathogens such as fungi and bacteria differ in their ability to survive, spread and reproduce. Different strains of pathogens may differ in how aggressive they are in causing diseases.Environmental factors such as tempera-ture, light and moisture can accentuate dis-eases. For example, cool, moist conditions are ideal for many fungal pathogens.Figure 2.—Disease cycle of apple scab: Overwintering fungi (a) produce sexual spores (b) that penetrate and infect trees in the spring (c). Soon scab lesions appear (d 1), within which asexual spores (e) are produced. These spores are released (f) and drift onto healthy tissue (g), where they cause more scab lesions (d 1 and d 2) and produce more spores (e). The cycle then begins again.(b) Released ascosporesAscosporeAscosporesApple tree in bloom(c) Penetration by germinating ascosporeInfection(g) Penetration by germinating conidium(d2) Scab lesionson fruit (d1) Scab lesionson leaf(e) Conidium(f) ConidiumIntercellular mycelium in leaf(a) Infected leaves on groundAscogonium StromaAntheridiumFertilizationPeritheciuminitialMature perithecium containing asci and ascosporesChapter 18—Plant Disease • 337In spring, the overwintered inoculum then infects or continues to infect a host plant. Some diseases, such as many canker dis-eases, have only one cycle during the year. Others, such as powdery mildew, continu-ally produce new inoculum, thus repeating the cycle many times during a single grow-ing season.Apple scab is an example of a fungal disease with multiple cycles each year (Fig-ure 2). The fungus survives the winter on fallen infected leaves (Figure 2a), where it produces small fruiting bodies that contain sexual spores. In the spring, starting about the time apple trees begin to grow, these spores are squirted out of the dead leaves (Figure 2b). Frequent or long rainstorms and warm weather favor spore release. The spores drift onto healthy leaves or young fruit, where they germinate and enter plant tissue much as a seed germinates and sends roots into the soil (Figure 2c). Once inside, the fungus gets all of its food from the plant’s tissues.In a few days or weeks, a scab lesion forms (Figure 2d1). Within this lesion, another type of spore is produced — an asexual spore (Figure 2e). When these spores are released (Figure 2f), they drift to healthy tissue (Figure 2g), where they cause more scab lesions (Figures 2d1 and d2) and produce more spores (Figure 2e). This cycle can be repeated many times during wet springs.Summer generally brings unfavorable hot, dry conditions. The fungus survives on leaves until they fall in the autumn. Then it invades the leaves and once again makes spore-bearing fruiting bodies.Disease diagnosisThere is no single set of questions or technique for diagnosing plant diseases. Experience and practice are the best teach-ers. It is easiest to diagnose plant problems through personal, onsite inspection. You may notice subtle influences of the site, environment or management practices that make identification easier.Diagnosis is more difficult when you see only part of a plant, which may or may not indicate the real problem. The worst situation is diagnosis by phone, which easily can lead to misunderstanding and inaccurate diagnosis. Many beginners use the picture book method of diagnosis: attempting to match a plant’s problem with a picture. The Ortho Problem Solver, for example, has many use-ful, high-quality color pictures. Although this method is useful for simple and com-mon problems, it usually is inefficient and inaccurate for local plant diseases, complex situations and difficult problems. Another simple technique is to ask a series of questions to build a case history of the problem. Questions should include the kind of plant, its age and its size. Also consider the location of the property and the plant’s location and relationship to other plants. Information on recent weather, soil conditions, mulch and care also is needed. Describing the plant’s overall condition is very important.Symptoms and signs also are used to diagnose a plant’s condition. Symptoms are physical disease characteristics expressed by a plant. Examples are wilt, galls, can-kers, rots, necrosis, chlorosis and general decline. Signs are physical evidence of a pathogen. Examples include fungal fruiting bodies (such as mushrooms or vase-shaped bodies called pycnidia), mycelia, bacterial slime or nematodes.338 • Plant Disease—Chapter 18Chapter 19, Diagnosing Plant Problems, will help you organize your approach to di-agnosing plant disease problems. This sys-tematic approach involves defining the real problem and distinguishing between living and nonliving causes of plant damage. Steps include looking for damage patterns, track-ing the development of damage over time and building a case history of the problem. With these steps, it usually is easy to nar-row the possibilities and turn to specialists or appropriate reference materials, such as textbooks or herbarium samples, for precise identification.Once you determine that a real problem exists and is caused by a living disease or-ganism, decide what type of organism may be causing the damage (fungi, viruses, bac-teria or nematodes). Some insect problems mimic diseases; however, the symptom de-scriptions below deal only with pathogens. Knowing what diseases a plant is suscep-tible or resistant to also can help in diagno-sis. You can eliminate possibilities if you know which diseases are likely to occur. Root symptomsExternal root symptoms include galls, discoloration and death of roots or parts of roots.Crown gall, caused by the bacterium Agrobacterium tumefaciens, is a common cause of galls on many plants. Some fungal diseases, such as club root of cabbage, also cause galls. Root-knot nematodes (Meloido-gyne spp.) can cause large or small irregular galls. Small, discolored, dead areas may be caused by a wide variety of fungi or root-le-sion nematodes (Pratylenchus spp.). Death of feeder roots or the entire root system is indicative of many fungi. Though Alaska does not currently have many problems with pathogenic nematodes, there is always the potential for the introduction of new species through imported plants. Remember that root injury often causes yellowing, stunting or wilting of above-ground parts. Many fungi, such as Verticil-lium and Fusarium, cause internal vascular discoloration in stems, as do some bacterial wilts.Symptoms on storage organsMany fungi and some bacteria cause discolored or dead areas that penetrate deep into storage organs such as tubers, bulbs, corms, etc. Dry rots often are caused by fungi, which also may produce mycelia or spores. Soft rots usually are associated with bacteria such as Erwinia spp. and can be accompanied by strong, repulsive odors. Often, bacterial soft rots follow rots caused by fungi, making diagnosis difficult. Other internal problems can be caused by bacteria, e.g. (ring rot of potato) or by several viruses. Scurfy, dead surface tissue may be caused by a variety of fungus-like organisms (e.g., powdery scab of potato). Fungi or nema-todes can cause galling of storage organs. Seedling symptomsSeedlings sometimes fail to emerge or fall over and die. This condition usually is referred to as damping-off. Fungi such as Rhizoctonia, Pythium and Fusarium are common causes; they affect seedlings just at or below the soil line.Dead areas on cotyledons (seed leaves), the first true leaves, or stems usually are caused by fungi, but occasionally by bacte-ria. Spots caused by fungi may contain hy-phae or fruiting bodies, while those caused by bacteria may look water soaked around their margins.Rusty-red, brown or black spots or stripes indicate rust or smut fungi. White, moldySee Chapter 19, Diagnosing Plant Problems.Chapter 18—Plant Disease • 339growth can be caused by powdery mildew or downy mildew fungi.Yellowing (either mottled or patterned) can be caused by several viruses. Ring spots, blotches and streaks of yel-low or green also may occur with viral infections.Nematodes such as Dity-lenchus can cause swelling or galling of stems or leaves.This nematode does not occur naturally in Alaska but can potentially come in on plants such as bulbs.Leaf symptomsMottling is the abnormal yellow and greenish patterning of leaves infected with viruses. Viruses can also cause leaf rolling and distortions. General or uniform yellow-ing, especially on leaf margins may indicate a root rot.Dead (necrotic ) areas on leaves can be caused by fungi or bacteria. Dead areas caused by fungi may contain hyphae or fruiting bodies, while those caused by bacteria often have water-soaked margins. Small, rusty-red, brown or black spots or stripes may be caused by rust or smut fungi. Moldy, white leaves indicate powdery or downy mildew.Wilting indicates lack of water, which may be due to vascular wilt fungus, root rot, nematodes or bacteria. Remember, examine the entire plant to find possible reasons for the symptoms.Stem, branch and trunk symptoms The leaf disease symptoms above also apply to most stem disorders of annuals and herbaceous perennials.Cankers (complete or partial death of woody stems or branches) can be caused bythe wood with a knife may reveal a sharp border be-tween healthy and infected tissue. Some bacterial can-kers excrete a sticky ooze in the spring.Wood rots and decays are may be accompanied by large conksor bracket-like fruiting structures.Galls can be produced by the crown gall bacterium Agrobacterium tumefaciens . A few galls or swellings, such as white pine blister rust, are caused by fungi.Witches’ broom (excessive branching) can be caused by several fungi or by mistletoes, a group of parasitic plants.Flower symptomsAbnormal color changes and/or distor-tions can be caused by several viruses. Partial or complete death of flower parts can be caused by fungi or bacteria. Fungi usually produce characteristic spores, while bacterial infections often look water soaked. Smut diseases convert individual flowers into masses of black spores; an example is corn smut.Fruit symptomsFungi cause a wide variety of decays, rots and superficial spotting or russetting. Im -portant symptoms include the specific color of rotted tissue, firmness of tissue and signs such as spores or fruiting structures. Virusescan cause discoloration and malformation. Bacteria may cause discrete spots on fruit in the field or soft rots in storage.340 • Plant Disease—Chapter 18Plant disease controlThe five basic principles of plant disease control are exclusion, avoidance, eradica-tion, protection and resistance. Although therapy is another basic principle, it gener-ally is not practiced by home gardeners. ExclusionThis method includes quarantines, inspec-tions and certification. These techniques prevent movement of diseased plant material into a particular country, state or geographic area where the disease doesn’t exist. The most visible use of this method is in Cali-fornia. At the state border, everyone must stop at an agricultural inspection station to be screened for fresh fruit, vegetables and plants coming from areas where certain dis-eases or insects are known to exist. Quarantines are regulations forbidding sale or shipment of plants or plant parts. There are many quarantines of plant mate--Phytoph-from entering Alaska. Lateka. Material with a proper phytos-anitary certificate certainly can besent to Alaska.AvoidanceIf a disease does occur inyour area, there may be waysto avoid its development onyour plants. Choosing the right site and time for planting, storing produce prop-erly and avoiding wounds to plants are a few of these techniques. Planting certified, virus-free stock is a good way to avoid viral diseases.Root rots can be avoided by not planting in heavy, poorly drained soils. Delay plant-ing until soils dry out.Wounds can be entry points for pathogens or can weaken a plant so it cannot defend itself. For example, the crown gall bacte-rium needs an injury to begin the infection process. Thus, avoid wounding plants when pruning or using equipment such as mowers or weed trimmers.Finally, use good horticultural practices, such as proper fertility, pruning, watering and training, to keep plants healthy and bet-ter able to ward off infection. EradicationWhen a plant is infected or an area is infested with a pathogen, eradication can eliminate or reduce the disease threat. Rotation, sanitation, elimination of alter-nate hosts, chemical applications and heat treatment are ways to reduce or eliminate diseases.Crop rotation is common in both com-mercial agriculture and home gardens. Rotation involves planting different crops in a given location each year. This practice can reduce soil populations of fungi and nema-todes.To practice rotation, you need to know the pathogen and what plants are its hosts. Rotation works only if you plant nonhosts. For example, turnips and cabbage are hostsSee Chapter 5,Pruning.。