Shen Xiaojie, please accept that environmental protection is a basic national policy of our country. The function of plants is mainly to control pollutants, prevent and monitor pollutants. However, due to the differences of environmental factors, plants play different roles in protecting environmental factors. Based on various environmental factors, this paper summarizes the role of plants in protecting various environmental factors, including the role in the atmospheric environment, the role in protecting the water environment and the role in protecting the soil. Key words: monitoring function of environmental protection and purification of plant environmental elements With the development of productivity and modernization of industry and agriculture, the pollutants discharged into the environment are increasing day by day, which greatly exceeds the natural purification capacity of the ecosystem and causes environmental pollution. In order to reduce environmental pollution, there are many measures, one of which is to use plants to prevent environmental pollution, because plants have the ability to purify the environment, absorb, accumulate, decompose and metabolize various pollutants, reduce the concentration of toxic gases in the atmosphere, maintain the balance between oxygen and carbon dioxide in the atmosphere, reduce the concentration of radioactive substances in the air, reduce noise, sterilize and remove dust, and purify environmental pollution. At the same time, because different plants have different sensitivities to different pollutants, they can also be used to monitor and predict environmental pollution. This paper mainly expounds the role of plants in environmental protection from three environmental factors: atmosphere, water and soil. The role of plants in protecting the atmospheric environment 1. 1 The purification function of plants has three main purification functions for the atmosphere, namely, removing microorganisms in the environment, physically adsorbing dust and absorbing transformed chemicals. Green plants can inhibit or kill bacteria. Using this function to plant suitable greening plants can reduce the number of bacteria in the atmosphere. On the one hand, the dust in the air in the green area is reduced, and the bacteria lose their breeding places, thus reducing the number of bacteria; On the other hand, plant secretions themselves have bactericidal effect. It has been found that many plants can secrete volatile substances and have the ability to kill bacteria, fungi and protozoa. For example, chopped green onion paste can kill bacteria such as staphylococcus and streptococcus. The water extract of Sanguisorba officinalis can kill pathogenic bacteria of typhoid fever, paratyphoid fever A and paratyphoid fever B and Shigella dysenteriae strains within 65438 0 minutes. The bactericide secreted by eucalyptus citriodora can kill pneumococcus, Shigella, tuberculosis and influenza virus. Citrus, rosemary and chlorophytum can greatly reduce bacteria and microorganisms in the air. . Plants generally have the function of adsorbing dust. The leaves of plants are wrinkled, rough or secrete oil, which can absorb or attach dust, thus reducing the content of dust and other particles in plants and purifying the environment. Plants covered with dust, once washed by rain, can quickly recover their adsorption capacity; In addition, the lawn also has a significant dust reduction effect. Ivy, fig, Penglai banana and common aloe can absorb dust. Plants can remove some chemicals from the environment through absorption and transformation. Plants can absorb carbon dioxide, sulfur dioxide, formaldehyde and other substances in the environment, and convert these substances into their own substances, reducing the concentration of chemical substances in the environment. For example, after phenol enters plants, most of it participates in sugar metabolism and combines with sugar to form phenolic glycosides, which are non-toxic to plants and stored in cells; The other part is free phenol, which will be oxidized and decomposed by polyphenol oxidase and peroxidase, and become non-toxic compounds such as CO2 and water, so as to remove its toxicity. Cyanide can be decomposed into nutrients in plants. Lichen, weeping willow, Ailanthus altissima, hawthorn, chestnut, oleander, clove, etc. The ability to absorb SO2 is strong, and more sulfides are accumulated. Weeping willows, kiwifruit and camellia oleifera have strong ability to absorb fluorine. Aloe, chlorophytum and Eupatorium adenophorum can absorb formaldehyde. Zi Yuan, Astragalus membranaceus, tobacco and Celosia cristata, these plants can absorb a lot of radionuclides such as uranium. Ivy, rose, rose, aloe and evergreen can effectively remove trichloroethylene, hydrogen sulfide, benzene, phenol, hydrogen fluoride and ether indoors. Asparagus can remove heavy metal particles. Phyllostachys pubescens, Eupatorium odoratum and Eupatorium odoratum can absorb more than 80% of indoor harmful gases. Roses can absorb more harmful gases, such as hydrogen sulfide, benzene, phenol, hydrogen chloride, ether and so on. 1.2 Plants can regulate photosynthesis. Photosynthesis refers to the process that green plants use light energy through chloroplasts to convert carbon dioxide and water into organic substances that store energy and release oxygen. Photosynthesis can not only convert solar energy and produce organic matter, but also adjust the contents of oxygen and carbon dioxide in the atmosphere, so that the contents of oxygen and carbon dioxide in the atmosphere are relatively stable. It is estimated that all living things in the world consume an average of 10000 t/s (ton/s) by breathing and burning various fuels. At this rate of oxygen consumption, the oxygen in the atmosphere will be exhausted in about two thousand years. However, this did not happen. This is because green plants are widely distributed on the earth, constantly absorbing carbon dioxide and releasing oxygen through photosynthesis, so that the contents of oxygen and carbon dioxide in the atmosphere remain relatively stable. 1.3 The monitoring function of plants can also monitor and indicate air pollution. Plant monitoring is to monitor the type and content of harmful gases in the air or the degree of air pollution by using the reaction of plants to certain air pollutants, so as to understand the quality of the atmospheric environment. When plants are harmed by harmful substances, generally harmful gases are drilled out through the pores on the leaves, so there are often all kinds of scars visible to the naked eye on the leaves. Different gases will cause different scars. Therefore, we can judge the environmental quality in the air by investigating the symptoms of leaf injury, measuring the growth of plants and analyzing the symptoms of tree rings. If it is caused by sulfur dioxide, it mostly appears between veins, which is punctate or massive, and in severe cases, herring bone effect appears; The scars caused by fluorine are mostly concentrated at the tip and edge of the leaves, which are annular or banded. For example, Moss died; Cedar is dark, cotton leaves are white; All kinds of plants have "tobacco leaf spot". This is a sign of SO2 pollution. Acorus calamus and other plants have obvious light brown or red stripes, which is a sign of nitrogen oxide poisoning. If lilacs and weeping willows are sluggish, there will be "white spot disease", which means that there is ozone pollution in the air. If begonia and sunflower suddenly give off flowers and leaves, it is caused by chloride pollution. Other indicator plants are: alfalfa, carrot and spinach can monitor SO2 pollution; Orchids and tulips can monitor fluorine pollution; Apples and corn can monitor chlorine pollution and so on. 2. The role of plants in water environment protection. Using aquatic plants to purify sewage is a simple, low-cost, energy-saving and high-efficiency method. At present, relevant departments at home and abroad are widely applying biological treatment measures to purify sewage. Someone once did an experiment: after planting reed in an experimental pond, the suspended solids removed from water decreased by 30%, chloride by 90%, organic nitrogen by 60%, phosphate by 20%, ammonia nitrogen by 66% and total hardness by 33%. The water in the pool is much cleaner after being purified by reeds. Plants can purify water mainly in the following ways: First, plants can decompose and transform some toxic substances. At low concentrations, plants can absorb some toxic substances and decompose them into non-toxic components in the body. For example, plants absorb butyl phenol from water. When butyl phenol enters plants, it can form complexes with other substances and lose its toxicity. The most common one is phenolic glycoside, which can be stored in vacuoles and become a non-toxic binding substance of plants. In the later growth and development process, it can be decomposed and utilized to participate in the normal metabolism process of cells. Other benzene, cyanide, etc. There is a similar situation; Secondly, the richness of plants. Aquatic plants can absorb and enrich toxic substances in water, and their enrichment ability varies with plant species, but generally it can be dozens, hundreds or even thousands times higher than the concentration of toxic substances in water. Experiments show that many higher aquatic plants have the ability to absorb, accumulate, decompose and transform nitrogen, phosphorus, various metals, phenol, cyanide, pesticides and other organic substances. Among them, water hyacinth, water peanut, water onion, duckweed, duckweed and water hyacinth can effectively absorb, accumulate and decompose nutrients and various organic pollutants in wastewater. Under the most suitable growth conditions, one hectare of water hyacinth can absorb nitrogen and phosphorus discharged by 800 people on the same day. Experiments further prove that many aquatic plants in nature can also remove heavy metals from water. For example, water hyacinth and water hyacinth can remove heavy metal elements such as cadmium, lead, mercury, thallium, silver, cobalt and strontium from sewage. In addition, duckweed can absorb and accumulate heavy metal elements in coal washing wastewater of power plant in summer and autumn. In addition, aquatic plants can purify a variety of organic pollutants in wastewater. Aquatic plants have their own magical powers in purifying sewage: plants such as water onion, thistle and aquatic mint can effectively kill bacteria in water; Plants such as Eichhornia crassipes, duckweed, Potamogeton crispus and Ceratophyllum japonicum have strong absorption capacity for heavy metals in water. China is rich in aquatic plant resources and has great potential for further research, development and utilization of new sewage purification. 3. The role of plants in soil environmental protection Soil pollution can be caused by air pollution and water pollution. Harmful gases such as waste gas containing heavy metals, smoke and dust, industrial wastewater and waste residue discharged from factories, chemical pesticides in agriculture, the application of some toxic herbicides and sewage irrigation will pollute the soil. Other radioactive substances can also pollute the soil. Soil pollution can cause soil acidification or alkalization and affect the normal growth and development of some crops. Therefore, using some plants to absorb pollutants in soil can achieve the purpose of elimination and purification and reduce soil pollution. Plants can not only absorb harmful substances, but also have the functions of windbreak, sand fixation and water conservation. For some soils that have been polluted or the environment is poor, plants can also be adjusted and improved to protect land resources. This plant with the ability to improve soil is called "green manure". People often ask them to be pioneers and "settle down" in the saline-alkali wasteland or red soil wasteland with drought, flood, saline-alkali, acid and barrenness. They can not only take root and grow in these areas, but also actively create a beautiful living environment for crops. In addition, green manure plants have developed roots and can fully absorb and utilize deep water and nutrients. So after they died and rotted, the soil surface layer left rich nutrients. According to the calculation, if you harvest 1500 kg of seeds per mu, the soil is equivalent to increasing 57 kg of nitrogen fertilizer, 12 kg of phosphorus fertilizer and 13 kg of potassium fertilizer! Some leguminous green manure, such as Chinese milk vetch and alfalfa, are small chemical fertilizer plants-they use nitrogen-fixing bacteria in nodules to synthesize nitrogen from the air into nitrogen fertilizer, and can produce about 50 kilograms of nitrogen fertilizer per mu. These plants have greatly improved the soil environment and are conducive to the protection and sustainable utilization of soil resources. 4. Conclusion: Plants play a very important role in environmental protection because of their unique physiological characteristics. It can not only purify the atmosphere, water, soil and other environments, but also indicate and monitor environmental pollution and improve environmental conditions, which plays a very important role in protecting and preventing the environment. In addition, the role of plants in environmental protection goes far beyond this. Plants can reduce noise and noise pollution. Green environment can also create a comfortable environment and improve mood. In addition, environmental protection pays attention to everyone's participation and the role of the masses. Afforestation can let everyone see the achievements of environmental protection, improve the environment, enhance everyone's confidence and motivation in environmental protection and better protect the environment. It can be seen that the role of plants in environmental protection is very huge, and the development prospect of improving the environment with plants is also quite huge.

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